Telwin wire feed and PWM problem

[Smallfry]

I have a forty year old Telwin Mastermig 120 which has been a great little machine until a couple of years ago.

It had an early form of synchronous wire feed ........ no separate wire feed control. The selector barrel switch fell apart, and I could not get a like for like replacement, so I had to use a different Kraus & Neimer barrel switch, and do away with the synchronous wire feed.

I used a small and cheap PWM module, one of these

It has been working fine up until recently, but has now become temperamental, by occasionally not working. The input voltage from the machine (60 volt DC) is working OK, but there is sometimes no output.
I can easily replace it, but looking on eBay, I see plenty of higher amp rating, but they are rated at 48 volt input.

Does anyone who knows electronics know if these would work ? Is there anything better I could use that is not stupidly expensive ?

Do I even need a module at all, and just have a potentiometer if it would take the current ?

 

[johnrev]

There are several on Amazon at 60v and one I saw at 90v (I only looked at the first page of a search for 'pwm controller'). The 90v one was actually only £7.49 and PWM is far better at controling a motor than a straight voltage adjustment. It gives pretty much full power at low speed so will produce a much smoother and more stable speed control.

John

 

[Smallfry]

There are several on Amazon at 60v and one I saw at 90v (I only looked at the first page of a search for 'pwm controller'). The 90v one was actually only £7.49 and PWM is far better at controling a motor than a straight voltage adjustment. It gives pretty much full power at low speed so will produce a much smoother and more stable speed control.

John

I saw the 90 volt one on eBay, so I ordered two. Plus a better (hopefully) potentiometer and knob that is physically bigger, so easier to change with a gloved hand. Waiting for them to arrive.

However, In the meantime, I discovered that the wire feed motor will sometimes not start even when the PWM module is bypassed. Giving the armature a push through the brush "window" with a wooden lolly stick will make it run.

The feed motor is a hefty thing compared to modern machines and has removeable brushes. I took out the brushes, and found they were a bit stiff in their holders, forty years old remember, so gave them a clean up, and polished up the armature with one of SWMBOs emery boards (nail file)

Whole thing back working now !

I don't get electronics at all, but with PWM the voltage remains more or less the same then ? Thats clever !

 

[Nix2]

Such PWM controllers as in the photo usually have 20A fuses installed (because they are "supposed" to handle 20A), however, in the MIG machine the fuse should be changed to 3.15A (for a 24V/30W motor).