Not ideal but in theory would a 16mm cable on Positive and negative 5.5m long jump start van (1 Viewer)

[PeterCarole29]

From my engine battery i have both Positive and negative cables 16mm to my B To B charger next to my just over 400amp leisure batteries(it was after i fitted them it was mentioned 30amp would be better but as yet still have the 16amp fitted.
My question is if the engine battery was below 12v and i used the 16mm to jump start would they melt/get hot .
An example is once we pulled in to service station once for a kip and left our lights on. van wouldnt start

 

[DavidCh]

Will work if you connect it first without trying to start for ten minutes it would go. The amount of time you would crank will not overheat the cables and connecting first will get some charge over.

 

[Lenny HB]

Good chance of it melting cranking current is around 100 to 150 amps and intial cranking current 300 to 600 amps. 16mm sq is rated at 110 amps, also the volt drop would be too high for it to work very vell.

Much easier just to connect a cable between the positive of the leisure and starter batteries and leave it to charge for a couple of hours, only needs to be a small cable say 4 or 6 mm sq.

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[xsparks]

Remember to remove before starting or you'll see some smoke.

 

[PeterCarole29]

Thanks it what my gut feeling was. but now i know.
I have had a wiring loom melt next to the petrol pump forecourt before.
I swung into the petrol station in my own work van 40yrs ago with my van that had no battery clamp on ,the battery terminals pressed against the metal bonnet took 3 seconds to start smoking down to bare wires. red hot then after. took 10 seconds to get bonnet open. A very unhappy garage

 

[Trevor Wbm]

If you can spare the cash, these devices are excellent:

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Keep one in the van all the time. Never needed it but have been able to help out others on a number of occasions.

(Tea towel tied around the back of my neck, underpants on the outside - "Is it a bird? Is it a plane? No - it's flat battery man!").

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[DavidCh]

Good chance of it melting cranking current is around 100 to 150 amps and intial cranking current 300 to 600 amps. 16mm sq is rated at 110 amps, also the volt drop would be too high for it to work very vell.

Much easier just to connect a cable between the positive of the leisure and starter batteries and leave it to charge for a couple of hours, only needs to be a small cable say 4 or 6 mm sq.

I think it is very important to understand what is going on here, although the cranking current high, its only for a very short period, once the engine is turning (not running) it reduces significantly, the big draw is the very short time to get it moving. Also, you are talking a few seconds here in total, if you are cranking for any longer than that its not going to work anyway. Interestingly, I (and many others) have used the lithium battery boosters to start, I think most of them are using 10 mm sq, 16 at them most. Key, in my opinion is to give it a chance by connecting up and leaving it for a while to put some charge back into the starter battery.

 

[Widge]

Depending on the leasure battery it may not have the umph to start the vehicle anyway, they are designed to give relatively low current for a long time, a starter battery is designed to give large current all in one go for starting, in fact you may even damage the leasure battery, so as suggested use it to charge, but disconect it before starting

 

[rwg]

You won't melt the cable, at least not quickly.... However it may not provide enough current to do the job.

16mm2 cable is 1.2 ohms per km, so your 11m has a resistance of 0.0132 ohms.
If you push 200 amps through it, that will generate 528 watts of heating in the cable itself, but the cable works out to be about 1.5kg of copper, so will heat up at just a bit less than 1 degree per second with 528 watts of heating. Yes, it will get hotter, but not significantly hot in the 10-15s or so that either let the engine start or mean it isn't going to.

Are you going to get more than 200 amps down it - not realistically... At 200 amps, the voltage drop in the cable is 2.6V, plus whatever the battery drops under that load means you will be lucky to deliver 9 volts to the starter. At 300 amps you will drop nearly 4V in the cable, plus a volt or two more at the battery, delivering only 6 to 7 V to the starter...

So, it might make the difference if the vehicle batttery is only a bit below the level needed to start the van, but it probably won't work if it is completely dead.

cheers,

Robin

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