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Must 5kva Inverter not charging


Trevor L

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Good Afternoon. 

I have a Must 5kva 48 volt inverter with 4 by 12 Volt 200 AH batteries and solar array of 5 strings of 2 (330watt panels) in series.

i am having an issue each morning whereby the inverter is detecting the solar array and the charge relay is activating. PV voltage is showing 70 Volts. However no power is being fed to batteries or inverter. I have to physically isolate the panels and wait a couple of minutes. I hear the relay click out. On lifting the circuit breakers the relay clicks in and the inverter immediately starts charging and supplying power. 

Where should I be looking or is there a chance that the inverter itself is the issue

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15 hours ago, Trevor L said:

is there a chance that the inverter itself is the issue

Yes. Most Must inverter-chargers are clones, and there seems to be an issue with several of the clones concerning the PV power dropping out. In this case, it seems that the PV power availability detection hardware or firmware isn't working correctly. Since it is reading 70 V at the PV input, the hardware would seem OK. Contact your supplier to see if there is a remedy.

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  • 2 weeks later...
2 hours ago, Michael 34 said:

Is there a input terminal for charging

I'm not understanding the question. What sort of charging (PV or utility or direct to battery or ?) ?

If you mean is there a PV input terminal block for solar charging, then yes all Mecer inverters that I'm familiar with have them. It would help to tell us the exact model that you have.

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  • 2 weeks later...

Hi Trevor, interesting one today with my Must. 

Installed new batteries yesterday, left solar breakers off last night so I could energise when sun was fully up to see what amps they added to my depleted batteries. 

This morning, when I lifted the breakers, the inverter registered the panels were supplying power to the inverter at max voltage, but both PV relay and Battery relay did not energise leaving load still supplied only by batteries. 

I cycled everything on and off a couple of times but no luck. Finally sent my oke on the roof and chucked a blanket over the panels and immediately the Mppt kicked in and the relays energised. 

Got no joy as yet from supplier, seems they haven't come across this yet. 

 

You or anyone here got any thoughts? 

 

Regards Doug 

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Evening Doug. I believe the problem is impatience. I was very worried that the inverter was not doing it’s thing, ie initialisation, self test, relays activated and still no power to inverter or batteries. Wait a bit and when it decides that panels won’t be overcome, it will kick in. 
confirm your solar array is all same voltage/wattage and all are exposed to light at the same time. If you have shaded panels or different spec panels in the array this will delay power output. 
I have gone as far as ordering a different inverter but realise that it’s not needed. Patience is the answer. 
Are you monitoring via computer or are you working off the display on the unit. The Must software isn’t great but it gives you a full picture of what is actually happening. Get back to me with any questions 

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19 hours ago, Trevor L said:

Patience is the answer. 

Even the genuine Axperts take up to about 2 minutes to ramp up to full solar charging power from switch-on of the panels. The PV icon on the LC Display doesn't even show up for 10-30 seconds. Eventually, one amp (battery side) of charging for a while, then a very gentle ramp up to full power.

I think it might be to ignore very early morning sunlight that has no real "guts" behind it.

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  • 1 year later...
  • 1 year later...
12 hours ago, Gerhard707 said:

why the must inverter will only charge my battery op to 88% and not 100%

The SunX is presumably an LFP battery. You may be making the mistake of believing the SoC as shown on the inverter. Like the Axperts that these are copied from, they have no clue about lithium battery state of charge, unless there is a special cable connecting the inverter to the battery's BMS.

Usually the battery will have an SoC reading, or at least indication (e.g. a series of LEDs). What does that say? 

You might also be running into the premature float bug, also copied from Axperts. Are you charging the battery primarily from solar or from utility? 

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  • 3 months later...

I had a little accident. i have a 5 kw inverter with 140 Ah batteries setup, for only to be used to 2 KVa i.e. 229 Volt Ac / 10 Ampere maximum. ( it worked for 2 months fantastically) . However I manual switch the main-switch off and then have a second switch by the inverter to switch over to feed my house. I did this, as I am not allowed to manipulate the main-switch board) Till I was so clever to exceed my max cable current from 10 Ampere to ??? a washing machine and dishwasher at the same time. The 220 Volt wall plug packed up and I replace that., but the inverter no longer has the red LED showing that the inverter sees the 220 Volt. What are my options? 

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  • 2 months later...

I have a Must 3kw inverter which has been working fine with grid and battery. On Friday I installed 6x460w solar panels. 3 in series and the 2 strings joined in parallel and then to the inverter. The PV voltage at the inverter is 135vdc. The maximum PV open circuit voltage is 145vdc.

The problem is that the inverter is not showing any pv connection or input on the screen. 

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  • 7 months later...
On 2023/12/03 at 5:05 PM, Juan du Plessis said:

Hi all i have a Must 5kw hybrid solar inverter with a Svolt 51.2v5.43kwh LifePo4 lithium battery( no solar panels connected) but inverter only charge the battery to 19-25%.  I only rely on the utility to charge the battery. Is there a setting that i have to change?

What is the actual voltage you see when it indicates 19-25%?

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Also, is the 19-25% reported by the battery or the inverter?

If the inverter is not connected to the battery's BMS, then it will have no real idea what the battery SoC is. 

On 2023/12/04 at 1:05 AM, Juan du Plessis said:

Is there a setting that i have to change?

Yes, you can't rely on the default settings, these will be set up for a lead acid battery. 

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  • 4 months later...

I have recently installed a 5kw Must hybrid inverter, 100ah lithuam battery. When the the battery is fully charged, the inverter cuts off power to the load.And a faulty red light will be flashing. When you switch off and on (inverter) ,power will be restored. 

What could be the reason of cutting off?

 

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