Silly question probably but...
I had to run a battery cable from the boot through the trans tunnel to the fuses/relays etc under the scuttle (2.5m), I used an offcut of cable from work but am now wondering if large cable has any detrimental effect on voltage drop etc, tried to have a "first start" of the engine today and it struggled to turn over and just wondered if it's a possibilty, if not then it's a new battery needed (which I strongly suspect). The cable is about 20mm2.
Cheers
Kev

For high current cables the larger the better.

Ahh, I see, never did understand electrickery.. Although that means im gonna have to splash out £70 for a new battery now Booo.
Cheers!

Your starter will draw 200 amps minimum, more when cold possibly 300 amps. 20 sqmm is rated at only 100 amp so over a long length you will get serious voltage drop.

Use the heaviest cable you can, 40 or 60 if you can get it.

Ahh but it's 20mmx20mm, (closer to 25x25 actually) not 20 square mm, which is why I wondered if it was too big

quote:

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Originally posted by flibble
Ahh but it's 20mmx20mm, (closer to 25x25 actually) not 20 square mm, which is why I wondered if it was too big

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Aww, I'm confused now, lol
I guessed at the 20mm measurement but putting the verniers across the bare wire (not the insualtion) it measures 23.9mm, I can't believe it's too small, its at least 3x the size of the battery wire on my daily SAAB!
It's got the same strand size as the normal auto wire I got from VWP, so not the heavy gauge thick cores.

If it truly is 23.9mm diameter conductor it's over 450mm^2 (!!!)
The downside will be the weight and the unwieldiness of using it - 60mm^2 (od with insulator of around 15mm) is good for 415A yours will be ok in the multiple 1000A's.

ETA: Assuming it's copper

[Edited on 1/5/11 by iank]

i used some spare arc welding cable on mine plenty thick enough, (about 1/2" your cable sounds as though it designed for a power station!

A v8 BMW 740 has the battery in the boot, which in a car that long means cable about 100m long!

It's about 13mm thick... I have one as it was only about £5 from the scrappy. Must be worth more than that scrap metal value now!

So if 13mm is enough for a v8 starter and all the 740's gadgets... it'll be more than enough for your little car!

Dont weigh it all down with 100kg of copper!

Cheers,
James

quote:

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Originally posted by iank
If it truly is 23.9mm diameter conductor it's over 450mm^2 (!!!)

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Got a weigh a lot as well. 24mm diameter conductor is enormous.

Remember to complete the circuit you also need an earth wire. I presume you are using the chassis for this??? If so then make sure all earth points are clean and secure. If not ,and you have run a cable ( any cable from the battery to earth) it needs to be of the correct size as well.

Lol, yes it is quite big, and someone guessed correcty, I believe it's grounding cable for one of the substations that keep the site running (industrial chemicals). It only has maybe 2-3mm of insualtion oddly, although that's not a problem as I've run it through B&Q white PVC(?) pipe so it's well p[rotected. Not sure if it's copper, its the same fine silver strands that my tiny thinwall cable uses?

On a side-rant:
It's amazing what some big companys throw away (this was in a skip, about 50m of it), and it was a general waste skip, not the dedicated recycling skip. There were also umpteen solid lumps of stainless (used for counterweights in the food side of the factory, so food grade 316 I assume), that were about 12" diameter and 18" tall, weighed a ton and real struggle to lift. Endlesss flat screen monitors under a year old, massive helical gearsets off something industrial that were still in the wrappers and said to be worth thousands and TONS of other stuff, etc, etc, . all being dumped.. and why..?
All beacuse the american HQ top dogs were coming over for a look around tour UK site (on a money saving mission ironically) and all this looked untidy.
I asked if I could Ebay it and split the profits with the company but no, all to be dumped

fibble him of B+ fame?? if so i i could have answered your comment elsewhere ;-)

should have read your profile a bit more.......Hi Fibble :-)

[Edited on 3/5/11 by snowy2]

16-20mm^2 will be plenty even with the battery at the back

Current capacities are the continuous load ratings. Starters only draw for a few seconds. Most car starters are rated at around 1.5kW which I make to be 125amps...

Use welding cable, nice and flexible and rated to at least 200amp continuous

You have made an earth cable from the chassis to the engine?

Same size as the Battery to Starter solenoid cable, as it carries the full current when starting the engine.

Also make sure you scrape the paint away down to the bare metal when you make any earth connections.

Cheers

Cheers for the replies,
Yes, I've earthed the chassis to the engine, almost 100% sure it's the battery now, will have to go to Halfords and see if they'll exhcange without a receipt (only 18 months old), If not then £70 for a new one.
Measuring across the terminals after charging for 16hrs showed 12.8v which is normal I think, but goes straight down to 8-9v when starter button is pushed. It then slowly recovers back up to 11-12v but takes a few minutes.

Hi Snowy!

[Edited on 4-5-11 by flibble]