SIP 130 wire-feed power supply - alternative approach

[ginettaman]

How would the Pwm circuit wire into and bypass the pcb circuit? I'm not very confident with wiring up machines hence why it took me some time to modify the 105. I was thinking of that pwm idea for the sip120 as that has no working pot?
Could buy 2 I guess?

 

[eddie49]

This PWM controller has a fused power feed:
https://www.ebay.co.uk/itm/10A-9V-5...ntroller-Volt-Regulator-Dimmer-F/192766962623
As for the wiring, I would guess that you already have wired the AC mains input of your new 24v PSU just after the power on/off switch, so that the PSU is always on when the welder main power is on ( as per Page 1 of this thread ). There is an additional relay with a 230v mains coil across the primary of the main welding transformer, so when the relay on the PCB turns the welder transformer on, this additional relay closes.
The relay should be single pole, double throw ( SPDT, 1-pole 2-way ). The output of the 24v PSU connects to the input of the new PWM controller, with two wires + and - on two of the four screw terminals. The pot on the PWM is set for whatever speed is required. The two-wire output of the PWM controller from the remaining screw terminals goes to the motor, with one of the wires routed via the moving pole of the additional 230v relay. The normally-open switch contact of that relay goes on to the motor. If desired, the normally-closed contact gets wired to the other side of the motor, so that the motor is shorted when off, to act as a brake.
In other words, the 24v PSU feeds the PWM controller constantly, and the variable PWM output is fed to the motor whenever the main welding transformer gets turned on ( which is when the torch trigger gets pressed ). The original PCB in the machine remains, but has now got nothing to do with the wirefeed motor.

 

[ginettaman]

I've ordered some motor controllers but it will be a while for delivery.

 

[Hutcho]

Dc brake works brilliant on these

 

[ginettaman]

Hello, and welcome to the Forum!
Which Ginettas are you into? My favourites are the G4, the G15, and the G21. I have never owned one, but I used to have a Fairthorpe Electron, and I own a Piper P2.

I would suggest the following hints about jittery wirefeed:

- worn brushes or bearings on the motor?
- too much drag on the spindle of the MIG wire spool?
- clean out and put fresh grease in the gearbox

I think the wirespeed controller on the PCB is just a simple variable-current driver, using a TIP35C or similar power transistor to reduce the current. In other words, it is just a big rheostat ( variable resistor, like a Scalextric hand controller ). At low speed settings, most of the supply voltage is dropped across the transistor, so the motor cannot produce much torque. The solution, especially after you have gone to the trouble of installing a stabilised power source, is to take the next step and fit a modern Pulse-width Modulated ( PWM ) motor speed controller. This circuit feeds variable-width pulses at the full 12v or 24v to the motor, so full torque is available at all speeds. The same type of circuit is used in the trigger control of a modern cordless drill.
Typical example:
https://www.ebay.co.uk/itm/12V-36V-...-Controller-Switch-12V-24V-3A-AL/400755823151

Finally, you may need a complete new wirefeed assembly - plastic:
https://www.ebay.co.uk/itm/Duty-MIG...d-Machine-for-Mig-Welder-Machine/383671546997
or metal:
https://www.ebay.co.uk/itm/DC-24V-0...e-Wire-Drive-Motor-Feed-Feeder-D/233682904367
or including Eurotorch socket conversion:
https://www.ebay.co.uk/itm/Assembly...ne-Welder-Euro-Connector-24V-12V/264894724829

Motor controllers ordered!

 

[Hutcho]

Motor controllers ordered!

Let us know how you get on with them - not done this one - I found by turning the psu voltage down a tad it was more usable and is a massive improvement

 

[ginettaman]

I've replaced the mig 120 ( no pot control) transistor only to find the pcb go up in smoke burning out a resister and possibly the relay so not good news.

 

[eddie49]

That is a shame, sorry that happened. I'm not sure why, its possible the new transistor was defective.
The speed control part of the PCB ( i.e. the pot and the power transistor and the resistors ) is separate from the welder on/off part ( i.e. the small transformer, a rectifier, and the relay ). Therefore it should still be possible to switch the welder on & off using the torch trigger switch. When your PWM motor speed controllers arrive, you will not need the speed control circuit on this PCB, so you may not need to replace this damaged board.

 

[ginettaman]

Yes my last option is to try some sort of pcb bypass or just use part of it to switch the 12v from the torch. Last night I got the sip170 working pretty well so that's good news but it's not mine sadly.