How many amps ?

[Scraperman]

I need to replace the positive battery lead on my Project 8 3CX. I can see that there are many choices in terms of amps capacity. Could anyone please tell me what amp figure lead I should be looking for please ? I presume it would be 300 amp at least ? Aplogies if it is a stupid question but, by and large, I don't do electrics. Replacing the lead is about the extremity of my capabilities. Thanks in advance for any help and/or advice given.

 

[V8Druid]

I need to replace the positive battery lead on my Project 8 3CX. I can see that there are many choices in terms of amps capacity. Could anyone please tell me what amp figure lead I should be looking for please ? I presume it would be 300 amp at least ? Aplogies if it is a stupid question but, by and large, I don't do electrics. Replacing the lead is about the extremity of my capabilities. Thanks in advance for any help and/or advice given.

50mm2 will carry 350A continuously - is about 13mm O.D. and circa 10 quid a metre or for another 6 quid a metre, could go to 95mm2 and be good for 600A

 

[Scraperman]

50mm2 will carry 350A continuously - is about 13mm O.D. and circa 10 quid a metre or for another 6 quid a metre, could go to 95mm2 and be good for 600A

Thank you very much for that, much appreciated. I just wondered what amp lead I require. Is it dependent on what length the lead is ? Haven't got the old lead off yet but I would say mine is about 18" - 2ft long from the battery terminal to the starter motor. I am going to replace the complete lead because the starter motor coupling on the existing one is damaged.

 

[V8Druid]

Thank you very much for that, much appreciated. I just wondered what amp lead I require. Is it dependent on what length the lead is ? Haven't got the old lead off yet but I would say mine is about 18" - 2ft long from the battery terminal to the starter motor. I am going to replace the complete lead because the starter motor coupling on the existing one is damaged.

if that's the only issue and you have slack, why not just crimp a new terminal on to replace the damaged one ? ... if it's gone hard and 'crispy' then go for a new one - a decent factors should have 'length-ed leads' in stock

 

[Scraperman]

Thank you for that advice. I had thought about doing that but couldn't find a coupling that had a decent insulation piece and in any case there isn't much slack and I don't want to go through all that trouble only to find that it's a bit tight where it goes onto the starter motor after I have cut the existing ring coupling off. I did look for a local factor that could make me one the right length but I just wanted to know what amp cable it should be. I presume that amps is related to the thickness of the wire inside the protective outer of the complete cable ?

 

[pettsy]

Last time i replaced a power cable I bought one on eBay with pre-crimped terminals. Wasn’t expensive and all done properly.

 

[Gecko]

The mantra for battery cables is "bigger is better". It's almost impossible to over-do a battery cable.
It's not a long cable on a P8, so you 'could' get away with a light cable, but why bother.
As for length, add 6" and you won't be restricted to any particular battery terminal layout.

 

[Scraperman]

Last time i replaced a power cable I bought one on eBay with pre-crimped terminals. Wasn’t expensive and all done properly.

Thanks for your response. I had seen those and they have lots of options, length, diamater of cable, and amps but I just wondered which of the last two options I needed for my machine.

 

[Scraperman]

The mantra for battery cables is "bigger is better". It's almost impossible to over-do a battery cable.
It's not a long cable on a P8, so you 'could' get away with a light cable, but why bother.
As for length, add 6" and you won't be restricted to any particular battery terminal layout.

Thanks again for your continued help. Much appreciated. I was going to add a bit more length than that which is being replaced. It can always be shortened at the battery terminal end if necessary.

 

[Gecko]

A bit of extra length won't matter at all (not until you start racing it).

Buy cable by mm^2 rather than amps - it's harder to lie about.
You can pull 1000A though a 6mm cable, but the insulation will melt and the cable will glow.
As above, 35mm^2 will give you a solid start.

 

[Scraperman]

A bit of extra length won't matter at all (not until you start racing it).

Buy cable by mm^2 rather than amps - it's harder to lie about.
You can pull 1000A though a 6mm cable, but the insulation will melt and the cable will glow.
As above, 35mm^2 will give you a solid start.

Thank you @Gecko. I have just measured the existing cable and it is 3ft (915mm) in length and the core is 8mm and the core + outer is 12.3mm. What I don't understand is what does your "35mm^2" mean ? Sorry to be such an ignoramus but I fight shy of anything electrical.

 

[V8Druid]

Thank you @Gecko. I have just measured the existing cable and it is 3ft (915mm) in length and the core is 8mm and the core + outer is 12.3mm. What I don't understand is what does your "35mm^2" mean ? Sorry to be such an ignoramus but I fight shy of anything electrical.

the square mm-age is calculated by taking the the core diameter and multiplying by Pi (3.142) so 8mm dia would give you circa 25mm2 roughly (it should be done with each individual core strand and then added together to get a true figure)

 

[Gecko]

Ah - I can't do a "superscript 2", so this is the common method to indicate area. It's pretending to be this: mm²
So, 35mm² means the cable cross-section is 35 square milimeters area.
Your 8mm cable works out to be 50 mm² (which is better than 35)

 

[V8Druid]

Ah - I can't do a "superscript 2", so this is the common method to indicate area. It's pretending to be this: mm²
So, 35mm² means the cable cross-section is 35 square milimeters area.
Your 8mm cable works out to be 50 mm² (which is better than 35)

yeh my senior moment this morning -
its Pi x r2 for area ...
Pi x D is circumference -
apologies Scraperman - good job someone has their head together today -
mine's totally bollo-ed this morning - AGAIN!!

 

[Lancs Lad]

Do love a good battery lead thread

 

[Scraperman]

O.K. folks. bit pushed for time now. I will respond to you all later but in the meantime I thought I would order this : https://www.ebay.co.uk/itm/20251129...KQNWZC&hash=item2f269d1f33:g:JmwAAOSwu9Jb9qnf
with specifications shown below. I won't order until one of you kind gentlemen tell me that I've got it right. I know the starter motor terminal is 7.35mm.
I have chosen 1250mm in length when the existing is 1m but I can shorten it at the battery end with this type of terminal.

 

[Scraperman]

I have just read all the answers in this topic again and have uprated the cable size as shown below and ordered one.

 

[Gecko]

Good call
I think you'll be happy with that

 

[Scraperman]

if that's the only issue and you have slack, why not just crimp a new terminal on to replace the damaged one ? ... if it's gone hard and 'crispy' then go for a new one - a decent factors should have 'length-ed leads' in stock

Yes, I had thought of that. But most of the new terminals that I found aren't insulated and it is all a bit tight in there and so for a few quid I thought it would be better to start all over again. But thanks again for your continued help. It is always very much appreciated.

 

[Scraperman]

The mantra for battery cables is "bigger is better". It's almost impossible to over-do a battery cable.
It's not a long cable on a P8, so you 'could' get away with a light cable, but why bother.
As for length, add 6" and you won't be restricted to any particular battery terminal layout.

Thank you for that. I took your advice and bought a longer length than I actually need.