Jump Start Destroying the Electronics - Myth?

Discussion in 'The Garage' started by Dan V., Jun 30, 2015.

  1. Dan V.

    Dan V. Been here awhile

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    For the second time in as many months, I felt like a dick for not helping someone who needed a jump start. (car to car). My reason is that I read/heard somewhere that it could cause an electronic killing spike in the system. I don't want to replace the ECU at $$$ for just being helpful.

    What is the truth on this - fact or not?
    #1
  2. Yinzer Moto

    Yinzer Moto Long timer Supporter

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    Maybe if there were no batteries in either vehicles. The batteries should buffer any spikes. Does your owners manual say how to jump start another vehicle?
    #2
  3. dtysdalx2

    dtysdalx2 Knowledge is horsepower...

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    If you reverse polarity accidentally this may cause problems. If not the battery is a huge buffer and should absorb any spikes in voltage. Like TR said. I've never had a fail in my own vehicle jump starting another vehicle before. And the better she looks = it's a good idea to jump her. :D

    I have fried a R/R on my old XT welding on a footpeg though.

    Most new vehicles are built better than yesteryear and can withstand stupid people better ( I hope). :lol3
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  4. Paebr332

    Paebr332 Good news everyone!

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    Earlier this year the battery in my new Toyota dropped a cell. In order to get to the dealer to have it replaced, I jump started it with my wife's Highlander. Both vehicles are LOADED with electronic gizmos. The night before that on the way home from work my car would not start after stopping for gas. Toyota Roadside Assistance came to the gas station... and jump started my car. (I did not go right to dealer at that time since they were closed for the night.)

    Follow the owner's manual and there is no issue with jump starting an electronics-laden modern vehicle.
    #4
  5. 9Realms

    9Realms Drawn in by the complex plot

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    The "procedure" has changed, at least in my experience- many vehicle manuals indicate not having the "donor" vehicle running while you attempt the actual "cranking" of the dead vehicle. I had a Ford Expedition , and was jump starting another vehicle. I thought if anything, having my vehicle running might have taken out the other fellows stuff instead of mine. We needed to get his truck going (cold outside). The day after we had done this, MY alternator took a shit.

    I think what some suggest now is, connect up the cables, yes. Let the donor vehicle run for several minutes, but do not attempt to spin over the dead vehicle. Instead, after several minutes, disconnect everything and attempt to start the vehicle "un-assisted", based on some nominal charge it might have "experienced" in the minutes you left it connected.

    As lame as that might sound, it's the only safe way to hope to not potentially fry something in either vehicle, in my case it was the other fellow's Chevy Tahoe from the mid 90's that crapped out my Expedition alternator, the Tahoe having about 200,000 miles on it, and my Expedition having about 40,000 miles on it. My chum was one of those guys that would brag about getting 8 years out of a battery, and would put up with having to jump or charge it a dozen times before he would reach in his pocket for a cheap battery. I would not trust, believe or assume one vehicle's battery is going to magically even out the HEI (high energy ignition) spikes, it's a poor "filter" as the extra juice is going to flow uphill easily to the first bit before your battery, typically the alternator.

    I think my experience, plus towing, cost me $600 bucks.

    I would not even jump a bike by having the donor bike run during the "cranking" anymore, I think a bike's electronics potentially more fragile, and certainly more expensive to replace, and the cost to diagnose it potentially twice as much once at the mechanic. Just my experience. :deal
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  6. showkey

    showkey Long timer

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    ^^^^^^^^^^^^^^^
    Not going to deep here but if your battery was dead ?........maybe the cause ......alternator was already shit or at least half shit ????

    The last time this topic came up on another forum it had 200 posts.........many making no sense at all.

    I agree with DT.....many horror stories are reversed polarity and stupid people don't not often fess up to their mistakes.

    I have two portable jump boxes ( one large and one of the new compact size). Takes the donor vehicle out of the equation. But you can screw up using a jump box. And some dead cars are already screwed up prior to the jump.
    #6
  7. broncobowsher

    broncobowsher Long timer

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    I have jumped hundreds, maybe even a thousand cars and trucks. Almost all of them late model full electronic everything. I know I have done a dozen in a day multiple times. Never killed anything. And these are not a jump and kick away, they are stuff that is kept around. If something died I would know about it.

    More myth than fact. I am sure that if you really did something ugly you might hurt something. I think the days of doing a 24V jump start on 12V cars is over now (Yes that was common many moons ago).

    I don't worry about it anymore.

    Slightly related, check the jumper cables. most of them are now known as booster cables. Lots of big fat insulation over glorified speaker wire. They won't jump anything that is really dead. They can be used to put a little charge into a battery that was run low (lights left on). Hook them up, idle the good car and WAIT. You are not trying to start the dead car off the good battery, you are charging the dead battery with the running charging system.

    There are the jump start packs, small battery in a tote with a good set of cables attached. They generally work really well, if they are charged.
    #7
  8. falcn

    falcn Squidless Soul Supporter

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    Buy yourself one of those jumper battery packs - problem solved.
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  9. Beezer

    Beezer Long timer Supporter

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    some vehicles (not cars & trucks) have voltage regulators that will try to regulate the donor's generator. that can result in damage to that regulator. of course, it can only happen if the donor is running.

    a properly connected donor vehicle is simply a parallel power source, and assuming you have matched system voltages (like both are 12v), all systems are operating on what they were designed for

    as for leaving the donor running while jumping, that shouldn't matter either. the alternator can only make so many amps, and it needs high RPM to max out. because of inductive reactance in the stator, there is only so many amps you can pull... thats why there is no current limiter in an alternator system like the old style generators had.... alternators are self limiting.


    I agree with broncowasher. and if a battery is shorted or frozen.... it's a waste of time unless you pull it out of the system..... how do I know these things
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  10. MrPulldown

    MrPulldown Long timer

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    Like Bronco I have jumped hundreds of vehicles. NEVER a PROBLEM.

    If you jump a motorcycle with a car though you have to be careful. Car off not running!!!! Otherwise you can fry the regulator rectifier of the bike. Maybe this is what you heard.

    Most issues with jumping cars come from reversing the polarity or shorting out the jumper cables. I connect the jumper cable to the negative post of the battery. I don't use a chaises ground.
    #10
  11. manstache

    manstache Flounder of ADV

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    #11
  12. bisbonian

    bisbonian Long timer

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    I tried to help a guy out a couple of years ago with a jump off my Prius.

    We opened the hood and then scratched our heads trying to figure out where to hook up the cables.

    I'd have looked in the manual but that things so damn thick that I leave it at home.

    So no harm done?
    #12
  13. concours

    concours WFO for 47 years

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    It's a total MYTH. The vehicles electrical system and all it's components are able to handle 13.6V nominal, junp starting will cause NO PROBLEM. The myth is spread by people with no understanding of basic electrical theory. :deal
    #13
  14. Dan V.

    Dan V. Been here awhile

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    That's me. Don't understand much electrical theory :puke1. Oh yeah, the manual... For my 02 Ranger, Ford says to turn on the heater fan of both vehicles, and turn off all other stuff. Keep donor running when ready to start. If the disabled vehicle starts, let them both run for three minutes before disconnecting. Otherwise, the routine is pretty standard.

    Thanks for all the learned advice. Myth Busted :D
    #14
  15. Schnurbart

    Schnurbart Been here awhile

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    This I don't understand, since most electronics have their own separate ground.

    Of course, I'm the guy that'll also disconnect my battery's negative terminal when I'm welding on a vehicle. Some people say there's no way to cause damage that way if you keep the ground nearby your welding. I'd rather not chance it.[/QUOTE]
    #15
  16. bmwroadsterca

    bmwroadsterca RadioFlyer

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    "If you jump a motorcycle with a car though you have to be careful. Car off not running!!!! Otherwise you can fry the regulator rectifier of the bike."

    I am skeptical. Perhaps you can explain why this would be the case? What difference does it make?
    #16
  17. Cataract2

    Cataract2 Where to?

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    Good ol path of least resistance. So, if your ground is not so good the current WILL flow to the best point for it. If that means going through your expensive electronics, well.....
    #17
  18. Beezer

    Beezer Long timer Supporter

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    again.... no problem with a car or truck... you can leave the donor running. every system is designed to run on the same voltage. you don't worry about it when you hook up a battery charger right?

    on the other hand, there are apparently some vehicles that have voltage regulators that can be damaged because of how the work. most "non automotive" regulator systems simply dump excess voltage to ground in the form of heat. some of these systems have limited current capacity. I had an aftermarket regulator on one of my vintage bikes some years ago & it made odd noises & got hot when the battery (in the bike) was hooked to a charger because it was trying to regulate the charger. chargers adjust the charge rate (amps) by changing the voltage. if you tell it to charge at 10 amps, it might go to 16 volts

    on bikes, I generally leave the donor engine off since that experience.

    I know someone that was a jet ski mechanic & claimed to have blown up several regulators by jump starting. also stating that the manufacturer warned it would happen.

    as for welding.... leave the battery in. it's a huge spike suppressor.
    #18
  19. anonny

    anonny What could go wrong?

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    All you are doing is paralleling the batteries, the voltage stays the same, it's like saying you will fry your electronics from upgrading your battery in terms of a/h rating. I don't buy it.

    Most problems come from idiots running the jumper cables.
    #19
  20. der_saeufer

    der_saeufer ?איפה בירה

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    The voltage isn't always exactly the same--different systems that are nominally 12V run different voltages. In theory, if your car's voltage regulator is set higher than your bike's, a shunt-type regulator on the bike could try to dissipate the excess as heat and fry itself. In practice, if you have the jumper cables connected that long, you're doing it wrong or one of the vehicles' voltage regulators is already defective.

    That said, I jump bikes from non-running cars because it's not as if a car battery needs any help to start a bike.

    This is 100% pure unadulterated truth.
    #20