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kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

2009 Defender 110 Puma 2.4 USW Santorini Black

Home made busbar

I want to build a busbar for my dual battery install

I will connect the factory installed earth cable to the busbar and then connect each of the two batteries to the busbar.

Will save me from drilling another hole on the battery box to run a cable to the transmission casing

I can get a 3.2mm thick copper strip - 25mm wide and 100mm long for less that £5. Copper is 99.9% pure

How many amps would that be good for? I have see a video on the web which says 1.4 amps per 1 sq. mm of copper but find that a bit odd as doesn't say how thick the copper is. Any engineers care to comment?

To buy, a 500Amp busbar is around 50 squids

14th Apr 2020 4:05pm

rallysteve

Member Since: 10 Feb 2014
Location: Cumbria
Posts: 2237

2002 Defender 110 Td5 DCPU Keswick Green

if your batteries are next to each other, why not just link the negative terminals together with a short length of battery cable?

I have done this with my own setup as it was the neatest option with the least connections.

Steve 02' 110 TD5 Double Cab Rebuild Thread

14th Apr 2020 4:08pm

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

It is well nigh impossible to connect anything else to the standard earth connector on the Puma.

How did you manage that? Unless I can get a ring lug that fits over the battery post

14th Apr 2020 4:13pm

DuncanS

Member Since: 06 Dec 2013
Location: Cumbria
Posts: 299

2008 Defender 110 Puma 2.4 USW Santorini Black

Busbars are easy enough. I've done mine a slightly unorthodox way but it works well. It was the only way to do it to wrangle 500a of power in such a short space, instead of using 95mm cable (which I've used everywhere else in the split charge).

This was 20mm wide, 5mm thick mains busbar copper (giving me 100m2 CSA). In terms of calculating current on copper, go with the CSA (Cross sectional area in mm2) which is somewhat irrelevant as to its makeup between solid or stranded for the currents and distances we're talking about.

In terms of linking the two batteries, I use 10mm Stud terminals and I reterminated the factory cables to suit.

https://www.durite.co.uk/s/c/wiring-access...-10mm-stud

Click image to enlarge

Click image to enlarge North Cumbria Search and Rescue - Team Leader

14th Apr 2020 4:26pm

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

Very cool set-up.

I've gone for two 3.2mm strips, 25mm wide and 100mm long.
Based on your calcs more than enough

I'm using 40mm2 cable for the rest of it as I am not expecting 500Amps other than when cranking.

Have you insulated your strips with heatshrink? or something else?

14th Apr 2020 4:38pm

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17443

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

Re: Home made busbar

kmac wrote:
I want to build a busbar for my dual battery install

I will connect the factory installed earth cable to the busbar and then connect each of the two batteries to the busbar.

Will save me from drilling another hole on the battery box to run a cable to the transmission casing

I can get a 3.2mm thick copper strip - 25mm wide and 100mm long for less that £5. Copper is 99.9% pure

How many amps would that be good for? I have see a video on the web which says 1.4 amps per 1 sq. mm of copper but find that a bit odd as doesn't say how thick the copper is. Any engineers care to comment?

To buy, a 500Amp busbar is around 50 squids

That will be 1 mm^2 of CSA, so your 3.2mm x 25mm strip, which has a CSA of 80mm^2 would, using that formula, be good for 112 Amperes.

14th Apr 2020 4:42pm

DuncanS

Member Since: 06 Dec 2013
Location: Cumbria
Posts: 299

kmac wrote:

Have you insulated your strips with heatshrink? or something else?

My strips were done with one layer of really big 3:1 glue shrink (clear) (to ensure a thick sleeve) with a layer of 2:1 on top in red for appropriate colour. North Cumbria Search and Rescue - Team Leader

14th Apr 2020 4:45pm

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

Thanks Duncan and Mr Wolf

I've gone for double strip so 6.4mm X 25mm

14th Apr 2020 5:05pm

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

Re: Home made busbar

blackwolf wrote:

That will be 1 mm^2 of CSA, so your 3.2mm x 25mm strip, which has a CSA of 80mm^2 would, using that formula, be good for 112 Amperes.

I'm not sure of their formula

95mm^2 cable is normally rated for between 240 and 300 Amps continuous

I will have a cross section of 6.4mm *25mm so 160mm^2

Should be good for more than 224Amps no?

Edit: Actually some sites say 95mm^2 is good for 500 Apms

14th Apr 2020 5:13pm

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17443

Yes, I think that the formula is completely wrong, but I was trying to explain its application!

14th Apr 2020 5:55pm

Outlaw1

Member Since: 11 Aug 2016
Location: east sussex
Posts: 268

2010 Defender 110 Puma 2.4 USW Santorini Black

What is this strange language you clever people talk

14th Apr 2020 6:14pm

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

blackwolf wrote:
Yes, I think that the formula is completely wrong, but I was trying to explain its application!

Thanks Mr Wolf - finally got it when Duncan mentioned it refers to the cross sectional area (which in retrospect is obvious now as that is how cables are rated (in simplist terms, I know there are all kinds of complications with number of cores and strands per core etc)

15th Apr 2020 10:17am

DuncanS

Member Since: 06 Dec 2013
Location: Cumbria
Posts: 299

Don't always trust the CSA figure purely for rating. Whilst the CSA does provide the direct current rating, you also need to factor in the insulation type and the strands. Hence why the traditional PVC 1mm2 cable is approx 8amps and the Thinwall 1mm2 cable which is more modern is 16amps.

The easiest bet when sizing a cable is just look at what the cable is rated for in Amps. Obviously the only reason we're having the discussion is that you were after solid copper understandably haha! I personally don't use any PVC wherever possible as Thinwall is much tougher and lighter (and apparently I never do "little" amounts of cabling on my projects) North Cumbria Search and Rescue - Team Leader

15th Apr 2020 10:25am

kmac

Member Since: 07 Oct 2009
Location: Middlesex
Posts: 1309

Thanks Duncan - I use Thinwall as well. It is the cooling properties that allow the higher amps I believe.

Anyway for my busbar I am going to go with a CSA of 6.4mm *25mm

15th Apr 2020 10:52am

dorsetsmith

Member Since: 30 Oct 2011
Location: South West
Posts: 4554

Outlaw1 wrote:
What is this strange language you clever people talk

http://copperalliance.org.uk/uploads/2018/...usbars.pdf

15th Apr 2020 12:08pm

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