principle of jump leads

"john hamilton" gurgled happily, sounding much like they were saying:

I work on the principle that it's bloody easy to knock one against the bodywork whilst connecting, so do the +ve first - that way, you reduce the risk of doing harm when (not if) you do so. If the earths are connected first, then the second end of the +ve is live relative to the bodywork of the car you're connecting to.

Doesn't matter which car's which for that.

Then start the "donor". Hold it at 1,500-2,000rpm or so. Then try to start the "recipient".

one of the things to avoid is making the final connection on to the battery, you should make the final connection the earth side on one or other of the vehicles to something like the engine block, that way any spark that may occur is away from the battery. it is not a vast risk, but an exploding battery can and does happen and it is not nice.

I'd personally do:

Flat +ve first, to good +ve (and this is the one to be careful you don't short anything with), then flat -ve, then good -ve, but as mrcheerful has said make the last connection away from the battery if possible.

I'd base that on the idea of carrying connected cables from a flat, rather than charged battery, so if you drop it it doesn't short.

Chris

OK, except for a positive earth vehicle...

:)

Mike gurgled happily, sounding much like they were saying:

I _nearly_ put "Assuming -ve earth", then thought "No, anybody dealing with a +ve earth car is going to be well aware of the fact - let's not confuse matters..."

It doesn't make any difference. If you connect the +ve first, and then touch the body with a trailing

-ve lead, you are still completing a circuit with a difference in potential of 12 volts (assuming a completely flat recipient) so you will still get a spark at the point of contact..

Connect the -ve first Connect the +ve to the flat battery Coonect to the good battery..

'Ere - Oo are you calling a matter?

Yes it does

But it'll be a much smaller spark than if you touch the body with a +ve lead. Much much smaller.

& if you get a spark you can pop the battery. Hence why every set of instructions since -ve cars became the norm says do it the other way .

& whilst I'm being crap, the -ve lead goes between the engine blocks, so that when you get the spark it's not next to the battery.

Don't see how - that doesn't make ANY electrical sense. Given a circuit good-battery >> dead-battery , then a current of X will flow between the two to charge the latter. The same current flows through all parts of the circuit, disconnecting or connecting any part of the circuit will effect the same current and produce the same spark..

You will also get a spark if you connect the -ve terminal second.. Or did you mean 'connect to the dead battery second'? Ok, given that the dead battery is likely to have little hydrogen around, maybe so - but as Mr Cheerful said, you are taking a fully charged lead to a engine bay where you may drop it, rather than a dead lead to a live terminal. You don't after all plug a flex into a mains socket, then try to wire it to your appliance. Anyway, arn't all batteries sealed now?

Next to the leaking petrol pump, or highly flammable brake fluid?

Because if you touch the +ve lead against the chassis it's a dead short, if you touch the -ve lead then the other battery is in the circuit.

Yes

No

No

If you're jump starting a vehicle with a leaking petrol pump then no amount of instrcutions is going to help you

If you've filled your brake system with flammable fluid then jump starting the car is only a slightly worse idea than starting it normally.

Yeah I had one - I was grinding next to a charging battery (stupid I know) and there was an almighty bang and as far as I can recall, no large parts remaining of a large battery. It took me a while to work out what had happened. Some safety warnings serve only to immunise against those that really matter.

It could be a good reason why the battery is flat..

Funny, most brake systems ARE filled with flammable fluids:

" Though not a volatile liquid, brake fluid is inflammable. Modern brake fluids are based on polyalkylene glycols. The author of this article conducted experiments which revealed that polyalkylene glycols ignited spontaneously on a surface heated to 390/400 deg C. Thus, if during a collision, a modern brake fluid should splash on an exhaust system at

400 deg C or over, it will ignite spontaneously. The fireball produced by brake fluid igniting on the manifold or exhaust system will burn with sufficient ferocity to spread to other plastics, such as cable covers, air filters and so on, unless quickly extinguished. Whether a fireball is created or not in a minor collision depends on the integrity of the brake fluid reservoir."

The risk is more likely to be the sudden charge surely rather than the connection spark..It is the CHARGING cycle that generates the hydrogen, so the fully charged donor battery will have little or none, the empty battery none - as the recipient is connected it will suddenly produce hydrogen and oxygen which may explode due to overexpansion (and then off course ignite)..

Excessive charging of a lead-acid battery will cause emission of hydrogen and oxygen from each cell, as some of the water of the electrolyte is broken down by electrolysis. This process is known as "gassing". Wet cells have open vents to release any gas produced, and VRLA batteries rely on valves fitted to each cell. Wet cells may be equipped with catalytic caps to recombine any emitted hydrogen. A VRLA cell will normally recombine any hydrogen and oxygen produced into water inside the cell, but malfunction or overheating may cause gas to build up. If this happens (e.g., by overcharging the cell) the valve is designed to vent the gas and thereby normalise the pressure, resulting in a characteristic acid smell around the battery. Valves can sometimes fail however, if dirt and debris accumulate in the device, so pressure can build up inside the affected cell.

And

Ford Switch Defect ExplainedThe Ford Speed Control Deactivation Switch, also known as a "brake pressure switch," costs about $21. The switch shuts off the cruise control when the driver firmly steps on the brakes. The switch is located under the hood of the vehicle and is attached to the brake master cylinder on one end and wired to the cruise control on the other. This position places it above flammable reservoirs of brake fluid.On most of its models, Ford designed the switch to be powered -- or "hot" -- at all times, even when the vehicle is off and the key is removed from the ignition.Inside the switch, a thin film barrier separates brake fluid from the switch's electrical components.Investigators say fires can break out under certain conditions, such as when the film cracks and brake fluid from the master cylinder seeps into the electrical side of the switch. This can cause a fire, even when the engine had been turned off and, in some cases, idle for days.

"The National Highway Traffic and Safety Administration's (NHTSA) has reported receiving 1,472 complaints connected to the defect, including

65 fires. The number of Ford fires reported to NHTSA is believed to be far less than the number that have occurred. The national law firm of Lieff Cabraser Heimann & Bernstein, the sponsor of this website, has received over 325 complaints of fires in Ford vehicles linked to the speed control deactivation system."

That's a lot of arguement for 'flammable brake fluid'

So not flammable at the temperatures in a brake fluid reservoir.