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Battery Jumping Negative/Positive ground cars

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You already have the resistance of the negative battery cable and the ground strap plus the interfacial resistances of all those connections inseries with the starting current. ---Keoke

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To put this into perspective - If the total circuit resistance including battery cables, solenoid contacts, battery cable connections, & sheet metal, is only 0.015 Ohms - At 200 amps starter draw (not unusual) there will be a voltage drop of three volts at the starter. You cannot even measure 0.015 Ohms on a conventional meter.

Since it is reasonable to already have a battery drop of three to four volts due to normal internal battery resistance, this leaves only five to six volts to turn the starter. Even 0.1 Ohms extra circuit resistance would reduce the available starter voltage to zero. At high currents, even seemingly tiny resistances will markedly reduce the available starter voltage.
D
 
/ubbthreads/images/graemlins/iagree.gif

The issue is "remoteness" from the load, not the battery.

There will be unavoidable power loss from the jumpered car due to the jumpers.

There will be further power loss depending on where the jumpers are connected, and those can be controlled.

For charging the battery you'd want it as close to the battery as possible. In most cases that is what I have done so that I can charge the dead battery for a while before trying to start the car, and to put a little power in the battery.

For starting the car it is just as plain that you'd want the connections as close to the starter as possible.

The issue as I see it is where the resistance happens and where the power originates, and the jumpered power does not originate with the dead battery.

If I connect a jumper to the engine ground strap the electricity flows from the load directly to it, not via the more distant battery.

The resistence then is reduced because of the closeness to the starting load rather than increased due to the "remoteness" from the dead battery.

I've done it both ways in the past, and probably will in the future. My Healey's still a basket case, but if I had to jump it. I'd use the battery terminals for practical and safety reasons. Trying to jump the starter in the engine compartment would seem far too likely to cause a short circuit. And its easier to make a good connection to the terminals than to most painted chassis or other, smaller terminals.

Connecting the jumper to the chassis side of the battery ground strap would put it 6 inches closer to the load and involve that much less resistance despite its slighter remoteness from the dead battery- and its distance from the originating car's battery/generator wouldn't be affected at all.

Wouldn't it?
 
Well maybe somebody is talking about remoteness from the load,What ever that is, Im talking about remoteness from the battery. That cumulative resistance is the problem I have been talking about Dave-Keoke
 
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ED-k That is the particular situation you want to avoid there is no gurantee that some remote part of the vehicle is connected to the battery via a low resistance.Further that resistance gets put in series with the batteries negative ground cable.--Keoke

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Right you are Keoke. And that is exactly what I am talking about. If there is a ( I think you meant to say high resistance as LOW resistance is the desired condition of all connections ) then this is what needs to be indentified and repaired. After all, there is a reason whay the battery is low , unless someone left the lights or radio on, or the battery is old or the generator is not putting out, then the reason for the low battery is very likely to be caused by a poor connection anywhere in the charge circut which includes having a good, low resistance, high current capacity ground connection to the battery post. This is just as important as the other side of the circut from the generator to the non ground post of the battery.
 
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/ubbthreads/images/graemlins/shocked.gif
Well John, now you know the average person on earth is walking around with about 10,000 volts electrostatic charge on his body and lightning just loves that diffence. On The Otherhand, don't be the tallest item on top of that sand dune when an electrical storm passes over.However, if you are fortunate enough to be hanging on to a Hang glider then you may live to tell the story.--- /ubbthreads/images/graemlins/angel.gif

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Did you know that when a woman with silk underwear walks across a carpeted floor in the winter when the humidity is very dry that she will develop between 14,000 to 24,000 volts of static charge ? This is why ESD tools and mats were developed for repairing sensitive electronic circuts without damaging the componets with this high static voltage. It just shocks a person but it blows apart semiconductor interfaces.
 
I agree with James and Dave in their two previous posts.
/ubbthreads/images/graemlins/iagree.gif
IMHO
 
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Well maybe somebody is talking about remoteness from the load,What ever that is, Im talking about remoteness from the battery. That cumulative resistance is the problem I have been talking about Dave-Keoke

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Keoke, don't shoot me, I was just illustrating what I thought you said. If you don't agree - well - pardon me!

Let me know when I can come out of the corner.
D
 
Nope! /ubbthreads/images/graemlins/iagree.gif You put in the right perspective.---Keoke- /ubbthreads/images/graemlins/thumbsup.gif
 
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Well maybe somebody is talking about remoteness from the load,What ever that is, Im talking about remoteness from the battery. That cumulative resistance is the problem I have been talking about Dave-Keoke

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I'll try to make this clear with an example.

Assume the problem is a poor corroded (hence higher resistance) connection between the chassis and the ground wire to the battery.

Connecting the jumpers across the battery terminals will be fine for charging the battery but ineffective for starting the car since the load imposed by the starter is still subject to the high resistance from the poor connection.

If the hot jumper is connected to the battery terminal, and the ground jumper connected then to the chassis this will not serve to charge the battery since the poor connection would interfere with that electrical flow. But if you try to start the car the jumpers are then placed so they avoid the poor, high resistance connection between the battery and ground and will work better for turning the starter over.

If I connect a jumper to the chassis the electricity will flow from that point to where it is used without regard to the dead battery's location. If the connection is further from the load it may have more resistance, if its closer it may have less.

If I'm going to jump start a car a good, direct connection to the ground and solenoid involves the least resistance, despite being "remote" from the battery whish is further away and involves more resistance then in delivering its charge (or the input from a jumper source if connected there).

Does this clarify things?
 
So it seems we have beaten this subject to death. In my experience much of the time when a battery fails to start a car, the resistance frequently is the corrision that has built up between the battery posts and the battery cable connectors. Just cleaning those generally solves that problem. On the other hand if the battery is truly shot (dead cell, whatever), jump starting may not work wherever you place the jump cables. So that leaves us with the run down battery (lights, radio left on, generator not charging properly, or just an older battery that may soon need replacement. I still like and most if not all battery manufacturers (name a couple that don't) suggest that the last connection be to unpainted ground away from the battery to avoid the very rare but possible battery explosion due to gases escaping from the dead battery. Should the car not start in this manner due to the increased resistance, one can always move the jump cable over to the grounded post. At my house we have 5 cars, 3 jet skis, one ski boat, and lots of dead batteries. But I have never had to jump start my hobie cat.
 
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So it seems we have beaten this subject to death.

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Is there any other way to do things around here?

I'm sure glad I asked a simple question that was susceptible to a complex answer(s). Thanks guys.
 
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I'm sure glad I asked a simple question that was susceptible to a complex answer(s). Thanks guys.

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You're welcome.

In the past I've found "simple" automotive electrics problems to be rather messy sometimes and much harder to solve than originally thought.... /ubbthreads/images/graemlins/confused.gif

I'd like to think this has reached a conclusion... rather than death. /ubbthreads/images/graemlins/crazy.gif
 
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