AGM still makes more sense than Lithium

Re: AGM still makes more sense than Lithium

zoneblue wrote: »

Interesting. Do you have a source for this material?

Just Me with, 40 years experience as and Electronic Engineer....

Batteries, Batteries, and more Batteries...

Re: AGM still makes more sense than Lithium

feedhorn wrote: »

.. AGM batteries work best in UPS or Grid Backup situations where the batteries are charged to 100% and maintained there for the life of the batteries.

Why limit yourself if solar conditions make it more attractive? AGM has about half the internal resistance of FLA (specialty types even less), and thus less heat when charging (even if you can't feel it, it is still part of the inefficiency process), so more energy goes into charging. You get out of bulk faster. And if you can manage the panel array, you can feed them with twice as much current as well. (typically max current FLA = C/8. Conventional AGM = C/3). Extreme cases like Concorde, Enersys and such have no such limitation, only the CV limit. AGM's are very useful in limited solar-insolation environments.

New AGM batteries need to float at proper voltage for about 6 months to reach initial 100% charge. Its important to reach a true 100% charge.

6 months? That kind of precision takes them out of the range of practicality and none would be useful. You manage float in solar on a cyclic basis by using an extended absorb, (setting your float voltage the same as the absorb voltage, and letting the sun time it all out and turn off before you exceed the manufacturer's maximum limit for absorb). This reduces the float time. See Deka AGM RE guidelines. Or in some cases, an IUI profile can compensate, but that was best meant for very short-cyclic duties, like warehouse foklifts, and EV's using lead acid back in the 90's.

Any portion of their capacity less than 100% will eventually turn to hard sulphate and that capacity will be lost.

True, but at what percentage of practicality? It can be managed to get the lifetime you need out of them without going to 100% each day. You just trade lab perfection for real-world conditions. It is manageable.

As for Lithium batteries: Cycling is better than not cycling, they are not so good as backup batteries.

I would agree, but only from an operational standpoint of wanting them to only be charged to about 50% capacity for long term storage/standby. They could be used in a fully charged condition if size and weight were of extreme concern, as long as you count on degradation, and may survive solely for a limited amount of events. Of course switching them back to a cyclic duty in a degraded condition makes no sense. One would have to weigh the pros and cons carefully. That being said, I still have my fully charged AGM's ready to go.

Capacity deteriorates over time. I have some 20 year old laptop cells that still have about 30% capacity.

Good point - here, LiCo02 laptop and cellphone type batteries do age quite rapidly. Not as much with lifepo4. If you live in a cool/cold climate, so much the better for ANY battery. Prof. Jeff Dahn at Dalhousie U. has a cell from the late 90's that kept at about 20% SOC, performs as well as the day it was made. Temperature is a major factor. Just like with lead.

However, I question the wisdom of hanging onto old batteries, even if they can provide limited service. What you don't know is that upon the next charge cycle, the degraded components decide to call it quits - or even worse, rapid disassembly. To me, that's much like the guys trying to nurse power from 20 year old rechargeable AA batteries with hundreds of dollars in equipment to do so. Perhaps fun, but not practical.

Satellites use Lithium batteries and have expected lifetimes of 15-20 years when deep cycled and recharged every 88 minutes.

They should be, what with living in the deep-freeze of space! Bring that thing down to earth in my backyard, and what - 6 years tops?

Everything is a tradeoff of one factor or another. Strive for the best fit. If you strive for perfection, they are only useful in the lab.

Re: AGM still makes more sense than Lithium

zoneblue wrote: »

Well the agms here spend most of their day in float, but people keep telling me that they are going to die of positive plate grid erosion if i do this. So I dont know.

I think the most important thing you can do us use a good Amp-Hour meter and make sure that you always put more charge back in than the discharge you take out.

See if you can get efficiency specs on your particular cells to help this process along.

Re: AGM still makes more sense than Lithium

PNjunction wrote: »

For the most part, all this goes away with Lifepo4 that has no absorb, nor need to float. If you make it - fine. If you don't - fine. No need for tweaking a standard CC/CV charge.

Amen to that! I can say that after 6 months my Lifepo4 has paid for itself in peace of mind and joy of using such a wonderful battery.

If someone with the worlds finest AGM bank offered to trade for my LifePO4, I would have to say no. Its just that good.

So glad I don't have to think about lead-acid anymore.

Re: AGM still makes more sense than Lithium

With agm, those end amps merely get you to the end of absorb, but only to a 99.9% SOC, not 100. Good enough not to be a factor for the very next duty cycle. But....

It may seem silly, but the effect is cumulative over time, especially when heat is added to the mix. Sure it is good enough for you to not notice it much on a daily cycle routine, but eventually, a shortened life due to the cumulative effects of daily minute sulfation, coinciding with natural aging takes it's toll.

A somewhat bad analogy is like brushing your teeth to 99.9% clean daily. Good enough right? However, plague under the gumline develops, and even though you might not notice it on a daily basis, eventually it hardens. A long float, um, removes the plague. Sick analogy.

Much depends on the manufacturer. Odyssey absolutely pounds you over the head about it, spurred by early EV adopters of the then-new pure-lead Genesis agm (prior to Odyssey) where many of the owners couldn't even get beyond 50 cycles and wanted their money back. Lack of a proper float spurred alternative algorithms like IUI to compensate, especially because they were starting the charge at a super-deep DOD like 80-100%. They sometimes couldn't even finish absorb, let alone spend quality time in float before the night was over.

Problem is, most consumers, especially the vehicular customers, don't read the voluminous Enersys application manual, and isn't mentioned in the short guides that come with them - mostly because in an SLI application, you will probably wear it out faster by shallow-cycling, improper charger voltages, heat etc faster than you do by lack of a good long float. For a storage application like solar, by all means, do a long float, or take compensatory measures.

Other manufacturers may not make much of it, figuring that most consumers think that 4 years is pretty normal for a battery, when in fact an agm treated well, will last many more - but that includes knowledge of a somewhat long and inconvenient float time - or measures to help compensate.

Re: AGM still makes more sense than Lithium

vtmaps wrote: »

Although, some sources claim that AGM batteries can become stratified....

Yes, that is true for mostly very tall industrial agm's. The wicking action of the electrolyte in the glass matt can't overcome gravity at the top. An example could be made by holding a long length of paper towel over the bathtub filled with water and dipping the bottom in. At some point, the wicking action cant make it any further up the towel, despite their being a whole bathtub of electrolyte, er water underneath.

Well, it's there, but the density gets smaller at the top as opposed to the bottom in a real tall agm battery leading to stratification.

Re: AGM still makes more sense than Lithium

That is actually done - mostly at a 45 degree angle or so in some installations.

Re: AGM still makes more sense than Lithium

feedhorn wrote: »

So glad I don't have to think about lead-acid anymore.

I hear ya'. I too found the claims beyond belief. Usually that means some sort of scam, hidden gotcha', un-obtainium, you name it. So like you I put large prismatic lifepo4 to the test and found the claims to be true.

For a guy that practically sleeps with the Enersys agm application manual under his pillow, the simplicity of it all was quite disturbing and still takes some getting used to. What - no absorb, float, eq, special algorithms, charging to 100% each day (and in fact being rewarded for NOT doing so in the long run - entirely opposite of my beloved tppl agm's).

Just bulk charge to a point that you feel is good? Other than going under or over voltage, is that all there is to it? Yep. they took all the FUN out of battery maintenance, something which I enjoy.

Still blows my mind every day. Ok, so one limitation is that you should operate these things terminals up. I can live with that.

Re: AGM still makes more sense than Lithium

zoneblue wrote: »

...... The question is: are traditional float charges really suited to
antimony-free lead-acid batteries? Practical situations on field as well as experimental
results say no. Standby VRLA batteries maintained under a constant float voltage to
compensate self-discharge encounter the problem of short service life, when our results
show that traditional float charge currents are far over what is needed to maintain the VRLA
battery state of charge.

I agree completely! But this is about putting those agm's in storage after first completing a full charge, which includes finishing absorb, followed by at least 8-16 hours of float first! So the thing here that confuses everyone is differentiation between what it takes to truly achieve a full charge for a vrla in the first place, as compared against the lesser requirements of followup storage. (providing that storage / standby doesn't have any parasitic loads).

.... In order to reduce overcharge, intermittent charges (open-circuit and periodical charges)
have been used instead of float charges and have given positive results in reducing thermal
runaway and increasing the battery life span.

WAAY bad, if that intermittent charging means bringing a previously fully charged vrla through a full absorb cycle again. Not necessary. Enersys found this out early on when commercial users tried to get around the complexities of proper charging by merely putting a charger on a timed switch, say once a month and taking a good vrla that was already at say 98% SOC through an entire charge cycle. Basically the extended absorb, even though separated by a month or so, accumulated damage. Old procedure not recommended by anyone these days.

Nevertheless, corrosion of the positive grid is also high during open-circuit periods of intermittent charges. Indeed, it is revealed in the
literature that corrosion is minimum when the positive polarization is between 40 and 80 mV. "

Yes, but this intermittent charge (already proven bad by most manufacturers) implies that the initial full charge was obtained, and as detailed before, that includes 8-24 hours of float.

I'm glad you are looking at the Enersys / Odyssey documentation. Add to your library the "white papers", where one of them goes into great detail about why intermittent charging is bad, and if you are going to float at all, it had best be done at a very specific voltage, like 13.5/13.6v. Otherwise, an improper voltage is actually contributing to the corrosion problem. So if you have your ducks in a row, you CAN float them and reduce corrosion, but that is a very precise window to do it in. If you don't hit that narrow window, you just contribute to the problem.

Search for "Intermittent Charging - Newark" (no quotes) and that will lead you to the pdf put out by Enersys about it.

In the end however, is your application a stationary / standby type? Nope. Once again, Enersys will specifically spell out what is and is not a standby or cyclic application. It has more to do with than just idle time. Very good information that I've not seen anywhere else in a consumer-available manual.

On the whole however, at some point how obsessive are we going to be about an 8ah ups-style battery that could just be replaced a bit sooner than applying commercial quality charging support to? (I'm not saying don't, and it is always good to treat your batteries right than wrong). At some point, practicality overrules perfection. Like trying to keep AA rechargeables from the 1980's going.

Re: AGM still makes more sense than Lithium

PNjunction wrote: »

I agree completely! But this is about putting those agm's in storage after first completing a full charge, which includes finishing absorb, followed by at least 8-16 hours of float first!

So an AGM that floats prior to noon has a good shot based on your theory. How do you determine how long that float period is? In practice ive noticed the charge acceptence drop to down below 0.1% C10 at the end of a long day. No way to tell how low it go.

WAAY bad, if that intermittent charging means bringing a previously fully charged vrla through a full absorb cycle again. Not necessary. Enersys found this out early on when commercial users tried to get around the complexities of proper charging by merely putting a charger on a timed switch, say once a month and taking a good vrla that was already at say 98% SOC through an entire charge cycle.

The paper talks about small float bursts only. However their point is that a fully charged bank left unconnected will also suffer grid corosion. Their final solution is a maintenance charge of microamps to achieve a polarisation bias that actively protects the positive grid. BUT..., in order to do this in practice, it involves dual redundant banks switched between loads, and charge/maintenace.

You cant not float a bank in service right. Except to lower the float voltage to something like half a volt over rest voltage, as Coot said. But getting the polarisation voltage right would be tricky, without current limiting.

Basically the extended absorb, even though separated by a month or so, accumulated damage. Old procedure not recommended by anyone these days.

With WBJR you have more control over absorb. Any attempts to reabsorb a charged bank, and it will just go straight to float. So thats no really an issue these days.

I'm glad you are looking at the Enersys / Odyssey documentation. Add to your library the "white papers", where one of them goes into great detail about why intermittent charging is bad,

Im not sure i found the exact enersys manual you refer to. Do you have a link?

and if you are going to float at all, it had best be done at a very specific voltage, like 13.5/13.6v. Otherwise, an improper voltage is actually contributing to the corrosion problem. So if you have your ducks in a row, you CAN float them and reduce corrosion, but that is a very precise window to do it in. If you don't hit that narrow window, you just contribute to the problem.

Yes.

Search for "Intermittent Charging - Newark" (no quotes) and that will lead you to the pdf put out by Enersys about it.

Abour a dozen links down:
http://www.newark.com/pdfs/techarticles/enersys/Intermittent_Charging.pdf

In the end however, is your application a stationary / standby type? Nope. Once again, Enersys will specifically spell out what is and is not a standby or cyclic application. It has more to do with than just idle time. Very good information that I've not seen anywhere else in a consumer-available manual.

Thats the thing RE use is one foot on both cycle and standby realms, and even that depends on your mgmt regime. PSOC is something where not a lot of research has been done i guess.

On the whole however, at some point how obsessive are we going to be about an 8ah ups-style battery that could just be replaced a bit sooner than applying commercial quality charging support to? (I'm not saying don't, and it is always good to treat your batteries right than wrong). At some point, practicality overrules perfection. Like trying to keep AA rechargeables from the 1980's going.

Well i spent NZD2.5K on 400Ah 24v. Its a small bank, (GC2s would maybe cost as much here?), but can charge and deliver as much as a bigger FLA. Hence my total cost is less, more money spent on PV less on lead. They are two years in now. Such batterys are widely available in a wide variety of brands and packaging stemming from the telcoms backup industry. However the documentation is usually poor, and hence finding the right setpoints can be challenging. Theres a reason few will offer opinions because no one really knows.

And that is what leads the old timers back to FLA, and the youngsters to LiFePO4....

Re: AGM still makes more sense than Lithium

zoneblue wrote: »

And that is what leads the old timers back to FLA, and the youngsters to LiFePO4....

Hah! Actually with LiFePo4, the thread would be maybe 5 messages long and would go something like this:

Q. Did you charge to 13.8v, (or 3.45v per cell) ?
A. No, it only reached 13.7v, am I ok?
Q. Are you ok with having a 95% SOC, since there is no sulfation or need to reach 100%?
A. Yeah. I've got enough capacity to make it. Can I do that every day?

Sure, in fact you'll be rewarded instead of penalized for running in a PSOC type of operation.

Q. Should I float these things?
A. No need to. Just reach the SOC you are comfortable with and call it a day.

Great - thanks
See ya!

Re: AGM still makes more sense than Lithium

THATS the one!

It shows that unless you are doing it at the specified float voltage, you may be led into a false sense of security that you are doing much better than just leaving it open circuit! So if you are going to do it, you better do it right, or don't do it at all. And of course, that includes temperature-compensation as measured at the terminals, not ambient.

This is what lead some commercial users to oversimplify things with intermittent charging (different from opportunity-charging!) on a timed basis. The requirements to get it right were just too much for some.

But that is for Enersys / Odyssey. I have not seen any graph like that from any other agm manufacturer, pure lead or conventional. However, this lead some charger manufacturers to proclaim that the Enersys batteries had "special needs" and were not really for consumer use, but specialist industrial batteries. No matter - lifepo4 kind of throws a wet-blanket over all that now.

Re: AGM still makes more sense than Lithium

zoneblue wrote: »

And that is what leads the old timers back to FLA, and the youngsters to LiFePO4....

Hey, I'm 68 and I switched to LiFePO4 and I will never go back to the nightmare of lead acid.

Thanks for making me feel young!

Re: AGM still makes more sense than Lithium

Cariboocoot wrote: »

What "nightmare" would that be?

I lived the last 11 years cycling lead acid batteries off solar panels every day.

I could write a book about all the hassles they caused me. One set lasted 4 years but the last year they were plagued by poor performance. My last set only lasted 2 years before one cell went south. Probably caused by the factory installing acid with too high an SG. Never a day went by where I didn't have to monitor the state of charge in hopes of getting to the mythical full charge state. Always trying to avoid sulfating the plates. What a Nightmare all that was.

I was so glad to finally get away from all that.

Re: AGM still makes more sense than Lithium

I think the most people that have good luck with lead acid batteries don't use them every day. Even one day off a week would be a great help to lead acid batteries.
AGMs work best in UPS or Backup situations.
Lead Acid works great for engine starting. A few seconds of load then immediately recharged.

Full time off-grid cycling is the nightmare with lead acid unless you can afford the cost and weight of 10X the daily amp-hour use in battery capacity. A 10% daily cycle is reasonable for lead acid batteries recharged with solar power.