Xantrex 60-20 repair tips needed

[Hole]

Hi all.

the other day I turned on my second hand Xantrex 60-20 and after some minutes simply idling around it made a loud bang and I could see an electric flash through the front panel. Then power went out, room was dark and inhabitants unhappy.

I opened it. Visual inspection: no burn marks, no parts with craters, nothing, all looks good. Only thing are various collections of deep black dust around the fans, air paths, inlet holes, outlet holes. Those places I would assume that stuff collects there when fans without filter blow air around. The photos shows some of this dust at the power switch. At some places it was a chunk of dust, I would call it Wollmäuse...

By location I would assume the spark happend at the four APT5028BVRG power n-channel mosfets (500v, 20a, 0.28ohms). They seem to be the main power side switching unit, system has an anti clockwise power path. I measured them in circuit, diode mode, each has around 0.61v gate-to-source, source-to-drain is open and drain-to-source is at about 0.44v to 0.47v. No short.

Bottom third has lots of analog stuff and the gpib-stuff: nat7210bpd/ieee 488.2, two mchc11f1cfne3/M68HC11/8bit cpu as GPIB master+slave. All looks fine.

Front panel has nothing at that location that could create such arc. No caps, all parts look fine.

Fuses are all good.

This leads to my conclusion: some dust clusters was blown near the 320v side of the mosfets, sparks, burned and did a self-repair-by-suicide.

I didn't turn it on again. I have a chickenheart.

Any suggestions and hints?

[coppercone2]

I got one of these too, it was too annoying to work on so its been on a shelf for like 5 years. Thankfully it has no crazy parts. Put a week of work on it last year but I gave up.

I have a working twin for that one that broke too.

I will just suggest, get shrowded probes when you work on these. The whole reason why mine is fubar is because I did not setup a work area during a minor repair and shorted out a power rail. Big clean table, showded probes (that are sharp and won't slip), and I recommend some kind of mini grabbers or something when you are probing the heatsinked parts.

Study the manual for a while to understand how the control loop works and what the signals should be doing, the PWM is intimidating because its switchmode but really this unit is not so bad to work on. It's just that you get pulse waveforms in certain places rather then DC, so you need to use a scope.

[edpalmer42]

Use a Dim-Bulb Tester when you power the thing up.  Start with a small incandescent bulb and work your way up.  This will help prevent further carnage if there are internal faults.  If I remember correctly, my Xantrex XKW33-33 needed a 100W bulb before it started up properly.

[coppercone2]

Yeah its perfect since the thing has studs on it and the bulbs usually have screw terminals, I should make a light bulb load in a cage for my lab, can put banana jacks on it too that way.

[edpalmer42]

Yeah its perfect since the thing has studs on it and the bulbs usually have screw terminals, I should make a light bulb load in a cage for my lab, can put banana jacks on it too that way.

You don't use a Dim-Bulb Tester on the output.  You use it on the input to limit the startup surge and, hopefully, prevent the power supply from damaging itself any more than it already is.

Ed

[coppercone2]

That power supply has studs for both power input and power output, the output is two bus bars with holes in it and the input is screw terminals. It should not have banana jacks on it, but I was thinking more along the lines of making a general lab use light bulb "test equipment" box.

What I meant is that for this project it might be a good idea to design a nice lab grade light bulb box that interfaces easily with multiple equipments.

You can also put a pass through for the neutral and ground to keep the cords nice (i.e. box plugs into IEC and has 3x screw terminals on output, you leave IEC disconnected if using as a load and connect power if you are using it as a series limiter. The only thing you would need to do is use a opposite gender IEC connector so there is no exposed high voltage pins on the outside of the box if you are using it as a load. Branching the wiring to accommodate a light bulb is ugly.

I guess if I go through all this trouble it makes more sense to get a rheostat instead of a bulb, but the light bulb has its own merits due to its resistance characteristic.