Hi all,
I have a 75AH Thumper in the Wrangler which charges off an Anderson plug. I was testing the battery with the car fridge to see how long it will last. Well in the car it charges upto max 12.9V and then I leave it on the fridge which sits in garage and in 12 hours its down to 11.5V and fridge is erroring. The fridge is 60L and is supposed to draw about 3 amps, so theoretically I should get about a day? Fridge set to 4C. Strangely the Thumper after disconnecting from fridge returns to 12V.
Is this strange? I have no clue, but 10 hours out of a 75AH battery is useless. Or is it not charging right. I got the car with it so no idea how its wired up.
Might sell the Thumper and just get 120AH slimline AGM and hide under the seat.
Hi, I have no experience with a thumper system but my experience with my 38L engle fridge is it will draw way more power if it is empty. When the fridge is empty it til flatten my battery in a day however I can get two days easy when it is full.
A 12V battery should be charged with about 13.6 to 14.6 volts. Normally, if you disconnect the charger (or turn of your car) and after about 10min the battery will fall to around 12.6V. A health battery should not fall bellow about 12.4V after fully charged. If the battery falls below this with no draw then its no good or on the way out. If your bat is 75amp.h and fridge is 3amp, then you should get 75/3 = 25 hours at full load (i.e. with the lid of the fridge).
No, its not strange that voltage drops when your fridge is pulling current. This is normal - current flow causes voltage drop.
One suggestion might be that you are not fully charging the battery via the anderson plug. You may have too much voltage drop in the conductor from the alternator/starter battery. What size cable did you run? Less then 16mm2 will not give you a good charge. Test the charge voltage with a voltmeter, it should be something like 14.2V (after the car has recharged the starter battery).
With car on it sits in low 13 but after car off it never stays there.
I will see what cable is there and get the meter onto it.
So am i right to say if its a charging issue, then no matter what battery i get it will have same problem?
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second battery and fridge help
1996 JEEP CHEROKEE
