Craig V -
On DC (battery), the refrigerator uses 10-12 amps of current. If your charger will supply only 4 amps, then the refrig will attempt to pull the remainder from the battery. If the battery is discharged or bad, it is not able to supply 6-8 amps, so the refrig does not work.
When you connect shore power, the TM's built-in charger (sometimes called a converter) is able to supply the missing current, so the refrig works.
There are two bottom line lessons here.
1. The refrig cannot operate solely on battery for more than a very short time, even if the battery is good and starts out fully charged. Most TM batteries have a capacity of about 70 amp-hours when new, and it can be discharged about halfway before it starts to incur damage. So if the usable capacity is 35 amp-hours, and you pull 12 amps from it, you will get about 3 hours of operation before the battery is discharged.
2. If you are driving down the road with the refrig set to battery, your tow vehicle is supposed to be recharging the TM battery as you drive. In reality, the tow vehicle can't/won't supply more than about 4 amps, so again, the refrig pulls the remaining 6-8 amps from the TM battery. And again, the TM battery gets discharged, and you will arrive at the destination with the TM battery near dead. In practical terms, this means you can't run the TM refrig on battery as you travel. You can run it on propane, which works but is discouraged for safety reasons (think about an open propane line in an accident). Or you can simply turn the refrig off, and it will function like a simple styrofoam cooler. It actually is a pretty good cooler - we routinely travel for 8 hours, and find it is still cool when we arrive.
FYI, our member Padgett has built himself a system with very large batteries, and the numbers above do not directly apply to him. However, his mod involves considerable expense. Another one of our members (rickst29) has overcome the tow-vehicle-can't-charge problem, again with a fairly elaborate fix. It involves changing the tow vehicle's 12-volt charging line to 24 volts, so it can push more charge current down the line. You can look up posts from either for more detail.
Bill
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