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Alternator Warning Light Question

I am looking, belatedly, at fitting an alternator failure warning light from the L post on the standard alternator. I have read on other posts that an LED light will need a resistor fitted into the circuit to stop the LED glowing dimly all of the time.
Can anyone advise what size of resistor is needed to fulfil this task.
Thanks
Derek
 
Not sure what you mean by standard alternator, but the plane power 60 amp alternator allows an optional light on the white wire with no resistor. I tried to use an LED but didn't figure out the current flow and ended up with a standard incandescent light from ACS (can't seem to find the one I used).

http://planepower.aero/pdf/AL12-EI60_C.pdf
 
Alernator Warning Light Question

Thanks John. That's the alternator I have and am trying to wire up. I had just found an earlier thread that said the incandescent was good, but if you go LED then a resistor was needed otherwise it glowed all of the time. But the original posters did not say what the value of that resistor was and I'm no electrician!
 
Just a general comment. A resistor is always needed when using an LED to limit the drive current. The only time a resistor would not be needed is when you are driving it with a constant current driver.

I'm not familiar with your application so I don't know if that unit has an internal resistor.
 
For a 14v system (assuming that output is system voltage), generally a resistor in the 400ohm range is good, but it depends on the specifics of your chosen indicator.

R= V - Vled / I

R= 14-3 / 0.03

R= 11 / 0.03

R= 366.6 ohm (use the next higher value available), so 470ohm is probably your best bet.
 
I?m using B&C alternator and regulator with a LED low v indicator. Light is dim most of the time but starts flashing at 12.6v. No resistors yet but plan to add them to get rid of the dim glow. Glow is not visible in sunlight, flashing is.
 
Just a general comment. A resistor is always needed when using an LED to limit the drive current. The only time a resistor would not be needed is when you are driving it with a constant current driver.

I'm not familiar with your application so I don't know if that unit has an internal resistor.

That is not universally true. The LED indicator lights that I use on my planes are set up for 12V and have built in resistors. I can even dim them with a standard Pot. Many 12V rated LEDs has the resistor built in.

Lary
 
There's a bit of arguing here over terminology. Strictly speaking, an LED is a diode like device that emits light. In nearly all applications something must be used to limit the current. While some manufacturers pre-package the LED with a resistor, it is not "just" an LED. It's an LED with built in resistor. If you install "just" an LED without a current limiter of some type it will self-destruct almost as soon as you apply power.
 
I used those same LED Indicators on non-aviation projects. They come in different colors, even bi-color if I recall and seem to work fine.
 
Mine Glows

I have a small red LED for my indicator(Radio Shack RIP), and it too glows dimly when all is fine. Its almost un-detectable in daylight flying, but when I did have an actual failure in flight (broken crimp terminal) the light became very bright and I noticed it immediately. I have got used to it, and its a reminder to me that the light itself is testing good...I'm leaving it well alone!
 
If you have an EFIS with engine monitor, you can tie it in directly as a contact and avoid another hole in your panel.
 
I am looking, belatedly, at fitting an alternator failure warning light from the L post on the standard alternator. I have read on other posts that an LED light will need a resistor fitted into the circuit to stop the LED glowing dimly all of the time.
Can anyone advise what size of resistor is needed to fulfil this task.
Thanks
Derek

The Plane Power Alternator indicator light is a 100mA, 12V incandescent bulb. If you are going to replace it with a straight LED, you should put in a 120ohm (R=V/I, thus R = 12/.1) resistor between the LED and the +12V rail.

When the field is removed, the Lamp circuit closes and current will flow from +12 to gnd via the LED+Resistor.

If you can navigate mouser or digikey and find an LED+Resistor combination, all the better; just remember the correct Resistance / current

On the G3X, you can wire the L circuit directly to one of the GPI's and configure it for active Low; I believe, and G3Xpert can confirm, GPI's are good for 30mA.

Cheers!

B
 
The Plane Power Alternator indicator light is a 100mA, 12V incandescent bulb. If you are going to replace it with a straight LED, you should put in a 120ohm (R=V/I, thus R = 12/.1) resistor between the LED and the +12V rail.
...
B

Please realize that a LED typically uses way less current than an incandescent bulb. Thus your match is off. Just because the PPA can supply 100mA is no reason you have to use it all (unless you want an LED or LEDs to light up the cabin and blind you in the process).

Use the 470 ohm resistor mentioned earlier and expect it to emit a small amount of light even when things are fine.

Possibly a 9 volt zener diode instead of the resistor may prevent the dim light.

Finn
 
Looking for knowledge, I came upon this slightly dusty thread and thought I'd add to it. Just for a data point, I've been running a 60 Amp Plane Power alternator for almost 6 years with an LED indicator lamp from Stein wired to the alt failure lug on the alternator and it's been working fine for the entire time. I suppose the Stein Air alternator may have a resistor built into it, but I sure didn't add one.

My actual problem however is that it's been working perfectly all too frequently. The thing has been tripping the Alt Field breaker since the beginning. Yes, I have a 7.5 amp breaker in place. Started with a 5, and changed it when the problem became obvious. Same result. Also, yes, I've changed the plug connector as well.

The problem has been intermittent. Some flights the breaker won't trip at all, sometimes for many flights. Other times, it'll pop once or twice per hour or more or less. I haven't been able to find any scenario where it happens more than others.

The weekend before last, In 10 minutes time, it would pop the breaker almost instantly each time I pushed it in. Assuming the main alt trash, I went for a flight last weekend using the backup SD8 and thought I'd try the main alternator. Pushed in the breaker and it stayed online for the full 40 minute flight.

Anyway, I'm about done with the Plane Power unit and want to switch to an off the shelf unit from O'Reilley or somewhere, but that means I'll have to add an external regulator and OV protection.

All that said, my actual question is, how do I wire the alt failure light with the new setup. It seems the PP alternator has a lug for that but standard car alternators don't. Pretty sure this has been done, so I'm looking for the easy answer from someone who has gone before.
 
Anyway, I'm about done with the Plane Power unit and want to switch to an off the shelf unit from O'Reilley or somewhere, but that means I'll have to add an external regulator and OV protection.

All that said, my actual question is, how do I wire the alt failure light with the new setup. It seems the PP alternator has a lug for that but standard car alternators don't. Pretty sure this has been done, so I'm looking for the easy answer from someone who has gone before.

This subject has been covered before many times . If you do a search there is a whole wealth of info available.

Having said that, these guys have an overvoltage module for use with internal or external regulators. Their page also has the wiring diagrams for both types for you. The external reg. diagram is showing the generic Ford type regulator hook up. https://www.periheliondesign.com/lovm.htm If you decide to go with a B&C external reg like this one, it has over voltage protection included. https://bandc.com/product/alternator-controller-regulator-14v-homebuilt/
 
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Me again

I?ve had a look at the alternator wiring I have. There are three wires, green vertical, blue horizontal (already cutoff) red vertical. The red and green were wired together and did the alternator thing with regards to the field wire. So, I separated them and wired only the green in as the field wire...no problems. Now I have tried to see if the red wire will work as an alternator fail light as per mention of a white wire I have seen mentioned but it does not. When alt spinning it shows 12v as per the green wire??
Any suggestions of what I have got here, and am I able to do anything about an alt fail light option here? I was trying to wire the ?spare? red wire into a contact port on the Dynon ems to achieve this function but no joy.
Thanks
 
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