AGM vs FLA

palausystem · April 2014

We are ready to shop for our next set of batteries. Our "learner" set is about gone.

I'm still a novice, wondering if the FLA would be more forgiving than the AGM, and in what ways?
We like the sound of less maintenance. We have a shunt-based monitor, and so could keep an eye on things that way, but I'm so trained to check SG and do EQ's when the system is "sluggish", that I wouldn't know how to care for the AGM's, how to tell if there was a problematic cell, etc.
So I suppose once you establish the correct charging regimen, and have enough panel to battery ratio, you're good. Do you check voltages on individual batteries every so often? What else?

Given a properly set up controller the only downside I've heard so far is about longevity. Some say almost as long as L-16 FLA but I haven't heard anything very specific.

Cariboocoot · April 2014

Re: AGM vs FLA

FLA's are definitely more forgiving of mistakes. They are also cheaper per Watt hour, and can be monitored by specific gravity which is as close to 100% accurate in determining SOC as you can get.

AGM's are capable of greater current in/out, lighter, and not hazardous to ship. They don't produce any gas under normal circumstances. Most of the makers do not recommend any EQ charging ever, but some do (carefully controlled).

"Less maintenance" also means "no maintenance possible" really. If you do cause them to gas and they lose electrolyte there's no practical way of restoring it. No hydrometer monitoring means you must rely on battery monitor, and that is destined to be wrong eventually as the real capacity of all batteries changes over time. Most of them you can't check individual cell Voltages, and there's nothing you can really do even if you find one off (that "no EQ" issue). As a rule they don't last as long, and perhaps this is because of the monitoring/maintenance limitations.

Now someone will tell you something different, giving you an option of which to believe. It doesn't help you make the choice, but it's what happens.

BB. · April 2014

Re: AGM vs FLA

If I had to guess--Something like 1-2 years less life on AGM vs a similar quality Flooded Cell battery bank. Nothing firm--And it would be difficult to lay -1 year solely at the feet of AGM on a 7-8 year bank life.

Before making the AGM or not decision... What is the new bank going to look like? Bank voltage and AH rating may limit your choices of AGM batteries/cells.

Personally, I like one series string of cells--Some folks like 2 strings so they have a "backup" if one battery fails.

Do you have problems getting distilled water (expensive)? Is checking water a huge pain or something that does not bother you? How long did your original battery bank last--Good value for the time and money?

One thing I do not like about most "Modern" batteries is that you cannot check cell voltage. A real pain for 12 volt bank with 12 volt batteries... You cannot tell bad from good batteries in a parallel string. Having a DC Current Clamp meter can help (you can measure charging/load current per parallel battery--if wired in such a way)--But it is not as easy as just measuring cell voltage.

With higher voltage strings, you have at least two batteries in series. And with larger AH battery banks, you can get 6/4/2 volt cells and are able to monitor voltage on a more granular level (and I think gives you better information on AGM strings).

AGMs are about the "ideal" lead acid battery... But it comes at a cost==More money for the bank, no specific gravity to check, more susceptible to "over charging" damage.

-Bill

palausystem · April 2014

Re: AGM vs FLA

We're looking at 6v 260Ah battery, x16, in 2 strings. 48v, 520 Ah. I figure that size will be good for 3kW of panel and our 5.2kWh of daily usage. I think it's the Concorde sun Xtender, or maybe the US battery.
The battery we want to replace soon is at 6 years and we may get through another winter with it. Watering is no big deal since we got the Pro-fill system. So maybe the biggest reason I'm feeling drawn to AGM is that I've spent way too much time trying to doctor the abused batteries. Hmmm. Not logical. OK, so, assuming I get the charging protocols ironed out, the next thing is not having to do EQ's. I suppose if all is well that should only be a twice or thrice yearly event.... my reasons to go AGM are getting fewer.

I guess the only way to tell if you got a bad one is a voltage reading?

I'm trying to picture where the user screw-ups would come in. You do your calculations to find the proper absorb times, use your monitor to see where 100% SOC is... but like the previous poster pointed out those monitors rely on a new battery for accurate readings. So you end up ball-parking it (which is what people always do anyway, right?) and my question would be how easy is it to screw it up? I mean, if it's in absorb for 2 hours past what is actually 100% SOC and voltages are proper, have you damaged the battery already?

zoneblue · April 2014

Re: AGM vs FLA

palausystem wrote: »

I'm trying to picture where the user screw-ups would come in. You do your calculations to find the proper absorb times, use your monitor to see where 100% SOC is... but like the previous poster pointed out those monitors rely on a new battery for accurate readings. So you end up ball-parking it (which is what people always do anyway, right?) and my question would be how easy is it to screw it up? I mean, if it's in absorb for 2 hours past what is actually 100% SOC and voltages are proper, have you damaged the battery already?

This is exactly the problem... you just dont know, as there isnt enough feedback from tbe battery, and whose numbers do you trust. Hopefully the manufacturer, but you could argue that have a vested interest in your batterys dieing.

Err on the low side and theyll sulphate, err on the high side and youll use up the recombinant catylst.

You only know at their end of life how well your mgmt regime was. I have 2v cells in a single string which i prefer, and 18 months on the cell balance is still very tight, in fact tighter than they were at new. My last check they were within 0.01V.

AGMs reportedly do prefer higher charge rates. 10% C is considered the minimum for AGM, as their low internal resistance means you can charge (and discharge) them faster, and this helps stir things up inside. They arent immune to stratifcation from what ive read.

Another problem is that there is no one "right" way to charge a battery, with competing models emerging such as SMAs model. I Use WBJr end amps down to 0.5% C. And hope for the best really. Its all you can do with them.

PNjunction · April 2014

Re: AGM vs FLA

AGM has advantages, BUT under your conditions, they may not make enough of a difference.

However, a quick list of those advantages:

Lower self-discharge than FLA. When fully charged, you can leave them for months to maybe up to a year without a float charge, provided you have NO parasitic loads. (or just physically disconnect the system) This is desirable for mobile / vehicle use that might see seasonal storage rather than daily cycling. High heat reduces this period. Not sure you'd benefit from that here.

Higher voltage under load - If your equipment is voltage sensitive or needs higher voltages under large demands, then agm is desirable.

As mentioned above, you can basically double the amount of current (or more!) that you could put into an FLA. The advantage to that would be the ability to charge faster provided you have the additional panel power. This would be handy for locations that have low solar-insolation periods like the pacific northwest, Europe, etc. Manufacturer's have different maximum current limits, and also some have MINIMUM current limits to stay within warantee, so be sure to read the battery docs.

Nope - you cannot measure individual cell voltages. The best you can do other than careful monitoring with a wh meter to determine if you are passing 50% DOD is to just measure the terminal voltage(s) after at least a 4 hour rest period (again, manufacturers may differ and want 8-24 hours) of no-charge and no-load. For AGM's, this is typical:

12.8v and higher = 100% SOC
12.5v 75% SOC
12.2v 50% SOC
12.0v 25% SOC
<12v - don't go there.

This is generic and gives you no idea of cell balance, amount of sulfation etc. But if you see rapidly declining capacity beyond the norm, then you may have issues. Poor quality agm's, like used UPS style agm's can be a source of frustration. If you do go agm, get the TRUE deep-cycle ones meant for RE usage, unless you are just playing around with recreational 12v stuff.

If you are putting these batteries into banks of serial / parallel connections, it is pretty important like any other battery system, to make sure each individual battery is fully charged first, and all wiring infrastructure is sound.

As always, buy reputable batteries from reputable sources. While agm may be touted as maintenance free, that does not mean that you don't need to do your homework up front to make sure they get enough of a charge under your setup.

palausystem · April 2014

Re: AGM vs FLA

zoneblue wrote: »

I Use WBJr end amps down to 0.5% C. And hope for the best really. Its all you can do with them.

Can you explain that for the newbie? I know for our controller we can set duration but not end-amps.
Thanks

Cariboocoot · April 2014

Re: AGM vs FLA

palausystem wrote: »

Can you explain that for the newbie? I know for our controller we can set duration but not end-amps.
Thanks

He's referring to the WhizBang Jr add-on battery monitor for the MidNite Classic which allows controlling the Absorb stage by state of charge. If you don't have a Classic it is irrelevant.

palausystem · May 2014

Re: AGM vs FLA

Thanks everyone,
I think I will stick with the FLA's for now. I need the forgiveness factor and don't see a great benefit at this time.

AGM vs FLA

Comments

Categories