Questions about 12VDC wiring


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Old 04-08-15, 08:21 PM
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Questions about 12VDC wiring

I just added 2 6v batteries to my camper for a total of 4.
I now have 2 banks of batteries, they will be hooked up to a selector switch which will allow me to run either bank or both together.
Here are my questions, 1) can I use the same wire to ground the banks to the body or should they have their own grounding bolt?
I also run a 1000W inverter, The positive wire will be connected to the common lug on the switch so that I can use it no matter which bank is in use. But what about the negative wire? can I jump the negative from both bank together? also can the negative from the inverter be grounded to the body or does it have to go to the battery?
Thanks for any input
 
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Old 04-08-15, 10:41 PM
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Welcome to the forums.

Good choice in battery bank setup. Two 6v batteries in series are superior to two 12v batteries in parallel.

Be sure to use a good switch as even the slightest resistance can cause a big drop in voltage and current. Each battery bank has its own ground wire but you can use the same grounding
point on the frame for both battery banks.

I like to bring the ground wire from the inverter back to the same location where the batteries are connected to the frame.

The key is to keep the path from the inverter to the battery bank as short as possible to keep the resistance and voltage loss as low as possible. I also use oversized battery cabling to connect inverter and usually use welding cable.
 
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Old 04-09-15, 12:04 AM
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I agree with everything that PJ wrote. I would suggest #2 copper welding cable for all the battery and inverter wiring. Hydraulically crimped lugs are the best.
 
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Old 04-09-15, 05:25 AM
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Thanks fellows!

PJmax you mentioned using a "good switch" to prevent voltage and current drop. I just have a marine grade battery disconnect made by "battery Doctor" I'm not sure if that's a good one or not....
Would you suggest hooking both banks together and deleting the switch, essentially making 1 bank of 4 batteries?
I'm not dead set on the switch idea
I would be running both banks most of the time anyways, just thought it would be handy to be able to conserve some power by turning 1 off if needed.. but I do carry a small generator and have the truck close by... so if I ever run myself dry, I can always charge somehow...

Also just to double check, It would be fine to install 1 ground bolt on the frame and bring 2 separate wires from the batteries and a 3rd from the inverter all connected to the same point?
All the wires will be under 3'. I have #4/0 welding cable on hand but I can get bigger if needed
 
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Old 04-09-15, 05:55 AM
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Incidentally, switching one bank of batteries out of the system will not conserve any power.

The lights, appliances, etc. will draw the same power regardless of the number of battery banks, all other things including actual voltage being eqyal.

Actually the power consumption might increase slightly with one battery bank switched out. If the total load causes a drop in voltage from the remaining batteries, the appliances might draw a little more current.
 
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Old 04-09-15, 03:32 PM
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Incidentally, switching one bank of batteries out of the system will not conserve any power.
No, it won't change the power usage but it will draw it all from ONE battery bank leaving the other to be used at a later time. It is also true that using only one bank will, with any given load, draw that bank down approximately twice as fast as using both banks in parallel.
 
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Old 04-09-15, 04:04 PM
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Also just to double check, It would be fine to install 1 ground bolt on the frame and bring 2 separate wires from the batteries and a 3rd from the inverter all connected to the same point?
All the wires will be under 3'. I have #4/0 welding cable on hand but I can get bigger if needed
Yes, a single point for both negative leads (grounding) is fine. Ideally all the wires from the batteries through the selector and the "ground" wiring should be of equal length so the load is split evenly between the two battery banks but as a practical matter it may not be worth attempting.

It all depends upon the loads, I based my response of #2 copper based upon the input load of the 1,000 watt inverter. 4/0 may be overkill but always better to use larger conductors than smaller.
 
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Old 04-09-15, 06:09 PM
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Always better to use larger wire than required. 4/0 welding cable is very good.
Just a little tricky to locate and attach the correct lugs.
 
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Old 04-10-15, 07:58 PM
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Thanks for all the replies. I've decided to scratch the switch and just have my 4 batteries hooked up in series/parallel. all wires to be #4/0 awg welding cables (only because that's whats laying around in the garage..) and under 3' in length up to the factory disconnect.
judging by your comments, this will allow me to get the most out of my batteries.

The switch idea was only to conserve power if something ever happened and I couldn't charge for some reason and needed juice to pack up.... but if I can't use the truck to power up the slide and awning there's really no need to bring them in cuz I obviously don't have a truck to pull it with... (unless the main fuse blew under the hood, but I do carry a spare 40A in the glove box)

Again thank you all
 
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Old 04-10-15, 08:53 PM
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I do carry a spare 40A in the glove box
Do you use the charge connection on your trailer plug to charge ?
 
 

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