The Negative Battery Terminal and Ground

[foolios]

In most directions I have found about jumping a car battery it directs to start with the positive terminal of the good car battery to the positive terminal of the dead car battery. Then from the negative of the dead car battery to an area on the engine block of the car with the good battery. One I found actually said to put it on the negative terminal of the good car battery instead of on the engine block. But most specifically state to not do that.

One of my questions is, how does current go from negative to positive if the negative is connected to the engine block?

I am guessing that the reason the negative shouldn't be connected to the other negative is because it may overcharge it somehow and cause an explosion or something.

If someone could clear that up for me I'd appreciate it.

 

[M107]

The reason for not connecting the neg to the battery terminal (& why the pos is connected to the good battery first) is to keep sparks away from the battery, just in case the battery is leaking fumes/gas that are flamable.

 

[Andy™]

One of my questions is, how does current go from negative to positive if the negative is connected to the engine block?

I am guessing that the reason the negative shouldn't be connected to the other negative is because it may overcharge it somehow and cause an explosion or something.

assuming that the car is negative earth (most are), the entire car is earth/negative. power goes from + of good battery to dead battery, thru engine starter motor and then go negative. either to the battery or the jump lead on the chassis. and the negative's are always connected. there is a large cable goes from negative of battery to chassis

 

[foolios]

How is it that we don't get shocked by electricity when we touch the parts of the engine or even other metal surfaces on the car?

 

[foolios]

The reason for not connecting the neg to the battery terminal (& why the pos is connected to the good battery first) is to keep sparks away from the battery, just in case the battery is leaking fumes/gas that are flamable.

If the negative is connected to an engine block or other metal surface of the car, where do the electrons go? So, we've got a negative on the dead battery going to a piece of metal on the car(not the negative on the good battery). How does this complete the circuit?

I am confused because as far as I understand it, electrons want to travel from the negative post on the battery to the positive post on that or the other battery. But I don't see how this connection is being made. So far I only see that we have positives attached from the good to the dead battery. Well, these positives are desiring electrons to even them out. Where is this coming from then when we are routing the negative wires as suggested? How are we powering up this dead battery?

Thanks in advance for the explanations.

 

[Andy™]

How is it that we don't get shocked by electricity when we touch the parts of the engine or even other metal surfaces on the car?

because its only 12V same way as you dont get a shock with SELV

even if it was a much higher voltage, just touching the metal work wouldnt do much - all at same potential. would only get a shock if you touched a higher voltage part and the metal body of the car

 

[Andy™]

not so good diagram, but should give you some idea

first, ignore the good battery and jump leads. power goes from pos of good batt, thru vehicle electrics, to car metalwork, and back to neg. got that?

now, with the good battery, you can connect 2 ways. either by diagram (+ to terminal, - to chassis). or if you look at diagram, you could also put - direct to dead battery -

now to with jump leads, power goes from + of good batt, thru lead to + of dead batt, then follows same route as before, until chassis. then rather than go to dead battery, it goes to good battery via jump lead.

 

[foolios]

Thank you so much, that was a wonderfully clear explanation.

I have a question about this difference in potential. It amazes me that the metal has current going through it and yet it won't go through us when touching it. Is it because we are more resistance to the current than the metal is? So the current doesn't leave it's easier grounding path?

That's what the diagram looks like with the batteries in parallel correct? I've read that you never hook up batteries in series, from end to end because the voltage adds up. Why would two car batteries in series explode(get 24V)? Isn't one compartment of positive only going into one compartment of negative? They're seperated, so why the increase? We have two batteries in series, the negative is going into the positive of the other battery and that negative of that other battery is going into the positive of this battery. It seems to me as though there is no connection in their circuitry that would cause doubling of voltage?

Thanks so much. I loved the diagram. =)

 

[Andy™]

Thank you so much, that was a wonderfully clear explanation. I have a question about this difference in potential. It amazes me that the metal has current going through it and yet it won't go through us when touching it. Is it because we are more resistance to the current than the metal is? So the current doesn't leave it's easier grounding path?metal has a lower resistance. electricity will always take the path of least resistance, but it can also take other paths. at 12v, powe may flow thru a body, but because of the voltage its a very small amount

That's what the diagram looks like with the batteries in parallel correct?correct I've read that you never hook up batteries in series, from end to end because the voltage adds up.you read wrong. batteries can safely be connected in series. try your TV remote. trucks normally have 2x 12v batteries in series Why would two car batteries in series explode(get 24V)? if you connected it in on big loop they wouldIsn't one compartment of positive only going into one compartment of negative? They're seperated, so why the increase? We have two batteries in series, the negative is going into the positive of the other battery and that negative of that other battery is going into the positive of this battery.not quite. from batt 1, + is connected to - of batt 2. 1 load is connected accross the unconnected terminals It seems to me as though there is no connection in their circuitry that would cause doubling of voltage?each battery the power flows thru, it gets the voltage of that battery. if you have 4 12v batteries in series, you will get 48V

Thanks so much. I loved the diagram. =)

my red. another diagram coming soon

 

[Andy™]

top half is series. power flows thru each battery, gaining 12V each time. since there is 4 batteries at 12V, you get 48V. if there was only 3 batteries, you wold get 36V

if you were to miss the load and put a solid link, then they would overheat, possibly explode

going back to parallel, see bottom diagram. current only flows thru any one battery so voltage stays the same at 12V. bit like in the car with jump lead - these in effect connect + and - between batteries

make any sense?

 

[foolios]

I think I see where I was confused. I was thinking that voltage and current from the polar ends were seperated from each other. But now I am understanding that that was in error. True that current is seperated, or I should say the extra negative electrons are seperated from the polar ends until a conduit is supplied for them to travel along, but voltage is not seperated at all within the battery. The entire battery is free to push voltage from either end of it, I think. Or is it that the negative end is designed to push voltage out while the positive only allows voltage in?

I see now that this addition of voltage can occur between car batteries.

For the parallel, if you took off the load and its wiring, no current activity would occur. But what if you left the wire and just removed the load? Wouldn't each battery just act as if they were connected to itself? A short circuit to each on its own and not an addition of anything right?

Thanks so much. I understand so much more about car batteries. And understanding the bit about avoiding sparks near the battery is a real comfort.

Thanks so much.