I’ve heard different opinions over the years about the dangers to the charging systems that can occur from jump starting. I know some people who don’t want to jump start anyone because they fear it will damage their alternator. Wondering if I can get a few things settled once and for all.
After hooking up the cables, should the good car be left running for a few minutes (to partially charge the dead battery) and then shut off before starting the bad car? I’ve heard that it should so that the (diodes in the?) alternator of the good car aren’t damaged. If it is shut off, will the battery alone and a few minutes of charging be good enough to jump start the bad car? I’m assuming that there would be too much resistance in the cables to give enough juice to the bad battery if the engine is shut off on the good car.
Assuming the following:
[ul]
[li]The donor car’s electrical system is in good condition[/li][li]The cables are correctly hooked up[/li][/ul]
The risk to the electrical system of either car is negligible. In fact in all my years of working on cars I have never seen or heard of a case of an alternator being damaged by a properly done jump start.
NOTE: It is possible to have a hydrogen explosion at one of the batteries from a spark, that is why jump starting instructions always tell you to connect the ground cable last, to a metal part of the engine, and not the battery.
When customers start messing with their car’s electrical system what I worry about is:
[ul]
[li]Them hooking up the battery backward (+ to the -, - to the +)[/li][li]Hooking up jumper cables backward[/li][li]getting their sleeves or necktie caught in the fan belt.[/li][li]hydrogen explosion[/li][/ul]
As far as procedure goes, I will hook up the cars leaving the donor running. I will try to start it right away. If the battery is only mostly dead, it will start. If the battery is very dead, I will leave it attached for a few minutes with the donor running. In no case will I turn off the donor engine, there is no reason to.
ETA: I see you are a guest here. Welcome to the boards. For the record, I am a professional technician with over 30 years of experience. I have also been a factory technical training instructor for a car company.
The good news is, the damage was minimal. 1993 Mazda Proteges have excellent protections built into their electrical systems, including a little known backup overload protection setup where any surge which makes it past the main fuse is handled by the sacrificial factory stereo.
In my experience yes. There is a voltage drop through the cables. The running voltage of a car is higher than battery voltage. So if i leave the engine running, I am starting at about 1.2-2V higher which will help overcome the voltage drop in the cables.
I’ve seen it recommended that the last ground connection, usually the - terminal these days, be made to the frame away from the battery. There is nearly always a spark when the last connection is made and making it away from the battery reduces the chance of a hydrogen explosion.
I always hook up + to + first. The connect - on the bad car and last - on the good car on the frame in the engine compartment. I’m not sure the order of ground connections is important.
Why did they start making side terminal batteries. I have uniformly found them a royal pain to jump start. And when you go to the store to buy a new battery, not infrequently the new ones have both top and side terminals.
In my experience, I’ve always hooked red-to-red, black-to-ground, good car to bad car, but does it matter in the beginning, good-to-bad versus bad-to-good? I’ve also seen it (usually by someone in a hurry) connect both poles on good car then red and frame on bad car. Is that bad technique?
Definitely. While you’re hooking up the live car, where are the other alligator clips? Are they on the ground, noodling like young lovers? If so, you could short the good battery. Putting the red clip on the dead battery first has the benefit of making sure it’s not touching the black clip (or touching something that is touching the black clip) when you approach the live car. I follow the recommendations of the jumper cable manufacturer: red/dead, red/live. black/live, black/ground.
FWIW my cables are similar to these where the positive and negative cables are joined. So when connecting the cables go to the dead car, and hold one end of the cables in my left hand, making sure the clamps don’t touch.
I then connect the other end to the positive and to a ground on the dead car. I then move to the good car, connect positive and then the negative to a good ground. (not the battery)
After the engine starts, I wait a few seconds, then disconnect in the reverse order, again taking care not to allow the clamps touch until the other battery is disconnected.
ETA: Bryan while the chance of a hydrogen explosion with a good battery is slim, it is still >0. Connect the negative cable to an engine / chassis ground on both ends. That way if you go to disconnect the cables and grab the wrong end, you won’t risk a hydrogen explosion.
This is true. Also, if you have nice heavy cables, and the dead car’s battery is REALLY dead, then the alternator is working very hard. Allowing it to do so at higher rpm keeps the fan/blower built into the alternator moving lots of air, which can help avoid burning up the doner alternator.
It should be pointed out that under no circumstances should any attempt made to charge or jump a frozen battery. And the battery electrolyte “acid” will freeze when the charge is lost.
I also think some of the apprehension against jumping off cars is warranted insofar as it is a very healthy current draw through the electrical system, and cars are full of sensitive electronics these days. So don’t go trying to jump off your friends '57 Belvedere with your Ford Fiesta. Too, a lot of people are penny-wise and pound foolish. After 5 years, any battery is a candidate for replacement. I suspect trying to save $100 has resulted in very expensive repair bills.
I agree with Kevbo that the quality of the jumper cables makes a difference. In my amateur (but long) experience, good quality 4 gauge cables do a better job ( I assume because there is less resistance), as well as being more flexible in cold weather when the batteries tend to croak. I also buy ones long enough to jump cars that are parallel parked so you don’t have to pull alongside or turn around.
I have a question about the frame ground connection. Is it only the dead battery that could produce a hydrogen explosion? Is there any danger connecting the donor battery negative terminal last, and connecting all terminals directly to ensure a better connection? I’ve worked in the ED a long time and never seen an injury from an exploding battery. This is not to say it doesn’t happen, but I’ve often wondered how common it actually is with modern batteries, especially the sealed ones.
So you’re disagreeing with Rick and claiming that jumpstarting is potentially risky enough as to warrant apprehension from giving one (or getting one)?
Good question. I Googled instructions for jumpstarting and I was surprised that every tutorial mentioned connecting the negative jumper cable to the frame of the dead car as the last step. I was always under the impression that the dead battery was the one with more danger from exploding in the presence of a spark, so I thought it would make sense to have the last connection be to the donor car.
Maybe there is a logical reason why connecting to ground of the healthy car does not give as good a charge, but connecting to ground of the car of the low battery car does not hinder accepting a charge?
I’m guessing that there is less danger from the healthy battery, but enough danger not to chance it.
I would say entirely unscientifically mind you, that I believe that the complexity of modern cars electrical system (plus the expense incurred for repair) places jump-starting another car, esp. with the unknown factor as to the true condition of that cars battery and electrical system decidedly in the “iffy” column. It’s not likely to cause damage but the possibility is there, even if everything is done right.
I have a perfectly fine running pickup that I use occasionally that utilizes only a generator and a battery for the electrical system. That’s it. The voltage regulator has mechanical points. There is simply very little to go wrong with such a system, it is very robust from that standpoint.
Modern cars have all kinds of “fusible links”, ICs and electronic control devices that run on relatively tiny voltages and at low current. Not supposed to be affected during a jump start, but why take chances. Just speaking generally, voltage spikes, sags and surges aren’t something that I want to subject a pricey car to, just on general principles. Car batteries are probably one of the most abused and ignored components on a car. Given the expense and complexity today, I wouldn’t try to eke out that last bit of oomph out of a battery, but replace before failure. I picked up a portable battery “jump starter” combination air-compressor (plus flashlight) for around a hundred bucks, which avoids this problem altogether. So does a “trickle charger”.
