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jumpstarting...can it kill alternator?

I have heard that jumpstarting a car with a bad alternator can kill my this true and why ?


  • edited October 2009
    I do not think so. The power for the jump start mainly come out of your battery not from the alternator.
  • edited October 2009
    This came from the experience of many drivers who jump started their cars and then let them run to have the alternator charge up the battery. Modern alternators are not very good at this and many have a warning on the box that says: "This alternator is not a battery charger".

    The best way to charge up the battery is to use a charger in the first place, or, after running your errand, shut thecar off and hook up a regular charger. I carry a spare battery booster in the winter, just in case.
  • edited October 2009
    maybe I didn't clarify my question... will jumpstarting another car ,that has a bad alternator , damage the alternator im MY car?
  • edited October 2009
    No, as long as you do it correctly. Otherwise, all bets are off.
  • edited October 2009
    As long as you use a battery cable prophylactic, you should be safe.

    Seriously, no it shouldn't. Nothing on your car should take any damage unless you hook up the jumper cables INcorrectly. (I stand corrected.)
  • edited October 2009
    I think Whitey meant "incorrectly"..
  • edited October 2009
    did some other research on the subject,... here is what I found so far....

    Well, yes and no.

    If your car is jumping the dead car, here's what happens. Let's say you put the cables on correctly. The instant you finish the connection, your alternator senses the new load and wants to put out a full charge. But if you're doing the jump with your car just idling, your alternator isn't turning fast enough to put out all it can. So, it heats up. And yes, you can end up burning out YOUR alternator by jumping someone else's car.

    Even if you get in your car and rev the engine, you're still asking your alternator to become a battery charger--something is isn't designed to do for any length of time.

    This is a case where being a good friend can end up costing you hundreds of dollars.

    You could try leaving your engine off and just jumping with your battery alone. Leave it attached to the dead battery for about 5 minutes. That shouldn't drain your battery all the way and should give the other battery enough of a boost to get it to start. Then you can start your car and drive it. The key word is drive it--to get the revs up and keep it cool.

    Best way to jump a car is with a booster pack.


    I'm a retired ASE Master/L-1 Technician. I still keep current with the latest automotive technology. Visit my blog for cool articles and TSB's: http://free-auto-repair-advice.blogspot.?
    2 years ago
  • edited October 2009
    I'm still not fully convinced, but I will say that I have had a couple of situations where I had an alternator start to go out a few days after giving a jumpstart. I think it does have something to do with the fact that the alternator is usually never subjected to the current draw from engaging the starter. I think it's probably only an issue with marginal alternators that were on their way out anyways.

    Like I said, I'm still not 100% convinced, but now I'll only charge someone else's battery with my engine running or give them a jump with my engine off.
  • edited October 2009
    The broken link is how does the alternator "wanting" to put out max output cause heat? I can see an alternator actualy putting out max output cause heat but just "wanting" too, leaves me scratching my head.

    As a tech I expect you to identify exactly what part of the alternator is "burned up" vague statements are to be expected from the general public but you should know better.People read what you write and you are held to a higher standard than the layman.
  • edited October 2009
    Interesting. I'm pretty sure that happened to me, years ago. I jumped someone's car with my '71 Datsun 510 and a couple of weeks later, the charge light comes on and I have to get a rebuilt alternator because the diodes had been fried. I always suspected that the jump did the damage, and I never used that car to jump start anyone else again.
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