I was getting really tired of the massive flat spots on Lister’s tyres that made moving it a serious effort. I got some pneumatic tyred wheels from Machine Mart, and some 20mm round steel bar, box section, and 20mm shaft collars.
By the tender ministrations of the Milwaukee Hole Dozer and angle grinder, the box section was turned into a set of axle collars.
I was too cheap to buy precision shafting for the axles, I went for so-called “round” mild steel bar which isn’t actually all that round. A lot of grinding was involved to get the shaft collars and wheels to fit onto it.
The next part was actually really fiddly and I apologise for not getting more pics of it. I had to jack the generator up, remove the existing wheels and axle, and offer up the new axles to the frame to mark out the bolt holes. As the unit is on loan, I didn’t want to drill any new holes in it, so I drilled the axle mounts to line up with the existing holes.
So far so good, but the next step was to fire up the generator and use it to weld its own axles together without having it vibrate its way off the temporary pieces of wood it was propped on.
It was getting dark and I was in a bit of a hurry as I couldn’t put the thing away and lock up until it had functioning wheels on it again. The welds turned out horrible, but as the saying goes:
My main motivation for borrowing Lister was to run the welder at Container Labs. My GYS Protig 201 AC/DC claims to be “generator friendly and protected” but also “minimum generator size 7.5kVA”.
Lister is rated for 3kW at power factor 1.0, but looks massively overbuilt, so I thought it would be worth a try.
My first attempt at welding was pretty anticlimactic, on striking an arc the welder instantly shut down with error code “US1”. According to the GYS manual this means input voltage over 265V RMS. On further reading the unit claims to withstand up to 400V RMS/700V peak without damage but will apparently shut down above 265.
Since the welder has a PFC front end, I tried substituting the Odin PFC to see if this would manifest the same issue. It is rated to run at 415V RMS and has 1200V semiconductors so I had no worries about blowing it up with overvoltage. I used the Tesla Model 3 cabin heater as a dummy load for the PFC output.
This was somewhat inconclusive as the Odin PFC happily ate all of the generator output, showing no signs of serious instability under load, and making an impressive blast of hot air from the cabin heater.
The unloaded peak voltage did look somewhat high, due to the PFC’s EMI filter capacitors resonating with the generator winding inductance at the tooth ripple frequency.
Unloaded
These scope shots only show one-half of the generator output voltage, as I didn’t have an isolated scope probe handy, and the generator output is centre tapped to earth. So the total peak voltage is 472V unloaded and 368V under full load. These would equate to 335V and 261V RMS with an ideal sine wave. Since the actual RMS is 256V unloaded and 232V loaded, we certainly have some evidence of waveform distortion under both conditions.
Fully loaded
So on the face of it I could see how this could trip the welder’s overvoltage protection. I also heard from a friend who had experience of using similar generators to power his ham radio field day stations, and he said the waveforms tended to be “thin” with too high peak voltage for their RMS.
I pondered various ways of attacking the problem, a filter to remove the tooth ripple? This would need some seriously expensive and bulky inductors, so I didn’t bother. My first experiment was to step the output voltage down using an autotransformer (as I had one handy) and clip the peaks off using a rectifier, capacitor and resistive load.
This contraption (which I’ll call the Happy Welder 3000) worked surprisingly well, using the 190V tap, the peak and RMS voltages were both brought somewhat under control, and I was able to crank the welder to about 150A output at which point the engine began to bog down and belch black smoke, but would recover by letting off the TIG foot pedal.
Voltage and current drawn by the peak clipper
The Happy Welder 3000 seemed like a bodge so I went looking for a more elegant solution. I discovered that just switching the generator to 115V would give a decent result with no extra hardware needed. Voltage drop in the 25m x 2.5 sq mm extension cord (used to get generator noise and diesel fumes away from me) now limited me to a somewhat lower welding current before I got error “US2”, undervoltage this time. I was able to do a small job on mild steel this way.
I spent way too long thinking about this problem and ended up building an AVR which to my surprise, made the problem even worse! The welder was quite happy with 200V from the autotransformer, but with generator output reduced to 200V by the AVR, it wouldn’t run for more than a fraction of a second before tripping on error US1.
I don’t know how it took me so long, but I eventually stumbled on the idea of filming the scope screen while welding and examining the footage frame by frame.
I believe this frame captures the instant that the welder shuts down on error US1. Top trace is generator output voltage, bottom is current drawn by the AVR’s peak clipping channel. DVM shows the voltage across the AVR’s filter capacitor, which should be one-half of the peak output voltage.
The waveform is completely different to any I saw previously, and leaves only one possible explanation, the impedance (resistance and inductance) of the generator windings is too high for the welder’s PFC front end, it goes unstable and wrenches the waveform out of shape.
The instability pushes the peak voltage way higher than anything I measured while not welding, and does this so quickly that the meters I’d been using didn’t have time to register it. The AVR’s peak clipper tries to keep the peak voltage under control but fails.
This explains why stepping the voltage down to 200, and switching the generator to 115V, both worked and enabled me to weld, but using the AVR to reduce the voltage to 200 didn’t.
Switching to 115V gives an impedance one-quarter of the 230V setting. A transformer that steps the voltage down from 240 to 200 reduces the impedance to 76%.
On the other hand, the AVR only compensates for relatively slow fluctuations in voltage by adjusting the field current. It has no effect on the resistance and inductance of the windings, so can’t do anything about the waveform distortion.
I think I earned my professional development points on this one.
I started with a 3mm piece of aluminium pre-cut to size by Metal Supermarkets. The existing screw holes were easily replicated with PEM nuts, but the old faceplate vibrated horribly, so I wanted to add 2 more mounting bolts, and oh dear, the drilling for the top one just missed the panel.
This was a perfect excuse to zap something with the TIG welder.
Zap and tap
With this done, a coat of gold paint and a pasting with letter punches…
Wanted a track light fitting for the living room and more aluminium welding practice 🙂
20x20mm square tube (ashamed to admit I bought it from B&Q) was cut into the shape of a lightning bolt.
Oh dear, the mitreing could have been better…
This is the nicest weld, there were much worse 😀 I got off to a bad start by burning several holes in it while trying to tack it together, and had to weld up the holes. I didn’t realise the tubing was only 1.6mm thick and started off with too large a tungsten and too much current. Another reminder to always test the welder settings on a scrap of the material you’re going to use… 🙂
After fully welding (OK I didn’t do the inside corners 🙂 )
I was looking for an aluminium welding project that wouldn’t kill anyone if it failed. And also some speaker stands that wouldn’t take up any desk space.
I started with a 1m length of 3″ x 3″ x 1/8″ box section.
After a whole afternoon of hacksawing, jigsawing and filing it was reduced to 2 columns and some wedge shaped pieces.
The pieces were then welded together into a giant C clamp shape and a 3mm plate was welded to the top to support the speaker. I decided to only tack weld the plate because I was worried the heat of a full weld would warp it.
I find the fillet weld the most difficult. This doesn’t exactly look great but it’s my best yet.
The stand base screws to the underside of the desk with some hefty wood screws.
The desk is completely clear and there is plenty of room underneath for oscilloscopes, soldering irons and so on.
I got fed up with the thumb controls on the torch that came with my welder and decided to try a foot pedal. They are extremely expensive to buy so I decided to make one out of an unwanted wah pedal.
First, a bracket 🙂
The main difference between a wah pedal and a TIG foot pedal is that the switch engages as you first apply pressure to the pedal, telling the welder to open the gas valve and go through its preflow and ignition cycle. Depressing the pedal further then controls the welding current.
To allow this operating mode I threw away the existing stomp switch and replaced it with a microswitch operated by a cam.
The other difference is that it needs a rather strong return spring to avoid igniting the welder by accident. I found this out by trial and error. D: Keeping with the musical instrument theme, I used some Strat tremolo springs from eBay.
I connected it to the socket for the hand controller as a spare plug for this was supplied with the welder. It thinks it is a torch with 1 button and thumbwheel. This seems to work fine, but I will try the foot pedal socket if I ever get round to figuring out the mating plug for it.
