Charging batteries through inverter & charger

Submitted: Tuesday, May 10, 2005 at 17:48
ThreadID: 22854 Views:14253 Replies:6 FollowUps:10
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Just kicking around some ideas for auxiliary battery setups while camping. Will eventually get a dual battery setup, but would also like to take an appropriate-sized deep cycle battery that can be removed from the vehicle and used "in-camp" for various purposes (fridge, flouros etc). I've seen a few references to charging batteries in-vehicle using an inverter and 240V charger, and was a little hazy on the maths for inverter sizing (while being aware that the inverter would need it's own wiring, and not run through a cigarette plug!).

Looking at using an AGM battery, so for arguments sake I've picked a 12V 10A Xantrax charger to get some numbers. Max output charge voltage is 14.8V, and a charge current of 10A, and an efficiency of 82%. So would this translate to 14.8V * 10A / 82% = 180.5W maximum power usage (i.e. P=VA)? So a 200-300W inverter would be fine?

If that's the case, would the max amp draw of the inverter (assuming a sine wave, say 90% efficiency), be 180.5W / 12V / 90% = 16.7A? Sounds very inefficient, but given there's losses in both the inverter and charger, might be right.

I'm hoping that on the odd occasions where we would be recharging the camp battery on the road, rather than just taking a battery along I've charged at home, a day's driving between campsites (i.e. about 8 hours on the road) would allow me to push up to 80A charge into the removable camp battery.

Lastly, where would the wiring for the inverter be run from in a dual-battery system if one was installed? Bit ignorant when it comes to this - will be my first dual battery setup. It draws power from "somewhere up front!", but assuming there's some dual battery management system in place, where do you get 20 odd amps from to run to the back of the vehicle to make sure there's ample juice? Or is the fact you've got dual batteries under the bonnet irrelevant?

I've been giving this some thought, and would rather have a dual battery and inverter setup, than a triple battery charging setup (i.e. Rotronics etc) permanently in the vehicle - will never buy a camper trailer or caravan that would require a battery bank in it, and it also makes use of a deep cycle charger I can then use out of the vehicle. Or is this a poor way of doing things?

thanks!
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