# 2 amp vs 12 amp charging



## vpoppv (Jul 27, 2009)

Theories/experiences with charging of lead/acid 12v batteries on different amperages? I have been charging my batteries at 12 amps every night, but I was wondering if charging at 2 amps instead might be better on the batteries? The test begins.....


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## JRP3 (Mar 7, 2008)

I know some LA batteries, such as Hawker/Odysseys, specify 25 amps or higher, at least once in a while. These are AGM cells.


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## Tesseract (Sep 27, 2008)

Charging at less than 0.1C is a great way to cripple lead-acid batteries, vpoppv. As a lead-acid battery discharges its plates are convert to lead sulfate (hence the term "sulfated") . Over-discharging them results in a layer of lead sulfate so thick a normal charger can't punch through (not enough over voltage, hence why "pulse chargers" that apply brief bursts of extreme overvoltage are popular with some).

If you have a 100Ah battery then the current during the bulk charging phase should be at least 10A, regardless of the particular type of lead-acid cell, to be able to overcome the amount of sulfation that results from normal discharging. The maximum acceptable charging current, however, varies greatly depending on the cell type: gel cells tolerate the least, followed by AGM then flooded.


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## Stunt Driver (May 14, 2009)

That goes copletely against my religion.

You say "not enough voltage", but charging at constant Amp rate would mean - voltage will go up as much as needed, so 2 Amp current can be provided.

From what I know - slow charge helps to cure LAs, by removing sulfate (which is a slow process). ANd this goes completely opposit to your post.

I hope more expertise arrives here.


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## Tesseract (Sep 27, 2008)

Stunt Driver said:


> ...
> You say "not enough voltage", but charging at constant Amp rate would mean - voltage will go up as much as needed, so 2 Amp current can be provided.


Give this site a careful read:

http://www.batteryuniversity.com/partone-13.htm 

... rest deleted because it's apparently ok to say I have no expertise but not vice versa ...


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## BHall (Aug 1, 2007)

Point made.

Brian


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## JRP3 (Mar 7, 2008)

I enjoy Tesseract's tone, it livens things up once in a while  Don't ever change T.


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## Sunking (Aug 10, 2009)

Stunt Driver said:


> That goes completely against my religion.
> 
> You say "not enough voltage", but charging at constant Amp rate would mean - voltage will go up as much as needed, so 2 Amp current can be provided.
> 
> ...


Stunt driver you might be confusing float and equalize charging methods both of which are constant voltage techniques

You are correct if you use constant current technique the voltage will rise, or at least we hope so. For lead acid batteries the best charging algorithm is what is called 2 or 3 stage charging. Both are similar.

3 stage uses bulk, absorption, and then float. During the bulk charge a constant current (c/10 to c/8) is applied until the battery reaches roughly 80% state of charge of 2.35 vpc, then switches to the absorption charge level of c/33 to c/50 until it reaches 100% state of charge of 2.45 vpc, then switches to float constant voltage method indefinitely of 2.25 volts per cell.

2 stage is very similar and uses the bulk constant current rate of c/10 until it reaches 100%, then switches to float.

There is another algorithm called 4 stage, it is the same as 3 stage except it adds an optional timed constant voltage equalize voltage setting which is higher constant voltage method than the proceeding three to burn through sulfate.


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## Tesseract (Sep 27, 2008)

BHall said:


> Tesseract, expertise like your is appreciated. However, what is not appreciated is the way you present it. Give this a try, when someone asks a question (most likely a stupid question to you) answer it like you have the utmost respect for that person and try not to make them feel stupid. Making a person feel stupid doesn't get any reward from the one who asked the question let alone the many others who come here for assistance.


Point taken... and you successfully claimed the moral high road until you wrote this...




BHall said:


> Remember, arguing on the internet is like the special olympics even though you win your still a retard. I know, I know that is over used and no doubt YOU have heard it before. *But don't expect any response from me no matter what cranial superior reply you come up with.*


So let me get this straight... it's okay for you to be rude to me as long as I was perceived to be rude to someone else?

And this instance of rudeness on my part was because that someone else said I must be full of it, have no clue what I'm talking about, etc., but didn't bother to do the slightest bit of research to make said claim?

Ok, I'll see your cliche and raise you two: "don't bring a knife to a gunfight" and "two wrongs don't make a right, but three lefts do!"





(JRP3 - quit egging me on, you know I get into enough trouble as it is!)

(Sunking - In retrospect, I suspect you have correctly interpreted Stunt Driver's misconception accurately. Maintaining the float voltage across a l-a battery is good for it, but the float charge rate should not be confused with the bulk or absorption charge rates).


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## DIYguy (Sep 18, 2008)

Tesseract said:


> . The maximum acceptable charging current, however, varies greatly depending on the cell type: gel cells tolerate the least, followed by AGM then flooded.


Hmm, I'd like to explore this a bit. It was my understanding that generally speaking, floodies have a max bulk charge rate of about C/8 while GEL's are lower..around C/20. AGM's however can have bulk charge currents that are sometime multiples of C... I think C/4 would be worst case. So then for a 200 ah flooded battery, 25 amps would be max current for bulk while a 200 ah GEL should have around 10 amps max. The AGM should be able to take much higher charge rates than either. 

I'm no expert...but I read this some time ago when researching battery chemistries. Did I get it wrong?


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## Sunking (Aug 10, 2009)

DIYguy said:


> Hmm, I'd like to explore this a bit. It was my understanding that generally speaking, floodies have a max bulk charge rate of about C/8 while GEL's are lower..around C/20. AGM's however can have bulk charge currents that are sometime multiples of C... I think C/4 would be worst case. So then for a 200 ah flooded battery, 25 amps would be max current for bulk while a 200 ah GEL should have around 10 amps max. The AGM should be able to take much higher charge rates than either.
> 
> I'm no expert...but I read this some time ago when researching battery chemistries. _Did I get it wrong?_


Not really. Here is some usefull information from Trojan. Scroll down to page 11 of 22 and you will see there recommended charging profiles for FLA, AGM, and Gel


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## DIYguy (Sep 18, 2008)

Sunking said:


> Not really. Here is some usefull information from Trojan. Scroll down to page 11 of 22 and you will see there recommended charging profiles for FLA, AGM, and Gel


Interesting...this shows floodies around C/10 with GEL's and AGM's both around C/5 ...at least for the Trojan version.

I must go look for ...what I think I remember...


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## Sunking (Aug 10, 2009)

Tesseract said:


> (Sunking - but the float charge rate should not be confused with the bulk or absorption charge rates).


I agree. Another way of looking at the float voltage is a trickle charge, except it is constant voltage at whatever level of current is needed to overcome the self discharge rate. Float voltage is intended to keep the battery fully charged and in standby until needed. It can be left on the battery 100% of the time.

In fact the telecoms and electric utilities use the float charge method for their only charging algorithm. The only disadvantage to doing this is it takes longer, and sulfation could be an issue if the batteries are cycled often. However telecom and electric utilities rarely ever use the battery power, the rectifiers supply the power until an outage occurs, so the batteries are used as emergency standby operation.


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## Sunking (Aug 10, 2009)

DIYguy said:


> Interesting...this shows floodies around C/10 with GEL's and AGM's both around C/5 ...at least for the Trojan version.
> 
> I must go look for ...what I think I remember...


Yes but note the voltages.


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## DIYguy (Sep 18, 2008)

That was easy... I had it saved as a favorite....

from this site.....
http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery Charging
Comes this.....
[h3]Battery Charging Voltages and Currents:[/h3]
Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps. Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. The *Concorde AGM* batteries are a special case - the can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle. However, since very few battery cables can take that much current, we don't recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less.​
Now this is talking about the Concorde brand, so... is there this much difference in manufacturers' designs??


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## DIYguy (Sep 18, 2008)

Sunking said:


> Yes but note the voltages.


The voltage during bulk charge is not usually controlled as I understand it. This first stage is current regulated so, there is no hard and fast rule on voltage...it is likely dependent on battery design (resistance) and charger characteristics.... Make sense?


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## Tesseract (Sep 27, 2008)

DIYguy said:


> ...floodies have a max bulk charge rate of about C/8 while GEL's are lower..around C/20. AGM's however can have bulk charge currents that are sometime multiples of C... I think C/4 would be worst case.
> ...
> Did I get it wrong?


Nah, you didn't get it wrong; if anything, I did! Although there does seem to be a lot more variability among the AGM lead-acids than there is among the flooded and certainly gel types when it comes to the range of recommended charging rates.

In general, though, you don't want to use "micro-fractions" of C to do your charging for any of the cell types, though gels can take charging at a lot lower fraction (indeed, need to) than the other kinds.


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## Sunking (Aug 10, 2009)

DIYguy said:


> The voltage during bulk charge is not usually controlled as I understand it. This first stage is current regulated so, there is no hard and fast rule on voltage..


Sort of but not exactly. Bulk charge is constant current, but the voltage level (somewhere around 2.35) triggers the next stage, so voltage does play a part.


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## dataman19 (Oct 7, 2009)

Ok Tesseract - good link post...
But I differ on the 14.4V issue....
..
In fact I think all of you are hung up on this algorithm math..
..
The math is simple...
Automotive Batteries flaot charge - meaning the 13.8V from the alternator supplies the initiative to energize and charge the batteries. This also applies to deep cycle batteries (even when you have two 6V deep cycle batteries in series).
..
14.6V is the gassing off point where the electrolyte will gass off (it boils the electrolyte). In solar power this is the process or normalizing or equalizing the batteries.
..
The only time you would use 14.4V would be in a large industrial tractor where you have four batteries parralelled.
..
As to the current at charging...
..
The reason you see your auto battery charger decrease in current has little to do with the battery chargers current regulation. At 13.8VDC a flooded cell battery will only draw the current necessary to put the plate/electrolyte back into staisis. The more the battery is discharged, the more sulfates attached to the plates and the more imballanced the chemistry. There fore the battery will require less and less current as it approaches equilibrium (hence the math algorithm to figure the theoretical point of staisis versus state of charge).
...
If you battery is drawing 12-Amps or more continually - Then You have A dead Cell!!! 12-Amps will charge a 120-AHr Battery from near dead (at about 40% Depth of Discharge for a Deep Cycle Battery). This is why there are different Battery Caharge capacity Chargers for different Battery syatems.
..
Or if you want to simplify your EV Bayttery experimentation life? Buy one of these:
http://www.circuitspecialists.com/level.itml/icOid/9441
Then you will only need a 45-Amp Bridge Rectifier, and two large 250V Electrolytics to smooth out the ripples...
..
Wah Lah - you now have a 0-130VDC 35Amp Battery Charger....
...
Dave Mason
dataman19


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## vpoppv (Jul 27, 2009)

dataman19 said:


> Ok Tesseract - good link post...
> But I differ on the 14.4V issue....
> ..
> In fact I think all of you are hung up on this algorithm math..
> ...


Thanks, but I usually just buy my coffee beans already roasted.

So basically what this would do is allow me to dial-in the voltage at which I charge the batteries? I assume a standard charger can't "gas" batteries if the voltage never gets to 14.6v, but apparently this device could? How long should the batteries be gassed? How often should that be done? Or maybe a desulfator would be better than trying to gas the battery?


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## TheSGC (Nov 15, 2007)

Tesseract said:


> Charging at less than 0.1C is a great way to cripple lead-acid batteries, vpoppv. As a lead-acid battery discharges its plates are convert to lead sulfate (hence the term "sulfated") . Over-discharging them results in a layer of lead sulfate so thick a normal charger can't punch through (not enough over voltage, hence why "pulse chargers" that apply brief bursts of extreme overvoltage are popular with some).
> 
> If you have a 100Ah battery then the current during the bulk charging phase should be at least 10A, regardless of the particular type of lead-acid cell, to be able to overcome the amount of sulfation that results from normal discharging. The maximum acceptable charging current, however, varies greatly depending on the cell type: gel cells tolerate the least, followed by AGM then flooded.


So I got reviewing my charging data, and then brought it to the Electric Vehicle and Battery Evaluation department on my college, and Tesseract is right about needing at least 0.1C for charging current. I noticed my batteries were loosing their oomph and during that time I was charging at less than 0.1C, actually I was at 0.05C. Long story short, I was not charging them fast enough to overcome the sulfation and after a week or so the performance was dropping like a rock. I now charge at about 0.11C just to be safe, and I plan on going higher when I get the wall power to do it.

Just, FYI.


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## vpoppv (Jul 27, 2009)

TheSGC said:


> So I got reviewing my charging data, and then brought it to the Electric Vehicle and Battery Evaluation department on my college, and Tesseract is right about needing at least 0.1C for charging current. I noticed my batteries were loosing their oomph and during that time I was charging at less than 0.1C, actually I was at 0.05C. Long story short, I was not charging them fast enough to overcome the sulfation and after a week or so the performance was dropping like a rock. I now charge at about 0.11C just to be safe, and I plan on going higher when I get the wall power to do it.
> 
> Just, FYI.


 Thanks for the confirmation. I actually have been charging at 12 amps and never got around to doing anything different. I'll stick with 12 amps....


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## DavidDymaxion (Dec 1, 2008)

The Hawker manual warns that too low an initial charge rate is not good for their batteries. I also have a small number of data points that say higher charge rates keep the batteries in better balance on my Optima batteries. Of course, this means charge rates that are not so high as to damage the batteries!


DIYguy said:


> Hmm, I'd like to explore this a bit. It was my understanding that generally speaking, floodies have a max bulk charge rate of about C/8 while GEL's are lower..around C/20. AGM's however can have bulk charge currents that are sometime multiples of C... I think C/4 would be worst case. So then for a 200 ah flooded battery, 25 amps would be max current for bulk while a 200 ah GEL should have around 10 amps max. The AGM should be able to take much higher charge rates than either.
> 
> I'm no expert...but I read this some time ago when researching battery chemistries. Did I get it wrong?


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