Volts dropped

[Thor RV10]

Wondering if anyone can tell me what is going on regards to my volts dropping from typical 12.5+ to 10.1 as I was leaving Prosser this afternoon. I shut down nav lights and lighting and it took about ten minutes to climb back to 12. I am thinking its time for a new stock alternator from Vans. I ordered my kit in 2014, so I think its the Plane Around set up. Also thinking of putting that second alternator in and welcome any thoughts. Thanks in advance.

[BobTurner]

Uh, what's going on is your electrical system is all screwed up. When the alternator is running properly, you should never see 12.5+ volts; more like 13.5 volts minimum if it's going to charge a standard lead acid battery; more like 14.1+ if it's an Odyssey sealed battery. If you see 12.5 volts it means your alternator is already off line. How it can climb back up from 10 volts, which is pretty much dead, when you don't measure anything higher is a complete mystery to me. Exactly where in the system is this measurement made?

[rv7charlie]

Assuming an accurate voltmeter, it dropped from 12.5 to 10.1 because your alternator was never charging. Otherwise it would have dropped from ~14.x volts downward when the alternator stopped charging.

It's worth doing a little troubleshooting before ordering an alternator; lots of things can cause loss of charging.

Charlie
(Aeroelectric list is your friend.)

[OkieDave]

Originally Posted by BobTurner

Uh, what's going on is your electrical system is all screwed up. When the alternator is running properly, you should never see 12.5+ volts; more like 13.5 volts minimum if it's going to charge a standard lead acid battery; more like 14.1+ if it's an Odyssey sealed battery. If you see 12.5 volts it means your alternator is already off line. How it can climb back up from 10 volts, which is pretty much dead, when you don't measure anything higher is a complete mystery to me. Exactly where in the system is this measurement made?

Batteries (any power source, really) drop more voltage when they're under more load; that's why you should always test a battery with a load on it. OP said voltage came up when he shed the nav lights; reducing the load will generally produce an increase in voltage.

I'd look at the alternator (for charging, and providing the baseline power), but I'd also consider that the battery may be going soft if the nav lights cause that much drop. If the alternator has been weak for a while, the battery is likely to have been called upon to assist many times, which would wear it out.

[Thor RV10]

Thanks for the advice. Rob Hicmans son Brian is going to take a look (I dont think Rob told Brian yet) at it tomorrow after work here at AWO. I suspect the gauge might have malfunctioned. I now recall the number is around 14.5 and I am running two Odyssey batteries as I am running with EFII for both electronic fuel injection and dual RLC. Ignition. Thanks again, Thor N63TM

[DennisRhodes]

Yes as others have said , charging system is the first place to look. It may be as simple as a loose or disconnected wire from the Alternator. Or possibly a loose belt if it is a belt drive setup. Loose or bad Ground straps will also prevent charging. Worst case may be an alternator but I would check out these other things first . How do I know this? There's a perfectly good alternator setting on the shelf in my hanger.

[DanH]

S40 to AWO? 150 NM over the mountains? Dude, don't do that. With electronic fuel injection and ignition, 10.1 showing on the voltmeter right after departure is an emergency.

[Carl Froehlich]

Originally Posted by Thor RV10

Thanks for the advice. Rob Hicmans son Brian is going to take a look (I dont think Rob told Brian yet) at it tomorrow after work here at AWO. I suspect the gauge might have malfunctioned. I now recall the number is around 14.5 and I am running two Odyssey batteries as I am running with EFII for both electronic fuel injection and dual RLC. Ignition. Thanks again, Thor N63TM

For your set up, low buss voltage is a "land right now" condition.

First rule, believe your indications and take action. Troubleshoot for a bad gauge on the ground. I offer however that from what you discribe your voltage indication is working properly and you lost your alternator output.

Carl

[Thor RV10]

I will be looking into this today. Thanks all for advice.

[Larco]

You might look at the alternator drive belt tension?? A loose belt can allow the alternator pulley to slip like crazy when under a load.