Today's Message Index:
----------------------
1. 05:18 AM - Re: Re: Pitot Current Draw (Chuck Jensen)
2. 05:35 AM - Re: Re: Pitot Current Draw (Deems Davis)
3. 06:05 AM - Aux Altenator switching. (Lapsley R & Sandra E Caldwell)
4. 06:24 AM - RG 400 into Molex crimp terminal, best way? (CardinalNSB@aol.com)
5. 06:41 AM - Re: Pitot Current Draw (Ernest Christley)
6. 06:49 AM - Re: Re: Pitot Current Draw (Lloyd, Daniel R.)
7. 06:55 AM - Re: Pitot Current Draw (OldBob Siegfried)
8. 07:44 AM - Re: RG 400 into Molex crimp terminal, best way? (SteinAir, Inc.)
9. 08:22 AM - Re: RG 400 into Molex crimp terminal, best way? (Dave Henderson)
10. 08:22 AM - Re: Re: Pitot Current Draw (Matt Prather)
11. 08:31 AM - Re: Pitot Current Draw (Matt Prather)
12. 08:33 AM - Re: Re: Pitot Current Draw (Ernest Christley)
13. 08:36 AM - Re: Aux Altenator switching. (Robert L. Nuckolls, III)
14. 08:39 AM - Re: Pitot Current Draw/Static Ports (Robert L. Nuckolls, III)
15. 08:46 AM - Re: Pitot Current Draw (Ernest Christley)
16. 09:18 AM - Re: Re: Pitot Current Draw (Robert L. Nuckolls, III)
17. 09:22 AM - Re: Re: Pitot Current Draw (Robert L. Nuckolls, III)
18. 10:04 AM - Re: Aux Altenator switching. (PWilson)
19. 10:15 AM - Re: Re: Instrument mounting screw washers (Mark Banus)
20. 10:20 AM - Re: Re: Pitot Current Draw (Chuck Jensen)
21. 10:40 AM - Re: Aux Altenator switching. (Robert L. Nuckolls, III)
22. 11:02 AM - Re: Re: Pitot Current Draw (Lloyd, Daniel R.)
23. 11:08 AM - DIY Starter Adapter for Lycoming (Robert L. Nuckolls, III)
24. 11:29 AM - Re: Re: Pitot Current Draw (Lloyd, Daniel R.)
25. 11:32 AM - Re: Re: Pitot Current Draw (Robert L. Nuckolls, III)
26. 11:36 AM - Re: Re: Pitot Current Draw (Robert L. Nuckolls, III)
27. 11:37 AM - Re: Re: Pitot Current Draw (Ernest Christley)
28. 11:49 AM - Re: Re: Pitot Current Draw (Robert L. Nuckolls, III)
29. 12:26 PM - Re: Re: Pitot Current Draw (Lloyd, Daniel R.)
30. 01:09 PM - Re: Aux Altenator switching. (PWilson)
31. 05:31 PM - Re: Aux Altenator switching. (Robert L. Nuckolls, III)
Message 1
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| Subject: | RE: Pitot Current Draw |
Hi, Keith,
That was exactly my thought process also. I didn't want a red hot
branding iron to bore my way through ice cubes...just warm enough to
keep the pitot stuffed full of rain water from freezing. If the icing
is bad enough that it freezes over a warm-to-very warm pitot, I've got
bigger problems that a red hot pitot won't solve.
Since no ideas have been tossed out, I wonder if there is an efficient
means of cycling the pitot heater on/off at some interval, such as on
for 30 seconds, off for two minutes. This would reduce the total
current draw if a person was in the soup, lost electrical and needed
whatever extra time available to get to safety but didn't dare to turn
off the pitot in marginal icing conditions.
Chuck Jensen
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Keith
Hallsten
Sent: Monday, December 04, 2006 10:36 PM
Subject: AeroElectric-List: RE: Pitot Current Draw
Chuck,
I mounted a 28v "Known Ice" pitot on the nose of my Velocity. Since I
have a 14 volt electrical system, its power consumption will be reduced
by a factor of 4 (power = V * V / R). I figure that is sufficient for
my purposes, because a Velocity is NOT a "Known Ice" type of airframe.
If I should find enough ice to overwhelm my "lightweight" pitot heating
system, I have bigger problems than the pitot. I'm not flying yet, but
that's my position for now.
Actually, now that we all have GPS available to us, loss of pitot is not
as critical as it used to be. With a fat margin to allow for wind,
flying by groundspeed is generally a fair approximation.
Regards,
Keith Hallsten
Subject: RE: Pitot Current Draw
From: Chuck Jensen (cjensen@dts9000.com
<mailto:cjensen@dts9000.com?subject=RE:%20Pitot%20Current%20Draw&replyt
o
=8984A39879F2F5418251CBEEC9C689B32870D7@lucky.dts.local> )
Wow, I must be hard-of-speaking (or writing). I concede that flying
into icing when not so equipped is not a good idea, but if a person
flies IFR in the winter most anywhere in the continental US, sooner or
later, they'll pick up some ice. Even if my wings start looking like
something that should be used to cool a gin and tonic, I don't want to
lose air speed indication. Granted, I may not know what my new stall
speed is, but I would like to know WHAT my speed is...and I can't do
that with a pitot full of ice.
So, the question on the table is still the same, is there a way off
'turning down the heat' and reducing current draw?
Chuck Jensen
Message 2
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| Subject: | Re: RE: Pitot Current Draw |
Chuck this is exactly what the Gretz heated pitot does.
http://www.gretzaero.com/ (ie cycles the power on/off to keep it warm
enough to melt ice, but not constantly hot.
Deems Davis RV10 # 406
Finishing - ( A Misnomer ! )
http://deemsrv10.com/
Chuck Jensen wrote:
> Hi, Keith,
>
> I wonder if there is an efficient means of cycling the pitot heater
> on/off at some interval,
>
> Chuck Jensen
> **
>
>*
>*
>
Message 3
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| Subject: | Aux Altenator switching. |
I am using Z13 with the 8 amp aux alternator.
I would like to insure that when I turn on the Aux Alt that the Main Alt
is off. I plan to use a dpdt (on-none-on) switch for the Aux
Alternator. The aux alternator would be wired normally. The main
alternator field would be wired in series with the Aux alternator such
that when the Aux Alt is off, the field power is enabled to the Main Alt
switch (Bat & main alt switch.). When the auxs alt switxh is on the
main alt field would be disconnected.
Does anyone see any problem with this plan?
Roger
Message 4
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| Subject: | RG 400 into Molex crimp terminal, best way? |
I need to bring RG400 marker beacon coax into my PS Eng., audio panel using
a "Molex" crimp terminal on the coax. This seems like a mismatch sizewise.
(I believe it is a Molex K.K. .156 Terminal Connectors (crimp pins), P/N
08-05-0302, Mouser P/N 538-08-05-0302, .33-cents each, looks the same as the
crimp pins for the Narco Mk12D and King KNS-80 and KI-206, the King part number
is KPN-030-1107-30. Can anyone verify this is the correct Molex number, the
measurements match what I have.)
1. What is the best way to connect the RG400 to the Molex crimp terminal?
a. Crimp the center conductor to Molex crimp terminal, if so the insulation
around the center connector is pretty large, do I simply trim it to #18 size
for the insulation crimp? I have been unsuccessful in obtaining a good
crimp on the RG400 and end up with a fragile connection. There isn't room to
add
heat shrink to stiffen it up, since the crimp is a tight fit in the
connector box.
I assume coax is generally designed for the bnc type connectors and that
center conductor flexability is not usually an issue.
b. Crimp or solder a short length of #18 to the center conductor for ease
of crimping the #18 to the Molex crimp terminal? Stabilize the joint with
heat shrink.
c. Strip back the center conductor about an inch, put some heat shrink on
the center conductor for better grip by the Molex on the insulation?
d. Is there an alternate coax that is more crimp friendly, to create a
pigtail that connects to the RG400?
I prefer to avoid extra connections (in general), and with my service loop
(coax bundled with intercom/mike/speaker wires) and mounting position I don't
forsee needing to disconnect the marker beacon coax for future
addition/deletions of avionics from the audio panel.
e. Other ideas?
3. I have tried crimping these with the "changeable jaw" crimper, not
pretty. It's probably my lack of technique, but can anyone recommend a user
friendly crimper-ebay has "Molex HTR1031E Crimp Tool" is this the right tool for
these Molex crimp terminals?
I couldn't find anything on the archives, my apologies if I missed it.
Thanks for any help, and Bob thanks for the reply on the alternator wiring,
I now understand the function of the extra A+ wire. Sincerely, Skip Simpson
Message 5
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| Subject: | Re: Pitot Current Draw |
OldBob Siegfried wrote:
>Dropping resistors sure wouldn't solve your problem,
>but an electronically cycled DC voltage may work.
>
>Hopefully, 'Lectric Bob will have an idea!
>
>Happy Skies,
>
>Old Bob
>
>
Actually, the dropping resistor could work. Heat output is a function
of wattage, which is given by V^2*R in a DC circuit. If you could find
a way to add an extra high wattage resister in series with the pitot
heating element, you would be dropping the current requirement. A 150
watt heater is going to have a resistance around 1 ohm in a 12V system.
Add a 1 ohm resistor in series, and the circuit will burn up 75 watts.
The resistor will suck down 37.5W and the heater will get 37.5
(ignoring line losses for the moment). If you could find a way to use
the pitot mounting as a heat sink for the resistor, it might actually be
workable.
I still don't think it's a good use of $time$, but that's just me 8*)
--
,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o http://ernest.isa-geek.org |
Message 6
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| Subject: | RE: Pitot Current Draw |
Keith
I think you have your assumptions are not correct. While your
transposition of the formula E=I*R is correct, The formula for Power
consumption is PIE or P=I*E, so if you have half the volts, the amps
will double to maintain the same wattage. So if you are counting on the
actual current draw to go down it will not in this case, in fact it will
double to keep the same heat. Now that is not to say you can not limit
the draw and run the pitot colder, but then that would negate having a
pitot.
Am I missing something?
Dan
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Keith
Hallsten
Sent: Monday, December 04, 2006 10:36 PM
Subject: AeroElectric-List: RE: Pitot Current Draw
Chuck,
I mounted a 28v "Known Ice" pitot on the nose of my Velocity. Since I
have a 14 volt electrical system, its power consumption will be reduced
by a factor of 4 (power = V * V / R). I figure that is sufficient for
my purposes, because a Velocity is NOT a "Known Ice" type of airframe.
If I should find enough ice to overwhelm my "lightweight" pitot heating
system, I have bigger problems than the pitot. I'm not flying yet, but
that's my position for now.
Actually, now that we all have GPS available to us, loss of pitot is not
as critical as it used to be. With a fat margin to allow for wind,
flying by groundspeed is generally a fair approximation.
Regards,
Keith Hallsten
Subject: RE: Pitot Current Draw
From: Chuck Jensen (cjensen@dts9000.com
<mailto:cjensen@dts9000.com?subject=RE:%20Pitot%20Current%20Draw&replyt
o
=8984A39879F2F5418251CBEEC9C689B32870D7@lucky.dts.local> )
Wow, I must be hard-of-speaking (or writing). I concede that flying
into icing when not so equipped is not a good idea, but if a person
flies IFR in the winter most anywhere in the continental US, sooner or
later, they'll pick up some ice. Even if my wings start looking like
something that should be used to cool a gin and tonic, I don't want to
lose air speed indication. Granted, I may not know what my new stall
speed is, but I would like to know WHAT my speed is...and I can't do
that with a pitot full of ice.
So, the question on the table is still the same, is there a way off
'turning down the heat' and reducing current draw?
Chuck Jensen
Message 7
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| Subject: | Re: Pitot Current Draw |
Good Morning Ernest,
That will drop the voltage and make the pitot tube
cooler, but it is my understanding that such was NOT
the problem he was attempting to solve.
What he wants to do is reduce the current.
Adding a dropping resistor just puts that current
somewhere other than into the pitot heater. Cycling
the power would reduce the heat AND the current
required.
Happy Skies,
Old Bob
--- Ernest Christley <echristley@nc.rr.com> wrote:
> Christley <echristley@nc.rr.com>
>
> OldBob Siegfried wrote:
>
> >Dropping resistors sure wouldn't solve your
> problem,
> >but an electronically cycled DC voltage may work.
> >
> >Hopefully, 'Lectric Bob will have an idea!
> >
> >Happy Skies,
> >
> >Old Bob
> >
> >
>
> Actually, the dropping resistor could work. Heat
> output is a function
> of wattage, which is given by V^2*R in a DC circuit.
> If you could find
> a way to add an extra high wattage resister in
> series with the pitot
> heating element, you would be dropping the current
> requirement. A 150
> watt heater is going to have a resistance around 1
> ohm in a 12V system.
> Add a 1 ohm resistor in series, and the circuit will
> burn up 75 watts.
> The resistor will suck down 37.5W and the heater
> will get 37.5
> (ignoring line losses for the moment). If you could
> find a way to use
> the pitot mounting as a heat sink for the resistor,
> it might actually be
> workable.
>
> I still don't think it's a good use of $time$, but
> that's just me 8*)
>
> --
> ,|"|"|, Ernest Christley
> ----===<{{(oQo)}}>===---- Dyke Delta Builder
> o| d |o http://ernest.isa-geek.org
>
>
> Click on
> about
> provided
> www.buildersbooks.com
> Admin.
>
> browse
> Subscriptions page,
> FAQ,
> http://www.matronics.com/Navigator?AeroElectric-List
>
>
>
>
>
Message 8
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| Subject: | RG 400 into Molex crimp terminal, best way? |
Best practice is not to wire the RG-400 directly into the connector, but
rather to use something like AWG20 on the center conductor, put a solder
sleeve over the shield with a pigtail of another AWG20 then run the two
wires into the connector - and of course support the coax so it does't rip
out the wires. You can see a picture of our typical Mkr Bcn pigtail here:
http://www.steinair.com/images/store/MKR.jpg We have a black/white strip
for the ctr conductor and a black wire for the shield (which is kind of
hidden in the picture).
Hope that helps.
Cheers,
Stein.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of
CardinalNSB@aol.com
Sent: Tuesday, December 05, 2006 8:23 AM
To: aeroelectric-list@matronics.com
Subject: AeroElectric-List: RG 400 into Molex crimp terminal, best way?
I need to bring RG400 marker beacon coax into my PS Eng., audio panel
using a "Molex" crimp terminal on the coax. This seems like a mismatch
sizewise.
(I believe it is a Molex K.K. .156 Terminal Connectors (crimp pins), P/N
08-05-0302, Mouser P/N 538-08-05-0302, .33-cents each, looks the same as the
crimp pins for the Narco Mk12D and King KNS-80 and KI-206, the King part
number is KPN-030-1107-30. Can anyone verify this is the correct Molex
number, the measurements match what I have.)
1. What is the best way to connect the RG400 to the Molex crimp terminal?
a. Crimp the center conductor to Molex crimp terminal, if so the
insulation around the center connector is pretty large, do I simply trim it
to #18 size for the insulation crimp? I have been unsuccessful in obtaining
a good crimp on the RG400 and end up with a fragile connection. There isn't
room to add heat shrink to stiffen it up, since the crimp is a tight fit in
the connector box.
I assume coax is generally designed for the bnc type connectors and that
center conductor flexability is not usually an issue.
b. Crimp or solder a short length of #18 to the center conductor for ease
of crimping the #18 to the Molex crimp terminal? Stabilize the joint with
heat shrink.
c. Strip back the center conductor about an inch, put some heat shrink on
the center conductor for better grip by the Molex on the insulation?
d. Is there an alternate coax that is more crimp friendly, to create a
pigtail that connects to the RG400?
I prefer to avoid extra connections (in general), and with my service
loop (coax bundled with intercom/mike/speaker wires) and mounting position I
don't forsee needing to disconnect the marker beacon coax for future
addition/deletions of avionics from the audio panel.
e. Other ideas?
3. I have tried crimping these with the "changeable jaw" crimper, not
pretty. It's probably my lack of technique, but can anyone recommend a user
friendly crimper-ebay has "Molex HTR1031E Crimp Tool" is this the right tool
for these Molex crimp terminals?
I couldn't find anything on the archives, my apologies if I missed it.
Thanks for any help, and Bob thanks for the reply on the alternator
wiring, I now understand the function of the extra A+ wire. Sincerely,
Skip Simpson
Message 9
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| Subject: | RG 400 into Molex crimp terminal, best way? |
I loved the way you did your wire marking. Is that available at
Steinair?
What is the part number?
Dave Henderson RV-7
N925LW (Lord Willing)
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
SteinAir,
Inc.
Sent: Tuesday, December 05, 2006 10:41 AM
Subject: RE: AeroElectric-List: RG 400 into Molex crimp terminal, best
way?
Best practice is not to wire the RG-400 directly into the connector, but
rather to use something like AWG20 on the center conductor, put a solder
sleeve over the shield with a pigtail of another AWG20 then run the two
wires into the connector - and of course support the coax so it does't
rip
out the wires. You can see a picture of our typical Mkr Bcn pigtail
here:
http://www.steinair.com/images/store/MKR.jpg We have a black/white
strip
for the ctr conductor and a black wire for the shield (which is kind of
hidden in the picture).
Hope that helps.
Cheers,
Stein.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of
CardinalNSB@aol.com
Sent: Tuesday, December 05, 2006 8:23 AM
Subject: AeroElectric-List: RG 400 into Molex crimp terminal, best way?
I need to bring RG400 marker beacon coax into my PS Eng., audio panel
using
a "Molex" crimp terminal on the coax. This seems like a mismatch
sizewise.
(I believe it is a Molex K.K. .156 Terminal Connectors (crimp pins),
P/N
08-05-0302, Mouser P/N 538-08-05-0302, .33-cents each, looks the same as
the
crimp pins for the Narco Mk12D and King KNS-80 and KI-206, the King part
number is KPN-030-1107-30. Can anyone verify this is the correct Molex
number, the measurements match what I have.)
1. What is the best way to connect the RG400 to the Molex crimp
terminal?
a. Crimp the center conductor to Molex crimp terminal, if so the
insulation
around the center connector is pretty large, do I simply trim it to #18
size
for the insulation crimp? I have been unsuccessful in obtaining a good
crimp on the RG400 and end up with a fragile connection. There isn't
room
to add heat shrink to stiffen it up, since the crimp is a tight fit in
the
connector box.
I assume coax is generally designed for the bnc type connectors and that
center conductor flexability is not usually an issue.
b. Crimp or solder a short length of #18 to the center conductor for
ease
of crimping the #18 to the Molex crimp terminal? Stabilize the joint
with
heat shrink.
c. Strip back the center conductor about an inch, put some heat shrink
on
the center conductor for better grip by the Molex on the insulation?
d. Is there an alternate coax that is more crimp friendly, to create a
pigtail that connects to the RG400?
I prefer to avoid extra connections (in general), and with my service
loop
(coax bundled with intercom/mike/speaker wires) and mounting position I
don't forsee needing to disconnect the marker beacon coax for future
addition/deletions of avionics from the audio panel.
e. Other ideas?
3. I have tried crimping these with the "changeable jaw" crimper, not
pretty. It's probably my lack of technique, but can anyone recommend a
user
friendly crimper-ebay has "Molex HTR1031E Crimp Tool" is this the right
tool
for these Molex crimp terminals?
I couldn't find anything on the archives, my apologies if I missed it.
Thanks for any help, and Bob thanks for the reply on the alternator
wiring,
I now understand the function of the extra A+ wire. Sincerely, Skip
Simpson
href="http://www.aeroelectric.com">www.aeroelectric.com
href="http://www.buildersbooks.com">www.buildersbooks.com
href="http://www.kitlog.com">www.kitlog.com
href="http://www.homebuilthelp.com">www.homebuilthelp.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
href
"http://www.matronics.com/Navigator?AeroElectric-List">http://www.matroni
cs.
com/Navigator?AeroElectric-List
Message 10
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| Subject: | RE: Pitot Current Draw |
Dan,
I believe the pitot heating element is a simple resistor. Adding series
resistance in line with the heating element will indeed LOWER the current
through the circuit, as well as lowering the voltage drop across the pitot
element. I am pretty sure the pitot heater is not a constant power device
(which is what I think you were describing).
Regards,
Matt-
> Keith
> I think you have your assumptions are not correct. While your
> transposition of the formula E=I*R is correct, The formula for Power
> consumption is PIE or P=I*E, so if you have half the volts, the amps
> will double to maintain the same wattage. So if you are counting on the
> actual current draw to go down it will not in this case, in fact it will
> double to keep the same heat. Now that is not to say you can not limit
> the draw and run the pitot colder, but then that would negate having a
> pitot.
> Am I missing something?
> Dan
>
> _____
>
> From: owner-aeroelectric-list-server@matronics.com
> [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Keith
> Hallsten
> Sent: Monday, December 04, 2006 10:36 PM
> To: aeroelectric-list@matronics.com
> Subject: AeroElectric-List: RE: Pitot Current Draw
>
>
> Chuck,
>
> I mounted a 28v "Known Ice" pitot on the nose of my Velocity. Since I
> have a 14 volt electrical system, its power consumption will be reduced
> by a factor of 4 (power = V * V / R). I figure that is sufficient for
> my purposes, because a Velocity is NOT a "Known Ice" type of airframe.
> If I should find enough ice to overwhelm my "lightweight" pitot heating
> system, I have bigger problems than the pitot. I'm not flying yet, but
> that's my position for now.
>
> Actually, now that we all have GPS available to us, loss of pitot is not
> as critical as it used to be. With a fat margin to allow for wind,
> flying by groundspeed is generally a fair approximation.
>
> Regards,
>
> Keith Hallsten
>
>
> Subject: RE: Pitot Current Draw
> From: Chuck Jensen (cjensen@dts9000.com
> <mailto:cjensen@dts9000.com?subject=RE:%20Pitot%20Current%20Draw&replyto
> =8984A39879F2F5418251CBEEC9C689B32870D7@lucky.dts.local> )
> Date: Mon Dec 04 - 12:06 PM
> Wow, I must be hard-of-speaking (or writing). I concede that flying
>
> into icing when not so equipped is not a good idea, but if a person
>
> flies IFR in the winter most anywhere in the continental US, sooner or
>
> later, they'll pick up some ice. Even if my wings start looking like
>
> something that should be used to cool a gin and tonic, I don't want to
>
> lose air speed indication. Granted, I may not know what my new stall
>
> speed is, but I would like to know WHAT my speed is...and I can't do
>
> that with a pitot full of ice.
>
> So, the question on the table is still the same, is there a way off
>
> 'turning down the heat' and reducing current draw?
>
> Chuck Jensen
>
>
Message 11
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| Subject: | Re: Pitot Current Draw |
Hello Bob,
Adding series resistance causes the total resistance rises, so the total
current drops. That will reduce the total circuit power as well as the
power delivered to the pitot (less voltage drop across the pitot).
I agree that this is an inefficient way to accomplish the task - wasted
heat on the dropping resistor.
A simple way (from a drive circuitry standpoint) to accomplish the task
would be to have a pitot tube with two heating elements. They could be
different sizes (wattage values). Turn on the "ground" element to keep it
warm while taxiing, and a "branding iron" element to stave off a full
arctic blast. Turn both on at once so you know how fast you're falling
out of the sky.. :)
Actually, your idea of cycling the pitot heat probably works great too
(maybe that's how it's actually done). The only downside I can think of
is that cycling a high power device can cause weird noise events on the
power bus (dimming lights). Probably not a big deal if installed/wired
properly (low impedance path to the battery).
Regards,
Matt-
> <oldbob@beechowners.com>
>
> Good Morning Ernest,
>
> That will drop the voltage and make the pitot tube
> cooler, but it is my understanding that such was NOT
> the problem he was attempting to solve.
>
> What he wants to do is reduce the current.
>
> Adding a dropping resistor just puts that current
> somewhere other than into the pitot heater. Cycling
> the power would reduce the heat AND the current
> required.
>
> Happy Skies,
>
> Old Bob
>
> --- Ernest Christley <echristley@nc.rr.com> wrote:
>
>> Christley <echristley@nc.rr.com>
>>
>> OldBob Siegfried wrote:
>>
>> >Dropping resistors sure wouldn't solve your
>> problem,
>> >but an electronically cycled DC voltage may work.
>> >
>> >Hopefully, 'Lectric Bob will have an idea!
>> >
>> >Happy Skies,
>> >
>> >Old Bob
>> >
>> >
>>
>> Actually, the dropping resistor could work. Heat
>> output is a function
>> of wattage, which is given by V^2*R in a DC circuit.
>> If you could find
>> a way to add an extra high wattage resister in
>> series with the pitot
>> heating element, you would be dropping the current
>> requirement. A 150
>> watt heater is going to have a resistance around 1
>> ohm in a 12V system.
>> Add a 1 ohm resistor in series, and the circuit will
>> burn up 75 watts.
>> The resistor will suck down 37.5W and the heater
>> will get 37.5
>> (ignoring line losses for the moment). If you could
>> find a way to use
>> the pitot mounting as a heat sink for the resistor,
>> it might actually be
>> workable.
>>
>> I still don't think it's a good use of $time$, but
>> that's just me 8*)
>>
>> --
>> ,|"|"|, Ernest Christley
>> |
>> ----===<{{(oQo)}}>===---- Dyke Delta Builder
>> |
>> o| d |o http://ernest.isa-geek.org
>> |
>>
>>
>> Click on
>> about
>> provided
>> www.buildersbooks.com
>> Admin.
>>
>> browse
>> Subscriptions page,
>> FAQ,
>> http://www.matronics.com/Navigator?AeroElectric-List
>>
>>
>>
>>
>>
>
>
Message 12
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| Subject: | Re: RE: Pitot Current Draw |
Lloyd, Daniel R. wrote:
> Keith
> I think you have your assumptions are not correct. While your
> transposition of the formula E=I*R is correct, The formula for Power
> consumption is PIE or P=I*E, so if you have half the volts, the amps
> will double to maintain the same wattage. So if you are counting on
> the actual current draw to go down it will not in this case, in fact
> it will double to keep the same heat. Now that is not to say you can
> not limit the draw and run the pitot colder, but then that would
> negate having a pitot.
> Am I missing something?
> Dan
Yes. You're missing http://www.sengpielaudio.com/calculator-ohm.htm
I keep a copy of that taped to the inside of my electronics toolbox's lid.
You've got 12V (actually 13.4). Double the resistance, you halve the
current (I=V/R). Halving the current will also cut the power in half
(P=V*I), decreasing the heater effectiveness as you state; but the
original problem was the builder willing to settle for a drop in
effectiveness in exchange for extended battery life.
--
,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o http://ernest.isa-geek.org |
Message 13
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| Subject: | Re: Aux Altenator switching. |
At 09:04 AM 12/5/2006 -0500, you wrote:
><lrsecaldwell@earthlink.net>
>
>I am using Z13 with the 8 amp aux alternator.
>
>I would like to insure that when I turn on the Aux Alt that the Main Alt
>is off.
Why?
> I plan to use a dpdt (on-none-on) switch for the Aux Alternator. The
> aux alternator would be wired normally. The main alternator field would
> be wired in series with the Aux alternator such that when the Aux Alt is
> off, the field power is enabled to the Main Alt switch (Bat & main alt
> switch.). When the auxs alt switxh is on the main alt field would be
> disconnected.
>
>Does anyone see any problem with this plan?
Don't see a need for it. Further, any part that is
NOT on your airplane is not going to be a part that
fails. Having one switch exert command and control over
systems that are supposed to back each other up
does not produce nice failure modes effects analysis.
There is no danger to any equipment on the airplane by
having both alternators on at the same time. I'll
recommend you install Z-13 as published.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
Message 14
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| Subject: | Re: Pitot Current Draw/Static Ports |
At 07:19 PM 12/4/2006 -0800, you wrote:
>
>
>Hi Bruce
>
>I know you said that with tongue in cheek, but it is interesting point. If
>I remember correctly an alternate static valve or heated ports are not
>required (Canada) if it can be demonstrated that the static ports are not
>susceptible to icing. I opted for alternate static valve on my RV's
>however I think that with dual static ports on the aft end of a tapering
>fuselage they would be immune to icing unless the aircraft was flown in a
>side slip. Anyone ever heard of side static ports icing over/up?
Don't know if anyone has actually seen them ice up but
static ports on our new Horizon are heated.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
Message 15
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| Subject: | Re: Pitot Current Draw |
OldBob Siegfried wrote:
>
>Good Morning Ernest,
>
>That will drop the voltage and make the pitot tube
>cooler, but it is my understanding that such was NOT
>the problem he was attempting to solve.
>
>What he wants to do is reduce the current.
>
>Adding a dropping resistor just puts that current
>somewhere other than into the pitot heater. Cycling
>the power would reduce the heat AND the current
>required.
>
>Happy Skies,
>
>Old Bob
>
>
>
Yes it would, but compared to adding a series resistor it will also add
a semi-complex cycling circuit (with the definition of complex being
left as an exercise for the reader). My suggestion would only be useful
if it were possible to use the heat generated from the resistor. If I
were trying to accomplish this on my installation, I would bolt the
resistor to the pitot's base using heat-sink grease at a point that
would put it under the fairing. The pitot becomes the heat-sink for the
resistor (as well as the internal heating element). Using the previous
numbers that I pulled out of the ether, the resistor and heater would
produce 37.5W of heat each. The heater's power would be as efficient as
the unmodified version, but the resistor's heat has to jump across a
couple interfaces and down the pitot's post. Overall, the pitot heater
would be less than half as effective.
--
,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o http://ernest.isa-geek.org |
Message 16
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| Subject: | RE: Pitot Current Draw |
At 08:18 AM 12/5/2006 -0500, you wrote:
>Hi, Keith,
>
>That was exactly my thought process also. I didn't want a red hot
>branding iron to bore my way through ice cubes...just warm enough to keep
>the pitot stuffed full of rain water from freezing. If the icing is bad
>enough that it freezes over a warm-to-very warm pitot, I've got bigger
>problems that a red hot pitot won't solve.
>
>Since no ideas have been tossed out, I wonder if there is an efficient
>means of cycling the pitot heater on/off at some interval, such as on for
>30 seconds, off for two minutes. This would reduce the total current draw
>if a person was in the soup, lost electrical and needed whatever extra
>time available to get to safety but didn't dare to turn off the pitot in
>marginal icing conditions.
We need to define "efficient". If this means highest
reliability and minimum parts count, then a series resistor
can be used to reduce energy dissipated in the tube
(and total energy consumed by the system) but even tho
the tube heat is reduced, the resistor dumps energy too.
The most efficient electrically is a switchmode step-down
converter that can supply power to the pitot heater at any
voltage while limiting losses in the heat controller to
20% or so of total power. But this is a busy piece of
electronics that adds parts count to the system but when
operating properly, offers the lowest risk for noise
problems while offering complete adjustability of the
low power mode.
You can also duty cycle switch the tube and while this
offers a VERY efficient means of controlling energy, it
puts repetitive pulses of current on the bus that
WILL generate considerable noise (I'm working a similar
problem right now on a $14M$ airplane that has a
$50K$ coffee maker installed on it).
Help us understand your primary goal. Certainly, energized
pitot tubes offer considerable hazard on the ground. How
about a switch that keeps the tube off unless RPM is over
1000 rpm? How about an airspeed switch? Both of these
systems could be fitted with warning lights that show a
de-energized pitot heater when the pitot heat switch is ON.
Help us understand your design goals. Using a 28v tube
is an option too. Given the temperature coefficient
for the heaters, running a tube at 1/2 voltage still
produces more than 1/4 rated power. But keep in mind that
there is a thermal resistance component between a heater
and the pitot tube's surface. See:
http://www.aeroelectric.com/Pictures/Curves/Pitot_Heater_R_Plot.pdf
The data point at 9.85 amps was taken while the surface
of the tube was being held at 0C in an ice bath. These
are the worst case conditions for icing but note that
while the surface was at 0C, the heater itself was running
at about 140C! See:
http://www.aeroelectric.com/Pictures/Curves/Pitot_tube_temps_at_altitude.pdf
This data was collected on a flight to 41K feet. Note that
at cruise, the pitot tube's SURFACE temperature (LT4) was
running over 100C at 200Kts IAS and RAT of -35C. This was
the same tube plotted in the earlier graph.
Just be wary of advice supported by anecdotal experiences.
The "numbers" that describe the tube's ability to shed
ice are locked into the physics and not all tubes are the
same. Attempts to control the tube's power consumption
increases parts count and raises needs for additional
monitoring to let you know when the control system has
failed so that you can bypass it and go to full power.
Some power control schemes have system integration issues
to consider as well. Be wary too of any notions that
"a small portion" of design power is a useful thing to
design into your system.
Let's consider your design goals. Exactly why and under what
conditions do you want to moderate pitot tube performance?
Bob . . .
Message 17
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| Subject: | Re: RE: Pitot Current Draw |
http://www.gretzaero.com/ga1000.html
If the control system for this tube is designed to actively
maintain the SURFACE temperature of tube at ice-shedding
temperatures, then it's a good thing to do. I've considered
pitot tube controllers based on measuring resitance of the
heater during OFF time of a duty cycle controller . . . but
knowing heater temperature is not the same as knowing tube
surface temperature . . . for reasons cited in the other post.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
Message 18
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| Subject: | Re: Aux Altenator switching. |
Bob,
Does your comment "There is no danger to any equipment on the airplane by
having both alternators on at the same time. "
Does this mean if I add a John Deere 20a and run at the same time
as my Rotax 18 Amp unit that I can get 38 amps max case? Any down
side to doing this?
Thanks, Paul
===============
At 08:35 AM 12/5/2006, you wrote:
><nuckollsr@cox.net>
>
>At 09:04 AM 12/5/2006 -0500, you wrote:
>
>>Caldwell <lrsecaldwell@earthlink.net>
>>
>>I am using Z13 with the 8 amp aux alternator.
>>
>>I would like to insure that when I turn on the Aux Alt that the
>>Main Alt is off.
>
> Why?
>
>> I plan to use a dpdt (on-none-on) switch for the Aux
>> Alternator. The aux alternator would be wired normally. The main
>> alternator field would be wired in series with the Aux alternator
>> such that when the Aux Alt is off, the field power is enabled to
>> the Main Alt switch (Bat & main alt switch.). When the auxs alt
>> switxh is on the main alt field would be disconnected.
>>
>>Does anyone see any problem with this plan?
>
> Don't see a need for it. Further, any part that is
> NOT on your airplane is not going to be a part that
> fails. Having one switch exert command and control over
> systems that are supposed to back each other up
> does not produce nice failure modes effects analysis.
>
> There is no danger to any equipment on the airplane by
> having both alternators on at the same time. I'll
> recommend you install Z-13 as published.
>
> Bob . . .
>
> ---------------------------------------------------------
> < What is so wonderful about scientific truth...is that >
> < the authority which determines whether there can be >
> < debate or not does not reside in some fraternity of >
> < scientists; nor is it divine. The authority rests >
> < with experiment. >
> < --Lawrence M. Krauss >
> ---------------------------------------------------------
>
>
Message 19
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| Subject: | RE: RE: Instrument mounting screw washers |
Bruce,
These are actually the screws that attach the Al 2 panel inserts to the
Glasair Fiberglass panel. I'm not sure what # they are. I'm looking for
washers that do not extend much past the diameter of the attaching screw.
Standard washers are to wide and look funny on the panel.
Mark
Message 20
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| Subject: | RE: Pitot Current Draw |
Robert L. Nuckolls, III wrote....
We need to define "efficient". If this means highest
reliability and minimum parts count, then a series resistor
can be used to reduce energy dissipated in the tube
(and total energy consumed by the system) but even tho
the tube heat is reduced, the resistor dumps energy too.
The most efficient electrically is a switchmode step-down
converter that can supply power to the pitot heater at any
voltage while limiting losses in the heat controller to
20% or so of total power. But this is a busy piece of
electronics that adds parts count to the system but when
operating properly, offers the lowest risk for noise
problems while offering complete adjustability of the
low power mode.
You can also duty cycle switch the tube and while this
offers a VERY efficient means of controlling energy, it
puts repetitive pulses of current on the bus that
WILL generate considerable noise (I'm working a similar
problem right now on a $14M$ airplane that has a
$50K$ coffee maker installed on it).
Help us understand your primary goal. Certainly, energized
pitot tubes offer considerable hazard on the ground. How
about a switch that keeps the tube off unless RPM is over
1000 rpm? How about an airspeed switch? Both of these
systems could be fitted with warning lights that show a
de-energized pitot heater when the pitot heat switch is ON.
The primary goal is to reduce power load of the pitot during all
operating phases, as the pitot runs unnecessarily hot (though I don't
know exactly what temp it should run at, my belief is branding iron hot
is more then necessary for a GA aircraft that is not ice equipped). Of
particular importance, should I have an electrical generation failure
and am in 'cold clouds', I prefer to leave the pitot as long as possible
to preclude loss of AS indication. The duration of this operation,
limited by battery life, will be directly, and primarily, affected by
the draw of the pitot heater. In fact, the 15amp draw is about equal to
everything else that needs to run. The goal is to reduce the effective
draw of the pitot to 7 amps, or less, either on a continuous basis or as
an average of the on/off cycle. A secondary goal is not to screw up
radios and reliability.
Help us understand your design goals. Using a 28v tube
is an option too. Given the temperature coefficient
for the heaters, running a tube at 1/2 voltage still
produces more than 1/4 rated power. But keep in mind that
there is a thermal resistance component between a heater
and the pitot tube's surface. See:
http://www.aeroelectric.com/Pictures/Curves/Pitot_Heater_R_Plot.pdf
The data point at 9.85 amps was taken while the surface
of the tube was being held at 0C in an ice bath. These
are the worst case conditions for icing but note that
while the surface was at 0C, the heater itself was running
at about 140C! See:
http://www.aeroelectric.com/Pictures/Curves/Pitot_tube_temps_at_altitude
.pdf
This data was collected on a flight to 41K feet. Note that
at cruise, the pitot tube's SURFACE temperature (LT4) was
running over 100C at 200Kts IAS and RAT of -35C. This was
the same tube plotted in the earlier graph.
In the Velocity, I intended to neither fly in an ice bath, or at 41K
feet--though I get your points :-).
Just be wary of advice supported by anecdotal experiences.
The "numbers" that describe the tube's ability to shed
ice are locked into the physics and not all tubes are the
same. Attempts to control the tube's power consumption
increases parts count and raises needs for additional
monitoring to let you know when the control system has
failed so that you can bypass it and go to full power.
Some power control schemes have system integration issues
to consider as well. Be wary too of any notions that
"a small portion" of design power is a useful thing to
design into your system.
Let's consider your design goals. Exactly why and under what
conditions do you want to moderate pitot tube performance?
During all phases of ground and flight operations. In short, I wish the
pitot (off a warbird) was a 28v unit that was run at 12v--I suspect that
would be about right for reduced pitot heat and current draw.
Bob . . .
Message 21
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| Subject: | Re: Aux Altenator switching. |
At 10:01 AM 12/5/2006 -0800, you wrote:
>
>Bob,
>Does your comment "There is no danger to any equipment on the airplane by
>having both alternators on at the same time. "
> Does this mean if I add a John Deere 20a and run at the same time as my
> Rotax 18 Amp unit that I can get 38 amps max case? Any down side to doing this?
There's a difference between risks for damage and performance as
shared suppliers of loads to the system. The problem is getting
respective voltage regulators of two engine driven power sources
to appropriately share total loads based on their respective
capabilities.
I've designed such regulators but the technology I've used
is not compatible with PM alternators. It would take a start
from scratch effort to get the proportionate paralleling
performance that's desired when running two power sources.
Yes, you can run two alternators and count on their added
capacities for total engine driven power . . . but without
hardware specific to making them share loads, you'll find
yourself fiddling with the regulation setpoints a lot.
If you can bolt a 20A PM alternator to your engine, why
not a 40A ND alternator with some REAL capacity to run
the whole airplane and save the smaller alternator for backup
a-la Z-13/8?
Bob . . .
Message 22
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| Subject: | RE: Pitot Current Draw |
But wouldn't you still be wasting electrical power as heat on the
resistor? If the overall goal is to reduce power consumption, IE make
the battery last longer, you would not want additional resistance. Or am
I all backwards?
I went with the Gretz Pitot, because it stays at a constant lower temp
and power cycles itself to maintain that temp, so overall I am using
less power, rather than just dumping it as heat.
Dan
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Matt
Prather
Sent: Tuesday, December 05, 2006 11:22 AM
Subject: RE: AeroElectric-List: RE: Pitot Current Draw
<mprather@spro.net>
Dan,
I believe the pitot heating element is a simple resistor. Adding series
resistance in line with the heating element will indeed LOWER the
current
through the circuit, as well as lowering the voltage drop across the
pitot
element. I am pretty sure the pitot heater is not a constant power
device
(which is what I think you were describing).
Regards,
Matt-
> Keith
> I think you have your assumptions are not correct. While your
> transposition of the formula E=I*R is correct, The formula for Power
> consumption is PIE or P=I*E, so if you have half the volts, the amps
> will double to maintain the same wattage. So if you are counting on
the
> actual current draw to go down it will not in this case, in fact it
will
> double to keep the same heat. Now that is not to say you can not limit
> the draw and run the pitot colder, but then that would negate having a
> pitot.
> Am I missing something?
> Dan
>
> _____
>
> From: owner-aeroelectric-list-server@matronics.com
> [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Keith
> Hallsten
> Sent: Monday, December 04, 2006 10:36 PM
> To: aeroelectric-list@matronics.com
> Subject: AeroElectric-List: RE: Pitot Current Draw
>
>
> Chuck,
>
> I mounted a 28v "Known Ice" pitot on the nose of my Velocity. Since I
> have a 14 volt electrical system, its power consumption will be
reduced
> by a factor of 4 (power = V * V / R). I figure that is sufficient for
> my purposes, because a Velocity is NOT a "Known Ice" type of airframe.
> If I should find enough ice to overwhelm my "lightweight" pitot
heating
> system, I have bigger problems than the pitot. I'm not flying yet,
but
> that's my position for now.
>
> Actually, now that we all have GPS available to us, loss of pitot is
not
> as critical as it used to be. With a fat margin to allow for wind,
> flying by groundspeed is generally a fair approximation.
>
> Regards,
>
> Keith Hallsten
>
>
> Subject: RE: Pitot Current Draw
> From: Chuck Jensen (cjensen@dts9000.com
>
<mailto:cjensen@dts9000.com?subject=RE:%20Pitot%20Current%20Draw&replyto
> =8984A39879F2F5418251CBEEC9C689B32870D7@lucky.dts.local> )
> Date: Mon Dec 04 - 12:06 PM
> Wow, I must be hard-of-speaking (or writing). I concede that flying
>
> into icing when not so equipped is not a good idea, but if a person
>
> flies IFR in the winter most anywhere in the continental US, sooner or
>
> later, they'll pick up some ice. Even if my wings start looking like
>
> something that should be used to cool a gin and tonic, I don't want to
>
> lose air speed indication. Granted, I may not know what my new stall
>
> speed is, but I would like to know WHAT my speed is...and I can't do
>
> that with a pitot full of ice.
>
> So, the question on the table is still the same, is there a way off
>
> 'turning down the heat' and reducing current draw?
>
> Chuck Jensen
>
>
Message 23
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| Subject: | DIY Starter Adapter for Lycoming |
Last week sometime someone mentioned an article for fabricating
an adapter that bolts an automotive starter to a Lycoming. I've
captured and .pdf'ed the article for easier downloading and
printing. This is a nice piece of work and worthy of consideration
if you're interested in such things.
http://aeroelectric.com/Reference_Docs/Starters/Lycoming_Starter_Adapter.pdf
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
Message 24
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| Subject: | RE: Pitot Current Draw |
I think it is better described like this, you double the resistance,
half the current is felt on each device, but the power drop across the
circuit is still the same, IE the pitot only gets half as hot and the
resistor is getting the other current, and no net gain or loss on
wattage consumption.
Correct?
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Ernest Christley
Sent: Tuesday, December 05, 2006 11:33 AM
Subject: Re: AeroElectric-List: RE: Pitot Current Draw
<echristley@nc.rr.com>
Lloyd, Daniel R. wrote:
> Keith
> I think you have your assumptions are not correct. While your
> transposition of the formula E=I*R is correct, The formula for Power
> consumption is PIE or P=I*E, so if you have half the volts, the amps
> will double to maintain the same wattage. So if you are counting on
> the actual current draw to go down it will not in this case, in fact
> it will double to keep the same heat. Now that is not to say you can
> not limit the draw and run the pitot colder, but then that would
> negate having a pitot.
> Am I missing something?
> Dan
Yes. You're missing http://www.sengpielaudio.com/calculator-ohm.htm
I keep a copy of that taped to the inside of my electronics toolbox's
lid.
You've got 12V (actually 13.4). Double the resistance, you halve the
current (I=V/R). Halving the current will also cut the power in half
(P=V*I), decreasing the heater effectiveness as you state; but the
original problem was the builder willing to settle for a drop in
effectiveness in exchange for extended battery life.
--
,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o http://ernest.isa-geek.org |
Message 25
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| Subject: | RE: Pitot Current Draw |
At 01:20 PM 12/5/2006 -0500, you wrote:
>
>Robert L. Nuckolls, III wrote....
>
> We need to define "efficient". If this means highest
> reliability and minimum parts count, then a series resistor
> can be used to reduce energy dissipated in the tube
> (and total energy consumed by the system) but even tho
> the tube heat is reduced, the resistor dumps energy too.
<snip>
>The primary goal is to reduce power load of the pitot during all
>operating phases, as the pitot runs unnecessarily hot (though I don't
>know exactly what temp it should run at, my belief is branding iron hot
>is more then necessary for a GA aircraft that is not ice equipped). Of
>particular importance, should I have an electrical generation failure
>and am in 'cold clouds', I prefer to leave the pitot as long as possible
>to preclude loss of AS indication. The duration of this operation,
>limited by battery life, will be directly, and primarily, affected by
>the draw of the pitot heater. In fact, the 15amp draw is about equal to
>everything else that needs to run. The goal is to reduce the effective
>draw of the pitot to 7 amps, or less, either on a continuous basis or as
>an average of the on/off cycle. A secondary goal is not to screw up
>radios and reliability.
Okay, get an adjustable power supply good for 7 amps or more.
Hook it to your pitot tube and adjust the voltage for 7A of current
draw. This probably won't be at 1/2 your normal system voltage but
something a bit lower. Wait for things to settle out as the
tube needs some time to arrive at a new temperature and load.
Once the new voltage is determined, calculate the value of
resistance needed to supply this new voltage assuming a 14v
bus.
Value of R = (14 - NewVolts)/7
Your resistor will dissipate something on the order of 50
watts and the needed resistance will be on the order of
1 ohm. I'd recommend you get a 2.0 ohm, 100W adjustable
resistor like an AVT100-2.0 found at:
http://dkc3.digikey.com/PDF/T063/1403.pdf
During the first opportunity to do some in-flight measurements,
I'd monitor the voltage across the pitot tube in flight
to see how much effect that slip stream air flow
affects power drawn by the tube. If you see a need to
increase the voltage, you can always adjust the resistor
to some new value.
In fact, you may want to install a 225w resistor. The
100 ohm resistor has a current rating of I^2*R=100
or 7A. This means that if you need to increase the
operating current above 7A, you'll overload the 100W
resistor.
A 225w resistor has a current rating of about 11
amps and would be most likely to cover all the bases
for your final adjustment setpoint.
These resistors are on ceramic tubes and relatively
robust as mounted when you use the brackets that come
with the resistor. Resist the urge to mount these
devices on heavy and/or rigid structure that might
put strong bending forces on the tube.
Bob . . .
Message 26
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| Subject: | RE: Pitot Current Draw |
At 02:01 PM 12/5/2006 -0500, you wrote:
><LloydDR@wernerco.com>
>
>But wouldn't you still be wasting electrical power as heat on the
>resistor? If the overall goal is to reduce power consumption, IE make
>the battery last longer, you would not want additional resistance. Or am
>I all backwards?
>I went with the Gretz Pitot, because it stays at a constant lower temp
>and power cycles itself to maintain that temp, so overall I am using
>less power, rather than just dumping it as heat.
Yes, the resistor gets hot too but TOTAL energy is down. Assume
a 1 ohm operating resistance for a pitot tube. 1 ohm produces a
current draw of 14A for a total wattage of 196 watts. Now put
a 1 ohm resistor in series with the pitot tube. Current drops
by half to 7A for a TOTAL wattage of 98 watts. Half this wattage
will be dissipated by the pitot tube, the other half in the
resistor.
Bob . . .
Message 27
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| Subject: | Re: RE: Pitot Current Draw |
Lloyd, Daniel R. wrote:
>
>But wouldn't you still be wasting electrical power as heat on the
>resistor?
>
Yes.
>If the overall goal is to reduce power consumption, IE make
>the battery last longer, you would not want additional resistance. Or am
>I all backwards?
>
>
This setup would only work if you arranged for the pitot tube to be the
radiator for the resistor. If you stick the resistor at the switch,
then you haven't gained anything (unless maybe you were also needing a
hand warmer).
>I went with the Gretz Pitot, because it stays at a constant lower temp
>and power cycles itself to maintain that temp, so overall I am using
>less power, rather than just dumping it as heat.
>Dan
>
>
Back to the original question, I just remember Eric posting a howto on
how to use some temperature gradient resistors he has for sale to
moderate pitot heat current.
--
,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o http://ernest.isa-geek.org |
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| Subject: | RE: Pitot Current Draw |
At 02:28 PM 12/5/2006 -0500, you wrote:
><LloydDR@wernerco.com>
>
>I think it is better described like this, you double the resistance,
>half the current is felt on each device, but the power drop across the
>circuit is still the same, IE the pitot only gets half as hot and the
>resistor is getting the other current, and no net gain or loss on
>wattage consumption.
>Correct?
no . . . at 1/2 current each device gets 1/4 the original
power dissipation because votlage across each device is
also down by 1/2.
Bob . . .
Message 29
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| Subject: | RE: Pitot Current Draw |
Great example, now I better understand.
THX
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Robert L. Nuckolls, III
Sent: Tuesday, December 05, 2006 2:36 PM
Subject: RE: AeroElectric-List: RE: Pitot Current Draw
<nuckollsr@cox.net>
At 02:01 PM 12/5/2006 -0500, you wrote:
><LloydDR@wernerco.com>
>
>But wouldn't you still be wasting electrical power as heat on the
>resistor? If the overall goal is to reduce power consumption, IE make
>the battery last longer, you would not want additional resistance. Or
am
>I all backwards?
>I went with the Gretz Pitot, because it stays at a constant lower temp
>and power cycles itself to maintain that temp, so overall I am using
>less power, rather than just dumping it as heat.
Yes, the resistor gets hot too but TOTAL energy is down. Assume
a 1 ohm operating resistance for a pitot tube. 1 ohm produces a
current draw of 14A for a total wattage of 196 watts. Now put
a 1 ohm resistor in series with the pitot tube. Current drops
by half to 7A for a TOTAL wattage of 98 watts. Half this wattage
will be dissipated by the pitot tube, the other half in the
resistor.
Bob . . .
Message 30
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| Subject: | Re: Aux Altenator switching. |
Yes, the small ND sure has merits and probably had the same issues as
any add on alternator for the Rotax. I wont need 40a but 25 or 30
would be nice to simplify my electrical system. Then the Rotax
marginal unit would just be a backup.
Thanks for your input, Paul
===================
At 10:39 AM 12/5/2006, you wrote:
><nuckollsr@cox.net>
>
>At 10:01 AM 12/5/2006 -0800, you wrote:
>
>>
>>Bob,
>>Does your comment "There is no danger to any equipment on the airplane by
>>having both alternators on at the same time. "
>> Does this mean if I add a John Deere 20a and run at the same time
>> as my Rotax 18 Amp unit that I can get 38 amps max case? Any down
>> side to doing this?
>
> There's a difference between risks for damage and performance as
> shared suppliers of loads to the system. The problem is getting
> respective voltage regulators of two engine driven power sources
> to appropriately share total loads based on their respective
> capabilities.
>
> I've designed such regulators but the technology I've used
> is not compatible with PM alternators. It would take a start
> from scratch effort to get the proportionate paralleling
> performance that's desired when running two power sources.
>
> Yes, you can run two alternators and count on their added
> capacities for total engine driven power . . . but without
> hardware specific to making them share loads, you'll find
> yourself fiddling with the regulation setpoints a lot.
>
> If you can bolt a 20A PM alternator to your engine, why
> not a 40A ND alternator with some REAL capacity to run
> the whole airplane and save the smaller alternator for backup
> a-la Z-13/8?
>
> Bob . . .
Message 31
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| Subject: | Re: Aux Altenator switching. |
At 01:03 PM 12/5/2006 -0800, you wrote:
>
>Yes, the small ND sure has merits and probably had the same issues as any
>add on alternator for the Rotax. I wont need 40a but 25 or 30 would be
>nice to simplify my electrical system. Then the Rotax marginal unit would
>just be a backup.
Keep in mind that your alternator has two functions: (1) carry the
max running load for equipment on board and (2) recharge the battery.
(Battery charging energy) = (alternator energy) - (running loads).
Just because your alternator is 'oversized' is not necessarily a
bad or even undesirable thing. If you had a hard time getting the
engine started or want to go flying after extended ground maintenance
ops from the battery, then being able to reload the battery quickly
with just your alternator output is a pretty nifty thing.
What's the weight difference? A 40A ND alternator compared to
the JD PM alternator + rectifier/regulator? I'll bet it's about
a wash and for my money, I'd take the 40A ND over a 20A JD
machine any day.
The SD-8 at 3.5 pounds and its compatibility with the AND20000
pad on the back of the engine is the recipe for success . . . but
I've never understood the perceived allure for the larger PM
alternators as compared to the smaller wound-field devices.
Bob . . .
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