[DeTomaso] Disconnecting the Battery - + or - first?

Thu Oct 7 06:50:22 EDT 2010

It's not voltage that kills you, it's current.

Steve

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of michael at michaelshortt.com
Sent: Wednesday, October 06, 2010 10:02 PM
To: Mike Thomas
Cc: List Pantera
Subject: Re: [DeTomaso] Disconnecting the Battery - + or - first?

I stand by the boosting/ jumping protocol, I was wrong on the
connect/disconnect method.

Michael

It's Negative First and Negative Last ( think of it as a fight with your
wife )

Here's the scoop.

When disconnecting the battery before commencing work on the car, you should
disconnect the negative, black lead first, here's why:

The battery has approximately a 12v "potential difference" between its
positive and negative lead and, due to the construction of the battery, it
is able to deliver extremely high currents (around 300A to start the car for
example). By contrast an AA torch battery will deliver only a few hundred
milliamps (thousandths of an amp). Your car battery is capable of delivering
around 2.7KW (KILOWATTS!)for a short time so the potential for excitement
and heat are large. Treat your battery with respect! It can't electrocute
you in the acknowledged sense as the volts are too low, but it can and will
produce enormous heat if connected in a way which shorts the two terminals
together.

All circuits need a complete loop of wire from one terminal of the battery
through the circuit itself (eg: the headlights say) and back to the other
battery terminal. So basically two wires are needed for each circuit - a
"flow" wire and a "return" wire.

In order to save on lots of unnecessary wiring, all cars with metal bodies
use the chassis of the car as one of the wires. This is called "grounding"
or "earthing" in car electrical parlance and thus saves 50% of the wiring
(and associated expense) that would otherwise be needed. (Thus fully
fibre-glass cars need lots more wire). It doesn't actually matter which
terminal, either positive or negative, is grounded to the chassis. Both will
work equally as well. However, in order to have standardisation in the motor
industry worldwide in terms of how components and equipment are constructed,
virtually all vehicles today use a negative earth. So don't go swopping
yours over!

Now to the crux..... you will only get a big bang if you connect the two
terminals together. So if you leave the negative lead connected and, whilst
disconnecting the red positive lead, your spanner happens to touch the
chassis while its other end is around the bolt on the positive, you will
have connected the two terminals together through your spanner and it will
become a permanent part of your chassis as 300 amps flow through it and weld
it to the car! You will also probably let go of it very smartly as its
temperature reaches that of the Sun!!

Conversely, if you disconnect the negative lead first, thus also
disconnecting the chassis from having anything to do with the battery, then
your spanner can be round the positive and touch the chassis with no ill
effects. I would suggest that, once you have disconnected the battery
negative, you close the protective cap on it so that nothing metal can
accidentally fall across the two terminals. There is no need to disconnect
the positive terminal of the battery unless of course you are taking the
battery out for some reason. If you do undo both, always remember, UNDO THE
NEGATIVE FIRST AND RECONNECT THE NEGATIVE LAST. When you have undone the
negative lead, tuck it safely out of the way so that it can't suddenly
spring back and touch the negative of the battery again before the work is
finished. And do undo the negative everytime you work on the electrics. A
minute's extra work is better than a fire.

On Wed, Oct 6, 2010 at 10:13 PM, michael at michaelshortt.com <
michaelsavga at gmail.com> wrote:

> When jumping, remember RUBBER
>
> Connect RED
> Connect Black
> Disconnect Black
> Disconnect RED
>
> So, if simply disconnecting, Red First, Black Second
> IF reinstalling, Black First, Red Second
>
> Michael Shortt
>
>   On Wed, Oct 6, 2010 at 9:52 PM, Mike Thomas 
> <mbefthomas at comcast.net>wrote:
>
>> When disconnecting the battery, does it matter which terminal is done 
>> first? Seems there was a string about this a while back, and I'm 
>> updating some procedures, most of which start with this step.
>>
>> Thanks
>> Mike Thomas
>>
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>
> Michael L. Shortt
> Savannah, Georgia
> www.michaelshortt.com
> michael at michaelshortt.com
> 912-232-9390
>
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-- 

Michael L. Shortt
Savannah, Georgia
www.michaelshortt.com
michael at michaelshortt.com
912-232-9390

This email is protected by the Electronic Communications Privacy Act, 18
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