Jump Starting

[Albannach]

However, the above can be mitigated by leaving the leads connected with both engines running for a few minutes.

And leave them connected for a few minutes before trying to start the lame vehicle.

Apologies for my reply earlier, I assumed folk would do both of the above as a matter of course.

Andy, the scenario you mention would need a disconnected battery(ies) to actually happen, i.e. the alternator charging nothing, is that correct?

[Apache]

is there any mileage in running as much electrical equipment as possible when doing so?

No, not really. The issue comes when suddenly removing a BIG load (hundreds of amps - ie a totally flat battery)

We test by starting the vehicle, adding a 300A load with an external load bank, disconnecting the battery so you still have a 300A load, setting revs at about 3000rpm, then switching out the load bank. Most modern vehicles cope quite well because they have well designed regulators on the alternators.

I suppose a transient COULD happen if your battery terminals aren't tight and you dislodge one slightly when removing the leads, meaning the alternator which WAS supplying a few hundred amps into the flat battery suddenly sees an open circuit for a fraction of a second.

The moral is, make sure your terminals are tight!

Really, done properly, there shouldn't be an issue.

[Apache]

Andy, the scenario you mention would need a disconnected battery(ies) to actually happen, i.e. the alternator charging nothing, is that correct?

Yep, see my last post for how this could happen at the exact worst time!

[darkdezigns]

is there any mileage in running as much electrical equipment as possible when doing so?

Rac and AA training both told me that with porkers in particular,you have to start with as much on as poss

[yoshie]

Nah, you lot all love me...

Very sad to admit, but yes true.

[Apache]

Rac and AA training both told me that with porkers in particular,you have to start with as much on as poss

All that will do is destroy far more in the unlikely event of a regulator failure or load dump transient when jump starting. The loads are tiny compared to that of a flat battery, so yeah, its b0llocks.

[slobodan]

On a different but related topic...

Should I disconnect the batteries before welding? (electric)

[Apache]

yesssss!!!!!

[slobodan]

yesssss!!!!!

The numbskulls never do at the exhaust repair shop. I tell 'em every time.

[POPEYE]

I know when i needed jump starting the other night the donor BMW was not able to power my starter right away even with his engine running and idle speed increased, in the end and after several attemps we just had to leave em connected for five mins till he'd put enough charge in my batterys to allow it to turn and start, neg jump lead was smokeing a bit when i try'd my starter, is that inadiquat(?) jump leads (cheapos) or wot? and are arc welding cables any good as jump leads? nice and thick cables!!

[BUSHWHACKER]

I know when i needed jump starting the other night the donor BMW was not able to power my starter right away even with his engine running and idle speed increased, in the end and after several attemps we just had to leave em connected for five mins till he'd put enough charge in my batterys to allow it to turn and start, neg jump lead was smokeing a bit when i try'd my starter, is that inadiquat(?) jump leads (cheapos) or wot? and are arc welding cables any good as jump leads? nice and thick cables!!

The more heavy duty, the better Ian. Diesels need a lot of amps to get them spinning fast enough to fire up.

[POPEYE]

The more heavy duty, the better Ian. Diesels need a lot of amps to get them spinning fast enough to fire up.

Aye Vince he had a little battery on the bmw, bit much to ask of it to fire up a big diesel i suppose, anyway he got me going for which i was gratefull as it was dark, cold and pi$$ing down, could'nt understand how it'd gone flat after me driveing 8-10 miles there only a few hours earlier untill i saw the volt gauge on the way back, it was reading under 11 volts!! i had the lights, wipers and blower all on, as i did on the way there so it wasn't chargeing enough to peplace wot i was useing, switch em off and it went up to 13v.