Jump starting a car

[vgames33]

I would assume that the 12v car would be badly damaged by the excess voltage. Some hybrids carry a 12v battery for accessories that can be used for jump starting.

[shorod]

I expect the high voltage is all contained to the driveline system, and not used for the accessories such as the radio, lights, 12V accessory port for you GPS, power windows, power locks, etc. I remember reading about training sessions being offered for rescue personnel so they would know where the high voltage wiring resides in the cars. It can be quite a shock (pun intended) to cut in to one of those wires with the Jaws of Life.

-Rod

[tomj76]

Never, ever, ever, ever connect two batteries that are not the same design voltage.

For example, a three cell lead-acid battery puts out ~6 volts. Do not try to jump a vehicle using a 6 volt, three cell battery with a "standard" six cell, 12 volt battery. You very likely will have a battery explosion on your hands. To make matters worse, it might be the good battery that explodes.

A high voltage battery like those used in a hybrid is a very dangerous potential energy source. If you were to connect one to a standard 12 volt battery you will probably see peak currents high enough to vaporize the metal in the jumper cables. Many an electrician has been killed or severely maimed by when working on a live junction box and making a mistake that causes the explosive vaporization of metal. Not only are they severly burned by the hot metal vapor, but this becomes a conducting path for electricity that further burns their body. Dispite the fact that I am a professional electrical engineer, I would not mess around with a high voltage, high energy hybrid battery without understanding all of the safety issues. This is one thing that is best left to trained people.

To help understand the amount of energy contained in these devices...

A standard car battery has at least 200 cold cranking amps. A cold cranking amp for a 12 volt battery is the current that the battery can produce for thirty seconds with at least 7.2 volts of output. Then battery power is then at least 7.2 * 200 = 1440 watts = 1440 Joules/sec. Now since the battery only does this for 30 seconds, the total energy available is 43,200 Joules. A gallon of gasoline releases about 100,000 BTUs when it combusts. This is around one million Joules of energy. Therefor a typical 12 volt battery holds the equivalent energy of 5.5 oz of gasoline. Burn that amount of fuel in less than a second, and you can begin to understand the explosive potential of even standard batteries.

Now, consider twenty, 12 volt batteries, each with 200 CCA, stacked in series to deliver 240 volts. This battery has 864,000 Joules of stored energy. This energy is equivalent to about 7/8 gallons of gasoline, or a little less than 1/2 a stick of dynamite.

Shorting batteries creates opportunities to release their stored energy very quickly. Jump starting is a process that carries a strong risk of shorting the battery. The potential for injury is extreem when dealing with hybrid electric batteries.

[CL8]

I read recently of a person jumping a dead car battery with the auxiliary battery (12 volt) and there was sparking on the dead car.

Can using the auxiliary battery of a hybrid be just as dangerous?