Charging batteries through inverter & charger
Submitted: Tuesday, May 10, 2005 at 17:48
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Scubaroo
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!
Reply By: drivesafe - Wednesday, May 11, 2005 at 07:41
Wednesday, May 11, 2005 at 07:41
Sorry folks but it just don’t make monitory sense. You are adding more work for you Alternator, it will cost an additional $500 +, It WILL take longer to charge the battery than just hooking the battery up to the Vehicle’s charging system.
All this to get if you are very lucky, may 5% more capacity and you may extend the life of your battery and even then this extended life still depends on how use or abuse the battery anyway.
You would be far better off putting a small portion of this money on fitting large cable and end up achieving the same thing and remember you still have to fit the heavier cable to get this system to work anyway.
As for toping up the battery without starting the motor. How long do you think your cranking battery will last putting a load like that on it.
Top up your auxiliary battery while you stuff the main battery.
Again, it’s not good value for money.
Mainey’s suggestion is also a good one, for what you are planning to spend on an inverter and a charger, why not invest in a small solar panel and then you will have charging power at all times during day light and and you can use it to keep the battery topped up when it’s not in use.
Cheers
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Follow Up By: Scubaroo - Wednesday, May 11, 2005 at 09:38
Wednesday, May 11, 2005 at 09:38
Hmm, last post disappeared.
If I were to put in a dual battery management system as an interim measure (ie just for charging the AGM while it's in the back of the vehicle), what happens when the battery is not in the vehicle and you're driving around day-to-day? Does the management system recognise there's no battery and work fine? Or does it require a battery to be hooked up at all times?
Budget just doesn't extend to a solar or three-way system at the moment, the most pressing need is to get the "mobile" AGM into use. Makes sense to invest in the heavy wiring to the back of the vehicle in place now though - that's money that doesn't need to be spent twice.
cheers
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Follow Up By: drivesafe - Wednesday, May 11, 2005 at 10:09
Wednesday, May 11, 2005 at 10:09
Good one Scubaroo, putting in the heavy cable in the first place means you can do what ever you like later.
As for the dual battery charge control system, it should make no difference whether the rear battery is in or not. Ours don’t as the main operation is to maintain the cranking battery first and foremost, once fitted, just forget it and do with your rear battery as you want.
Cheers.
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