Jump Starting

[Martin75]

Does anyone know if there's a sequence to follow prior to attempting a jump start from a 400 watt jump start booster. I had a new 230 SLK Merc ten years ago which was left for about six months in my garage whilst I was in the States. Upon return the new battery was dead (alarm drain) and I attempted a start with my power pack. Result; defunct electric brain (Ouch £1500) - fortunately replaced on warranty! There was a sequence you followed which was;

1) With Booster off - Ignition and all accs (heater etc off)
2) Connect Positive on Booster to Car Battery
3) Connect Negative on Booster to Car Battery
4) Switch on Booster, WAIT a few minutes
5) Start the Car
VERY IMPORTANT;
6) Disconnect Negative from the Booster First
7) Disconnect Positive Booster Secondly

However it was one of those 'secrets' you only learnt about later, from the mechanic who was plainly nervous about divulging it to me!

I have a booster and my batteries good, but one day it's going to happen, and thought maybe someone had knowledge of this circumstance?

[windrush]

All ways disconect the EARTH lead first and connect up last this way with no earth there wont be a short circet

[lightpainter]

RAC patrol man advised me to switch my full headlights on after he had given me a jump start and before he disconnected his power pack, said something about frying the onboard computer.

[welly]

The handbook states ' DO NOT connect a booster cable to the negative (-) terminal of the discharged battery'

Instead it states that the negative booster cable goes to an earth (an engine mount or bare surface) at least 0.5 metres away from the battery.

[Keith]

Worrying things boosters especially if they don't have a clean DC output.
Do you have the ability to connect it first and then switch on and does it have a soft start circuit?

If not I would not risk it

[raykay]

The main concern with jump starting a car with a flat battery is voltage 'spikes' damaging the electronics, waiting for a few minutes with the two batteries connected before trying to start will allow some power to flow to the flat battery, and having the headlights on will both help reduce the 'spike' and therefor the damage to the electronics.

The main reason for not connecting to the negative battery terminal is the possibility of a spark igniting any gas emitted by the battery, the negative is the last connection and there will often be a spark.

[Martin75]

Worrying things boosters especially if they don't have a clean DC output.
Do you have the ability to connect it first and then switch on and does it have a soft start circuit?

If not I would not risk it


Keith,

It does have the ability to switch on after connections are made. I'm not sure what a 'soft start' circuit is?

I feel it's probably best to heed all the offerings so far (and thanks everybody) - and only use in an extreme emergency, if it does happen I think I'd prefer to remove the battery and recharge off the car. The comment from 'Raykay' - on spikes was the problem with the merc I remember.