Thread: Jump Starting - negative terminal or body earth?

Originally Posted by EastFreo

I have been really surprised by all the posts on this. Maybe I have been blissfully unaware but I have merrily jump started countless batteries with no ill effects and always connected to both terminals of the battery.

Read post #4 by 67hardtop to see why you may have been lucky.

No-one is suggesting that a battery will explode every time you connect to the terminal. However given how serious a battery explosion can be, it is worth reducing the chances of it happening by making the last connection well away from the battery.

Originally Posted by JDNSW

On a similar subject, when connecting or disconnecting a battery, always connect or disconnect the earth side last. This is because if you do this, there is no risk of your spanner shorting when doing up the live terminal because it is not live until the earth is connected, and when doing up the earth terminal it doesn't matter if the spanner hits the carrier or body since it is at earth potential anyway.

John

Learnt that one the hard way, playing with some old bomb after school. Undoing a battery terminal, had my left arm resting on the RSP or something. I touched the spanner against my watch bracelet and just about ring barked my arm. If I hadn't managed to jerk my arm away I would have been seriously burned. I had to break the watch band, as all the links were welded together.
This was my first lesson in car batteries, and also my first in never wearing watches or jewellery when working on or near machines.

Originally Posted by cuppabillytea

Beat me too. I had a car once which was positive earth, but I can't remember which one.

My 1963 MGB did. Morris 100s, LandCrabs, most British cars of the era.
There was a serious school of thought that +ve earth, the yanks say ground, helped prevent rust. Anode v cathode thing apparently. Dunno myself, but I haven't seen a lot of rusty 1100s.
I think the change to -ve came with alternators, but I'm happy to be corrected.

Originally Posted by vnx205

Read post #4 by 67hardtop to see why you may have been lucky.

No-one is suggesting that a battery will explode every time you connect to the terminal. However given how serious a battery explosion can be, it is worth reducing the chances of it happening by making the last connection well away from the battery.

No, batteries explode when they are making gas. Thing is, you never know when that is. But, when charging or recently been charging, when under load or recently etc., when faulty, at high temperatures, the list goes on.

At 2 Base Workshops Vehicle Shop we had a seperate battery room. This was enclosed with Cyclone mesh for ventilation. All battery charging, no exception, happened in there. We used to laugh at the bloke whose job it was to work in there because of the PPE required. That is, until an explosion took out around eight batteries. He is lucky to be alive. If he didn't have the mask on he would undoubtedly be blind. He was saved from serious acid burns by the quick thinking of one of the Sergeants and the close proximity of a shower, put there for that specific purpose. Sulphuric acid was thrown about 30 metres and the battery room partially demolished.
Lead acid batteries have come a long way since then, but the electro/chemical reaction is the same.
Oh, and sulphuric acid is also highly corrosive.... Of course.
But don't worry. They are no more dangerous than the gas bottle you carry around to cook with....... That's why removalists refuse to carry them; same as gas bottles.

Originally Posted by johntins

My 1963 MGB did. Morris 100s, LandCrabs, most British cars of the era.
There was a serious school of thought that +ve earth, the yanks say ground, helped prevent rust. Anode v cathode thing apparently. Dunno myself, but I haven't seen a lot of rusty 1100s.
I think the change to -ve came with alternators, but I'm happy to be corrected.

See my post back on the 6th for why positive earth was used. As to why this changed, it was more generally semiconductors coming into general use than alternators, although alternators are one of aspects of these coming in. Specifically, it was simpler to make radios and other solid state devices with the negative side of the power supply grounded.

John

With regard to Anderson plugs, I have dual batteries and each has an Anderson plug mounted behind the drivers door on the tray (defender ute). I have two jumper leads, one with Anderson plugs on each end and the other just on one end and alligator connectors on the other. Therefore I can jump start myself or anything else without going near the battery box. Works very well.

Cheers
Simon


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Originally Posted by JDNSW

always connect or disconnect the earth side last. This is because if you do this, there is no risk of your spanner shorting when doing up the live terminal because it is not live until the earth is connected, and when doing up the earth terminal it doesn't matter if the spanner hits the carrier or body since it is at earth potential anyway.

John

Yes this..

Originally Posted by drivesafe

Almost there.

Disconnect all battery negative ( - ) terminals first.

Reconnect all battery negative ( - ) terminals LAST.

not necessarily this. I had this argument at ALTC with and instructor who wanted to hear me say that the negative terminal was the earth terminal.

one quick walk down to the FFT trailer open up the battery box put the 12 inch shifter on the clamp nut of the -24v terminal on the batteries and then left it hanging and asked them to just twist it in the direction of undo until it touched the frame.

Originally Posted by Blknight.aus

.......

not necessarily this. I had this argument at ALTC with and instructor who wanted to hear me say that the negative terminal was the earth terminal.

one quick walk down to the FFT trailer open up the battery box put the 12 inch shifter on the clamp nut of the -24v terminal on the batteries and then left it hanging and asked them to just twist it in the direction of undo until it touched the frame.

Don't leave us hanging - did he do it?

John