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It might be more important to do this with thin gauge cables.
I was with you up to this point. The gauge and length of the cable determine how much resistance is in the cable. The thinner the gauge, and the longer the length, the more resistance to current, not to mention that, when you're going battery-to-battery, you're adding the resistance of the dead/weak battery on top of that. This, in turn produces heat, and can lead to jumper cables burning up in the worst case scenario.
I was with you up to this point. The gauge and length of the cable determine how much resistance is in the cable. The thinner the gauge, and the longer the length, the more resistance to current, not to mention that, when you're going battery-to-battery, you're adding the resistance of the dead/weak battery on top of that. This, in turn produces heat, and can lead to jumper cables burning up in the worst case scenario.
Yeah, but if you have thin cables they are still capable of charging the battery of the other car. So waiting a few minutes with it revved a bit above idle might charge their battery enough that it does not draw much through the cables from your car when the high amperage loads are pulled by the starter.
If the battery is still low, then when they go to start, much more amperage will want to flow through a thin high resistance cable. In fact, you might even be able to charge for a few minutes and then disconnect the cable.
So much bad information in this thread, it's incredible ...
1) Jump starting modern computer controlled electronics cars puts them at serious risk of failures due to voltage spikes. This can affect the jumped car as well as the donor car electronics.
It's not uncommon to see car owner's manuals advising against doing so due to the subsequent problems.
2) Older cars without the electronics are safe to jump start or to use as the donor car, but such cars are becoming fewer and fewer on the road today.
3) I've seen a lot of damaged electronics in cars when the battery was discharged or nearly so and the car was cranked up.
It appears that the damage may happen due to high current draws in components or when the alternator comes on-line with a voltage spike.
4) if a car with computers has a dead battery, it's best to charge it up outside the car electrical system and then reconnect when it's charged.
5) I won't put my car electronics at risk to jump start your car. However, I do carry in most of my vehicles a jump start unit/tire inflator unit. If it is sufficient to jump start your car, so be it. It is battery powered so there's no possibility of it having a voltage spike from an alternator, and it has an on-off switch so that there's no spark generated when a battery jumper cable is connected/disconnected. If you are willing to take all the risks of a low/discharged battery start up on your car, I'll jump start it with the unit which is not connected to my car electronics/charging system.
Please explain the underlined part. Good cables or cheap cables has nothing to do with the RPMs or the alternator output of the car with the good battery.
I would help to "charge" the dead car for a few minutes to build up a charge and reduce the demand on the "good car". It might be more important to do this with thin gauge cables.
We have maybe 3 cars a week that won't start here at the hospital... it would be more if we didn't make announcements of lights being left on.
Rarely are these batteries dead... they are just weak and start instantly with jumpers... I have a set I keep in engineering available upon request.
Batteries may or may not be easily accessible... last week we had a van with MN plates... the battery was complete encased in a cold weather package that had to be partially removed.
A few weeks ago a patient had a 71 VW Bug... she was clueless that her battery was under the back seat and she had lots of boxes on the seat... also she had the wrong battery and I could see where the seat springs had shorted against the battery terminal at some time.
The Auto club typically takes 20 minutes for a jump...
One of the Docs drives an older BMW... he said he just didn't have time to replace the battery... another Doc used the Hospital jumpers from his car... the cable was not well secured and when the car started it fell off and shorted against the engine and blew out the good Samaritan Doctors Lexus electrical system... turns out it was a large plug in fuse that blew... no one knew and the car was towed to the dealer...
The 56 with a 6 volt starter/battery has massive battery cables.
The 57 with the same 312 V-8 engine and 12 volt starter/battery has cables half the size... because it is 12 volts.
Yes, it takes the same wattage to turn the engine over, but you still need to push more voltage to get the amperage through.
An analogy could be for the voltage to be the pressure, and the amperage to be the flow.
The voltage being lower with the higher amperage, is largely to do with the charging system not being capable of keeping up the voltage at the higher amperage.
As to the OP; Consideration also needs to be given as to whether or not the flat battery is totally dead, (finished), and may not take any charge. In this situation, the vehicle donating the charge would need to have a somewhat larger battery, to have any chance of starting the car, especially with all the resistances involved in all the connections.
Everyone ought to have a jump start unit/tire inflator unit in their car. Sooner or later you will need it for your own car, as well as being able to help someone else.
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