JPI voltage readings bounce around...?

[joepilotmooney]

Hi All,

Just wondering if anyone has ideas on this. On my 78 J, the EDM700 will show 12.2 volts for 10 minutes, then up to 12.5 for 15 minutes or so, and back to 12.2.  Sometimes down to 12.0 for a few seconds but then back to 12.2 or 12.3, sometimes sits on 12.6, etc. etc. Also, my (original I think) ammeter oscillates terribly, back and forth a lot when gear is moved, then it settles, and every so often will oscillate, mostly to positive side and then settle again. Now this has been going on for over five years, so not broke so don't fix it, or? I haven't ever in 15 years replaced voltage regulator, and wondering if that is it...

[Browncbr1]

First, Look for a loose fitting on your alternator,   Then look for a loose fitting where the alternator power cable attaches to your buss bar.  If not one of those, look for loose connection with your jpi voltage signal wire on the buss bar and pin on your jpi display.  

[LANCECASPER]

1 hour ago, joepilotmooney said:

Now this has been going on for over five years, so not broke so don't fix it, or? I haven't ever in 15 years replaced voltage regulator, and wondering if that is it...

Fix it. Develop the mentality that no squawk is OK or is it going to fix itself. Don't stop until you or someone else qualified gets it figured out.

The reason I say that is that these little symptoms that show up are your airplane's way of speaking to you. They are either easy fixes or indicative of something bigger going on - like a slowly failing alternator or bad wiring from the alternator or regulator or something else. Even though this is not a primary instrument, it is there for advisory. It's not fun to have a complete electrical failure in IMC (especially in an all electric airplane with one battery) or an electrical fire. You can't pull over to the side of the road and get it figured out. Definitely not trying to be harsh but I'd suggest to write down what's "normal" on every flight so you can see easily when it's not normal anymore. Write down squawks on your flight log and get them knocked out soon.

[Andy95W]

To go along with the suggestions above, I’ll add that this sounds similar to Don Maxwell’s explanation concerning fluctuating ammeters.

https://web.archive.org/web/20190207032748/http://donmaxwell.com/fluctuating-ammeters/

[joepilotmooney]

All: thanks for the feedback, appreciate it.

[mooneyflyfast]

I fixed my voltage fluctuations on my 81J by cleaning the battery negative cable connection to airframe ground

[Ragsf15e]

On 6/16/2022 at 7:25 AM, joepilotmooney said:

Hi All,

Just wondering if anyone has ideas on this. On my 78 J, the EDM700 will show 12.2 volts for 10 minutes, then up to 12.5 for 15 minutes or so, and back to 12.2.  Sometimes down to 12.0 for a few seconds but then back to 12.2 or 12.3, sometimes sits on 12.6, etc. etc. Also, my (original I think) ammeter oscillates terribly, back and forth a lot when gear is moved, then it settles, and every so often will oscillate, mostly to positive side and then settle again. Now this has been going on for over five years, so not broke so don't fix it, or? I haven't ever in 15 years replaced voltage regulator, and wondering if that is it...

Is it actually showing 12.5ish?  That’s real low.  Like, does it charge your battery??

Heres a quick check… take a digital volt meter next time you fly.  Measure voltage on the bus bar behind all the breakers (bus bar to ground).  It should be 14.0.  Either way, I’d work on finding the problem as @LANCECASPER suggested, but if it’s really 12.5, you might want to work on it with some haste…

You can also measure at the cigarette lighter if you want.  This doesn’t mean the battery is getting full voltage, but it’s a place to start.

 

[EricJ]

41 minutes ago, Ragsf15e said:

Is it actually showing 12.5ish?  That’s real low.  Like, does it charge your battery??

Heres a quick check… take a digital volt meter next time you fly.  Measure voltage on the bus bar behind all the breakers (bus bar to ground).  It should be 14.0.  Either way, I’d work on finding the problem as @LANCECASPER suggested, but if it’s really 12.5, you might want to work on it with some haste…

You can also measure at the cigarette lighter if you want.  This doesn’t mean the battery is getting full voltage, but it’s a place to start.

 

+1, and an easy way to do it is to put a USB adapter in the cigar lighter that has a voltage display on it.   They're handy to monitor system voltage if you want to verify the other indicator.   Like this:

https://www.amazon.com/LIHAN-Charger-Display-Voltage-Compatible/dp/B01JA627KU