Electrical questions

[Chris_B]

So, if an alternator is pumping out about 150 amps and 14.6 volts how long would it take to charge a 12v 19 amp car battery? or would the battery just fry?
thanks.

[goat]

for curiosity's sake, how did you get the 150 amps figure? Thats a lot of current.

[Chris_B]

A car alternator puts out 150 or so amps, i think :dunno:  but this is what i though when i went on my bike ride a few minutes ago. If it takes one amp hour to charge a 12 volt one amp battery, then, since 19 (we'll call it 20) amps goes into 150 (we'll call 140) 7 times, it should take one seventh of an hour, or about 8.5 minutes? mabye. Im no electician or anything, but this is what i came up with, probly not right, haha.

[The Buddha]

OK what is that 150 amp calculation. Its really not the extra amperage it has. 150 amps will be used to light, power the ignition, brakes A/C and what not ... you prolly have 8-10 amps left, whihc is plenty to charge its battery and yours if you have it hooked to the car and car is running.
Cool.
Srinath.

[starwalt]

So, if an alternator is pumping out about 150 amps and 14.6 volts how long would it take to charge a 12v 19 amp car battery? or would the battery just fry?
thanks.

In short, 150 Amps into a 20 Amp battery would result in boiling battery acid in a few minutes. Too much charge rate. You cannot convert the solution back to a charge state that quickly.

Batteries have different charge rates recommended by the manufacturer. My high tech Shumacher charger will push up to 12 amps into a battery. It also has an 8 and 2 amp setting. If we are assuming a lead acid battery, wet plate immersion type, the charge time will vary on the decision of the engineer that designed the charger.

Each charge/discharge cycle results in a little less lead sulfate deposited back onto the lead plates. Eventually it dies and like Humpty Dumpty, you can't put it back together.

[The Buddha]

Hey I have a related question ...
I dropped a ES14BS (in reality a 12 amp battery) into a virago 1100 whihc is supposed to have a ES blah blah 18 ... which is a 20 amp ... It ran for about 25 miles over 3 days, and like a dozen starts ... and then the final run it ran 3 miles and died ... right with the throttle open ... like someone yanked out the keys ...
The bike felt like it wanted to start back up, but was cranking weakly and didn't start. I had a friend pick it up, sat at his place for 3 days, I bring it home, and it starts and runs like nothing happened. Worse ... makes decent voltage and runs like a top. Then I pull that one out, and drop in a ES20BS battery. Its then run for 2+ weeks and not had any trouble, 130+ miles over 20 or so starts ...
So what you firgure happened then - when it died with the 12 amp.
Cool.
Srinath.

[starwalt]

Hey I have a related question ....So what you firgure happened then - when it died with the 12 amp...

The larger battery would indicate that the starting current of the bike required the higher amperage. The running current of the bike would probably be fine with the 12 amp.  Now why did the 12 amp quit?

The charging systems of bikes are notoriously slow to recharge a deeply charged battery (except maybe BMW). My guess is that you just hit the 12 amp too deep too many times for it to recover. It may have even caused too much draw on the system to drop the voltage below what the electronics needed to operate. I don't have a clue what the magic value would be.

The 12 amp battery can generate a couple hundred amps instantaneously. Try shorting it out and see.   The rating is probably a continuous rating for an amount of time.

An interesting situation, but a PITA when it is your bike dead on the road.

[The Buddha]

OK maybe ... I am notorious for having a bike that is jetted and fiddled with so to the point of being perfectly set up ... usually I never get into anyhting near what can be called taxing a battery ... I touch the starter and bike is running ... fractions of a second is all that I run the starter for usually ... The 12 amp progressively fared poorer and poorer over the 3 days prior to the death ... The day it died, I barely got it started. I might have boiled it into a crisp ... but then it was alive and started the bike just fine 4 days later ... it regenarated itself
Cool.
Srinath.

[starwalt]

... fractions of a second is all that I run the starter for usually ... The 12 amp progressively fared poorer and poorer over the 3 days prior to the death ...

Fractions of a second = Much current. In truth, it is probably more than 3 -4 seconds. If the plates of the battery are undersized for the load, they suffer.

... The day it died, I barely got it started. I might have boiled it into a crisp ... but then it was alive and started the bike just fine 4 days later ... it regenarated itself

Batteries will "recover" after a huge load. Not completely, but enough to possibly start an engine. The chemistry is fickle with time.

If you could get an accurate measurement of the specific gravity of the acid, that would tell the charge state of the battery relative to its "Fresh and New" condition. I too have one of those cheap a$$ hygrometers that provide a good, relative indication. I can't believe they are extremely accurate. I guess it would take a titration test to get it absolutely right.

[The Buddha]

Yea mine is fiber mat ... sealed battery ... so no acid that can be sucked out ... In any case ... yea testing it is harder than swapping out another battery ... Just wanted a theory ...
Cool.
Srinath.