15 amp Chgr - Hrs to charge

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how long to charge 12 volt battery on 15 amp charger with 100 amp boost. unit is from the 70's and meter only has low/good/boost on screen. Currently screen is on line of low and good.
 
How many amps is the battery? If its a "normal" size car battery charge for an hour then test the battery repeat on the hour.
Without knowing what the charger is capable of, the size of the battery and its current state of charge its impossible to give an answer that's even close.
 
Battery is Voltage: 12
Format: BCI Group 24F
Lead Acid Type: Starting
Cold Cranking Amps: 725
charge state is unable to start vehicle without boost
 
Assuming say, 80-90% charge is the same as "full" to the layperson, it's a matter of calculating the following:

(0.85 * Nameplate Ah)-(initial SOC * Nameplate Ah)/ 15 = how many hours you need to charge.

It's far more complex in reality. And, usually there is a current decay that makes it much longer to get to a full SOC.

But for "good enough" ballpark, that's sort of your start.

Issue is that most batteries don't provide nameplate Ah values.

For an old school charger like yours, Is not want to be topping the battery.

Id target running two-ish hours for a known low battery (unloaded voltage around 12-12.4v.

Reduce time before checking from there.
 
Yeah, it depends on the battery. You can convert reserve power to amp hours. Typical batteries are anywhere from 40-80 amp hours. So at 15 amps, anywhere from about 2.5 hours to 6 hours at 15 amps if the battery is fully discharged, less if it's not.
 
Originally Posted By: CarlGR
Battery is Voltage: 12
Format: BCI Group 24F
Lead Acid Type: Starting
Cold Cranking Amps: 725
charge state is unable to start vehicle without boost

Need to know Ah value.
 
Chargers are a bit better now than 40 years ago. Maybe ask for one for your birthday!.
smile.gif
 
Last edited:
Originally Posted By: JHZR2
Assuming say, 80-90% charge is the same as "full" to the layperson, it's a matter of calculating the following:

(0.85 * Nameplate Ah)-(initial SOC * Nameplate Ah)/ 15 = how many hours you need to charge.



FWIW, if the battery label doesn't list its amp-hour rating but only gives "reserve capacity" in minutes, the amp-hour rating is approximately 0.416 times the reserve capacity. IOW, AH=RC/2.4

For example, if the battery lists a RC of 100 minutes, then its roughly a 42 amp-hour battery.
 
A group 24 battery is generaly 75 to 85 amp hours.

I'd not necessarily believe a 15 amp charger is capable of 15 amps.

No voltmeter and no ammeter is like no speedometer and no mile markers or clock.

but in this case it is like how long does it take to go from a to b, not knowing where a or b or located, or the speed one will travel.

So, my answer is yes
 
Originally Posted By: Snagglefoot
Chargers are a bit better now than 40 years ago. Maybe ask for one for your birthday!.
smile.gif


Not really for lead acid. Supplying current to a battery is pretty much the same now as 40 years ago.
 
A 15 amp smart charger would take about 8 hours to charge a dead 85Ah battery. 5 hours for bulk and the rest for absorption.
 
Originally Posted By: tmorris1
Originally Posted By: Snagglefoot
Chargers are a bit better now than 40 years ago. Maybe ask for one for your birthday!.
smile.gif


Not really for lead acid. Supplying current to a battery is pretty much the same now as 40 years ago.


Smart chargers are worth the money. That 70’s charger belongs with the platform shoes. Not to be unkind.
smile.gif
 
Last edited:
Originally Posted By: Snagglefoot
Originally Posted By: tmorris1
Originally Posted By: Snagglefoot
Chargers are a bit better now than 40 years ago. Maybe ask for one for your birthday!.
smile.gif


Not really for lead acid. Supplying current to a battery is pretty much the same now as 40 years ago.


Smart chargers are worth the money. That 70’s charger belongs with the platform shoes. Not to be unkind.
smile.gif


I agree they are worth it, but they are not anything magical. They do the same thing as the old ones except they are smarter on when to shut off. They don't really charge any better. My point was an old charger will probably just charge just as well as a new one, but you will have to babysit it more.
 
If I was to replace the circa 70's charger, what 15 amp auto charger (medium grade)with approx 50A starting ability would you look to buy. The schumacher sc1359A for $51.52 look good but I'm reading quite a bit bad info on that maker.
 
+1 That's the one I bought, my only complaint is no carry handle making it a bit cumbersome to schlep around but its not a deal breaker on an otherwise a great charger.
 
If all a person is doing is charging the neighbor's battery because he left his lights on, it doesn't matter what charger you use, but if you are maintaining RV batteries or topping up boat batteries that were depleted because the kids played the stereo, a smart charger will make your batteries last a lot longer. Here is a primer on what smart chargers do. Enjoy.

https://www.batterystuff.com/blog/3-stages-of-smart-chargers.html
 
Originally Posted By: CarlGR
If I was to replace the circa 70's charger, what 15 amp auto charger (medium grade)with approx 50A starting ability would you look to buy. The schumacher sc1359A for $51.52 look good but I'm reading quite a bit bad info on that maker.


Keep your old charger and get a cheap lower amp smart charger. Use the old charger for a few hours then switch it over to the smart charger. Your old charger will probably outlast any consumer grade charger you can buy these days. If all that you're doing is charging your car every once in a while most will work fine.
 
Originally Posted By: tmorris1
Originally Posted By: Snagglefoot
Originally Posted By: tmorris1
Originally Posted By: Snagglefoot
Chargers are a bit better now than 40 years ago. Maybe ask for one for your birthday!.
smile.gif


Not really for lead acid. Supplying current to a battery is pretty much the same now as 40 years ago.


Smart chargers are worth the money. That 70’s charger belongs with the platform shoes. Not to be unkind.
smile.gif


I agree they are worth it, but they are not anything magical. They do the same thing as the old ones except they are smarter on when to shut off. They don't really charge any better. My point was an old charger will probably just charge just as well as a new one, but you will have to babysit it more.

Not sure about that. They're not simply smarter about shutting off, but they don't have any kind of linear charging which helps with longevity, completeness of charge, and desulfation. Also smart systems with regards to reversed clamps. I remember using a voltmeter on my terminals and I saw that it was constantly changing voltage, which is consistent with modern microprocessor-controlled charging.

I had an "analog" maintainer with auto shutoff. It had a completely analog mechanism but was probably safe to keep on at all times. I guess that kind of bridged the gap until the modern ones using microcontrollers and firmware.
 
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