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R C Allen low voltage warner, wiring details/diagram

Philly5G

Registered User
England
Does anyone know the correct wiring order of the 3 wires on the circuit board, to the 3 terminals in the warning light plug please?

Also the correct fuse to use?

Thanks!! [emoji41]


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What system are you using? All the low voltage lights I'm seeing only use two wires directly to the light.

Web
 
What system are you using? All the low voltage lights I'm seeing only use two wires directly to the light.

Web

Thanks for the quick response Web :) It’s the R C Allen 14v one. In all the pics I’ve seen, the bulb unit looks to be connected to the long tube unit (that looks like an orange/red shotgun cartridge) but in my aircraft they’re separate and the 3 wires that connect the units together were so brittle they came apart when touching wiring nearby, hence my question :)

The other end of the shotgun cartridge DOES have just 2 wires, black and white


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Was it supposed to be separate? If not, you may have to contact RC Allen for info.

Web

From looking at the pics, I’d say it was supposed to be one piece, but looks like it’s come apart over time.

I’ve put an email in to R C Allen support and hope it’s fixable, but as the fuse was blown and of an indeterminate amperage, could be board component damage as the wires may have shorted out.

If it is toast, think I’ll just replace it with a voltmeter as much more useful I think, any thoughts? :)


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Check this out https://www.davtron.com/product-detail.php?11 I have one in my Cub it tells me what the alternator/generator amperage output is. The bus voltage and the amount of amperage going into or out of the battery. Tells me everything that I need to know, accurate to one decimal point.

m475vaa_5x2.jpg
 
Philly

I pulled this up from the LAA TL3.26 (Technical leaflet)

"A low voltage warning light is still mandated on certain UK aircraft with Certificates of Airworthiness by means of Generic Requirement 6 in CAP 747."

Possibly worth a read

Frank
 
You'll have to verify any legal requirements, but the most useful electrical monitor is a unit that allows you to read voltage AND amps. If you are required to have a voltage warning light installed, consider a unit like the Electronics International VA-1A. It reads volts, amps, and has over/under voltage lights built in.

Traditionally the shunt for the ammeter was placed in the main bus wire. With a generator this made sense as when a generator stops charging, current from the battery will flow to ground through the generator itself, showing as current coming FROM the battery instead of INTO the battery (reverse current). If you have an alternator installed, I prefer to install the shunt in the alternator output lead. Alternators will not create a reverse current situation, if they stop charging, as they use diodes to control current flow and diodes only allow that flow in one direction. This shunt location will allow you to monitor total current flow from you alternator at any time, which is useful for troubleshooting. It also allows you to actually measure the current flow to individual systems by noting the amps reading before and after turning on a switch/breaker. For example, you show a reading of three amps on the ammeter. You turn on the nav lights and the ammeter shows five amps. Therefore your nav lights pull two amps. In the future, if you turn on the nav lights and the ammeter does not increase by two amps, you know at least one of them is inoperative.

As for normal monitoring of the charging system, I prefer watching the voltage. Over or under voltage conditions usually show up quickly and catching those conditions can keep you from burning out components or allowing you to turn off systems to preserve battery voltage for the trip home. If you only have an ammeter, how do you know what is causing a high or low reading?

Web
 
Philly

I pulled this up from the LAA TL3.26 (Technical leaflet)

"A low voltage warning light is still mandated on certain UK aircraft with Certificates of Airworthiness by means of Generic Requirement 6 in CAP 747."

Possibly worth a read

Frank

Thanks for this Frank :) As my 12 is on an LAA permit this isn’t compulsory, but we always consider this kind of compulsory stuff as very probably good to have and I’d already decided to source a replacement if the low volt system couldn’t be fixed :)


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Maybe this one? It has a discharge light and an over voltage light:

Screen Shot 2019-01-18 at 3.41.27 PM.png

It's probably overkill just for a light, but it's pretty bulletproof.
 

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You'll have to verify any legal requirements, but the most useful electrical monitor is a unit that allows you to read voltage AND amps. If you are required to have a voltage warning light installed, consider a unit like the Electronics International VA-1A. It reads volts, amps, and has over/under voltage lights built in.

Traditionally the shunt for the ammeter was placed in the main bus wire. With a generator this made sense as when a generator stops charging, current from the battery will flow to ground through the generator itself, showing as current coming FROM the battery instead of INTO the battery (reverse current). If you have an alternator installed, I prefer to install the shunt in the alternator output lead. Alternators will not create a reverse current situation, if they stop charging, as they use diodes to control current flow and diodes only allow that flow in one direction. This shunt location will allow you to monitor total current flow from you alternator at any time, which is useful for troubleshooting. It also allows you to actually measure the current flow to individual systems by noting the amps reading before and after turning on a switch/breaker. For example, you show a reading of three amps on the ammeter. You turn on the nav lights and the ammeter shows five amps. Therefore your nav lights pull two amps. In the future, if you turn on the nav lights and the ammeter does not increase by two amps, you know at least one of them is inoperative.

As for normal monitoring of the charging system, I prefer watching the voltage. Over or under voltage conditions usually show up quickly and catching those conditions can keep you from burning out components or allowing you to turn off systems to preserve battery voltage for the trip home. If you only have an ammeter, how do you know what is causing a high or low reading?

Web

BRILLIANT!!! Thanks for this Web!! Read on for the last thrilling instalment!!!

Thanks to the ace team at Kelly Manufacturing, Heather, Josh and James, who make the R C Allen stuff and dug out and sent me the wiring details (attached) and fuse spec (250V 1A) and after pulling a night shift tonight, the low volts light is restored to health and looks to be working as before :) HOORAY!!!

On searching for a panel mount USB port to charge my phone when using it for GPS nav, I came across one with an inbuilt voltmeter yesterday and initial radio noise testing when iPhone charging tonight has been very successful :)

It’s obviously nowhere near as sophisticated or industrial strength as the fantastic devices suggested above, but it’s more info than I had before AND at a tiny fraction of the budget the nicer ones cost. I’ll give it an air test and feedback on its value and whether I end up splashing out on the grown up version :)

Thanks to everyone who’s contributed to this thread (and my others) and I hope the info I’ve found will help someone else :)IMG_4380.JPGIMG_4381.JPGIMG_4384.JPGIMG_4379.JPGIMG_4386.JPGIMG_4387.JPG


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I keep one of those cigarette lighter, plug in, volt meters to loan out for troubleshooting. Takes the mystery out of a straight ammeter.

Let us know how the flight test works out.

Web
 
This one is plumbed into the 12V wiring system via 2 spade terminals on the back Web and I completely get the mystery removal thing over just an ammeter. My BA4B had a similar digital voltmeter and I found it WAY more informative than the minor needle movements of the ammeter, which are basically just a +/- indication.

I bought it 99% for the USB ports and the voltmeter is a bonus and topical, given the subject of this thread. I was using my meter to test the volts and resistance when wiring the low volt stuff and this little voltmeter was spot on in sync :)

The lack of radio interference from the USB ports under load is a really nice surprise, as I was pretty much expecting it :)

I’ll let you know if it continues to be good in the air :)


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I rempved it in favor of a tablet with GPS app,
but my old Garmin 196 which I'd hardwired into the aircraft power included "voltage" in the available data fields.
 
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