Charging battery with alternator

[JDgreen227]

OP here, excellent post, Jake Brake....:thumbsup:

 

[BobRip]

I think we need to distinguish between a discharged battery and a defective battery.

The OP left the ignition key on and the battery discharged completely eventually. If he jump started the tractor and let it recharge on the alternator, the alternator would put out maximum amps, which may damage the alternator.

On the other hand, most of today's "maintenance free" batteries fail suddenly with no warning. In other words, it starts fine one time and then next time, maybe five minutes
later, it's dead as a hammer. In most cases you can jump start the vehicle and move the vehicle to a convenient location. When you try to start it again, it's dead. In this case the battery will not take a charge. "Maintenance free" batteries almost always fail open. The battery is open even if you can measure 12VDC across the battery terminals. So, the alternator cannot charge the battery and will not have an excessive amp drain. So the alternator should not be harmed by jump-starting and moving the vehicle to a convenient location.

By the way, the "maintenance free" battery on my Kubota is over 6 years old. I start the tractor in the barn and I don't turn it off until it's back in the barn.

I worked with industrial lead-acid batteries during my working career. These batteries are never allowed to discharge completely. If the batteries do discharge completely during a natural disaster or some such, the batteries are recharged when power is restored but replaced as soon as possible.

Jake. I don't think the alternator will put out max amps for very long. At idle the alternator will only put out limited amps. Alternators only put out rated amps with the engine reved up. Also the battery voltage will quickly climb to limit current.

 

[Soundguy]

"Maintenance free" batteries almost always fail open. The battery is open even if you can measure 12VDC across the battery terminals. So, the alternator cannot charge the battery and will not have an excessive amp drain. .

that in and of itself can also be an issue.

an unloaded alt / vreg can suddenly spike with changes in the vehicles electrical load. ie running with lamps on alternator with an open battery, and then you turn lamps off.. load suddenly drops.. v can spike before reg makes a recovery and clamps it... not great ont he rest of the electrical system IMHO..

soundguy

 

[Soundguy]

Jake. I don't think the alternator will put out max amps for very long. At idle the alternator will only put out limited amps. Alternators only put out rated amps with the engine reved up. Also the battery voltage will quickly climb to limit current.

i think you may be surprised about an alts rated output vs rpm..

dc generators are terrible about low rpm charging.. alt's on the other hand are quite efficient at it.

soundguy

 

[BobRip]

i think you may be surprised about an alts rated output vs rpm..

dc generators are terrible about low rpm charging.. alt's on the other hand are quite efficient at it.

soundguy

I looked this up. This link Alternator Output vs. Engine RPM
Shows that at 575 rpm engine speed the output of a 63 amp alternator is only 16 amps. Yes they are better than generators, but they do drop. At idle and a few loads on you may be discharging your battery.

 

[jmurray01]

What Bill is doing is 100% correct.

An alternator should never be used to charge a battery from dead.

OK, if you are away from home and the only way to get going again is to get a jump start, fine, but if you have the means of putting the battery on a slow charge, do it!

An alternator is designed to keep a battery topped up, not charge it from flat, however if will charge it from flat if necessary, but that doesn't mean you should let it.

 

[Soundguy]

how many cars you got that idle at 575 rpm?

all my vehicles are around 800.

specs i see show up to 60% of rated amps at normal idle speeds.. least a 10/12SI gm does..

soundguy

 

[Soundguy]

An alternator should never be used to charge a battery from dead....

...An alternator is designed to keep a battery topped up, not charge it from flat, however if will charge it from flat if necessary, but that doesn't mean you should let it.

yep.. just like.. you can pull a choke knob and choke an engine to shut it down.. but it's not a good idea..

 

[JDgreen227]

What Bill is doing is 100% correct.

An alternator should never be used to charge a battery from dead.

OK, if you are away from home and the only way to get going again is to get a jump start, fine, but if you have the means of putting the battery on a slow charge, do it!

An alternator is designed to keep a battery topped up, not charge it from flat, however if will charge it from flat if necessary, but that doesn't mean you should let it.

Pretty hard to find an outlet for a charger many times, so to say I am 100% correct is not always right. And how many of us carry a charger around? So far I have not seen anything about how much a charge jump starting puts back into a low battery, although one member said it's a good idea to connect the two batteries together for a period of time and let the good battery charge the run down one.

Problem is, in the very rare cases I have asked a stranger to help me jump start my vehicle (once in the last 25 years) I pretty much hate to ask them to stick around an extra 5 or 10 minutes.

 

[Mark Page]

I've jump started other vehicles many times. If you hook up your cables and let the charging vehicle run for 10 or 15 minutes the dead battery will absorb enough juice to put a lesser load on the charging battery when you start it. I can't say I've ever had an alternator problem as a result.
Chances are I'll be replacing the once dead battery in short order.