Actually ,due to both reasons…the alternator is NOT supposed to charge a DEAD battery for one, due to heat , and ofcourse because of the possibility of an internal defect in the battery…use a jump box…AAA does , and any reputable towing service will as well…when was the last time you saw a AAA service vehicle or a tow truck with the hood up and jumper cables out ?
I agree the warnings are there and I agree that occasionally an alternator will fail after jump starting a battery, but nothing in this discussion explains why.
If I have a 100amp alternator, it means it’s designed to drive 100amps of accessory load in the car while I’m driving down the road. It also means it’s regulated to not produce more than 100 amps.
If it spending those 100 amps charging a battery or providing juice for all the electrical accessories today’s loaded cars have, it doesn’t know the difference.
For learning purposes, I’m just trying to understand what the weak link is in the alternator or what part commonly fails under these conditions. I’ve repaired many alternators (years ago) and I’m curious. Saying “heat” isn’t enough.
"If you read the instructions when replacing an alternator , you will see that the warranty for the alternator will be voided if the battery is not replaced as part of the alternator replacement for this very reason."
I won’t and don’t dispute that some/many alternators say this. However, you should be aware that this is not a universal issue. It depends on the car. The 150 Amp alternators used in my cars carry no such warnings. The car’s electrical system consumes about 50 Amps or so, that leaves 100 Amps for battery charging. That’s more than most batteries can consume, so the alternator is never maxed out.
well Joe , do as I did , and do a thorough search…that was only one article I read concerning this , and I recall reading in another article that the diodes can fail due to excessive heat…as well as windings and other components within the alternator … thats the best I can offer you…thanks for your reply ,… if you can find more info concerning this , I want to learn as well
This really is outside the realm of true. Some may believe that a circuit will sacrifice and die in order to meet the load demanded. In truth electronics are too stupid to do so. They just put out the juice and hang the volts until the battery holds the voltage. They do not overheat since they are current limited. The alternator never burns out this way. A dicey regulator may but the current allowed and called for is not that big. Maybe jumping a 800 hp diesel from a ford focus might do this but electronically very much unlikely.
Yes a bad voltage regulator on the jumping alternator can be killed but was nearly dead already. I have never spent more than $130 dollars for an alternator and that includes my several mercedes, renault, vw, ford, chrysler, and volvo cars over the last 30 years.
Hmm never seen this in an alternator warranty and since autozone was the seller you would think they would have talked me in to that as well.
The diodes WILL NOT overheat in five minutes of jumping. Check the manufacturer spec on these diodes. They are ROCK SOLID and seriously overrated and have large heat dissipation built in. A five minute jump will NOT kill these components. The winding on the alternator is 1.5 times rated above the regulator current and will not die without existing internal damage. These units are built to last 100k miles and usually do. The stuff on the net can be less than true.
If it got any deeper, we would need hip boots to get through this thread…
Alternators are rated in AMPs. 40, 60, 80, 100 amps. They are limited by current, voltage and heat to protect themselves from the problems caused by overloads. They are not fragile, delicate things easily destroyed by asking them to produce maximum output for a few seconds. They are designed to do that.
Alternators do not have to put out their rated output to still be considered good. My text lists 10amps less for todays alternators but earlier generation alternators were given up too 75% of rated output before they were called bad.
I can’t put the secondary parameter of the OP post in its proper place, I like to say "jump starting a car that has a totaly dead battery may not be sucessfull and will stress the “jumping car’s alternator”, that one I like (notice I did not say “burn up” the jumping cars alternator)
Lastly manufactures provide terminals for jump starting their cars, this puts more than a quasi blessing on jump starting.
Unrelated but if the alternator cannot provide the needed amperage to operate all systems selected the battery starts to be used as a source.
The alternator can get very hot when jump starting. Don’t do it unless you have to.
It can kill both.
My company rebuilds and repairs alternators, starters, motors and carburetors.
I charge $35-ish to replace regulators damaged from jump starts several times a day–from jumpers and jumpees.
Small car alternators max out at about 90 amps. Trucks top out around 200 amps stock. A battery that is dead from powering headlights all day could easily draw 1200 amps. A small starter can easily draw 140 or many more amps.
Alternators actually produce 3-phase alternating current (hence the moniker). A set of diodes (rectify) correct the direction of current and a regulator limits its minimums and maximums to something resembling 14 volts DC. In modern alternators, regulators and rectifier diodes are small, cheap internal components of the alternator, exposed to all the heat generated inside the frame.
In normal operating conditions, the alternator experiences little resistance, a few tens of amps, generating manageable amounts of heat. When you hook up a black hole of current like a dead battery, the regulator first fights extreme fluctuations in voltage, then an extremely heavy load on its out side, as the whole system rapidly heats up far beyond tolerances.
Alternators with blown regulators sometimes actually continue to charge, only at absolute maximum, with voltages reaching 40 volts dc and random AC voltages depending on rotation speed. This does strange things to electronics. Strange things like fire.
A typical regulator is about the size of a 3-pack of durex condoms. It has about the same level of heat tolerance, too.
To jump a car, I disconnect both batteries and jump them together for a couple minutes, then reconnect the donor battery and start the donor car and idle high for 10 or so minutes. Rinse and repeat.
Best bet is a charge. If he wants to use a jump box, its his alternator.
To illustrate (these are large images):
Here is an exploded view of a fairly heavy duty alternator, standard 10SI:
http://img217.imageshack.us/img217/2433/dscf0277.jpg
note the three small pieces under the front housing in the upper right.
Here is a close up of those important components. 1. Diodes, 2. Brush holder, 3. Regulator.
http://img263.imageshack.us/img263/6599/dscf0251copy.jpg
Heavy duty indeed… A good drop on the floor ruins the diodes.
Tester
“If the battery is “only used to crank the engine over” then why cant I disconnect the battery, and continue operating the engine, after it’s started?”
I did this once many years ago on a 72 camaro. My brother’s battery was stolen, so we jumpstarted it and drove it home on alternator power only.
This is not advisable with computer controlled engines since the electrical system voltage will vary excessively.
“A battery that is dead from powering headlights all day could easily draw 1200 amps.”
This is B.S., pure and simple. Not even a fork-lift battery can draw or provide 1200 amps…Regulators are damaged when careless people hook jumper cables up backwards. Modern alternators protect themselves against overloads. Warning labels like those shown below are designed to limit warranty claims against poorly designed or rebuilt alternators.
“A battery that is dead from powering headlights all day could easily draw 1200 amps.”
Let’s assume that battery is at 0 V (It would never recover, usually the battery would only be drained down to 10 volts)
Let’s assume that alternator is set for 15 volts (normally it would be 14.2)
To pump 1200 amps from a 15 volt source into 0 v, the resistance of the wiring + the internal battery resistance would have to be no more than 0.0125 ohms. There’s no way that going to be true. There’s more than that in just the battery cables.
(In the more realistic situation of 14.2 volts into a battery at 10V, total resistance would have to be less than 0.0035 ohms. sporkme, you must have some magic batteries and wiring.)
If the car senses the load wouldn’t the PCM just tell the IAC to raise the idle to meet the demands.
Over the years I’ve jumped started my cars many times with no problems. But one day, very much in a hurry, I reversed the negative and positive jumper cables on my 1994 Camry XLE (loaded with electronic junk). It cost me $800 to get it working again.
The last time I made that mistake, it cost me about $60 for a new voltage regulator (on a car that had a separate voltage regulator).
I understand that the voltage surge from jump starting can damage the ECM and PCM. The solid state devices are not designed to sustain this surge. Has anyone else heard this? I certainly agree that certain solid state delivers can’t take a surge, but it seems to me that this could be avoided by buffering the electrical circuits so that the voltage surge is stopped before it runs through the entire system.