Jump start bike with car?

[embee]

Connecting one flat 12V battery to a moderately charged one won't usually charge it very much (it will a little), a lead acid battery needs more volts to charge than one can usually produce (say >13.5V to charge well, a good battery will only be around 12.7V or so).

The usual advice when jumping one car from another is to connect the jump leads, then start and run the donor for 5mins or so to give the recipient battery a bit of a kick (it'll warm it up a bit if nothing else), then stop the donor and try a start. If you try starting the recipient with the donor running you more or less short circuit the alternator output into the starter motor (can take a few hundred amps on a decent sized engine) which can do it a nasty if you're unlucky. You'll probably get away with it but it can be a bit expensive if it does fry.

Originally Posted by Sid Squid

The 'not connecting the neg lead to the battery' is a hangover from the days of unsealed batteries, there could be some flammable gas from the battery and if there were a spark on connecting the second lead - you do connect the leads in the right order, don't you?

Even if it were not for that, connecting the neg lead directly to, preferably, the engine ensures the least resistance in the jump circuit.

If connecting the neg jump lead to the battery made the electronics suffer so would connecting the lead to the frame/engine - the engine, battery, frame are directly connected together already, the engine and frame by being big metal things bolted together, and the battery has a fat lead that goes from the neg terminal to a bolt on the engine.

Im glad you brought this up.

The other month, I was trying to figure out why everyone was saying connect - to frame not terminal for reason other than ignition of gases risk.
I read every where that there was risk of damaging electronics? but i could not see how its all connected to each other, i then searched online and couldn't find any explanation either, just rumours.

dont think id want to be connecting a jump lead to the frame... it'll scratch it... car jump leads wont be easy to connect to a bike battery as they are huge

[tigersaw]

Originally Posted by Sid Squid

you do connect the leads in the right order, don't you?

I was taught,
Connect the positive lead first, ground lead second.
Remove ground lead first, positive lead second.

Reason being that if you connect the ground first, then when you have the positive jump lead in your hand and catch it on any bit of metal.. crackle .. doesn't happen the other round.
Of course if you remember +ve earth cars it doesnt apply. They were always tricky to fit a radio as I recall.

yep, i caught the spanner on the bodywork before lol soon learnt.

Before recently replacing my battery I was always jumping off a running car, no probs.

I tend to connect the negative lead directly to the main earth point on the bike. But then if it's a faired bike, that point is likely to be hidden and inaccessable.

[_Stretchie_]

Originally Posted by beabert

I then searched online and couldn't find any explanation either, just rumours.

In the front of Haynes manuals. I'm sure, It's just I was told this, and then when I got my first Haynes it also said that.

Interesting reading though..... This thread, not the Haynes

Well, had a fright this morning.

Key in, lights on, thumb starter, nothing. Zilch.

Check kill switch, check N light/side stand, all ok.

Hmm.

Turned out that with the new adjustable levers, I have to have it at max setting to hit the clutch switch...took me a few mins to figure that one out!

I thought it might be useful as a theft deterrant until I realised that would hardly stop a determined thief. Once on my way I readjusted down to minimal setting and it rides fine.

So I'll probably bypass it at some point.

Passed MOT, no issues!

Taxed on the way back, rode it to work....ahhh, the adrenaline and sense of freedom returns

[keith_d]

Originally Posted by embee

The usual advice when jumping one car from another is to connect the jump leads, then start and run the donor for 5mins or so to give the recipient battery a bit of a kick (it'll warm it up a bit if nothing else), then stop the donor and try a start. If you try starting the recipient with the donor running you more or less short circuit the alternator output into the starter motor (can take a few hundred amps on a decent sized engine) which can do it a nasty if you're unlucky. You'll probably get away with it but it can be a bit expensive if it does fry.

Most jump leads aren't able to carry the full starter current for a car, even my old 10mm leads were only rated for 100A for short periods. By charging the battery for 10 minutes we can get a large part of the starter current from the recipient's battery.

I wouldn't worry about shorting the alternator to ground. A fully charged car battery can deliver a huge current (over 100A) with very modest voltage drops because of the low cell resistance. So the voltage at the donor end of the jump leads shouldn't drop far enough to damage the alternator.

Keith.