AGM battery problems

[arnolde73]

[Moderator note: I split this out from the "PIP-4048MS and PIP-5048MS inverters" thread because it is an off-topic fork from a discussion there. It comes logically after this post, but the discussion began here. -- Weber]

I'm a little worried my batteries are pretty shot... I have 4x12V/280Ah AGM in series, bought in December 2016.
This evening the inverter started beeping (at voltage <44V) so I hooked up the generator to charge, charging started at 19:29 with 15% SOC reported, and already 10 minutes later at 19:39 the SOC is reported at 95%. Now I know the original SOC value is everything but accurate, but that huge swing during charging does worry me, during a charge of 17-18A.

The charge current does stay at 17-19A and the voltage constantly rises, now at 20:34 it's reached 57.6V, at 20:54 it's reached 58.4V, and still shows 95% SOC. If I leave it running all night it will probably stay that way for another hour or 2 and then slowly go down in current.

Update: it's now 21:48, drawing 12A, voltage at 57.0V (which is what float is set to), SOC still reports 95%. Theoretically the generator should have put about 2kWh into the battery this evening.

Update 2 at 21:58: i just changed the float voltage to what it should be (55.2v) and the charge current is now 9-10A. So the batteries are still "eating" about 500W.

Code: Select all

Device mode	Time			AC_volt	AC_freq	PV_pow	app_pow	act_pow	Bat_vol	SOC	Chg_cur	dch_cur
Line Mode	2018-11-26 21:58:00	-	-	0	-	-	55.2	95	10.0	0.0	// added manually
Line Mode	2018-11-26 21:48:00	-	-	0	-	-	57.0	95	12.0	0.0	// added manually

Line Mode	2018-11-26 19:42:13	241.2	49.1	0	241.0	180.0	54.1	95	18.0	0.0
Line Mode	2018-11-26 19:41:43	238.5	48.5	0	238.0	170.0	54.1	95	18.0	0.0
Line Mode	2018-11-26 19:41:13	240.6	48.5	0	168.0	126.0	54.1	95	18.0	0.0
Line Mode	2018-11-26 19:40:43	242.2	48.6	0	193.0	136.0	54.2	95	17.0	0.0
Line Mode	2018-11-26 19:40:14	243.4	48.8	0	194.0	154.0	54.4	95	17.0	0.0
Line Mode	2018-11-26 19:39:44	241.3	49.1	0	217.0	169.0	54.7	95	17.0	0.0
Line Mode	2018-11-26 19:39:13	242.3	49.1	0	121.0	70.0	52.3	95	18.0	0.0
Line Mode	2018-11-26 19:38:42	247.7	49.6	0	123.0	85.0	49.7	75	17.0	0.0
Line Mode	2018-11-26 19:38:12	248.0	49.3	0	173.0	119.0	49.4	72	18.0	0.0
Line Mode	2018-11-26 19:37:42	248.4	49.7	0	197.0	142.0	49.3	71	18.0	0.0
Line Mode	2018-11-26 19:37:13	247.9	49.8	0	198.0	155.0	49.2	70	17.0	0.0
Line Mode	2018-11-26 19:36:43	249.0	49.2	0	199.0	153.0	49.2	70	16.0	0.0
Line Mode	2018-11-26 19:36:13	247.9	49.1	0	198.0	152.0	49.3	71	17.0	0.0
Line Mode	2018-11-26 19:35:43	245.8	49.4	0	197.0	142.0	48.9	67	17.0	0.0
Line Mode	2018-11-26 19:35:14	244.2	48.9	0	268.0	195.0	49.1	69	18.0	0.0
Line Mode	2018-11-26 19:34:41	243.1	49.0	0	268.0	217.0	49.1	69	16.0	0.0
Line Mode	2018-11-26 19:34:13	244.9	48.8	0	267.0	204.0	49.1	69	18.0	0.0
Line Mode	2018-11-26 19:33:42	243.2	49.1	0	267.0	221.0	49.0	68	17.0	0.0
Line Mode	2018-11-26 19:33:13	227.4	46.8	0	770.0	692.0	49.2	70	17.0	0.0
Line Mode	2018-11-26 19:32:43	227.4	46.8	0	737.0	737.0	49.1	69	19.0	0.0
Line Mode	2018-11-26 19:32:13	228.1	47.3	0	752.0	646.0	48.9	67	19.0	0.0
Line Mode	2018-11-26 19:31:43	227.0	47.2	0	681.0	646.0	48.7	65	19.0	0.0
Line Mode	2018-11-26 19:31:12	230.9	47.1	0	777.0	675.0	48.1	59	19.0	0.0
Line Mode	2018-11-26 19:30:43	235.4	48.2	0	783.0	783.0	47.4	52	8.0	0.0
Line Mode	2018-11-26 19:30:10	233.4	49.4	0	755.0	755.0	43.9	17	0.0	0.0
Line Mode	2018-11-26 19:29:44	239.6	49.2	0	718.0	680.0	44.0	18	0.0	0.0
Line Mode	2018-11-26 19:29:11	273.8	50.3	0	216.0	204.0	43.7	15	0.0	0.0
Line Mode	2018-11-26 19:28:44	264.5	50.2	0	158.0	131.0	43.9	17	0.0	0.0
Battery 	2018-11-26 19:28:12	0.0	0.0	0	92.0	37.0	43.5	13	0.0	0.0
Battery 	2018-11-26 19:27:42	0.0	0.0	0	68.0	44.0	43.6	14	0.0	1.0
Battery 	2018-11-26 19:27:10	0.0	0.0	0	92.0	46.0	43.7	15	0.0	1.0
Battery 	2018-11-26 19:26:43	0.0	0.0	0	92.0	47.0	43.6	14	0.0	1.0
Battery 	2018-11-26 19:26:13	0.0	0.0	0	68.0	37.0	43.6	14	0.0	0.0

[coulomb]

I'm a little worried my batteries are pretty shot... I have 4x12V/280Ah AGM in series, bought in December 2016.

So that's nearly two years old; that's about what you get from lead acid that sees voltages like 44 V and even 37 V [ edit: 37 V was a misread, sorry], if these low voltages are a regular event.

But this battery at the very least needs a really solid charge before you can tell what's going on. Like about 15 hours of generator charging (the full 280 Ah of your battery capacity), or the equivalent from PV or PV and generator combined.

This evening the inverter started beeping (at voltage <44V) so I hooked up the generator to charge, charging started at 19:29 with 15% SOC reported, and already 10 minutes later at 19:39 the SOC is reported at 95%. Now I know the original SOC value is everything but accurate, but that huge swing during charging does worry me, during a charge of 17-18A.

This indicates that the battery is in a high internal resistance situation. That's not good for them, and they need charge urgently.

The charge current does stay at 17-19A and the voltage constantly rises, now at 20:34 it's reached 57.6V, at 20:54 it's reached 58.4V, and still shows 95% SOC. If I leave it running all night it will probably stay that way for another hour or 2 and then slowly go down in current.

Those figures sound OK, but the data you sent tells a different story. [ Edit : my bad, I didn't realise that the data was in last-to-first time order.] The data starts with the battery at 54.1 V and around 18 A of charge current. That's 13.5 V per 12 V module, a reasonable value for charging. But then around 19:39 the battery voltage starts falling, to around 49.7 V and falling. This is the battery just starting to recover, the electrolyte is changing from almost water to actual acid, and is showing closer to its true state of charge. At about 49 V total (12.3 V per 12 V module), the SOC is (without looking it up) roughly 25%. But the total battery voltage falls again to below 48 V total, which is about 5% SOC (again, without looking it up). But at 19:30, the charge current is inexplicably down to 8 A, and drops to zero the next sample. With no charge current to push the battery voltage up, it plummets to 43.7 V (10.9 V per 12 V module, dead flat), and you turn off the generator at that point, so the inverter goes to battery mode, just when you need charging the most. Presumably, you just needed to add petrol or whatever, and resumed charging again. By that time, the battery would have gone high resistance again, so the terminal volts under charge would shoot up, and you might be taking false hope from this that the SOC is reasonable.

Update: it's now 21:48, drawing 12A, voltage at 57.0V (which is what float is set to), SOC still reports 95%. Theoretically the generator should have put about 2kWh into the battery this evening.

I think what happened there is that the battery was at a high internal resistance state for long enough that the inverter went from bulk/absorb to float, when the battery was nowhere near fully charged. That brings the charge current down from around 18 A to around 12 A, but hopefully, even though this is only 0.06C, the battery will still get some charge.

Update 2 at 21:58: i just changed the float voltage to what it should be (55.2v) and the charge current is now 9-10A. So the batteries are still "eating" about 500W.

This isn't "eating", this is charging. Your battery needs a lot of charge. I'd leave the float voltage setting up higher temporarily, so that you get closer to what your generator can output (looks like only around 1 kW), so you aren't wasting too much fuel. That generator seems small for your battery; you should be able to charge your battery at around 15% of its amp-hour capacity (0.15C), which is over 40 A. So hopefully your maximum total charging current setting (program/setting 02) is set to 40 A.

Thanks a lot for the data; it helps tell the story better than your occasional reports.

I don't hold a lot of faith that your battery will recover; when the battery voltage comes down after charging, it's a sign that the battery is in big trouble. It may recover with a good charge, but sadly, it's more likely that it won't.

I see that you're the gentleman that is having trouble updating your 72.60 factory firmware. Factory firmware is known to have charge bugs; these prevent the battery from charging fully, even when there is plenty sun, but this is bad for batteries, especially lead acid batteries.

Edit: don't leave the float setting too high for long, just while you're trying to get the real SOC towards 100%. No sealed batteries can cope with over-charging, since you can't add water to compensate for water lost during gassing.

[ Edit: changed the paragraph relating to factory firmware; I initially didn't realise he already told us about his factory firmware and his problems updating it. ]

[arnolde73]

@Coulomb thank you for the detailed analysis. I'm sorry that my data was badly formatted, unfortunately the preview does not match the final view so although I spent some time formatting the preview, it still slipped when posting. As a result I think you were mislead in a few points, i.e. the voltage never went down to 37v (and never has, I have the hard cutoff set to 42V as per battery datasheet recommendataion) and I didnt switch off the generator. I've reformatted the data again, mybe it's easier to read now. I also manually added 2 more lines at the top for easier comparison. You can see that I have about 600W motor load running during the first few minutes otherwise the inverter wouldnt start charging at all. But yes 44V happens almost every day now that it's winter, cloudy, and the batteries seem to have a lower charge.

Unfortunately I can't charge more than 20A (~1000W) from generator because the inverter loses the AC if it goes over 25A (the known charge cycling issue). The generator would be capable of almost 2000W, so 30A would be possible plus a small electric load. Anyway I did let the generator run for several more hours, I'll check the logged data this evening.

About the float voltage, yes I understand I should leave that set higher only for one really good charge and then set it back to normal. Unfortunately I had it set to max voltage (58.4?) for over a year so I guess maybe the batteries were overcharged a lot... It it really impossible to top up AGM batteries, even if I open the seal somehow?

I wonder if 2 of these https://www.aliexpress.com/item/48v-120 ... 6ab6315a6d batteries might be a decent replacement, if I need one, at least it would "only" be twice as expensive as the AGM's I have...

[coulomb]

As a result I think you were mislead in a few points, i.e. the voltage never went down to 37v (and never has, I have the hard cutoff set to 42V as per battery datasheet recommendataion)

Oh, my bad then, sorry. Still, 44 V, even though it's "allowed" according to the data sheet, is bad for life, and of course 42 V is worse.

and I didnt switch off the generator.

Then I don't understand why the last several entries have AC_Volt = 0.

I've reformatted the data again, maybe it's easier to read now.

Much better, thanks for the effort.

But yes 44V happens almost every day now that it's winter, cloudy, and the batteries seem to have a lower charge.

So they're getting near 100% DOD every day. They won't last long like that.

Unfortunately I can't charge more than 20A (~1000W) from generator because the inverter loses the AC if it goes over 25A

Yes, you told us, sorry. There are so many forum posters to keep track of.

Unfortunately I had it set to max voltage (58.4?) for over a year so I guess maybe the batteries were overcharged a lot...

That will have damaged them, unfortunately.

I[s] it really impossible to top up AGM batteries, even if I open the seal somehow?

I've heard stories of people adding distilled water with eye droppers. It may be possible, Google it. But most likely it's not worth your time.

I wonder if 2 of these https://www.aliexpress.com/item/48v-120 ... 6ab6315a6d batteries might be a decent replacement, if I need one, at least it would "only" be twice as expensive as the AGM's I have...

They might be, if they are any good. I'd be very wary of batteries from China whose pedigree and BMS is completely unknown. Two of those in parallel (240 Ah) would be more than twice as much useful energy as 280 Ah of lead acid, if they are of reasonable quality.

[ This has drifted off-topic. Please continue battery related comments on a new topic. ]
Edit: Weber has split this off now, so we can continue.

[andys]

Just adding my 2 cents. One reason I hated AGM batteries was how much power they waste when being topped up.

After bulk charging is complete, the resistance and temperature rises, while you need to keep pouring energy in to soak them and complete the charge.

So you are generating power from PV and basically wasting it as heat.

Also the PIP unit can do some really nasty things during this phase, like if you have a heavy load and suddenly remove it, the SCC does not respond quickly, it tries to dump all the PV generation (up to 4kW) into the batteries, and the voltage skyrockets, potentially causing damage. This doesn't happen with LiFePO4, where a big battery bank is pretty efficient at soaking up more power even at 95% SoC.

[andys]

Its always been really bizarre to me that the manufacturer of PIP-4048MS does not want to recognise that their product works way better with LiFePO4, and can easily explode when used with AGM.

IMO, they don't adequately explain that the PV input must be sized according to the AGM battery bank. (If you plan to attach all 4kW of PV you need a HUGE battery bank to soak up the SCC's slow responses.)

Its been my experience that lead acid will last about 3 years in average conditions, or 5 years for a high quality battery in used in good conditions.

[coulomb]

In a private message, so as to not extend the off-topic battery discussion on the main inverter thread, @arnolde73 said:

The log is sorted with the newest entries at the top That was just before starting the generator. Sorry if that was confusing, thats jut the way Watchpower exported it.

Ah! My bad; I somehow didn't notice that (you can tell I don't use Watchpower much). That means all that stuff I said about the internal resistance going down was wrong.

But it remains the case that the internal resistance is high, quite likely due to the extended time with a too-high float voltage setting. Possibly this was done (intentionally or not) as a reaction to the charge bug, where the batteries don't get enough charge with factory firmware. Voltronic Power, are you listening? Your firmware bugs are damaging batteries! And it's really easy to fix! </rant>

[dRdoS7]

Hi,

My 4 x 260AH AGMs failed after 4 years, actually 3 did, the 4th is still OK (ATM). Actually, 1 failed after about a year, but that was replaced under warranty and is the one still OK.

I replaced them, in 2016, with 40 x 200Ah NiFe batteries. So far, much better. Especially since I upgraded to a 5048MG inverter. There's a long involved story of getting the 40 NiFes to work with my old inverter.

dRdoS7

[paulvk]

I have both flooded and VRLA (type of AGM)
It is important with ANY sealed lead acid not to go above 57V (48V nominal bank) for any length of time higher than this will cause gassing and drying out of the cells it is also important not to exceed 1/10 of the Ah rating in charging or discharging the battery.
For example a 100Ah battery must not be charged or discharged at more than 10amps.
My 1100Ah VRLA (44 x 100Ah) is set to 56V and the maximum current will only go to 100amps.

For flooded lead acid batteries gassing actually helps mix the acid in the electrolyte and reaching 62V is often recommended
note in the newer PIPs they can get to 62V this is after pointing out the manufacture that this is recommended by the makers of the battery.
I would choose flooded lead acid and not sealed as this enables a smaller battery based on charge/discharge currents.
Note my 1100A VRLA was second hand and cheaper than flooded at the time.

My experience shows me that the smallest sealed battery needs to be 500Ah for one PIP and 225Ah works for flooded.
Now people are mostly unaware of the central watering kits for flooded batteries which remove the need to manually top up every cell
the whole battery as topped up in one operation , there are also automatic topping up systems available.

I am now at four years so the flooded is just over 4 years and the VRLA is now 7 years old both working well.

Now the PIPs suffered from cutting off too early when charging I installed 40A E-Smart3 MPPT chargers on additional panels which continued the charging after the PIPs cut off this greatly improved battery performance.

[dRdoS7]

Hi,

Now people are mostly unaware of the central watering kits for flooded batteries which remove the need to manually top up every cell the whole battery as topped up in one operation , there are also automatic topping up systems available

I've been looking at that for my NiFes. 40 batteries take a while to top up, so I think it will be a worthwhile investment (my wife probably wouldn't agree).

dRdoS7

[paulvk]

There are a number of manufactures of the systems so searching around may find them at a reasonable price
considering how long they should last it will not cost much in the long run.
The only thing is when you have to change the electrolyte in the NiFe cells thats going to be messy!

[dRdoS7]

Hi,

There are a number of manufactures of the systems so searching around may find them at a reasonable price
considering how long they should last it will not cost much in the long run.

The BWSs I've looked at have push-in fittings, or small screw-in, none are 35mm, at lest not so far (unless I missed them). Maybe I need to buy a 3D printer, and make some adaptors!

The only thing is when you have to change the electrolyte in the NiFe cells thats going to be messy!

https://permaculturenews.org/2018/05/31 ... nt-2116656:

Nickel-Iron Batteries

Nickel-iron and Nickel-cadmium cells both last a very long time. Nickel-cadmium cells are not that attractive as one must deal with the cadmium waste disposal problem at the end of their life cycle. Nickel-iron, on the other hand, is Nickel and Iron; the NiFe cells name comes from the periodic table. The electrolyte in a NiFe cell is alkaline-based potash, which is just distilled water and potassium hydroxide. This is a commonly used plant fertilizer. Your biggest decision when getting rid of the electrolyte once neutralized is deciding where you are going to grow your pumpkins and Jerusalem Artichokes. They both love potash.

I've read that it could be anywhere between 5 to 10 years. I can't see why it should be messy. I can do them 1 at a time, it's not like they'll just stop working, there should be a tapering off period. Maybe I'll buy one of the battery packs mentioned earlier, as a backup.

dRdoS7

[weber]

The electrolyte in a NiFe cell is alkaline-based potash, which is just distilled water and potassium hydroxide. This is a commonly used plant fertilizer. Your biggest decision when getting rid of the electrolyte once neutralized is deciding where you are going to grow your pumpkins and Jerusalem Artichokes. They both love potash.

This is very misleading. potassium hydroxide is not a commonly used plant fertiliser. It's common name is "caustic potash" and it is just as dangerous as caustic soda, i.e. you need to wear gloves and eye protection when working with it. You'd need to have acid soil, and greatly dilute it, to be using caustic potash as fertiliser. However you could leave the spent electrolyte exposed to air, in a place where animals and children can't get at it, so it can absorb more carbon dioxide from the air and convert first to potassium carbonate and then to potassium bicarbonate, before diluting it and using it as fertiliser. Alternatively you could neutralise it with vinegar, but you'd need an indicator to know when to stop adding vinegar.

However LiFe electrolyte often contains lithium hydroxide as well as potassium hydroxide, about 1:5 by mass. Lithium is toxic to plants in a similar way to sodium.

[dRdoS7]

Hi,

Blah, blah, blah.

It does say "once neutralized".

I'll post how it went in about 7 years time!

dRdoS7