Volts dropping mid flight on my 1985 201 (14v)

[cyrill]

I had the low voltage alert and Alt field breaker popping mid flight a couple of times now. I haven't seen the issue on the ground and always seem to happen in the air.
I've reviewed the different posts here on the subject to try to get a better understanding of what's going on. My next step is to follow the troubleshooting guide from Zeftronics (got the R15300 model).

I also downloaded the voltage monitoring data from my JPI 900 and that's what it looks like when it happened. I thought I would share and get your thoughts.

During this flight, the Alt Field popped where the Amps go to zero, then put it back in but popped right after again.

During this flight, I got the low voltage alert but the Alt Field breaker didn't pop.

 

 

Edited August 11 by cyrill

[N201MKTurbo]

You must have a short to ground in your field circuit. Check the wiring first. It could be something in the VR, but most likely wiring.

It would be helpful if we knew what kind of airplane you had.

[Aaviationist]

Well, that’s what the field does. 
 

there are about a half dozen reasons this could be happening. Stop flying with faulty equipment and get someone knowledgeable in electrical systems to look at it. 

[DXB]

Yikes - in flight fire waiting to happen. Figure out where it is shorting.

[N201MKTurbo]

1 hour ago, DXB said:

Yikes - in flight fire waiting to happen. Figure out where it is shorting.

That’s why we have circuit breakers. To stop the fire when something shorts.

[DXB]

8 minutes ago, N201MKTurbo said:

That’s why we have circuit breakers. To stop the fire when something shorts.

Absolutely, but repeatedly resetting a tripped breaker in flight without knowing what tripped it is certainly tempting fate.

https://planeandpilotmag.com/should-you-reset-a-circuit-breaker/

[Aerodon]

There is a lot of vibration around alternators, and a lot of deterioration of wires forward of the firewall.  It's not at all expensive to redo terminals, replace simple wires etc.  Then look at your logbooks - when last was your alternator replaced or overhauled.  

ACU's are a little more difficult to troubleshoot.   

Use this as an opportunity to give your charging circuit an overhaul.  Including the alternator mounting bushes etc.

Your airplane is 'talking to you' - listen, get it fixed before you go fly.

 

 

Aerodon

 

https://pinpointharnessing.com make nice replacement wiring.

 

 

 

 

 

[cyrill]

10 hours ago, N201MKTurbo said:

You must have a short to ground in your field circuit. Check the wiring first. It could be something in the VR, but most likely wiring.

It would be helpful if we knew what kind of airplane you had.

Thanks, yes I plan on checking the wiring first with my A&P. It's a M20J from 85 - 14v

[LANCECASPER]

On 8/6/2025 at 12:24 AM, cyrill said:

I had the low voltage alert and Alt field breaker popping mid flight a couple of times now. I haven't seen the issue on the ground and always seem to happen in the air.
I've reviewed the different posts here on the subject to try to get a better understanding of what's going on. My next step is to follow the troubleshooting guide from Zeftronics (got the R15300 model).

I also downloaded the voltage monitoring data from my JPI 900 and that's what it looks like when it happened. I thought I would share and get your thoughts.

During this flight, the Alt Field popped where the Amps go to zero, then put it back in but popped right after again.

During this flight, I got the low voltage alert but the Alt Field breaker didn't pop.

 

 

Your title,"Volts dropping mid flight on my 201 from 85 - 14v" is still confusing at first glance. It sounds like your "volts" are dropping from 85 to 14.

You might consider "Volts dropping mid flight on my 1985 201 (14v)" or something like that.

[cyrill]

On 8/8/2025 at 6:52 AM, LANCECASPER said:

Your title,"Volts dropping mid flight on my 201 from 85 - 14v" is still confusing at first glance. It sounds like your "volts" are dropping from 85 to 14.

You might consider "Volts dropping mid flight on my 1985 201 (14v)" or something like that.

Right, updated.

[Yetti]

wiring

[Bolter]

As this is tripping the breaker, it must be a short somewhere, correct?  We often see loose connections at the alternator, and that would not include a tripping breaker?

-dan