Charging an AGM with Xantrex C-60 charger

[electricthot]

I have a new 12v AGM and am in the process of learning how to correctly charge it. Going from golf cart batteries, I can see it's a differnt ballgame, and I fear I already have made serious mistakes. All of my general questions were answered searching this forum. I came across some posts by RCinFLA and mikefitz that were very specific in detailing AGM needs. I would only add, I have read overcharging can "pop the seal", after which the battery will dry out in hours.
My Xantrex C-60 can be configured for absorption and float voltages. I am at 14.6 and 13.6 currently, following manufacturer's (Renogy) recommendations. How well does this suit the AGM, and how long should float stage be to properly "top off" my battery?

 

[sunshine_eggo]

On AGM I prefer absorption at the low end of any range and float at the high end of the range.

An AGM is full when the current has dropped to about 2% of the rated capacity at the absorption voltage, e.g., a 100Ah battery would be fully charged at prescribed absorption voltage when current has dropped to 2A.

Charge current matters. AGM are typically charged at 10-20% capacity

 

[electricthot]

On AGM I prefer absorption at the low end of any range and float at the high end of the range.

An AGM is full when the current has dropped to about 2% of the rated capacity at the absorption voltage, e.g., a 100Ah battery would be fully charged at prescribed absorption voltage when current has dropped to 2A.C

Charge current matters. AGM are typically charged at 10-20% capacity

That makes good sense. My prior golf cart battery bank took a punishing, both in DoD and regular equalizations, my new AGMs won't tolerate. I have even installed an inverter that will tolerater 16.5 volts before shutdown so I could equalize at 15.6 volts. I gave the AGM an hour of 15.3 charge right after I got it, and my internal resisance took a hit, from 1.06 to 4.29. Oops!!

 

[sunshine_eggo]

AGMs shouldn't be equalized unless following the manufacturer's recommendations.

You did substantial damage to your batteries @15.3V. Never exceed the stated absorption voltage unless the manufacuturer says otherwise.

AGM equalizations, when allowed, usually just allow for a much longer absorption charge.

 

[electricthot]

AGMs shouldn't be equalized unless following the manufacturer's recommendations.

You did substantial damage to your batteries @15.3V. Never exceed the stated absorption voltage unless the manufacuturer says otherwise.

AGM equalizations, when allowed, usually just allow for a much longer absorption charge.

I'm also temperature compensated, which can raise my charge voltage on a cold morning. My battery room is poorly heated. Is this recommended?

 

[sunshine_eggo]

Ah. I didn't consider that in my response. Yes, you should use temp comp. If it was very cold, around -3°C, temp comp could drive voltage to 15.3 if temp comp at -.005/°C/cell. If you're comparing room temp IR to cold IR, I wouldn't be too concerned.

AGM may have temp comp as low as -.002/cell.

 

[littleharbor2]

C-40's and C-60's have test points on the circuit board to accurately set the actual true voltage. Those little dials have removable caps that can be replaced incorrectly and you may think the setting it is at is, actually, wrong. Best to verify the voltage with the test points. Look in the manual to learn how they work.

 

[electricthot]

Ah. I didn't consider that in my response. Yes, you should use temp comp. If it was very cold, around -3°C, temp comp could drive voltage to 15.3 if temp comp at -.005/°C/cell. If you're comparing room temp IR to cold IR, I wouldn't be too concerned.

AGM may have temp comp as low as -.002/cell.

C-60 uses 77F as neutral, and my batteries were probably 20 degrees below that.

 

[electricthot]

C-40's and C-60's have test points on the circuit board to accurately set the actual true voltage. Those little dials have removable caps that can be replaced incorrectly and you may think the setting it is at is, actually, wrong. Best to verify the voltage with the test points. Look in the manual to learn how they work.

Yes. I use a voltmeter to set both float and absorption voltages. I have never needed to remove the caps, but they are not needed when using a voltmeter. But then you need an allen wrench to make the adjustment, without the caps..

 

[littleharbor2]

Yes. I use a voltmeter to set both float and absorption voltages. I have never needed to remove the caps, but they are not needed when using a voltmeter. But then you need an allen wrench to make the adjustment, without the caps..

I believe that's a safety feature to keep settings from getting changed.

 

[sunshine_eggo]

C-60 uses 77F as neutral, and my batteries were probably 20 degrees below that.

77°F = 25°C, and I can only remember °C values. I can say for certain if it was 57°F, 15.3V was WAY too high. Should be no higher than 14.93 if your set point is 14.6V.

 

[electricthot]

77°F = 25°C, and I can only remember °C values. I can say for certain if it was 57°F, 15.3V was WAY too high. Should be no higher than 14.93 if your set point is 14.6V.

Yeah. I hurt it. I think the internal resistance going from 1 to 4 says it all. It's been now on float since noon and I will check it when the sun goes down. but I don't expect much. Of course, it's not dead by any means. But I'd better stay on top of it now. I'm going to add another just like it next week. I can then compare it with a new one.