Mach4

Yes the 20 is diameter in mm which is an indication of how much energy it can absorb and the 560 is the voltage rating. But be careful, with some brands the 560 needs to be read differently... it could be 56x(10 to the power of 0) which is 56V. For 560V the numbers would be 561. Check the datasheet to be sure. The voltage rating is normally AC_RMS but can be either the nominal voltage or working voltage (definitions depend on manufacturer). Again the datasheet will explain. Its a bit of a minefield.

Pimping the ride... Why do something simply when you can over-complicate it? On my 8kW Sunsynk I'm going to use 4x 12V Sunon fans which have 3 wires - red, black and yellow. The yellow wire provides a square wave output proportional to the fan speed. I'm using this to detect if a fan is slowing down or has stopped using a small monostable electronic circuit which lights a green led if fan speed is ok or red led if fan speed is below a minimum. This way a simple visual indication tells you whats up with the fans. Breadboarding on the bench has produced satisfactory results so now I've designed a pcb and am busy ordering components. The board and fan work off 12V which I get from a 48-12volt buck converter (Mean Well model PSD-15C-12) connected to the Li-ion battery via an inline fuse. Putting the fans, power supply and pcbs into 40x100 trunking should work nicely. Next level would be to add a microcontroller and display all fan speeds on a small OLED. Or would that be going to far? Mind you with that in place you could easily add a bluetooth link to a phone app to display fan status... or even link it into the Sunsynk wifi dongle to show fan status as part of the Sunsynk online app. Now that could be useful. PS: here is the schematic for the fanspeed monitor. and a rendition of the pcb

Besides MPPT considerations also bear in mind that more current means thicker cables so I tend to go for higher voltage lower current (for same power levels) and try to balance that with MPPT sweet spot requirements. If I cant meet those then thinner cable requirements wins (lower cabling costs). Granted its only a consideration if you are on the borderline of having to go for thicker cables.

Finally all's well that ends well. Replacing the IGBTs and molly-coddling it during start-up revived the inverter. Altho the failure mechanism for the IGBTs is still a grey area, the customer is happy so what else can I say. Thanks to @BritishRacingGreen @Coulomb @wael_fathe and others for the insight and information this forum has provided. I'm not yet expert level but I'd like to think I'm on the way there if more inverters come my way.

The saga continues... after replacing identified dead components D40 U16 Q6 and the main PSU caps I power up on the bench and all primary supplies and HFPW+ are present and accounted for. BUS+ also rises to dizzy heights when U17 is enabled via CN11P14, so all good so far. The display tho says HS and error 81 but I dont have PAR pcb connected so I'm not worried besides the current limited 50V supply is not hitting 500mA limit, it goes up to 200mA approx when the power supplies are turned on via AC Start connector. So time to put it back in the box and test. All connected incl. PAR pcb and SCC etc, and try power up via AC Start button the bench PSU hits 500mA limit, I check everything its the same as on the bench now what? Disconnect PAR board but no change. I'm monitoring Vbus but its not starting up. So I up PSU current lim to 1000mA (thats 48W) and try power up via AC Start multiple times each time current limit is reached, I switch off and check everything again. Then on next try suddenly display comes on, no current limit but after few seconds display shows HS and ERROR 09! Then shuts down. What the hell that means bus undervoltage. I strip everything fearing the worst sure enough QB and QD IGBTs are short circuit E-C. This implies enough energy existed to blow these monster IGBTs short circuit! Possibly there was a shoot-thru across the bridge how could that happen under control of the DSP? The 4066 IGBTs have a rugged spec including guaranteed short circuit SOA for at least 10uS. How could this happen? And with a current limited bench PSU? In truth I dont know. I am now at the point of recommending to the client to scrap it and start again with a Sunsynk. Hopefully he agrees because the engineer in me wants this unit to further analysis.

Thanks for the info. I am familiar with the UC38xx family having repaired other products that use them. Still need to design a flyback with them at some time tho. The parts have arrived, its this weekend's task to get this inverter up and running again. Will feed back my progress as and when.

Thank you, I will proceed as instructed above.

My goodness, I am bowled over by the detail of your insight into the inner workings of this machine. You have given me a whole bunch of avenues to investigate piece by piece. I will report back as I go. EDIT: Minor edit to your block diagram added R222 between +12V and U8 LED else Q8 when ON would apply full 12V across the LED.

Thanks @BritishRacingGreen I have the needed bench power supplies.

If I may ask my first Axpert-related questions on this forum... I was handed a 5kVA unit for repair recently circa 2015 model. It had the by now classic blinkenlightsundclickenrelays issue. I inspected the underside of the board and noticed D40 had a white dot on top of it, a telling sign that a mini volcano had erupted under the conformal coat and sure enough it was short circuit. Replacing it and powering up via the battery terminals using 7Ah batteries, the symptoms were unchanged. Thats when I researched the topic and came across this mighty forum. I replaced the 5 caps and on re-powering up, nothing. No response from the unit at all. U16 (UC3845) part of the bus soft start circuit now had the white dot of death on it and sure enough it was fried. As was the MOSFET Q6. The gate resistor is fine. No other MOSFETS or IGBTS were affected. I am awaiting arrival of replacement parts and my questions to the hugely knowledgeable members out there are these - once I replace the fried parts, what else can I expect to happen on power-up? Are there any other issues I should be looking out for? I am going to use a more conservative testing approach by using an energy-limited bench PSU instead of batteries and following the recommended bench power-up procedure. I would very much like to avoid damaging the expensive IGBTs or MOSFETS. And I would very much like to understand the chain of events that happened here. D40 going short circuit seems unrelated to U16 failing. Same thing with repairing the main power supplies by replacing the caps - how could that precipitate a failure of the bus soft start circuit which is what seems to have happened. PS: I have to say a huge thank you to all contributors to this forum, I have read it cover-to-cover and learned a great deal. Especially to @BritishRacingGreen and @Coulomb for the schematic diagrams particularly main board_rev 10j.odg It has been a huge time saver.