Connecting batteries

[Sniggib]

Hi all,

Getting myself a little confused with this.

Planning on wiring together two 90Ah batteries as per the below;



Where I am getting stuck is battery cable sizing.

The batteries are in effect wired in parallel to balance, this doubles the amps and keeps voltage the same.

So, for the connections between batteries;

- 90Ah batteries
There is the potential for these to balance and therefore max draw is 90A between the batteries

But, for all other wiring, the batteries in parallel double the amps, so I need something that will handle 180A.

As such, my plan is to use 35mm2 wire with a rating of 240A for all wiring.

I will also install a maxi link fuse between the batteries at 125A - Is this the correct place to put the fuse?

Appreciate if someone could double check my thinking!

Cheers,

 

[oldiebut goodie]

I will let others put you straight on the cabling. ( can't read your sizes with my old eyes)

But, these are the ratings for Webastos fuses:
Diesel heater fuse should be 15A for a 2Kw, 20A for 3.5Kw/5Kw /5.5Kw

( I used 250A rated cable between my 2 110Ah batteries but only because that was hanging around left over from a boat wiring project )

 

[Sniggib]

Yes sorry, not sure how to make the image bigger / zoomable!

Thanks for the info on the diesel heater. It was a guess as I was not sure on the rating! I will probably be having someone fit the heater so I hope they will fit the fuse at that point.

Cheers,

 

[DXX]

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

 

[Sniggib]

Thanks @DXX I have been using their guide and been ok with the rest of the wiring, its just the batteries I am not sure of, whether 240A is overkill or not.

 

[Deaky]

The cable size should reflect the total load required, not the maximum the batteries are capable of supplying. Just make sure you have the correctly rated fuse for the load directly after the battery bank.

 

[Sniggib]

Thanks @Deaky that's what I'm unsure of, the total load between batteries as they balance out. Presumed I needed to account for 90A on the basis that each battery could supply 90A as they balance? T then the total load to earth from the battery bank being 180A?

Load from batteries to fuse box (and then onto the individual circuits) will be about 20A, wiring rated for 50A, with a 40A fuse just after the battery bank.

 

[Deaky]

In theory, if one was totally flat and the other was full. In reality this will never be the case. Are both batteries next to each other?

 

[Sniggib]

They will be almost next to each other.

Checked the voltage drop on both 25mm2 and 35mm2 cable and both were fine for 1m (which it will be much less than). I was just unsure on the max amps.

Many thanks.

 

[Eclipse Custom Vans]

They will be almost next to each other.

Checked the voltage drop on both 25mm2 and 35mm2 cable and both were fine for 1m (which it will be much less than). I was just unsure on the max amps.

Many thanks.

VD on that distance will be negligible. not worth thinking about

 

[Deaky]

They will be almost next to each other.

Checked the voltage drop on both 25mm2 and 35mm2 cable and both were fine for 1m (which it will be much less than). I was just unsure on the max amps.

Many thanks.

I wouldn’t bother fusing the battery interconnects if they’re next to each other just make them as short as you can. 25mm is overkill IMO too

 

[Eclipse Custom Vans]

this will give yo an idea on CCC for stranded cables 25mm 136 amps etc,

16 or 25mm will be fine for the battery links but ensure you fuse outgoing correctly. We've just fitted 95mm cable and 250A fuses but this was linking 2 x 160AH batteries through a combiner

 

[Sniggib]

Thanks. I was questioning myself on it as I thought for a bigger bank of say 8 batteries, how would you ever get thick enough cable!

Makes sense though that they will never pull 90A from each other.

Can I check, the cable from battery to ground. Does this need to be able to take my total amps for the whole system?

 

[Sniggib]

this will give yo an idea on CCC for stranded cables 25mm 136 amps etc,

16 or 25mm will be fine for the battery links but ensure you fuse correctly


View attachment 95387

Thanks.

When you say fuse correctly, do you mean between batteries?

I will be adding in fuses as the wiring diagram in my last post. Appreciate your thoughts on any more fuses needed.

I've basically fused everything just after it exits a power out in battery or CTEK. Then all smaller circuits fused in the fuse box.

Thanks,

 

[DXX]

Then you use a solid busbar

 

[Eclipse Custom Vans]

Thanks.

When you say fuse correctly, do you mean between batteries?

I will be adding in fuses as the wiring diagram in my last post. Appreciate your thoughts on any more fuses needed.

There is no harm in fusing in case there is a problem with the batteries but unlikely. We don't normally fuse between the batteries if they are side by side only if they are in separate locations, cheers

 

[Sniggib]

this will give yo an idea on CCC for stranded cables 25mm 136 amps etc,

16 or 25mm will be fine for the battery links but ensure you fuse outgoing correctly. We've just fitted 95mm cable and 250A fuses but this was linking 2 x 160AH batteries through a combiner


View attachment 95387

Wow, 250A outgoing, that must be some serious kit needed in the van!?

I've only got about 20A going from battery to fuse box so have that at 10mm2 cable and a 40A fuse to allow for extra capacity in future.

Thanks again.

 

[Eclipse Custom Vans]

Hi all,

Getting myself a little confused with this.

Planning on wiring together two 90Ah batteries as per the below;

View attachment 95371

Where I am getting stuck is battery cable sizing.

The batteries are in effect wired in parallel to balance, this doubles the amps and keeps voltage the same.

So, for the connections between batteries;

- 90Ah batteries
There is the potential for these to balance and therefore max draw is 90A between the batteries

But, for all other wiring, the batteries in parallel double the amps, so I need something that will handle 180A.

As such, my plan is to use 35mm2 wire with a rating of 240A for all wiring.

I will also install a maxi link fuse between the batteries at 125A - Is this the correct place to put the fuse?

Appreciate if someone could double check my thinking!

Cheers,

Solar panels need a fuse. Don't forget fuses are there to protect the cable form heating and burning, so ensure the fuse is smaller than the CCC of the cable

 

[Sniggib]

Thanks, will put it in as close as I can to the panels. Though will be once the cables are inside the roof!

Yes I've opted for thicker cable than needed really to give me peace of mind, and kept the fuses toward the lower end. There is something like a minimum of 10A + between fuse value and cable capacity.

 

[Eclipse Custom Vans]

Wow, 250A outgoing, that must be some serious kit needed in the van!?

I've only got about 20A going from battery to fuse box so have that at 10mm2 cable and a 40A fuse to allow for extra capacity in future.

Thanks again.

It was for a military communications vehicle and they needed 60mins back up power for batteries. So not your typical camper

10mm cable will take 70-80 amps so I would up the fuse size to prevent nuisance tripping. I would keep all the same cable sizes with the same fuse for simplicity. Aw rarely go larger than 50A on campervans.