When Boosting another Vehicle is this correct.

Thousands of dollars is a bit of overstatement by a few thousand dollars, but yes damage can happen.

The electronic controls in modern cars *can* be damaged by connecting them together wrong when boosting. Some of these electronic controls can also be damaged by the transients that happen when connecting the boost...those particular electronics were designed by idiots at best. Some of those idiots manage to convince their even bigger idiotic marketing types to add statements prohibiting boosting or being boosted to their owner's manuals. This is incompetence at best given how cheap it is to protect the electronics, but it is sadly all too common. It is a copout to cover incompetence and cheapness of design.

As for not allowing anyone to boost his car, he could be in deep trouble if his battery ever dies.

Some folks hook the negative to a good body ground for safety, but your method works just fine.

I've had vehicles that wouldn't boost, had to hook the other car up and charge my local battery for 15-20 minutes, then use it to start.

However if your vehicle is able to spin the starter but won't start, may want to check the electronics and engine oil [too thick].

If the vehicle giving the boost is running when the cables are connected, the sudden load on the electrical system can cause a voltage spike that can damage the alternator, computer, ignition or any other electronic part. So, yes the owners manual is correct. But wait! theres more! If the cables are connected with the boosting vehicle off, thats good. However, if the vehicle giving the boost is running when the dead car tries to start, it can also cause a voltage spike. POOF! If that doesn't make sense, remember that a good starter requires around 140-200 amps to start from a GOOD battery. Amps and volts are related. As voltage drops, amps will increase. So a car with a dead battery trying to start may pull in excess of 500 amps thru the battery cables,even more if the starter is defective. The boosting car's battery and alternator is going to try to provide that, and it CAN cause problems. Lots of times you can get away with it, but it only takes one blown computer to empty the bank account.

A final note. Connect your positive cables first, then negative on the dead battery and connect the other negative cable to an engine brakect on the boosting car. This is to prevent sparks from causing explosive vapors from the battery from igniting.

A few hundred dollars if you pop the main controller.

As for the fanciful explanations of voltage and current, good heavens. And you may want to patent that magical system where amperes increase as the voltage drops...you'll be famous.

Attention All.. Effective immediately, Ohm's Law has been repealed.

Regards,

Jim

Actually, that's not the marketing types. It's the actuarials who've calculated the cost of possible warranty problems and convinced management that there's a potential costly payout if millions of people suddenly jump-start their cars and accidentally damage something. They probably have a couple of years of warranty claims to back them up showing that the CEO could have had another 100K in bonus if they'd marked this as "voids the warranty" earlier.

Actually in the case of starter motors, the current draw will increase as the voltage drops. See

This question of battery boosting a stalled vehicle comes up time after time. Each time there is a flurry of myth and misinformaion that is posted on the subject. A person who honestly wanted a good answer would go away puzzled. Yet every winter the mall will have crew going out to jump start vehicles, even Nissans. And everyday citizens will continue to jump start the neighbor's vehicle when necessary. Usually, they are careful and follow the standard recommendations. Almost all the vehicles will start. There will be someone somewhere that will have an electronics problem.

Why dont you see Ed's reply above before you cast any stones. I don't see you offering any help. I may not have explained it well, but I was more constructive than you.

Curly

Ohm's law remains in tact. Electric motors have a power output. P = VI, so as V drops, I increases to maintain power. I cannot explain why electric motors operate this way, but I do know electric motors will run hotter on low voltage (from experience, you should not run an air compressor for extended periods on a couple of light duty 100' extension cords strung together). Power in the form of heat loss = I^2R and this causes the motor to run hotter as current increases.

voltage drops. See

If you stall most DC motors, they will *attempt* to draw more current. On the other hand, your battery will supply less current at lower voltage.

Ohm's: It's not just a good idea, it's the Law!!!

However, the motor will only be able to do this if fed from a power supply able to provide that higher current. A battery which is low on voltage doesn't qualify, as the lower voltage is also accompanied by less current available and often higher internal resistance in the battery which is now in series with the starter motor.

as the voltage drops. See

A DC motor will most definitely draw more current as the load is increased. If you watch battery voltage you will also see that decrease as the load and current increase. Bob

Hey, good news. I just spoke to Congress. They'll repeal Ohm's law and end the argument as long as we throw in a rider that limits the insurance companies payouts to $25/car and give all the generated repair work to Halliburton in a billion dollar no-bid contract.

Oh... and no one will be allowed to buy half cost repair parts from Canada even though they make them in the USA and ship them there for sale at a lower price.

Allowing the dead vehicle's battery, a while to absorb a donor charge before a start attempt, will lessen the draw from the donor. Decreasing the possibility of failure. True or false?

voltage drops. See

No, they WILL draw more current as they are loaded. And even though the battery voltage (at the terminals) begins to drop because of the battery's own internal resistance, current still goes up.

In fact, a battery will deliver its absolute maximum CURRENT when the voltage at its terminals falls to zero. It won't do that for long, because it will begin heating internally and also discharge rapidly.

The correct circuit model to use for a battery is an ideal voltage source in series with a resistor representing the battery's internal resistance. The maximum current out of the battery will occur when you short the terminals, and by definition you've now reduced the battery's voltage to zero. All the power will just be dumping into the internal resistor, though, and the voltage across it will NOT be zero.

True, provided you do this with the donor car's engine RUNNING. Hooking a fully charged 12v battery to a dead 12v battery will NOT charge the dead battery. You have to have a running alternator to push the voltage above the charging threshold of the battery in order to get it to charge.

If the current from a battery, goes up and the internal impedance of that source increases, the voltage drop across the source increases.

It is impossible to drop the voltage across a lead acid battery to zero.

As measured at the terminals, indeed it won't be zero. Which is the difference between the model and the battery.

It might. There are some vehicles that draw so much power from the battery for starting that they are extremely difficult to jump from an external source...as opposed to charging their local battery and using that to start.

As for avoiding damage to the jumping vehicle, it would need to have a rather marginal electrical system to really hurt it during a jump.

I could be wrong, but this sounds like bullshit. When you connect 2 or more batteries together the charge will equalize among them. Explain what a charging threshold is.