Why boosting a battery - to - is bad?

congo_90

Just a quick question...

over my time on the road i've been jump started and jumped cars in the past using the jump leads I carry in the boot. tonight I had to jump start a van (my das) as it mysteriously gave up suddenly. Anyways. Sometimes i would follow procedure of + to + and - on good car to earthed point on dead car.

Yet sometimes i just hook + to + and - to - yet in all cases the dead vehicle does restart. I have jump started vehicles from 80 reg to 07 yet all have survived. While i realise there is a spark issue if not connected correctly, There has never been an issue. (despite his headlights failing now but highs and side lights working).

So I ask why must we connect - on a dead car not to the battery?


On a side note his van just 'died' as I was there. It started several mins previous no probs. Are we just victims of winter and a fiat or should I look deeper?
He started while in gear and it just completly fubar'd the system. as he stopped the starter naturally.

On a side note my golf acted similar last week and after a jump start and whack with a hammer to the starter she started and is still going strong. I'll probably replace the battery soon for peace of mind.

bmw535d

is anyone else really confused?

congo_90

Sorry I know my original post is all over the place.

Why is it in almost every car manual etc it says when jump starting that + to + is ok but not - to -

The procedure above works yet they suggest + to + and - on good car to earthed point (not the battery).

Divorce Referendum

congo_90 wrote: »

Sorry I know my original post is all over the place.

Why is it in almost every car manual etc it says when jump starting that + to + is ok but not - to -

The procedure above works yet they suggest + to + and - on good car to earthed point (not the battery).

I think that they suggest to earth the - lead because if there is a spark as u said earlier then it could ignite battery gases.

Something similar to this battery:

http://www.youtube.com/watch?v=jwWwCZF6FW0

Bumpstop

This type of battery explosion occurs during the use of battery charger, or jump leads connected for a prolonged time. Hydrogen is generated during the charging, but it takes a while for enough to build up to cause a battery explosion. always unplug the charger before removing the leads, or the jump leads from the healthy car.

I am not a fan of using the car body as a point of connection, heavy currents are drawn during cranking, and these currents will cause arcs or fire at any poor connections in the body work or engine mounting bolts, these arcs can damage sensitve electronics like ecus etc..

I always use the battery posts as these connections are designed to carry the huge cranking currents.

It is usually good practice to connect the positive clamps first. As both car bodys are connected to the negative battery terminal. If you accidently brush the positive clamp off a car body or something sensitive without the negative connected there is no circuit and no short circuit.(for negative earth vehicles)

It is a good idea to run headlights or the heater blower on the good car while connecting clamps, This current draw helps to damp any voltage spikes or electrical noise as you connect the clamps, and try to crank the faulty car.

Remember the huge power to start your car is stored in that innocent looking little battery, treat it with respect, there is massive short circuit current available, and your jump leads don't have fuses. there is plenty of power available to burn you if your not carefull.

congo_90

Bumpstop wrote: »

This type of battery explosion occurs during the use of battery charger, or jump leads connected for a prolonged time. Hydrogen is generated during the charging, but it takes a while for enough to build up to cause a battery explosion. always unplug the charger before removing the leads, or the jump leads from the healthy car.

I am not a fan of using the car body as a point of connection, heavy currents are drawn during cranking, and these currents will cause arcs or fire at any poor connections in the body work or engine mounting bolts, these arcs can damage sensitve electronics like ecus etc..

I always use the battery posts as these connections are designed to carry the huge cranking currents.

It is usually good practice to connect the positive clamps first. As both car bodys are connected to the negative battery terminal. If you accidently brush the positive clamp off a car body or something sensitive without the negative connected there is no circuit and no short circuit.(for negative earth vehicles)

It is a good idea to run headlights or the heater blower on the good car while connecting clamps, This current draw helps to damp any voltage spikes or electrical noise as you connect the clamps, and try to crank the faulty car.

Remember the huge power to start your car is stored in that innocent looking little battery, treat it with respect, there is massive short circuit current available, and your jump leads don't have fuses. there is plenty of power available to burn you if your not carefull.

Good advice on the explosion. I know not to connect postive last due to sparking and even on an open bonnet on the side of the the road to be cautious. As for running elec items in good car.. I tend to avoid so the surge isn't so bad on the alt and have a person keep the good car hold the revs up to around 2k rpm to make sure the alt is providing sufficient voltage to charge and take up the surge caused from cranking dead vehicle.

cml387

Excellent post Bumpstop,especially about the + to + connecting first.

snowman707

Bumpstop wrote: »

This type of battery explosion occurs during the use of battery charger, or jump leads connected for a prolonged time. Hydrogen is generated during the charging, but it takes a while for enough to build up to cause a battery explosion. always unplug the charger before removing the leads, or the jump leads from the healthy car.

l.

not wishing to hijack the thread but i recently experienced a battery to blow up for no apparent reason

http://www.boards.ie/vbulletin/showthread.php?t=2056083655

I had the alternator checked and it is working as it should ,

I am 40 years "on the road" and between agri, commercial and private we have usually 12 to 15 working vehicles, This was the first time and hopefully the last I have seen a battery to blow

Pkiernan

The reason for the procedures is that an old worn out battery may be more prone to leaking hydrogen gas.

To help minimise explosion of the battery, you should connect the last lead as far as possible from the battery e.g to a ground point on the opposite side of the engine bay. There is always a degree of sparking, whether visible or not when connecting.

The easiest way is to use a jump charger pack with an on/off switch. No chance of sparking if it is tuned on after leads have been properly connected.

Del2005

congo_90 wrote: »

On a side note his van just 'died' as I was there. It started several mins previous no probs. Are we just victims of winter and a fiat or should I look deeper?
He started while in gear and it just completly fubar'd the system. as he stopped the starter naturally.

Diesels draw a huge current to start and so when you start a diesel you should let it run for at least 10 min to recover, petrols don't draw as much current to start so don't need as much time to recovery. Then you are driving with heater, wipers, lights on so more juice is being drained from the battery. If the battery is failing, in this cold weather, starting then stopping will kill it.

Put the battery on charge over night and get to your nearest motor factors for a new battery as that one is going to go, especially if you keep starting the van every few minutes:D

BrianD3

Wear eye goggles when connecting/disconnecting batteries. I have never seen anyone do this but it is good practice as if a battery explodes electrolyte (acid) will spray everywhere.

congo_90

Del2005 wrote: »

Diesels draw a huge current to start and so when you start a diesel you should let it run for at least 10 min to recover, petrols don't draw as much current to start so don't need as much time to recovery. Then you are driving with heater, wipers, lights on so more juice is being drained from the battery. If the battery is failing, in this cold weather, starting then stopping will kill it.

Put the battery on charge over night and get to your nearest motor factors for a new battery as that one is going to go, especially if you keep starting the van every few minutes:D

We jump started off my car no problem and left the battery to charge overnight but to no avail so off the motor factors to replace with new battery. Guess the battery was just too far gone.