When I looked up how to jump a car battery, they tell you WHAT to do, butnot WHY, which is infuriating as it's harder to remember unless you knowwhy. they say the cars shouldn't touch.Why?Then they said positive first.Why?Once started, they say remove the negative cable first.Why?Here, they say adding water damages the batteries. Why? how often do you need to add water?This says to add water after every ten charging cycles?Isn't that like every ten days?And how do you know how much to add?They say add water to the "splash plate" but what is that?They say the six chambers produce 2.1 volts each for 12.6 volts?Isn't it more than that?They say adding water before charging will make it overflow.Does it really change the water level that much from dead to charged?And what happens if you tap water instead of distilled?

These three questions only need one answer.In case there is any hydrogen gas that has developed in the battery and may be still concentrated enough to burn, any spark from completing the circuit should be made at some distance from the battery. That is, but connecting the earth to some metal part of the chassis, not to the battery terminal itself.The chassis is (usually) negative, which is why that is the first and last contact point.If there is any ionic content in your tap water, it is likely to precipitate as conductive salts in the bottom of your battery, increasing the self-discharge rate. Here in Sydney, our water is clean enough not to need to bother - any effect on battery life is negligible.CH

OK, so I missed that. Here's one that does address the dead battery youwould be connecting the vehicle to. My apologies for missing the deadone that is not charged. Link is below: are similar articles to connecting batteries to capacitors (which is basically what a battery essentially is), although we're dealing with DC circuits.Good Luck.Charles Lucas

Can somone explain WHY positive first when jumping a car battery?

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Charles Lucas 3 years ago

Although the thread is rather lengthy and has been virtually exhausted, I am going to venture out an explanation here.

Prevents Sparking or Arcing if in the event wires did touch. More energy passes from the negative (anode) to the positive (cathode) side, due to the way electrons flow, which create a potential for arcing on the positive side. So, you go to the "stronger" or more energetic side first, then you apply either the chassis or earth ground. It also puts less strain on the stator and rotor on the electric motor in your alternator.

Follow or look up this enclosed link below. It gives details on arcing here.

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Accordingly, the batteries (depending upon their chemical composition and make up) have to maintain the correct specific gravity. Most people do not know about this, but it ties in when a chemical reaction is actually created through the EMF of the battery during operation drawing from each of those cells.

Actually, I heard about 13.5 to 13.8 Volts is common for vehicles and traditional automobiles with regular gasoline engines. Diesel uses up to 14.2 volts because more power is generated through the glow plugs (and with diesel, the pre-firing). I am not a diesel expert, but that is what I have heard.

The reaction will be slightly different chemically, but not by much, if the specific gravity remains intact. I try to get distilled because there is by nature less sediment in the water which reduces wear on the internal chambers or cells in the battery and less likelihood of calcification.

Good Luck. Hope this helps.

Charles Lucas

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Charles Lucas 3 years ago

OK, so I missed that. Here's one that does address the dead battery you would be connecting the vehicle to. My apologies for missing the dead one that is not charged. Link is below:

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There are similar articles to connecting batteries to capacitors (which is basically what a battery essentially is), although we're dealing with DC circuits.

Good Luck.

Charles Lucas

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Peter W. 3 years ago

This is the 94th post on the basics of separating fly-s*it from pepper - oops, how to jump-start a vehicle. What we have learned: a) this venue is proof-positive that common sense is rarer than an ethical politician or a moral evangelical preacher. b) that this venue exists to give the most impractical, obscure, possibly dangerous advice to the mostly lazy, ignorant or otherwise challenged individuals who appear to look for and cherish such device rather than seeking it for themselves, or reaching out to organizations that actually might know. c) that if there is an opinion - fact-based or not - there will be an equal-and-opposite opinion - fact-based or not. d) that the posters in this venue as exemplified by the above should not be exposed to anything sharper than a rubber spoon, more powerful than a D-size battery (large enough to make swallowing it difficult), or requiring reading or understanding directions, written or otherwise.

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Now, how hard was that?

Peter Wieck Melrose Park, PA

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Carlos E.R. 3 years ago

The "bad" battery will start charging when connected, and there will be no current limiting.

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Michael Trew 3 years ago

The last time I had a really flat battery, and jumping it didn't work (perhaps the cables weren't heavy enough gauge), I started it with another battery installed (cables semi-tight pushed-on)... then with the alternator keeping it going, I disconnected that battery, and hooked up the flat battery. You could instantly hear the engine bog down from the alternator kicking into high-gear. This was a 1960's car, BTW, with a modern 12v battery. Perhaps this isn't the hottest idea with a new car using expensive electronics, but it works fine on older rigs with a good alternator.

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Charles Lucas 3 years ago

Remember, this can be done only if what this man said is true and/or the voltage regulation circuitry can handle it. I would try using a load resistor Run to ground at the base of the circuit to handle the load and to prevent overload. The resistor should be of adequate size (1/4 watt at so many mega ohms) to absorb the energy.

Good Luck,

Charles Lucas

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Can somone explain WHY positive first when jumping a car battery?

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