12v Fridge experiment.

Was a discussion about towing/charging and battery life when running the fridge on 12v...

OK, so we got home from camping, fridge still loaded. Parked and leveled camper. Fridge had been on 12v for 5+ hours while towing home.

Dual batteries, only a couple months old. All measurements were taken in the following order, batt A, batt B, batt A+ batt B-, battB+ battA-. At no time, out of 52 individual measurements was there a deviation to  the .000 point. I only recorded to .00, but they were always the same to three decimals..
Measurements taken at 1 hour intervals, =/- a minute or two. Ambient temperatures were in the mid 80's trailer was closed up, vent open a crack, no fan. Full sun.

Start: 12.78
1) 12.63
2) 12.54
3) 12.50
4) 12.47
5) 12.40
6) 12.34
7) 12.28
8) 12.21
9) 12.12
10) 12.02
11) 11.98
12) 11.91

So.. 12 hours for my batteries to go to just above 40%.

An extrapolation is that a single battery system should be able to run the fridge 5 hours pretty easy. And it's important to note my batteries were fully charged (at least 12.6v = 100% charge) at the end of the tow.

My take on it is it should be absolutely fine to tow with the fridge in 12v, as long as you don't stop for a 5 hour lunch.

Originally posted by secretbard That explains why my battery (when I only had one battery) went dead on me after a long 5.5 hour trip.  I now have 2 batteries, but I am still going to travel with the frig. on propane power... my longer trips necessitate the use of propane.

You should maybe check your charging circuit.. You really shouldn't find your battery running down when towing.. Start your truck and use a DMM to check the poles at 1 and 7 o'clock in the connector.. you should see +13v..

The only reason I can think of (beyond a bad charging circuit), is if you didn't pre-cool your fridge.. and thus needing more power than the circuit could push back there...

Make sure your +12 line is at least 10 gauge, and even better would be 8 gauge.  Most places install 12 or 14 gauge and it is impossible to push 10+ amps (what the fridge uses in 12 volt mode) through that.  Add in a battery that is partially discharged and so is also demanding many amps, and a small charge line is hopeless.  Oh, and make sure the negative line is either attached to the frame within 6-12 inches or that it also uses 10 or 8 gauge line back to the battery.

I never gave precooling a thought but it would make a big difference.  I always plug in the day before I leave so the fridge is cold when I leave.  Sometimes its easy to forget something when you automatically do it.

Terry

If the wiring is sized correctly it won't matter if you precool or not.  10 amps is 10 amps whether its steady for 3 hours during prechill or intermittent for 10 minutes three times every hour once its cooled down.  Either way the 10 amp load will cause a voltage drop on the charge line below the voltage potential of the pod's battery if the wire is too small, which will force your pod's battery to handle the load.  The only difference with an already-cold fridge is it will discharge and then slowly recharge your battery between cycles.  Possibly not all the way, either.  With 10 gauge wire and a 10 amp load you should still see about 13.2 volts at the Bargman which is above the 12.7 resting voltage potential of the pod's battery, so it won't discharge.