What size cable for jumper leads?

Submitted: Tuesday, Nov 11, 2014 at 23:02
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The brother in law came around earlier to show off his new toy, an XC Falcon coupe. Dead battery, so I got my jump starter pack out to give him a jump, and it wouldn't crank it. The battery in the unit must be on its way out.

I knew I had a set of jumper leads somewhere, which were a set of el-cheapo auto store ones from years ago. I found them, and after a bit of dicking around managed to jump start the big Ford off our car.

The cable got quite warm during this process and smoke poured out of one of the clamps. I binned them and have decided to make my own. I've made a set before, for motorbikes, but those don't have anywhere near the amp capacity to jump a car. Plus the clamps are too small.

Will 4 B&S be sufficient for automotive use? 20mm2 is the cable cross-section, I don't need to be able to jump start a Mack truck but I don't want any burnies or any melting funny business.

I figured this is the place to ask as I have no doubt there would be a few old hands here who still prefer to make and fix their own gear - so any pointers would be appreciated.
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Reply By: ABR - SIDEWINDER - Tuesday, Nov 11, 2014 at 23:34

Tuesday, Nov 11, 2014 at 23:34
We sell a 25mm2 set.

Good heavy duty product.

You cant buy the cable and clamps for the price.

Tools-ABR

Regards

Derek from ABR
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Follow Up By: Member - Bruce C (NSW) - Wednesday, Nov 12, 2014 at 07:51

Wednesday, Nov 12, 2014 at 07:51
That is a good price Derek, and plenty of conductors in that cable too.

Make good Xmas presents.

Cheers, Bruce.
At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Nov 12, 2014 at 09:38

Wednesday, Nov 12, 2014 at 09:38
3m cables of 25mm2 with heavy duty clamps all for $19.95 from ABR Sidewinder.
The cable alone would cost $60 plus $20 for heavy duty spring clamps, if you could source them.
You would have to be daft to make your own....... unless you were nicking the cable & clamps! lol
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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 12, 2014 at 11:17

Wednesday, Nov 12, 2014 at 11:17
RW,

Though I've answered your question below, I concur the remarks above. It would seem illogical to go down the DIY route, given the availability of Derek's product at a fraction of the cost.

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Reply By: Member - Frank P (NSW) - Tuesday, Nov 11, 2014 at 23:42

Tuesday, Nov 11, 2014 at 23:42
Two on-line wire size calculators here and here support minimum 4 B&S for a 200 amp load (my guess) at nominal 12V over a total cable length of 5m (2.5m for each of pos and neg leads) with a reasonable voltage drop.

I'd say you're pretty much on the money.

Decent connections to your clamps will help keep the smoke in.

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Follow Up By: Member - Frank P (NSW) - Tuesday, Nov 11, 2014 at 23:45

Tuesday, Nov 11, 2014 at 23:45
Play around with the numbers if you want longer cables or higher current.
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Follow Up By: Zippo - Wednesday, Nov 12, 2014 at 01:59

Wednesday, Nov 12, 2014 at 01:59
Frank P: "Decent connections to your clamps will help keep the smoke in."

This is the key. Most cheaper sets have lousy crimping, which is what lets them down (and the smoke out) long before the cable itself causes an issue.
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Reply By: vk1dx - Wednesday, Nov 12, 2014 at 08:26

Wednesday, Nov 12, 2014 at 08:26
I may be wrong but don't you need some kind of surge protection. Mine have a box on them for something like that. No mention of that in the above posts. Slip of the pen possibly.

I would buy them, not make them. I also wouldn't be search for a primarily cheap set. Car parts suppliers would be a good place to start. Maybe even the ARB ones mentioned above. I didn't loo at them. We got them at the super place and they work well.

Another thing that we have that has only been used for the benefit of others. Ahhhh Isn't it fun.
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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Nov 12, 2014 at 09:54

Wednesday, Nov 12, 2014 at 09:54
Surge suppression on jumper leads is a nonsense perpetrated for sales promotion. Just think about it........ Is there surge suppression on auxiliary batteries connected via solenoid relays? Is there surge suppression on starter motors? Of course not.
The low impedance of a 100ah battery, charged or flat, is about the best surge suppressor you could wish for.

With respect, it was ABR (ABR Sidewinder) mentioned above, not ARB. A significant difference in pricing structure.
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Follow Up By: vk1dx - Wednesday, Nov 12, 2014 at 12:30

Wednesday, Nov 12, 2014 at 12:30
As you can tell Allan, I wasn't too confident about it myself. But I had to put it up for discussion.

I wonder if it would make a difference having two systems connected. ie two alternators, one in each car etc. They would be directly earthed but still two undepoendant complete wiring, computers and sensors. This wouldn't be the case for multiple batteries in one car. What do you think?
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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Nov 12, 2014 at 13:46

Wednesday, Nov 12, 2014 at 13:46
If jump starting a 'flat' battery (call it 'A') from a good battery (call it 'B') then it is usual to have B's engine running during the jumping with its alternator contributing ... all's good. Vehicle A is not running until its engine fires-up so vehicle B alternator is contributing charge to the two batteries now in parallel. After vehicle A starts its alternator will also begin contributing charge to the two batteries. Each alternator will contribute current based on its own regulator algorithm and the voltage that each 'sees'. There is no problem with that, certainly not in the short term during the jump start operation although there may be some minor regulation confusion if the alternators remained in parallel until the batteries approached full charge.
It would be no different for "multiple batteries in one car".

If your question was in regard to 'surge suppression' with the two systems in parallel then the answer is 'no problem'. The considerations remain as for each single system as I explained before.

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Reply By: TomH - Wednesday, Nov 12, 2014 at 08:36

Wednesday, Nov 12, 2014 at 08:36
I have a set I made myself out of welding cable. They are long enough to go across two cars side by side. Ends are soldered onto clamps.

Have started innumerable cars with them. Never get hot or smoke.

Cost me all of $15 in 1996 We used them when driving taxis to start the cars who left the lights on on a Saturday night at the pub.

They have an suppressor box on them as well.

Paid for them on the first job LOL
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Reply By: Ron N - Wednesday, Nov 12, 2014 at 11:30

Wednesday, Nov 12, 2014 at 11:30
Welder cable is the way to go. More importantly, buy a set of heavy duty clamps from an electrical wholesaler.
Heavy duty clamps have real thickness of metal in them, not the paper-thin metal you get in Chinese clamps.
The heavy duty clamps also have heavy duty springs that get a proper grip on the battery terminals.
Solder the wire connections and you have 100% guaranteed connections, no chance of any corrosion.
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Reply By: Robin Miller - Wednesday, Nov 12, 2014 at 11:37

Wednesday, Nov 12, 2014 at 11:37
4 Gauge 16mm sq is about right Road Warrior however it must be copper - some are copper plated wire .

Also keep length down to under 3M , 2.7m is common .

I also carry an 8 gauge set which is 8mm2 , it works just as well because its under 2m long and instead of big clips I use terminals on one end which you attach to supply battery via the batteries nuts.
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Reply By: Road Warrior - Wednesday, Nov 12, 2014 at 12:18

Wednesday, Nov 12, 2014 at 12:18
Thanks for the replies everyone. I'm not sure where to go with this given the choices. I'm not averse to making my own things, but I'm not spending $100 to do it just for bragging rights either.

I think the motorbike ones I made would have cost me $50 all up with the parts, which I know you can buy a set off ebay for $20 or less, but I know that mine will last me a lifetime...and then some.
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Follow Up By: TomH - Wednesday, Nov 12, 2014 at 13:52

Wednesday, Nov 12, 2014 at 13:52
Its a no Brainer Buy the ABR ones
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Follow Up By: Ron N - Wednesday, Nov 12, 2014 at 17:37

Wednesday, Nov 12, 2014 at 17:37
RW - Unless you're regularly jump-starting starting trucks, tractors, or earthmovers, those jumper leads of ABR's will do just fine for 98% of 4WD's.
At the price he's offering them at, you couldn't even buy a couple of clamps in Supercheap for the money - let alone 3M of cables.

Cheers, Ron.
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Reply By: Honky - Wednesday, Nov 12, 2014 at 19:46

Wednesday, Nov 12, 2014 at 19:46
Thought I would be a smart &*s and bought a set of heavy duty jumper leads to use the wire to connect two batteries as it was a lot cheaper than buying the cable by the metre.
When I cut the wire it was so thin that I just threw them out and did what I should have done in the first place.

Honky
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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Nov 12, 2014 at 19:55

Wednesday, Nov 12, 2014 at 19:55
There are some real cons around Honky. This is just one.
Fat plastic cables with minimal copper conductor is simply a fraud.

If you cannot see the conductor size at the termination then perhaps the best way to judge the size of the conductor in jumper leads is by weight. Good ones are quite heavy.
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Reply By: The Bantam - Wednesday, Nov 12, 2014 at 23:30

Wednesday, Nov 12, 2014 at 23:30
I have to agree that most of the commercially available jumper leads are just rubbish....mostly the cable is more plasitc than copper.

It is actually surprising how light jumper leads can be and still "work", particularly if it is a fairly small low compression petrol engine involved.

But as soon as you start talking about diesels...ahh different story.

years ago I made up some jumper leads out of the modified clips from some cheap jumper leads and some 6mm2 twin and earth scrounged off a building site.

Iver the years they have started many petrol engined cars.....a couple of years ago I tried to jump start a mates diesel fork lft with them......yeh not going to happen.

20mm2 would be damn fine compared to most commercially available jumper leads.......but if Derric can do 25mm2 at 3m long for $20......HELL.

OH one thing that improves the performance of most jumper leads is butting a copper strap from onejaw to the other.

All the decent welding clamps have this strap and a very few jumper leads.

Strapping the jaws of your clamps improves the connection resistance out of sight.

cheers
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Follow Up By: Ron N - Thursday, Nov 13, 2014 at 12:00

Thursday, Nov 13, 2014 at 12:00
All good points, Bantam - particularly the one about ensuring the clamp jaws are coupled with a strap.

In an act of desperation, I've actually jump started a diesel Commer Knocker truck, using strands of heavy gauge fencing wire, twitched together!

I've got a set of jumper leads made up from 3.5 metres of 400 amp welder cable and the biggest and heaviest-duty booster clamps I could buy from Ashdown-Ingram - because I often have to jump start forklifts, earthmovers, and trucks with big batteries.
There's nothing I've found yet, that those leads can't handle!

The heavy duty booster clamps from Ashdown-Ingram are very conservatively rated, unlike so much of the Chinese consumer rubbish.

I actually bought 8 sets of Chinese "200 amp-rated jumper leads" from Repco last year - when they were throwing them out on special - for $6 a set!

They are bloody useless as jumper leads - but the light-duty clamps and cable are excellent for use in other light lead applications - where you don't need to carry 400 or 600 amps - and I couldn't buy the clamps and the handy light-duty cable individually, for less than $25!

Cheers, Ron.
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Follow Up By: Road Warrior - Thursday, Nov 13, 2014 at 12:08

Thursday, Nov 13, 2014 at 12:08
RE: the bridging strap in the clamps, my Projecta jump starter has that, although it is more like a bridging wire.

Incidentally, when I was looking online at jumper leads, I saw a set of "Michelin" brand (as in the tyre mob) which had this feature - wait for it - Automatic Polarity Correction - meaning that even if you crossed the leads, it would still jump the car. It was a dirty great brain box in the middle of the leads, like a massive spike protector but obviously more to protect people from themselves who perhaps shouldn't be trying to jump start a car in the first place!!!
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Reply By: MactrolPod - Thursday, Nov 13, 2014 at 06:55

Thursday, Nov 13, 2014 at 06:55
I have made some from welding cable, a 50mm lug was a tight fit so call it 50mm cross sectional area cable. Bought some from a mob in Bairnsdale, they are brass clamps with a braided copper strap that links both parts of the clamp, they are rated at 1000amps, with the 5 metres of cable they are very serious leads and unfortunately a bit heavy.
The reason I did this is my batteries failed in the outback, a fellow traveller had 900amp leads from a auto shop, they were not up to the task and we tow started the car until we could get another battery.
The problem with most clamps is they are plated steel, look good but starting a diesel after preheating just doesn't happen.
That was one brand of leads others may well be better, that I don't know.
I don't do this for a piddling contest, I simply want them to work when I need them with no problems.
I was going to get a spike / surge arrester, the comments above have me thinking it is not necessary. Interesting.
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Follow Up By: MactrolPod - Thursday, Nov 13, 2014 at 07:05

Thursday, Nov 13, 2014 at 07:05
Bought some "clamps" from.... Sorry about that.

Here is the clamp, some one here said something about the pain the price of quality is soon forgotten. something like that

http://www.ebay.com.au/itm/2x-1000-AMP-PROJECTA-ALLIGATOR-CLAMPS-BATTERY-STARTER-JUMP-LEAD-CLIPS-BC1000R-B-/290822217903?pt=AU_Car_Parts_Accessories&hash=item43b65ae0af
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