Modding a really cheap SWIZ AC Welder - some help please?

[mike 109444]

Ref the motor speed control. The motor in "normal" operation (connected to the feed unit/gearbox) will run at a very fast speed and the gearbox reduces this down a lot. Motor rpm = probable 1000, final output from gbox rpm = 20 rpm ! The DC geared motors on the equipment I work on have a 3000 rpm motor and three possible gearboxes of 48, 210 or 310 output with lots of torque. see pic
The MOV should be across the diode pack output. If you look at the pic in post 16 up and to the right of the top white circle is a light brown disc device, this is the MOV in that machine. Looking at the 2nd and 3rd diagrams in post 10, they are shown as an oblong device with a stepped line through it at an angle. Clarke seam to fit them before and after the diodes, go figure.... Note also if using the Clarke diagrams that they sometimes have a center tapped transformer (pro 90) and at other times a standard transformer (150 TE)
With the inductor you should be able to experiment "externally to the welder with the number of turns using an old car jump start lead connected to the work return lead. Ref the wall wart. Fit the socket on the outside and run it's thin DC lead into welder until a better sized/shaped psu can be got.

The 1500cc capri had much the same engine as the MK1 1500 cortina (my first proper car!) and some corsairs had the same 1500cc as well as some early MK2's
The engine was an uprated version of the 1200cc which was an uprated version of the anglia 998 (Harry potter car) That is the basics , but purest would no doubt say there is more to is than that. ps the lotus cortina was also a 1500 block with lotus magic sprinkled over it

 

[Peter Millerchip]

Thanks once again Mike.

I understand about the motor gearbox - I was more concerned (to start with) that the motor would whizz away with much screeching or do nothing. Obviously it needs careful study and testing under "weld/wire conditions" but that is for later.
At least, for now, I have a stable, separate power supply and a working motor speed controller.
The pic. you sent shows quite a nice gearbox in a very small space - would it fit in a RC model boat? Looks like it could pull like an Oxen?

I think understand where the MOV should go. Am I correct in thinking they do not have a "value" as such.
I have a couple of them (from the scrapped power boards) - they are epoxy disc construction with radial leads. They measure 3 ohms across the terminals in both directions (non polarised?). Black in colour with the silver characters :-NTC 2.5D-20. I think the "NTC" means "negative temperature coefficient"? They were connected in parallel on the power board and seem to be ok following the rigours of de-soldering. Will one or both of these suffice?

I have fitted the double pole micro switch to the handset. It meant a certain amount of fettling with a burr and Dremel to pare away some plastic to get it to fit, I haven't yet soldered the wires in - they will be a bit of a squeeze in the hand-torch around the trigger/micro-switch, but we'll see.

Ah, the Lotus versions - much lusted after, to get that green stripe down the side of a white Cortina. I always hankered after a Chrysler Sunbeam Lotus a bit later on - really cool I thought and maybe a bit classier?
I had a Ford E93 Pop (3 speed, fabric roof, 6Volt electrics and vacuum windscreen wipers) whilst at college - it had an air conditioned floor and very weird bowden cable wired brakes! Happy days.

 

[mike 109444]

I to had a pop (sit up and beg type) that I was supposed to be customizing...... Well that never got done Yep fabric roof and so on. Dad towed me in it the couple of miles from his house to my then house with me steering sat on a milk create, that was scary. Think dad forgot it was not a modern car he was towing. Glad it was on a solid (scaffold pole) tow hitch. Think there was a sad tail of a sunbeam lotus on retro rides. http://retrorides.proboards.com/thread/78084/19-chrysler-sunbeam-2.
Any hoo There is sometimes a value on MOV's usually max peek voltage. Not sure what you would need. What's the worse that could happen pop (and I don't mean a 1950's ford ) NTC is correct as you understand it.
I have a bucket (big bucket!) load of those motors used but most working. Was going to try and mod them to make up wire feed assemblies or replacement motors for the likes of the small SIP welders that a lot of forum members seam to own but despite having been a machinist in a machine shop (BAe) I no longer have access to a lath to knock up the modded shaft to make them suitable. They are quite weighty (not sure I have suitable scales to weigh one, maybe the wife's food scales). If you are any where near Barnstaple then I do work in there from time to time (service and testing on some weekends) Your welcome to half a dozen FOC to play with. Note they are 24vDC but will run from 12v.
Ref the motor controller, the Chinese are able to turn out some of these electronic for peanuts now. No wonder Maplins are no more.
I bought a DC to DC switch mode speed controller (< £10 !) rated for around 15 amps to control a mobility scooter motor I had modded to drive a sheet metal bead roller. Will drive the motor from stop to full speed with very good control. A box the size of a fag packet. Pic does not show it wired up but shows the size of the motor it controls.

 

[Peter Millerchip]

The milk crate sounds scary.
I remember towing a mates Ford Consul (mark1) to a scrap yard - it had no brakes whatsoever, so to save the rear of my car, we inserted an old settee (tied on with binder twine) between his front bumper and my boot lid. Fortunately we did not run into Mr. Plod on the somewhat harrowing but overall exciting journey. The settee did not make it unscathed.
Thanks for the MOV info - I'll suck it and see.

If you need some machining - I have a reasonably well equipped workshop, my lathe and mill could use a workout and I have nothing but time! - if you want something turning up (keep it fairly simple - I'm still a self taught makee learnee model engineer, but I have completed a few stationary type mill-engines and steam boilers that work, and I really enjoy tool making) - give me a spec. I would be delighted to help, so as to repay your kind help in posting so much useful info.

Or drop into my man-cave if you are in East Devon, and have a play.

I would really love a couple of those motors to try out, but unfortunately, I am now on a horrible drugs regime which makes me somewhat wobbly at times, and a drive up to Barnstaple (I live in East Devon) is probably not within my capabilities at present - much as I would like the trip.
Can they be mailed - By all means let me pay for the postage?

I'll bite the bullet - your picture (?), something being driven by one of your geared motors - its either a canal lock mechanism, or some sort of anti personnel undershot Gatling killer weapon?

I'm still building the capacitor pack, should be done soon and I'll post some pics of that and the pwm board and the carcass of my opus.

I read somewhere (American forum I think) that a suitable choke for the output of a DC wire welder turns out to be 25 - 30 turns of 8 gauge wire, close wound, on a 2" diameter iron rod, 5" tall!
By simple maths, that's around 15 ft. of wire.
Now a 2" mild steel rod would be easy to source, but Iron?? (Cast Iron bedpost etc.) Does steel have the same permeability as iron? Anyway - that might be an interesting thing to make?

Peter

 

[mike 109444]

Scary some of the motoring things you use to be able () to get away with. A bunch of CB'ers myself inc went to w-s-m and on to way back one of the cars a MK2 cortina broke down and a call was put out on the CB for a tow back to Bristol as no one had a tow rope . Guy replied and stop off on his journey up the A38. He had a tow rope and even offered to tow the broken car back to Bristol but he was in a hurry so would have to get a move on with the towing. Well I'm glad it was not my car cos to follow a car being towed at 50 plus up and down the 15 or so miles back to Bristol along thee A38 past the airport if you know the road you would know what I mean.
The "pic" is of a mobility scooter motor (about the size of a car starter motor) it drives a sheet metal bead roller/jennie The tool that puts, well beads in sheet metal. It is not shown in the pic but I used one of the Chinese speed controllers to control the turning speed down to a craw. Bit crude with the cycle chain as that was all I could find AND even that took some finding. Was not that long ago that ever street had an old bike dumped at the end but any metal left out now goes before it could even flash rust!
I do on odd occasions get down to Exeter (a privet hospital Nuff said ) and also the TNT down there as it's quicker for me to go from Barnstaple to TNT Exeter then home (south Bristol) than go up to TNT Bristol (Yate) then home !
Will try and get some of the motors to you at some point.
If you look at the inductors in most of the Clarkes and most other small to medium welders they are like a transformer, using the same "E" and "I" arrangement as most transformers do. So You could wind one on an old large transformer frame as the steel used in them is of a grade too suite this use. Maybe even an old arc welder, buzz box type transformer might work as it is (see sketch below). Using the secondary side and it would be variable ! (kept meaning to try this myself) As the inductor can be connected externally it means some experimenting can easily be done.
Mild steel would not make a very good inductor core. Even the tuning cans in a radio have ferrite (type of iron) cores.
If you have a cast iron bed (post) I think you need to get yourself off to somewhere like DFS cos that's an old bed
Maybe a chunk of an old engine cylinder head or gearbox as a source of iron.

 

[Rig Pig]

Old weights and car brake disks and drums are a handy cheap source of iron.

 

[Peter Millerchip]

At the risk of deviating from welding briefly, a really scary motoring thing, much like yours, Mike - I was driving home from a holiday in Wales through really heavy rain, back to Ottery St. Mary.I had crossed the Blackdown hills from the M5 at Wellington by side lanes and just reached the bridge over the river Otter outside Honiton. The river had burst its banks and the water was flowing in the road, on the bridge, half way up its walls. Just then, a car came splashing through the flood, going the other way. The driver told me it wasn't too bad to drive through - keep a steady forward momentum and you'll be o.k.
So I did.
My car was a brand new company Peugeot 306 turbo diesel - one week old. I had barely got used to it, and had never raised the bonnet. At that time, I didn't realise that the turbo air intake is BELOW the chin spoiler down at the front - so guess what? I learned how incompressible River Otter water is! A rumbling non-musical noise from the motor which literally ground to a halt, and a strange warning light came on (one I had not seen before - referring to the manual, if this came on, it was really BAD). We stopped literally mid stream. The river was now flowing through the car as well as around it and rising over the carpets fast. My two lads were in the back, they were quite young then, and getting a little frightened. Fortunately, a passing farmer in an Isuzu pick up, came by and saw what had happened and offered a tow, up to town, which I accepted with thanks. Unfortunately, as we towed away, I realised his tow rope was only about ten feet long, and he wasn't hanging about. We finally got to a telephone on the Honiton by-pass, after I had rammed his rear bull bars several times - much bodywork damage to my new car! The engine needed a re-build with new con rods, crankshaft and so on, plus about 300£ worth of body repairs and new carpets!!

I do know the Nuffield hospital in Exeter, very very well - and its heart and MRI departments.

Get the motors any time- will be nice to look forward to.

Thanks for confirming what I thought might be the case about steel cores for an inductor.
I am kicking myself thinking of all the old cast iron bits of car engines, gearboxes, axles and so on that I've scrapped over the years - what a throw-away society we were?
I remember long ago, in days of long short trousers and scabby knees, when pram wheels were a much sort after commodity and traded for all kinds of "soap box" carts. An old ironing board or plank and a set of wheels, and the world was your oyster. Let alone scrapped bikes.

Here are some pics. of what I've been up to :-




This is the pwm motor control module - I have fitted a better pot and bridged the switch contact






The capacitor pack and bleed resistors. (The Marmite mug for scale!)


The caps are rated at 250V which gives plenty of elbow room (working voltage is around 37Volts), but are alas only 1000uf each. The blue can type is rated at 60V 10,000uf. Total is therefore 22,000Uf. All my other high value caps are rated at 50V or less which is too low for safety as has been pointed out. So I'll go with what I've got.
I tried earlier to connect the caps with copper pipe hammered flat - as sort of bus-bars.
I tried that for these caps, but as Mike said, there is a real risk of poor/dry soldered joints on heavy copper. I did not want to play my propane torch around the ends of the caps so as to get some heavy heat, and my dear old Weller soldering gun has burned through its tip. So I've gone with tinned copper wire as a connecting medium.
After soldering it all together, I gingerly connected the pos/neg ends of the pack to my bench power supply, and very very slowly powered up, keeping a close eye on the ammeter. No problems - it pulled about 250ma. briefly at times and powered up to 25Volts quite happily. I let it sit, holding that charge for a few minutes, no signs of distress or "hot" joints, then turned off the power supply and the bleeders did their thing, it went to zero in about 3 seconds.
I appreciate 25 volts, smoothed bench current is not like a welding situation with surges and what not, but I wanted to check as far as I could that my soldering/layout was safe and functioned properly.
I shall be swaddling the whole pack with self amalgamating (radio antenna type) tape to act as a proper insulator over the bare wires and hold everything together firmly.
The bleeders are a pair of 180 ohm 5Watt ceramic resistors in parallel. They got mildly warm when I switched off after the capacitor power up.



A couple of heat sinks, one of which to be used with the bridge rectifier.


The black one (from a scrap circuit board) will need to be be cut in two - where the square hole is.
I don't know enough about heat sinks - apart from using heat sink paste and not letting connectors/wires touch the metal surfaces.

Can any kind soul advise which one would be best for keeping cool, to use with the bridge rectifier? The big black heavyweight or the more delicate multi finned one?

I have gone for the e-bay full bridge rectifier, single phase one after all, which is without a heat-sink, but with a steel plate at the bottom for mounting on (with paste) - rated at1600V, 200Amp (so it should not overheat and self destruct). I intend mounting the rectifier on one of the two heat sinks, with the fins out-board of the side casing of the welder and the rectifier sitting on the casework, with wiring through the sheet steel (big holes and grommets etc. for safety). I shall also mount my spare muffin fan next to it, on stand-offs so as to pull hot air out of the enclosure through the casework slots and maybe help with overall cooling to get the duty cycle up a bit?

The next job then is to sort out the relays to control the hot-tip and primary side of the mains input and the separate feed-motor system.
I appreciate that the pwm motor controller should be left "on" (it will not like being triggered on and off during welding), so its output to the motor must be switched via a set of relay contacts- yes?

Rig Pig - thanks for the suggestions - I should start to cultivate my local garage a bit more so I can see what's in their scrap pile- what you say makes a load of sense.
I've got a set of iron weights for an old fashioned balance type weighing machine - but they are all rather flat and smallish in diameter.

I shall start hacking away at the side casing tomorrow I think.

Thanks again to you kind people.

Peter

 

[eddie49]

After typing "cast iron" into eBay I found that sash window weights may be an ideal core for your inductor. There are a fair few on sale, at low starting prices, and perhaps there are some near enough to you for local pick-up ( which most of the listings require ).

 

[Peter Millerchip]

Thanks Eddie - I always thought they were made of lead!! What a good idea.
I'll take a look late

 

[Peter Millerchip]

Whilst rummaging in the darkest depths of my scrap box, I found this :



I think its a weight from inside the plastic casing of the base of an angle-poise lamp?
Anyway - it looks to be cast iron, toroidal in shape, about 3" external dia. 3/4" thick internal dia. 2".

I have a goodly supply of 6mm stranded copper wire (I acquired a reel of this - earthing wire from a friendly electrician) and so will see how many turns I can get around it.
Then add it to the pos. (clamp) lead if I can find space in the welder case.
If it doesn't add any benefit to the welding result, then it doesn't owe me but I may as well give it a go as I have these bits to hand.

I'm re-positioning the welder transformer further to the back again, by moving the muff fan out the rear and adding a filter/guard.

Available space is going to be tight it seems, so I've had to re-think the layout internally. I've stopped wiring stuff in, until the space is sorted.

 

[KemppiFrog]

Welcome Peter
Really enjoying this thread.
While I might wonder about taking a (sub)basement price MIG and bringing it up to usable standard, rather than a 'pre owned' better model. Kudos for effort. The wire feed motors are a weak point, usually because of plastic gears....

We are probably of similar vintage on the cars. Our airfield manager had a Corsair and decided to spray the roof to give it the 'Executive' look. Unfortunately, he used some matt cellulose paint that had a shrinking effect, so we all hid our grins when it contracted and looked like crazy paving, with the cracks exposing the white underneath.

As for towing.. I bust the crank of my very modded Mini, so a friend towed me from Herts to Norfolk with another Mini Cooper that I had built from a shell. 8ft of washing line and he was quite keen, hitting 80 mph at intervals. My nerves were in better shape back then... The sofa might have given me a bit more security, or obscured the view.
Following another friend, whos financial state dictated a very old Rover, I saw a tennis racket being put out of the window and paddling to to help it up a hill.

Good luck with the project
KF

 

[Peter Millerchip]

Thank you KF!
I really owe a lot to Mike - I've learned quite a bit from his and others' advices.
I did consider a" previously enjoyed" rig, but I could not be sure it would not be a dud, and my current disabilities mean I cannot really consider driving - so buying new/posting was the only viable way to go.
Anyway - I'm having fun!!
Towing at 80m.p.h. must concentrate the mind somewhat!

 

[Peter Millerchip]

Yaaaay - It works!!

Well, anyway, the DC power side works in a power up non-welding test, but nothing blew up, or seemed to overheat (apart from the bleeders - more of that later).

The output voltage measured between the tip and the clamp :-

Power Switch on "Minimum", rocker switch 1. - 38.5V; switch 2. - 42.5V
Power Switch on "Maximum", rocker switch 1. - 47.5 v; switch 2. - 52.9 v.

(I'm glad I took the advice given earlier re. the 50v working capacitors!!)


I finally finished wiring in the larger components - making the connections using thick cable took some time, and I had to "adapt" what I had in the way of spade and ring connectors to make it all fit.

A Dremel with small grinding wheel is really useful to clean up the sheet metal after drilling holes, and a bunch of slitting discs becomes almost essential when cutting the casing for the rectifier.



Here I started to wire up the bridge rectifier, having cut out suitable space for it to fit in the casing. I am using 7 strand, 6mm earthing wire (I got a job lot reel from our local hardware shop at a real bargain price years ago). The rectifier is sitting on a heavily finned heat sink, with sticky white compound.
(Have you noticed how, when employing heat sink compound, one little blob can spread its presence over everything in the room?)

The thickness of the transformer and connection wires and its stiffness made for a few interesting problems. I ended up using bits of copper pipe, bashed flat and drilled out as connectors. For safety and to avoid confusion, I marked the casing with coloured Sharpies re. the polarity of the terminals.



Here is the (final version) of the capacitor pack, with the cable from the welder gun to its right hand side (having severed its crimp connector to the transformer secondary). As someone said on a separate thread, the Chinese made transformers are all Aluminium, with 6mm thick Aluminium epoxy coated cable/wiring. This is really inflexible, and I did not even attempt to solder the ends of the secondary winding to the bridge rectifier. As you can see, I used a simple pair of screw connectors.
I do not like crimped power connections which are not soldered, but as the welder will not be moved about and probably just sit in my workshop, jolting/vibration should not be a problem, so I'll go with the two screwed connectors for now.
All of the other connectors have been soldered and wrapped with insulating tape.

This is the right side of the welder (secondary windings).



The left hand side (transformer primary) with switched "power level" tappings and thermal cut out.



These are the bits and bobs yet to be fitted in the upper floor.
The pwm motor controller board, the voltage step - down module, and relays. I have two automotive relays with 5 terminals - 12 volt and 24 volt coils. I think the 12 volt coil one could be powered by my separate wall wart power supply for the wire feed motor.
There is also a 240Volt coil relay with 4 sets of contacts.

I am still trying to get my head around how to sort out the relay(s) wiring. Squeezing the trigger should power up the mains primary of the transformer (its a "hot tip" welder at present - which is not really desirable as the Mod said earlier), and run the power output from the pwm controller. This module should switch on at the power up, and stay on - its output to the motor being triggered by the hand piece. Can anybody offer a simple circuit diagram?

Should I also think about some sort of diode and capacitor protection across the terminals the wire feed motor - or would this interfere with the pwm module?

At present, the trigger switch is connected to a pair of wires running within the sheathing to the welder, but not connected to anything.
If necessary, I can substitute the single pole micro switch for a double pole one and add a second pair of wires.

Then, I might have a go at winding the cast iron ring as a toroid, using my reel of green and yellow 7 strand heavyweight "earthing" cable - I have got plenty left.

The bleed resistors (at present, a pair of 5 watt 180 ohm cement resistors in parallel) did get very hot during the earlier testing, so I shall be changing these for a 25 watt wire wound/finned resistor of similar value.

All in all, this has made me very happy - job is half done now.
I'll have a look at relays tomorrow.

And again, thanks to all for the help and advice.

 

[eddie49]

Some suggestions for your new control circuit diagram:

To get a non-live torch, use the 12v "auxiliary" power ( from the wall-mount PSU ) through one pair of contacts on the new double-pole microswitch in the torch handle, to your relay with the 12v coil. The relay contacts then feed mains to the primary of the welding transformer.

For the new wire feed setup, it depends on how the new motor controller works. Did it come with any documentation? Is it capable of reverse? It is perhaps a PWM driver feeding the gates of a MOSFET H-bridge. I would agree, as you said, the board should be supplied with continuous 12v power. It does not need any diode protection across the motor. For on/off control, rather than soldering a link across what were the switch contacts on the pot, test using the second pair of torch microswitch contacts to do that. Maybe the motor will then start running, at the speed dialled-in on the 100K pot.

 

[Peter Millerchip]

Thank you Eddie for your kind advice.
I guess I was over thinking the way to go forward with the relays' control, and getting a bit mixed up over it.
I had a sit down with a Marmite sandwich, thought it through logically, and came to the same plan as you have suggested re. the "hot-tip fix".

First job was to make sure everything would fit inside the original hand-piece. I had to do quite a bit of careful paring away of plastic moulding with the Dremel and a burr, to get the double pole micro switch to fit. (Its much fatter). It has two NO and two NC sets of contacts. I cut away the two NC contacts to save a bit of space for the wiring, which was going to be tight!



The area pared away is lighter grey in colour.
The original trigger (shown above - red thingy with tiny spring!) became impossible to fit properly, but the micro-switch button is pretty big, and functions as well as a trigger.
I'll have a look at making a better (proper) trigger later, but for now, the micro-switch is fine and functions just as well as a separate trigger. It's firmly buttoned up inside the hand piece.

The wiring/soldering to the micro switch of 4 wires was o.k., but the real problem was trying to fit a pair of wires down the outer rubbery plastic sheath to the electrode cable. It took me nearly two fruitless hours of messing about (I even tried using washing up liquid as a lubricant) before I hit on a way of doing it fairly easily - by cutting around the circumference of the sheath every 9" or so, and using a length of thin brass tubing, pushed up each "segment" in turn, then pushing the new wire through the tube, a section at a time and removing the brass tube afterwards. The job then took only a few minutes to do!!

I then tested it all thoroughly with a meter - all seemed fine, the micro-switch/trigger working easily.



I then turned to the upstairs area and mounted the pwm wire feed motor control module.
I had earlier re- located a better pot to the front of the welder and bridged the on/off contacts of the original switched pot.
Just in front of the module is a 12v automotive relay mounted on the front wall. of the enclosure.
I wired a diode across the relay coil contacts, and then pretty much followed what you said Eddie. I switched the neutral feed from the main on/off switch, via the relay and 15V psu.

It worked fine. No more hot tip!



I tidied up the wiring a bit with the usual cable ties!
The new 25watt finned power resistor only got mildly warm to the touch.

Tomorrow, I'll fit the second automotive relay, and wire it for the output from motor control module to the motor itself and see how the motor speed it behaves with the original value pot.

Finally I've to fit the MOV, and perhaps then have a go at making an inductor to go in line before the clamp (positive).

Do I need to fit any sort of small value capacitor or resistor across the motor contacts?
(I seem to remember seeing this on some older threads which I cannot find).

Eddie - there was no real documentation with it. There is no reverse control as such. There are 6 Mosfets in ?H? configuration to drive the motor. It can handle from 12Volt in to 50 volt input, at up to 40Amps!
Here's the link to the flea bay listing :- https://www.ebay.co.uk/itm/1pc-12V-24V-48V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-2000W-MAX-9-50V/263117804952?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
There is quite a number of cheap controllers available now (from China!).

 

[mike 109444]

Good practice to protect the circuitry feeding the motor with a reverse wired diode.See pic below, The diode will not conduct when the red line is "+" and the green is "-" But when the motor feed is stopped (trigger released) there will be a back emf that may get feed back to the motor driving circuitry and blow it! The diagram shows the feed motor relay (RL2) in the "NOT feed" position and you may notice it is shorting the motor "+" feed and the "-" connection is disconnected so NO feed. When RL2 is operated (yellow line taken out of circuit) the feed goes through the motor, through RL2 contacts and via TR1 & TR2 (speed control) to zero volt rail thus completing the circuit. Note by shorting across the motor when RY2 is de-energized it acts as a brake to stop the motor from running on which would cause the weld wire to stick to the cooling molten weld pool. I hope that all makes sense.
ps you may need to fit a sheet of plastic over the mot speed control pcb as a lot of metallic dust gets generated near a welder (grinding, welding sparks)

 

[mike 109444]

I know this machine is gas-less only but if you were to up grade it to a gas mig (would need gas pipe through torch cable, that will be tight!) then you may also need a diode across the gas valve IF it was a DC solenoid, again to snubb back emf.

 

[Peter Millerchip]

Thanks again, Mike for your kind help and good advice and the circuit diagram which I understand insofar as the relay coil protection is concerned.

I had not considered any "dust" protection for the vulnerable electrics - good point, I shall make it so!

I had already come across several different posts about motor run-on, and connecting the NC contacts of a relay as a "short" across the motor to prevent this. I was all set to do this with the spare NC connectors on the motor control relay I am about to install.
However, from testing the pwm motor controller, on releasing the hand-piece trigger, the motor stops dead, immediately. So maybe I do not have to do the NC contact wiring from the relay - I'll keep that in mind though, just in case.

As a sort of "vanity project", I am fitting a double-pole, double throw change-over switch to the front of the casing, as a motor direction change-over switch. Eddie49 mentioned reversing earlier, which set my mind thinking - not a bad thing to have if it is easy to add.

So I tested reversing the pwm module output polarity to the motor by just reversing connections to the two output leads and the motor changes direction with no apparent ill effects or change in speed.

I have a choice of switches from my toy box. A small panel mount one with centre off position, but the contacts are so close together, and so its wiring will be a work of art.
I also have a heavy duty latching push switch (I used it as a "stomp switch" when making a guitar phaser for my son), which is physically bigger and much more robust with contacts much easier to get at. I think I will go for this one. It will certainly be easier to use, when wearing welders' mittens, than trying to flip a tiny panel switch!

Just to add to the classiness of the front of the welder, I'm also fitting a green and a blue led, wired up to show "direction of travel" of the motor. (Green = wire out feed, blue = wire back). LED's and switches always make something look more expensive than what it is, so, as well as being a useful visual control, this will also tart up the Swizz frontage!

Back in posts 23, and 24, MOV's were mentioned, and the fateful words I used ;- "suck it and see". Maybe those words are on someone's headstone.
I wired in the MOV, across the rectifier bridge output (pos. and neg. connections) and tested the welder, on its lowest power setting (38Volts). All ok it seemed.
However, when I switched to Max. power and rocker switch position 2 (52 volts), the MOV immolated itself. Lots of orange/yellow sparks around its edge, and a blue/white flaming core, like a Roman candle!! I guess its power rating was too low, or I wired it in wrongly.
I killed the power pronto, and fortunately, there doesn't appear to be any co-lateral damage. Everything works fine.
So for now, I do not have the benefit of an MOV.

More later, with a pick of the tarted up front panel!

 

[mike 109444]

Yep recon you exceeded the max for that device and it MOVed out
One thing I added to the welder I reworked was a led voltage meter on the voltage supply to the feed motor. As the machine has a always on supply for the motor with relay to activate. I was able to display the voltage that would be going to the motor. This allows me to set and or adjust the motor very finely and it's surprising how small a range of voltage it works best at (on most welders it would be with in 2 or 3 of the "lines" that are on most welders. This is why I think some people have difficulty "dialing in" there welder as they for example try the welder with dial set to say line (position) 3 and it may weld poorly so they knock it up a notch to say 4 but that may be TO much and they should have tried between the notches. There is probable some backlash in most wire feed pots as well which won't help...
Take care when and if using the reverse motor function as when you stop welding (using gas wire, not sure if same for gasless) there tends to be a blob on the end of the wire which will be bigger that the welding tip hole so it will jam in tip if reversed. Snip wire end at an angle before reversing. Reason for angle is that most side cutters squash the wire a bit before cutting making the end bigger! It is sometimes necessary with gas mig wire to change the tip and if the end is not cut cleanly the tip jams when unscrewing.

 

[Peter Millerchip]

Here's the finished effort with the wiring tidied up a bit.



And the front. The led's in "chrome" bezels are in the "t" and "e" of "Switzer". The stomp switch is in the "w"!
At the very top are two black cap screws holding the relays.
The bridge rectifier sticks out under the big black heatsink on the left.

Mike, good idea re. a volt meter across the wire feed motor. I didn't realise they were now so cheap for a simple rectangular panel meter - of many colours! I've got one on order.

I actually carried out my first ever wire welding efforts. Just a simple right angle joint between two bits of 2mm plate. A really simple beginners' project I found on the net (making a weld-gun stand).

I never used this Swizzle in anger as originally bought, so I cannot comment as to how it now performs as a DC machine compared to the original AC configuration.
I did made a bit of a bollix of it at first and the result needed a bit of fettling with an angle grinder/flap wheel to remove the unwanted blobby bits. Eventually I seemed to get it right with just a few splatters, and the bits of steel close to a right angle!

I discovered during my welding efforts that the "sweet spot" for the wire feed is about number 4 on the front dial which corresponds to about 4.25Volts across the motor, and a resistance off the pot (which is nominally 100K log) 0f 74.9 Kohms. Just a tiny movement around the number 4 made quite a profound effect on the weld result/wire feed. Just as you said Mike!

Following on from the point regarding a voltmeter, it occurred to me that maybe I could re-do the pot. to give a bit more fine-tuning around the 75Kohm mark. Sort of "stretch things out a bit".
I have three wire wound multi turn pots left from various projects of long ago. 2K, 10K, and a double ganged 50K. Also I have a spindle mounted multi turn counter kit to go with them.
It would make sense to use one of these in place of the 100k pot?

So a question - can I remove the 100k pot, and use one gang of the 50K twin gang pot, plus another resistor (either fixed or a multi turn trimmer) of say 50K - so as to give me a better/finer control over the voltage from the pwm board?
I think it is not possible to use the twin gang pot by wiring the gangs in series to give 100Kohm, as the wiper(s) will still only be controlling up to 50K0hm at each end - unless some clever sparky knows how to do this?

Hopefully I can now have a go at making a simple dragonfly for my wife's garden!