How do you do yours?

**Ffoeg** · 05-03-2002 09:17

In the pub over the weekend, an electrician, a mechanic and myself (amateur mechanic/electrician) had a long discussion on the correct way to take a battery off. Black or Red first?.

I've always took the Red off first, cos it makes sense to kill the circuit, but leave the earth for safety.
The electrician also agreed as this is the best way - that's the way he was trained.
However the mechanic says he always takes the black off, so the current cannot get to the battery.

A long (3hour) debate then followed, and it was finally agreed by all that the 'red off first' is the safest and best way.

After sobering up - i looked in the gospel according to Haynes and it says 'black off first' but gives no reason why.

How do you do yours and why?

**stranger** · 05-03-2002 10:25

Here's something else that I do.....if I'm resetting ECU, I don't bother removing both terminals - just the red cause that's broken the circuit, whats the point taking off the other one????

???

**Ste_nova** · 05-03-2002 10:50

on a nova you HAVE to take the brown off first
cause the spanner/rachet touches the body work when taking the red off

**Orbital** · 05-03-2002 11:07

I take ground of first and put it back on last. i never take positive of first cause you could accidently toch any part of the car and spark.

**Animal** · 05-03-2002 11:13

sunny side up.

**Ffoeg** · 05-03-2002 11:37

If you take the red off first, the whole car circiut is dead so there is no chance of accidentially touching anything to make a spark/short circuit - unless you touch the live terminal of the battery (which is usually under a plastic shield on Delco batteries) and the body work at the same time. Plus the whole car is earthed during disconnection.

That's my logic, and the outcome of the pub discussion.

I was just wondering what he benefits are in black off first.

**Vauxweb** · 05-03-2002 11:43

negative first (black) then the live (red) when removing.

then the live (red) first then the negative (black)

The reason for doing this in the above order is that if, when you are removing the battery and you was to undo the live first and you short it to ground it will arch (spark), but if you touch the black to earth sweet fa happens.

**Orbital** · 05-03-2002 11:54

Ffoeg is you take the black of first you have broke the circuit also but to make it spark you have to touch the positive connection on battery yet if you take the positive of first it will spark if you touch anything metal coz it's all grounded.

**Ste_nova** · 05-03-2002 11:56

so this brings us to the question..... why do rally cars disconnect the live???

**trebor** · 05-03-2002 12:01

I would have thought that if any sparks are created you would want them to go to earth as quickly as possible. i.e. by taking the black lead of first.

**SteveW** · 05-03-2002 12:08

I thought the Haynes Book of Lies always said "Disconnect the Battery Positive lead."

Gonna have to check now.

**Joekont** · 05-03-2002 15:17

Originally posted by Orbital
I take ground of first and put it back on last. i never take positive of first cause you could accidently touch any part of the car and spark.

And this is the reason they gave at college too!

**Engine_Swap** · 05-03-2002 15:43

I always do black first - this is the way I was taught by my Dad who was in the AA for 15yrs....

The principle is disconnecting the red first could cause a surge through the wire to the ECU....as well as sparks...

**green manalishi** · 05-03-2002 15:49

haynes does indeed say black off first, on last. when you remove the negative, if you are leaning on the body work and making contact, so what? you're essentially touching both ends of the same piece of wire.

if you are disconnecting the live first (hand on spanner, on nut, on live terminal of battery), and your fly touches the bodywork and makes an electrical contact, and your knob has fell out of your bills and is touching your fly....

...

../ | \
BA*NG!
..../\

see?

this is the sort of crap you learn working for HSE

**Andy K** · 05-03-2002 17:56

Blimly. Remind me not to let you lot loose on my car !
Maybe them vauxhall dealers aren't so bad after all lmao

black first off and last on

It's nothing to do with electric shocks or completly disconnecting the circuit or safety leaving the ground connected.

But as stated, if you try to disconnect the positive first then your spanner can short between the positive and the body work and create sparks.

**green manalishi** · 05-03-2002 18:09

yeah, that's it really, your bodywork is one big electrode. disconnect it 'cos it can cause grief.

**cavgsi** · 05-03-2002 18:19

what about if getting a jump start?? - I would connect black first

**Andy K** · 05-03-2002 18:24

Jump starting you connect black last and disconnect first.

When you are connecting the posotive wire up and accidently touch the body work it can't do any damage if the negative is not connected

**rgb** · 17-04-2002 06:37

Black off first and back on last - That is what i got taught doing my NVQ in Auto- electrical.... So i take it they must now what they are talking about.

A normal electrician donthave a clue about car electrics as they have three wires not two.

**green manalishi** · 17-04-2002 11:57

yeah... dc different to ac.

heard a tale about electrician got a job on a cruiser, had a small prob and fused the whole thing. had to helicopter in a replacement who was a dc expert. thing was stranded in the middle of the pacific with no power. lmao

house electrics are not car electrics.

**AL_P** · 17-04-2002 14:54

take the neg off first for some dumb reason its somethin to do with when you are re connecting its so the car dont get a electrical surge just read bout it

**Damian Hayes** · 18-04-2002 07:01

If you disconected the batery then had to turn the engin Ie to TDC or to do tapet adjustment ect then wont the alternator power up the circit, or is it not turning fast enuf to make electrisity. and if so could you bump start a car with no battery if the alternator is conected, one without an ecu anyway?

Shal I shut up and go back to sleep now?

**green manalishi** · 18-04-2002 17:34

you can certaily bump some cars without a battery, never tried mine.

**cavvysri** · 18-04-2002 17:44

[ labcoat ]
An alternator cannot generate a voltage without having a voltage present already at its terminals (if that makes sense) it needs a voltage to energise its field coils, so it can produce an output. this is how it regulates its output, if it needs a more output it increases the voltage to the field coils, if it wants less output it reduces the voltage to the field coils.
a dynamo can generate an output with no input though(well apart from rotational kinetic energy)
so can a magneto.
[ /labcoat ]

**green manalishi** · 18-04-2002 18:46

that makes sense.

the only cars i can think of you can run without a battery are, like pre '60s - '70s stuff. and some bikes.

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