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Size of Fuse to leisure batteries


fred22

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I have two 110a batteries connected to the 12v syystem via a 20amp blade fuse. Is this of sufficient size and is it correct to run them through one fuse?

I know leisure batteries have been covered in many threads but can't find one about size of fuse??

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Hi Fred,

 

I also have two 110amp batteries in parallel. The second battery is wired to the terminal of the first original battery, with a 20amp fuse on the positive strap leading to the positive terminal of the orginal battery.

 

The two power out wires from the original battery that go to the MH distribution box, has the original 20 amp fuse fitted, so the amount of power supplied by the batteries, and loaded on the MH wiring from the batteries to the distribution box will not exceed 20 amps, otherwise the fuse will blow.

 

Regards Terry

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I don't quite see it the same as Terry as one battery has effectively 2 fuses in line and the other just one in his picture.

 

Have a look at my versions :-

 

http://www.motts.dsl.pipex.com/second%20leisiure%20battery.htm

 

As has already been said the fuse size is to protect the wiring.

 

If you were for example going to wire in a large inverter then seperate wiring with bigger fuses would be required. (Probably those supplied with the inverter!)

 

If in doubt use a professional for electrics.

 

Take care

C.

 

 

 

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Hi Clive,

 

I suppose the reason I have my batteries wired as shown is because they are around 5ft away from each other. I used automotive twin 20 amp power cable, fully trunked from battery to battery, the fuse was fitted very close to the additional battery.

 

I did play around with the idea of fitting a fuse at each end of the second battery run, just incase the wire did go short as it runs in a locker, but I reckon the plastic trunking will give good protection to the cable.

 

I couldn't fit the batteries adjacent to each other as in your illustration No1, that would be the preferred method.

 

On your second illustration, would not both batteries try to supply 20amps each, that's 40 amps to the motorhome wiring which was probably designed for only 20 amps, or have I got it wrong?

 

Regards Terry

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Thanks again.

I have checked my wiring and am now happy with how the two batteries are connected and fused.

They are both togeher and the second battery has been installed using wire of the same thickness as the original installation. They are fused in accordance with your first diagram, Clive.

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Hi Terry,

Yes, lots of permutations, none are "wrong" but you are correct about my diagram with two fuses. The two fuses would need to be of half the rating each so that the outgoing wiring remains protected. In many examples the wires that parallel the two batteries together can be much fatter and the fuses correspondingly higher rated but the single outgoing connection has the original vans fuse there to protect the wiring. Typical example being if you have a largish inverter. The inverter being connected before the vans single outgoing fuse but via its own inverter fuse.

What I try to achieve is a similar wiring and fuse resistance to each battery so that they share the charge and discharge currents equally.

Regards

 

C.

 

 

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Hi Clive,

 

I didn't think there was so many ways to connect batteries together, and was suprised to learn that with multiple batteries you really do need to connect them so they a properly balanced for charge and discharge, its possible to lose 50% current from one battery on a group of four, especially if using an inverter! See link http://tinyurl.com/66wqwz can explain it much better than I can.

 

Regards Terry

 

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Yes Terry,

This is why I always advocate when replacing leisure batteries use 6 volt units of double the ampere hour capacity and connect them in series.

This ensures that they all share equally. Much better than two 12 volt units connected in parallel. This is what I have.

 

Regards

 

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