Which Battery Terminal (+ or -) Do I Unhook To Disconnect Car Battery?

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[ARCHIVED THREAD] - Which Battery Terminal (+ or -) Do I Unhook To Disconnect Car Battery?

Posted: 2/18/2006 6:35:17 AM EDT

It's a BMW. I just need to disconnect my battery while I do some work.

Posted: 2/18/2006 6:36:31 AM EDT

[#1]

-

Posted: 2/18/2006 6:37:56 AM EDT

[#2]

always cut the green wire

Posted: 2/18/2006 6:39:52 AM EDT

[#3]

Yep. Disconnect the negative terminal.

Posted: 2/18/2006 6:40:32 AM EDT

[#4]

take this the way you wish,
but if you do not know how to disc. a batt.
Perhaps you should take the ride to a mechanic

FTR-- the Ground ( thats the one with th "-" on it )

Posted: 2/18/2006 6:40:32 AM EDT

[#5]

In true arfcom way

I say : +ive

It's DC so it doesn't matter too much.
FYI, Depending on the age of your car you might see an extra cable on -ive, Thats attached to the body of the car. (for grounding)

Posted: 2/18/2006 6:41:40 AM EDT

[#6]

- terminal unless you want things to arc and ignite any stray H2 your battery is producing

Posted: 2/18/2006 6:42:07 AM EDT

[#7]

With an older car I would think it wouldn't matter too much, but it's a free call to a BMW dealer if you want to know for sure. Sometimes with more modern or fancy cars you risk messing up the computer if you don't do it correctly.

Does your owner's manual give you any clues? I imagine it has the standard "see your dealer" notation regarding anything more complex than checking the oil...

Posted: 2/18/2006 6:43:09 AM EDT

[#8]

Always remove the ground (-) first. If you tried to loosen the hot cable first, and the wrench slipped, you could conceivably short it out to ground. The battery could explode.

Think about it: if you are working in the negative terminal, and the wrench slips and touches metal, it's already a ground, so nothing will happen.

Posted: 2/18/2006 6:45:02 AM EDT

[#9]

C'mon, it's ARFCOM. Do both.

Posted: 2/18/2006 6:46:05 AM EDT

[#10]

Thanks! I just have some kind of mental block with understanding electricity. I have rebuilt numerous engines, but I never can remember anything about how electricity works.

Posted: 2/18/2006 7:11:30 AM EDT

[#11]

tannerite......somebody had to say it!

Posted: 2/18/2006 7:19:56 AM EDT

[#12]

Post pics!

TTIWWOP!

Posted: 2/18/2006 7:25:15 AM EDT

[#13]

Current flows from negative to positive. Always unhook negative first. When reconnecting, always connect positive first.

Posted: 2/18/2006 8:13:28 AM EDT

[#14]

Quoted:
Always remove the ground (-) first. If you tried to loosen the hot cable first, and the wrench slipped, you could conceivably short it out to ground. The battery could explode.

Think about it: if you are working in the negative terminal, and the wrench slips and touches metal, it's already a ground, so nothing will happen.

+1 What he said. Electrically it doesn't matter, but from a safety standpoint the ground is the best. Mine for some reason has an aftermarket quick-disconnect on the positive side, so I usually just pop that. The battery would have to be outgassing an incredible amount for there to be any ignition danger, with as fast as hydrogen dissipates.

It's not like there aren't ANY sparks when you disconnect the negative terminal, urban legends aside.

Posted: 2/18/2006 8:15:18 AM EDT

[#15]

Make another thread when its time for you to put gas in your car.

We are here to help.

Posted: 2/18/2006 8:19:38 AM EDT

[#16]

Exlosions do happen. When i was 16 or 17 I was up at the mall. Jumped in my moms car and turned the key. Blew the top off the battery and bent the corner of the hood up about an inch.

TRY EXPLAINING WHAT HAPPEN TO YOUR DAD!

Negative first

Posted: 2/18/2006 8:20:50 AM EDT

[#17]

Negative cable first.

Does your car require a radio security code to activate it after you disconnect the battery? If you don't have it your radio will not work.

Posted: 2/18/2006 8:22:51 AM EDT

[#18]

Negative side, Clyde.

Posted: 2/18/2006 8:38:13 AM EDT

[#19]

For safety reasons, always disconnect the negative cable first. That way if your wrench accidentally comes into contact with ground when disconnecting it, it won't ARC.

Posted: 2/18/2006 8:39:07 AM EDT

[#20]

Quoted:
It's a BMW. I just need to disconnect my battery while I do some work.

You remove the negative.

Posted: 2/18/2006 8:41:30 AM EDT

[#21]

Quoted:
Thanks! I just have some kind of mental block with understanding electricity. I have rebuilt numerous engines, but I never can remember anything about how electricity works.

The most difficult part is getting the magic smoke back in the wires

Posted: 2/18/2006 8:42:08 AM EDT

[#22]

Quoted:
Negative cable first.

Does your car require a radio security code to activate it after you disconnect the battery? If you don't have it your radio will not work.

Posted: 2/18/2006 8:56:38 AM EDT

[#23]

Quoted:
It's not like there aren't ANY sparks when you disconnect the negative terminal, urban legends aside.

I don't think the explosion danger is related to sparks; I believe it has to do with the heat that builds up if the positive battery terminal is grounded. It would be the same thing as connecting a cable directly between both battery posts.

You don't want to work on ANY hot (positive) cable or wire without first disconnecting the ground cable. The risk of damage from an accidental short to ground is too great.

Posted: 2/18/2006 9:00:20 AM EDT

[#24]

Quoted:
Quoted:
It's not like there aren't ANY sparks when you disconnect the negative terminal, urban legends aside.

I don't think the explosion danger is related to sparks; I believe it has to do with the heat that builds up if the positive battery terminal is grounded. It would be the same thing as connecting a cable directly between both battery posts.

You don't want to work on ANY hot (positive) cable or wire without first disconnecting the ground cable. The risk of damage from an accidental short to ground is too great.

If I accidentally lay a wrench across the battery, then I am arguably safer since nothing else is connected to the ground if I disco the negative. However, my quick-disco has a rubber cover, and having laid a big wrench across BOTH terminals once (so that no matter which wire i disconnected I still would have had problems) I am always careful when around batteries with exposed terminals.

I just wanted to point out that (1) electrically there is no difference and (2) the urban legend of "the positive sparks but the negative doesn't" is BS.

Posted: 2/18/2006 9:25:09 AM EDT

[#25]

Quoted:
Quoted:
It's not like there aren't ANY sparks when you disconnect the negative terminal, urban legends aside.

I don't think the explosion danger is related to sparks; I believe it has to do with the heat that builds up if the positive battery terminal is grounded. It would be the same thing as connecting a cable directly between both battery posts.

You don't want to work on ANY hot (positive) cable or wire without first disconnecting the ground cable. The risk of damage from an accidental short to ground is too great.

The explosion danger IS (or at least can be) related to sparks. Especially if the battery is overcharging. Hydrogen gas builds up and leaks out the vent caps. I saw a battery explode once because some smarty towtruck driver pulled off the vent caps and went to check the electrolyte level with a lighter for light.

Posted: 2/18/2006 9:30:09 AM EDT

[#26]

Quoted:
The explosion danger IS (or at least can be) related to sparks. Especially if the battery is overcharging. Hydrogen gas builds up and leaks out the vent caps. I saw a battery explode once because some smarty towtruck driver pulled off the vent caps and went to check the electrolyte level with a lighter for light.

What a dumbass!

Posted: 2/18/2006 10:49:22 AM EDT

[#27]

Quoted:
Quoted:
The explosion danger IS (or at least can be) related to sparks. Especially if the battery is overcharging. Hydrogen gas builds up and leaks out the vent caps. I saw a battery explode once because some smarty towtruck driver pulled off the vent caps and went to check the electrolyte level with a lighter for light.

What a dumbass!

Yeah. No kidding. He was seriously messed up. I felt bad for the guy, but what a dumbass.

Posted: 2/18/2006 10:54:17 AM EDT

[#28]

Quoted:
For safety reasons, always disconnect the negative cable first. That way if your wrench accidentally comes into contact with ground when disconnecting it, it won't ARC.

BINGO - there's the correct reason.

Posted: 2/18/2006 12:37:59 PM EDT

[#29]

Quoted:
Quoted:
For safety reasons, always disconnect the negative cable first. That way if your wrench accidentally comes into contact with ground when disconnecting it, it won't ARC.

BINGO - there's the correct reason.

It can't be - I don't use a wrench - only pliers!!

Only on Arfcom can such a thread hit 2 pages.

Posted: 2/18/2006 12:58:59 PM EDT

[#30]

Quoted:
Current flows from negative to positive. Always unhook negative first. When reconnecting, always connect positive first.

Incorrect.

Electrons flow from negative to positive. Current (also known as holes) flows from positive to negative.

Posted: 2/18/2006 5:13:41 PM EDT

[#31]

Quoted:
Quoted:
Negative cable first.

Does your car require a radio security code to activate it after you disconnect the battery? If you don't have it your radio will not work.

Since I did not steal my BMW, I happen to be in possession of the radio code.

[ARCHIVED THREAD] - Which Battery Terminal (+ or -) Do I Unhook To Disconnect Car Battery?

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