Jump starting cars

What are the risks of jump starting modern cars with all the electronic gizmos and computers? A family friend asked me to jump start her car and I was afraid to do it fearing damage to either car.

Jump start it with the same method you would use on a car built in 1965 and you will be fine. Red (positive) to the battery of the dead car, red to the positive battery terminal of the running car, black (negative) to the negative terminal battery of the running car, black to a bare metal engine point on the dead car. Start the dead car. Disconnect in reverse. Done.

Get a AAA membership. They’ll use a power pack that won’t get turned on until the connections are made, precluding the possibility of any arcs and reduce the possibility of pulses. And if they blow the car up, they’re insured… {:slight_smile:

Consider this. I assume that the jumper cables have been connected correctly, that the jumper cables are capable of carrying substantial amperage; that the good car’s engine is running; and that the cables are disconnected correctly.

As the good car,s alternator is charging the down car’s battery that alternator will be producing near peak amperage which is rough on the good car’s alternator. When the down car cranks, the voltage on both batteries will be pulled to about 9-10 volts so the good car’s alternator will definitely be charging at its maximum capablity. Now the down car’s engine starts; its alternator kicks in; the down car’s starter is disconnected; and at this point a voltage spike on both electrical systems is likely. This is when damage can be done to any solid state device connected to the electrial systems.

Its much better to change out cheap batteries every four years and maintain your charging system than risk damage to computer systems costing thousands to replace.

Auto electronics are supposed to be tested for voltage spikes, the so called “load dump” test. That is somewhere about 40 volts if I recall, and high current.

An arc, of course, is thousands of volts, but that is damped out by the battery, which acts like a huge capacitor.

But you are still taking a chance. some protection circuitry may be marginal, a high resistance wire, a bad ground, and the spike could get through. I’d not take a chance.

I have used this several times, much easier than trying to get two cars together, less risk to the donor car. Pretty inexpensive.


SteveCBT, nice item, but how do you recharge the battery, it doesn’t seem to have a 120 VAC input?

I don’t jump start cars. Nor do I get my own car jump started. And I advise others owning cars modern enough to have electronic fuel injection the same. I adopted this policy after burning out an alternator diode on my Corolla jump starting a neighbor’s car.

The preferred method is simple enough: charge the dead car’s battery with a battery charger. If a neighbor asks me for a jump start, I offer to drive them to a nearby store that sells battery chargers. So far nobody has ever taken me up on that offer. If they need to get their car running immediately, or if someone in a parking lot asks me for a jump start, I offer to phone up a tow truck company who will send a truck out to jump start their car for them.

Sorry, but with modern engine technology, don’t do that.

@BillRussell and @SteveCBT If you buy the Harbor Fright jumper box, be sure to get the extended one year warranty. I’ve had three of them replaced that way before a bought a Stanley from Sam’s Club. I bought the two year warranty there too, and used it once before the first year was up. It still has nine months to go. I’m on my second Stanley now, third if you count the warranty replacement. It was bigger than the original. I’ve also opened up both brands at different times, and replaced their batteries with ones from a battery shop for about $25. The new ones had more cranking power, but still didn’t last.

I would note that the Harbor Fright unit comes with it’s own short extension cord, or at least it did the last time I bought one. The “Inside Track” flyer I got in today’s mail had their unit on sale on the front page. I didn’t note the price because I don’t need one right now.

@“Bill Russell” the unit has a 120 cord for monthly recharging. @“MG McAnick” - good idea on an extended warranty, the quality of the unit matches it’s price.

I just don’t think I agree with…don’t jump start others. I have cables in my car and would help anyone out that asks. I am capable, and knowledgable.

Why not? I don’t think there is much risk of burning out my electronics. The risk is certainly there, but in life…risk is always present.

I say jump away!! But certainly like the idea of people not comfortable to have one of those battery charged jumpers. That would reduce risk too.

I no longer jump start cars, and I don’t accept the offers of well-meaning people to do so to my own car. I call AAA. It’s much safer. I don’t want to be blamed for having damaged someone else’s regulator (or whatever) and I don’t want anyone damaging my car.

An old story of problems caused by jump starting, happened to me back in the 70s, with an MG1100. The car was positive ground, 6 volts. Someone jump started me after I ran the battery down trying to start it in sub-zero weather.

Connected it backwards of course, but the car started up and ran fine. Turns out you can repolarize the generator from negative output to positive output. Even the radio worked. But the battery was being discharged at a high rate.

Needed a new battery and the generator repolarized.

But if I need a jump from any passerby…I do the connections myself…not them.

-discovered a major flaw in the Expedition a year ago the reinforces the notion about technology, ‘‘just because you could does not mean that you should.’’ The 08 Expedition has ONLY an electric solenoid operated rear hatch latch.
Dead battery ?..NO OPENING THE REAR HATCH ! ( it shoulda’ just been a simple ol’ mechanical handle )
But that’s where the tools and cables are !
My daughter ran down the battery so SHE had to climb over three rowas of seats to get the cables.