Noticed amp discharge on night flight home yesterday

[AlexLev]

Was flying home in the middle of the night yesterday - had all the lights on for night flight and noticed about a 20-30 amp discharge on the factory gauge. I turned off some stuff and got it down to a 5-10amp discharge. However, my ALT INOP indicator never came on (I've had the alternator inop once and that light did come on and I noticed the needle completely deflected for the discharge in those cases) so I don't think it was an alternator failure. If I turn off everything except the anti-collision lights (during day flight), it's just slighly below the 0, which I may not have noticed in the past during the scan.

Any suggestions? Could it be a bad probe? Is there a way to test if my battery is truly discharging in these circumstances? I have one other night flight planned later this week and wanted to see what I could do to figure this out beforehand. It's one of those factory gauges, nothing fancy.

Edited July 23, 2018 by AlexLev

[Yetti]

I vote slipping belt.  Stat with the easy stuff.

[1964-M20E]

Do you have another instrument that will show you volts?  Look to see if you are showing 13.8 or 9 or higher this will tell you if the alternator is working and the problem maybe in the ammeter circuit only.  You can also use a volt meter in your cigarette lighter plug to test the voltage and the engine running of course.

The other first thing to check with this problem is the field wire to the alternator.  Make sure it is tight on the terminal and the wire is good condition back to the voltage regulator.

 

 

 

 

[AlexLev]

19 minutes ago, 1964-M20E said:

Do you have another instrument that will show you volts?  Look to see if you are showing 13.8 or 9 or higher this will tell you if the alternator is working and the problem maybe in the ammeter circuit only.  You can also use a volt meter in your cigarette lighter plug to test the voltage and the engine running of course.

The other first thing to check with this problem is the field wire to the alternator.  Make sure it is tight on the terminal and the wire is good condition back to the voltage regulator.

 

 

 

 

Thanks for the suggestions, everyone!

I'll call the shop and see if I can get in and test some things out before my next scheduled night flight. If the cigarette lighter is charging iPads, etc. with no issues - does this indicate there may not be a problem? I'm not really sure how that plug works and whether it's driven off the alternator, how much voltage, etc.

[1964-M20E]

Just now, AlexLev said:

Thanks for the suggestions, everyone!

I'll call the shop and see if I can get in and test some things out before my next scheduled night flight. If the cigarette lighter is charging iPads, etc. with no issues - does this indicate there may not be a problem? I'm not really sure how that plug works and whether it's driven off the alternator, how much voltage, etc.

As for the I pads not necessarily so since the ship battery maybe charging the I pad and the alternator still may not be working.

If you do not have a volt meter you can probably get one of the st plug in volt meter at the auto parts.  Plug it into the cigarette plug.  If you see less than 12.5 volts then something is amiss in the alternator charging circuit.

 

 

[jaylw314]

2 hours ago, AlexLev said:

Thanks for the suggestions, everyone!

I'll call the shop and see if I can get in and test some things out before my next scheduled night flight. If the cigarette lighter is charging iPads, etc. with no issues - does this indicate there may not be a problem? I'm not really sure how that plug works and whether it's driven off the alternator, how much voltage, etc.

The cigarette lighter will charge regardless of how bad the voltage is.  If it's normal one, it has it's own DC regulator to step down the voltage to 5 V, so in theory everything will charge as long as the input voltage is above 5V. 

[N6018Q]

Cheap double check (and useful too)

[jaylw314]

23 minutes ago, N6018Q said:

Cheap double check (and useful too)

Oh, that's a useful one!

[AlexLev]

Update: seemed to be a simple loose alternator belt at first. After tightening, seemed like the battery was charging again (in fact the ampere was showing a full deflection to the right). So I was flying home and then all of a sudden, noticed a discharge again so I turned around to troubleshoot.

The field wire was showing a voltage, but the battery wire was not. Turns out that it seemed to short circuit the main circuit breaker, perhaps on the high amp charge on the flight home to the battery. Ordered this ancient beauty for $160 + $80 overnight shipping (ugh): http://www.aircraftspruce.com/catalog/elpages/klixoncb-pdlm-70i.php - Hopefully replacing the breaker will be the end of this!

For reference I have the PlanePower alternator (generator to alt conversion on this Mooney).

Edited July 25, 2018 by AlexLev

[Yetti]

beats putting a coin in the fuse block or covering the fuse in aluminum foil.   Glad you got it sorted out.

[AlexLev]

Heh yeah - got it fixed today. I think what happened was after tightening the alternator belt, the higher current from alternator to catch up to charging the battery tripped and maybe short circuited the breaker, so we had to replace the breaker ($160 for the part) and we also charged the battery externally before firing up so as not to have a similar problem and now all works swimmingly.

Edited July 25, 2018 by AlexLev