Charging battery with alternator

[JDgreen227]

Guys, I left the key switch on my JD on and ran the battery flat, thankfully it has been unseasonably warm recently so the fully discharged battery never froze. I have a charger on it right now, and am going to let it charge that way instead of starting it up immediately with the boost feature on the charger.

In the past I have read that the quickest way to ruin an alternator is to use it to recharge a dead battery, but what about the motorists who run their battery down and get a jump start, and then use the alternator to recharge the battery? Does a jump start actually put enough current into the run down battery so the alternator isn't damaged?

 

[Willl]

In the past I have read that the quickest way to ruin an alternator is to use it to recharge a dead battery

I have never heard of this. Links please.

 

[irwin]

I have never heard of this. Links please.

Hiya Willl.. It's something I've heard about for many years. The typical alternator is designed to keep a battery fully charged, not to charge a dead battery..this puts a load on the diodes and can overheat them (at least that's what I've been told by the electrical motor sales representative from NAPA..(not the counter person, I run a auto repair shop and we get visits from representatives of part supplier main office)

Many alternator boxes from parts store state "do not use an alternator to charge a dead battery, use a battery charger"

This doesn't mean you can't get away with doing it, people do it all the time, but it's not recommended by the manufacturers.

I don't have time to do any real research.. but there is anecdotal info that's easy to find.

Will I damage my alternator by using it to charge a flat battery?

 

[Fixemall]

I agree with Tim, today's electronics suck out a lot of juice and usually the manufacturers put in just big enough alternators to barely cover, the exceptions being Police pkg and heavy service systems in trucks. If I were in your situation I would charge the battery then take it in to be tested, if it fails I'd be spending the money for a new one, no sense in making a small problem bigger.

 

[JDgreen227]

Hiya Willl.. It's something I've heard about for many years. The typical alternator is designed to keep a battery fully charged, not to charge a dead battery..this puts a load on the diodes and can overheat them (at least that's what I've been told by the electrical motor sales representative from NAPA..(not the counter person, I run a auto repair shop and we get visits from representatives of part supplier main office)

Many alternator boxes from parts store state "do not use an alternator to charge a dead battery, use a battery charger"

This doesn't mean you can't get away with doing it, people do it all the time, but it's not recommended by the manufacturers.

I don't have time to do any real research.. but there is anecdotal info that's easy to find.

Will I damage my alternator by using it to charge a flat battery?

Thanks, I was searching for a good link and saw that one you supplied. I am rather skeptical of what searches turn up, just wondering if anybody here on TBN had real life experiences with the situation. The part that most interests me about the issue is just how much charge a jump start puts back into a low battery.

 

[Cat_Driver]

I even saw a set up where a guy used an electric motor connected with a fan belt to an alternator all bolted to a plank of wood as a battery charger.

 

[JDgreen227]

I even saw a set up where a guy used an electric motor connected with a fan belt to an alternator all bolted to a plank of wood as a battery charger.

My biggest charger puts out a maximum 10 amps, most alternators put out about 60-70 amps, would be interesting to compare the two methods side by side and find out the difference in charging times...!!! Also have to wonder just how fast the electric motor on that jury rigged setup is turning the alternator as compared to the OEM belt driven speed.

 

[Soundguy]

IMHO.. jumpstarting a car with a truly dead batter is a bad idea.. 'BOOSTING' a car with a battery just too weak to start is quite a bit different.

remember.. it's not just the charging that the alt has to do.. but all the onboard power hungry electrics. lamps, etc.. etc...

soundguy

 

[boomer1025]

I've seen it, what happens is the alternator burns up trying to charge a dead battery. Alternators are not made to operate for long periods at max output like charging a dead or very low battery. Another thing, an alternator won't fully charge a very low battery, it will being up the voltage to a point and the battery will work, but won't be fully charged. So if you have to jump start a battery to get a vehicle running fine, after you get home or done using the vehicle, put a charge on the battery and top it off or there is a good chance the voltage won't stay up.

 

[MF 1532]

I have always been told , an alternator will never fully charge a battery . The last place I heard it was from my Interstate Battery rep . and in their magazine .