# Amps of a car battery

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#### TomWarrant

In need of a better explanation of what happens if a person touches the negative terminal or metal on the vehicle with a wrench while touching the positive terminal on a car battery when both are connected.

I remember hearing that it can heat up to the point of melting the wrench or the metal on you.
The current is so much higher, with practically no resistance, correct?

#### bertus

Hello,

Read the PDF in the link , it states this:
A “shorted” lead acid battery has the capability of delivering an extremely high current, 100 to 1000 times the typical discharge current used in most applications. Electrical systems using batteries must be properly protected to avoid potentiallydangerous fault conditions. In this paper, we compare the short circuit currents as predicted using generally accepted estimation methods versus actual measured values for individual batteries and battery systems. Practical considerations such as the effects of temperature, state of charge and type of circuit protection device are also presented.

Bertus

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#### TomWarrant

Thanks.

Does anyone know approximately how many Amps would be going through that wrench, compared to how many Amps travel through the load in the running vehicle?

what is the best formula to figure this out?

#### ron simpson

approximately how many Amps
A wrench is not designed to conduct electricity. It does conduct but not predictable. It might be wet/dry, oily, dirty, new/old. There are too many unknowns. The battery has a "internal resistance" that limits the current under a short. This resistance changes with time, temperature, how hard the battery was used. A new battery probably will produce 4x more current than a old battery. There are so many things I do not know, like how much of the wrench is touching the terminal.

I think if bertus , Tom and Ron all went and measured our batteries the numbers will not be the same. From what Bertus posted a "100A" battery could produce 10,000 to 100,000 amps. (for a short time, when new, and worm)

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#### Pascal

How much resistance would a wrench even have?

#### ron simpson

How much resistance would a wrench even have?
Very hard to know. What metal, what finish, covered with oil? How long is the wrench? I think a wrench is a poor conductor in that it was never designed for this. But it is good enough to conduct 100s or 1000s of amps.