Advice needed - Unbalanced or dying batteries

Batteries Lead Acid-Wet-Gel-Sealed
1

Good morning everyone,

It took me a while to move over here as I was stuck in limbo trying to figure out where everyone disappeared to. It took me some Googling to end up finding a thread on MyBB with a link here and now I have arrived.

In any case. I had some discussions with @plonkster & @TheTerribleTriplet just over 2 years ago about a working from home backup system and I ended up settling on a Mecer trolley system that I bought in April last year (not necessarily what was recommended, but as I am renting and canā€™t really explain loadshedding to my German employer it was either that or a generator).

It is a Mecer IVR-2400LBKS 24v inverter and 2x 12V 100Ah Vision 6FM100-X AGM batteries. Itā€™s always on, but only inverts when thereā€™s a power outage.

They used to work perfectly fine and we could get through 4 hours of loadshedding and power outages without a problem or a beep from the inverter. I have got the trolley setup next to the TV which is also where the routers are and then the office is connected up to it which has a laptop and 2x monitors, an access point, NAS and also a PC with a monitor although the PC doesnā€™t get used when thereā€™s a power outage. With loadshedding in the evenings weā€™ll have the TV on along with a bedside lamp thatā€™s next to the TV and Iā€™ll run an extension cord to the bedroom to have bedside lights and chargers up in the bedroom.

We had a power outage about a month ago (the newly upgraded Roosevelt Park substation is just wonderful) and after about 2 hours the low battery alarm sounded on the inverter. I had a look and could see the inverterā€™s battery level flashing on the 25% block (itā€™s basically got 4 blocks which indicates battery SoC with 25% being the last one). After simply switching off the TV which consumes just over 200W the low battery alarm disappeared and the battery SoC went back to the 75% block. The exact same thing happened again last night.

The power came on at 11pm last night and the inverter only stopped charging at 7am this morning (based on the fan running and the charging indicator being on). I know itā€™s trickling in the last bit and I can see that on the energy meter, but as this took half the time in the past Iā€™m just mentioning this as part of what is happening.

My first thought was that the batteries are most likely dying and will have to be replaced, but Iā€™m not sure if they may still be saved in case they are simply unbalanced and I thought Iā€™d ask here before doing anything.

Does anyone have any recommendations on what to do? Does this sound like unbalanced batteries which means I can look at getting a battery balancer to try and resolve it or does it sound like dying batteries? I know the lead acid / AGM batteries wonā€™t last forever, but I was hoping to get about 3 years from them as theyā€™re only used when there are power outages and donā€™t get discharged to a low SoC.

My idea at the moment (based on what Iā€™ve learned on the forums over the last couple of years) is that it would be best to buy a battery balancer and a BMV now to try and get them balanced (BMV to be able to monitor going forward) and if that doesnā€™t work or do much to then go ahead and replace the batteries which will then have a balancer and BMV from day 1.

Weā€™re looking at moving into our own place around about this time next year with a blue system going in ~6 months later which is why I would prefer to make these last until then.

I might be getting ahead of myself here, but if the batteries are indeed dying and need to be replaced:
Is it OK to replace them with the same batteries and keep using the same inverter or should I look at other batteries and/or other inverters?

2

It sounds like a bad battery. Actually, if you get really technical, it is probably a single cell that is going bad. There must always be one that goes firstā€¦

The 25% vs 75% SOC indicatorā€¦ thatā€™s because it uses Voltage. And Voltage is a terrible measure of SOC. As you noted, when you removed some of the load off the battery, the voltage bounced back and the SOC indicator celebrated a fake 75%. Woohoo!

So here is what you do. Put some load on the battery (ie unplug the power and let the television run from the inverter for example) and measure both batteries. Almost guaranteed, one of them is going to hold a nice 12.5V or moreā€¦ and the other one is dropping out below 12V. Then let it recharge and measure again. Again, you will almost certainly see one battery (most likely the one that was low on discharge) jump up to a higher voltage. That battery has a bad cell.

Next thing you can do, once you know which battery has the bad cell, is discharge it a bit, then recharge. Feel the side of the battery (if you can reach it), often times you can see the outlines of the cell separators on the battery molding. Feel each cell. One of them is quite likely going to be warmer than the others.

Now to address the extremely long recharge time you mentioned. That is worryingā€¦ if you have a bad cell in there, that might be dragging things down and causing a lot of heat. In extreme cases it can lead to a fire. No need to freak out immediately, just do the homework. Check the battery temp while recharging.

If all of my guesses check out, the only fix is new batteries. Sorry about thatā€¦ :slight_smile:

3

This is very annoying.

Vision 6FM100-X AGM batteries brochure says 10-year life (obviously on standby) and 200 cycles to 100% DoD.

Now I bet there were not 200 100% DoD cycles.

Other than a obviously faulty cell, and no warranty, I would wonder about the charging algorithm on the Mecer.

Titbit: Iā€™ve recently learned that APC UPSā€™s tend to up the volts over time, causing more premature failures on the replacement batteries. They all start to bulge. And there are a host of vids to fix that, if you are into that kind of thing.

So I decided basta that, get a BMS and some lithium cells, and did this:
image

But I got it wrong, those cells and BMS is too small for my 700va UPS. So I had to order a 2nd set ā€¦ just watch for that.

Ps. I need the UPS for my protection ā€¦ for I switch off the solar inverter, forgetting my PC is on, :wink:
Pss. Iā€™m getting proper holders for those cells ā€¦ just be patient.

4

And Iā€™m guessing that adding a balancer wonā€™t prolong the life by another year if itā€™s 1 cell on a battery thatā€™s bad :frowning:

I did a reading with everything switched off:
Bat1: 13.66V
Bat2: 13.74V

I measured after about 2 minutes after switching the inverter on which powered the TV, MiBox, fibre, router, ap, laptop, 2 monitors, Pi-hole and NAS:
Bat1: 12.80V
Bat2: 12.82V

I also switched on my PC ~15 minutes later for good measure and measured it again another ~15 minutes later (so running with a slight load for ~35 minutes) with the SOC dropping the 100% bar and sitting on 75%:
Bat1: 12.45V
Bat2: 12.60V

Thatā€™s happening now. Iā€™ll go grab some measurements once I hear the fan quiet down after the charge. I did a measurement after about 3 minutes of it charging and both were at 13.56V, but looked to be climbing (Iā€™m guessing to reach the same as what it started off with)

Is there any verdict on it yet? Iā€™m not clued up enough on batteries to really know, but I donā€™t see that big of a difference between the batteries. Especially not near a drop below 12V that was expected.

I can only reach 3 cells of the 6. I canā€™t see the outlines in the molds, but I can feel it though. Iā€™ll have a feel a bit into the charge.

I would really be satisfied with 200 100% DoD cycles, but alas.

Thatā€™s why I linked the page to the inverter, but apart from it showing a float voltage of 27.4 VDC which matches up to the 2.27V to 2.30V float / cell mentioned in the Vision document thereā€™s not much info there.

The only other thing worth noting is that the switch on the inverter is set to 20A maximum charge current. After the outage last night when everything came back the house was using ~800W and Iā€™m guesstimating a max of about 680W coming from the inverter charging the batteries. I can flip that to 10A, but the Vision document mentions a max of 30A or is there some math Iā€™m missing and it should be set to 10A? If itā€™s better for the batteries to have it at 10A Iā€™ll make the change. I guess the only visible benefit that Iā€™ll see with it on 20A is the fact that it can charge up faster for our morning and evening loadshedding days.

I suspect Iā€™ll still need it as well. Iā€™m so used to having the inverter available for power outages that I didnā€™t take into account that switching it off will also bring the NAS down which tends to hate me when thereā€™s an unexpected shutdown.

5

On a 24v 100ah bank ideally one should charge at 10% of Ah, so 10amps.
For fast recharging deu to LS, one can go 15%, so 15amps.

Now Vision says 30amps ā€¦ that is a lot more than the ā€œrule of thumbā€.

Once a batt is not performing anymore, it is tickets.

You can try and get a 2nd hand batt from somewhere, one that is still in good nick, pay the lead price for it, and extend the other battery a wee bit. I did that with success when I still had lead-acid, wanting to go 48v from 24v. But it can be a tough one to source.

I know Dixon may be able to help. Give them a call asking them if you can get a 2nd hand one that is on the floor before they get picked up to be recycled.

6

Okay okayā€¦ this is not as bad as I thought!

The batteries have aged somewhat disproportionately, and a balancer might help eliminate this difference, but at this point im the game I think itā€™s too late to add a balancer.

It is also possible that the batteries have simply aged to the point that it only has two hours of capacity. Or again this could be a single cell. I had an old Trojan T145 bank way back that was like that. It would discharge more or less linearly, but then at some point one of the cells would just drop off a cliff.

Of course some aging on batteries are normal. Thatā€™s usually what it means if you say the battery can do 500 cycles to 50% (or some such number), it means that after youā€™ve done that 500 timesā€¦ the battery will have lost 50% of its capacity. It will for all practical purposes become a 50Ah battery.

Now of course Iā€™ve found that the average AGM battery, despite the cycle life promises, tend to do the usual warranty thing: It fails just on the other side of it.

7

Iā€™ve flipped the switch to 10A. Makes me feel just a bit more relaxed. Itā€™s quite strange how much less the fan spins up when itā€™s inverting and charging now that itā€™s on 10A.

I know, but Iā€™m hoping that maybe there wonā€™t be a lot more outages and I can make it last just enough, although Iā€™ll most likely end up getting new batteries before winter season next year. Or once I realised trying to balance them does nothing.

Yeah, I also think that it might be a bit too late, but seeing how Iā€™ll need a balancer for the next set I think Iā€™ll start with a balancer for now, see what it does and then keep my fingers crossed that it maybe improves it a bit and that there arenā€™t any or a lot of outages for a while and then get a new set of batteries before next yearā€™s winter.

And yet we still loooooove our electronics.
I knew when I bought it that it was a ā€˜cheapā€™ solution that will be better than having to go switch on a generator every time. I was just hoping to get about 3 years or so out of it, but itā€™s not the end of the world to get some new batteries.

It reminds me of a conversation we had about the cost of a full PV + Battery install. Yes, you might not necessarily make a ROI, but you also canā€™t really quantify having basically everything still up and running during a power failure or loadshedding stint.

When I told my wife we may need to get a balancer and new batteries to fix this issue she asked how much it would cost and said that sheā€™ll cover half, because even though she doesnā€™t work from home the comfort in being able to have some lights on, watch tv and charge phones during an outage far outways the cost for her.

8

Maybe, MAYBE it is an idea to get lithium batteries next, as the next step towards PV + Battery install.

Say you get batts from LithiumBatterySA, 24v, you can always add more cells later when you go 48v, and at that stage, with a new 48v BMS to go with the 48v bank.

Just a thought to consider.

9

I thought about it. Actually thought about it earlier this year as well, but I specifically remembered reading that the Mecer inverter doesnā€™t support lithiums and my DIY / knowledge isnā€™t that great that Iā€™m willing to pay ā€˜skoolgeldā€™ on tinkering with it. Iā€™m getting scared just thinking about having to wire up the balancer.

The idea for us down the line (Iā€™m hoping ~18 months, but more realistically 24-30 months) is to have ~200Ah worth of batteries. So the plan in the little spreadsheet that gets updated every now and then is either US3000ā€™s, Revovā€™s or LBSAā€™s built units. (With some blue boxes of course)

Iā€™ll most likely keep the trolley as a UPS for when Iā€™m doing silly things (like switching off the inverter forgetting my PC is on :wink:) or Iā€™ll sell it on the cheap to one of our friends who envies the fact that we can watch TV with the power off.

10

Follow my logic.

What I recently did, on a APC UPS, having to replace 4 x 7ah 12v batteries, I asked Bain from LithiumBattSA: Tell me, why can I not use the cylindrical lithium cells on said UPS?
He asked: What is the volts the APC charges at, or the float volts?
I said: Ā±27.4v (= 3.425v per cell)
He said: Why not?

Now, on my 152ah cells, the absolute max volts they can be charged at is 58.4v = 3.65v
Plonkster told me rather go for 55.2v = 3.45v per cell.

The trick lies in the max volts the Mecer charges at, or float, which on the Mecer is 27.4v = 3.425v per cell.

Measure the volts when the Mecer charges the bank in the bulk stage too.
As long as one does not reach the max volts the cells can be charged at, the BMS will sort it all out, as with a UPS, 95% of itā€™s life it sits at float volts.

If anyone thinks Iā€™m missing something, now is the time to speak ā€¦ or forever hold your peace. :laughing:

ā€¦
ā€¦
ā€¦
ā€¦ so no-one complained
ā€¦

Taking it one step further.
If you have lithium batts, why not use them?
Iā€™m thinking, seeing as you have an inverter and it can use Eskom to charge i.e. the volts are within the cells min/max volts, why not get a BMV, an MPPT, and a couple of panels, and use the lithium bank all the time. And by keeping Eskom disconnected from the inverter, it will only recharge during the day from the panels ā€¦ with the MPPT programmed to the exact/similar voltages, as per the manufacturerā€™s specs?
Eskom is there as backup ā€¦ BMV to help you not go below 20% DoD.

Go one step further:
A UPS like the Mecer is not designed to run 24/7 ā€¦ so get a couple of spare ones? Cool the one you have even more, to make it last a bit longer.

Or next level:
Get an online APC UPS 2nd hand, or any online UPS, that needs a battery replacement so the people sell them cheap, and put one of them in place.

You get 24v ones, or go for a 48v one, as long as it is the online models as they run 24/7/365 off their batts in any event.

I just think, unless you can get 2nd hand lead-acid AGM batt somewhere to tie you over till you get where you want to be, that this 2nd lead-acid expenditure, is kind of a waste.

Ps. I have a 48v 2.4kw APC Online inverter ā€¦ in case I need to take my MPII in for repairs.

11

It honestly doesnā€™t feel like 2 months later, but yet here we are. Sorry about the radio silence.

Just an update from my side and some more advice please. :slight_smile:

After using a slightly better multimeter (and just putting some load on and taking measurements) it is pretty easy to tell that one battery definitely went. After roughly an hour with ~250W load it just drops off a cliff voltage wise in a matter of minutes.

To have as cheap as possible a replacement using the same inverter I ended up ordering another set of the same Vision 100Ah batteries as a drop in replacement. Weā€™re looking at buying a house relatively soon and then get a proper inverter + LiFePO4, so we just need something cheap to last ~1-2 years as a power out solution until that happens.

After chatting with @JacoDeJongh a bit he also recommended monitoring the batteries better and mentioned the BMV-700 that was for sale here. As it happened to be 5 minutes away I went and picked it up the next day. Now weā€™re just waiting on the batteries. At least we can watch TV for ~45 minutes if thereā€™s an outageā€¦

My questions though:

What size cable should I be using here?

  • As the batteries will connect to the shunt first Iā€™ll need more cable and if what I have at the moment isnā€™t right Iā€™ll just do everything over.
  • Using this calculator it recommends that on 1m I use 10mmĀ² for 60A (1440W / 24V if my math is correct), but 25mmĀ² for 100A (2400VA / 24V). That changes to 10mmĀ² and 25mmĀ² for 2m at 3% loss and 25mmĀ² and 35mmĀ² for 2m at 1% loss. Iā€™m not exactly sure which one to use.

Will I need DC fuses?

Anything else to think of?

Just some background again:
This is a Mecer IVR-2400LBKS 24V inverter that I bought as a trolley system, so it simply plugs into the wall and has 3 AC out plugs.
The capacity shows as 2400VA / 1440W hence the above calculations.
It didnā€™t come with any fuses, so thereā€™s 2 cables from each end running into the inverter and the cable to put them in serie.

Thanks again for all the help as always.

12

Just my 2 cents. Having moved from 12v to 24v to 48v, in the end I standardized on 50mm2 cables.

They work from 12v - to 48v, never again did I have to change or upgrade cables.

And the voltage drop becomes a non-issue.
And the BMV has the rights lugs.
So when you change inverter, this part is sorted.

13

Your calculations regarding the Amps is correct. Max that you would pull from batteries is 60A so you can just get an 80A DC fuse (24 or more V) snd put it on positive lead. Fuse is there only to protect the cable from burning in case of a short.

With regards to the cables, as TheTerribleTriplet said if you plan to upgrade later on then take cables that you would be able to use later

14

I kinda have a rule against using anything less than 25mm^2 on the battery. Maybe for small systems you can go down to 16, but for anything >1kW it just seems proper to me.

You have to consider the full cable length, so positive and negative cables combined. Itā€™s a trolley system, so you are probably around the 1m-2m mark. Also, 100A will only be used for short amounts of time (if at all). So 25mm^2 should be more than sufficient.

The fuse is there to protect the cable. A 125A fuse will be fine. It will blow long before the cable goes up in smoke.

With all due respect to my buddy TTT, 50mm^2 is overkill, hard to work with, and expensive. I do use 50mm^2 on my own 24V system, because I want only a 1% voltage drop, but I ran that same system on 35mm^2 for years without any problems.

My PV chargers still use 16mm^2 to the busbar. I only use the thick expensive stuff to the inverter, where it matters.

15

With all due respect to my maatjie Plonk, let me get this straight ā€¦ so we spend 10ā€™s of thousands, some even 100ā€™s of thousands, on systems yet when we need to get a couple of meters of wire, then we want to worry and haggle about a couple of cents more for a cable ā€¦ :laughing:

25mm2 vs 50mm2 ā€¦ ā€œhard to work withā€ ā€¦ why do you want to keep on working on them?
Leave well alone! :smile:

25mm2 / 50mm2 / dang, I now have 70mm2 ā€¦ and the level of difficulty is not here nor there.
It is supposed to be installed once and left alone for years to come ā€¦ :wink:

All Iā€™m thinking, having walked the talk, drank the beer, burnt the cables ā€¦ if you are crimping new lugs, adding fuse holders, adding a BMV into the mix, then you want a cable that can ā€œmoveā€ with you into the future as you change and alter, a cable that has the length and thickness ā€¦

Use it, or not, Iā€™ve got no more skin in the game. :+1:

16

He doesnā€™t need 50mm^2. Bigger isnā€™t always better. That cable is not going to move with him, itā€™s a short length that will stay with the trolley. Save the R100 and buy some beer with it.

Even if the cable does end up being reused, there are enough places where you need shorter lenghts of thinner cable. Parts of my DC distribution board uses 25mm^2. Itā€™s the thickest that will fit in the breakers.

1 Like
17

I actually agree with this, BUT Iā€™m not going to do this :laughing:
In this case itā€™s a trolley system and space is starting to run out with the Balancer and now the BMV and fuse also getting mounted on it and I want to use as short as possible cables which may mean not being able to reuse them.
I also plan on keeping the trolley as is and either giving it to a friend or family member running low on candles or selling it as a whole, so it wonā€™t be going to waste at least.

If itā€™s only needed on the positive lead thatā€™s perfect as I can run the same cable length from the batteries to both the fuse (on positive) and BMV (on negative) and the same length from them to the inverter.

100% sure thereā€™s no need for a dual pole fuse for both positive and negative in this case?

The late night reading Iā€™ve done also pretty much says the same. I think Iā€™ll go for that then. Now to find out if my local store is willing to cut and crimp for me.

So thatā€™s based off the 100A (2400VA / 24V) calculation, right? So just something like a 125A MEGA on the positive side should cover it?

18

Ah, missed that as I took ages to reply, but the above basically sums up my point on it. Although at this stage the savings can only be used to buy non-alcoholic beerā€¦

1 Like
19

Correct. Make the fuse a little larger than the max current it should ever see, but small enough that it blows before the cable does. A Mega-fuse is perfect, and again, buy the 32V variant as it is MUCH cheaper than the 60V one :slight_smile:

20

PERFECT ā€¦ you thought about what I said and it will not work for you. Nothing wrong with that!

FWIW
When I reply on forums I tend to share that what I ran into and why, because 1/2/3 years from now, someone else reads the thread and gets a brand new idea.

I also know that the question/s asked, will get detailed specific answers, from the knowledgeable guys on this and other forums.