Thread: Battery question

Originally Posted by crump

What volts should a healthy 12v battery show on a multimeter across the terminals?

If it's disconnected from the car - and is fully charged - then in excess of 12.2v - If it's connected to the car there may be 'something' draining the charge - computers/lights etc.,

If it's connected to the car and the engine is running then about 13.5 v

However the volt measurements will not always tell you if a battery is healthy -

I'm getting 11.6 at my fridge outlet from my auxillary battery and the fridge keeps tripping out, so is it more than likely the battery is the problem??

possabley not between your hookup point and your battery you could have a bad earth...

grab the biggest headlight (110 watts worth should do for a field check) that you can find, hook that up directly to the terminals and then read the volts.

A perfect battery will stay over 12v (for a little while anyway)but only just and if it reads anything under about 11.5 then its on the way out but not done yet. Anything under 10 is bad.

If it will hang on till i get back from course I'll put it on the toaster for you and let you know how it really is.

it could be a combination of wiring and battery

what is your actual voltage at the battery, rested i think is the term, say first thing in the morning after it has been sitting all night, if this is somewhere over 12V than i would look at your wiring

you could buy an engle as they don't have low voltage cutout fitted........umm not good for you battery though

With the fridge running, check the battery voltage at the battery and then at the fridge.

Subtract one from the other to find out the voltage drop along the supply cables.

It should be low. If not, the cable is too small for the load. How low is low? Hmm, hard to say but I'd be looking for less than 1 volt. Drivesafe will have a better view than me.

Tell us what you measure and we can discuss that.

Ron

what I'm trying to work out is whether my problem is the Batt or the fridge.Got 11.6v across the terminals and at the fridge outlet first thing this morning after having the fridge running all night(and it had cut out).Started the car and let run for 5mins and switched off, both points read 12.4v.I get the same readings on the batt and at the end of the fridge plug, so volt drop isnt the problem.Voltage cutout on the CF 40 is supposed to be 10.4 on the low setting, which is where I have it set.Why do these things happen before a fishing trip?

ahhhh...

Did you check the voltage at the battery and the socket with the fridge in and running...

Voltage drop on a cable will only be apparent while under load unless there is a high resistance earth/connection somewhere.

If the battery isnt as healthy as it could be you might find that its dropping below 10.4 and then tripping the battery protector but isnt "recovering" enough to reset the protector.

Big reds Aux battery is doing this when running the aircompressor (engine off) now so it cant be long till the fridge starts doing it too. 3+1/2 years out of one battery isnt bad and the primary still tests ok with plenty left on the pass mark....

Also make sure that you have a earth aswell as the power from your Aux battery running to your Aux power socket for the fridge

Reason being who ever wired my car up before i bought it used the dual core wire for 2 positives to 2 sockets and just run earths from both sockets to the body it caused all sorts of drama,s($$$$$) till i worked it out