Hello all,

I just recently setup my first inverter. so happy with it but I did notice something a little concerning. I spent quite a lot (as I'm sure we all have) and I'm very protective over my battery health.

I have

2x 12.8V Revov 200Ah batteries (in series with an HA11 balancer)

Axpert style 3KVA/2.4KW inverter (clone?) which I purchased from a friend.

I believe it could possibly be a PIP-2424MSE1/MS board. not quite sure how to identify. 

After load shedding the fans kick on and the CHG LED flashes along with the top battery bar on the LCD. On my battery internal BMS I can see a charge current of 7-16A or so until it reaches 13.7V and then the CHG LED goes solid green on the inverter and it stops charging.

I have read quite a lot about this premature float bug, and I'm not convinced that is what is at play ? as its rare on utility charging. I am wondering if it is because I am not discharging my batteries enough ? I have yet to discharge beyond 13.3V does this mean the inverter will stay in float mode ? I have been using the battery equalizer function every now and then to top the batteries up as you can see in my settings. 

is it best to always charge to 14.1V after any discharge even be it a small one ? will continuously charging to only 13.7V damage my batteries ? Is this normal behavior or is there a firmware patch that can fix this if its not ?

 

Id really appreciate any feedback at all. just worried about the safety of my batteries.

My settings are:

00: ESC
01: Uti
02: 40A
03: UPS
05: USE
06: Ltd
07: ttd
09: 50 Hz
11: 25 A
12: 24.5 V
13: 28.0 V
16: CUt
18: bOF
19: ESP
20: LON
22: AON
23: byd
25: FEN
26: 28.2 V
27: 27.4 V
29: 24.0 V
30: EEN
31: 28.2 V
33: 5
34: 120
35: 2d
36: Ads

Firmware: U1 09.53    U2 03.52

Pics: Screenshot of HA11 battery voltage log for past 24H where I did not use the inverters battery equalizer function to reach 14.1V per battery. 

HA11 is a pretty good balancer it does a better job than what is displayed in the app. I believe the ADC that it uses internally to log/display voltage to the BT app is not as calibrated as the circuit it uses for balancing. as they are closer together on a multimeter / internal BMS reading than what is displayed on the HA11 log.

Edited November 26, 20232 yr by zylinx
title

1 hour ago, zylinx said:

Hello all,

I just recently setup my first inverter. so happy with it but I did notice something a little concerning. I spent quite a lot (as I'm sure we all have) and I'm very protective over my battery health.

I have

2x 12.8V Revov 200Ah batteries (in series with an HA11 balancer)

Axpert style 3KVA/2.4KW inverter (clone?) which I purchased from a friend.

I believe it could possibly be a PIP-2424MSE1/MS board. not quite sure how to identify. 

After load shedding the fans kick on and the CHG LED flashes along with the top battery bar on the LCD. On my battery internal BMS I can see a charge current of 7-16A or so until it reaches 13.7V and then the CHG LED goes solid green on the inverter and it stops charging.

I have read quite a lot about this premature float bug, and I'm not convinced that is what is at play ? as its rare on utility charging. I am wondering if it is because I am not discharging my batteries enough ? I have yet to discharge beyond 13.3V does this mean the inverter will stay in float mode ? I have been using the battery equalizer function every now and then to top the batteries up as you can see in my settings. 

is it best to always charge to 14.1V after any discharge even be it a small one ? will continuously charging to only 13.7V damage my batteries ? Is this normal behavior or is there a firmware patch that can fix this if its not ?

 

Id really appreciate any feedback at all. just worried about the safety of my batteries.

My settings are:

00: ESC
01: Uti
02: 40A
03: UPS
05: USE
06: Ltd
07: ttd
09: 50 Hz
11: 25 A
12: 24.5 V
13: 28.0 V
16: CUt
18: bOF
19: ESP
20: LON
22: AON
23: byd
25: FEN
26: 28.2 V
27: 27.4 V
29: 24.0 V
30: EEN
31: 28.2 V
33: 5
34: 120
35: 2d
36: Ads

Firmware: U1 09.53    U2 03.52

Pics: Screenshot of HA11 battery voltage log for past 24H where I did not use the inverters battery equalizer function to reach 14.1V per battery. 

HA11 is a pretty good balancer it does a better job than what is displayed in the app. I believe the ADC that it uses internally to log/display voltage to the BT app is not as calibrated as the circuit it uses for balancing. as they are closer together on a multimeter / internal BMS reading than what is displayed on the HA11 log.

I feel that 13.7V is not damaging but I could be wrong. With the HA11 doing very well between total balancing between the batteries the reason why one would want to charge higher than 13.7V is for the battery internal BMS to balance between the 4 cells inside each battery. 

In order to achieve this try and increase your setting 26. The charging bug is from what I know more or only a problem from PV charging. Go as high as 14.4V for this setting. You can do this may be on a every 60 days if you find the charging never switches off just to try and get balancing inside the battery to take place. 

I have a clone and I don't use equalisation at all and is switched off under my setting 39. Even if setting 34 has a voltage given 39 can toggle if on or off. 

Using Hubble S-100 now for 3 years. Can still provide a very high current if needed. 

The hardest my inverter has worked ever as I am using the aircon in this heat. Paving outside is now 62 degrees. 

Thank you for your reply @Scorp007

Quote

I feel that 13.7V is not damaging but I could be wrong. With the HA11 doing very well between total balancing between the batteries the reason why one would want to charge higher than 13.7V is for the battery internal BMS to balance between the 4 cells inside each battery. 

Ok that's reassuring, I am still learning about LFP chemistry and how they should be charged and maintained. I thought maybe never charging to 14V was potentially a bad thing. 

Yes the HA11 is doing a great job and so is my internal BMS, the individual cells are within 0.015V of each other at all time, I check often.

Quote

In order to achieve this try and increase your setting 26. The charging bug is from what I know more or only a problem from PV charging. Go as high as 14.4V for this setting. You can do this may be on a every 60 days if you find the charging never switches off just to try and get balancing inside the battery to take place. 

Thanks I will try this, the reason I had it set to 28.2V is the batteries are rated for bulk charge at 14.1V as they are 2nd Life cells. I will try increasing to 28.8V to see if that will get a proper bulk/absorb charge to activate.  Does your inverter charge to 14V+ after every discharge ? or only when you discharge it a lot ?

Also I'm a bit confused by what you mean by "If you find the charging never switches off" ? did you mean on ?

 

Quote

I have a clone and I don't use equalisation at all and is switched off under my setting 39. Even if setting 34 has a voltage given 39 can toggle if on or off. 

Using Hubble S-100 now for 3 years. Can still provide a very high current if needed. 

The hardest my inverter has worked ever as I am using the aircon in this heat. Paving outside is now 62 degrees. 

That's great to hear they are still going strong.

Edited November 26, 20232 yr by zylinx

8 minutes ago, zylinx said:

Thank you for your reply @Scorp007

Ok that's reassuring, I am still learning about LFP chemistry and how they should be charged and maintained. I thought maybe never charging to 14V was potentially a bad thing. 

Yes the HA11 is doing a great job and so is my internal BMS, the individual cells are within 0.015V of each other at all time, I check often.

Thanks I will try this, the reason I had it set to 28.2V is the batteries are rated for bulk charge at 14.1V as they are 2nd Life cells. I will try increasing to 28.8V to see if that will get a proper bulk/absorb charge to activate.  Does your inverter charge to 14V+ after every discharge ? or only when you discharge it a lot ?

Also I'm a bit confused by what you mean by "If you find the charging never switches off" ? did you mean on ?

 

That's great to hear they are still going strong.

I never get mine to 14V but then I don't try too hard. I only use 1 panel and that charges enough for LS. Some evenings I don't even switch loads to the inverter. They normally charge to 13.7V each and drops to 13.4V when charging stops. I got this inverter as it could drive any single loads I have including my heat pump if ever we get a power failure. Lucky to only have LS. Now and again say 5 times in 30years we had a 6hour or so power failure. About 3 times our power went of 15min after switch on after LS. 

My routers run directly from the 1 battery. I use a HA2. 

Thanks for your insight, I'm still curious why my inverter never charges at the set bulk/absorb voltage. as I don't have PV I use Utility charging only I would expect it to do a proper charge cycle after every discharge. The inverter indicates its 'charging' with a flashing light and LCD but as soon as float voltage is reached it seems to abandon mission and just stop.

It sounds like your inverter is suffering from the dreaded premature float bug. There is some tests you can do should you have the means. Charging lifep04 to 3.65v/cell shortens the cell lifespan in the long run. There is very little capacity between 3.45v/cell and 3.65v/cell. You can increace (26) to 28.4v and then for a test increace float(27) to 28v then see if the voltage of the 2 batteries in series would increase to 14v. If lifep04 is fully charged it would not accept any current charging will stop even if the inverter applies voltage to the batteries. The only accurate method to determine if the cells are fully charged is to observe the current flow into the batteries once the current falls to 0A the batteries are fully charged. Do you have the means of checking the current flow into the batteries? Did you top balance the 2 batteries before connecting them in series. The way to top balance: Connect both batteries in parallel then you can charge them(12v lithuim charger) together until 0A current flow. Disconnect the charger leave them connected in parallel for 8 hours then connect them in series and apply the balancer.

29 minutes ago, TaliaB said:

It sounds like your inverter is suffering from the dreaded premature float bug. There is some tests you can do should you have the means. Charging lifep04 to 3.65v/cell shortens the cell lifespan in the long run. There is very little capacity between 3.45v/cell and 3.65v/cell. You can increace (26) to 28.4v and then for a test increace float(27) to 28v then see if the voltage of the 2 batteries in series would increase to 14v. If lifep04 is fully charged it would not accept any current charging will stop even if the inverter applies voltage to the batteries. The only accurate method to determine if the cells are fully charged is to observe the current flow into the batteries once the current falls to 0A the batteries are fully charged. Do you have the means of checking the current flow into the batteries? Did you top balance the 2 batteries before connecting them in series. The way to top balance: Connect both batteries in parallel then you can charge them(12v lithuim charger) together until 0A current flow. Disconnect the charger leave them connected in parallel for 8 hours then connect them in series and apply the balancer.

Hi @TaliaB, Thanks for your reply.

From what everyone in this thread is saying it seems only charging to float voltage 13.7V should not shorten the lifespan of my batteries ?! I am able to get my inverter to charge them to 14.1V by manually activating the equalize now function and setting the EQ voltage to 28.2V

Yes I did indeed top balance them with a constant current power supply in parallel slowly, and then let them rest in parallel for 24H. I can observe the current flow using my DC clamp or just as accurately using the batteries internal BMS it has BT and I can monitor current that way too.

I am not really concerned about the cells being balanced, everything seems really well balanced. my only concern is my inverter ignoring my bulk/absorb set voltage.

Yes I am also concerned it is the premature float bug, or if it is just that my batteries are not discharged enough during load shedding and that this is somehow normal behavior ?

I thought this might not be the premature float bug because I have seen others describing it as when the charge LED immediately goes solid green indicating a full charge and it simply applies float voltage. and also that it is rare on utility as you need a combination of setting 2 and 11 that are very far apart.

However in my case the LED does flash, indicating charging and the LCD also flashing the top battery bar. but yet it stops at float voltage and then turns green. never reaching above 27.2V (13.7V /batt) 🙁

Could this possibly be a similar yet separate bug ?

I see @Coulomb is quite knowledgeable on firmware bugs, hopefully he could lend some insight if he sees this. (cheeky tag)

Edited November 26, 20232 yr by zylinx

6 minutes ago, zylinx said:

thought this might not be the premature float bug because I have seen others describing it as when the charge LED immediately goes solid green indicating a full charge and it simply applies float voltage.

That is the question indicating a full charge is there any or minimal current going into the battery?

@TaliaB When the battery voltage closes in on 27.4V (13.7V /batt) after a load shedding cycle. the current flow is far from the selected charge current of 25A. I have actually never seen my inverter kick out the full 25A. usually around 7-16A while climbing. and after only a few minutes of being at float voltage the current drops to 0A

Edited November 26, 20232 yr by zylinx

15 minutes ago, zylinx said:

it seems only charging to float voltage 13.7V

That would not be a problem 3.425v/Cell that is close to 100%soc

1 minute ago, zylinx said:

When the battery voltage closes in on 27.2V (13.7V /batt) after a load shedding cycle. the current flow is far from the selected charge current of 25A. I have actually never seen my inverter kick out the full 25A. usually around 7-16A while climbing.

In Absorption stage the voltage stays at the set voltage of 28.2v then the current tapers down to 0A before going to float that is how the charge algorithm is suppose to work CC/CV

@TaliaB So you are saying I never see 28.2V on the battery because my current draw tapers off too quickly?

In the specification of the inverter it says it should charge until the batteries reach bulk/absorb voltage (0A current draw). This is the bulk charge. Then it will hold the voltage there for a calculated period of time based off of how long it took to get there (absorb period) before dropping to float voltage. 

From what I am observing. It charges to float voltage and never beyond that. And the current tapers off on its own.

 

I am happy to hear this because is not going to damage my batteries in the long term. But just curious as it's not expected behaviour.

Edited November 26, 20232 yr by zylinx

7 minutes ago, zylinx said:

rom what I am observing. It charges to float voltage and never beyond that. And the current tapers off on its own

If the settings in (26) are correct then you have a problem on the charging algorithm maybe @Coulomb can shed some light 

3 hours ago, zylinx said:

@TaliaB So you are saying I never see 28.2V on the battery because my current draw tapers off too quickly?

In the specification of the inverter it says it should charge until the batteries reach bulk/absorb voltage (0A current draw). This is the bulk charge. Then it will hold the voltage there for a calculated period of time based off of how long it took to get there (absorb period) before dropping to float voltage. 

From what I am observing. It charges to float voltage and never beyond that. And the current tapers off on its own.

 

I am happy to hear this because is not going to damage my batteries in the long term. But just curious as it's not expected behaviour.

The reason why the green LED goes to steady on should be because it reach the full level for lead acid for which these inverters were designed. As @TaliaB said 13.7V is actually fully charged. The portion up to 14.1-14.4V is normally for the internal balancer to start balancing. In you case it starts balancing early so no problem that it only goes to 13.7V.

You might find you have to up the bulk voltage to get to nearly 0A charge and leaving it long enough it should go to over 14V if setting is high enough. Try setting it to 28.4-28.6V. The measurements of these inverters are not 100% correct. Check with a multimeter. As you have already found out with the HA11

Edited November 26, 20232 yr by Scorp007

@zylinx I have an almost identical setup to you. I have the same inverter (3kVA, 2.4kW). Mine is the Synapse 3.0V+. It is a legit rebrand of the Voltronic VM-3000+ (MPPT). Judging by your serial number, yours is a legit rebrand also. I also have the same HA11 balancer and 2 x 200Ah LFP batteries in series.

Bulk set to 28.4
Float set to 27.2
EQ set to 28.4
I never see the bulk charge voltage go above about 27.4 during charging (as checked on the HA11 and the inverter's readings).

I've been running my setup for about the last 5 months with no issues. The only time I see the bulk voltage go near or above 28v is when activating equalization (manually or automatically) on full batteries. That is, if the batteries are still charging, and I activate equalization, the charge voltage remains where it is, at about 27.2-27.4. This suggests to me that the inverter is in fact charging at the correct bulk voltage but due to the batteries still charging, it does not reach 28.x volts. If you force this voltage on full batteries via manual equalization, you then see it rise.

In short, I think the batteries are being charged just fine. I'm open to ideas if anyone disagrees.

@zylinx You might want to check my post on voltage calibration for this inverter. I got the inverter to report the same battery voltage (within 0.1v) as my HA11 and my multimeter.

Edited November 27, 20232 yr by jbroo

And no, there is no FW available for these inverters. I've asked @Coulomb a number of times.

Oddly, I seem to have newer main FW than you, but you have newer FW for the display board.

U1: 09.56
U2: 03.39

Edited November 27, 20232 yr by jbroo

Thanks for the replies @Scorp007 and @jbroo

I tried increasing the bulk charge voltage didn't really change much. I am happy to hear its relatively a non-issue for LFP. Strange behavior nothing like what the spec documents.  I will just leave it as is and every few days bring it up to 14.1V with equalize (as revov insists on a full charge every cycle to 14.1V to maintain warranty ).

I am interested in the firmware as 3KVA seems to be semi-popular here in South Africa. my unit is second hand when so I don't mind busting it open maybe I can dump the firmware over SPI.

If you can tell me how to extract firmware, I'm happy to send you mine.

Also, you can turn on auto-equalization. I had mine set to auto-equalize every 5 days for 30 min. Saves you having to remember to do it.

Edited November 27, 20232 yr by jbroo

18 hours ago, zylinx said:

Thanks for the replies @Scorp007 and @jbroo

I tried increasing the bulk charge voltage didn't really change much. I am happy to hear its relatively a non-issue for LFP. Strange behavior nothing like what the spec documents.  I will just leave it as is and every few days bring it up to 14.1V with equalize (as revov insists on a full charge every cycle to 14.1V to maintain warranty ).

I am interested in the firmware as 3KVA seems to be semi-popular here in South Africa. my unit is second hand when so I don't mind busting it open maybe I can dump the firmware over SPI.

Try changing your float voltage to 28V and see if you reach it that way, if you do then it's the algo going to float early.

Some BMS have what's called intermittent charging when they get full and start balancing, the BMS switches off and on and this fools the inverter into thinking the battery is full because the current goes to 0.

@zylinx I graph my inverter stats (github link coming soon) so to allay your fears here is an image of the inverter's charging curve. Note the peak before settling on float.

And here's the corresponding LS dropout

@jbroo thanks! yeah I'm pretty much running the exact same numbers.

5 hours ago, jbroo said:

@zylinx I graph my inverter stats (github link coming soon) so to allay your fears here is an image of the inverter's charging curve. Note the peak before settling on float.

This short spike to bulk voltage and almost instant drop to float voltage is what I was referring to above, there is no absorption stage in the charge curve. To charge properly, the battery should spend some time at the bulk voltage so it has time to do internal cell balancing in order to reach 100% SOC.

To overcome this on my 5kVA inverter I use the "Bulk Charging Time" setting (32) at 120mins to get the absorption part of the curve. If there is no setting 32, then one can use the Equalization settings (33-39) set to bulk voltage to do the same thing... if neither of these settings exist in the firmware then one needs to push up the float voltage to just below bulk voltage to get a proper charge... I have to do this on my 3kVA inverter as it's really old.

On 2023/12/02 at 7:12 AM, jumper said:

This short spike to bulk voltage and almost instant drop to float voltage is what I was referring to above

That "short" spike is still about 25 min, and the total charging time is just over 2 hours. In my example, the charge exceeds the float value (27.2) and keeps climbing for another 25 min, until it reaches the peak of 27.57V, then drops. I have my bulk charge set quite low at 28.4V. My batteries were minimally discharged since my house idles 200-300W when we are not home.

 

 

Quote

To charge properly, the battery should spend some time at the bulk voltage so it has time to do internal cell balancing in order to reach 100% SOC.

I don't think that applies to LFP type batteries, and the BMS should balance the cells internally. It appears that there is no need for absorb time, not beyond a few minutes anyway. Image source.

I'd be interested to see if the above charging behaviour is different on a system not running LFP batteries.

Edited December 4, 20232 yr by jbroo

On 2023/12/04 at 2:27 PM, jbroo said:

That "short" spike is still about 25 min, and the total charging time is just over 2 hours

What I'm referring to is not the constant current part of the curve, I'm referring to the constant voltage part of the curve which is usually flat, the charger should stay at bulk voltage while the current drops.

 

(source)

As you can see from the above, the CV part of the charge curve is necessary for lfp cells. I've also observed on my battery that it needs to sit at bulk voltage for a while because internal cell balancing also happens during this stage and if it is terminated early the BMS doesn't report 100% SOC. On my battery some cells need to be above 3.5V for balancing to even start, so the CV voltage needs to be high enough for that.

Are you getting your SOC reading from the BMS or inverter? If your BMS reports 100% then you're fine, I just know I needed to extend the CV part of the curve to hit 100%.

This image is from an axpert manual which shows the algo should have the constant voltage part of the charge curve as the current falls: