SIP MIgmate voltage regulator mod

[WindWalker]

Does this look like what you need ?
It's what I put on my welder.
Just mount Q1 on a heatsink.
http://www.mig-welding.co.uk/forum/album.php?albumid=918&pictureid=3062
Robert

Been searching for voltage regulator and this seems ideal. Any chance of more info in layman’s terms? Ie, what do I need and is it straight forward

Looked in again after some time as I decided mine is just too sensitive on the wire speed control. The original voltage stepping for coarse control with wire speed knob for fine control was easier to set up. Having lost that with a 24 volt transformer it would be nice to have a similar option again.

It welds ok and is consistent, just very difficult to set correct wire speed; a touch either way and it changes dramatically in use. The pot is 100 ohm so nothing to be gained there, adjusting voltage seems a like a good option.

Off to put obscure numbers into google

 

[WindWalker]

Right, so obscure numbers not so obscure now

Found all on rs components except 330 ohm ½ watt. I presume it is a standard resistor?

What about the switch? Any pointers on what to use?

do I need any cable or just solder componants to each other?

Many thanks

edit: ERJB2AF331V on rs components shows a 330 watt 1/2 watt resistor but it is different to other resistors. Am I on right path?

edit2: Found 330 0hm .6 watt on rs companents

 

[shenion]

It would only take 3-4 components to make a voltage regulator for the motor circuit.
A TIP transistor a zener or two and a resistor, you could rig it to put out 12,18 or 24v with just a tap or two.
Robert

That's more complicated than using a regulator.




Click on image for PDF version.

2k pot is a trim pot to set the minimum speed. This is for about 2-20V out, Ic an calc values for different ranges.

 

[R Kraft]

Many small welders have OC voltage higher than 35v ,the one using individual components is good to 60v,and only has about 5 parts.
Robert

 

[shenion]

Was assuming using a separate supply. 50V caps would increase input range to 40V.

Adding a pot instead of the 3-position switch would give a better speed range for the zener version. Would add caps also to protect from spikes and increase stability..

 

[R Kraft]

I was just making a general purpose regulator,I figured a max 60volt input rating at 5 amps would allow for a margin of error,spikes, larger motors etc.
The Cemont versions of the welders power the motor from the welder output, and they depend on the output voltage going to zero, so I didn't add capacitors.

It always seemed to me that just putting a zener into the original SIP speed control circuit would give a better result than the odd circuit that they use.
With no real point of reference , it is no wonder that they are so erratic.
Robert

 

[WindWalker]

I think I’ve got my head round this now, got all parts except the zener diodes and when they arrive I will experiment. One thing to check, when it shows the circuit going to earth I presume it means the dc negative as opposed to the ac earth point?

Once I have made the voltage controller I will also make the regulator shenion posted then compare results of each in use. On the regulator, again when it says to earth which earth are we talking about? The dc negative or the ac (yellow/green) earth point?

 

[shenion]

The ground symbol is the DC negative. In schematics, that is just the point voltages are referenced from. There is a different symbol for case/earth grounds.

 

[WindWalker]

The ground symbol is the DC negative. In schematics, that is just the point voltages are referenced from. There is a different symbol for case/earth grounds.

Thanks shenion

 

[WindWalker]

I’ve made the circuit for the voltage regulator but it’s not regulating the voltage on the output. If I check with a meter on the connections on the board at the zener diodes, I have full voltage (21.5), 17 volts and 12 volts on the three different diode positions and then on to the switch. When the tip122 centre leg is connected to the switch it ends up at full voltage on all switch settings.

The switch is a rotational switch with the three voltage feeds on the outside and the centre is connected to the tip122. (Collector) The Base is connected to the input voltage and the Emitter is the power out. Correct?

So as diagram, 30v in is to Base, SW1 is Collector, Out is to Emitter.

I built it on a circuit board and have checked all connections for shorts, all seems fine.

I get the correct voltages until the switch is connected to the tip122, then it all goes to full voltage, no shorts or stray solder bridging anything, what have I missed?



Edit: Think I may have the collector and base reversed? Been looking online and seems the adjusted voltage should go to base, sound right?

Damn this electronic malarky is complicated!

 

[shenion]

You may have the pinout of the TIP122 wrong. Check the datasheet, as it is BCE when facing the front of the transistor.

 

[R Kraft]

Base should be to the regulated zener voltage,Collector should be to positive input,Emitter should be regulated voltage output.
Robert

 

[WindWalker]

Thanks chaps, will swap the base and collector leads over

 

[WindWalker]

One new tip122 later and a quick re-solder and it works

I’ve got three positions now and it definitely makes a difference. I find using it on the lowest setting, about 12 volts, is enough for car bodywork. It’s easier to trim wire speed now but still have the two higher settings for thicker material.

It will never make it a portamig but it is easier to use now so well worth the few pounds to do

 

[WindWalker]

Thought I’d just show a bit about building the voltage regulator for anyone that is considering it.

Parts from RS Componants:

206 5879 – 1 sided stripboard

313 6900 – Tip122

131 198 – 330R resistor

687 8133 – Zener diode 6.2v

625 6568 – Zener diode 12v

234 2328 – High power heatsink

320 679 – Rotary switch

223 742 - knob



Parts laid out



Shows layout. Note: red line shows where resistor should be



Reverse showing in yellow where resistor should be







Assembled and fitted


I originally got the base and collector connections the wrong way round, hence the red line and yellow arrow on reverse shown in pics. Thanks to Robert and Shenion for their help, I connected it properly and it all works.

When done, I cut the board down to size, and on the reverse side I removed the copper tracks from the board where the metal mounting bracket fits. This came off very easily using a dremel. (edge of a cutting disc lightly going over it)

The switch is a 12 position single pole and has a washer with a tab so you can alter how many clicks round it goes. I set mine to three. Wires are soldered to the end of the board and then routed to the switch, to earth and to the supply. One wire goes from the centre pole on the switch to the TIP122. This is the regulated voltage. (to base)

Final pic shows the switch on the front panel. It’s set to low voltage, full voltage is in the upright position and the position in between is the medium voltage.

 

[WindWalker]

In the above pics the connections on the board are:

C31 = regulated voltage from switch centre

D32 = live in

C29 = regulated voltage out to motor

D28 = full voltage to switch position 1

D18 = 18 volts to switch position 2

D26 = 12 volts to switch position 3

D20 = negative (black lead on motor to bridge connection)

 

[R Kraft]

It's really good to hear from someone how things turned out.
Sorry you had trouble with the transistor pin-out.
My welder uses a different motor drive circuit than a SIP does.
I ended up with my welder set on 18v and haven't needed to change it.
Robert

 

[BChild]

One new tip122 later and a quick re-solder and it works

I’ve got three positions now and it definitely makes a difference. I find using it on the lowest setting, about 12 volts, is enough for car bodywork. It’s easier to trim wire speed now but still have the two higher settings for thicker material.

It will never make it a portamig but it is easier to use now so well worth the few pounds to do

Excellent - nice to see another variation for the wire speed issues when installing a separate wire feed transformer

 

[WindWalker]

Robert, it was nothing more than my inexperience with electronics, thanks for clearing up what pin went where

BC, in my mind I was trying to replicate the coarse voltage switching that is lost when the transformer mod is done. It’s not expensive and gave me the chance to experiment with circuit boards, solder and the need for three hands

I may yet tweak it again at some point and make up the regulator Shenion posted just to do a comparison. I do find that even with the voltage switching that my feed motor runs quite quick even on 12 volts. Must be a hot motor Found a sticker inside saying September 93 so shows how old mine is. Maybe the spec is different on later units?

It is much more user friendly now though and further experimenting will be down to me being inquisitive rather than need. I still have a smallish window of movement on the wire speed control for acceptable welding so may look at widening that at some later point. It is much easier to fine tune now though so is definitely worth doing

 

[R Kraft]

Did you hook the regulator between the PCB and the motor, or between the 24v power in and pin 1 of the control board ?
Robert