Help deciphering battery information

[DavidH]

Hi,

I have two Casil AGM 12V 100Ah batteries. I'm connecting them in series and have a Midnite classic 200 to charge them. I pulled up the information sheet for these batteries to find the optimum charging voltage settings (to program the midnite classic 200) but I'm having a little difficulty working this out from the sheet. Would anyone be able to have a quick scan of it and help me out and tell me how I can work it out from the information given?

http://en.casilbattery.com/products_...ductId=76.html

Thanks!

[Mike90250]

First, it looks like the battery is designed for standby-float use, so it's not going to last long in daily solar cycles.

BatterySpec.jpg

So, when you decide which service duty (Cycle or Standby) use, use the numbers from the appropriate line in the data sheet.
if you have 2 batteries in series, double the number.
In the classic, use the battery temp coefficient

[DavidH]

Thanks Mike. Yeah it's going to be interesting to see how long they last.

I read the sticky post that Sunking had started on "Are you killing your batteries? Part 2" and he recommends not having the absorption stage - just charging with bulk until the battery is fully charged, due to there not being enough time to get the battery to 100%.

If I use 14.7V for the bulk and then 13.8V for float to start off with (29.4V and 27.6V respectively for 24V battery) that puts me within the range for this battery and is the same as the recommendations for the Rolls AGM:

Bulk = Absorb = 14.7 @ 25c
Float = 13.8 @ 25c
C-Rate = 10 to 30% of C

Though Sunking recommended starting off at 14.8V bulk. I did read that the AGMs are more sensitive to overcharging though. So on the Midnite do I set the absorb parameter to exactly the same as bulk - or is there a way to turn off absorb?

My only other query is regarding equalization - is it still once a month for AGM or should the AGM not require equalization?

Thanks

[Mike90250]

DO NOT EQUALIZE AGM batteries.

As to charging stages and times. You will have to figure this out on your own.

Used to be, when panels were expensive, folks would be underpaneled and chronically undercharge their batteries. But now, with cheaper panels, you can design properly, and be able to complete Bulk and Absorb stages and not have to use "max smoke" settings.

And understand, AGM batteries will not tolerate over charge. They will build gas pressure and vent gas, which is H2O, and you cannot refill AGM like you can refill flooded batteries with distilled water.

[littleharbor]

Bulk charging doesn't need a setting because in Bulk phase you are giving the battery max smoke, so to speak, starting at the battery's sitting voltage and giving it all your array can produce until the voltage rises to the Absorb setpoint. At this point the controller holds the voltage steady while your battery absorbs current in ever decreasing amounts.(usually terminated by time or % of the battery's Ah capacity.

[DavidH]

Ok, thanks Mike and littleharbor. Overcharging seems to be what I really need to keep an eye on for my AGM batteries then. I'm guessing that the Whizbang Jr would be a useful addition to my system as it would allow me to measure end amps and end the absorb cycle, preventing overcharging.

I realize now why all the advice when starting off is to buy cheaper batteries because you're likely to ruin them haha. AGM's probably aren't the best to learn on, but I got these two cheap and I think they'll do the job as I learn more.

I found this link to an article by Rolls "Calculating Proper Charge Settings for Flooded Lead Acid Batteries"

[littleharbor]

AGM batteries can handle about twice the amperage that a similar flooded battery can. The thing you need to be careful with is the voltage settings Typically AGM voltage settings are lower than flooded batteries. As the voltage rises lead acid batteries will off gas, Too much gassing and AGM batteries cannot recombine this gas fast enough and will vent excess pressure. This venting causes AGM batteries to lose precious liquid. AGM batteries are 98% saturated glass mat between the lead plates, this is why they are considered "Non spill able".. They can't afford to lose any moisture . Always refer to mfg. recommended settings.

[Mike90250]

AGM batteries can handle about twice the amperage that a similar flooded battery can.........

Just to clarify. They can handle Surges, either in charging or delivery, because they have lower internal resistance. But for the same size battery case, their actual 20 hour capacity is about the same, being a factor of lead and acid.

[PNjunction]

I'll reiterate what Mike said (and world too) about NOT equalizing AGM batteries. Most aren't meant to.

However, some charge controllers don't *truly* do equalization, confusing the issue just a little bit. I'm not familiar with the Midnite Classic 200, but..

When you see a controller that does a monthly equalization, for the most part all they are doing is increasing the CV voltage by about 0.2V for 2 hours a month. This is an attempt to try and keep the agm's healthy, since agm's don't truly get charged to 100% by solar in a cyclic scenario for most people, and they walk down in capacity little by little. This slight boost of CV voltage tries to counteract that fact of life with agm's and solar gently.

Compare this to a *real* flooded EQ, where the voltage after the absorb is raised to about 15.5v, held there for many hours, hydrometer readings taken, and so forth.

So manufacturers take liberties with their own nomenclatures, and the real world meanings that most of us are used to.

Obviously, 15.5v will kill an agm. But if you look at the controller specs for what it mistakenly calls an "EQ", is just a short two hour tickle about 0.2v above normal for an hour or two, or they just simply raise the CV to that before going into float for one cycle.

In other words, if your agm can handle 14.6v, but you have it normally set for 14.4v, then the slight so-called "eq" raise to 14.6v once a month won't hurt it. And of course we're talking a temperature-compensated controller.

But *check* what Midnight calls an EQ! If this is the wimpy little boost for an hour or once a day per month, then ok. But if it is a TRUE EQ, like going to 15.5v - then NO, do not obviously enable that function.

So yeah, the generic answer is do NOT EQ an agm. But if your controller is not doing a REAL eq, then you won't have a problem. Just check the manual to make sure.

[DavidH]

Ok thanks PNjunction, I'll have a read of the manual and see what it says about this.