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Just installed new LED landing light, not working!


Buckaroo

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LEDs are diodes that emit light. If you reverse bias them, they act like closed gates. It does no harm to them unless you surpass the breakdown voltage, thereafter an avalanche occurs which causes a brief REALLY BRIGHT flash for a split second, then dies. It's rare to have LEDs that are damaged by reversing them, usually that only happens because of a poorly designed power controller for said LEDs.

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I tested my LED landing light both forward and reverse polarity. Worked each way. I still get low voltage alarm as I clear the runway. My solution is to keep the rpm a tad high. The original reason for the LED landing light was to resolve this problem. Before I used to get the alarm on final. Wondering if there is a regulator problem?

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That's not good new for me as this little $100 light may not work reversed. Tomorrow I'll be out at the airport reverse poling it and wanting it to work.

 

I'd ask others to chime in on your alarm voltage situation. I've never gotten a low voltage alarm in my limited experience with this aircraft. Sounds like you have something deeper going on!

 

Thanks for the heads up!

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Too many electronics with a low idle rpm can indeed get a low charging alarm. It isn't a big deal as it is temporary, but if you don't want it then either increase rpm or shut off things like lights or other electronics. No regulation that says you have to have lights on and maybe you have something plugged into the 12V lighter port?

 

Just ideas and thoughts. It's temporary.

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My idle RPM is about 1700-1800 and I don't have any charging problems.  That is with a TT autopilot, D-100 EFIS, and keeping my LED landing light and position/beacon lights on all the time.  I can imagine airplanes with all that plus an EMS and other goodies running into issues, the alternator is only 18A on the 912ULS.  

 

Interestingly, when I had a failing battery a long while back the alternator did not have enough juice to run all of the above and cycle the flaps at idle RPM.  Worked fine in flight, but on the ground I could not retract the flaps until I turned the landing light off.  So even with my modest equipment I am right on the edge without the battery to back up the alternator.

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I tested my LED landing light both forward and reverse polarity. Worked each way. I still get low voltage alarm as I clear the runway. My solution is to keep the rpm a tad high. The original reason for the LED landing light was to resolve this problem. Before I used to get the alarm on final. Wondering if there is a regulator problem?

 

This is highly irregular for LED devices to work in both directions, mainly because it's not necessary. Possible, but not necessary. Are you sure it's an LED?

 

Also, clean up the terminal connections and make sure you don't have any high resistance connections to the regulator. Don't use the landing light and see if you have the same problem.

 

That's not good new for me as this little $100 light may not work reversed. Tomorrow I'll be out at the airport reverse poling it and wanting it to work.

 

I'd ask others to chime in on your alarm voltage situation. I've never gotten a low voltage alarm in my limited experience with this aircraft. Sounds like you have something deeper going on!

 

Thanks for the heads up!

 

Almost all electronics are not designed with bi-directionality on DC power simply because it's not needed. As for low voltage alarms, it's common in those with high power draw, especially if they have an old style light and a loaded panel.

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It's actually a good thing. There are interesting uses for diodes that could double as a warning alarm. Let's take, for example, your polarity warning lights on battery chargers. When you hook it up the correct way, the LED is reverse bias and no current flows, so the warning LED doesn't light up. But if you hook it up the wrong way to the battery, it makes the diode forward bias, causing the warning light to light up!

 

Before, with standard lamps, we would have to use a separate diode to do that, or if we want to go far enough back in history, a vacuum tube.

 

Diodes might make polarity mildly annoying, but they have made so, so, so much more possible, and it's a tiny price to pay!

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