jump start advice

[edgedemon]

Are there any jump start kits that can also be used to charge the battery once home again?
Missus drove her car and left it elsewhere last night and has phoned to say the battery is flat so I was looking at JS kits, but ideally would like one that would charge it as well once she gets back home

 

[Dogbreath]

Why is the battery flat, did she leave the lights on or has the battery simply expired in the cold weather? Obviously a charger/jump starter isn't going to be much use in the latter case.

I presume you are talking about jump starters that are powered from the mains rather than a portable battery pack, in which case most of them provide a lower current battery charger as well as the high current jump start. However, they are large and expensive and something that's difficult to justify unless you use it somewhat regularly.

e.g. This will be able to jump start you car immediately. The lower powered/smaller ones like this are simply fast chargers and not proper jump starters. You'd have to leave this connected to a battery for several minutes before you got enough charge to turn the engine over.

If you mean the portable battery packs, then I don't know of any that will charge an external battery, but since a small car battery charger can be had very cheaply (e.g. Lidl/Aldi sell a pretty good smart charger) this isn't really much of a problem.

 

[GeX]

but ideally would like one that would charge it as well once she gets back home

The alternator will charge the battery when she's driving it home. How much distance are we talking? If it's not much, then take the car for a drive for a bit afterwards (but don't turn it off until you've done that). If the battery is still going flat, then don't waste money on a 'jump start kit' - find and fix the problem. The battery could be knackered (they don't like being fully discharged) or there could be an electrical fault that's causing a power drain.

 

[edgedemon]

She is a bit cagey over why the battery is flat. Im going to go down there tonight, and either jump start her or take the battery out and charge it overnight, just thought there might be a quick fix.

Cheers

 

[bledd]

Just get a good set of jump leads

http://www.machinemart.co.uk/shop/p...rofessional-jump-leads?da=1&TC=SRC-jump+leads

Drive it round to charge the battery back up, if it goes again, either the battery is knackered or you've got a drain somewhere (or lights were left on etc)

-Shows you how to test for a drain..

When jumping..

Engine's off when connecting!
Connect red/positive on good car battery to red/positive on dead car battery
Connect black/negative on good car battery to black/negative on dead car engine on an unpainted surface

Start good car, wait a few minutes, try starting second car.

Going battery to battery with both cables can damage them.

 

[GeX]

Connect red/positive on good car battery to red/positive on dead car battery
Connect black/negative on good car battery to black/negative on dead car engine on an unpainted surface

Going battery to battery with both cables can damage them.

Just add; engine off when connecting.

I always thought the point of completing the circuit away from the battery was just down to the fact that it will spark when do it, and the battery can release hydrogen.

 

[teenwolf]

drive it around for a bit then take it to a mechanic to test the battery.

 

[miniyazz]

Just add; engine off when connecting.

I always thought the point of completing the circuit away from the battery was just down to the fact that it will spark when do it, and the battery can release hydrogen.

What's the problem in connecting the batteries with the engine running?

 

[GeX]

With the engine running, the voltage in the system is ~13.5v. With it off it's 12v. Modern cars have many ECUs are as electronic devices they are susceptible to damage from voltage spikes. By having a voltage on the 'good' car that is closer to that of the 'dead' car - you run a lower risk of inducing a dangerous spike.

 

[Armageus]

What's the problem in connecting the batteries with the engine running?

Agreed - never had any problems before and have jumped several cars over the years.

Connect black/negative on good car battery to black/negative on dead car engine on an unpainted surface

The battery Earth strap tends to be a good point for connecting the negative lead (Seem to think it was even recommended in the owners manual for one of my cars.)


Edit:

With the engine running, the voltage in the system is ~13.5v. With it off it's 12v. Modern cars have many ECUs are as electronic devices they are susceptible to damage from voltage spikes. By having a voltage on the 'good' car that is closer to that of the 'dead' car - you run a lower risk of inducing a dangerous spike.

12v spike is going to be just as bad as 13.5v spike... I believe the ECU damage was one of those throwbacks to the early days of ECUs, much like the scaremongering with Catalytic converters etc.


Alternators output is not a fixed 13.5v either... it depends on engine rpm/load and draw by things such as headlights. Obviously when you crank the starter the voltage to everything else also spikes as evidenced by headlights flickering if you have them on when starting the car - the ECU(s) have to cope with this as well.

 

[GeX]

By 'scaremongering' with catalytic converters do you mean about bump starting causing damage to them? That's not a myth, it throws fuel into the exhaust which IS bad for them.

I know the output isn't fixed at 13.5v, it's why I put the little tilde there. I meant 'around 13.5v, obviously it'll vary on load - and it'll dip a lot when you connect that to a 'dead' car.

I've heard of modern cars being damaged by voltage spikes, it's certainly not a throwback to early ECUs - older ECUs were considerably more stupid, with basic (but tougher) parts. I'm sure there was a thread on here recently about a car being jumped with the key in the ignition and it wipes out the key/ECU immobiliser sync, requiring a trip to the dealer to get it sorted.

My view is that if you are connecting two electrical systems together, they should be switched off when you make the connection.

I don't see the point in not connecting straight to the -ve terminal though, I can't think of any 'electrical' reason for it - just what I said earlier about sparks and hydrogen.

 

[Gilly]

Our lass's Dad had a caravan battery charger. Worked well for us after the cold got to her car.