RCT-AXPERT 1K (24V) Killing Batteries

[PixelZA]

Hi all,

I'm new to the forums, as well as to inverters and batteries in general, so I really hope that you will be able to guide me before I mess something up. A little more than a year ago, I purchased an RCT-Axpert 1K (24V) inverter, along with 2 x OmniPower 120 Ah batteries, which are connected in series to provide 24V. I know its not the best by any stretch of the imagination, but to me it was quite a lot of money and seemed that it should fit my needs, at the time. I have no solar panels at the moment, even though my goal is to eventually add one or two panels to start generating a little bit of my own power. The inverter acts like a UPS at the moment, charging the batteries from mains, and is only running my TV and Computer. Individually those two items consume around 100W of power each. I do not "cycle" the batteries, however I do switch off the mains to the inverter once in a while, perhaps bi-weekly, just to see the state of things, and I will run it till the inverter reaches around 24.5 - 25V then switch the mains back on.

After exactly 1 year, my OmniPower batteries "died", they would not even power the computer for 10 minutes before starting to beep, even when the inverter showed they are fully charged and they are in float charge. I went and bought two new batteries, this time "SkyKing 100Ah AGM" batteries from the local solar shop around the corner, and they appear to be taking the same route as the OmniPower batteries, except much much sooner. They are now 4 months old, and they can hardly keep my PC powered for an hour. Whats odd though, when I switch on the mains so the inverter can charge the batteries, it immediately indicates that they are full again.

I have a Victron Battery Balancer connected to the batteries which hardly ever indicates that they are out of balance during charge, and I ordered a Victron BMV 712 which is literally on its way to my house as I type this, but I feel that it might be too little, too late? Is there a way I can "test" the batteries to make sure they are still fine? If they are not, I might be able to get a warranty replacement since they are still so new, but I'm starting to think that its actually the inverter not treating them correctly?

I have never depleted them fully, even the previous batteries, the longest they were on power was the duration of load shedding, and according to what I heard, they should be able to power my load for around 7 hours? They hardly ran for 3, so if time is any measure to go by, they should in theory not even have been discharged 50%?

I guess, long story short, I really need some help to get my system sorted out, on a very tight budget, if that is even possible. I would hate to have to take out my installation, since I really enjoy at least having power when there is none provided by the utility. Even though we don't have load shedding right now, we do have a lot of shorter power interruptions.

Thank you for your time

(edit: So the BMV-712 just arrived, I'll be installing that within the next few minutes )

Edited July 8, 2020 by PixelZA

[Richard Mackay]

48 minutes ago, PixelZA said:

I went and bought two new batteries, this time "SkyKing 100Ah AGM" batteries from the local solar shop around the corner, and they appear to be taking the same route as the OmniPower batteries, except much much sooner. They are now 4 months old, and they can hardly keep my PC powered for an hour. Whats odd though, when I switch on the mains so the inverter can charge the batteries, it immediately indicates that they are full again.

Take these batteries back to the supplier to get them checked.

They should still be under warranty!

[introverter]

4 hours ago, PixelZA said:

I have never depleted them fully, even the previous batteries, the longest they were on power was the duration of load shedding, and according to what I heard, they should be able to power my load for around 7 hours? They hardly ran for 3, so if time is any measure to go by, they should in theory not even have been discharged 50%?

I guess, long story short, I really need some help to get my system sorted out, on a very tight budget, if that is even possible. I would hate to have to take out my installation, since I really enjoy at least having power when there is none provided by the utility. Even though we don't have load shedding right now, we do have a lot of shorter power interruptions.

Hi and welcome 

100-120Ah 24V battery @ 200W load or so should get you to about 5-6 hours for 50% discharge (obvoiusly give or take). Now I am no lead acid boffin but something seems off if the batteries hardly see a year...or worse not even 4 months.

I suggest you post your inverter settings for things like charge/ float voltage and also charge current (if I can't help there are a couple of 24V axpert type inverter using members that hopefully will chime in)... a pic or two of the battery connection/setup can't do harm .... and double check balancers etc are actually 24V (seems too obvious but who knows).

Not casting any aspersions yet but I think there was a thread sometime back where somone also felt a RCT was killing their batteries...will have to search a bit.

[PixelZA]

Thank you very much

As mentioned, I installed the BMV earlier today, then ran my PC from the inverter for about 20 minutes before the BMV started beeping, I opened the app, and it was complaining about "midpoint voltage" - said that there was a 7% difference? I then switched on mains again, the within a few seconds the Midpoint Voltage went down to 0.40% where it is still currently at.

As requested, here are my current settings, but please note that this has changed so much recently since I started troubleshooting the cause of my horrible battery life...

My balancer is one exactly like this:

I will take some pictures of the actual installation for you as well, will have to open the battery box, its one of those steel battery boxes large enough for 2 batteries, with the inverter mounted on top, and the balancer on the side

Edit:

I forgot to add, the batteries have their charging requirements on the side, they read as follow:

Cycle Use: 14.5 to 14.9V

Standby Use: 13.5 to 13.8V

Max Initial Current: 25A

 

Edited July 8, 2020 by PixelZA

[PixelZA]

2 hours ago, PixelZA said:

Thank you very much

As mentioned, I installed the BMV earlier today, then ran my PC from the inverter for about 20 minutes before the BMV started beeping, I opened the app, and it was complaining about "midpoint voltage" - said that there was a 7% difference? I then switched on mains again, the within a few seconds the Midpoint Voltage went down to 0.40% where it is still currently at.

As requested, here are my current settings, but please note that this has changed so much recently since I started troubleshooting the cause of my horrible battery life...

My balancer is one exactly like this:

I will take some pictures of the actual installation for you as well, will have to open the battery box, its one of those steel battery boxes large enough for 2 batteries, with the inverter mounted on top, and the balancer on the side

Edit:

I forgot to add, the batteries have their charging requirements on the side, they read as follow:

Cycle Use: 14.5 to 14.9V

Standby Use: 13.5 to 13.8V

Max Initial Current: 25A

 

I just tested the system again with the BMV connected. After drawing 4.7Ah, the mid-point voltage was at 9.4%. So I measured the batteries separately, the one battery was at 12.8V, the other was at 10.5V, even after standing for a few minutes with no load applied. So I suspect the one battery might be damaged? Is it possible for one battery in a bank of 2 to be damaged, without the other being damaged as well?

[introverter]

I do not see any glaring issues with the current settings you posted - other than the low battery cut-off of 21V which will be safer a bit higher. Based on you use/load/charge/discharge settings the batteries appear to be treated very gently.

So unless you had very different settings on the omnipowers the settings of the inverter should not have been the problem. Based on the time-frame the omnipowers very likely were in service when we had the wonderful week of reaching stage stage 6 load shedding - I guess during that week with less than optimal settings the batteries could have taken some punishment.

With the omnipowers and the new batteries their initial level of charge could have been very different and you then started with an out of balance bank. Unfortunately with the high demand for batteries I will not be surprised by less than new/sub-quality batteries being pawned off as "new, never been used, kept @25 degrees in climate controlled room".

Something that I do not know is whether the inverter set with the "user" battery type might cause some weird change to the charging algorithm that potentially has a negative impact on the AGM type batteries. Maybe @Coulomb would know/have a suspicion (even though this is a 24V system). Without solar not even the premature float issue seems likely.

Btw, yes it is possible for one battery to have problems while the other one seems unaffected... this makes multi-battery systems bit of pain when one problematic battery can mean replacing the whole bank.

Edited July 9, 2020 by introverter
typo

[Coulomb]

20 hours ago, PixelZA said:

So I measured the batteries separately, the one battery was at 12.8V, the other was at 10.5V, even after standing for a few minutes with no load applied.

That's about a 2 V difference; lead acid cells are nominally 2 V. So one cell of the 6-cell (nominally 12 V) battery module is almost certainly dead, zero volts. If you charge it immediately on its own, there is a small chance you could recover it, but most likely it would always be weak, probably very weak.

There is also a small chance that it's just very low in state of charge (so all the cells are at close to 10.5/6 = 1.75 V), if so, charging it immediately on its own might bring it back to say 95% of original capacity. Sadly, the dead cell is the far more likely situation.

[PixelZA]

6 hours ago, introverter said:

Based on the time-frame the omnipowers very likely were in service when we had the wonderful week of reaching stage stage 6 load shedding - I guess during that week with less than optimal settings the batteries could have taken some punishment.

With the omnipowers and the new batteries their initial level of charge could have been very different and you then started with an out of balance bank. Unfortunately with the high demand for batteries I will not be surprised by less than new/sub-quality batteries being pawned off as "new, never been used, kept @25 degrees in climate controlled room".

Yes, you are right, they were in service, however I was at work so they basically only powered my router, decoder, and the TV which was in standby - the PC was switched off during that time, so they would not have seen much power drawn

I went to the shop this morning with the two batteries, showed them the BMV screenshots, especially the one where the voltage dropped almost 2V in under 3 minutes.. They tested the batteries by hooking them up to an inverter and putting a load on it, and confirmed that the one battery is definitely faulty. They would have replaced both, but only had one left in stock, but said the other appears fine so it shouldn't be a problem.. I hope they're right, because my 6 month warranty is coming to an end in 2 months...

Before I connected any of the batteries, the OmniPower or these "Sky King" batteries, I charged them with an external charger and let them stand for a while to ensure they are at an equal, or very close to, voltage. So I hope that I did it right, and that I didn't inadvertently mess something up at that point...

The shop mentioned one thing though, they said that I can set my Bulk Charge and Float Charge voltage the same, they said my float charge of 27.6 could be a bit low, I should set it the same as the bulk charge which is 29.2V? Does that sound about right? I'm in no position to argue with them, but would like to make absolutely sure of what I'm doing...

Quote

Something that I do not know is whether the inverter set with the "user" battery type might cause some weird change to the charging algorithm that potentially has a negative impact on the AGM type batteries.

It was Sinetech who told me that the inverter should not be on the AGM setting, that its not optimized for those batteries, that it should be on user... I quote: "A pre configuration of AGM was selected which is not correct for the OPR AGM GEL hybrid batteries." This was said to me when I tried to have the batteries replaced under warranty, which they rejected because of my inverter config... It was set to the AGM mode..

[Coulomb]

6 minutes ago, PixelZA said:

Before I connected any of the batteries, the OmniPower or these "Sky King" batteries, I charged them with an external charger and let them stand for a while to ensure they are at an equal, or very close to, voltage. So I hope that I did it right, and that I didn't inadvertently mess something up at that point...

No, you did right. I was groaning up till that point, two battery modules of wildly different states of charge in series... Actually, it's still not great (due to the difference in ages), but hopefully that won't be a big issue.

8 minutes ago, PixelZA said:

It was Sinetech who told me that the inverter should not be on the AGM setting, that its not optimized for those batteries, that it should be on user... I quote: "A pre configuration of AGM was selected which is not correct for the OPR AGM GEL hybrid batteries." This was said to me when I tried to have the batteries replaced under warranty, which they rejected because of my inverter config... It was set to the AGM mode..

Well, it's true that the Axpert's  "AGM" setting is really a "generic gel" setting; the bulk/absorb voltage is quite low (14.1 V per 12 V module, when most AGMs want more like 14.6 V, which is the value for the FLD setting). There is nothing magical about the AGM or FLD values for setting 05 (battery type); they merely set default values for bulk/absorb, float, and battery low voltage cutoff; no special algorithm.

[introverter]

2 hours ago, PixelZA said:

Before I connected any of the batteries, the OmniPower or these "Sky King" batteries, I charged them with an external charger and let them stand for a while to ensure they are at an equal, or very close to, voltage. So I hope that I did it right, and that I didn't inadvertently mess something up at that point...

Other than singing them a lullaby every night I think you have done all you can to look after the batteries (I see the skyking battery manual advocates a 72hour float charge when connecting batteries in series before doing anything else..)

The omnipowers on the "AGM" setting might have suffered from chronic undercharge if only charging to 14.1V per battery (as per @Coulomb's explanation of the AGM setting). I see a 14.4V charge voltage advocated for the omnipowers (OPR AGM / GEL). So that is maybe a bit of bad luck when initially setting what seemed to be the most obviously correct options that ended up being incorrect .  (i.e. the omnipowers set as "user" with corresponding voltages etc. probably would have lasted (much?) longer).  

I will not hold my breath for the new and older skyking combo to be trouble free but floating at 29V does not sound like such a wonderful idea. The other side is that based on your recent experience if you get 3 months out of the batteries it will be par for the course, so maybe try a higher float (not convinced of the 29V+ though) for a week or two and see what happens (do your own discharge tests to get a sense of capacity, check individual voltages, etc. a couple of times) so before the original 2 month warranty is over, and while everything is hopefully still fresh in the supplier's mind, you should have a sense of whether the batteries are coping better - if they don't then the supplier must be happy to keep on replacing the batteries every 3 months or explain what the problem is and how to remedy it... or refund you the original amount.

[introverter]

19 hours ago, PixelZA said:

The shop mentioned one thing though, they said that I can set my Bulk Charge and Float Charge voltage the same, they said my float charge of 27.6 could be a bit low, I should set it the same as the bulk charge which is 29.2V? Does that sound about right?

Btw, you could (maybe) find with a higher float voltage that the batteries last longer in terms of powering the load (i.e. they power the computer for 2 hours and not  just 10 minutes) but the overall life time of the batteries will be shorter (instead of giving you 2 years service they just happen to pack up 1 month outside of the 6 month warranty).

MAYBE there could be justification for higher voltages to compensate for low temperature but I doubt this is the intention (and also not sure it will explain batteries failing in 3 months with what seems to be battery manufacturer spec settings on the inverter in general South African climate).

Last thing to rule out is measurement error by the inverter  -  the BMV should make this easier already but comparing voltage readings with a multimeter compared to what the inverter reports should also help rule out that the inverter says it is charging to 29V while it is actually charging to 24V or 32V. (could also help confirm that the settings via software are actually applied by the inverter).

[PixelZA]

Thanks @introverter I think I need to take the batteries back again... My wife phoned me earlier, we had load shedding, wasn't 30 minutes before the inverter started beeping... I did set the cut-off voltage to 22.5V, and it does start beeping a few millivolts ahead of 22.5V, but there is definitely still not nearly enough capacity. The only thing running at the time was the computer, which according to the BMV puts a 155W load on the batteries, so 155W for 30 minutes is not right? When I left for work this morning, I confirmed, the batteries were 100% fully charged - there was 0A flowing into the batteries. I set the float voltage to 28V last night to see if it makes any difference. Unfortunately I'm not home yet, so cant access the BMV to see what happened.. But I suspect one of the two batteries started running flat again

As previously asked, here is a photo of my two batteries - they plug into the inverter with a Anderson plug on the side. The wires are 16mm2, multi strand core, wire. The BMV's 500A shunt is behind that battery, and that is it Simple installation, no solar panels or anything yet (Although, at the rate my batteries are dying, probably never ) Those three wires coming through the lid (two blue and one red) laying on its side are the three wires for the Victron Balancer I mounted to the lid, and the thin red wires with the fuses are the BMV's wires..

I think I'll take that whole kit to them, as is, perhaps they can test it and advise...

 

edit: fixed some typo's

Edited July 10, 2020 by PixelZA

[Iggy]

Hi, I’m having this extact same issue, same setup - RCT 1kva, with 2x 100ah, have been running this for the past year now. Load is 80-100w. Today during the latest load shedding spell I noticed I got an hour’s use before it switched off. After the power restored, the batteries displayed they fully charged in a few minutes. @PixelZADid you manage to find/ resolve the issue?