Hi all- I need help with the settings on my 48v off grid system. I have a MUST 5kva 48v inverter. I have 6x 405w panels. My battery bank is 4x 12v 270ah AGMs which are 5 years old. My Inverter reads 55v on a sunny day by 10:30am. They never get to the Bulk stage of 58.5v or maybe since I'm a low energy user, they go straight to Float stage? When my water pump goes on, I see the volts go up to 57v but then the volts drop back to 55v when the pump goes off.

My Bulk is set to 57.6v and Float is set to 55.2v

Not sure if all my other settings are correct?  Attaching my inverter settings. Thanks in advance :-)

@MonaLisa hi the good news is that you got just under 2000 cycles from your lead acid batteries. The bad news is they are rated for 500 cycles.

Lithium batteries have become much more affordable than 5 years ago and most are rated for 6000 cycles. Now that you brought it up I'm wondering if anyone has had their Lithium batteries for ten years and how they are performing. 

Thanks for the great info. Still wondering why the batteries aren't getting up to the 58v mark?

 

3 hours ago, MonaLisa said:

Thanks for the great info. Still wondering why the batteries aren't getting up to the 58v mark?

 

[Quote=]

What is Battery Sulfation?

Sulfation, a build-up of lead sulfate crystals, is the number one cause of early failures of lead-acid, sealed AGM or flooded (wet cell-filler caps) batteries.  A sulfated battery can lead to:

• loss of cranking power
• longer charging times
• excessive heat build-up leading to "boil out"
• shorter running times between charges
• dramatically shorter battery life

    Other causes of battery failure include: vibration, contamination, damaged charging plates (due to overheating) and under or over charging. [/quote] https://www.batteryminders.com/avoid-battery-sulfation/#:~:text=Sulfation%2C a build-up of,longer charging times

On 2023/12/19 at 10:54 AM, MonaLisa said:

My Inverter reads 55v on a sunny day by 10:30am. They never get to the Bulk stage of 58.5v

Some of the early Must inverters were clones of Axpert inverters. All Axpert inverters suffer from a thing called the premature float bug. Maybe Must copied that bug?

One way around the premature float bug is to use utility charging (with sensible settings). If you are completely off-grid, you could use a generator.

Quote

or maybe since I'm a low energy user, they go straight to Float stage?

I'm 99% sure that every time the inverter starts solar charging, it is supposed to go to the bulk and absorb stages first. With the premature float bug, it can go to float when there is a passing cloud. You can probably watch an LED on the front panel to see what stage it's in (e.g. charging light changes from flashing to solid when it reaches the float stage).

Edit: So it's possible that your battery is still OK.

However, something else is possible: if the internal resistance has increased substantially (as happens at end of life), it's possible that the battery shoots up to 58 V very quickly, the inverter assumes that it's full, and goes to float mode. It might be worth checking the voltages of each nominally 12 V module; some may be very different to the others. If so, you could disconnect the low one(s) and charge it(them) with a car battery charger until their rest voltage is similar to the rest voltage of the others. If one or two modules are at low state of charge, they will likely be high internal resistance, which could trigger the early float stage (bug or no bug).

Edited December 21, 20232 yr by Coulomb

On 2023/12/21 at 11:47 PM, Coulomb said:

Some of the early Must inverters were clones of Axpert inverters. All Axpert inverters suffer from a thing called the premature float bug. Maybe Must copied that bug?

One way around the premature float bug is to use utility charging (with sensible settings). If you are completely off-grid, you could use a generator.

I'm 99% sure that every time the inverter starts solar charging, it is supposed to go to the bulk and absorb stages first. With the premature float bug, it can go to float when there is a passing cloud. You can probably watch an LED on the front panel to see what stage it's in (e.g. charging light changes from flashing to solid when it reaches the float stage).

Edit: So it's possible that your battery is still OK.

However, something else is possible: if the internal resistance has increased substantially (as happens at end of life), it's possible that the battery shoots up to 58 V very quickly, the inverter assumes that it's full, and goes to float mode. It might be worth checking the voltages of each nominally 12 V module; some may be very different to the others. If so, you could disconnect the low one(s) and charge it(them) with a car battery charger until their rest voltage is similar to the rest voltage of the others. If one or two modules are at low state of charge, they will likely be high internal resistance, which could trigger the early float stage (bug or no bug).

Thanks for your reply. Much appreciated. I have the Inverter set to Utility First and yes, I am off grid. I run a generator in winter when needed through a smart battery charger that desulfinates the battery bank. My batteries measure around 13.8v at lunch time and the inverter display reads 55v-55.2v but never reads higher unless I run an appliance. When the appliance turns off, the battery volts climb to 56v-57v but go back to the 55v after 30 seconds. Thoughts?

3 hours ago, MonaLisa said:

My batteries measure around 13.8v at lunch time and the inverter display reads 55v-55.2v but never reads higher unless I run an appliance. When the appliance turns off, the battery volts climb to 56v-57v but go back to the 55v after 30 seconds.

That means it's aiming for around 55.2 V. I'd say it is in float stage. The 56-57 V for 30 seconds is the overshoot.

Can you report on what the charge LED (if any) is doing please?

Edited December 23, 20232 yr by Coulomb

4 hours ago, Coulomb said:

That means it's aiming for around 55.2 V. I'd say it is in float stage. The 56-57 V for 30 seconds is the overshoot.

Can you report on what the charge LED (if any) is doing please?

Thanks for the confirmation. I don't have that charge LED. It's an old school inverter. 

8 hours ago, MonaLisa said:

I don't have that charge LED. It's an old school inverter. 

Are you sure? It's very common. What model do you have? The settings you posted correspond with those of Axperts, so yours is likely an early model that is an Axpert clone. All Axperts have the charging indicator LED, so I would expect Must to have copied that. The below is the first clear image I could find; it seems to be a later model than the early Axpert clones:

Edited December 23, 20232 yr by Coulomb

Yes, you're correct! Mine charge indicator is flashing and it's 5pm here in New Zealand. Merry Christmas by the way 🙂

9 hours ago, MonaLisa said:

Mine charge indicator is flashing

Oh. Flashing probably means it's in bulk or absorb stage, meaning that it should be aiming for more than 55.2 V.

Please report whether it is flashing when you find it at 55.2 V and you think it should be aiming for higher, and the charge current is low. By 5pm, often the charge current is so low that the inverter reverts to bulk charging, especially following a high load that causes the battery voltage to fall significantly.

12 hours ago, Coulomb said:

Oh. Flashing probably means it's in bulk or absorb stage, meaning that it should be aiming for more than 55.2 V.

Please report whether it is flashing when you find it at 55.2 V and you think it should be aiming for higher, and the charge current is low. By 5pm, often the charge current is so low that the inverter reverts to bulk charging, especially following a high load that causes the battery voltage to fall significantly.

Today is rain with cloud but at 2pm, the Inverter led light is static (not flashing) and battery volts reading 55 on the Inverter. I'm fairly certain this is what is happening on a daily basis even when there is full sun. The Inverter or Multi Meter never read above 55.2 volts. What do you think? 

3 hours ago, MonaLisa said:

Today is rain with cloud but at 2pm, the Inverter led light is static (not flashing) and battery volts reading 55 on the Inverter.

To be clear, we're talking about the middle led marked CHG, not the AC/INV led? If so, it's saying that charging is over (in float stage). The problem is likely a combination of the premature float bug and an ageing (high internal resistance) battery.

I assume that there are no settings higher than 31? I can't read the page numbers on your photos to see if there is a page missing. If you had settings 32 or 33+, you could work around the premature float bug.

What is your main (U1) firmware version? It's risky with a clone, but you may be able to update to patched Axpert firmware, which fixes the premature float bug. There are three versions that might suit your model, it's a bit tricky telling them apart.

Unfortunately most likely, your 5 year old lead acid battery with chronic undercharging due to the premature float bug is simply worn out.

Edited December 25, 20232 yr by Coulomb

Correct, it's the charging LED

Setting #31 is the last setting on the Inverter. The manual says U1 Firmware Version (Main CPU version checking is U1 14 04 and Secondary CPU version checking is U2 03 03

I think you're right about the undercharging. Been trying to figure this all out and with your help, it's all making sense. 

 

Edited December 25, 20232 yr by MonaLisa
adding information

1 hour ago, MonaLisa said:

The manual says U1 Firmware Version (Main CPU version checking is U1 14 04

Those are example numbers; we need to know the actual number from the front panel (press up or down buttons till you see U1, tell us the two numbers beside it).

Right-o

Here you go U1 is 52 30

Getting there- you are the only one who has actually explained this and I am very appreciative 🙂

1 hour ago, MonaLisa said:

U1 is 52 30

Wow. That's quite old. As in about 10 years old. But that tells me that you have a PF0.8 model (i.e. rated at 5 kVA but 4  kW), so you would benefit from updating to fully patched firmware version 73.00e. You would use the lead acid flavour with your present batteries. If you later decide to update to any sort of LFP battery, you would then update again to the LFP flavour. All the instructions are there, though I'll admit that it's a bit daunting at first.

Good luck, and let's hope that it allows you to limp along a bit longer on your existing battery.

Will have a look at the link. Thank you. Yes, it's an older inverter than my original one which was replaced under expired warranty. Will let you know the outcome!!!