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Old 06-12-2018, 04:55 PM   #1
Mini-Skoolie
 
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Existing 12 volt battery to 2 new 6 volt house batteries

Hello,
Bought a Skoolie with an existing 12volt battery used for the wheelchair lift that I have since removed. I want to use the existing 12 volt (with the existing wire coming from it) to connect to 2 new 6 volt batteries wired in series (12volts)

Any problems with that? Will I need a fuse in between the 12 volt battery and the new 6 volts?

Thanks for any help.
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Old 06-12-2018, 05:32 PM   #2
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We need more info in order to be much help:
How do you plan to charge the battries?
Are all the batteries deep cycle?
Are the amp hrs the same in all three batteries?
What size wire connects the batteries over what length run?

In a nutshell your plan will work electrically though how effectively will depend in part on the answers to the above questions. Also, typically the fuse if you use one would be located at the +tive terminal of the last battery in the series hook-up and would be of high amperage rating---like 450 to 500 amps. Its sole purpose is to protect the complete down stream electrical system from catastrophic failure (dead short). Hope this helps, Jack
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Old 06-13-2018, 08:01 AM   #3
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Sorry 'bout that.
Charging with:
Engine/Alternator
Solar
Shore Power/Generator

The two 6 volts are deep cycle, the existing 12 volt is not.

The two 6 volt amp hours are 225 each. Do not know what the 12 volt amp hours are. Will see if i can find out.

Existing 4 AWG from 12 volt to back of bus (about 10 feet) to the 2 new 6 volts. I will use 4 AWG for series connection.
Can I use same gauge out to fuse block and 3000 watt Inverter?

Thanks for the help!
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Old 06-13-2018, 09:25 AM   #4
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2 6v at 225 ah will make a 12 v 225 ah.
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Old 06-13-2018, 09:58 AM   #5
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You should only use deep cycle batteries for this. Regular lead acid batteries can't be drained low without being damaged. They are designed to stay near the full mark and deliver short bursts of high current.

Also, mixing batteries that have different nominal voltages (due to technology, or wear level) can cause problems. Electricity will flow from a higher voltage to a lower one, wasting your power, causing heat, and adding additional wear. Running 2x shiny new 6v in parallel with 1x old 12v is sure to have this issue.

Your 12v battery may not advertise an AH rating, they're just not built for storage purposes. It'll probably have a CCA rating which is more useful for automotive purposes.

Your best bet in my opinion is to remove that 12v battery from your system and add another pair of 6v to increase your capacity.
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Old 06-13-2018, 11:01 AM   #6
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Quote:
Originally Posted by MobileHolmes View Post
Existing 4 AWG from 12 volt to back of bus (about 10 feet) to the 2 new 6 volts. I will use 4 AWG for series connection.
Can I use same gauge out to fuse block and 3000 watt Inverter?

Thanks for the help!
Probably not.

If you ever pull 3000 watts from the inverter you will be pulling at least 250 amps from your battery. Wire size is dependent on current, length of conductors, temperature and acceptable voltage drop.

Use a wire size calculator to determine what is correct for your application :https://www.wirebarn.com/Wire-Calculator-_ep_41.html

IMHO, running a 3000watt inverter on 12 volts is a bad idea. Here is some good info regarding battery /inverter sizing : https://www.solarpaneltalk.com/forum...-size-tutorial
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Old 06-13-2018, 11:47 AM   #7
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The 12v and 6v batteries you have require different charge cycles--regular fast charge for the 12v and 3 rate charge for the deep cycle 6v. A single charge type will greatly shorten the life of all three batteries as well as keeping them from fully charging. Your 3000 w inverter should be inches not feet away from the batteries to eliminate line voltage drop and the leads should be made of many fine strand conductors like welding leads. Someone else will better be able to advise you about your solar set up. Here is a site dealing with wire sizing you may find interesting. Jack

American Wire Gauge Chart and AWG Electrical Current Load Limits table with skin depth frequencies and wire breaking strength
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Old 06-13-2018, 10:16 PM   #8
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My 3000 watt inverter charger calls for 4/0 (0000) wire and a 300 amp fuse between the batteries and inverter.
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Old 06-15-2018, 07:41 AM   #9
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Thank You all for your replies and suggestions.
Time for me to do some more studying and rearranging in the electrical department.
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