Varying voltage

Sun Apr 01, 2012 3:20 pm

I have a 185 that was not keeping the battery charged. Took the starter/generator off and had it repaired by a generator shop. After reinstalling, I checked the voltage across the battery terminals to see if it was charging, but the voltage keeps changing, varying anywhere from 12 to 4.
Is this normal or do I still have another problem?

Re: Varying voltage

Sun Apr 01, 2012 3:25 pm

My guess is you are using a relatively cheap digital meter. Electrical noise is messing it up. Try using an analog meter.

Re: Varying voltage

Mon Apr 02, 2012 9:02 am

Ditto to what Jim says. I have one that is so sensitive that waving my hand near it makes it go nuts.

Re: Varying voltage

Tue Apr 03, 2012 7:40 am

You are correct, I was using a cheap meter. I will use the "good one" next time.
Thanks again for all of your excellent guidance.

Re: Varying voltage

Tue Apr 03, 2012 12:05 pm

Not always a question of cheap vs expensive but likely is related to the sensitivity or ohms/volt of the meter. My 40 year old vacuum tube voltmeters will do the same thing and are both good quality. The digital meters are so sensitive that they can pick up stray voltage or fields. The older style analog meters, even the cheap $5 meters are less sensitive and less likely to be affected by EMF stuff hanging in the air.

Most of the time I use my $5 analog meter for automotive measurements. 1000 ohms per volt vs millions of ohms per volt.

Re: Varying voltage

Tue Apr 03, 2012 1:18 pm

Sometimes people pay too much and still get a cheap product.

It requires very little electronics to make a simple (cheap) voltmeter. Making one that is relatively immune to stray EMF or spikes in the circuit being measured requires some filtering. Filtering means more components and additional cost. Cheap meters don't have filtering. An analog meter gets a lot of filtering for free just because of the inertia of the mechanical movement that holds the needle.