Today's Message Index:
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1. 05:48 AM - Re: Name that Voltage Regulator (Robert L. Nuckolls, III)
2. 05:54 AM - Current limiter used as ammeter shunt (user9253)
3. 08:34 AM - Re: Current limiter used as ammeter shunt (Jeff Luckey)
4. 10:36 AM - Re: Electrical System with Dual Batteries & Brownout Prevent (Jeff Luckey)
5. 11:38 AM - Re: Current limiter used as ammeter shunt (user9253)
6. 11:59 AM - Re: Current limiter used as ammeter shunt (Robert L. Nuckolls, III)
7. 12:39 PM - Re: Re: Current limiter used as ammeter shunt (Jeff Luckey)
8. 04:43 PM - Re: Current limiter used as ammeter shunt (user9253)
Message 1
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Subject: | Re: Name that Voltage Regulator |
At 17:37 2015-02-01, you wrote:
>
>I got a momentary spike of voltage (needle pegged for about two
>seconds) the other day while taxing to do my run-up. I checked my
>alternator (ALY-8520R) wiring and found that F1 was grounded to the
>starter, and F2 was connected to the field output of the
>regulator. No shorts or opens, but the wiring was in poor shape. I
>re-wired the alternator with F1 to field output on VR, and F2
>grounded on alternator case (does it even matter which way F1/F2 are wired?).
No . . .
> Wiring on the VR is also in poor shape (cracked insulators). I
> will probably replace with the B&C LR3C-14, but it's about four
> times the size of my current regulator! In the meantime until I
> find a place to mount the B&C, I'd like to replace the existing
> regulator as a quick fix, but can't find a match. No part numbers
> or markings other than "12V" and "Nov 1984".
Go to a car-parts store and get a
generic replacement for a 1980's
Ford. If it looks like this
http://tinyurl.com/nfwuxtl
it will work no matter what brand/
part number. Should be able to pick one
up locally for $20 or so . . .
Tie "A" and "S" leads together and route to
your alternator switch. Take the F lead
to the alternator. Ground the case. Leave
the "I" lead open.
See
http://tinyurl.com/ku2nb5t
for exemplar wiring. This will get you by
until the better alternative becomes
more attractive.
Bob . . .
Message 2
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Subject: | Current limiter used as ammeter shunt |
Considering that many modern EFIS ammeters can be calibrated to match any shunt,
is it feasible to use the alternator current limiter (ANL fuse) as a load-meter
shunt? If so, one device could serve a dual purpose.
The LittleFuse MEGA line of fuses are much less expensive than the ANL. Are
the MEGA fuses just as good as the ANL?
http://tinyurl.com/LittleFuse-MEGA
Thanks, Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437958#437958
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Subject: | Re: Current limiter used as ammeter shunt |
That's a really interesting question, Joe -
Shunts are designed to maintain their highly-calibrated resistance over a wide
temperature range. I don't know if that is true for current limiters, since their
mission is very different. Also, I wonder if:
1. a current limiter's response is linear
2. their resistance is consistent from manufacturing batch to batch
-Jeff
On Monday, February 2, 2015 6:01 AM, user9253 <fransew@gmail.com> wrote:
Considering that many modern EFIS ammeters can be calibrated to match any shunt,
is it feasible to use the alternator current limiter (ANL fuse) as a load-meter
shunt? If so, one device could serve a dual purpose.
The LittleFuse MEGA line of fuses are much less expensive than the ANL. Are
the MEGA fuses just as good as the ANL?
http://tinyurl.com/LittleFuse-MEGA
Thanks, Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437958#437958
Message 4
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Subject: | Re: Electrical System with Dual Batteries & Brownout |
Prevent
"Good workmanship will prevent short circuits."
Yeah, good workmanship is definitely a requirement but it is not enough. Over-current
protection devices: fuses, circuit breakers, current limiters, prevent
melting stuff and fires (that's why they were created). All the Good Workmanship
in the world cannot foresee every possible bad event.
We just had a case-in-point on the VansAirforce forum. Bad stuff happens no matter
how diligent we are in trying to prevent it - Murphy's Law. It seems irresponsible
of us as system designers to ignore that fact, especially when circuit
protection devices are so cheap, easy, and simple.
-Jeff
On Thursday, January 29, 2015 7:02 PM, user9253 <fransew@gmail.com> wrote:
Attached is a diagram that I drew of an electrical system with two engine-cranking
batteries and brownout prevention. It is intended for a seaplane that will
fly into remote lakes. Either battery can crank the engine. One of the batteries
will run a bilge pump. If the engine is cranked using only one battery,
then the other battery will provide 12 volts to avionics to prevent brownout.
The electrically dependent engine will be powered by the same bus as the avionics.
With multiple current paths through two contactors and two relays, the
chances of this bus losing power are slim. Good workmanship will prevent short
circuits.
Go ahead and point out any faults with this diagram or give suggestions. You
will not hurt my feelings. I want to fix any shortcomings or design errors.
I used Bob N's Z-19/RB as a staring point, although you might not see any resemblance.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437846#437846
Attachments:
http://forums.matronics.com//files/dual_bat_brownout_prevention__202.pdf
Message 5
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Subject: | Re: Current limiter used as ammeter shunt |
Jeff, thanks for the input. Manufacturing variations would not matter because
the EFIS ammeter would be calibrated to match the installed fuse. You are probably
right that a current limiter resistance might not be linear as temperature
and current vary. If the ammeter were an important instrument, then accuracy
would be a concern. Others might not agree, but to me, the ammeter is not
important. The voltmeter tells me that that alternator is working. Accurately
measuring current and troubleshooting is best done on the ground. Even if the
aircraft ammeter is inaccurate, the pilot will learn what is normal under certain
conditions. If the voltage drops and the ammeter shows high current, then
there is a short circuit some place. If the ammeter indicates low or no current,
then the alternator has failed. If no dedicated shunt is installed, then
there is one less thing to fail.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437973#437973
Message 6
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Subject: | Re: Current limiter used as ammeter shunt |
At 07:52 2015-02-02, you wrote:
>
>Considering that many modern EFIS ammeters can be calibrated to
>match any shunt, is it feasible to use the alternator current
>limiter (ANL fuse) as a load-meter shunt? If so, one device could
>serve a dual purpose.
> The LittleFuse MEGA line of fuses are much less expensive than
> the ANL. Are the MEGA fuses just as good as the ANL?
To be a calibrated 'shunt' the temperature coefficient
of resistance would have to be very close to zero.
Just over a century ago, the grandfather of precision
measurements . . .
http://tinyurl.com/3f79fgy
. . . offered up an improvement on his earlier
low tempco wire (Constantan) dubbed Manganin
http://tinyurl.com/ln5q4at
This material is favored for use in ammeter
shunts and precision resistors. Fusing alloys
are modified for their I(squared)R melting
characteristics. fast blow fuses (like a
glass, AGC1) probably have a higher tempco
than say a current limiter with robustness
approaching copper wire.
Using the copper in a b-lead isn't a 'terrible'
idea . . . it's certainly no less useful
than the legacy -0+ battery ammeters used
in millions of vehicles.
Ammeters are generally not a flight operations
or diagnostics instrument. If the bus volts
are up, all is right with the universe. If
the bus volts are too low, then implementation
of plan-b is called for. The precise value
of ANY current in the system may be interesting
but it's of little use in comfortably
terminating your flight.
Bob . . .
Message 7
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Subject: | Re: Current limiter used as ammeter shunt |
Joe,
1. "Manufacturing variations would not matter because the EFIS ammeter would be
calibrated to match the installed fuse.
On Monday, February 2, 2015 11:54 AM, user9253 <fransew@gmail.com> wrote:
Jeff, thanks for the input. Manufacturing variations would not matter because
the EFIS ammeter would be calibrated to match the installed fuse. You are probably
right that a current limiter resistance might not be linear as temperature
and current vary. If the ammeter were an important instrument, then accuracy
would be a concern. Others might not agree, but to me, the ammeter is not
important. The voltmeter tells me that that alternator is working. Accurately
measuring current and troubleshooting is best done on the ground. Even if the
aircraft ammeter is inaccurate, the pilot will learn what is normal under certain
conditions. If the voltage drops and the ammeter shows high current, then
there is a short circuit some place. If the ammeter indicates low or no current,
then the alternator has failed. If no dedicated shunt is installed, then
there is one less thing to fail.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437973#437973
"
There may be variations from batch to manufacturing batch therefore you may have
to re-calibrate your EFIS if you ever have to install a new current limiter.
(granted, we hope that doesn't happen very often)
Also - how would you calibrate the current limiter?
2. "Others might not agree, but to me, the ammeter is not important."
If the ammeter is not important and it is not displaying accurate info, then why
bother with it?
3. "If no dedicated shunt is installed, then there is one less thing to fail."
There's not much that can go wrong with a shunt (except maybe melting - and if
that happens, you've got other problems) It's a solid-state hunk a calibrated
metal and therefore very unlikely to fail. (it's probably one of the most reliable
electrical components in the airframe)
4. For the scenarios you outline above, it seems that the voltmeter gives the appropriate
indications.
I like ammeters for a few of reasons:
1. In a battery-only situation, they help the pilot confirm that electrical loads
have been appropriately minimized so that you will achieve the designed endurance.
In this case, you want fairly accurate information because a few amps
might be critical to endurance calculations.
2. To the trained eye, they can provide hints to other problems
3. They can help make testing & trouble-shooting easier
-Jeff
Message 8
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Subject: | Re: Current limiter used as ammeter shunt |
> how would you calibrate the current limiter?
I thought that could be done in the EFIS software.
> If the ammeter is not important and it is not displaying accurate info, then
why bother with it?
If the EFIS has the ammeter feature but a builder does not want to install a shunt,
then maybe the ammeter could be connected to the alternator fuse. I was
not recommending that, only asking if it was feasible.
I did see an electric hi-low battery-charger shunt fail at work. The likely cause
was a loose connection that generated heat.
Jeff, I can not argue with your reasoning. Everything you wrote makes sense.
Your response and Bob's indicate that using a current limiter as an ammeter shunt
is a bad idea. Look at the good side. This topic filled a void on the AeroElectric
list between more important questions. :-)
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437996#437996
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