Friday, Feb 28, 2014 at 16:16
Holty,
We are assuming it's a 3 way fridge - if it's a compressor fridge then it won't be so demanding on 12V from the vehicle and some of what's been said here will be less important.
As said, it is important not to allow your van batteries to power a 3 way. It is ok to run it from the alternator while driving, using the anderson plug setup. This then means that if the batteries were sharing that line for charging then the fridge would need to be disconnected from the alternator (=batteries) line when you stop. This disconnecting could be done automatically using a trembler switch.
There is another issue that shouldn't be overlooked. The 3 way fridge draws considerable current on 12V, typically 12-15 amps, which will result in a significant voltage drop due to resistance in the
wiring. This loss of alternator voltage will severely limit your ability to charge the batteries. Two options - I use two anderson plugs, one feeding the fridge and a completely separate plug and
wiring for battery charging. Even this may not be adequate where there a long runs of cable, or if the cable is too light. The other option is to use a dc-dc charger to take what voltage is available and increase it so as to deliver a full charge to the batteries. (The mention of dc-dc chargers on this
forum is like waving a red flag at aggressive bulls, but they do have a place and this is one of them!) There are some considerations with dc-dc chargers - notably can your alternator supply the required current for an extended period? (These chargers draw extra current (amps) in order to generate the higher voltage required to fully charge your batteries.)
The above assumes that yours is a 3 way fridge ( ie can run on gas). If it's not, then the electrical demand is far less.
You may find
Electricity for Camping a useful read.
Cheers
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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