XPost: alt.home.repair, sci.electronics.repair
From: ehsjr@verizon.net
On 1/18/2023 10:28 AM, Peter wrote:
> wrote:
>>> I always did positive first. I will switch!
>>
>> Think it out first - then decide.
>
> I'm thinking... I'm thinking... I'm trying to think this thing out.
> I don't think it matters all that much which cable goes first or last.
Yes it does. First, set any thoughts of sparks causing an explosion
aside. That's a *very* low probability occurrence as compared to the
real reason. Unfortunately, a lot of people focus on the sparks
issue and don't mention the real reason. And please note that the real
reason also involves sparks.
The real reason has been mentioned earlier, but apparently
needs to be repeated, maybe with more detail, so here goes.
The real reason: there is a huge area of metal in the engine
compartment, the car bumpers and fenders (if metal) etc. It
is very easy to inadvertently touch the bare end of a jumper
cable to that bare metal. If the negative jumper cable is
connected first, and you're connecting the positive cable
to the bad battery, you'll get a short circuit with that
inadvertent touch, powerful sparks, a possible tack weld of
the jumper cable, and a very bad day. (Possible fire, burns,
dead battery, ruined cables, etc.)
If you connect the positive jumper first, the end of the cable
CANNOT cause a short when it touches ANY bare metal in the
car receiving the jump.
The proper procedure:
1 Put the cars close together but NOT touching.
2 Stretch the cable out so the bare positive end
is away from the car with the good battery.
3 Connect the positive cable to the positive of
the good battery
4 Connect the other end of the positive cable to
the positive of the bad battery.
5 Connect the negative cable to the good battery
6 Connect the other end to the other car battery
negative, or to the other car engine compartment
metal where you can get a good solid mechanical
clamping spot.
7 When finished do the above in reverse order
The above recognizes - and mitigates - the possibility
of sparks, but focuses on the real potential hazard:
short circuit. I wish all this talk of exploding
hydrogen gas had never appeared, because it hides
the extremely more probable event of a short circuit,
which, of itself, creates a more powerful spark than
connecting (or disconnecting) a jumper cable to a
battery.
Ed
>
> As far as I can think about it, the last connection is the one that sparks.
> And that means the first disconnection is the one that sparks.
>
> Since you don't want that spark to be near any concentration of flammable
> hydrogen gas, I guess the theory that I'll concoct is you want the negative
> cable to be as far from that hydrogen gas as possible.
>
> That makes it the negative cable to be the last to connect.
> And the first to disconnect.
>
> Now, if the theory is to proceed accordingly, we have to decide which
> battery has the most chance of having excess hydrogen gas.
>
> The answer likely is neither will have any, but if we have to choose, which
> battery will have more hydrogen outgassing?
>
> (A) The donor battery (which is likely already topped off) or
> (B) The recipient battery (which is likely taking the greater charge)
>
> The answer seems, to me, to be neither battery will have excess hydrogen
> gas, but if I was forced to choose, I guess the battery being charged the
> most has the most excess hydrogen gas, which would clearly be the donor.
>
> All this is just "thinking it out" so tell me if I'm wrong so I learn from
> your expertise (the royal your that is, as everyone has something to say).
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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