I recently bought a SIP Migmate 150 DP gas/gasless welder, and as my first project using it I started building a cart for my welder. But when I started welding I was puzzled by the bad results I got. I have not been welding for may years, but then using a PRO ESAB welder. But now all my welds where really bad, and with a lot of splatter. I noticed that the wire feed was very uneven, and googling around I found a lot of information about this brand of welders and their inherent wire feed problems. In addition to the wire feed problems I had several occasions of porous welds, indicating that there was problems with the gas-feed.
Fixing the Gas-feed problem:
I noticed that the torch trigger, if not pressed hard enough, only trigged the wire feed, but not the gas. I had to ensure it was fully pressed down in order to have the gas flowing. This resulted in several bad, porous welds, similar to the one in the image below.
The gas valve is inside the torch handle, and the torch handle can be opened by removing four screws. Opening it revealed the micro-switch triggering the welding, and the brass valve for the gas.
I found that the micro switch was activated well before the gas valve due to some residual plastic inside the trigger from the plastics molding process. This residual plastic pushed towards the micro switch and made it activate too early. To fix this I mounted a small (4mm) end-mill in my drill press and carefully shaved off a few tens of a millimeter from the plastic.
Now the point of the trigger pushing towards the gas valve activates the valve and gas flow before the point touching the micro switch activates the switch, and the gas-flow problem is no longer present.
Fixing the Wire-feed problem:
Searching around the web for information about my welder I stumbled upon the magnificent forum page www.mig-welding.co.uk. There where several posts abouth the SIP Migmate wire-feed issues, and my modification is based upon a thread posted by user BillJ. The thread can be read here: http://www.mig-welding.co.uk/forum/showthread.php?t=11532
There are a couple of differences between BillJ´s description and mine. First of all, my welder is the Dual purpose welder, supporting both welding with gas and no-gas wire. Therefore its internal connections and schematics are a little bit different than the one posted by BillJ. Secondly I did not have a 240V relay, only a 12V relay, an OMRON G5LE-1-DC12.
Below is the schematic for my welder, and a version with my modifications added. Click on the images to view in full size.
By using a relay with both Normally open and normally closed contacts an electronic motor break function is implemented by short-circuiting the motor leads when motor power is disconnected, effectively stopping the motor dead. This is a very nifty trick that I got from BillJ´s solution, as linked above.
The following items are required to do this modification:
- 12V DC relay OMRON G5LE-1-DC12, or similar 12V relay able to break at least 24VDC / 2A.
- Power supply able to support at least 1,5A steady current withdrawal (higher peak current) at 24V
- Some wiring for the relay control (AWG 30 / 0,25mm or heavier)
- Some wiring for the wire feed motor (AWG 18 / 1mm or heavier)
- Heat shrink tubing
- Soldering iron + solder
First I had to find a suitable power supply. I connected an ampere meter to the wire-feed motor and measured the current. It showed around 0,9A steady during operation. The peak-current (current-rush) during motor-start is much higher, but I did not bother measuring this (can be measured using an oscilloscope and a suitable high-power, low ohm series resistor). Then I measured the voltage with the wire-feed speed controller set at both minimum feed, and maximum feed. The voltage range was approximately 27V at lowest speed, and 43V at highest speed.
Schematic below shows how to connect the Ampere meter (A) and Voltage meter (V) to measure the motor current and voltage.
I had an old lap-top switched power supply rated at 2A/22,5V. Although this voltage is well below what I measured at the motor I decided to try with this one, as the voltage at the motor is dropping during welding (this is partly what causes the jagged/uneven wire feed).
Specification label of my power supply
The powersupply had a LED to indicate correct operation, so I decided to drill a hole in the front panel of my welder and place the powersupply in such way that the LED is shown, enabling me to check that the powersupply is alive. Then I glued the power supply to the back side of the welder front panel so the LED is showing trough the drilled hole.
Now it is time to connect everything according to the schematic above.
The 220V input for the power supply was connected to the output of the power switch using piggy-back spade connectors, enabling me to easy add a second set of wires to the power switch.
The negative (ground) output of the power supply was connected to the negative (ground) wire of the motor. The power input wire to the controller PCB was cut from the welder rectifier, and connected to the positive output of my power supply.
The relay contacts was connected to the motor terminals and the positive terminal of the motor. Note that the relay must be wired in such way that when the relay coil is un-energized, the (normally closed) contacts short-circuit the motor windings. And when the relay is energized it breaks the short-circuit, and connects the positive terminal of the motor to the motor power output of the controller PCB, as shown in my schematic abow. The relay coil was then connected to the back-side of the controller PCB by soldering its two terminals to the two coil terminals of the main relay on the control PCB. This makes the motor relay just added activate simultaneously with the welding current.
Check that all wires are correctly mounted, and according to the shematics, and that the two cuts (blue wavy lines in the schematic above) are made.
Your new, stable, wire feed motor power supply is now ready.
Increasing the Wire-feed mechanism robustness:
Another modification I found at www.mig-welding.co.uk is posted in a thread from user darrencambs, http://www.mig-welding.co.uk/forum/showthread.php?t=3993. This modification adds a metal strap between the two wire-feed wheels, ensuring a steady no-slip feed of the wire. Below is a picture of my welder with this modification in place.
With these modifications in place I was able to produce acceptable welds with the SIP welder.