Charging AGM batteries

BFL13 wrote:
I don't know if it "overkill" to use the specified 14.5-14.9 voltage or whether they need that to get the acid up to required strength.

There seems to be one kind of AGM that specs 14.8ish and has limited spec charging amps (about 30%) while others (Lifeline eg) want lower voltage but will take huge amps during bulk. There are more types of AGMs too, like those UPS ones guys are getting, which the say you have to be careful to use their stated specs. (not as bad as GELs though, AFAIK)

I know many chargers and solar controllers that have Wet, AGM, and Gel settings have the AGM voltages set lower than the Wet settings. That seems wrong to me, since my AGMs specs batter match the Wet settings on those.

Adjustable chargers are the way to go these days.

The AGM settings are lower because that is what they need for optimal charge. A bit higher doesn't hurt and will be faster, but AGM's can take a very high current that a flooded cell just cannot due to the lower internal impedance and while they can take a higher charging current there is still a limit beyond which the heating will be destructive.
The acid chemistry is the same in all types, that is not the variable. The intimacy of contact of the plates to the acid is what varies. There are various reasons why they may be speced differently, including intended use (if it's rated less charge cycles they can rate for more abuse) if they require temperature sensing (as was mentioned some do) then they can run higher voltages when the temperature requires that and monitor for excess current etc. etc.

I don't know if it "overkill" to use the specified 14.5-14.9 voltage or whether they need that to get the acid up to required strength.

There seems to be one kind of AGM that specs 14.8ish and has limited spec charging amps (about 30%) while others (Lifeline eg) want lower voltage but will take huge amps during bulk. There are more types of AGMs too, like those UPS ones guys are getting, which the say you have to be careful to use their stated specs. (not as bad as GELs though, AFAIK)

I know many chargers and solar controllers that have Wet, AGM, and Gel settings have the AGM voltages set lower than the Wet settings. That seems wrong to me, since my AGMs specs batter match the Wet settings on those.

Adjustable chargers are the way to go these days.

I see these want 14.4 - 14.58 for charging. Don't have the amps spec if any.
http://www.wegosolar.com/products.php?product=Deka-8A27-Absorbed-Glass-Matt-92-AHr-Solar-Battery

BFL13 wrote:

horton333 wrote:
The AGMs are rugged and this charger will do ok. AGMs always need less voltage than flooded cells for proper charging, they have inherently lower internal impedance, so you may want to put in a larger charger as off grid as even a small AGM can take a lot more than 45 AMPs easily without overheating and why run your generator longer than needed if your solar cells don't give enough on a given day.

AGMs do not "always need less voltage than flooded" and some do have charging amps limits. Mine do. These 100AH ones want 14.8ish (same as Trojan flooded) and 27% charging rate.

http://www.hespv.ca/hesproductspecs/HES/Stark_Battery_TD_ENG.pdf

Sure some are *specified* to take overkill like 14.8 volts and may even survive, but it's not *required* like it is with large flooded cells.
Part of the reason why AGMS are designed the way they are it to take more current at a given voltage (and store the power more effectively too), so always is the appropriate term.
BTW that specification sheet indicted a current limit of only 27 AMPs, to prevent the stress that a high power supply and 14.8 volts would do perhaps.....

horton333 wrote:
The AGMs are rugged and this charger will do ok. AGMs always need less voltage than flooded cells for proper charging, they have inherently lower internal impedance, so you may want to put in a larger charger as off grid as even a small AGM can take a lot more than 45 AMPs easily without overheating and why run your generator longer than needed if your solar cells don't give enough on a given day.

AGMs do not "always need less voltage than flooded" and some do have charging amps limits. Mine do. These 100AH ones want 14.8ish (same as Trojan flooded) and 27% charging rate.

http://www.hespv.ca/hesproductspecs/HES/Stark_Battery_TD_ENG.pdf

BFL13 wrote:
It is important to know exactly which AGMs you have, since different AGMs have different charging specs. EG, some want to be charged at 14.8-14.9 volts while others only want 14.4ish volts. A regular PD at 14.4 would "undercharge" an AGM that wants 14.8 or so. You can get a PD from Randy that does 14.8

Some AGMs have a specified amps limit while being bulk charged too, like 27 or 30 amps per 100 AH. My two 100s are like that, so a 55 amp charger is just right for the pair. OTOH some AGMs can take more amps per 100AH.

Mex says do not obsess about the various charging specs, but IMO if you can meet the specs, then why not do what they say?

And as we've discussed before ad nauseam here on the forums some manufacturers (East Penn being one) insist that temperature compensated charging be used. Mex may not care but my bet is with East Penn's recco. :W

The AGMs are rugged and this charger will do ok. AGMs always need less voltage than flooded cells for proper charging, they have inherently lower internal impedance, so you may want to put in a larger charger as off grid as even a small AGM can take a lot more than 45 AMPs easily without overheating and why run your generator longer than needed if your solar cells don't give enough on a given day.

It is important to know exactly which AGMs you have, since different AGMs have different charging specs. EG, some want to be charged at 14.8-14.9 volts while others only want 14.4ish volts. A regular PD at 14.4 would "undercharge" an AGM that wants 14.8 or so. You can get a PD from Randy that does 14.8

Some AGMs have a specified amps limit while being bulk charged too, like 27 or 30 amps per 100 AH. My two 100s are like that, so a 55 amp charger is just right for the pair. OTOH some AGMs can take more amps per 100AH.

Mex says do not obsess about the various charging specs, but IMO if you can meet the specs, then why not do what they say?

If you are getting a new converter anyway, check out the new PowerMax line called their " LK" model which has two modes: three stage and adjustable voltage mode. That gives you a range of 13 to 15.5 volts you can set to meet almost any battery charging specification.

BTW, the only way to tell if an AGM is fully charged is by noting how many amps it is accepting. When amps taper down to (depends!) you are "full." THAT means you must have an ammeter that can do big amps (for when first starting the recharge), which hardly any RVer has. I use my Trimetric as an ammeter for that, but also you can use a portable charger- many of them have an amps display.