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Forum Index : Electronics : Recovering from disaster by using Wiseguy's mosfet driver design
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| tinyt Guru  Joined: 12/11/2017 Location: United StatesPosts: 459 |
So, I started removing the blown mosfets using suction desoldering tool. And I added more damage by tearing the top side copper foil. Luckily, I can beef up the connection at the bottom side. To avoid further copper foil damage, I cut two adjacent legs of the mosfet (my small cutter can reach only two) so that I can easly desolder and pull the remaining leg. I will be replacing all 24 mosfets anyway.  One pair of totem pole transistors also was damaged together with their solder pads. I will be replacing all four pairs. Note also the solder pad damage of the badly blown mosfet.  Here is close up of three blown mosfets. The top mosfet shows one of the source terminal bond wire sticking out which measures roughly .013" (.33mm) dia. with a caliper. The bottom mosfet seems to show that there are two bond wires for the source terminal. And apparently their explosion caused the body to crack.  |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 559 |
Good luck with the repairs Tiny. That was a pretty good blow up. I hope it all goes well and that you find all the damaged components first time. The box you have the inverter in is very tightly packed, that looks really compicated. There are so many different boards packed in there. Pete |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
It also took out the 48V to 12V buck regulator and opamps. Still testing for more damage. Way back I started a technical manual for my sons when I am gone. But I have not finished/updated it. I think this page is still good except for the auto pre-charge board which is now replaced with a simple pushbutton/power resistor combination.  |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 559 |
Nice diagram Tiny. I have done similar for my place for the next people who live here after I leave the planet. But my system is very simple, there are a few change over switches so the Grid inverters can feed back through two different battery inverters and there is a system of switching for using the EV charger Plus a voltage controlled relay that switches the GTI inverters off when the batteries are charged. No ethernet Batteries are Valve Regulated Lead Acid, so no complicated BMS. Just 4 regulators for the panels, and two GTI inverters for another two banks of panels. So instructions required for anyone else to know how a system that has grown from 1.2 kw of panels and one inverter, to 10kw plus of panels and 3 inverters. Good luck Pete |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1171 |
Tiny, On the Diagram, I'm curious about the CB 80A on the solar charger input..... Cheers Aaron Off The Grid |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
That is what I had on hand, I don't if it should be lower rated at 60A. But it is mainly used to remove/apply PV power to the SCC. Note that the PV- connections are not shown in that diagram. Edited 2025-09-05 00:06 by tinyt |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
After removing all 24 mosfets and four pairs of totem-pole drivers, I tested to see if the 48V to 12V buck converter circuit is working. Of course it is not. Found shorted components and it took me a while to 'discover' a burned copper trace hidden under a connector. In the process, learned a little bit about how the UC3845 works. Replaced the shorted and suspect components, jumpered the burned copper and I now have 12 volts.  |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
Made corrections to the Opto-driver schematic. I hope I got it right this time. Opto Driver_Bias(Rev2).pdf Edited 2025-09-09 02:57 by tinyt |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
So, I assembled the two identical circuits on two prototyping boards.  I tested the ouput voltages and they were as expected. With no input, the output of the FOD3182 is at negative bias voltage. I drilled and tapped the top of the heat sinks to mount the boards.  I then looked at my reverse circuit drawing of the inverter. To fit the new driver circuits, I have to make 12 copper trace cuts, solder 2 jumpers, and solder a total of 22 wires for the connector harnesses. And I chickened out.  A lot of things can go wrong: MY reverse is not accurate, mistakes in copper trace cuttings, etc. Also, I have no spare inverter. I have decided to save my work in case I really need to do it in the future. I think for now I will just concentrate on the compressor motor soft-start. And make sure I don't overload the inverter really bad. Edited 2025-09-09 13:20 by tinyt |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2710 |
Re the AC compressor. This may be a longshot but it is worth checking that the start capacitor measured capacitance matches the value printed on the side. Long ago I was asked to fix a large air compressor that wouldn't start, just sit and hum till the overload tripped. When he brought it into the workshop it worked perfectly. He had been using it on a long extension lead so we tried that and it wouldn't start. With the high start current the voltage at the end of the lead while starting was only about 10V low, but that was enough. That should not have been a problem so checked the capacitor and it was only one third of the marked value. Cut the can open and found it contained 3 parallel caps, 2 open circuit. A new one solved the problem. So the possibility is that your AC may be ok on full mains volts but not if the inverter sags with the high start current. Regardless of whether that is the problem here the triac starter should still help. |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 459 |
Thanks for the tip. The HVAC that blew the inverter is newly installed (about 8 months). Nameplate says 2024.  Here are some pages of the spec (schematic included). goodman-glxs4ba6010-specification-some sheets.pdf We have decided not to power it with the inverter, we think it is overkill to power it with our inverter, besides battery capacity is not enough to power it long enough. My other son's A/C is much older, close to 30 years and still running. We have operated this with the inverter several times already with no problem. But, we don't want to stress the mosfets, so we are going to use soft start on this one.  Micro-air is still not affordable, so I ordered these.   The plan is to set the ramp voltage time of the SSR to about 1/2 second or even less so as not to stall the motor, then with a tbd. delay circuit activate the HD relay to bypass the SSR. This way we don't overheat the SSR. I hope this works. |
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| analog8484 Senior Member  Joined: 11/11/2021 Location: United StatesPosts: 160 |
Can't blame you. That's certainly more mods than I expected. |
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