[Sunking]

Originally Posted by DIYguy

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

[DIYguy]

Originally Posted by Sunking

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...

[Sunking]

Originally Posted by Tesseract

(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.

[Sunking]

Originally Posted by DIYguy

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.

[DIYguy]

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

from this site.....
http://www.windsun.com/Batteries/Bat...ery%20Charging
Comes this.....

[top]Battery Charging Voltages and Currents:

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??

[DIYguy]

Originally Posted by Sunking

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?

[Tesseract]

Originally Posted by DIYguy

...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.

[Sunking]

Originally Posted by DIYguy

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.

[dataman19]

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

[vpoppv]

Originally Posted by dataman19

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

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?