Alternator Fooled Me

[SmilingJack]

Thanks Bill! I'll be doing the upgrade as soon as the new parts come!

[Raven31]

Jim,

Did you ever find the issue with this problem?

[Raven31]

Originally Posted by jimgreen

This is also a timely thread for me.
I have a PP 60 amp alternator with the idiot light. My ammeter only shows bus amps, not total amps. My PC680 battery is only about 6 months old.
Recently I notice the idiot light showing dimly at about 1200rpm and 14 amps.
At 28 amps the light is full red but the voltage shows 13v.
At 28amps and 2100-2400 rpm the light is on dimly even though the voltage is showing 13.9-14.1
First thought was loose belt, and it was a little loose but I adjusted it to the high end of the range and no change.

It doesn't make sense to me that I show plenty of voltage to be charging the battery and yet have a red light on. How is that idiot light wired exactly?

Ever find the issue?

[jimgreen]

At PP's suggestion I replaced the voltage regulator unit which includes the brushes. This made no difference to the behaviour of the red light, but there was a change in the way the regulator behaved. It seems more 'dead beat' than the old one. It ramps up the voltage much more slowly and also puts out a lower voltage at low rpm.
I plan to remove the alternator and get it tested. Our local shop was too backed up at the time but I'll give it a go when I have the cowling off next.
I can't fault its performance, but that light should not be flickering.

Did you have a similar problem?
Jim

[Raven31]

Originally Posted by jimgreen

At PP's suggestion I replaced the voltage regulator unit which includes the brushes. This made no difference to the behaviour of the red light, but there was a change in the way the regulator behaved. It seems more 'dead beat' than the old one. It ramps up the voltage much more slowly and also puts out a lower voltage at low rpm.
I plan to remove the alternator and get it tested. Our local shop was too backed up at the time but I'll give it a go when I have the cowling off next.
I can't fault its performance, but that light should not be flickering.

Did you have a similar problem?
Jim

Yeah the other night flying home for Christmas .. it flickered and then stayed on steady with 14.6 volts and 2 amps.. I found a broken ring terminal on the main airplane ground cable engine to airframe and thought that was it .. I replaced that terminal and still have an alternator light on .. tested many things today and still have the light .. I turned every electrical switch on and it still maintains 14.4 volts and 2-3 amps. I'm stumped.

[Rupester]

Recently, my low voltage light light began to appear frequently, on and off, for the better part of an hour. When I went to the EFIS engine page, the voltage was fluctuating up and down from 12.6V to 12.1. ( the alarm limit 12.0). No matter how long I watched, the voltage never stayed steady, it was constantly up and down across 0.5V spread, almost sinusoidal in pattern. I could see the alarm sound whenever the voltage dropped below 12. Turning on the boost pump dropped the bottom voltage in the fluctuation to 11.9V, then it would stay in alarm until acknowledged nearly.
My voltage is measured at GRT EFIS display #1, and due to the Schottkey diode (AeroElectrics Z-11), always shows less than 13.0 volts.

- Battery voltage checked fine (PC680 only 5 mo's old), as did field voltage at the Plane Power 60A alt, and supply voltage at the B+ terminal.
- Belt tension is fine per torque spec.
- I have tug-tested all wire connections, especially those at the Plane Power plug. No loose connections found.
- Had the alternator tested at a local alternator shop .... they found no problems.

Will now install a new 3-terminal plug a la Dan's discovery. Fingers crossed that takes care of the issue.

[gasman]

Originally Posted by Rupester

Recently, my low voltage light light began to appear frequently, on and off, for the better part of an hour. When I went to the EFIS engine page, the voltage was fluctuating up and down from 12.6V to 12.1. ( the alarm limit 12.0). No matter how long I watched, the voltage never stayed steady, it was constantly up and down across 0.5V spread, almost sinusoidal in pattern. I could see the alarm sound whenever the voltage dropped below 12. Turning on the boost pump dropped the bottom voltage in the fluctuation to 11.9V, then it would stay in alarm until acknowledged nearly.
My voltage is measured at GRT EFIS display #1, and due to the Schottkey diode (AeroElectrics Z-11), always shows less than 13.0 volts.

- Battery voltage checked fine (PC680 only 5 mo's old), as did field voltage at the Plane Power 60A alt, and supply voltage at the B+ terminal.
- Belt tension is fine per torque spec.
- I have tug-tested all wire connections, especially those at the Plane Power plug. No loose connections found.
- Had the alternator tested at a local alternator shop .... they found no problems.

Will now install a new 3-terminal plug a la Dan's discovery. Fingers crossed that takes care of the issue.

Set your alarm limit to 13 so you will be notified when the alternator fails. With it set at 12 volts, you are notified that your BATTERY is now at 25% and your safety margin is gone.

If my alternator fails and I see it at 13 volts, my battery will out last my fuel supply.

[Kingfish]

Hi Terry

I had a very similar experience and replaced a perfectly good alternator only to find the real problem was a slightly loose screw securing the positive cable connector to the positive buss.

Worth checking.

Mike

[Rupester]

Thanks, Mike. That was in my first round of connection checks. 😉

[Rupester]

Put the bird back together and flew for 1.0 today. Charging system worked perfectly .... just like prior to the problem on 4/12. The puzzling part is why it's performing well. Here's the scoop:
- 60A PP alternator bench tested fine at the alternator shop
- I did not replace the Sumitomo 3 contact plug. I looked closely at both the new one I ordered and the one still on the airplane. I could see little benefit to replacing with an identical-in-very-way new plug. The prongs on the alternator were not corroded and looked fine, as did the plug's female sockets. Decided to reassemble and fly; if the problem was still there, THEN I would replace the 3-wire plug.
- tug tested all connections a second time... found nothing
- cleaned both pulleys with MEK to reduce the possibility of slippage
- carefully examined the existing belt ... looked fine
- put it all back together; tightened the alt belt to the same torque as before, 8 ft-lbs.

And today the previous problem was magically gone. That implies it was either a slipping belt or a flaky 3-contact plug (that worked fine when re-inserted). I'm betting it's the latter vs the former. Time will tell.