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Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 1797

Posted: 06:12am 02 Apr 2026

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Now thinking back to my last test after I put all those scope pic's up with no replies I did think everything was right

I had the power supply set to 26 volts 400mA current and the voltage did rise to around 160volts AC then a click click click coming from the power board. The AC voltage dropped to zero and the power supply was drawing the full 400mA.

So the question after the AC voltage was ramping up why did it fail and go that clicking sound as the board has passive parts.

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 3104

Posted: 07:24am 02 Apr 2026

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Quote that clicking sound

My guess is it is that bank of big caps suddenly discharging when something reaches it's breakdown voltage. The caps recharge at the current limit until the cycle repeats.

To see if this is the case reduce the current limit to slow the recharge down and monitor the voltage across the caps. It should slowly rise then suddenly fall.

Several times KeepIS said You cannot power up an inverter with a fault with 60000uf of CAPS in circuit - PERIOD!

They can discharge thousands of amps into a short which means your power supply current limit gives no protection at all.
Remove them until all faults have been found.

E = 0.5 * C * V^2 where E = energy (Watt Seconds), C = Farads, V = Volts

E = 0.5 * 0.06 * 26^2 = 20.28 Watt Seconds

So if the discharge lasts 1mS that is a 20kW pulse! More than enough to destroy MOSFETs etc.

(If the discharge lasts 0.1mS that is a 200kW pulse!)
Edited 2026-04-02 17:28 by phil99

Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 1233

Posted: 07:36am 02 Apr 2026

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I thought it looked ok too, but I never measured (this test inverter on the bench) that way, now at 23vdc and 400mA I get 144vac on this one, not sure why yours was clicking unless its the power supply limit and the invert wants more to reach 230vac? See the photo of it working 2 pages back.
Edit: last photo is the working one.

Was it the power supply clicking and the inverter is still ok or is something shorted again?
Edited 2026-04-02 17:41 by Revlac

Cheers Aaron
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Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 634

Posted: 07:57am 02 Apr 2026

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I remember when Oztules was about that he always suggested removing the capacitors when testing a repaired board.
That is the process I used when fixing my Powerjacks when they blew up.
Took the caps off the board
replaced mosfets and sometimes drivers
test board, if it works then put capacitors back on and cross fingers

mab1
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Joined: 10/02/2015
Location: United Kingdom
Posts: 277

Posted: 08:21am 02 Apr 2026

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Bryan1 said Well just sacrificed another 4 mosfets

soldered one on each leg then set it all up turned it on saw the AC voltage rise to 168 volts then a tick tick tick started on the power board which caused the lcd to flicker so that the end of trying to get this inverter to work as I do think the power board is shot.

Well the scope waveforms seem ok.

I assume this was on the bench psu?
What did you have the current limit set to?

Just thinking that the clicking/flickering display could be the result of hitting the current limit of the psu rather than a fault - if the current draw > the psu limit the voltage would drop, possibly causing the driver board to stop and restart. but it would be helpful to know what the current limit was set to at the time.

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