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

[Peter Millerchip]

(My first post here and so apologies if this is the wrong section to post in. Perhaps the Mods could move it if its in the wrong place?)

This may take a bit to explain, but here goes :-

Background:-
Following some serious heart problems and several surgeries and having to sit on my bum for nearly two years recovering, I decided a new"challenge" might get me up and running again.
As a makee learnee model engineer, I have always thought it would be nice to be able to stick and wire weld, so as to be able to attempt better projects, plus crerate a bit of "sculpture" for my wife's garden.

I have just invested in a really cheapo Chinese gasless wire welder. Budget concerns meant finding the cheapest wire welder I could, and after a lot of trawling the net and reading many many posts, youtubes etc., came across this "Switzer" welder on E-bay (no connection/affiliation) as just about the cheapest at under £70.



General view

It was marketed on E-Bay as an "inverter mig welder", which it clearly is not. However, the price was right.

(Just as an aside, I had words with the agents selling this on ebay, who had no idea what an "Inverter" was. Evidently they had relied on their suppliers' description (?from China?) who had possibly stretched the truth of the matter. Anyway, the sellers said they would immediately change their advert. description after we touched on "Trades Description Act" and so on. They were honestly unaware of what they were selling and of course offered to collect it and refund me.)

However, the price was right, so I kept it with a view to doing some mods to bring it up to a respectable DCEN machine.
Prior to my purchase, I had spent much time reading "stuff" on the Net about wire welding, and I must say that this site is by far the most useful, friendly and helpful I have found. Respectful chat is nice to find these days!

This welder - named a SwitZer SZ-MIG130 - manufactured in China by Zheijiang Juba Welding Equipments Manufacturing Cop. Ltd.
I suspect that the manufacturers make thousands of these in various forms and coloured boxes?

Anyway, a quick inspection of the (thin) "manual" reveals its a 240Volt input, 50-120Amp output at 37Volt max. Duty cycle is pathetic :- 105 @15%!!!
Flux cored wire dia :- 0.6 - 0.9mm.
Unfortunately, there is no circuit diagram or schematic.

Controls are two rocker switches which change taps on the primary side of the main transformer to give 4 "power settings" - between 30 and 37 Volt AC output as far as I can measure.
There is a wire feed motor speed controller knob - a 1 megohm log pot.
An overheat warning light and that's about it.

Internally there is a very good looking boat anchor of a mains transformer (the components and standard of assembly looks quite well done), a very small pcb which appears to be the wire motor controller, a thermal cut-out, and a very nice hefty muff fan at the back.
The wire feed motor is stamped 12V, 1A and under no load I measured 11v dc on its terminals.
There is also a label on the motor giving ?wire speeds? "2-11 /in" whatever that means?

The upper deck contains a standard (flat mounted) wire feed mechanism and wire spool axle.

The nozzle/trigger appears pretty heafty.
The clamp is somewhat flimsy!!



Note the transformer and very little else!



Circuit board - contains a tiny bridge rectifier, a couple of small electrolytics, a BT151 scr, a small switching transistor, a few resistors, signal diodes and small power diodes, etc. a fuse, and connectors to the pot (at the bottom) and the 4 way one (on the side) - two wires to the motor and a pair to the earth clamp and the trigger switch (the trigger is spring connected direct to the electrode tip thus providing 30-37volts AC).
I tried drawing a circuit diagram from the pcb layout but got horribly confused! I think this is some kind of pwm controller?



The muff fan - rated at 240V ac - runs off the mains switch.

That's the background explained.

The Project :- 1.simple mechanical stuff; 2. AC to DC conversion; 3. wire feed motor controller sort-out.

1. The first jobs done were to change the clamp for a decent Parweld heavy duty jobby.

Next, I removed the (chocolate) sheet metal screws which hold the transformer to a sub-frame and casing.
I re-drilled for M6 holes having shoved the tranny further back to get more space at the front, and used cap head bolts and nuts to secure. The fan still works fine.

2. Next I intend to do the AC to DC conversion. At this stage I do not anticipate fitting a choke to the output line to the electrode.
On order is a three phase 1000 - 1600 Volt, 150 amp bridge rectifier (on a finned heat sink).
I have made up a reservoir "capacitor pack" viz:-



This is 4 X 15000uf 50V caps soldered to copper rods. This should fit in the base of the enclosure in front of the main Tranny.

Noted :- these caps do look rather small for their rated values?
I have a pair of 30,000uf big blue fat bellied screw terminal ones, but only rated at 40Volts which may be a bit close to the edge? They also take up a LOT of space.

I have yet to fit 10W power (bleed) resistors across them.

I do not foresee any problems putting this together, but my questions relate to the wire feed motor sort-out part of the project. (3)

Now here I am not sure how to proceed.
Once the DC conversion is done, I presume the voltage at the tip of the electrode (currently max. 37Volt AC) will be increased by ?up to 50%? because the AC out is being rectified and smoothed by the reservoir caps. So will I be looking at over 50Volts on the electrode?
Whatever this voltage is, it becomes the switched signal in the trigger wire.

I have the idea of removing the little motor control pcb completely.
To provide power for the basic wire feed motor, rather than fitting another tranny/rectifier etc., I could use a stabilised "wall wart" power supply? I have a 12Volt 1Amp one in mind.
It would mean simply drilling the front [panel for a mini power socket, and having to us a second mains socket for the wall wart itself.
I will use this power source to power a separate pwm motor controller (sourced via ebay, costs less than a tenner! - 12-48Volt, 40Amp motor controller module - in a nice case with control pot too!!) via the relay for the wire feed motor.
Relays seem to be a problem - they are either 24Volt, 12 volt (automotive) or 110/240Volt mains rated.
Because my trigger switch may be providing between 37 and (say) 50Volts, I need to step the output from the trigger switch down to 24Volts.
Again, on e-bay I have sourced a "Dc-DC Buck step-down 12-60Volt down to 3/6/9/12/24 volt out at 10Amps! (Just over a fiver).
So if I use this to attenuate the voltage signal on the trigger wire, I can then use it on a 24Volt relay?
Then, wire the relay contacts to power the motor and act as a motor brake to stop run-on.

Have I missed anything or made a total **** of it?

I would appreciate some help please.

Peter

 

[Morrisman]

Welcome to the group, but you lost me with the ac to dc conversion bit. Not sure what that is for, but it may be a good thing.

 

[rtbcomp]

Does it have permanently live torch? The PCB will control the motor speed but it might or might not also switch the transformer on and off when you pull the trigger. If it is a live torch it will be a good idea to modify that to a switched one at the same time.

I'd be inclined to install a 13A socket inside the machine to plug the wall-wart into, it would take its mains after the mains switch.

 

[MoreWellie]

Hello and welcome Peter

Hopefully you are doing this work as part of the "challenge" as otherwise I think you might unfortunately be making

a total **** of it

This is only an opinion and with everything you are working through health wise if you "are" looking upon this a bit of education and entertainment then fine

In my opinion you would have been better served by just using it as it was or by putting more money into the initial purchase rather than spending all the time and money trying to make it something more than it was designed to be

You really wanted a bridge rectifier rather than a three phase one but you should be able to wire it satisfactorily albeit just ignoring 2 of the diodes

Your 50v rating is slightly under what is required for the capacitors as the ac voltage increases by a multiplier of approx. 1.41 when put through a bridge rectifier, in this case to approx 52v dc. You also need them to be capable of high current flow in this particular application so I feel these particular capacitors may be prone to failure

As you have a 12v motor the 12 to 48v controller won't do much for you as it can only be set to minimum and let the motor run at full speed as anything higher will risk burning out the motor

The poor duty cycle isn't going to be improved by anything you are adding to the machine as this will mostly be limited by the (aluminium wound?) transformer

hope this helps your understanding of things without hurting too much

 

[Peter Millerchip]

Thank you all for the kindly replies.

Morrisman - thanks for the kind welcome - appreciated. I read a number of posts both here on this forum and a lot elsewhere (many American ones) on the advantages of turning a basic AC wire welder into a DC output one. That set me thinking it would be a good project to try - given that I wanted to wire weld a simple metal dragonfly sculpture for my dear wife's garden and have never wire welded before!

rtbcomp - yes the torch is permanently live! Its fed directly off the secondary of the big tranny.
I had not considered switching this - just re-wiring a new rectifier/capacitor network and making the outputs Clamp = pos. Electrode = negative.
So a meaty (amps wise) relay contact, switched by the trigger might be a good idea to power up the tip from the reservoir capacitor bank? Makes a lot of sense - thank you.
Thanks to you also - a better idea for wiring in the wall wart. I think there is enough space inside, but if not it means cutting the casing for the mains socket access and the wart looking like a wart on the outside. (I rather liked the clean grey and blue paint job of the Swizz!)

MoreWellie - Yes - the work gives me something to have a go at, sensibly and hopefully without harm to me, my dog or anyone else. Mentally I've been a bit adrift for a while and I've let my man-cave lie idle for too long (I cannot remember where much of my stuff is!).

My rationale is :-If I had spent more money (which I did not want to do) on a "slightly" better wire welder (there are so many to chose from, all about £25+ more but seemingly of uncertain quality) , judging by the posts on here I would pretty much be in the same boat, still having to modify the wire feed motor side and possibly making it a better full wave rectified machine. If my project results in a machine giving as good a weld as a more expensive one costing a lot more, then hooray! Much satisfaction, and maybe to encourage others - as I was encouraged by reading a number of "project threads".

The three phase rectifier IS a bridge rectifier is it not - that has been referred to in many previous posts in the forum (its cheaper to buy this three phaser than a single phase bridge rectifier of the same power ratings) - as you say, wire it up as a straight bridge rectifier. ignoring one of the diode inputs. (use 2 of the three input pins).
Incidentally, although it comes on a heatsink, I've another bigger heatsink to add to it and mount the lot on the outside of the enclosure. I understand heat kills diodes!

Yes, thanks for the heads up about the capacitor voltage ratings, I think The ones I have pictured may be too short on voltage elbow room. Could be dangerous if "surged", so back to the toybox for these.
Without spending more, I do have a screw terminal can capacitor, rated at 60Volts, but only 10,000 uf - is that enough capacitance or do I need to be looking at 50,000uf plus?

I should have said the input of the pwm controller can accept voltage inputs from 12 to 48 volts. At 12v its rated at 40W which is somewhat higher than necessary?
If this doesn't work out I do have a torroidal 100VA mains transformer, with two secondary windings of 25 volts each, and a 5W bridge rectifier and reservoir caps. in my toy box. I've also got a couple of home brewed (from decades old published circuits) perfectly working pwm motor controllers I built on vero board for mini drills, and the like. So I could knock up a separate psu for the wire feed motor, but for reasons of space inside the welder enclosure and neatness and (dare I say it) "seeing if it would work", the wall wart and ready made motor controller looked favourite. I can mount the motor controller and voltage step down board "upstairs where there is space beside the wire feed roller thingy.
The duty cycle is poor, but doesn't really worry me at this stage. I do have another good quality 25V muff fan I could install to add extra cool breezes from the side if that would help!
I have never tried wire welding before, and am still getting to grips with stick welding, so I have a long long way to go.

 

[rtbcomp]

You switch the primary with the contactor/relay, not the secondary much less current!

 

[Peter Millerchip]

Thanks rtbcomp. I agree, it would be better to to use a relay to switch on the primary side of the main tranny. BUT I am sorry, I don't see how to do it!
I only have one switched output from the electrode trigger (at 50V DC or so) on the secondary side of the main power transformer, and that only appears once the main transformer is fed 240V ac. (The 50V signal to be dropped to 24 Volts via a module). How can I switch the mains transformer on via a relay contact fed from from the trigger when the trigger is dead?- is it not "chicken and egg". Until the transformer is powered up, I have no trigger signal? Am I making sense or am I confusing myself.
If I disconnect one of the main output 240V wires from the illuminated mains on/off rocker switch to the various primary tappings of the power transformer and wire this into a relay contact- I then have nothing from the trigger switch to use at the other end. Everything will be dead, apart from the fan.
Sorry - am I making sense?

Peter

 

[MoreWellie]

You switch the primary with the contactor/relay

This is especially relevant as you are going to be adding a second supply for the motor you can use that to power the relay through the trigger switch and the motor circuitry

I do have another good quality 25V muff fan

all cooling helps but I suspect it wouldn't significantly increase the duty cycle and would leave any existing thermal protection in place

 

[rtbcomp]

Thanks rtbcomp. I agree, it would be better to to use a relay to switch on the primary side of the main tranny. BUT I am sorry, I don't see how to do it!
I only have one switched output from the electrode trigger (at 50V DC or so) on the secondary side of the main power transformer, and that only appears once the main transformer is fed 240V ac. (The 50V signal to be dropped to 24 Volts via a module). How can I switch the mains transformer on via a relay contact fed from from the trigger when the trigger is dead?- is it not "chicken and egg". Until the transformer is powered up, I have no trigger signal? Am I making sense or am I confusing myself.
If I disconnect one of the main output 240V wires from the illuminated mains on/off rocker switch to the various primary tappings of the power transformer and wire this into a relay contact- I then have nothing from the trigger switch to use at the other end. Everything will be dead, apart from the fan.
Sorry - am I making sense?

Peter

You use the wall-wart, which will be on all the time, (eg connected to the same place as the fan), and switch the power from that with the trigger to call the contactor, start the motor and open the gas solenoid.

I hate to suggest spending more money, but a Euro torch has both trigger wires floating so you can use them as you like. You may be able to disconnect the wire on the trigger that connects to the welding voltage and run a separate wire into the welder.

It's beginning to look like it would be easier to dismantle the welder completely and rebuild from scratch.

 

[mike 109444]

Pete if you look at the pics below you will see that the smaller Clarke welders (110's, 90's) are much like what you have (once you have added the rectifier!)
As you can see even in the Clarke range there are differences between similar models (110's). You should also find that the smaller SIP's (130's and below) and many other sub 150 machines are basically wired the same. The smaller machines generally have a small (usually undersized ) transformer mounted on the pcb for the supply needed before/connected to the primary side
There should be lots of links to manuals (esp Clarke machines) from which you can see how they generally wire up machines. Generally they don't give pcb diagrams though .

 

[mike 109444]

And some SIP stuff

 

[mike 109444]

Cebora

 

[mike 109444]

And welcome BTW

 

[Peter Millerchip]

MoreWellie - you = brilliant, me = stupid. What a neat idea re. the second supply. Got to think about this.
The torch handle contains a single pole micro switch, connecting the wire running down the side of the main welder cable, to the tip (35V+). To be fair, the torch handle is of very good quality and well made. The wiring, grommets and seals are excellent.
Not much space inside the torch handle for any more, but I'm looking at an idea.

rbcomp (do I really call you that?), thanks for the thoughts. There is so little to this rig, component wise, apart from the mini pcb, its virtually disassembled anyway. However your wall wart suggestion has given me an idea that maybe can be done - will get back to you later. It is a gasless welder by the way.

Mike - Bless you sir for all your kind help and work in posting all these schematics. Its given me a lot to think about. I owe you a packet of wine gums.
Either way, I'm spurred on to get this thing going - still waiting on delivery of electronics from China dammit.

Can anybody advise whether 10,000uf is enough for the reservoir capacitor? I need to know how much space inside the enclosure to reserve for the caps if I have to get more.

Peter

 

[mike 109444]

You might want to think about adding an inductor see this post https://www.mig-welding.co.uk/forum/threads/earth-lead-connections.44713/#post-494919
Shenion has explained in another post how to make up an inductor using some iron pipe (old cast iron gutter down pipe ?) and wrap the ground lead around it (more turns = more inductance, thus an adjustable inductor !!
Ref the cap value. I remove the cap for my (very) old Clarke 120 as I was getting intermittent poor penetration and after lots of checking found that the riveted spade connectors on to the cap had become loose and a poor connection = lack of penetration! So got a new one of 47000 uF (ori was 33000) welds were better BUT I believe that was just down to having a good connection to cap rather than the increase of capacitance. So took a good look at orignal cap and managed to retighten the rivets on the spade connections (I'm a tight wad ) Got it working and tried some test welds with new 47 ori 33 and the two combined. Note this was using CO2 gas
Welds were on aprox 2.5 mm. Machine has 6 power settings.
Also the copper coil device is the inductor in that machine and is aprox 8" tall and 2" diameter
The pic of caps are the ori (blue one) and new (black one) They are aprox size of a small tin of peas.
Remember a mig is just a high amp DC power supply, capable of being shorted out.

 

[mike 109444]

Another inductor as in a Clarke 90 (I think that is the machine) The inductor is bottom left and looks like a transformer BUT only has one lead in and one out. You can see it is attached to the work ground lead post on it's out put and the Neg side of diode pack out put (the two white circles) Note this is a Gas machine not a NoGas like yours. Note also it does NOT have a cap which is typical in most of the Clarke 160's and below. SIP's below 130's much the same.

 

[Peter Millerchip]

Mike - thank you for the info and great pics. It explains a bit more.

I am awaiting delivery from RS Components, a double pole micro switch which should nicely fit/replace the single pole one in the torch handle. Then I run in another wire down the cabl and connect up to the second switched contacts and I have a neutral, trigger switched facility. The other contacts still carrying the signal from the tip of the electrode as before. I should then be able to use this new switched facility on the separate psu to power the relay to switch the primary of the main board if you see what I mean.

I had read various posts on here containing some references about inductors, and what they do to Amps but I still do not really understand them It's a bit of a black art to me - inductering. I know caps. block DC and chokes (inductors) block AC - yes?

However, amongst my ill gotten gains, I had been given a couple of large scrappo circuit boards (inverter power boards from Axminster/Seig lathes that had lost their mojo). They each contain a toroidal (dust iron I think) inductor 1" diameter, 1/2" thick, and 1/2" hole in the middle, wound with 5 or 6 gauge enamelled copper wire. Two sets of coils on each toroid (4 legs). Thinking that they might be of use, I re-wound one of them, joining the copper wire together of the two windings, so as to make a single coil winding around the toroid (2 legs).

(Now, to show my age, back in the good old days of "hobby electronics" in the '70's and 80's, Practical Electronics was the comic of choice for me. Amongst its many and varied projects/kits, I built a "digital" (wow - in those days) capacitance and inductance meter!!! It still works fine today.)

For what its worth, I measured the inductance of my re-wound toroid - 342 NanoHenys! I have no idea if this is good, bad, indifferent or rubbish. But its useable, and I could make another from the other junko circuit board toroid.
Can this be employed usefully in my (hopeless to some) sinking ship of a project? If so, where should it go in the circuit?

As to capacitance, I have found a bunch of used electrolytics :- 250V, 1000uf, also from the junked circuit power boards. 12 of them in all. They are quite small (50mm tall, 25mm dia. - plug-in type contacts). I could make these up into a pack and add the 10,000uf can type one to give overall 22,000uf. (With the assumption that they all work and have not been harmed in the dis-assembly/assembly processes. Overall the pack would still be quite modest in size and easily accommodated inside the enclosure. Your pics. of the mega - cans are frighteningly big and something like that, although very tasty might be problemnatic to fit!
If I can achieve welds as good as yours at 33,000uf, I should be quite satisfied. To my inexpert eye, there doesn't seem to be much difference between your three groups of test werlds / or am I missing something - I do not wish to offend sir.

Despite, probably tilting at windmills, I am enjoying this project and trying to overcome the bumps in the road. Ultimately, I can still put Swizzo back the way it was if all else fails, but I'm having fun!

If its not rude to ask - Is your avatar a 1960's ish Ford Capri (came out as a fastback version of the Ford Classic)?
How cool is that - respect to you sir - big time. I have not seen one for years and years - as rare as a juke-box Vauxhall Cresta - or rarer?

 

[mike 109444]

Inductors act as a resistance to AC BUT at a certain frequency. So an inductor may have no influence on an AC signal if the inductor is not "tuned" to the frequency which may or may not be the property the inductor has been wound for (tuned circuits/filter ) BUT as the output of the diode pack should be DC then the inductor will be there to affect the rise and fall of the DC output this affects the final arc at the wire.
A capacitor in a welder acts as a store of charge such that as the arc is struck by the wire hitting the work the voltage available does not dip to much and helps to smooth the arc. The above is the simplest way I can think to explain there use in a welder. There is a proper description of the interaction of a inductor+capacitor circuit somewhere on the net but for what's needed here I would skip reading that !
The pic below is a SIP and the green added is where a capacitor would be (AND IT IS IMPORTANT TO HAVE THE CAP CONNECTED THE CORRECT WAY ROUND WITH REF TO PLUS AND MINUS) and the "choke" shown is the inductor. They have the inductor in the plus/positive output but that machine can have it's polarity reversed to do gas OR no gas welding and it should not be important as to which lead it's in. The inductors you have made up are not likely to do much, just not big enough. The caps may work but be aware the terminals may get hot.
I did forget to say with the test welds that there was not a lot of difference between the combinations and machine ended up with just the one new one in it and found a home for the old one in another welder.
Keep at it with the welder and I will chip in when I can but work can get in the way at times.
Yes that is a Ford consul capri (the first capri before the later MK1) It's a work in progress.......

 

[Peter Millerchip]

Thank you once again Mike for your kindly assistance.
Now I understand a lot better.
My little inductor is clearly not worth the effort. (I have since found that a "Nano Henry" is one billionth (0.000000001H) of a Henry so this aint going to do very much in a welder.

Following reading your kind post, It spurred me to do a further search and came up with an earlier thread (Mar 15 2008 - by Dandumit :-

https://www.mig-welding.co.uk/forum/threads/help-needed-for-homebuilt-mig.5330/

In it, Shenion gives a lot of help and advice and useful picture of his home made cast iron pipe inductor.

Another site (www.edaboard.com) found where there was a post giving a neat little interactive programme to calculate inductances.

https://www.edaboard.com/showthread...equired-inductance-of-a-welder-rectifier-coil

This may be of use to somebody?

Anyhow, I am making up a new capacitance pack using copper rods again (thanks for the heads up re. "hot" joints) and still waiting on ParcelForce (a mobile black-hole?) for some bits and bobs.

In my little town there is a kindly builder/undertaker/building materials vendor - I shall see if I can blag a bit of cast iron rainwater goods.

I did like the Ford Classic as a lad (cos it looked American with twin headlights) but later was quite taken by the Ford Corsair (cleaner lines) - did they have the same motors?

 

[Peter Millerchip]

The postman arrived finally with a load of bits and pieces I had ordered. I finally have the pwm motor controller, the bridge rectifier, a choice of relays, and the double pole micro switch for the trigger handle. I also have a couple of very hefty finned aluminium heat sinks (from scrapped sources) slightly larger footprint wise, than the bridge rec.

First on my list to try out was the pwm motor controller module, as some doubts had been cast about it working which had worried me.

Its a single pcb with two side mounted heat-sinks enclosed in a plastic case. The pcb/guts can easily be removed and the board mounted bare on stand-offs. There is a 100k switched pot on the front, and a tiny red led.
The power feed in and motor feed out screw connectors are nicely mounted at the rear and readily useable.

I did a quick lash-up to this with croc. clip leads and so on, powering it from my 12v 1A wall wart and connecting to the bare Swizz welder motor (no wire feed). The motor controller module seems to spin the motor very well. At switch on, nothing happens advance the pot a few degrees, the motor crawls (I cannot stop it with fingers on the rollers - quite high torque?). As the pot is wound up, the motor iincreases speed slowly and steadily to a reasonable lick, with no sparking at the brushes or whining sounds. So it Looks like this might work well in a wire feed situation - yet to be attempted.
The "switch" on/off part of the pot is not necessary and the pot itself is very small physically - it slips through the hole in the welder case left from the original pot. So I've removed it, bridged the switch solder connections with a soldered wire jumper, so its permanently on, and fitted a new 100k pot into the hole from the original one, fly leads will be wiring this to the motor controller pcb connectors. I think I will mount the module "upstairs on stand-offs.

At the moment, I have drilled/fitted a mini power socket for the wall wart input. Space does not allow for the mains socket to be put inside. It just means I will have two items to plug into the mains and an extra trailing wire to the welder from the wall wart.

A question - help please - I appreciate there may be the need to add a MOV (metal oxide varistor) to quench any voltage surges, and for safety. Where should it go, and what value should it be?

Things may be looking up?