Today's Message Index:
----------------------
1. 09:11 AM - Re: Relay sticking (Robert L. Nuckolls, III)
2. 09:12 AM - Re: Relay sticking (Robert L. Nuckolls, III)
3. 02:45 PM - Schottky Diode (Peter Pengilly)
4. 04:36 PM - Re: Schottky Diode (user9253)
5. 04:40 PM - Re: Schottky Diode (Robert L. Nuckolls, III)
6. 06:04 PM - Re: Relay sticking (FLYaDIVE)
7. 06:15 PM - Re: Schottky Diode (Charlie England)
8. 07:02 PM - Re: Relay sticking (Robert L. Nuckolls, III)
9. 07:03 PM - Re: Schottky Diode (Robert L. Nuckolls, III)
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Subject: | Re: Relay sticking |
At 07:14 PM 12/24/2018, you wrote:
>We had a strange event last week with our O-200 powered CH750. After
>running the battery down during a fuel gauge calibration that lasted
>over an hour, one of our pilots tried to start the engine to taxi
>back but with the already depleted battery and a less than perfect
>start procedure they gave up after a couple weak start attempts. I
>walked over to the aircraft to brief them on a prop start and when I
>asked for the master on the starter ran.
The vast majority of starter contactor
sticking events occur during an attempt
to crank the engine with a weak battery.
The fact that you got immediate starter
action on closure of the master switch
says your starter contactor was 'stuck'
shut.
> Shut the master off, cycled the start button rapidly a dozen
> times, master on again and the starter ran again. I could hear the
> starter relay clicking loudly each time power was applied so it
> does not seem like there was a physical failure of the relay but
> more some electrical short activating the relay each time power was applied.
Contacts are welded . . .
>The build team inspected the relay and found a loose connection.
>Tightening it took the problem from continuous to intermittent; in
>their words "it's fixed but it did it again once".
>
>We have removed the relay for replacement, I still think the switch
>is suspect but they've decided the problem is the relay. Does the
>aeroelectric list think there would be value in cutting open the
>relay and examining it? Any suggestions on how best to do so?
Go to a car parts store and pick
up a starter contactor that looks
like the one in the aircraft spruce
catalog . . . it will work just fine.
See if the contactor is marked "diode
suppressed" or has the word diode on it
anywhere or on the packaging.
Emacs!
Bob . . .
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Subject: | Re: Relay sticking |
At 11:56 AM 12/25/2018, you wrote:
>Sorry, I didn't know Lycoming made an O-200,
>this one is a Continental. In any case we think
>the problem is in the relay or switch, not the starter itself.
>
>We are planning on replacing the relay with one of these:
>
><https://aircraftspruce.ca/catalog/elpages/starterrelay.php>https://aircraf
tspruce.ca/catalog/elpages/starterrelay.php
>
>At $20=C2 it seems a good idea.
Any similar contactor from your local car-parts
emporium will do nicely . . .
>What I'm wondering about is how to best cut open
>the old one in order to see how the failure may have occurred?
Send it to me and I'll conduct an
'up town' failure analysis and report
back.
Bob . . .
Message 3
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Dear Aeroelectric People,
I'm in the process of designing an electrical system for a sailplane and am
looking for some advice on selecting a Schottky Diode.
My aim for this system is to avoid the pilot having to manage the battery
power during flight. Ideally the batteries should be switched on before
take-off and nothing more done until they are switched off after landing and
removed for re-charging. It is accepted the batteries will need charging
each night.
The batteries cannot be changed because of the provided battery trays. The
avionics are primarily powered by 2 x 7Ah gell cells. The equipment specs
say the total current drain is 1.7A (including a transponder), therefore it
is quite possible to run short of amps after a long flight, a 6 hour flight
is not unusual, and longer is definitely possible. I suspect the power
numbers are a little on the high side and are also somewhat variable,
depending on radio usage, screen brightness and other factors. Until the
system is in use its difficult to be sure of the electrical load. There is
also a 4Ah battery in the fin for cg management purposes that is usually
kept in reserve to ensure a flight can be completed with power in hand - its
is rarely possible to predict exactly how long a flight will take. Often it
is essential to keep a GPS logger running at all times for competition
scoring purposes, it is desirable the glide computer is operating at the end
of a flight to help with planning the final glide.
This aircraft also has a get-you-home 2 stroke motor that extends from
behind the cockpit to guard against an out-landing, known as a "turbo". A
15Ah gell cell extends and retracts the engine using an electric spindle
drive, it is dive started and has no throttle or generator. I want to make
the engine battery available as a back-up to the avionic batteries.
The problem is to design a system that requires minimum management and
provides maximum endurance. Connecting all batteries to the bus results in
stronger batteries back charging the weaker and wasting power. Installing
regular diodes to prevent the back charging drops too much voltage. Having
to switch batteries in and out manually is bound to lead to increased
workload at the most inconvenient times. I want to run on the main avionic
batteries initially, keeping the engine battery to run the engine when
needed and the fin battery in reserve. Theoretically Schottky Diodes, with
only a 150mv forward voltage, on each battery line will prevent back
charging with an acceptable voltage drop.
It is possible to use a pair of DPDT switches to split the avionic system
and use 2 batteries to power the 2 halves of the system, but allowing one
battery to power all if one depletes before the other. However, if both main
batteries can be connected directly to a single bus system management will
be more straight forward.
I know little about electronic components, and have only confused myself
looking at the various tables. The maximum instantaneous current draw is
around 4.7A on the avionics bus (3.2A for the radio plus 1.5A for other
services), the engine can pull 8A instantaneously when it is raised. I have
only been able to find one device that comes close to meeting what I think I
need, https://www.mouser.co.uk/datasheet/2/205/L497-1110523.pdf, but this is
quite expensive and is described as a rectifier, not completely sure it is
suitable. This
https://uk.rs-online.com/web/p/rectifier-diodes-schottky-diodes/1023567/ may
be a candidate, but the forward voltage is higher than I would like, it
seems that the temperature must be high (over 100*C) to reduce it to my
150mv target.
Does anyone know of a component that may be suitable? Sketch of architecture
below.
Am I going to have to accept a small overhead in managing the battery power
on a long flight?
Regards, Peter
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Subject: | Re: Schottky Diode |
I do not think that "back charging" is going to be an issue. There would have
to be a large voltage difference between batteries before one would charge the
other. Just connect the two 7ah batteries in parallel and let them both discharge
simultaneously. A load will draw current from whichever battery has the
highest voltage.
Consider using discrete, through hole, diodes which cost 51 cents each.
https://www.mouser.com/Semiconductors/Discrete-Semiconductors/Diodes-Rectifiers/Schottky-Diodes-Rectifiers/_/N-ax1mjZ1yzvvqx?P=1z0z63xZ1yuoc72Z1yuoc5bZ1yuoc76&Ns=Pricing%7c0
Or dual diodes are available in a TO-220 case for $1.50
https://www.mouser.com/ProductDetail/Diodes-Incorporated/SBR10U40CT?qs=sGAEpiMZZMtQ8nqTKtFS%2fNX0wTwLhSQZv372G1bq%2fbs%3d
Insulate the mounting tab from aircraft ground.
The stated forward voltage drop is for maximum current. The voltage drop will
be less with less current.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=486574#486574
Message 5
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Subject: | Re: Schottky Diode |
I'm in the process of designing an electrical system for
a sailplane and am looking for some advice on selecting a Schottky Diode.
Hi Peter, long time no hear!
My aim for this system is to avoid the pilot having to manage the battery
power during flight. Ideally the batteries should be switched on before
take-off and nothing more done until they are switched off after landing
and removed for re-charging. It is accepted the batteries will need charging
each night.
<snip>
The problem is to design a system that requires minimum management and provides
maximum endurance. Connecting all batteries to the bus results in stronger
batteries back charging the weaker and wasting power.
This is a myth. Batteries cannot charge
batteries. Any number of serviceable
batteries can be connected in parallel
irrespective of capacity. All energy
stored in every battery is available
to the intended task . . . there is
no 'exchange' of energy between batteries.
Installing regular diodes to prevent the back charging drops too much voltage.
Having to switch batteries in and out manually is bound to lead to increased
workload at the most inconvenient times. I want to run on the main avionic
batteries initially, keeping the engine battery to run the engine when needed
and the fin battery in reserve.
A 'reserve' battery seems a confession
as to lack of knowledge of the
total energy needs compared to battery
capacity. The only reason you need
a 'reserve' is to carry out a near-
emergency move because the system went
dark unexpectedly. You should be able
to design the unexpected event . . .
Theoretically Schottky Diodes, with only a 150mv forward voltage, on each
battery line will prevent back charging with an acceptable voltage drop.
Diodes are probably unnecessary . . . pending
further discovery . . .
It is possible to use a pair of DPDT switches to split the avionic system
and use 2 batteries to power the 2 halves of the system, but allowing one
battery to power all if one depletes before the other. However, if both
main batteries can be connected directly to a single bus system management
will be more straight forward.
I'm not so sure than ALL the batteries
cannot be operated in parallel with no
diodes. Further, if capacities of SVLA
batteries prove marginal, have you
considered a lithium system? More capacity
in same volume and weight constraints.
I know little about electronic components, and have only confused myself
looking at the various tables. The maximum instantaneous current draw
is around 4.7A on the avionics bus (3.2A for the radio plus 1.5A for other
services), the engine can pull 8A instantaneously when it is raised.
<snip>
You need to do a load analysis that seeks to
define your ENERGY requirements. A 15 a.h.
battery JUST to raise and lower the engine
seems huge overkill . . . that's a LOT of energy
to supply a need that persists for mere seconds
per flight cycle.
<snip>
Does anyone know of a component that may be suitable? Sketch of
architecture below.
Am I going to have to accept a small overhead in managing the battery
power on a long flight?
I think your 'cart' is overrunning the horse
. . .
I would advise some further research and
perhaps experiments to ascertain
real energy requirements. I'm 99% certain
that a system can be devised that needs no
diodes and may well offer energy reserves
that far exceed your greatest expectations.
But we need some real NUMBERS first . . .
Can you share an equipment list? Are
these equipment items in-hand? If
so, what's the possibility of powering
these items up on the bench and getting
good current draw numbers? If not on
your constellation of intended equipment,
how about on examples installed on other
aircraft?
How long is an extend/retract cycle on
the engine?
Bob . . .
Message 6
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Subject: | Re: Relay sticking |
Bob,
Cutting open of a relay depends on the design of the relay. If you are
talking the standard hermetically sealed / rolled over edge type, you do
NOT cut it open... You simply grind off the rolled over edge. This can be
done very carefully so none of the metal filings enter the relay. If done
carefully you may even find water inside the relay. That is what I found
in mine!
Next trick: If you replace the relay with the same kind (hermetically
sealed) do the following:
Get a pint of epoxy paint.
Mask the terminals of the relay.
Using a heat gun heat the relay hot enough that you can not touch it.
Then totally submerge the relay in the epoxy paint.
As the relay cools it will suck in the epoxy paint into the rolled edge and
seal out any paint.
NOW! You have a hermetically sealed relay.
Not done yet... Next trick: Make sure you mount the relay so the edge of
the rolled edge is facing DOWN. Now water and ice will not collect.
Barry
On Thursday, December 27, 2018, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 11:56 AM 12/25/2018, you wrote:
>
> Sorry, I didn't know Lycoming made an O-200, this one is a Continental. I
n
> any case we think the problem is in the relay or switch, not the starter
> itself.
>
> We are planning on replacing the relay with one of these:
>
> https://aircraftspruce.ca/catalog/elpages/starterrelay.php
>
> At $20=C3=82 it seems a good idea.
>
>
> Any similar contactor from your local car-parts
> emporium will do nicely . . .
>
>
> What I'm wondering about is how to best cut open the old one in order to
> see how the failure may have occurred?
>
>
> Send it to me and I'll conduct an
> 'up town' failure analysis and report
> back.
>
>
> Bob . . .
>
--
Barry
"Chop'd Liver"
If you wash your hands before you go to the bathroom you may have the
makings of a Crew Chief.
Message 7
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Subject: | Re: Schottky Diode |
On 12/27/2018 4:43 PM, Peter Pengilly wrote:
>
> Dear Aeroelectric People,
>
> Im in the process of designing an electrical system for a sailplane
> and am looking for some advice on selecting a Schottky Diode.
>
> My aim for this system is to avoid the pilot having to manage the
> battery power during flight. Ideally the batteries should be switched
> on before take-off and nothing more done until they are switched off
> after landing and removed for re-charging. It is accepted the
> batteries will need charging each night.
>
> The batteries cannot be changed because of the provided battery trays.
> The avionics are primarily powered by 2 x 7Ah gell cells. The
> equipment specs say the total current drain is 1.7A (including a
> transponder), therefore it is quite possible to run short of amps
> after a long flight, a 6 hour flight is not unusual, and longer is
> definitely possible. I suspect the power numbers are a little on the
> high side and are also somewhat variable, depending on radio usage,
> screen brightness and other factors. Until the system is in use its
> difficult to be sure of the electrical load. There is also a 4Ah
> battery in the fin for cg management purposes that is usually kept in
> reserve to ensure a flight can be completed with power in hand its
> is rarely possible to predict exactly how long a flight will take.
> Often it is essential to keep a GPS logger running at all times for
> competition scoring purposes, it is desirable the glide computer is
> operating at the end of a flight to help with planning the final glide.
>
> This aircraft also has a get-you-home 2 stroke motor that extends from
> behind the cockpit to guard against an out-landing, known as a
> turbo. A 15Ah gell cell extends and retracts the engine using an
> electric spindle drive, it is dive started and has no throttle or
> generator. I want to make the engine battery available as a back-up to
> the avionic batteries.
>
> The problem is to design a system that requires minimum management and
> provides maximum endurance. Connecting all batteries to the bus
> results in stronger batteries back charging the weaker and wasting
> power. Installing regular diodes to prevent the back charging drops
> too much voltage. Having to switch batteries in and out manually is
> bound to lead to increased workload at the most inconvenient times. I
> want to run on the main avionic batteries initially, keeping the
> engine battery to run the engine when needed and the fin battery in
> reserve. Theoretically Schottky Diodes, with only a 150mv forward
> voltage, on each battery line will prevent back charging with an
> acceptable voltage drop.
>
> It is possible to use a pair of DPDT switches to split the avionic
> system and use 2 batteries to power the 2 halves of the system, but
> allowing one battery to power all if one depletes before the other.
> However, if both main batteries can be connected directly to a single
> bus system management will be more straight forward.
>
> I know little about electronic components, and have only confused
> myself looking at the various tables. The maximum instantaneous
> current draw is around 4.7A on the avionics bus (3.2A for the radio
> plus 1.5A for other services), the engine can pull 8A instantaneously
> when it is raised. I have only been able to find one device that comes
> close to meeting what I think I need,
> https://www.mouser.co.uk/datasheet/2/205/L497-1110523.pdf, but this is
> quite expensive and is described as a rectifier, not completely sure
> it is suitable. This
> https://uk.rs-online.com/web/p/rectifier-diodes-schottky-diodes/1023567/
> may be a candidate, but the forward voltage is higher than I would
> like, it seems that the temperature must be high (over 100*C) to
> reduce it to my 150mv target.
>
> Does anyone know of a component that may be suitable? Sketch of
> architecture below.
>
> Am I going to have to accept a small overhead in managing the battery
> power on a long flight?
>
> Regards, Peter
>
Hi Peter,
(edit: looks like others have made most of these points while I was
'distracted' with other stuff, but here you go, anyway.)
I'm certainly no expert, but I'll take a swing at a few of the questions.
1. I'd prefer to have a single battery at 14AH, vs 2 @ 7AH, if it's
physically possible to do it. Simpler, and you intend to have a backup
anyway.
2. Gell is not the same thing as the currently common SLA, 'starved
electrolyte' battery. Gel cells may still be available, but they're a
lot more finicky to deal with than a common SLA battery.
3. I have not yet gotten excited about flying a powered a/c with a
lithium-iron battery, but have you considered it for your 'total loss'
system? Charging the battery outside the a/c removes a significant
percentage of risk, and you could carry a *lot* more capacity in a much
lighter package (for a price, of course...).
4. Since knowing your exact loads are a bit more critical than a typical
a/c, rather than look at mfgr data sheets, consider directly measuring
each item's current in actual operation. Most data sheets will show you
a conservative number, to be sure the installer doesn't 'short change'
the device's needs.
5. The Mouser device you linked is a bit of overkill (200A), and will be
a bit of a hassle to mount. The mounting surface is also the cathode,
meaning you'd need to isolate it from the air frame and for safety, from
any heatsink you mount it on. The 2nd one you show has an isolated
mounting tab. But there are hundreds of choices. Here's one:
https://www.ebay.com/itm/Schottky-Diodes-Rectifiers-2X60-Amp-15-Volt-DIODE-MODULE-ISOTOP/273285163944?epid=1718397917&hash=item3fa110aba8:g:cbkAAOSwgd1axcQL:rk:4:pf:0
Another:
https://www.ebay.com/itm/1-S20SC9M-SCHOTTKY-RECTIFIER-DUAL-COMMON-CATHODE-DIODE-90V-20A-MTO-3P/390680777077?hash=item5af6639175:g:az0AAOxyoahSXtlc:rk:9:pf:0
6. If you can go with one main battery (or parallel the pair of 7As),
there'd only be one switch for the 4A backup. The switch for the 15A
starting battery you will need, regardless of the rest of the architecture.
Charlie
---
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Message 8
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Subject: | Re: Relay sticking |
At 08:02 PM 12/27/2018, you wrote:
>Bob,
>
>Cutting open of a relay depends on the design of
>the relay.=C2 If you are talking the standard hermetically sealed
hermetically sealed implies
absolute atmospheric isolation
between interior and the
environment. Contactors with
rolled on caps are not 'hermetic',
only very secure.
> / rolled over edge type, you do NOT cut it
> open...=C2 You simply grind off the rolled over
> edge.=C2 This can be done very carefully so none
> of the metal filings enter the relay.=C2 If done
> carefully you may even find water inside the
> relay.=C2 That is what I found in mine! =C2
Yep . . . been there a few dozen times.
https://tinyurl.com/p2x7fbl
https://tinyurl.com/kcc26jt
Cessna attempted some DIY sealing techniques
on the whisky barrel relays . . . right
after the noise reducing, floating cowl
was incorporated onto the SE aircraft.
Virtually no help. You could not guarantee
quality of seal. Liquid water sucked in
during a cooling event had to exit as a vapor
over successive atmospheric 'breathing'
cycles . . . i.e. once inside it stayed
inside.
>Not done yet...=C2 Next trick: =C2 Make sure you
>mount the relay so the edge of the rolled edge
>is facing DOWN.=C2 Now water and ice will not collect.
or cap facing down with a #40 drain
hole added right in the center. Now
trapped liquid had a place to get
out.
Bob . . .
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Subject: | Re: Schottky Diode |
>
>
>4. Since knowing your exact loads are a bit more critical than a
>typical a/c, rather than look at mfgr data sheets, consider directly
>measuring each item's current in actual operation. Most data sheets
>will show you a conservative number, to be sure the installer
>doesn't 'short change' the device's needs.
BINGO!
Bob . . .
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