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Topic: Weird Voltage Problem (Read 551 times) previous topic - next topic

Weird Voltage Problem

Well, I installed our rebuilt alternator. It was completely rebuilt and looked like new. Seems the internal regulator melted and this might have been caused by some dumbass (no names here, please) who hooked up the engine start batteries in the dark in the storage building.
Anyway, the alternator is a 130A and could not be distinguished from a brand new one.
I noticed, on the way to our campground site that the voltage gauge on the dash was only reading about 12V, so NOT charging my two five year old truck start batteries. Plugged in to 50A at the CG there was no need to worry. The inverter kept all the batteries charged.
But, on the way home my monitor indicated LOW VOLTAGE. So I started the Onan Generator and got us home.
Now, is it possible that the engine start battery that I tried to hook up bassakwards is toast or are both batteries aged out?

Re: Weird Voltage Problem

Reply #1 –
Quote from: nitehawk –
Is it possible that the engine start battery that I tried to hook up bassakwards is toast or are both batteries aged out?

Norm,

Only way to know if the batteries are good is to fully charge them and then load test them.  Once charged, any place that sells batteries can do that in a couple of minutes.  Yes, get actual status you will have to separate the batteries for testing.

But, before doing that, I would suggest pulling out your digital voltmeter and doing the following test (assuming you still have the OE design BATTERY ISOLATOR.)

With engine off, shore power disconnected, check voltage between good chassis ground and each outer lug of the battery isolator.

Start the engine and run it at around 1,100 RPM.  Check the two outer lugs again AND the center lug. The center lug comes from the alternator B+ terminal.

Let us know what you find.

Re: Weird Voltage Problem

Reply #2 –
Here we go again. Search DUVAC.

Re: Weird Voltage Problem

Reply #3 –
The alternator should charge the battery , even if they are weak. 
Plugged in they charged and started your engine. 
Most likely a sense wire fault or charge circuit open .

Re: Weird Voltage Problem

Reply #4 –
Agree with posts #2 and #3 as well as mine.

The test in #1 will give you quite a lot of information.  Remember, a failed battery isolator , bad battery, bad alternator or alternator not wired correctly can all give the  same symptoms.

The battery isolator is really the easiest place to check voltages to evaluate all three and should lead you to the root cause.