Battery on/off -- Pos or Neg side?

[racedaymechanic]

Originally Posted by Walke

Always switch the positive side,(unless you are in Europe) the direction of the current doesn't matter to a contact switch. I don't believe a sound technical reason can be made for switching the negative (ground) side of a battery.

On the disconects for our race cars I always put the on off switch on the ground period, that way it kills the system Dead, Nascar agreed with me and now recommends it in all 3 top divisions

[Walke]

Like I said, there are no technical reasons to put it on the ground side just opinons !!

[dnaraG_1M]

Originally Posted by Walke

Like I said, there are no technical reasons to put it on the ground side just opinons !!

As a retired electrical engineer - who never designed RV electrical
systems - it certainly seems that there is no difference between
opening the "hot" or ground lead.....If, and only if, the switch is
very close to the battery posts.........

If the switch is in the hot lead and is quite a distance from the
battery, you will have a long lead and one (switch) terminal that is
ALWAYS live. This opens the possibility of a "short" to ground.
The ground lead is usually quite short - connecting to the nearest
chassis point - so a switch in the ground lead would likely not
have this situation.

I would call that a "technical" reason...........YMMV.

cheers,
johnd

[Herk7769]

Originally Posted by dnaraG_1M

I would call that a "technical" reason

John,

It has been my experience that no amount of "reasoning" (technical or otherwise) will convince some folks to change their mind. Tightly held opinions (or beliefs) do not yield well to facts or tolerance of another's view of reality.

Caveat Lector and press on

[dnaraG_1M]

Originally Posted by herk7769

John,

It has been my experience that no amount of "reasoning" (technical or otherwise) will convince some folks to change their mind. Tightly held opinions (or beliefs) do not yield well to facts or tolerance of another's view of reality.

Caveat Lector and press on

Doggone it, I forgot all about that.

Well maybe my wife's right when she says that "when I
retired, I left my brain lying on my desk at the office".........

D'oh!

Be happy,
johnd

[Nigels]

Originally Posted by Walke

Always switch the positive side,(unless you are in Europe) the direction of the current doesn't matter to a contact switch. I don't believe a sound technical reason can be made for switching the negative (ground) side of a battery.

I thought I was a positive person until I started reading this thread then negativity started creeping up on me and now I don't know what I am

"unless you are in Europe" Hey I am in Europe I'm positive about that, so I must be negative, right, not sure why Europeans must all be negative tho when most of Europe is positively bankrupt? This is so confusing

[Herk7769]

Don't feel bad Nigel; Ken's post confused me, too.

[jim44646]

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

[Herk7769]

Originally Posted by jim44646

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

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.

[dnaraG_1M]

Originally Posted by Iggy

Switch the Positive side. The reason why is if you jus switch the negitive you can still make a direct short inside the trailer from a positive line to the frame which is ground.

If you switch the positive at the battery you will never have the posibility of a short inside your trailer.

My 2 cents

If you put the switch in the ground lead and OPEN it, the chassis
is *NOT* ground!!! It is "floating" - just a plain old hunk of metal
with no connection to the battery - and you don't have a completed
circuit. No current flow; no sparks.........

Now if you are connected to a tow vehicle and the electrical systems
of the two are interconnected (including chassis connection), that's
a whole 'nother Barrel of Snakes!
Also the same in the case of a MH, rather than a TT where you
have multiple batteries to consider. But that's not what we were
talking about............


cheers,
johnd

[jim44646]

Originally Posted by herk7769

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

[07ultra]

Originally Posted by jim44646

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

[dnaraG_1M]

Originally Posted by jim44646

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............


cheers,
johnd

[jim44646]

Originally Posted by dnaraG_1M

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.

[Herk7769]

Originally Posted by 07ultra

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."

[Herk7769]

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.

[dnaraG_1M]

Originally Posted by herk7769

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

[Len & Cheri]

Originally Posted by LFugate

You are correct, no one will agree.

That guy ^^^ really knew what was going to happen with this thread.

[Herk7769]

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.

[dnaraG_1M]

Originally Posted by jim44646

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