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I have not used jump leads for 15 yrs and am not too sure of how to do it safely, so I would be ever so grateful if you could give me a step-by-step explanation on how to do it with plenty of precisions as I am not mechanically aware ! Thanks
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connect the pos jump lead on top of the pos terminal of the flat battery then the other end of pos on to pos terminal of the jumping supply battery,connect the neg jump lead on to the neg terminal of the jump supply battery then connect the other end on to a clean earth point such as a bolt or a bracket away from the battery and start car,connecting in this way prevents a flat/faulty battery from soaking up the power passing through the jump leads .this would not apply to really old systems with a positive earth wiring.I hope this is clear enough for you.
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Thanks defender, so after starting the 'healthy' battery car, I then immediately start the 'flat' battery one, right ?
Then, how long do I keep the leads and engine on on for ?
(it's a 1.5 L) 10 minutes and I run the car for 10 miles, will that do ?
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Best with modern cars with sophisticted electronics to leave the donor car switched right off, key out, if it's engine is running when the recieving car's engine starts the change from battery drain as the engine is cranked to charge as the alternator kicks in can confuse or even damage the donor car's electronics.
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agree with cheddar that its safest for electrics to leave donor engine stopped on modern cars,pre everything computerised it helps to have it running as it increases the voltage.if the battery needing help is very flat ,ie hardly puts ignition light on connect pos to pos and neg to neg on batteries and run donor car for a few mins,stop the engine then change the neg lead on to an earth point before trying to start the car ,remove leads immediatly after starting car with flat battery
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Aside from the risk of damage, I have never seen the slightest point of having the donor car's engine running. Even at full output its alternator will only be delivering a fraction of the current needed to start the other engine. And if it will start its own engine reliably, why won't it start the other engine?
In a previous thread on this topic someone warned that even with the engine not running, the donor car's electronic system was at risk.
The only safe rule seems to be never volunteer to jump start someone else's car.
I suppose you could disconnect one terminal from your own battery first - assuming you possess all the radio codes etc!
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Agree, I would never offer due to the risk of damage to my car.
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The only safe rule seems to be never volunteer to jump start someone else's car.
I would agree.
Obvious warning - keep both vehicles from touching each other - unlikely - and keep all leads from touching any of the bodywork.
IIRC My user manual says the heated rear window but not the lights of the sick car should be switched on BEFORE disconnecting the leads.
It seems to be a case of RTFM even for what seems a simple job like this. Cooked electronic are not cheap to replace.
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I was taught by my Grandfather that you should keep the donor car running. There are two reasons for this:
1) at the point of connection the flat battery will take a considerable charge current. By keeping the donor running its alternator is able to use its output to charge the flat battery. I was taught to wait at least five minutes before attampting to start the striken car. This would give the donor time to put around 1 to 3Ah back into the flat battery, lifting its voltage off the floor and enabling it to contribute to the starting process. Without this initial charge the flat battery would instead be soaking up valuable current that could be going to the starter.
2) the donor alternator will be contributing to the starting current and voltage if the donor engine is running. Most cars will have at least a 50 amp alternator - and (depending upon the engine and other conditions) the start current is likely to be in the range 200 to 600 amps. The donor alternator will thus be contributing from 10 to 25% (maybe more) of the starting current. In addition it will be working to keep the starting voltage as high as possible which will help to negate the losses which are bound to occur through the jump leads and their connections. When cranking the striken car the revs of the donor should be raised to about 2000 to enable the alternator to give its all.
Basically it's about giving the striken car the best possible chance to start at the first turn of the key. To illustrate the point, the following is true:
My company Focus has recently started to suffer flat battery. It will always start easily when boosted from my spare battery. When I had a similar problem with my Rover Turbo (petrol) about 4 months ago (I'd forgot to connect up my battery master) It would not start from the same spare battery and leads. It did however start first turn of the key when connected to the wifes (running) Metro 1.1S. Oh, the spare battery is a nearly new one from a Discovery TD5 diesel (a big brute).
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With respect the fact that it was your Grandfather that taught you says it all. This procedure was recomended practice until 10-15 years ago a however modern cars electronics can be damaged this way. However connecting a spare battery that is not itself connected to another car cannot do any harm at all and is an ideal way to jump start any car.
Regards.
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if you are concerned about the electrics of the donor car put the jump leads on to the batteries and run the donor car for 10/15 mins boosting the flat battery then take the leads off before starting the car which had the flat battery,this will obviously only work if the flat battery is fit to take a charge but there would be no danger of damage.
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Cyd's grandad method works well enough for me, and I have to jump start modern vehicles several times a week. One thing I always do before disconnecting is to switch on the headlamps of the newly started car. Apparently a heavy load irons out any voltage spikes caused by disconnecting the batteries.
Incidentally, if both cars are of the same earth and have metal bumpers, you can get away with one jump lead just by touching bumpers.
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The Best way to jump start cars filled with electronic gizmos has had to change somewhat.
I used to use grandads method, but now (if you really have to)
Both cars turned off. Not touching
Positive lead on to good battery
Postitive lead on to flat battery.
Negative lead on to good earth on engine block on both cars.
Start good car and run for 10 minutes.
Start duff car and run for 10 minutes.
Turn both cars off.
Disconnect negative from both ends
Disconnect positive form both ends
Start duff car.
Why positive first? There are less chances of a spike on the positive feeds when the negative is connected second. Any spikes on negative tend to get disipated through the engine and body earthing.
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Disagree, while it is a good idea to connect up and start the good car for 10 mins to charge the duff cars battery, with modern cars NEVER leave the key in the good car yet alone have it running when trying to start the duff car.
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Son's MX5 would't start monday morning, Battery gone. I was at work, he borrows jump leads and "donor" car, jump starts his. In what order it was connected I don't know. Next day, fuse blown, Fault traced to burned out electric radio aerial. Was it "live" when jump start was done? Don't know. Coincidence? Again, don't know. Mazda MX5 is pretty "bullet proof". So far nothing else has surfaced. Anyone know where we can get new aerial at a reasonable cost?
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I wonder if honourable son may have inadvertantly touched the aerial with the pos jump lead while connecting to the battery in the Mazda boot? Incidentally NEVER EVER leave the ignition switched on in an MX5 without firing up the engine, the coils burn out (VERY expensive!)
Andrew
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Simplicate and add lightness!!
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its funny how a little spark can sometimes do damage then the next time it does no harm.we were unfortunate to have 11000 volts of mains power cable land on a machine ,it set a tyre on fire shorting to earth ,it touched machine on several parts including the arial which burned the top of but there was no other electrical damage,alternator ,battery etc all fine much to my surprise despite being left running for ages as we had no means of getting back to turn it of because of the sparks untill the mains shorted out.
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I don't think so, battery is one side of the boot, the aerial is the other, he isn't quite that clumsy, or is he? I wasn't there, can't say for certain. What I think happened was a coincidence. The battery was the original, 7 years old, cried enough. The temperature was about -3, heavy frost after damp night. Aerial mast frozen, car is started, son turns on radio, starts playing cd, so no idea if aerial is going up or not. I stripped the aerial down and the motor and surroundings were well burned and melted. Good job fuse went, really.
Thanks for the tip about the coils, I will pass it on to son and heir and remind him at intervals! At least he isn't a fiddler with the car, that must help.
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