A quick jump perhaps

[Richard_C]

Not moved the Synergie (1.9 TD) since Christmas, battery seems to have expired. Not enough volts to work the central locking when I came to it. Its on charge now but I suspect beyond redemption.

I need to move it tomorrow, so that means a jump start from my C5 (X7 Hdi 163). In any case I'd really like to see if it will start and its nothing more serious before I go and buy a new battery.

Its ages - like years and years, maybe yellow Dyane from blue Dyane - since I jump started anything, and certainly not since cars had fancy electronics to worry about. Common sense suggests get C5 running, connect jump leads carefully, pre heat and start Synergie, disconnect jump leads.

If I can't start and move the Synergie tomorrow its a bit of a bother, if I damage the C5 its much much worse. Any advice ? (including don't do it if that is the consensus view).

[BenC5HDi]

Connect the leads with both cars turned OFF. Positive first, then leave 5 mins or so to allow everything to stabilise.

Start the C5, let it run for a few minutes, THEN start the Synergie. Let them both run at a fast idle for 10 mins or so, then switch both off, disconnect leads. If the battery isn't dead, the Synergie should have just enough juice to start it in.

[rory_perrett]

Attach the negative lead to an earthing point, such as a bolt or bracket, away from the battery on the Synergie not to the negative terminal of the battery.

[wurlycorner]

If you connect the batteries without the engine running and leave them to stabilize for 5 mins, all you'll end up with is 2 batteries drained down to less than 12v (one will drag the other down) and probably 2 cars that won't start!
Connect them up with the engine in the c5 running, is the only way to avoid that.

I've jumped plenty of cars off my c5 in the last year like that, with absolutely no issues.

[BenC5HDi]

Well, you'd better tell the AA then as that advice is taken straight from their website about jump starting with modern cars...

[wurlycorner]

Really? I'm surprised!
I guess it must work if that's what they're saying, but... It goes against common sense.
I can understand the leaving it connected for a while before starting the second car (I normally do that, unless it's cold/wet/raining/somewhere inconvenient ) but not the bit about connecting it up and leaving the first car not running for 5 minutes while connected.

[BenC5HDi]

I'd imagine it's to stop any voltage spikes damaging ECUs rather than anything else. I've just reread it with glasses on and it says 3 mins not 5.

I've never done it like that either. I connect the red lead, then the black one, start the good car, start the dead car. Leave a minute or so, take leads off while running.

[Richard_C]

Thanks all, a useful discussion. Here's what happened.

I thought about the 'connect while off' method and agree that it could end up with both batteries flat, but I guess the internal resistance of the battery will slow that process. I can see the value of it, it stops the ECU etc of the receiving car getting a sudden spike of up to 14.1 volts off the one that running, and if you are tentative about connecting the jump leads you might get 2 or 2 spikes in quick succession. I suppose if the 'voltage donor' car is well warmed up before you try you aren't cold starting it and it will be OK.

Meanwhile late Saturday I remembered that I hadn't taken the old C5 battery to the recycle tip yet, I changed it last Autumn as cranking got awful slow and econ mode was permanently on, it was worth £70 or so not to have it fail one day when it mattered. I put it on charge with my old charger (price sticker says one pound four and thruppence so no electronics there) and left the proper charger on the Synergie.

After 32 hours charging with a modren charger, the Synergie registered 11.47 volts - so end of that battery - but I still wanted to start it because last time I tried there was all kinds of flashing lights and clattering relay noises suggesting something serious was amiss. Plan A - connect my spare slightly duff battery, see what happens then move on to jump start from C5 using the engine off at connect method.

So, connected the battery using jump leads, all the lights and relays behaved well and it turned over very sluggishly. Reassured me that the problem was just the battery. Then it all went to sleep again. Sort of rrrrrr-rrrrr-rrr-dunk.

Now, anyone who read from the start and is still with me, you recall that the last time I jump started a car was Dyane to Dyane. Those 30+ year old cheap jump leads weren't built for the cranking current of a 1.9 diesel, obvious now with perfect hindsight. The oily hand marks on the plastic sheath were smoking merrily and the PVC sheath all soft and gloopy at the crocodile clip end. Stage 2 - the C5 jump - was abandoned.

New battery and new jump leads (in case in case ever again) being collected this afternoon.

Meanwhile the good news. It was 13 degrees and mostly sunny. All the timber cutting I wanted to do in the space with dead Synergie in it could be done out of doors

[wurlycorner]

Ah yes.
Jump starting my CX DTR T2 (which has a knackered battery) requires that 2 sets of very heavy duty jump leads... Nothing else can cut it without getting red hot

[Mdon]

I'm with wurlycorner, I've jumped lots of cars recently (normally work cars that sit for weeks) and I always have the running car ticking over as I connect the jump leads. Most of our work cars don't have any visible none painted earth points so the leads just go battery terminal to battery terminal. Then after 3 or 4 minutes we crank the dead car, fire it up, let it run for 5 minutes then disconnect the leads. Job done.

[old-un77]

Yeah good leads are a must, I made mine up, 40 years ago using 12 feet lengths of welding cable, and the heaviest clamps I could find. I was in the fork lift hire game at the time, and cranking a Hyster or a Coventry climax on a frosty morning was a task in itself........

Bob

[Zelandeth]

Best bit of advice is get decent leads. I picked up the beefiest ones Halfords had at the end of last year when the Xantia had a flat battery, they're about the same weight and thickness as the ones I used to use to jump buses and I'm well impressed by them. I did a test when I got them to see how good they really were - battery for the Xantia (1.9TD) on the ground out the car, connected via the jump leads, and it started as though the battery was in the car as normal.

I wouldn't worry about voltage spikes. A flat battery presents a pretty low impedance load and should smooth out anything like that before it gets into the electrical system, plus the voltage regulator on modern alternators is actually good at giving a nice smooth output. Plus remember that the electrical system in any car has to be designed to handle quite significant nonsense from in the car itself - you see quite a big spike when you switch off a big relay coil for instance. I got quite a nasty belt from a starter solenoid just a couple of weeks ago which proved that to me! In fact, given how much more stuff there is being switched on and off all the time, the supply on modern cars with all the electronics is probably more full of voltage spikes and other mess than an old car without all that..at least that's my theory.

My proceedure has always been this, whether it be a Mini, a Xantia, a Routemaster or a Rolls-Royce (even though that's fiddly because the battery is in the boot).

1. Start vehicle you're jumping from and let it idle for a few minutes.
2. Connect positive on the booster battery to the positive of the flat one.
3. Connect negative on booster battery to a solid ground *not the battery terminal* and be prepared for sparks if the battery is really flat.
4. Raise the engine speed of the vehicle providing power to a fast idle for five minutes or so to get a bit of juice into the flat battery (especially if you don't have the best leads).
5. Start the other car, and allow it to idle for a few minutes.
6. Disconnect leads, negative on the jumped car, negative on the boost car, then positive in whichever order you like as there's no circuit any more. Do not be tempted to disconnect both at one end then go to the other - that's how you accidentally end up shorting things out.

[bobins]

Just bear in mind with all this jump starting that alternators aren't really there to raise a battery from the dead. Regularly expecting an alternator to charge a dead battery will prematurely wear the alternator. Don't believe me ? See what the alternator manufacturers have to say about it !