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Inverter MPPT Module Burnt

Graham Muvirimi

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Joined
Jul 8, 2022
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Hie Guys.

I encountered this problem and still dont understand the cause.

I was called by a client, They had aa Kodak OGplus 5.48 offgrid inverter (5kW 48VDC), Mppt V Range 60-115VDC, PV in Max 4kW.
Pylontech 48VDC, 2.4kWhr Li-Ion Battery
6 panels, 345Wp, Voc 41.76V, Vmpp 34.99A, Isc 10.54A, Impp 9.86Aa, Brand Ja Solar.

Configuration was 3 modules in series, then 2 such strings in parallel

The system was also paralled with utility programmed to prioritise solar for loads and only utility when solr is not sufficient

His worry was that he was not benefiting from solar. He still had the same cost of power and when utility is down his battery was not lasting much time.

When we went ther we recomended he upgrade is battery and add more solar panels.

He had an extra Ja Sola module 345W with above specs. So he bought 5 more panels. Unfortunately these Ja Sola 345 wher no longer on the market. So he got 374W Jinko Modules with the following specs

375Wp, Voc 41.12V, Vmpp 34.53A, Isc 11.59A, Impp 10.86Aa.

So we added 6 more panels (5 x 375W and 1 x 345W)

Configuration, 3 in series and 2 such strings in Parallel.

So we now had 4 strings in parallel to the inverter.

But on commissioning we realised the inverter was getting only around 1.5kW from the panels and it would take balance from utility. This was so weird as the PV plant capacity was supposed to be more than 1.5kW

On troubleshooting why it was behaving so, i switched of main utility MCB to simulate a condition where we do have utility.

And we started loading the system bit by bit by switching on different appliances at a time.

1. We started with 1 AC and load was around 700W, and all coming from solar panels
2. We switched on another AC and load was around 1.6kW, and all coming from solar panels
3. We then switched on a kettle (water heater) and load went to 3.7kW, and all coming from panels.

Then we thought we had won, then switched off kettle and the 1 AC.

AAfter about 3 min, we had a slight boom from the inverter and some smoke. We opened the inverter and realised some transistors on the PV Input card were burnt.

I removed that inverter to take it for repair, then took an exact similar unit and went to install it. I did the installation in the evening and left the client running on utility, The following morning when the sun came up and the system switched to solar the inverter went up in smoke again, the same card had been burnt.

II have repaired one of those inverters but i need to know whats causing that before re-install it. I have reseached all angles but um hitting dead ends. Has any1 encountered such, help me team....

PPoint to note: the first installer did not put external surge protection and DC MCBs for the PV and Battery Circuits. Client is very conservative when we came in and suggested such he said its been working like that lets leave it.

All the 4 strings are combined on the roof and only one set of cables coming down to the inverter. Cable size is 6sqr . mm
 
60 to 115VDC. i have attached full spec
 

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MPP Solar issued a warning that you can only use 3s if the panels have max 60 cells.
And even then it is risky.
So usually I recommend to use 145-150Voc MPPT inverters with only 2s...p solar panels.
 
@OP, can we see the pictures of the burnt out card?
BTW, what is the measured DC Voltage at the PV input terminal of the SCC?
 
MPP Solar issued a warning that you can only use 3s if the panels have max 60 cells.
And even then it is risky.
So usually I recommend to use 145-150Voc MPPT inverters with only 2s...p solar panels.
Can I see that warning? I have two MPP Solar units myself.
 
Can I see that warning? I have two MPP Solar units myself.
It was on the Australian or South African forum maybe 2 years ago .... possibly the second.

They were (are) the leading factor on the development, repair, firmware, and features for the MPP Solar inverters.
 
You have a total of 12 panels? 7x345W=2415W and 5x375W=1875W making a total of 4290W?
The spec sheet you gave says max DC power 3600W. Is this the inverter maximum PV input power?
I found a spec sheet saying 4000W Max PV array power.

Does anyone know how things behave when panels with different specs are mixed together in the same string?
Screenshot (8).png
 
yes tbis one is the original spec from kodak, and even on the inverter name plate its 4000W...

my thinking was, nomater how many panels you put up on an inverter if you respect the V and I specifications, even if power capacity is too much, it should not affect the inverter because power is per demand
 
Yes many get over spec in regards to total wattage.

Would be good to clarify what the maximum solar input current is.
Do you have around 40A potential through that single 6mm?
 
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Unforrunately it does not specify the max solar input current,

the only spec closer to that is Max Solar charging current which is 80A
 
Have you checked for earth faults? I have seen an inverter blow up from this. The fuse on the pv side did not blow. A different brand of inverter was then installed and it came up with earth fault.
 
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