Jump start gadget, right way to connect?

Spark from terminal + gas from battery = explosion. Dunno whether there is a real risk with modern "sealed" batteries, but I've seen it happen at close quarters and I can assure you it's something you would want to avoid.

Paint isn't a good conductor. You should earth it to bare metal - generally a chunk of the engine, or a bracket will do.

Biggles

Definitely don't clip it to a painted part. It won't make contact with the metal like this.

Rob Graham

one on the battery plus first, then one on the engine block is correct. main trick is to connect it, then leave for three minutes before even trying to start.

mrcheerful

The message from Brian Pears contains these words:

Nothing much, but taking the -ve[1] straight to the chassis can have minor benefits because it removes one and two joints from the circuit.

However, since I tend to use jump-starting as a way to warm the recipient's battery and prefer to spend ten minutes connected them start with the "dead" battery rather than try to pump sufficient current down the leads it doesn't matter to me.

Of course it does. It requires contact with metal, not paint.

The method you gave first is for jump leads in the *very* unlikely case that a gassing battery has left hydrogen around that a spark could ignite. But since a flat battery can't have been gassing, making the final connection to the flat battery prevents any likelihood of this.

But if your starter pack is like mine, it will have an on/off switch, so just connect it direct to the battery then switch on.

Ooh, seconded. I once forgot I'd left a battery on charge in the corner while I started grinding metal. Blew both battery and charger apart.

Or more if it's a Mini! Did this to my Elf tonight (flooded it), connecting to solenoid terminal and earth strap - much easier than removing two cylinder heads from the boot and the floorboard too, and more effective into the bargain!

These days I just carry a tow rope or tow bar. Everything has front and rear loops so no more grovelling around underneath tieing on to wishbones and drive shafts (or live rear axles when I started). Buy a pair of shackles to make hitching easier. I find tow starting far quicker and more reliable. It's also insurance in case you stop on a motorway. Hitch up the rope and stand in front of the car waving it, and someone will soon stop.

The message from "Newshound" contains these words:

I've welded a coupling to my towpole. Far easier to attach to my car now

- and more comfortable than pulling off-centre, too.

Yes - but that's from a battery that's being charged by a (probably) not regulated charger and was fully charged.

Most car alternators over the last 20 odd years regulate the charge current to almost eliminate gassing. Otherwise, you couldn't have the so called 'sealed for life' batteries.

And the act of lifting the bonnet or boot to access the battery to jump start another car means that any hydrogen - much lighter than air - will escape. Unless it's done in a confined space.

Make sure the final connection of the jump leads is done to the car with the flat battery. That can't have been gassing.

Fine if you don't have an auto. ;-)

Try telling that to the Transit I jumped last week.

Connected to slave battery, then connected negative on transit, then connected posiBOOOM.

It was a sealed battery, the van had not run for a day or so, and the bonnet had been open a few minutes, but despite all that it still had enough gas around to completely blow the top of the battery, showering me with acid while it did it.

While in theory a modern battery will not gas, if you have one with a shorted cell, the other 5 cells will be being overcharged, and therefore gassing, and even a 'sealed' battery will allow that gas to leak out.

No, it wasn't fully charged, and it was a trickle charger. The grinding sparks ignited the gas. BANG!

Unless my physics have got it horribly wrong, a battery doesn't start releasing hydrogen until nearly fully charged.

The message from "Dave Plowman (News)" contains these words:

That's chemistry.

No, it releases hydrogen throughout the charging cycle. Put two lead plates in a beaker of acid and apply a current, you will get gas released immediately. That's from experience as a science teacher.

The message from Chris Bolus contains these words:

Shouldn't do. For one thing, if it did batteries would need topping up all the time - which may once have been the case but certainly is no longer.

You'll find, I think, that one plate is actually lead dioxide - as the battery discharges water builds up in the acid - the hydrogen ions reducing the lead oxide. When charging the hydrogen returns as ions in the water - that's why the water becomes more acidic as it charges.

I reckon if the charger charges fast enough, it'll make even a flat battery gas. I've got quite a powerful charger - one of the ones that you can use to start the car off the mains. I used it last weekend to charge the battery on a car that hadn't been started for a few months. The "high charge" setting made battery fizz loudly straight away.

Cheers,

Colin.