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Date:         Tue, 21 Sep 2004 20:46:28 -0500
Reply-To:     Bruce Nadig <motorbruce@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Bruce Nadig <motorbruce@HOTMAIL.COM>
Subject:      Re: Q: Battery Disconnect Sequence?
Comments: To: felder@KNOLOGY.NET
Content-Type: text/plain; format=flowed

The answer below is close to the truth, but not right on.

True, the body of the vehicle is negative. Chances are that any tool (such as a socket or box-end wrench) you would use to loosen the battery terminal would be metal. If that metal tool was being used to disconnect the positive terminal first and it hit the body while doing so, things would get real exciting real quick. I have heard stories of mechanics even having their rings (ie. wedding rings) getting "welded" between a positive and negative connection.

If you take your metal tool and disconnect the negative side first, you won't have a problem if your wrench touches the body because the body is just an extension of the negative side of the electrical system. If your negative is still connected and you are attempting to disconnect the positive terminal and that same tool contacts the negatively charged body, at a minimum, you will get a large spark. Being so close to the battery, that spark could very well ignite any hydrogen gas that has been discharged from the battery (that is why you don't connect your negative cable on your jumper cables to the battery).

What is stated below isn't quite true. Once the positive cable is disconnected from the battery terminal it no longer has a charge in it, so it doesn't make any difference if it hits the negatively charged body (which is no longer negatively charged, by the way, because there is no longer a complete electrical circuit). You could, in fact, safely put that positive terminal to the negative terminal to the battery and nothing would happen so long as there is nothing connected to the positive terminal of the battery.

Make sense?

Be Safe.

Another electrical tip: When giving someone a jump start, make sure that the vehicles that are involved in the jumping process are not touching in any way.

Cheers, Bruce motorbruce motorbruce@hotmail.com

>From: Jim Felder <felder@KNOLOGY.NET> >Reply-To: Jim Felder <felder@KNOLOGY.NET> >To: vanagon@GERRY.VANAGON.COM >Subject: Re: Q: Battery Disconnect Sequence? >Date: Tue, 21 Sep 2004 19:56:31 -0500 > >It's not the sequence. > >On any car but old english ones, the negative is the ground, and it's >strapped to the car frame somewhere. So you could say that everything >on the car is "negative" that is connected to the frame by even a >fastener. If you take the positive cable loose, it stands every chance >of hitting one of these negative frame or body members (engine too, >everything) and you'll get a big hot spark in the best-case scenario. > >Letting the negative cable hit anything but the positive terminal, and >nothing will happen. > >Jim > >On Sep 21, 2004, at 8:46 PM, Jack wrote: > >>Ok, I need help. >> >>In several manuals, including a Ford Owner's manual (forgive me) and a >>Haynes repair manual, I've noticed that they specify that the negative >>battery cable must be removed first when disconnecting the battery. >>Why??? >> >>What possible difference can it make which terminal is disconnected >>first??? >> When I first ran across this, I ignored it as a harmless error by >>someone >>who didn't understand electrics, but now I find it in "professional" >>references. >> >>Help! What am I missing? >> >>//Jack >>


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