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The dreaded premature float bug (Axpert 3kva 24V)


Fox
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Good morning

Thank you for all the info I’ve gathered to date.

I have recently installed a 3kva Axpert inverter (24V) and am struggling with the premature float bug (as far as I know there is no firmware patch for the 3kva and setting 32 is not available to adjust the time spent at maximum voltage).

As far as I understand the premature float bug only occurs under certain conditions (voltage above float AND low charging current).

This morning I did a test with charger source priority set to utility (output SBU and solar panels disconnected). I discharged the batteries down to the back-to-grid voltage (24.5V) and I hoped that I would get my batteries up to the CV voltage (28.2V).

But again, it got to the float voltage (27V) and stayed there – never reaching CV voltage.

My back-to-discharge voltage is 27V and max charging current = max AC-charging current = 20A.

Any ideas? Is there any way to somehow trick it into fully charging the batteries?

Thanks in advance

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43 minutes ago, Fox said:

setting 32 is not available to adjust the time spent at maximum voltage

I don't suppose you have equalisation settings? There are half a dozen of them up to about 38. Those can also force higher charge voltage.

If not... It's really not fit for purpose if even a utility charge doesn't work properly! 🤔

Edit: and sorry, I don't know any other tricks.

Edited by Coulomb
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Hi Coulomb

Thanks for the quick response.

There are actually equalisation settings which I can configure from Watchpower.

Should I do something like reduce equalisation voltage to bulk charging voltage and set to equalize daily?

Your help is much appreciated

 

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On 2020/02/20 at 8:57 PM, Fox said:

Should I do something like reduce equalisation voltage to bulk charging voltage and set to equalize daily?

Yes, exactly. It won't stop charging automatically when it's full, so you have to be careful. If your battery is a sealed lead acid type, especially if it's not an AGM type, you need to stay under the gassing voltage, about 14.2V per 12 V module in summer. You mentioned 28.2 V, so that's fine. Now you get to play the "guess the equalise time" game. Too much and you risk overheating the battery and reducing life; too short and you chronically undercharge the battery, reducing life. It's probably better to err on the side of too much charging, rather than too little.

I wonder though if Watchpower really knows your inverter model properly, and really can perform equalisation. 

Edited by Coulomb
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  • 1 month later...

Hi 20VT

I increased my float charge voltage and lowered my expectations :)

I'm afraid I'm far from being a guru, so please take my advice with a pinch of salt.

Essentially, with my inverter, the bulk charge voltage is pretty arbitrary because it never gets there (due to the premature float bug). So my only lever is the float charge voltage. This should probably be in the 26.4 to 27V range but I've increased to 27.4V.

On some days when I'm at home all day (there are a lot of those lately), I do a manual bulk charge by increasing the float charge to 28.2V for a few hours in the morning.

I'm not sure if this method will destroy my battery life, but it seems to kind of work for me right now.

Good luck

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On 2020/04/09 at 9:09 AM, Fox said:

Hi 20VT

I increased my float charge voltage and lowered my expectations :)

I'm afraid I'm far from being a guru, so please take my advice with a pinch of salt.

Essentially, with my inverter, the bulk charge voltage is pretty arbitrary because it never gets there (due to the premature float bug). So my only lever is the float charge voltage. This should probably be in the 26.4 to 27V range but I've increased to 27.4V.

On some days when I'm at home all day (there are a lot of those lately), I do a manual bulk charge by increasing the float charge to 28.2V for a few hours in the morning.

I'm not sure if this method will destroy my battery life, but it seems to kind of work for me right now.

Good luck

Thanks for responding and sharing what you are doing to get around this issue.

I assume that you have Lead Acid batteries.

 

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  • 7 months later...
  • 5 months later...

Hi everyone, I have the same issue in that even after a deep cycle my batteries go straight back to float voltage of 27.6 (user defined) and never go above this for a bulk charge. I fear this is damaging my batteries. Does anyone have any suggestions on how to get the 3KVA 24V inverters to bulk charge? I have played around with the charge currents as suggested above but still no luck. My only other option is to manually set the float voltage higher for a period of time as described above.

 

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Posted (edited)
18 hours ago, Andy07 said:

my batteries go straight back to float voltage of 27.6 (user defined) and never go above this for a bulk charge.

Do you have enough solar power to charge them higher? [ Edit: Can you charge them from utility? With reasonable settings, you should not get the premature float bug biting with utility charging. Though some 24 V models have very low charge current capability, possibly also from utility. ]

Quote

I fear this is damaging my batteries.

It is indeed not good for lead acid to be chronically undercharged.

Edited by Coulomb
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  • 2 weeks later...
On 2020/02/20 at 3:40 AM, Fox said:

22am struggling with the premature float bug

 

On 2021/05/19 at 9:41 AM, Coulomb said:

It is indeed not good for lead acid to be chronically undercharged

Good day all

I have an 18 month till now fully operating Axpert 1 Kva 1000 W MPPT Inverter recently(?) suffering from the same issue.

I met this forum starting with Coulombs analysis on "code 03" and have never again had a good nights sleep.... he he

I am Of Grid so my routine since mid Autum (April-May in Chile ) Includes a "Top Up" with Internal combustion Generator ( 2000 W ) 2 hrs past Sun Down and at wake up in the morning 6-7 AM . If it is a too cloudy/rainy day I have to run the generator (Axpert 20 A Utiliyu charge ) for about 1/2 - 1 hrs every 3 Hrs. ( Mostly to keep the home ferigerator going ). I stop when chargin power descends to lower 100 w. ( Starts with 250 W app )

Since descovering code 03 and as Fox says "the threaded under....." , the only way I have managed to reach 14.1 V bulk charge voltage is by adding a selfmade "Charger" out of an PC UPS transformer + Rectifier bridge  which gives me 15A additional  + Car battry charger 4A on top of all.

But this lasts only a few minutes ( maybe 15 min ) and Axpert ( which is controlling the total amount of charge as I understand it) kicks back to float. My battery bank is 2 x 170 Paralell  Ah Narada AGM VRL with recommended maximum charge of 25 A a piece. I , of course monitor the whole process with self made Software with readings every 10 sec.

Apparently the Axpert 1Kva is done.....

We have decided to upgrade our system to 3Kva 24 V and because mostly of the low price I am obviously looking for an Axpert Good offerings ( plenty ) in Chile.

Problem beeing,  "How do I make shure I get a "Good One" ? Manufacturing date ? Serial Number ? ....

Most of the upgrade money will obiously go into new batteries.....

I thank you very much for past and future help. If ever possible.

It has been very interesting for me to read for hours throgh this forum. Thanks to the all the community again.

Greetings

Francisco

Chile

 

 

 

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On 2021/05/19 at 3:41 PM, Coulomb said:

Do you have enough solar power to charge them higher? [ Edit: Can you charge them from utility? With reasonable settings, you should not get the premature float bug biting with utility charging. Though some 24 V models have very low charge current capability, possibly also from utility. ]

Hey @Coulombsorry for the delayed reply, I did not see that you had replied to me. I have no solar so only charging from utility, these are my settings:

Float Voltage: 27.3

Bulk Charge: 29.0 (I've never seen it even close to this as it always goes back to float)

Cutoff: 23.7

Utility Charging: 20A

Recharge Voltage: 24.3 (although not needed without solar as far as I understand)

Total Charging 20A

The above is all in USE mode but even if I set to AGM i experience the same behavior in that it always just goes back to float voltage and never above)

Thanks for your help!

 

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On 2021/06/02 at 8:22 PM, frasenci said:

"How do I make sure I get a "Good One" ?

The main thing is not to end up with a clone, despite their lower price. Some clones might be OK, but you just don't know what you're getting, the the temptation to cut corners is always very high. Axpert quality is already so-so; I have replaced the capacitors and MOSFETs in mine (I have two, bought in 2015) to extend their life.

All the non-clones are basically made in the same factory to the same quality standard; there are a few odd brands that seem to get special treatment. Consider also that whoever you buy the machine from is probably the only place to get firmware updates, replacement comms boards, etc. You might be able to get firmware updates from a web site like this forum, but 24 V firmware update files are less common. You can sometimes get replacement boards from Ebay and the like, but it's almost impossible to be sure you're getting the exact right board (there are so many variations), and the quality is unknown.

 

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Posted (edited)
21 hours ago, Andy07 said:

Bulk Charge: 29.0 (I've never seen it even close to this as it always goes back to float)

As an experiment, perhaps set the float voltage to be 29.0 V (same as the absorb/bulk voltage). That will tell you whether the charger is capable of 29.0 V, and it will give your battery a much-needed full charge. Watch the charge current carefully (don't leave it unattended like this); when the net charge current into the battery reaches about C/20, change the float voltage setting back to normal. (If your battery is rated at 100 Ah, then C is 100, and C/20 is 5 A). Note how long it takes to get to that point, from when the voltage gets close to 29.0 V (if it gets there, of course).

Quote

Recharge Voltage: 24.3 (although not needed without solar as far as I understand)

Yes, you will presumably be in UTi output source priority (setting 01), which will ignore settings 12 and 13 (back to utility and back to battery voltage settings).

Quote

Total Charging 20A

It probably doesn't matter much, but I would set this to about 0.15C for your battery, or another value if your battery manual specifies a different maximum charge current. The inverter will actually pay attention to this value, even though you can't reach it with utility charging; it uses this value to decide when to switch from absorb to float stages. [ Edit: At least, that's what the 5 kVA models do. 24 V models may operate differently. ] Exactly your problem, right? But increasing this value will make it switch to float sooner. But try the above experiment first. Let us know the result.

Edited by Coulomb
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