SPL Tech Posted January 2, 2015 Report Share Posted January 2, 2015 I often live out of my Cmax for extended periods, and I would like to buy a 12v fridge/ freezer. It draws about 30w and runs about 50% duty cycle during peak summer months. Anyway, I am thinking of getting a second 12v battery and a 30w solar panel. Any ideas how to charge the battery from the vehicle? I dont want to get a battery isolator because those have 0.9v drops across them, and the 12v system sounds like it's already weak in the Cmax. I cannot just wire the second battery in parallel either as I dont want to kill the main battery as my freezer will be plugged in 24/7. Quote Link to comment Share on other sites More sharing options...
Adrian_L Posted January 2, 2015 Report Share Posted January 2, 2015 Good question. In a car-with-alternater setup you'd want a smart battery isolator for a two battery set-up. No voltage drop. Not sure how that would work with the C-max but since it is just wired between both batteries' positive leads, it should be the same. http://www.colehersee.com/home/smart_battery_isolators/ OR if you only want to charge the auxiliary battery from the solar panel, a solar charge controler between the panel and the battery will keep you happy. I'd recommend going with a Mono solar panel rather than Poly. obob 1 Quote Link to comment Share on other sites More sharing options...
SPL Tech Posted January 3, 2015 Author Report Share Posted January 3, 2015 I will add in a solar panel, but the solar itself is not sufficient to charge the battery, I have to use the vehicle. The solar will only reduce the amount of time it takes to deplete the battery.The other concern is if I use a battery regulator, if my fridge battery is dead and I start the vehicle, the DC/DC converter is probably going to pour 100+A into the battery to charge it just like would happen with an alternator. I am not sure how the DC/DC converter is going to like that. It might be better to use some form of current limiting device to limit the charge current to 35A or so. Quote Link to comment Share on other sites More sharing options...
Adrian_L Posted January 5, 2015 Report Share Posted January 5, 2015 You won't pour a milliamp of juice into that dead fridge battery. The isolator ONLY engages when the starting battery is full-ish (13.2 volts if I remember). When I had my old VW bus with twin batteries the solenoid kicked in after driving about 15 min. Quote Link to comment Share on other sites More sharing options...
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