Conner Labs

A small 3 phase load bank built for work

Now the PFC is sorted, time to have a look at the bridge. One of the gate drivers was playing up with a shorted diode and mysteriously smashed MOSFET. I have no idea how this happened, but after replacing the bad parts the gate drive undervoltage error is gone, all four gate waveforms look good and the IGBTs all appear to be switching. Also a package from AliExpress turned up…

Odin PFC is fixed 🤩 I had to replace the FETs (obviously) a burnt gate resistor and a CT with a pin blown off and partially melted core. (actually I reused the melted CT as I forgot to order a replacement) I also replaced the diodes even though they still tested OK.

Post mortem on the EMF Tesla coil explosion. All MMC caps measured at their rated capacitance except the exploded one, which was open circuit. The PFC’s silicon carbide MOSFETs had exploded violently, and one of the SiC diodes also showed signs of heavy arcing between its anode and cathode legs, enough to blow chunks of copper out of them. One of the IGBT gate drivers had a shorted diode causing it to get very hot. And the main IGBTs themselves were undamaged 🤔

So I think the most likely explanation is that as the PFC was literally sitting in grass in a field, damp or an insect got into it and caused a flashover between the diode legs. This bypassed the inductor and caused a dead short between the FETs and all of the fully charged DC bus capacitance. Said FETs probably vaporised in microseconds before the PFC’s current limiter could do anything about it.

The overheating gate driver and burnt MMC had probably been like that for some time with the coil working acceptably in spite of these faults.

I’m bringing Odin to EMF this year! This has always been on the Conner Labs bucket list.

Finishing the Clarke petrol generator repair. Waveforms look slightly better than Lister, but voltage regulation worse, 275V unloaded! Got 3.6kW out of it before engine stalled, which equates to 4.5kVA at the usual 0.8 power factor. A bit down on manufacturer’s claimed 5kVA. 🤔

Oh no, Octavia’s check engine light came on. Luckily just a burnt out glow plug.

In my diary: Board ships May 2nd. Can’t remember if PCB or piracy 🤔

Caution: Congratulations? 🤔🤔 better than Error: Success I guess

Fixing generators is becoming a Sunday afternoon ritual at Container Labs. This 5kVA petrol unit was only producing 12 volts, and one of the capacitor terminals looked burnt and came off in my hand, so I tried bodging another capacitor in its place. It burst into life with an enthusiastic 260V output.

The motor demo rig I built for Weeteq’s stand at Embedded World. Consists of a PM synchronous motor and an induction motor coupled together.

Angle grinder is the best tool for cutting plexiglass. Saw Grind Hard Plumbing Co doing this and thought “it can’t possibly work” but it does!

The selenium rectifiers can nae take it, Captain! Voltage started sagging horribly under load. Replaced with silicon. I took the opportunity to do a 4 wire resistance measurement on the series field coils (0.2 ohms) and bypass resistors (1.0 ohms)

For today’s experiment I tried chopping Lister’s peaks off to make the welder happy. My idea was to connect a rectifier, smoothing capacitor and some kind of load to draw lots of current only at the peaks. This was very effective, by burning a few hundred watts this way the peak voltage was squished down to less than 300V. The welder still threw an occasional overvoltage error until I also stepped the voltage down to 210 with a transformer from the junk pile. Then it was finally happy and I was able to run some beads on a scrap piece of aluminium.

The voltage regulation on this generator is actually pretty good, it doesn’t sag or overshoot on load changes. It’s just that horrible tooth ripple that pushes the peak voltage way up. At 475V peak, Lister is officially a danger to modern electronics.

Prototype of the Dino-Solar 3000, a device to automatically switch between solar and generator power for battery charging and 12v loads.

I had to find 2 identical permanent magnet synchronous motors for a project at work. It was a challenge but after a lot of searching eBay delivered these fine Allen-Bradley servo motors. They look like they spent a few years at the bottom of the sea and one has bad bearings.

Ahh, peace and quiet. Actually the silencer doesn't make much difference tbh.😒Next weekend we'll see if it can power the welder!

Lister has come to me for rehab. He's given up producing electricity and just sits around and drinks.

Well done Greggs, sandwiches might be freshly made but Windows 7 is well past its sell-by date!

Will our kickass new motor fit the bench drill? 🤔 I’m going to say yes with a longer belt.

Fixing an Invertek VFD that I bought very cheaply on eBay. It arrived a bit smashed with something rattling around inside, and tripped out with “Output fault”. The rattling thing turned out to be a capacitor that had come completely off the circuit board. Soldering it back on made no difference, but a factory reset fixed the problem. 🤔