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Pete:
HI Solar, I used Oz's ideas when repairing my inverter boards.
It requires that  you take out the big capacitors in the centre of the heatsinks. This reduces the inrush current and prevents the caps from supplying power to the mosfets and blowing more up
Then use a resistor in the supply line to limit the current (in case there is a shorted mosfet).
It will need a transformer connected as there is a feedback loop there that needs to see a return.
Good luck
Pete

Pete:
Hi Solar from memory, I started with a 20 watt 10 ohm resistor in series with the power supply to my board, then after I checked the current drain and gate drives of the mosfets I reduced it to 10 ohm then to 5 ohm.
When the board still ran with that I connected the supply directly to the board.
As I said the big capacitors need to be removed or they store enough power to blow mosfets if there is still a problem.
Usually when mosfets blow they take out their driver transistors and sometimes resistors too.
Make sure that they are all getting a clean gate drive when you fire it up.
If it all runs good then replace the caps
pete

solarnewbee:
Found that a IRF640 fet was shorted. Removed it and the current went to zero. Have new ones on order. Extras in case something goes wrong again. The diode mur680g seemed ok. I have a feeling it will come to life when a fresh fet  is installed. Some people power up using an incandescent light bulb to charge the caps slowly. Hard to find in a country that outlawed incandescent bulb sales and now florescent bulbs too.

On another subject I am replacing 1 bank of lfp’s with 4. 200ah VRLA batteries. The lfp’s are running on 15 pieces and appear to be giving out about 2/3 ah they used to. I replaced a cell and the new cell immediately went bad and bloated. I bought 4 new and so 1 out of 4 was bad and I installed another. That one goes bad. I call the factory. They tell me that since my internal resistance of the old batteries is so far apart from the new battery that this is what happens. Stop and don’t put anymore. It’s like changing tires on a dual tire truck if you don’t change both tires the new one will fail early. Surprisingly the bank charges up to 57.8 volts then settles to 54.3 ish most days. Unknown to me the breaker to the good bank had tripped and wasn’t being charged. I was getting 9 hours out of the bad bank. These are 200ah batts. Just weird stuff.

Question, I am short on space, can I stack these VRLA batts 2 together?

Pete:
Hi Solar not sure what you mean by " can I stack the VRLA batteries  2 together, if you mean parallel two banks then sure.
It is not the greatest practice but from what I read up to 4 banks is not too bad to parallel.
I have had heaps of parallel banks of Flooded batteries in the past, no real problems.
As long as a cell doesn't short out then all is good. And as long as the battery banks are similar age and capacity.
Hope it all goes good with the repairs when the parts turn up.
Pete

solarnewbee:
I meant to say put one battery on top of the other. They are sealed so no checking levels.

On the other subject, I have a short across the battery connections on this inverter board. Thought it might be the caps or the mosfet over by the egs board but not so. I reckon I was sold at least 1 bad hy4008. Jumped the gun and didn’t get out the tester before putting them in. I am officially trashing this board because I would have to desolder every single fet. No thanks.

Thanks for your help tho. Adios!

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