Alternator warning light on 912 Rotax

[avidflyer]

First off, my least favorite thing is wiring, most likely cause it seems a bit like black magic. Or something like that...Anyway, I'm wiring up my Kitfox 4 rebuild project, and I want to just have a in panel light that goes off once the engine starts and the alternator starts charging. I have that on my Avid Mk IV with the Jabiru and it works for me.. In the Rotax installation manual, it says use a 3 watt lamp. All I can find it seems are LED lights that draw far, far less then that. Does anyone know if it will make any difference using a much smaller wattage light? Thanks, JImChuk

PS, here is the panel so far. Leaving the upper right side open for a 8" tablet running Avare GPS when needed or wanted. Still have a couple of holes to cut. Forgot the ELT remote for one thing... :-()

[Av8r3400]

I'd say you want to either find a 3 watt bulb or add a resistor to the circuit with the LED to get the resistance the same as the 3 watt bulb.

[avidflyer]

Thanks Larry, that then brings up the next question. What size resister would it take to get up to the 3 watts. I believe the LED light uses 0.2 watt. Like I said, electronics is not my strong suit... :-) JImChuk

[jrevens]

Jim,

With conventional automotive alternators, something like a 3 watt load is necessary for that light to work. I don't know about the Rotax specifically, but an LED should be able to be used, as Larry said. Here is one drawing that I had, and I've attached a .pdf file with another. I hope one or the other will help you. Anyway, you may be able to use this information to fabricate a simple circuit for use with the Rotax. Here you go -

24426

I like your panel. Looks like you're using my favorite simple TruTrak autopilot. I've got one just like it. I wish they still made them.

[avidflyer]

Hi John, Thanks for the drawings. I sent you a private message. Thanks, JImChuk

[Delta Whisky]

Jim - the light is grounded by the regulator-rectifier (not powered) upon fault detection. Any 12v DC light will work just fine. It can't be more than 3W because the regulator isn't designed to handle more than that. Should you buy a 12V LED, it will have the necessary voltage drop down resistor in it. I used this (539-FL1M8SW-1-R12V) from Mouser.

[avidflyer]

Thanks everyone, I think I have it figured out now. JImChuk

[CoClimber]

A note here from an electrical engineer. The LED itself only draws maybe 20 milliamps. 20mA x 12 volts is .24 watt. In the above circuit, there is a secondary current path to dissipate through that parallel resistor. You would need a 48 ohm resistor to draw 3 watts. Now, here's the important part. 3 watts as a fair amount of heat so you want to get a resistor that can be mounted to a heat sink. I would think that the firewall should be fine.

[desertdave]

Reviving this thread. I am joining the 21st century and installing EFIS. I would love to match the alternator warning light with my EarthX battery light. Will this suffice?
https://earthxbatteries.com/product/5mm12-12v-led-fault-indicator/

12V LED Indicator Light$29.99
Specifications:


Color: Amber
Mounting: Nut and Washer (included)
Termination style: Wire 20ga- 48″ length
Voltage: 12V
Built in resistor: 500 ohm, 1/2 Watt
Drill bit size: .325 or 5/16″



30399

[DesertFox4]

Dave, I have maybe four of those L.E.D. caution lights at my hangar. You can have one or a couple if needed. I have different colors too. Green, red and yellow I believe.
Will bring them down next week when I visit Deer Valley.

[SilverFox5]

I think I know my answer but I am also not an experienced electrical guru. I want to confirm the indicator light we are talking about here (picture of Rotax electrical dwg attached) is a fault light and will only be on if no charging is detected correct?

Joe
Kitfox5
912uls

[Geek]

Yup. That's its job.

G

[Eric Page]

Think of the "L" terminal on the regulator as a switch, controlled by the charging state. If the regulator is charging the battery then the switch is open (no current flows through the lamp), and if the regulator is not charging the battery then the switch is closed (turning on the lamp).

[SilverFox5]

That is what I thought but was not positive.
Thanks for confirming!

Joe