The Stovebolt Site Forums The Shop Area The Electrical Bay 57 3100 stupid battery question

OK the battery is not stupid I am!

I am getting ready to smoke test (hope not) the new wiring harness.

But before I connect the battery leads I did a simple volt meter test on the battery.

voltage accross the battery poles is 12.5 with no cables attached. good.

Voltage from the positive pole to any ground on the truck is 7.5 Volts What???

Voltage from the NEG pole to any ground on truck is 5.00 V (measured with red test lead from volt meter on NEG and Black test lead from volt meter on truck ground) Hmm?

Add those together and you get 12.5 volts.
Hmmm.


This just sounds bad. I expected that the voltage reading should drift or be zero or random millivolts but it is registering in volts.


I get the same readings if I use one of the metal side hold downs on the battery as the ground.

But I swear that there is no sign of acid or any connection from the battery to the battery tray or the hold downs.

I have the stock type of tray and hold downs. but have a front (side mount) flush poles that are below the hold down bracket.

Here is a picture battery setup

That is an older picture with the cables connected but it shows the setup.

I am getting these readings with no cables attached.

The battery tray has been recently stripped and painted, battery cleaned, hold down box on top has been cleaned and painted and the side bolts are new.

What am I missing?

Why is it reading 7.5 and 5.0 volts from the POS pole to a ground and the NEG pole to a ground when there are not cables connected and no way the battery should have a way to complete a circut?

Maybe there is a none visible acid blead from the caps over the cells to the top metal frame? Would that do it?

Is that normal?

I am kind of affraid to hook up the cables with it this way.

I am former submarine battery electrician where we watched grounds very closely. I can say
You have your mind right to be asking the question.

Take a 5 or 10 watt lite bulb from each post (with batt cables disconn) and see if it lites. I think I would start with a 6V bulb and end up with a 1.2 or so V bulb (flash lite bulb?). I bet teh bulbs will not light so if you hooked up it would not be a problem HOWEVER it could be enough to bleed down battery over a matter of days to weeks.

I would bet your problem is more than likely acid tracking. Wash battery with soap and water to get rid of grease then baking soda water and rinse well with fresh water. NO soap or baking soda in the cells of course.

Dan Bentler

I was thinking of doing that with the bulbs and also taking the hold downs of and cleaning again. I will give that a try.

It has only been mounted back together in the battery tray for about a month. I have charged the battery with the caps loose with a battery tender, very low charge that took 3 days to put the charge back in it as the battery has set for about 12 months without being used in the truck as I have been restoring the interior and rewiring.

I guess it may have blead residual acid out of the caps. Nothing visible yet but maybe. I will try cleaning it real well and do some more measurements.

Thanks for the ideas.

Possibly you checked this already, but could it be a bad ground connection? Recheck the ground cable from the battery to wherever it goes and make sure it is a good connection. Then make sure the ground cable from the engine to chassis is good.

I do not have any cables connected. Just the battery sitting on the tray and the hold downs on. The readings are between a battery poll and a ground on the truck. There should be no connections. There are no cables attached to polls yet.

So it is not the groind cable as it it not connected to the battery. The earlier picture is for reference for the general setup cables hoowever are disconnected and i still get the 7.5 and 5.0 volt readings from the polls to a ground on truck. 12.5 volts between polls.

I don't like those side post batteries, only use ones with the 'correct' clamp type top posts .... if there's no cables connected the only way you could be getting any reading between either battery post and the truck is if your hold down bolts are shorting the battery ... weak or cracked case on the battery?

try taking off the hold down and put a thin piece of rubber or plastic under the battery, you may have cinched it down too tight

Bill

You are probably using a digetal voltmeter. It takes very little current to energize these. The slightest amount of dirt or moisture will conduct enough current to show these readings. It will probably take 6 months to drain a good bat. down at this rate. Try it with an analog meter or test light & you won't get anything. Dont worry about it. Go ahead & hook everything up correctly.

Second the analog meter and or lite bulb test as opposed to digital. I have both digital (fluke) and analog (Simpson). Both are top grade instruments and have their good and bad points.

Also like the idea of some rubber or other insulation between upper hold down and battery - that dipit plastisol stuff?

Dan Bentler

Ditto above
I have been a residential remodeler for over 30 years and have used multimeters almost everyday in my business. A few years ago I decided I should move into the 21st century and ditched my anolog meters and thought I should go high tech with digital instead.
Well, I tried for two years to adjust and have finally abandomed them and gone back to by analog meters which I can rely upon and understand. Maybe it is just what I grew up with but, it appears more logical to me.
Not everything new is a step forward.

Have you checked the multimeter on a different battery? It almost sounds like a meter issue or a bad ground. What are you grounding to? My 57 Suburban's battery grounds right to the firewall then firewall to motor/trans. If you have 12.5 from post to post and not 12.5 through the body.. sounds like a connection issue to me. Just my .02 worth.

Seems to be a micro leak/blead that the Digital meter senses. I did try on another batter that is sitting on the floor and it does not show that problem.

I also diconnected the top hold down bracket and when it is off there is no volts.

ALso if it is sitting loose on top there registers some volts and as you tighten the side bolts the volts read higher.

I tried cleaning it real good, there was not any perceptable acid or anything, both the battery and the top bracket. But it still had the issue.

I think a thin piece or rubber or some felt tabs or something under the hold down to lift it off the batter top might help. Have not tried that yet.

leaving it connected over night does not seem to have drained it any so it must be very light. I have not tried a light bulb on it yet.

Thanks everyone.

Digital meters are an absolute necessity when dealing with super-low current draw items like transistors, integrated circuits, etc. The current draw of an analog meter will load down a solid state circuit enough to give a false reading or even damage the circuit. DC charging systems, even those with alternators and solid-state regulators, are so low-tech and rugged that the analog meter is usually the best choice for diagnosis and repair. There's virtually no solid-state circuit (such as a computer) that carries hundreds, or even tens of amperes- - - - -more like milli- or micro-amps!
Jerry