dying batteries...help

hillbilly · December 2009

So I could use some help/suggestions here. I'll try to keep a long and convoluted story as brief as possible and still include some of the key details:

Our battery bank of Surrette S-460's (2 sets of 4 paralleled for a 24V system, rated 700AH, estimated 500AH currently) has had to suffer through some classic beginner mistakes in my hands. This last March I realized that some of the cells were reading much lower than others, after much EQ'ing and lots of help from the tech support guys at Surrette I was able to get things to a level that we all sort of agreed was probably "as good as it'll get". At that point there was one cell in particular that always read low, and one or two that were always high with the spread being between 1.256-1.275.

Things seemed more or less stable throughout the summer, but this fall I started to have a growing spread in the SG levels and the low cell has become more and more stubborn in it's low SG level. The low cell now seems to top out at more like 1.246 after EQ'ing (the high cell typically reading about 1.272). I'll skip several twists and turns here to get to the present point; the other day I was doing a load test of sorts to try and verify just what kind of capacity we were dealing with. After drawing the batteries down to a voltage of 23.2V while under a 20amp load, which should be right about 50% SOC I checked a couple of cells and the SG levels were way out of line. The highest cell read ~1.232 and the lowest was ~1.168, with others varying from 1.205 to 1.185. The Trimetric read exactly -250Ah from full.

I fired up the generator, and charged them for a while until I ran out of gas (thought I had a full can, but didn't). When the generator shut off it was after dark, so no PV input, and the voltage was up to 28.4V... and the trimetric indicated that I was back up to roughly 75% SOC (-130Ah from full). The weird part is that after running some minor loads that evening the voltage never dropped below 25V, and this morning after sitting all night with a minor 0.5 amp load the battery voltage was 25.3V and the trimetric was indicating we had about a 69% SOC. Checking the SG levels the low cell was 1.177 and the high cell was 1.232, others were within 0.01+/- of 1.200. Regarding the trimetric readings, I am aware that there are a lot of factors that could throw them off but I had just EQ'd the batteries before starting the load test, and I had a pretty good guess that our batteries had a capacity of ~500AH, and the AH readings of the trimetric pretty much jived with all of this completely so I'm inclined to believe them.

Biggest questions I have are:
-why the supper high voltage reading, this is much further than I've ever seen a "false high" voltage reading on this bank. Could something other than sulfation be causing this?
-is this as bad as I think it is?
-since the lowest cell readings all come from the same string of batteries, should I cull them and just run with my 4 best batteries? I'm torn on this one, since going with half the capacity during the winter months means that we will be cycling them much deeper and having to run the generator a lot more frequently.
-any other suggestions for squeaking out as much life as we can from these batteries?

Thanks for the help...
HB
(sorry for the long winded post, I just wanted to try to give out as much detail as possible)

mike95490 · December 2009

Re: dying batteries...help

I'd do any load testing with full gas and a full day of PV ahead. This is a bad time of year (short days) to be playing around. Keep the batteries full, and hope for the best. I would isolate the string with low cells, so it does not pull your good string down. (put it on charge every other day to keep it alive)
Make sure you get into float for several hours once a week, and to float daily, maybe run genset in AM for an hour to bulk the batteries.
Is an expermintal de-sulphator worth trying - maybe if it does not cost much.

BB. · December 2009

Re: dying batteries...help

If we go with Trojan's recommendations of equalize if SG is >0.030 difference between cells--I would just pick the range that most fall into (1,200-1.230) and call those "normal". Then look at what is outside that range.

And you are down to one cell (???). Sounds like, for what ever reason--that cell is the limiting factor for that battery string. You might try and get a used/new battery just to replace that one with the "bad cell".

Now, the one string that is lower SG than the other(s) (by the way is this 2 strings of 6 volt batteries--I would guess). That one bad cell is probably limiting the rest of the cells in that string from reaching full charge (at least without extensive equalization to push the current "through" that bad cell--which probably causes more damage to that cell and the "good" cells on the "good string" from over equalization).

So, your choice. Find a used/new battery to replace your one of 8 batteries, or take 4 out of service, send one to the recyclers (or to vendor to see if warranty issue) and keep the other three charged for "hot spares".

It really gets back to how good do you think the other batteries are. If they have lots of years left on them, it may be worth buying one replacement to get the string back to relatively full capacity (your tests may be mostly testing the good string as the bad string with the bad cell/low over all charging is not contributing as much).

If, the rest of the batteries start failing in the next few years--at that time you may choose to junk the whole bank and start over with a new one (perhaps, keep the one "newer battery" off to the side as your hot spare if you ever get a bad cell in the future).

For 1/8th the price of a whole new bank--I would be tempted with the new/good used battery experiment... The chance may be that all the rest of the bank will function well for years into the future.

Regarding the weak bank, I would see if you can charge them separately from the good bank and get the rest of the cells up to "charged" SG first, before removing the bad battery and replacing with a fully charged new battery. You want to get everything relatively balanced so you don't end up stressing your cells (say over charging the new battery to get the "rest of the old/weak bank" back to full charge--which would overcharge the new fully charged battery to do that).

I hope it makes sense (trying to clarify low + high SG cells in series charging--to recharge the low SG cells with high SG cells all in series--the high SG cells will have to out gas a lot to accept current required to charge the low SG cells--can be done but is kind of hard on the high SG cells).

-Bill

Dave Angelini · December 2009

Re: dying batteries...help

If you have treated a great battery poorly there is no way to "bring it back"
The damage is done. Some improvement can be made but how much is your time worth?

Use them up and do not repeat bad habits/strategies on the new set.

The classic battery failure symptom is, "my battery does not hold charge like it use to or, it sure does charge fast!

hillbilly · December 2009

Re: dying batteries...help

Thanks for the replies.
Mike, I agree on the full tank of gas I thought that I had a lot more gas than I did. But thanks for rubbing my nose it it :-) I should say that I wasn't really playing around as much as trying to get a better handle on how charged my batteries were, and how quickly they might be sliding south. I was planning an EQ via the generator anyways so having to run the genny a bit more wasn't a big issue. The batteries have been getting recharged on a very regular basis for a while now, 98% of the summer days they have at least a couple hours in float. During these winter days they get a full charge at least 2-4 times a week (depending on the weather), but we have been running the generator a bit more than last winter.

Bill,
Yes they are 6v batteries wired in two parallel strings. They are a bit over 3 years old now, and have had one cell that's been notably lower than the rest since last spring, however there are now several cells that are slightly lower (more variance overall throughout).
I had thought about buying a replacement battery and I still may do just that. The only thing that makes me hesitate is that I'm not totally sure just how healthy the best batteries are. I have split them into separate banks about two months ago so that I could EQ the string with the weekest cell a bit more aggressively (didn't seem to do much). I did a load test on each string individually too, and actually the "better" (with overall higher SG levels) string tested a bit lower capacity, unfortunately when I did those tests the temps were varying quite a bit so it's hard to say for certain. One thing is certain is that these batteries were subjected to some varying levels of abuse, so I don't really want to drop more money into this bank unless I am pretty sure I can get at least a couple more years out of them. I'm also tempted to replace these batteries with a different make when that time comes, so the idea of keeping hot spares wouldn't work in that case...

Any guesses about that voltage reading, that's the thing that most confused me...

hillbilly · December 2009

Re: dying batteries...help

Dave Sparks wrote: »

If you have treated a great battery poorly there is no way to "bring it back"
The damage is done. Some improvement can be made but how much is your time worth?

Use them up and do not repeat bad habits/strategies on the new set.

The classic battery failure symptom is, "my battery does not hold charge like it use to or, it sure does charge fast!

Thanks Dave,
I wouldn't say that I've treated them poorly in general, but back in the very beginning I did certainly make some typical errors. It's hard to say for sure what did what, but my strongest suspicion is that the time I spent using a cheapo hydrometer that was giving me consistently high readings was what really did them the most damage. This would have been at least 6 months or so, in that time I'm guessing that they were not getting charged fully (except for a monthly mild EQ).

On the classic symptoms you list, these batteries haven't really shown either of those (yet?). They seem to hold voltage very well, they do take a fair bit longer to recharge than they used to (longer absorb times). Water consumption has been moderate. The strangest part to me was the overnight dramatic change; I mean the overall capacity had dropped a bit, and the SG levels seemed to be slowly getting worse and then things just went really weird all at once. SG levels spread much further apart, and the voltage level reading over 25V when the SOC was probably under 75%...

niel · December 2009

Re: dying batteries...help

batteries start doing wild things as they deteriorate and it'll show it reaching voltages sooner and even higher upon charging. you can use it as is and you can make the decision as to when to pull the bad ones out of line as either way it's gonna be bad, in or out. unfortunately, the certainty is you will need to save for new ones and they can cave in quickly when you least expect it. also, the load tests can further stress the batteries so you may want to refrain from doing that or do it less often. try to gauge it more by your meters and sg readings as to how much you have left and you will semi know just by how they act when things are worsening. keep an eye on their behavior until you can get new ones and in addition to more charges needed, you may need to cut back on the loads as lighter loads may also help extend the life.

hillbilly · December 2009

Re: dying batteries...help

Thanks Niel,
I kinda figured that a couple of radical changes spelled B A D for the battery bank. On the voltages, it seems pretty normal while charging (it's currently on a charge via the generator, and seems to be responding "normally"). It was just the high voltage while discharging last night that was weird. As for the loads, they are pretty light most of the time, even for the load testing I can't really put more than about a 20-25 amp draw on them for any length of time.
One of the reasons for testing the capacity was so that I'd have a bit better sense of what the ending amps of Absorb should be, as the SG levels were not in agreement. One other reason was that I was trying to get a better guess at how much longer I might get out of these batteries; I could tell that they were probably on the downward trend, but I wasn't sure just how quickly they were changing. Do you think that it's possible that the stress of the load test, mild as it was, could have sort of tipped the balance so to speak?
thanks again...
HB

BB. · December 2009

Re: dying batteries...help

It is possible that your battery temperature from Summer/hot/testing to now (winter, cold, low current) can affect the per cell voltage by upwards 0.1 volt per cell.

Cold batteries read a higher resting voltage than warm batteries.

For a 24 volt / 12 cell bank, that could result in anything to a 1.2 volt change (24 volt bank) between the two states. Probably, realistically a 0.3-0.4 maximum Summer/Winter offset voltage (0.04 volt per cell over a reasonable temperature range from looking at the chart in the first link).,..

-Bill

niel · December 2009

Re: dying batteries...help

"Do you think that it's possible that the stress of the load test, mild as it was, could have sort of tipped the balance so to speak?"

well it didn't cause it to go bad, but it will speed up the process.

hillbilly · December 2009

Re: dying batteries...help

BB. wrote: »

It is possible that your battery temperature from Summer/hot/testing to now (winter, cold, low current) can affect the per cell voltage by upwards 0.1 volt per cell.

Cold batteries read a higher resting voltage than warm batteries.

For a 24 volt / 12 cell bank, that could result in anything to a 1.2 volt change (24 volt bank) between the two states. Probably, realistically a 0.3-0.4 maximum Summer/Winter offset voltage (0.04 volt per cell over a reasonable temperature range from looking at the chart in the first link).,..

-Bill

I'm confused too Bill. I hadn't really noticed any different "resting" voltage between summer and winter. Since I don't ever really have a true resting battery bank, don't usually pay too much attention to the voltages other than while on charge or under load. I can say that a voltage of over 25V is common first thing in the morning when the batteries are over say 85% SOC summer or winter, or under load when they are over 90%. I say that based on past observances (read: rough, fuzzy memory here), the voltage reading I had that evening while under a 6 amp load at less than 75%SOC, normally would not have been much above 24V (opposed to 25.1V).
Anyways, I'll keep an eye on them over the next couple of weeks and post my experiences here. Hopefully others can benefit...
HB

RCinFLA · December 2009

Re: dying batteries...help

Treating a battery 'badly' has several dimensions. The two primary issues are sulfation from not fully charging and other is grid corrosion due to overcharging.

From a recharge perspective to achieve proper and matching SG, the two can show the same symptom of not being able to get SG up to 1.27 range.

Sulphation will rob capacity, grid corrosion will increase internal resistance.

Load testing can be helpful to detect grid corrosion. The voltage degradation will be more abrupt with high internal resistance then the more gradual voltage degradation due to capacity degradation. It is easier to distinguish between the two if you have a previous history of the load test performance.

Don't get too carried away with equalization. If you have grid corrosion you will make it worse with a lot of overcharging.

hillbilly · December 2009

Re: dying batteries...help

RCinFLA wrote: »

Sulphation will rob capacity, grid corrosion will increase internal resistance.

Load testing can be helpful to detect grid corrosion. The voltage degradation will be more abrupt with high internal resistance then the more gradual voltage degradation due to capacity degradation. It is easier to distinguish between the two if you have a previous history of the load test performance.

Let me be sure I follow you on this, as this could well be a key distinction: So with higher internal resistance that would show higher voltages while charging, would the same be true while discharging or resting too then? The term "degradation" kind of has connotations of a reduction in my mind, so I just wanted to clarify. I couldn't say for sure exactly how much the overall capacity has dropped, in part the batteries are colder now than in the summer, and I don't have much in the way of records from the very beginning. I am sure that there has been some reduction of capacity though, so I had assumed that it was due to sulfation. To be honest, I don't really know anything for certain with these batteries since I didn't really know what I was doing in the beginning...
Any further recommendations on diagnostics for them?
Thanks a ton,
HB

Photowhit · December 2009

Re: dying batteries...help

hillbilly wrote: »

I fired up the generator, and charged them for a while until I ran out of gas (thought I had a full can, but didn't). When the generator shut off it was after dark, so no PV input, and the voltage was up to 28.4V... and the trimetric indicated that I was back up to roughly 75% SOC (-130Ah from full). The weird part is that after running some minor loads that evening the voltage never dropped below 25V, and this morning after sitting all night with a minor 0.5 amp load the battery voltage was 25.3V and the trimetric was indicating we had about a 69% SOC. Checking the SG levels the low cell was 1.177 and the high cell was 1.232, others were within 0.01+/- of 1.200. Regarding the trimetric readings, I am aware that there are a lot of factors that could throw them off but I had just EQ'd the batteries before starting the load test, and I had a pretty good guess that our batteries had a capacity of ~500AH, and the AH readings of the trimetric pretty much jived with all of this completely so I'm inclined to believe them.

Biggest questions I have are:
-why the supper high voltage reading, this is much further than I've ever seen a "false high" voltage reading on this bank. )

What false High? When the genny quit you were in the 2nd stage of charging, the Absorption Charge, you should see 28.4volts every day, as the batteries are 90% full the charge controller maintains this max high voltage until the internal resistance is increased(faq says increases, but I thought it was reduced? I've been wrong before), your charge controller will reduce the charging current, for me it falls to 27.2VOLTS pretty quick then gradually to @26 volts.

Your Trimetric is only as good as the numbers you have given it, likely you don't have a good idea of what the capacity of your batteries is yet. If you want to have some idea set the capacity for 300 amp hours after equalizing, also as your batteries are unbalance they are working on them selves, the stronger batteries are trying to bring up the weaker batteries so your daily self discharge rate needs to be increased. This might at least give you an idea of the use / replacement.

If your batteries live outside the cold will also reduce the capacity.

hillbilly · December 2009

Re: dying batteries...help

Photowit,
Sorry let me clarify, the moment before the genny cut out the batteries had reached a high of 28.4V totally normal, but still a ways off from absorb particularly due to cooler temps. With temp compensation, the absorb stage would have kicked in at about 29.9V (probably another 50+AH into the batteries). At that point yes the CC would gradually reduce current as the resistance rises as the batteries become more and more charged... only I the batteries weren't that charged yet.
The false high that I refer too was the 25.1V reading that evening when the batteries were under a load NOT charging, and by morning after almost resting (but still under a continuous 0.5amp load) the morning voltage reading 25.3V. The trimetric amp hours from full reading that morning was something like -155AH... so whatever the real capacity it was still quite a ways from full, and at that kind of DOD I've never seen voltages that high.
Regarding the Trimetric, I've fidgeted with mine quite a lot and I think that I have a pretty good handle on it now. It's currently set to 500ah, which was at one point in time (a year ago) a very conservative estimate but appears to be pretty much on target right now. True the colder temps are certainly affecting the capacity, that's not really what I am concerned about.

Photowhit · December 2009

Re: dying batteries...help

hillbilly wrote: »

The false high that I refer too was the 25.1V reading that evening when the batteries were under a load NOT charging, and by morning after almost resting (but still under a continuous 0.5amp load) the morning voltage reading 25.3V. The trimetric amp hours from full reading that morning was something like -155AH... so whatever the real capacity it was still quite a ways from full, and at that kind of DOD I've never seen voltages that high.

My guess is your reading correctly and interpeting poorly.

Yes you had a load on after a charge and 25.1V at night...

.5 Amp load is just your Trimetric meter and your inverter idling. An inverter will draw more than that, alone, unless you have a tiny inverter. My 1800prosine draws no less than 30 watts before load.

I think you just saw the difference in loads.

Heavy charging, as in off a genny, might well have increased the temp of your batteries, I'll still bet I'm on the money.

hillbilly · December 2009

Re: dying batteries...help

Photowit, I'm not sure that I see what your overall point is here. Yes the loads were small: the evening loads which produced a voltage of 25.1V were about 6amps total (read on the Trimetric), and the continuous loads of through the night that were present for the morning reading of 25.3V were ~0.5amps (that's the CC, Mate, Trimetric, and a small DC fan). When the Genny shut off the batteries were still coolish to the point where the temp compensation was adding an additional 0.4V to the charge setpoints (the thermometer on the Hydrometer usually agrees more or less with this temp probe too). Those voltages seem right in line if the batteries were up over say 90%SOC, which I don't see being possible given the amount of amp hours that had been drawn out vs the amount of charging they received
Was your point that the batteries seem to be behaving normally, or was there something else that I'm missing?

Photowhit · December 2009

Re: dying batteries...help

hillbilly wrote: »

Was your point that the batteries seem to be behaving normally, or was there something else that I'm missing?

Nope, Hope every thing works out, Good Luck!

hillbilly · December 2009

Re: dying batteries...help

Thanks Photowit, I hope so too!

An update for those of you who are curious (or bored):
So yesterday ran the generator (full of fuel with two extra tanks!) all the way through a 4 hour absorb cycle at 29.4V, I missed the exact cut off from absorb but I think that the charging current was pretty close to 10Amps at that point. The SG readings were better, though still a bit out of line from where things had been: "average cells" were about 1.255, the high cell was 1.265 and the low cell was 1.226. I turned the charger back on at a 25AMP current for another hour, but was unable to get the SG readings afterwards (pretty sure this was just about what it would take to finish charging all the cells back up from that deep discharge the day before).
By this morning we had drawn things down -50AH (trimetric read 25.2V and 90%SOC) and the cells read even better! Which is a bit odd as usually the SG levels tend to be closer after charging than after discharging, although perhaps this isn't so odd since we are still fairly close to a full charge. The SG level of one of the average cells read 1.250, the high cell 1.264 and the low 1.234 (unusually high for any discharged state at all). I'm encouraged by this, but not sure what to make of the wild SG fluctuations the past couple of days (and yes I did take those measurements several times to be sure). Could be the deeper discharge sort of "stirred things up a bit"? It's cloudy now, but we have two full days of sun in the forecast starting tomorrow so I'll just let the batteries discharge through today and see how things look after two days in a row of recharging.

RCinFLA · December 2009

Re: dying batteries...help

A sulfated battery has parts of the plates insulated and therefore you effectively have a lower capacity battery. The sulfate also locks up some the sulphur needed to re-make sulphuric acid so it is not available to be recharged back into electrolyte resulting in lower SG reading at full charge.

Grid corrosion causes some of the grid to have higher resistance and bad contact to the lead dioxide plate material of the positive plate. Instead of having maybe 3 to 5 milliohm equivalent series resistance of a good battery you might have multiple times this number depending on degree of corrosion. The extra resistance gives a greater voltage drop when the battery is subjected to significant load current. Charging voltage will not be effected too much because the current is not that high.

I don't know the chemical reason but grid corrosion also seems to have a slight degradation to fully charged SG. A charged battery with grid corrosion also seems to have normal unloaded voltage. Your batteries have lead antimony alloy grid which is more resistant to corrosion then lead-calcium or pure lead grid of auto/marine and AGM batteries.

Load testing can help diagnose the actual situation. Pulsing load can be used to measure effective series resistance of battery. There is a normal degradation in series resistance as battery is discharged but grid corrosion has an additional resistance that shows up immediately on a heavy load on a fully charged battery.

You can discharge a battery by 20% to 40% (80% to 60% state of charge) and see if the open circuit, rested battery voltage and SG tracks the expected level for that given amount of discharge. If a cell shows a greater delta drop in SG then others and off of the expected discharge amount then that cell has a reduced effective capacity by sulfation.

hillbilly · December 2009

Re: dying batteries...help

RCinFLA wrote: »

Grid corrosion causes some of the grid to have higher resistance and bad contact to the lead dioxide plate material of the positive plate. Instead of having maybe 3 to 5 milliohm equivalent series resistance of a good battery you might have multiple times this number depending on degree of corrosion. The extra resistance gives a greater voltage drop when the battery is subjected to significant load current. Charging voltage will not be effected too much because the current is not that high.

I don't know the chemical reason but grid corrosion also seems to have a slight degradation to fully charged SG. A charged battery with grid corrosion also seems to have normal unloaded voltage. Your batteries have lead antimony alloy grid which is more resistant to corrosion then lead-calcium or pure lead grid of auto/marine and AGM batteries.

Load testing can help diagnose the actual situation. Pulsing load can be used to measure effective series resistance of battery. There is a normal degradation in series resistance as battery is discharged but grid corrosion has an additional resistance that shows up immediately on a heavy load on a fully charged battery.

Thank you for the details RC,
I think that this confirms my suspicion that I've got some degree of sulfation of at least that one low cell. When you're comparing charging and discharging currents, to be clear I only rarely see more substantial discharging currents, usually in our system it's the other way around where we have a bit higher charge currents (particularly if running the Generator).
We don't seem to be seeing sharp drops in the voltage, if anything it usually reads slightly higher SOC than the SG levels indicate (if averaged that is, as the low and high cells offer a wide range of what the SOC could be). This would cause me to think that it's sulfation rather than grid corrosion.
I really appreciate the helpful suggestions,
HB

hillbilly · December 2009

Re: dying batteries...help

Update:
So we've had more sun than was forcasted, and the batteries have been getting nice long absorb times. I've been watching the charging/discharging currents and comparing them with voltage levels and SG levels closely; thus far it seems that more or less that the Voltage levels and SG levels are agreeing with each other and the capacity seems pretty much what I thought it was: about 500AH in 40F ambient conditions. The SG levels seem to be fairly stable right now, but the difference in readings between the one high cell and the one low cell is hovering between 0.03-0.04.

I am leaning to try and separate the batteries for now, and maybe finding a single replacement battery for the one weakest. From what I've always heard this is too big of a gap in the SG readings, anyone have experience with a battery bank with that kind of a spread in SG levels between the cells? My only hesitation on splitting the battery bank up is that I would then be cycling the remaining batteries much more (half the rated capacity, plus peukert's law regarding the discharging currents now being higher in relationship to capacity...); I just don't know enough to really tell which would be harder on the batteries.
I've also thought that I might try to work a bit harder on the weakest battery, but not having any 6V charging options I'd have to hook it up with another battery to make up a 12V battery (I could pull the next weakest one I suppose). At 12V, I could hook the battery up to an Iota charger but, being off the grid, this would be in essence using one set of batteries to charge another... which seems pretty inefficient at best.
I could also hook it up to a small PV charging set up that I use for road trips (30 watts PV, Bluesky SB 2000 mppt charger), but this is less than a 1% charge rate so I'm not sure that it would do anything more than float the battery.

Any further thoughts, advice, hopes and prayers... battery voodoo, condolences???

P.S. anyone know of any used Rolls S-460 batteries for sale in Central California?
Thanks, HB

bryanl · December 2009

Re: dying batteries...help

pure lead grid of auto/marine and AGM batteries.

is this true? It doesn't fit with what I've read elsewhere.

RCinFLA · January 2010

Re: dying batteries...help

bryanl wrote: »

is this true? It doesn't fit with what I've read elsewhere.

Non-alloyed grids require a packing support. AGM are one construction that can be pure lead.

Lead-calcium is by far the most common for Marine/AGM's primarily for their low leakage characteristics.

bryanl · January 2010

Re: dying batteries...help

re "Non-alloyed grids require a packing support. AGM are one construction that can be pure lead. ... Lead-calcium is by far the most common for Marine/AGM's primarily for their low leakage characteristics. "

this does not fit with what I have seen from battery dissections nor from the various papers on battery construction I have seen nor from consideration of the basic issues of impedance and capacity.

calcium doping is to reduce gassing which is needed in sealed (VRLA) batteries. antimony is used for strength. AGM's and gel cells primary difference in construction is in how the electrolyte is held. and on.

Cariboocoot · January 2010

Re: dying batteries...help

If both plates (anode and cathode) were made of pure lead you wouldn't have a battery, as there would be no electrochemical difference between the two to react. One is (basically) lead, the other (basically) lead dioxide.

Doping electrolyte with calcium is not the same as alloying lead with calcium. Antimony is also frequently used to strengthen the lead, as well as tin and some other elements. Battery manufacturers do not all use the same formula for their alloys or even one formula within a manufacturer. What is most commonly used is not an absolute.

The glass mat in AGM's is both a separator and a strengthener for the plates, reducing the likelihood of plate collapse/shorting. Therefor this type of battery may have less or in some cases no strengthening alloy added.

And as is so often the case with anything, specifications are subject to change without notice!

GreenPowerManiac · January 2010

Re: dying batteries...help

"Our battery bank of Surrette S-460's (2 sets of 4 paralleled for a 24V system, rated 700AH, estimated 500AH currently) has had to suffer through some classic beginner mistakes in my hands".

We all make some beginner mistakes, I've made plenty, especially on batteries. Does the weakest link in a battery get to suffer ? I'd say Yes. Sounds like an experiment or an overcharge went in the wrong direction. If and when someone thinks of a better way to store power other than a battery, that may be the day of glory. A better way may indeed be heat capture like a Hurricane draws it's energy from a Ocean with warm waters.

Does not sound like the battery is sulfated, however couldn't hurt to experiment with a desulfator. They've been known to clean up old batteries providing the insides are intact. I use them all the time.

hillbilly · January 2010

Re: dying batteries...help

GreenPowerManiac wrote: »

Does not sound like the battery is sulfated, however couldn't hurt to experiment with a desulfator. They've been known to clean up old batteries providing the insides are intact. I use them all the time.

Curious why you say that it doesn't sound like they are sulfated? Any ideas are a welcome help at this point.
Thanks,
HB

bryanl · January 2010

Re: dying batteries...help

re: "Doping electrolyte with calcium is not the same as alloying lead with calcium" - now that gets into something to think about, the difference between doping and alloy - I always thought of doping as the verb and alloy as the noun. In any case, my use in this context was strictly for the plate base structure and only for concept, not engineering.

As for the electrolyte, from what I can tell, you don't want anything except water and sulfuric acid. Only the concentration is tweaked for various goals.

The matter of distinguishing between positive and negative plates in a lead acid battery - the process of forming the battery - is another interesting aspect of these batteries.

On these topics, I think we need to be careful not to get too deep into the technologies as, from what I have seen, it is easy to get lost looking at trees and not see the forest.

On the sulfated indicators - good question there. A sulfated battery acts like an aged battery in that its capacity is reduced and its impedance increased. I'd agree with the idea of using a desulfator as a 'no harm' maintenance thing. Sulfation can creep up on you and long battery life is best achieved by keeping it at bay as best you can. It is why prompt and full recharging is so important and why you shouldn't just let batteries sit, especially in a discharged state.

RCinFLA · January 2010

Re: dying batteries...help

Besides load testing, knowing the history of the battery can help diagnosis.

My system is primarily UPS, mostly continous float charge from grid tie. After 4-8 years mine go by grid corrosion.

For a solar off grid, more likely to be short on full charge cycles, having higher likelihood of sulfation.

RCinFLA · January 2010

Re: dying batteries...help

bryanl wrote: »

re "Non-alloyed grids require a packing support. AGM are one construction that can be pure lead. ... Lead-calcium is by far the most common for Marine/AGM's primarily for their low leakage characteristics. "

this does not fit with what I have seen from battery dissections nor from the various papers on battery construction I have seen nor from consideration of the basic issues of impedance and capacity.

calcium doping is to reduce gassing which is needed in sealed (VRLA) batteries. antimony is used for strength. AGM's and gel cells primary difference in construction is in how the electrolyte is held. and on.

Never heard term doping used. Both plates are lead until charge formed that coats positive plate with lead dioxide.

Antimony grid is between 4-11% antimony and very small amounts of other things like arsenic, tin, copper, and silver and few other concocsions depending on what 'special sause' a given manufacturer wants to optimize.

Calcium alloy grids are 0.06-0.12% calcium with variable amounts of tin, aluminum, silver, and some other manf. unique pixi-dust. Several manf. have more tin then calcium. Weakness is corrosion. Strength is less self discharge when it ends up over at negative plate.

The alloying gets kicked out when aging corrosion burns deeper into positive plate converting grid to lead dioxide. It can cause problems after it migrates over negative plate. Bad news anyway when grid starts getting converted to lead dioxide which has higher resistance and can only convert to lead sulfate and back in battery reaction which is worse yet for resistance.

There are a few materials mixed in the paste which might be called doping. Primary ones are barium sulfate and lignosulfonate which help in the dissolution and reforming of the plates during discharge and recharging. They help keep the lead sulfate from bunching up to unrechargable blobs.

dying batteries...help

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