Telwin telmig 281/2

  1. js876 Member

    Just thought to take some pictures of the welder inside (seeing how dusty it is)and what do other people think of the build quality. Thing what I think is that the wire feed motor has a bad design allways issues with it. Had this welder for a year now and bought this one brand new. once welding a full one hour it seems to weld better, why is that?

    Anyway heres some pictures






    Being welding with this mild steel 100% CO2 gas, with argon mix perhaps would be easier to weld with. According to the place were I bought this from this welder will last a lifetime, thinking in the future of changing the wire system to a better one, one question is this that can the pcb handle a wire feed motor which takes more wattage than that small stupid motor, will it burn the pcb out. Anyway thanks for any replies.
    • IMG_20191030_165737_8.jpg
  2. eddie49 Member

    Agreed, that motor is rather small, and the mechanism is all plastic. There are better ones available:

    When replacing a plastic wirefeed assembly with a decent all-metal one, it should be noted that the whole assembly is "live" and will need to be isolated from the metal case of the welder. This is often done with shouldered nylon washers for the mounting screws, which may or may not be supplied with the new unit.

    I think the larger wirefeed motors typically draw 30 or 40 watts. The plastic-encapsulated transformers typically found on the Control PCBs are rated at only 1.5 or 3 VA, and just run the small relays. However, the transformer on your PCB does look a little larger than average.
    Power for the wirefeed motor usually comes from an additional "auxiliary" power supply, with a mains-to-24v transformer. On low-end machines the power may be taken from the main welding transformer. Your machines seems to have a stack of three laminated/wound components. The top one is the inductor ( choke ). Are there two transformers?

    As well as voltage, the PCB also has to have capacity for the motor speed control circuit to handle the motor current. There is a power transistor, but I don't see any heatsinks on your PCB?
  3. js876 Member

    Thanks for reply eddie49,

    Yes the top one is the choke and the bottom two ones are power transformers for the welding voltage/current connected from the heat switch what go from 1-8. The transistor has not even got any room for a heatsink, I was thinking of getting a wire feed motor like this:

    But the pcb might not just handle the motor. Them motors what you showed from ebay look pretty decent and look like the pcb could handle buy no doubt.
  4. eddie49 Member

    That is a very impressive 4-roll wirefeed !
    However, as you said, the 3.5 Amp motor current draw may be too much for the original PCB.
    You could maybe get an idea of the current used by the existing circuit by setting to maximum speed, putting an ammeter in series with the motor, and then using a gloved hand to put a heavy load on the motor drive roller, to check how far the current rises.

    There are 5- or 10- Amp PWM motor speed control modules available:

    but you'd have to integrate that with the existing welder trigger/control logic, and perhaps add a regulated 24v DC power supply.

    "Yes the top one is the choke and the bottom two ones are power transformers for the welding voltage/current connected from the heat switch what go from 1-8. "

    Interesting - I have never seen a MIG with TWO welding power transformers...
  5. north Member

    No problem you have a TELWIN....dont worry--- :waving: ---They are wokrhorses. :thumbup:
  6. js876 Member

    Heres part of the schematic diagram of the welder. I would like to ask what do pins 3 and 4 on the pcb do? they go straight to the rectifier +and earth(-) do they tell the pcb how many volts is selected and then control the wire fead speed and can this feature be disabled(by just pulling the wires off and putting electric tape over the connectors what pull off the rectifier). When you select how many volts(heat switch) on this welder the wire speed goes up or down without even touching the wire speed knob.
    • IMG_20200213_162843_0.jpg
  7. eddie49 Member

    On some MIGs as you increase the welding power with the voltage selection switch, the wire speed will increase. This gives a kind of "synergic" effect. Personally, I don't like it.
    As you have suggested, this feature may control the wirefeed motor speed. For example, it happens that way on Migatronic machines - the selected MIG voltage is used to bias the motor speed controller. However, on many low-end machines, the selected MIG voltage IS the wirefeed voltage. They do not have an "auxiliary" power supply, with a medium-sized transformer that provides 12v or 24v AC, and then rectifiers and smoothing capacitors. The MIG output voltage is simply "borrowed" to run the motor speed controller. This will provide the auto-speed-increase feature. However, it can also have a negative effect on the stability of the wire speed, since that voltage will tend to fluctuate during the welding process.
    From the circuit diagram that you provided, and the small physical size of the transformer on the PCB ( about 5W max ), your machine is one of those that tap off the welding power to run the motor. At least this has been done just at the rectifier, before the inductor, so the voltage will be fairly stable.
    So that voltage is supplied on pins 3 and 4 of the PCB. If you pull them off, the wirefeed will stop.
    If this auto-speed feature is a problem, you could avoid it by using a small stabilised power supply instead.
  8. js876 Member

    So could I use like a battery charger and feed 24 DCvolts to pins 3 and 4 and try out if the wire feed would be more stable, if it has any good affect then I will get a seperate 230VAC/24DC power supply and plug that to the on and off switch, which is on the welder itself. The wires what come off the rectifier are brown and white, is the brown one + and then the white one is- (minus)??

    The max what comes out of rectifier is 25.7 volts at 235 amps so 24 volts should be just fine, feeding 3 and 4 pins??
    Last edited: Feb 20, 2020
  9. eddie49 Member

    I do not know the existing wire colours, but pin 3 input to the PCB should be negative, pin 4 needs to be positive. This feeds the wirefeed motor power control circuit on the PCB, so it is important to get the polarity right.
    Your plan to test initially with a "24 volt" battery charger could be OK, but a low-end battery charger for lead-acid car/truck batteries is often a rather crude thing - sometimes just a transformer and one diode, and also the output voltage to charge a 24v lead-acid battery, without load, could easily be 32v, so that would be a bit risky.
    Replacing the welder output power feeding the wirefeed circuit with a constant voltage source will avoid the "step-up/step-down" effect when the welder power range is varied, so it will give you the functional change that you want. If you use a stabilised power supply, such as this one:
    the wirefeed voltage will not vary during the welding process.