[sailingdog]

Generally, if you're drawing more 12 VDC electricity than the charger can supply, the excess will be drawn from the batteries and draw down the batteries until they are depleted.

For example, say you have a 15 amp battery charger. Say you are using the refrigerator (12 vdc 2.7 amps), and have the stereo cranked (16 amps), and the lights on in the cabin (four at 1 amp each), you're effectively drawing 22.7 amps or so... the charger will supply 15 amps of that, and the batteries would generally make up the remainder... however, if your batteries are discharged, you will eventually kill them by doing this.

Originally Posted by TonyInNewportOregon

Upon excellent advice from my Sailnet peers, I have chosen installing mostly 12v devices -- lighting, etc. -- enabling me to use most of those while away from my 120v shore power. (It made sense to me from the start, but I wanted to hear from some of you more experienced folk anyway.)

The next question is: I have purchased a new 120-12v converter, one that has multiple, automatic settings (full charging, trickle, etc.) So, in port I have unlimited 120v shore power (at least up to 30amps, of course); and I now have a new 12v converter. But, if -- as a liveaboard -- I am using a greater number of 12v devices than the boat's electrical system was designed for -- despite having a brand new converter -- am I harming my batteries? Does the majority of the power used go into and out of the batteries; or does it go from the converter, to the battery terminals, and -- bypassing the batteries, for the most part -- go straight to the devices?

I know it's a strange question. And, as a former Navy electrician, I should know the answer. But I have some-timers disease -- sometimes I forget things -- and I just don't know whether using more lights, more chargers, more fans, etc., is going to wear out my batteries.

Sorry for the long drawn out question.

TonyInNewportOregon