Plane Power alternator dying?

Hi ya'll,

I'd like to request diagnostic assistance:

I'm on the way to OSH and noticed an odd thing: normally my master bus voltage is 13.6. However, on the last leg of my flight it dropped to 13.2 and then 12.9. I was like 'uh oh' - I have an ebus, but wasn't looking forward to swapping alts at OSH.

So I started turning things off. As soon as I turned off the autopilot servos, it went back up to 13.6 (yay! alternator working again). Later in the flight it started to creep down to 13.4. Then I turned off strobes and it went back up to 13.6.

So, is my alternator dying? I'm thinking it is unlikely a connections problem because lowering the draw allows the current to stay up. (Also, if you are thinking this is due to the ~.6V drop from the e-bus diode, my voltage is measured from the master fuse bus)

if you are close to C09 Morris, IL ... i would be happy to meet you at the airport and you are welcome to use our tools to look into it.


chris @ checca.net

Why is your master buss voltage at 13.6 normally? It should be hovering around 14 volts, no?

Jamie said:

Why is your master buss voltage at 13.6 normally? It should be hovering around 14 volts, no?

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I would have thought the same (expecting 14.2), however back when I switched to a PP alt it was 13.6 - I had presumed that they bumped the regulator down a bit compared to automotive uses. Anyone here have a PP alt and can report what their normal voltage is?

Of course - I'll call em on Monday from OSH or hopefully they are there.

my PP runs 14.2 volts.

AltonD said:

my PP runs 14.2 volts.

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Thanks Alton, Chris and Jamie!

I'll give em a call on Monday.

In my 8 endurance bus read 13,6 Volt with PP Alternator, but this is because I feed this bus from main bus with a diode.

Just my 2 cents

My PP alternator is rock steady at 14.35 volts- I know this because my EIS is constantly going back and forth between 14.3 and 14.4 volts...

Mine's 14.3-14.4V...always.. never seen it below that. I'd think that 13.6 should work, but it's kinda on the lower end of the scale...

I did some more testing this morning. It is 14.2 volts at the master bus and the EIS (which is on the ebus so behind a diode) slows 13.6.

The dynon is on the master bus and I don't know why it has started bouncing around all of the sudden. When it is a bit cooler I'll make sure the connection it has to the master bus is good. But now that the mystery is solved I can investigate more at home.

For the benefit of future searchers who might have something similar:

Tightening the screws on the dynon dsub fixed it - I guess I had a marginal contact for the power pin on that connector.

kevinh said:

I did some more testing this morning. It is 14.2 volts at the master bus and the EIS (which is on the ebus so behind a diode) slows 13.6.

The dynon is on the master bus and I don't know why it has started bouncing around all of the sudden. When it is a bit cooler I'll make sure the connection it has to the master bus is good. But now that the mystery is solved I can investigate more at home.

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