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Old 01-24-2012, 05:55 PM   #51
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Originally Posted by herk7769 View Post
While the spark business above may be true, the "making and breaking" is limited to the interior of the switch. That "spark" at the contacts will occur regardless of where the switch is located.
I realize the spark would be contained. I was just saying that's probably where negative disconnect theory started.
To be sure disconnect both. All bases covered
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Old 01-24-2012, 08:26 PM   #52
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Originally Posted by jim44646 View Post
I believe it goes back to disconnecting and connecting battery cables on a car. If you take the positive off first or connect positive last you can get a spark which can ignite the gasses from battery. By doing it opposite you get no spark. Holds true with jumper cables. Positive first then Neg. but not to battery but to another ground
the reason you disconnect the neg post first on a car is so if your wrench hits the frame on the pos side it won't spark
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Old 01-26-2012, 08:40 AM   #53
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Originally Posted by jim44646 View Post
I believe it goes back to disconnecting and connecting battery cables on a car. If you take the positive off first or connect positive last you can get a spark which can ignite the gasses from battery. By doing it opposite you get no spark. Holds true with jumper cables. Positive first then Neg. but not to battery but to another ground
When you complete or break a circuit, you can get a spark.
Doesn't matter whether you open/close the positive or
negative wire - same circuit, same result.

The REAL reason for connecting/disconnecting the negative
first/last does, indeed, have to do with igniting the hydrogen
gas generated by the battery. The positive is connected to
to battery terminal - CLOSE TO THE GAS - but the the negative
is connected to the frame/chassis - FAR FROM THE GAS.
The spark occurs where it's less likely to ignite the gas............


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Old 01-26-2012, 09:24 AM   #54
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Quote:
Originally Posted by dnaraG_1M View Post
When you complete or break a circuit, you can get a spark.
Doesn't matter whether you open/close the positive or
negative wire - same circuit, same result.

The REAL reason for connecting/disconnecting the negative
first/last does, indeed, have to do with igniting the hydrogen
gas generated by the battery. The positive is connected to
to battery terminal - CLOSE TO THE GAS - but the the negative
is connected to the frame/chassis - FAR FROM THE GAS.
The spark occurs where it's less likely to ignite the gas............


cheers,
johnd
Basically that's what I said in my last sentence.
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Old 01-26-2012, 09:39 AM   #55
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Originally Posted by 07ultra View Post
the reason you disconnect the neg post first on a car is so if your wrench hits the frame on the pos side it won't spark
This is exactly why; having done it backwards and caused a "light show."
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Old 01-26-2012, 09:42 AM   #56
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At some point this thread got hijacked to a discussion on battery jumper cables. A permanently mounted properly installed selector switch should not "spark" a gas explosion regardless of which battery cable it is installed in.
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Old 01-26-2012, 10:06 AM   #57
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Originally Posted by herk7769 View Post
At some point this thread got hijacked to a discussion on battery jumper cables. A permanently mounted properly installed selector switch should not "spark" a gas explosion regardless of which battery cable it is installed in.
Right-O.
And a really good switch would have a hermetic seal to keep
any gas out. No gas, no danger.......
[Even if not totally sealed, the hole(s) to the outside world
might be small enough to allow the internal flame to "cool"
enough that it would not propagate outside the switch.
Wouldn't want to trust MY life to that though......]

The only concern then would be the external exposed connection,
if it was hot, and then some good insulation and regular inspection
would lessen any danger.

At that point, only danger would be damage to the insulation
of a "hot" cable due to vibration, etc. Maybe same problem
as with with aircraft wiring and same solution - secure them
wires and inspect often!

Possibly that's why the switched-ground solution came
about - unwillingness to do regular inspections....??.....
A little more safety margin for Bozo?

Whatever.


cheers,
johnd
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Old 01-26-2012, 10:15 AM   #58
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You are correct, no one will agree.
That guy ^^^ really knew what was going to happen with this thread.
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Old 01-26-2012, 10:30 AM   #59
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One more thing

While battery explosions DO HAPPEN.

If the battery compartment is properly vented and caps (if provided) are remove for "fast charging" a low, but healthy, battery; the odds of a gas explosion are exactly ZERO. You still need an explosive atmosphere (the exact mix of air and gas) to cause an explosion.

Too much gas and not enough air - nothing...
Too much air and not enough gas - also nothing...

The Goldilocks Environment is needed.

This explosion occurred by trying to charge a FROZEN dead battery.
Pure water and lots of amps equalled a perfect environment for a stray spark. Note: the caps were ON before this battery went up. The spark was inside the battery and only ONE cap was found. The others are most likely being tracked by NASA.
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Old 01-26-2012, 11:36 AM   #60
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Quote:
Originally Posted by jim44646 View Post
Basically that's what I said in my last sentence.
This is the issue I addressed from your posting:
Quote:
By doing it opposite you get no spark.
Unquote:

What I said was:
Quote:
The spark occurs where it's less likely to ignite the gas.
Unquote:

Very different reasoning for the same methodology.
One is based on reality and one on a false premise.

It may be important to know WHY we do what we do.....

cheers,
johnd
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