Maybe I would use my wife’s new car like that in a jump situation……but I have been jumping vehicles with the rescue vehicle running for nigh on to 30 years now without causing any damage.
If a donor vehicle is running when giving a jump start the excess voltage going into the recipient vehicle causes the circuit board in the ECU to overheat. If the excess heat doesn't kill the ECU, it at least degrades it. Excess voltage causing overheating can also degrade resistors, capacitors, diodes in other electronics.
@@nunyabidness323 Are you saying that your vehicle got a jump start from a vehicle with an engine that was running during the jump start process? If yes, what problem did your alternator develop after that?
@@LoneTinaja I have no way of knowing, but it makes me wonder. I should have phrased it better. I have jumped cars with the car running. I have had to replace starters and an alternator. This just made me wonder that is all. I would think modern cars have safeguards to prevent damage.
@@LoneTinaja Funny, he obviously already had a flat battery, jumpstarted it, and immediately found the alternator wasn't working. I think the alternator was already stuffed.
Ive heard this for 40yrs and have never seen a battery blow up, had electronics destroyed, etc. I have had them jumpstart with no problems...ever. I guess there might be a first time for everything. Still find this channel informative.
Yeah exactly. I know a guy, who knows a guy, whose aunt heard once that somebody blew up a fuse doing this 😂 There is always a corner case that can cause a problem in theory, but it is so rare and dependent on pure stupidity that it never happens.
This is why you don't listen to people who "think" they know why or why not. Parallel connection will never go higher than the highest source (which should be 14.4V). Meaning the video is dead wrong and you Mr Ego are correct
@@MrVincemims And when you have a 1 volt difference between the higher source and the lower source, connected by 50 mOhms what would be the current flowing? And what would happen when that current is interrupted?
And here's me with a vehicle with twin alternators and solar system feeding the same common grounded system with both 12v and 24v in the same system. That being said, modern cars, if you dont have surge protected jumper leads, the ecu might not like the voltage drop/spike
Not I but it makes sense and would still start the manner he explained. I do like the idea to keep the good car connected for 10 minutes and then try the dead one. I also used to hook up the ground to the battery post and have read massive warnings about it..but never once had an issue.. so it's kinda cautionary tales. The alternator thing doesn't make sense because doesn't the nature of the battery 'regulate' that type of influence??
I do that if I'm jumping a motorcycle, lawnmower, etc with a car. You can overpower it and pop the fuse. Yes, I learned what I did wrong after the fact. If it's comparable sizes, like car to car, it should not be a problem.
Right on a bike you pop fuse but cars we all used letting both run,I think with new cars things are changing , I think you have a regulator and the dead battery going take the amps away
But it makes perfect sense does it not… not precisely what he said “turning against each other”, but they are separate circuits each monitoring voltage and each attempting to correct. It’s bad enough to jump start a car period
What Scotty is saying will not happen. Both alternators have built in regulators. Every other circuit in the car has a fuse to keep an overcurrent from ruining the electronics. This is just an old wives tale.
@@lubrew5862 the regulator can’t protect against a load-dump voltage spike, it actually is part of the problem, and since fuses are over-CURRENT devices (as you correctly say), they won’t protect against a **voltage** spike.
If you are jumping someone else's car, YOU SHOULD HANDLE THE CABLES yourself. Do not let them handle the cables or they can carelessly remove the cables and put both cable clamps together, thus shorting your car out.
Can't find any tech basis for that. The two alternators are dc generators, any excess or spike would be sunk in the batteries, one of which is even empty.
Being a construction equipment mechanic for over 30 years,I've never had that problem...But I'm not saying it couldn't happen because anything is possible.
because the mistaken perception that if the engine is running and spinning the doo-dad that makes electrons, power will magically flow out of it and if you rev the engine enough you can start anything
The spinning alternator output is AC, which gets rectified to DC by the diodes in the regulator. The 2 AC outputs should never meet. I must've Jumpstarted dozens of cars over the years or seen them Jumpstarted with donor car running. Never, ever seen or heard of a problem.
…except when one alternator is malfunctioning, with a burned diode or a regulator that isn’t regulating. I think that is the one thing everyone is missing here. It doesn’t happen often, but it can happen. If I’m giving the jump, my car goes off before you try yours.
The difference between Alternators and DC Generators is that the Alternator only gives you 1/2 the sinewave. The DC Generator might rectify the output to give you DC. The DC Alternator puts out DC but it will Pulse, which is bad for Electronics and your meter thinks it's AC. A DC Generator has Brushes that wears out. So they use a Brushless AC Generator and rectify it to give a DC output. With an Alternator they just chop off 1/2 the wave. To save money.
As an electrical engineer who has done this wrong multiple times... He's absolutely right. Having 2 different devices trying to regulate voltage connected together is ALWAYS a recipe for disaster, and it's honestly incredible to me that it doesn't cause more issues now that I think about it.
Wouldn't it be because the battery is absorbing the current due to it being the path of least resistance? That's why there's virtually never an actual problem?
As an electrical hobbyist I can tell that the battery will act as a buffer so there is no danger of anything going bad here. Except maybe flat battery charging too fast as it will be fed from 2 alternators not 1.
As long as the battery is connected properly on both cars, the voltage will be regulated thus no issues whatsoever. I’ve done this for 20 years. Including my Toyota that has over 450,000 miles.
This is very true for modern vehicles, but not ones on the older side, or somewhat older. Most people have at least a somewhat newer vehicle. Scotty is 100 percent correct.
@@lawrencehenry1326 You have both been doing it correctly, I must in this instance strongly disagree with SK on this on as an electrical/electronics engineer. There will be a short lived bus swing as the voltage heads skyward but the voltage regulators will pull it in within about 0.5ms. SAE and ISO standards specify an automotive electrical system must be able to withstand voltage spikes for up to 60 seconds.
@@peterpeterson9903 this is a failsafe implemented in the last few years in an attempt to force a person to return to dealer for repairs car manufacturers will suck you dry.
Never knew two alternators could spin against each other. Usually they spin with each other (meaning they increase the amperage output capacity but still remain within a 12-volt system). They don't short each other out.
Scottie is a typical old fashioned mechanic...he wouldn't understand electronics/electrics if it smacked his bottom for him. You want the donor car running before you connect the jump cables and you want to rev the donor car to normal driving revs before trying to start the other car
Usually the car being jumped, the cables are being diconnected as soon as it's running. I don't really see the issue here. The systems are connected for a very short time. I see your point, but people have been doing it for years. I know, you'll say cars have changed and yes they have, but for those couple moments that cars systems are connected, can any real damage occur in such a short period of time?
I think what he's saying is, if there is a problem in the electrical system of the car being jumped, it can cause damage to your alternator if you have it running when you engage the starter of the dead car. I always try to check the voltage with my multimeter, to make sure I'm getting the full 14 volts through the cables first, and to the battery second, before I ever even bother trying to crank the dead car. Because most of the time a jump fails, it's because there's a poor/incomplete connection, and there's no way to really know that without checking the voltage with a meter. You can waste a lot of time waiting for a battery to charge, when you're not getting full power flow, through the cable to the dead battery.
I'm 75. Been jumping cars since I was 14. Always did it the way he said not to. On a cold day I didn't take a chance on my old 55 Ford not starting again so i left it running until We got my friends old 54 Chevy going then we ran them around for a while to charge everything up. Good times.!
me too. nothing ever bad happened, except the one time I jump started a saturn vue, but that thing was an electrical nightmare. I guess it's ok to do it the "wrong way" unless you have an old pos chevy, ford or saturn with problematic electrical systems..
Not regarding alternators spinning against eachother he isn't. That's total guff. However, letting a booster car charge a dead car up a little first is definitely good advice.
Yeah, I'm also curious as to why this is bad. The amp draw shouldn't do anything bad to the donor alternator. The alternators don't make alternating current that would be out of sync with each other, they make dc current. The batteries do a majority of the load. I suppose you could say that a dead battery could be a sign of other things that could be seriously wrong and you wouldn't want that to affect your vehicle. I don't get it yet.
Maybe if you have a luxury car like a Ferrari maybe ?? It’s too risky to start it with your car running ? I’ve always done it like that and no problem whatsoever. The point may be accurate but perhaps it causing damage is extremely rare …I’ve never seen anyone have problems with it 🤷
Yes. When you’re stuck rather than have someone jump start you, walk to the nearest store and purchase a jump box. Do you think at ALL before you comment?
@SonnyGTA you clearly don't think before you comment. He is saying to have one in your trunk on hand for just such an occasion. Not to go buy one when you need one. "Better to have and not need, rather than need and not have"
@@junito1008 I watch them here an there. Honestly the shorts get my attention but usually aren't relevant to my vehicle then he says things like this when I know my jeep wouldn't ever start from a jump wo a more powerful battery or a revving engine.
That’s because you should do it wil the alternator on your jump start is supposed to charge the battery to running voltage 14.4 v otherwise you risk. Overloading your good battery
He’s actually saying to connect the wires first, THEN start the donor car. Run it for 10 minutes. Shut it off. And then start the dead car. (For ppl that interpreted what he was saying to jump it without starting the donor car at all.)
Just saying. I ran a side business for 15 years slinging used yard eninges into blown junk and rebuilding wrecks. Over 100 engines/transmissions swapped here. Never a problem.
Scotty is wrong here, the alternators wont spin against each other, whatever that means...they have voltage regulators, once both cars start there will be 14volts across both batteries coming from both alternators
When you hear the words “Can” or “May or May Not” it is up to you to do your own research because almost every profession out there relies upon repeat customers. They will use scare tactics like Scotty K. did here 🤨.
@@Yonder27so, him giving people free advice, is somehow inherently wrong; you believe somehow he has some hidden agenda? I don’t get where you’re coming from.
@@TURTLEORIGINAL Regardless, what Scotty says about the two alternators working against eachother is nonsense. However, his advice for letting the booster car put some charge into a car with a completely discharged battery before sterting is spot on. Less strain on the alternator of the vehicle with the discharged battery.
Don't be too hard on him he's spent his time learning mechanics, I've spent mine learning electronics. Its good to learn from each other. And no one is too old to learn.
Scotty has been a mechanic for over 50 years, so i think he probably knows what he is talking about. He's also referring to "modern" cars, with sensitive electronics and computer crap. So there's that. Also, for everyone saying, "I've been doing it "____" way for years, no problems!". You can cross a street with your eyes closed a million times and live to make it to the other side, it just takes that one time. 🤷♂️
That's the argument from authority fallacy. You can be wrong for an unlimited amount of time. You can damage the electrical system by giving jumps, but that's not the argument made. It's that the two alternators running causes a problem. They don't. My advice is always double check claims whenever possible. Is there support for what scotty is saying? Not that I can find.
This gentelman is mistaken. He might be a good mechanic but his electrical knowledge is based on rumours rather than understanding of electrical circuits. The only risk here is that the flat battery could be charging too fast because it will be receiving power from 2 alternators but that is unlikely to cause problems if done for a short time (couple of minutes). Alternators "don't spin against each other" and electronics damage part is completely made up.
@@SpiderKidwarzone yes, it makes perfect sense for anyone that knows how to read. There wasn’t anything complex about it. If you’re having trouble with that I would suggest you start over in kindergarten. Also, thank you for identifying yourself as a child. LOL. This explains so much. 🤣
He’s right. Don’t ever leave the donor car running. It wasn’t even cool on old school vehicles because you could wind up frying a voltage regulator or occasionally rectifier on an alternator.
it's like when they say to remove the negative terminal when doing anything electrical even tho the likelihood of something going wrong on lets say changing a bulb is next to nothing but there is always that chance
It's true on modern vehicles! But not on older or somewhat older vehicles. Most people own a newer or somewhat newer vehicle. Scotty is 100 percent correct!
It's really best to charge the dead battery offline to bring it back to full charge, because if the battery is really bad and draws an excessive current from the started car's charging system, it could overload it from the excessive charge current and cause damage to it. But, being an unlikely situation and in interests of time, no one will ever go that route and simply start and go. Millions of people can't be wrong 😉
@@slackersurf not always. For some reason (electric fuel pump or ECU, maybe?), sometimes you just can't. I'm certain of that because one year ago, a Nissan np300 got its battery drained by the lights. At the end of the work day we tried bump (push) starting it several times, with no luck.
This is sooo true! It happened to me yrs ago, and because of that, I never helped jump start another vehicle (although I wanted to.) Now that I know the proper way to do it, I will give it a try! Thank you!!
I kinda rushed my message. I do remove as fast as possible.. I'm a little paranoid. But what about cases where you have to Rev the Engine to get some extra power???
Scotty what you are saying makes sense in theory and you are probably right no doubt but I will say I have been jump starting cars the wrong way for 40 years and never had an issue. With that being said I will probably do it your way from now on to avoid the outside chance of ruining some electronics.
If only the cars had bridge rectifiers to convert the alternators AC voltage to DC voltage so you hook them together, share potential, and function as one DC system.... oh wait. 😶
No need, I am 40 and I have busted this myth many many times, now something real is on most vehicles especially side post cars have a spot to hook cable terminals to rather than trying to hook it to battery posts, but this alternator spinning thing, never heard that before
Can you explain how the alternators "spin against each other" please? This doesn't sound like it makes sense. Surely they are working in parallel to both contribute to charging both batteries?
@@bladi496 No, if they were in serial it could be 28 volts, but they're in parallel, so they won't be. The current could theoretically be doubled, but that's not likely to be an issue as long as the jumper cables aren't made of thin CCA chinesium. Long story short, this is a case of Scotty talking absolute nonsense and he does it with such assuredness, it begs the question of what else does he talk nonsense about with confidence?
They spin in opposite directions causing massive drag. It will literally make the cases white they get so hot. Then both cars become positively charged and explode. It’s crazy to see in person.
Good tip. Thank you. The clarification I need is it’s ok to run the donor car to help charge a dead battery as long as you turn the donor car off before attempting to start the car with the dead battery.
I'm quite unsure of this. If you are to jump start a car with the donor car's engine off, the dead battery will just eat up the charge of the good one which may result in the donor car not starting due to low battery voltage. What I always do is keep the engine of the donor car on, rev it around 2k rpm for a minute or two, start the car with the bad battery and if it does start, disconnect the jumper cables almost immediately and let the alternator of the recover charge the battery. I also advise the other car to rev the engine or leave it idling for a few minutes before turning on any accessories and before driving. Works like a charm all the time with no issues.
Don't have both vehicles started at the same time, it will fry electronics, or one of the alternators. This is not true on older or somewhat older vehicles tho!
One good advice, NEVER connect the black cable to the negative (-) terminal on your dead battery, this is very dangerous and could result in a possible explosion. 👋🏻😊 Thank me later
I mean theres some logic to it maybe with a smaller vehicle like a motorcycle or lawn mower that happens to run on a 12 volt system... that being said ive never had an issue lol
@@jamesmize665 your just lucky, I thought it was common knowledge, I've known this since I was a teenager beginner home garage car repair enthusiast in the mid to late 1970's .
I have jumpstarted many many cars over the years. Never had an issue with having the car run. In fact I actually have had cars not start if the good battery car was not running while connecting and then it had a very weak start because the cranking of the dead car almost killing its battery. I use the good car alternator as a somewhat charger.
You are correct…. But the key to good jump starting is 1) good strong cables, thick gauge, not those wimpy ones that feel like plastic 2) yes leave the donor car ON for 3-5 minutes minimum to charge the dead car’s battery, maybe even hold it above idle to make the alternator put out max amps. But when it is time to start the dead car, turn the donor car off first. Some folks wanted to do this with me jumping, and I shout NO WAIT!!! Because they aren’t going to pay for my alternator or my electronics if they go down. Also the biggest reason that I just mostly gave up on that altogether and just carry a jumpstart power bank.
It's true on modern vehicles! But not on older or somewhat older vehicles. Most people own a newer or somewhat newer vehicle. Scotty is 100 percent correct!
@@A42yearoldARAB just be careful, you can still pop fuses on old vehicles, but that's easily replaceable! Modern vehicles, all sorts of things can happen.
Gotta be careful with those 3-phase AC to DC alternators “spinning against each other”. Safer to just connect the dead battery positive to your cable coax center lead and the negative to a garden hose. Make sure the water is off though! You don’t want to trip all the breakers in your neighbor’s house.
hey einstien ALL alternators are AC they convert to dc internally. and this proceedure is in every manual ive seen that covers jump starting, as well as all modern shop manuals.
If you actually try to do this the way he's saying the car isn't going to start. Everytime I jumped a dead battery I had to rev the other car to get even more juice to it, never had an issue. Literally if you a hook up a battery jumper/charger it's going to do the same thing.
Sorry, but It's true on modern vehicles! Not true on older or somewhat older vehicles. Most people own a newer or somewhat newer vehicle. Scotty is 100 percent correct!
@@chancehastings6227 I get what he's saying I'm just saying it's not realistic in the real world, 1. Are your jumper cables even thick/expensive enough to carry enough amps. 2. Are you going to find someone who has the time to sit around for 10+ minutes while your battery charges.
The alternator on the dead car isn't going to spin, maybe electricity could run through it, maybe overvoltage? I've never seen damage caused by this and have jumped off cars thousands of times
@@thomascolbert2687 if you crank the car the alternator would spin, but it isn't going to "spin against" the other alternator.. They're connected to the engine with a belt, so if the motor is turning then that turns the alternator.
Scotty is meaning to say with both alternators spinning you will get a voltage and amperage spikes. Which can more than likely fry your control modules. ECU, ECM, PCM, BCM... look them up if you don't think they exist. Then price them out for your car. Still want to gamble?😂
@@pflaffik - As an engineer I believe you are correct. The cables and the wires in the car will mathematically balance things and this problem will not exist. Wires have resistance no matter how big they are and the currents will all come into balance. A problem is very very unlikely.
Back in the good old days, when there weren’t so many computers, I think you were safe to have the donor car running. These days, I make sure all electronics are off on both, just to be safe.
agree.....in the good ole big V 8 gm n ford days, engine stayed running n revved up while dead battery car was being started. worked fine. no damage done.
yeah I think this needs a caveat to your point. I hate the computerized cars.. simply turning on the stereo used to take 1/4 second now it takes 5 seconds just to see it light up.
No don't stay quiet. Call him out. Doing it Scotty's way will leave a lot of DONOR vehicles DOA and two motorists needing assistance. When it's 20 below zero after dark in February with the wind howling that could be a fatal situation. NEVER turn off the donor vehicle as it could be your only lifeline to safety.
I am an electrician for buildings, but as a human being and as a young man that's driven a ton of crummy cars I've had a million jump starts. I have never considered this but after hearing it it makes perfect sense
No it doesn't make sense. Maybe if the two alternators were out of phase sense an altenator makes alternating current but direct current is direct current. There is no phasing
Scottys word means everything. Trustworthy guy and accomplished gentleman. He would not lead you ashtray. His advice is knowledgeable, genuine and caring. Thanks for being for here for us, Scotty!
This is literally mind blowing. It's not electrically possible. I have more questions that I shouldn't have. Sorry buddy. There are alot of us that has been in the game for way to long.
@@pflaffik well actually I remember when I was a kid about 10 years ago, my dad had his car jump started the way that scotty just said not to, and guess what the other car with the good battery had all of its headlights fried out almost instantly when we started my dad's car 😆 so yea scotty is spot on on this one goofy
@@pflaffik are you a mechanic or an engineer? I’ve been in the industry for a long time and know that if you jumpstart a car enough times with it on, it will eventually kill your electronics. It happens all the time cuz people are ignorant
I never knew that as well I've been doing it wrong my whole life there's no telling how many times I messed up an alternator you're a genius Scotty.... why haven't I already known this I'm 55 years old
