Fixin' The Land Yacht
With a good ammeter hooked up, one by one I pulled the fuses in the power panel, figuring that any drain of the battery had to be going through one of the fuses to some device that was sucking the battery flat. Nope! All fuses pulled, and there was still a draw on the battery.
Taking the power panel apart, I found that the shore power charging system wasn't going through the fuse panel, and was going straight to the battery when in shore power mode. When not hooked up to shore power, an automatic switching should take place and disconnect the charger.
Further checking showed that although the auto switch was cycling, it was not completely disconnecting, leaving a path for the battery to discharge back through the charger. It was a fairly high resistance path, so it would take several days to discharge the battery.
The auto switching was done in what must have been the cheapest way they could come up with! A small micro-switch was riveted to a bracket above a small solenoid. When you plugged into shore power, the solenoid would move, and the micro-switch would switch you from the battery to the shore power. The little tiny switch on the right in the picture is one of the micro-switches.
I grabbed my trusty Grainger catalog and started paging through the section on relays. If you don't have a Grainger's Catalog, you should get one. Any right of passage ceremony into manhood in North America should include giving the young man his first Grainger's catalog.
Pages and pages of relays, different current ratings, different control voltages, different number of contacts, normally open, normally closed, it was like being a kid in a candy store, but it was all relays and switches!
It looked like a 5Z552 should be just the ticket. What a beauty! That's it on the left in the picture. 12 volt control voltage, single pole, double throw, and able to handle 30 amps of current. I'll bet that's a really conservative figure, looking at the size of the contacts.
You can guess what I'll be doing this afternoon...........