Internal or external wire feed controller

[Josh hector]

So after a few messages too and from with people who make pwm controllers and a chat with a really helpful chap named mike on the forums I've taken a route with (what I've welded with it so far) a fairly old decent welder.

Stitch timer was removed before my ownership but there was obviously a wire feed fault and previous owner removed the controller and diy'd a psu. I've gone the route of switch mode power supply and pwm controller. I've utilised a switching relay to activate the 24vdc output.

My question is do I create a small boxed up wire feed controller mounted on the lid of the welder or on a trolley. Or do I try an squeeze it all in and power it off the main internal voltage switch? Any pros and cons either way?

Also, any advice on a motor brake? I haven't put wire through it yet so don't know how much the pressure of the roller and the weight of the wire roll will slow the motor down, but currently it runs on quite a bit!

 

[rtbcomp]

Motor brake is easy, arrange for a relay to short the motor out as soon as the supply to the motor is switched off.

 

[Josh hector]

How do I go about doing that? Positive to both poles or something? As if I switch the motor wiring round it will just reverse!

 

[rtbcomp]

RLA is a mains operated changeover relay, NC are the normally closed contacts, NO normally open.

When the trigger is closed RLA calls and the contacts switch from NC to NO and the motor is connected to the PWM controller.

When the trigger is released RLA drops and the contacts return to the normal position as shown in the diagram. The NC contact shorts the motor and it stops quickly.

EDIT - for "Trigger" substitute "Relay operated by trigger".

 

[Josh hector]

Makes sense, I've got my RLA after my PWM controller simply because the circuit I removed took the power led with it.

Diagram makes sense at least, I'll get it sorted tonight, I ran the motor with wire through it and it carries so much momentum at high speeds the wire continues to feed by 3-4"

 

[rtbcomp]

Does the relay operate OK at lower speed settings?

 

[Josh hector]

The relay operates at all settings as it's triggered off the main transformer. I've wired the power supply off the main 240v input

 

[rtbcomp]

....... I've got my RLA after my PWM controller.......

I thought you were saying you connected the relay after the PWM.

 

[Josh hector]

My poor explanation, apologies!

Relay is powered by the main transformer and triggered by the torch switch so 40vac or something iirc.

It switches the power feed after the pwm, instead of before it. So the switch mode psu and controller are always live when the welder is live. The the 24vdc supply gives me pretty good control over the wire feed, but it goes a lot faster than I'll ever need it to!

 

[Josh hector]

This is what I ended up with...

The lock top box is all I had to hand until the aluminium one I ordered comes through.

Switch mode power supply and pwm controller in lock top box with a separate switched live wired to the main welders plug terminals. 24vdc+ goes straight to motor and left side of relay switches the 24vdc-. Right side of the relay closes and loops the motor to short itself and brakes it rather well! Although I am tempted to put a small capacitor on the brake as it still runs on a bit. Would that work?

Pickup on the motor is a bit slow, is there any way to put a but more into it from the start or is this just the nature of dc brush motors?