Amps jumping around on AGM finishing charge

My theory is the amps bounce each time a drop of water falls from the catalyst inside a cell. There is really nothing else discontinuous going on in the system I can think of.

I don't hear any bubbling at all. My reading literature (especially setting up AGMs as standby battery banks) told me that AGMs probably gas a little, far more often (but undetectably) than people think, so I came up with a way to detect the bubbles by placing the valves under distilled water.

Mine will stay at .01a for a long time then drop to unmeasurable - that is 2 paralleled new 92 Ah Dekas.

I think the batteries are not quite charged too mena, despite sort of first glance indications that they are. Thanks for the encouragement! I have basically found 3 modes.

1) 4 digit (hundredths of a volt) temperature corrected float. Tiny micro bubble from just 2-3 of the cells, very infrequently. Pin head bubble from one of them maybe every 15 minutes or less often. I think this is just green batteries settling in. A chemist could say how much water is lost but the volume is very small because of the large amount of H and O even A gram of water will create. Presumably normal for break in.

2) above float up to lowest charge voltage of 13.8v, .05A-.15A charge rate, volatile value hops all around a few minutes after charging starts. Not dropping voltage back to float will cause a few bubbles a minute total, but *all* cells generate the occasional bubble. I believe this is charging too fast- breaking in the green cells is supposed to end up evening them out. All bubbling makes me think this is just overcharge. Still would not be detectable without water on the valves, still very low gas volume, but not something I want to see. At all. The normal directions are to charge a string before placing it on float, but I am going to see what just being on float for more hours does.

3) above .15a charging when approaching very full, 1 degree post or valve temp increase. Similar to above but does not totally stop the bubbles for an additional few minutes after voltage is removed. Useful in a pinch, but more lag in detecting venting.

Now that I can float more easily and to a tighter voltage with the buck converter (with manual temperature correction), I am just going to float and watch, periodically checking the rest voltage.

Jim

Jim;

Could the Amp bouncing be related to the bubbling? IMHO, bubbling is not normal.

It is odd that you are the only AGM owner that has reported hearing any bubbling unless performing recovery charging on known problem AGMs. Are you sure your batteries are healthy and the valves have not been compromised?

There was a poster that reported chalking on his AGMs. It turned that Lifeline knew about a few AGMs that had bad valves and they shipped new AGMs at no charge. You might want to call Deka.

What Amp acceptance reading indicates fully charged to you? The only time I see zero Amps is with my SC-1200A 2/8/12A Schumacher portable charger because it floats with an on-off method every few seconds.

HTH;
John

It seems like they're still not fully charged. BTW, thanks for doing all this. This fantastic information.

Discharge hours of the battery over time are cumulative. Many hours at say 3% discharge add up in a similar way to sitting around a shorter time at 80% or 50% charge. Any time spent discharged is by definition time spent sulphated to some small degree. Recovering from sulphation seems more problematic than with flooded batteries.

But tactically I want to characterize the battery baseline performance and to do that I want to start from fully charged. Similar to getting a baseline SG in a flooded battery.

Right now I am float charging at a temperature corrected 12.39v. The batteries have taken in almost an amp hour yesterday and today and are down to .05a draw right now. The half amp hour yesterday and 12 hours rest brought the voltage up from 12.89v to 12.90v. When I was fully charged the first time I got to 12.93-12.94v.

Jim

HiTech wrote:
I suspect outgassing below the venting level is as good for AGMs as it is for flooded batteries...in moderation. But it's a tightrope to walk.

Jim

What is the payback for walking the high voltage tightrope?

How many years life can you gain opposed to how many you stand to lose?

I trust my Morningstar controllers to maintain my AGMs unattended. I have never heard any of the sounds of internal gassing or vent gassing, and I don't ever intend to! :)

I have never seen zero Amps in any charging tests. I don't believe 100% fully charged is a necessary/affordable goal. When Amps are below 1% of AH20, I consider my AGMs charged enough.

HTH;
John

HiTech wrote:
My brand new ones not in service yet. Yes they do, and they outgass during settle in.

I finally have some short #4 wires so I can do a realish (700w) load test and get some decent discharge plots. I'd like to start out charged. I have noticed there is no point in even attempting the last few percent charge when it is over 90 out. Sneeze and they want to outgas.

Jim

Bring them up here Jim, it's 9.8C (49.6F) outside right now! (10:30PM) not forecast to get over 12C (53.6F) tomorrow!

HiTech wrote:
My brand new ones not in service yet. Yes they do, and they outgass during settle in.

I wonder if this is just due to them being green. PNick's are well broken in and that's probably why his do not exhibit this behavior.

Yes once the volts are up high enough. It does not take much current at all. Probably really not a problem at all - the literature seems to indicate AGMs typically outgass at 1/5 to 1/10 the rate of flooded batteries their whole life and this is normal, but this is often what eventually kills them if sulphation does not get them first.

I'm trying to walk that magic balance in between, float is one way to get there. I think solar is too, but it has a lot more variables than float, so I want to really understand float first. The temp variation here is giving me fits. I may drag the things into the air conditioned space just to eliminate that variable. But I do feel like this hundredth digit behaviour gives me a leading indicator to avoid outgassing from the valves. I suspect outgassing below the venting level is as good for AGMs as it is for flooded batteries...in moderation. But it's a tightrope to walk.

Jim

.

Jim, when your AGM(s) start to out-gas if you hit them at the end ... does the ammeter still show current flow into the battery(ies) while the out-gassing is occuring?

The reason I ask is ... maybe my AGMs are actually out-gassing when they're up against the full charge "hard-stop" I see along with the zero current flow shown on my ammeter.

Intuitively (not remembering the electro-chemical reactions/equations involved), it SEEMS that the outgassing would/could NOT occur unless current flow was occuring at the same time. The energy to drive the outgassing process has to be coming from somewhere ... and I doubt that only the electromotive force field from a charger ("charging voltage") could cause the out-gassing process with zero electron flow indicated. I could be wrong, though ... I've long since sold my chemistry textbooks!