Charging antimony-free VRLA batteries without float

You never want to either. It is an extreme recovery procedure for an otherwise dead battery. Lifeline has one for batteries that have run dead and some other recovery procedure too. I used only as a last resort and it did work, but guaranteed the battery was stressed. It was not valve noise, it was a bubbling/crackling sound inside the battery.

Jim

As a practical matter, my Deka AGM batteries are 5 years old, and they have been on charge 24/7 when we are not on the road. My converter is a Xantrex that puts out a float of 13.6 volts. The batteries seem to be performing fine.

I just recently got one of those HF I-R guns. I will be curious to read your experiences in various battery temps.

Maybe I need a stethoscope. I definitely don't want to hear a valve make any noise. Can you explain the bubbling noise more as I have never heard any.

Optima says unlimited Amps but cap the Volts and Temps. My approach is to focus on getting Amps over Volts into my AGMs. That is more aligned with AGM mfgr specs.

Both solar controllers are MS PWM with temp comp and set for 14.4V and 14.35V, the WFCO converter/charger never does more than 13.6V and the portable has an AGM setting and ambient temp comp.

HTH;
John

Definitely not trying to walk the tight wire or go over voltage. I am trying to validate and feel safe with the OEM float voltage (along with the accuracy of my instruments and power supplies).

When my New AGMs are still just a few percent below fully charged, they can sit for days and days at float at the proper temp, barely, sloooowly, gaining charge.

When they are truly full, just a tenth of a volt high with temps outside in the low-mid 70s seems to develop a stray bubble here of there in less than an hour. It seems at times even just the OEM float voltage will do this. How would anyone not testing for this gas from the valves ever know it is happening? Crazy swags at this level of out gassing and the water it would remove suggest it would be years before that level of gassing would remove many ounces of water. So it may not matter.

I wonder if in the end I may need to run .05 or .1 v less than the recommended float if I really want to float full time.

Next thing I am going to do is run some temp studies at different voltages for float on a full battery. Mex suggested this and I got an IR gun (the one the chemist uses to make his tea on Breaking Bad in fact). Mex told me even one degree of temp increase to too much so I am going to look for that as a sign the energy in is exceeding the self discharge. The exothermic nature of the valves means they heat up even before a bubble of gas escapes, I believe, due to their catalytic purpose of recombining the oxygen and hydrogen back into water. I will check both terminal temp but also the temp of each valve. Hmm thinking about that the temp of each valve under heavy charge may actually show me which cells are stronger, and I could see if the temps settle closer together over time as the string settles in to run as a more balanced set of cells.

One thing this all convinces me of is running AGMs in an untemp-controlled environment without temperature compensation can leave them chronically undercharged, overcharged, or oscillating between states with the weather. It's amazing to me they do as well as they do in starting ignition lighting service. Maybe it is because most starting batteries are chronically undercharged and AGMs handle this better than Flooded batteries. It still kills them, but supposedly they sulphate from it more slowly.

Jim

Hi Jim;

As a hobby or test case I can understand your curiosity about your AGMs. Thanks for posting your details as the info is beneficial to any interested parties, including myself.

An AGM is pressurized. I do believe there is capacity loss in the same manner that a tire loses pressure simply by the movement of atoms. I believe that is baked into the design. However, to deliberately walk a high voltage tightwire that could possibly lose gas, means a loss of H and O that is not baked into the design, is asking for trouble. I trust my two MS PWM controllers, with temp comp, to work unattended every day.

If the valves are intact, it should be nearly impossible to reintroduce H2O because AGMs are watertight submerged to 30ft. Another plus in a marine use if there is a concern for Chlorine gas.

If the valves are broken, then you really don't have a proper AGM battery. Yes it has a-g-m but the chemistry is not to spec.

HTH;
John

Trying to find the routine for max battery life.

When bringing the AGMs into service my research showed that all strings vent a little from the stronger cells for the first few weeks. When I reconditioned my car AGM which ran flat, the procedure was actually designed to create bubbling and a small amount of venting.

I devised a simple way to find with each battery if there was any gassing going on by routing the vent hose into water or floating a ring of distilled (in case it were ingested) water on top. Based on watching these, and based on following manufacturer recommended charging protocol with various different chargers, it is my belief that AGMs vent a *little* (at a level you cannot hear or smell) far more than their owners may realize.

For example after our power outage, the first real use of the AGMs in production (I've still yet to load test them - need better short cables for the big inverter), I thought they were charged back to full. But this is tricky. I have found if they are really full they will have a voltage of 12.93v after 24 hours. They were only at 12.87.

I noticed the smart charger (I know, I know!) floats other batteries within a few hundredths of the manufacturer recommended float and temp was within a few degrees of 77, so I gave it a try. After not too long I saw a bubble, then a few minutes later one from another cell.

Because I do not leave them full time on float but top them off at least once a week, it is possible the string has not fully gone though it's initial equalization (supposed to take weeks under full time float) after which that initial minimal outgassing is supposed to stop.

SO I decidedly want to stay away from any venting (the bubble is not a bubble in free electrolyte, but it is still gas that escaped the regulation valve and was not recombined internally to electrolyte in the battery). The reconditioned AGM did make some bubbling noises as part of the reconditioning procedure. ABsolutely that dried out the AGM some but it restored capacity compared to a badly sulphated AGM that it was.

My desire here is to be able to really float indefinately, without any undected venting taking place. I think to really do that I am going to need a temperature compensated float charger.

Looking at the paper it was interesting to see what happens to a battery between no charging and an upper bound of float charging. I don't trust any charger I have yet to leave on the battery 24x7. Cranking something slightly to the low side is interesting to me - not sure if that or the daily cycles of solar would do the battery more good (since the battery sits not charging all night every night and does a tiny shallow cycle every day due to tiny self discharge).

Really it is more for my learning than anything else. But getting my little string on a near telecom grade of standby charge since it's usage is very much more like standby service than cycling service is just a bit of a hobby at the moment.

Jim

HiTech wrote:
I have been floating mine to manufacturer spec when temp is close to 77, and using the PWM solar controller tweaked to the recommended charge voltages (on battery temp compensated) the rest of the time.

So far so good. I only see outgassing (like a bubble a minute) if the temp climbs above 90 and the battery is on float.

I guess my biggest takeaway from this paper is running say a tenth of a volt under temp compensated ideal float may not be the end of the world. My own experience is that a tenth over on AGMs could potentially be slowly destructive.

Every bubble causes me pain lol.

Jim

Is this an OCD in trying to stay on the highest voltage tightwire? If so, why? What are the expected improvements?

I would be very concerned if my AGMs were bubbling at all. Do you mean to say you are exceeding the valve pressure and releasing gas?

IMHO, every bubble that escapes translates into lost capacity. That is a no-go for me.

A proper temp compensating charger should prevent any gassing at the plates. If plates are bubbling, does charging take place under the bubbles? Is gassing really needed with AGMs, after all, there is no need to stir? What good can come from any bubbling?

HTH;
John

It goes beyond mere adherence to a given constant voltage.

The PERCENTAGE of kWh consumed in float mode over a given period of time is the key fundamental that must be implemented. If a pure Pb or calcium calcium cell has been calculated to lose 1.06% A/H capacity 30 days and you discover 2.95% being delivered...it's time to find out why. This absolutely can not be done by voltage control only.

The key word is FLOAT. Maintenance.

Hi Jim,

I do not have the luxury of 24 hour shore power charging. I feel that a sophisticated solar controller with temperature compensation is the "way to go". Put one between the charger and the battery bank. The controller won't care that the energy is coming from shore power instead of from a solar source.

-or-

Do as I mostly do and let the solar system meet the needs of the battery bank. Self discharge rates on agm format are extremely low.

I have been floating mine to manufacturer spec when temp is close to 77, and using the PWM solar controller tweaked to the recommended charge voltages (on battery temp compensated) the rest of the time.

So far so good. I only see outgassing (like a bubble a minute) if the temp climbs above 90 and the battery is on float.

I guess my biggest takeaway from this paper is running say a tenth of a volt under temp compensated ideal float may not be the end of the world. My own experience is that a tenth over on AGMs could potentially be slowly destructive.

Every bubble causes me pain lol.

Jim