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Question on boosting car batteries
#251114 - 04/07/11 03:04 AM
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I used to think that one should connect negative to negative first, because I reasoned that no charge was coming out of the negative terminals. And I don't recall ever observing any adverse effects, so I kept on doing it that way when necessary.
Only now, when Googling how to treat a new car battery, did I read that one is supposed to connect positive to positive first!  So I was wrong all this time? What is the reason, then, for + to + first?
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Re: Question on boosting car batteries
[Re: Mojo2000]
#251117 - 04/07/11 03:15 AM
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If you hook the negatives first, then a positive, you could short out the battery by accidently touching the last cable end to a ground (almost anything metal in the car) If you connect the positives first, then a negative, you might accidently get a spark by brushing a piece of metal, but you won't short out the battery
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Re: Question on boosting car batteries
[Re: Mojo2000]
#251118 - 04/07/11 03:15 AM
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> I used to think that one should connect negative to negative first, because I
> reasoned that no charge was coming out of the negative terminals. And I don't recall
> ever observing any adverse effects, so I kept on doing it that way when necessary.
>
> Only now, when Googling how to treat a new car battery, did I read that one is
> supposed to connect positive to positive first! So I was wrong all this time? What is
> the reason, then, for + to + first?
I've always done negative from good battery to GROUND in the dead car; not the negative terminal in the dead car. You sometimes can get a spark (or more) connecting negative to negative.
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Ground is really "common return" ***EDITED*
[Re: Mojo2000]
#251122 - 04/07/11 03:37 AM
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Edited for clarity.
When "grounding" the negative terminal to the dead battery car's ground... it's not really a ground... think of it more as a "common return." The car's chassis is part of the circuit. Each car is a two-wire system as far as battery power is concerned. Ground is a common buss used to replace one of the wires to the battery. The chassis and engine block become part of the circuit, which can be tapped into for an electrical device. That saves having to run a separate negative wire to each device. In the case of the starter, there is only a positive cable running to it. The engine acts as the negative cable and the circuit is completed when the starter is bolted to the engine. If you put the negative clamp on the dead battery's negative terminal, and not to the chassis, you cut the starter out of the "jump" circuit, making the "jump" much less effective. Lights and other electrical devices also use the chassis to complete the circuit.
Discharged batteries release Hydrogen gas which is very flammable. Always hook up the jumper cables to the car with the dead battery first to avoid creating a electrical spark (arc).
You hook the Positive first because the electrons flow from the Negative terminal... you want to make sure those electrons have somewhere to go before adding them to the circuit.
dead positive
good positive
good negative
dead chassis
Edited by Gatinho (04/07/11 04:21 AM)
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Re: Ground is really "common return" ***EDITED*
[Re: GatKong]
#251145 - 04/07/11 07:45 AM
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> You hook the Positive first because the electrons flow from the Negative terminal...
That's the part that's most important for everything electrical (and seemed missing from the original post). Electrons are negative, and they come from the negative side of the battery. The + is the return end.
OK, now everybody just... don't look at the diode symbol.
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Muchas gracias
[Re: GatKong]
#251159 - 04/07/11 02:51 PM
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OK, thanks very much everybody. 
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| jopezu |
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Re: Ground is really "common return" ***EDITED*
[Re: GatKong]
#251163 - 04/07/11 03:24 PM
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> If you put the negative clamp on the dead battery's negative terminal,
> and not to the chassis, you cut the starter out of the "jump" circuit, making the
> "jump" much less effective. Lights and other electrical devices also use the chassis
> to complete the circuit.
thanks!
i already knew and followed the order you've got, and knew about the car being part of the circuit rather than a ground, but i'd never even considered/realized the starter getting cut out of the loop with a terminal-only hookup
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So I was wrong all this time? What is the reason, then, for + to + first?
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