iwm mig 140 round 2

  1. paulo1974 Member

    i own a iwm mig 140 wich the motor voltage is to weak from 1 to 5 to get welding with that kind of wire speed. taken on 1 min power setting
    1-0,6 v
    3- 1,35 v
    4- 1,8 v
    5 - 2,3 v
    6- 3,6 v
    7 - 5,6 v
    8- 8,5 v
    9- 15.6 v
    10- 18,8 V

    the specs of the welder
    20a/16v - 140a/22v
    135a 20% - 78a 60%
    230vac 13 amp

    it has 4 settings 1min, 2 min, 1max and 2 max
    the pcb its a re253 rev03
    the potenciometer that stands alone is a y512lin 10k
    my 3 question are:
    Instead of putting another 24v transformer for the motor can i replace this (10k) for a 5k or similar cause on clarks manuals any wire speed starts at 5 up so i can get the voltage of the 5 speed on the 10k on the 1 and 2 with the 5k(half of 10k). As i only complain about the useless for 5 motor speed or less.
    can anyone now that i have the specs of the pcb tell me how to connect the solenoid valve in case i go for euro-torch? maybe a 220vac will be better cause i don´t want o mess the 24vdc from the motor feed. if the potenciometer fails where do i connect the 24vdc?
    for the 24vdc motor power supply can i use this of the intermittent on and off will blow the psu?or should i install a 230vac/24vac transformer and a bridge rectifier?
  2. Memmeddu

    Memmeddu Member

    Italia Sardegna
    A pwm controller and an electronic or traditional transformer and bridge rectifier
    Should be good for the purpose
    You take 230V to the transformer (if electronic take one with DC output) a rectifier in case you use a traditional transformer and the pwm ,the output of the pwm to the DC motor on the wire feeder
    It's probably that the solenoid valve needs AC from the same auxiliary transformer so I think it's better use a traditional transformer
  3. paulo1974 Member

    The solenoide valve should plug to the main 230vac of the transformer that comes from the pcb (l1 and n on the schematics) i think no major flutuantion on the 230vac to the main transformer.
    Changing the 10k potenciometer for the 5k potenciometer doesn´t seams to damage the pcb because in the 10k the speed 5 should be around 5k. but my knowledge of eletrocnics its very basic no digital only resistors, capacitator and diodes.
    any problem to use a Switched-mode power supply as a secondary power supply to thhe wire feeder or it will blow up from turn it on and off?
  4. eddie49 Member

    It's good that you have located a copy of the circuit diagram for the PCB !
    A simple first step would be to try a 5K pot instead of the original 10K one. From the circuit we can see that the motor speed control is not PWM, it is just a linear analogue current control. The driver transistor Q1 ( BDW93 ) is an NPN Darlington pair. Driving the base positive will make the transistor conduct. The wirefeed speed position "5" ( out of 10 positions ) on the 10K pot provides a 5K resistance. If you changed to a new 5K pot, that value of resistance would already be seen in position "1", and position "5" would be 2.5K. That would give you the same speed as you are currently getting at "7" or "8". Effectively, the useless low speeds "1" to "5" would disappear, and you would get the usable high speeds from "6" to "10" spread over the full rotation range of the control knob.

    For the gas solenoid, use a 230V AC part, and put it in parallel across the primary of the main welding transformer ( pins N1 and L1 of the PCB ). That way, the Triac TC1 which switches the welding power on when you press the torch trigger will also control the gas solenoid.

    If you do decide to upgrade to a stabilised 24v DC supply for the wirefeed, instead of the present way using the welding voltage ( which as you say will vary during the welding process ), then I would suggest that the new supply should be on all the time. I did mention this in posts 12 and 20 on your original forum thread:
    Memmeddu likes this.
  5. paulo1974 Member

    As for the solenoid you are right it´s N1 and not N cause the triac is before n1 when switching he connects to n closing the circuit.

    For the psu a Switched-mode power supply will be more compact and cheaper but i don´t if it can handle the trigger´s switching on and off. Any experience on this type of psu?
    The old transformer and a 50v 25a bridge rectifier whould be better?

    As for the addicional 24vdc voltage my idea is that it goes through a potenciometer or a pwm module that is controled by the pcb and for that i need some advice how to connect it. For me the simplest and cheaper way is to change the 10 k potenciometer.
    Note: the pcb fuse is only a 0,1A.
    If i cut the resistance in half ,the amperage will double? i ask this because i don´t want to fry the pcb

    As for my previous post it was getting to long and as i got some info on the pcb and schematic i decided to create a new post.
    Last edited: Oct 14, 2019
    Memmeddu likes this.
  6. eddie49 Member

    A switch-mode PSU starts by rectifying the 230v AC mains and then smoothing the resulting 325v DC with some big capacitors. There will be a large switch-on current surge when these caps charge. This could be damaging in the long term, or with cheap components, or with frequent switching ( such as when triggering multiple joined-up tack welds to avoid burning-through thin sheet metal ). Some PSUs have a "soft-start" circuit to reduce the current surge.
    In the other thread I suggested that the new 24v PSU, of whatever type, should be wired to the output side of the main welder power switch so that it is always on. The 24v output goes straight to the new PWM motor control module. You set the desired wirefeed speed using the control knob that is already present in the typical eBay PWM modules. So these two new units will always be on, set up, no surges, no power-on delays.
    The two wires from the wirefeed motor will go to the poles of a new double-pole, double-throw ( DPDT ) relay, with a 24v DC coil. The normally-closed contact are shorted together, to brake the motor. The normally-open contacts go to the output of the PWM module.
    The relay coil is controlled by the MIG torch trigger switch.

    [ If the new 5K pot does not help, and you want to make these improvements to the wirefeed power source, then it could be enough to just install a stable 24v power supply, still using the original speed control circuit on the PCB. However, from the circuit diagram that you obtained, we can now see that the speed control is very basic. It reduces the motor speed by limiting the current. This will reduce the motor torque, so the wire feed at low speeds may be erratic. A PWM control is more stable; it provides constant torque by maintaining the power with 24 volt pulses of varying width. ]

    The original pot starts at 10K Ohms, and drops to zero when fully rotated to speed position "10". Even at that setting, there is still a 330 Ohm resistor in the path to the base of transistor Q1. The motor current ( about 1 Amp ) goes through the Collector-Emitter path of the power transistor, not though the potentiometer. The pot controls the base of the transistor, biasing it into higher or lower conduction using a base current of just a few microamperes.
  7. paulo1974 Member

    I ain't happy with my Welder so I bought a ac DC multi meter and yesterday I toke readings from the welder. On min+1 19v min+2 22v max +1 (22.2v) max +2 (26v). They are far from 20amp 16v on the low end. Them I measure the amperage with 0.24 wire and the letter didn't push pass 37 amps. What went wrong? The link to video on YouTube
  8. eddie49 Member

    The 20A 16v low and 140A 22v high stated on the machine label may be on-load voltages, which would explain why your OCV readings are higher.
    Does your clamp-on DC ammeter have a "Max Hold" function, which would record the peak current?
    Have you checked the meter accuracy using a known load? E.G. a 60Watt 12v car headlamp bulb should show 5 Amps.
    In an earlier post you stated that the motor voltage was low, and mentioned possibly using a stabilised external 24v PSU. Have you done this?
    To get maximum Amps, you need a high wire speed. Did you test the maximum weld current with the speed dial set to maximum?

    [ E.G. to see 140Amps you would be welding 3mm - 4mm thick steel at MAX/2 with a wire speed of about 9 metres per second. Does your wirefeed motor reach that kind of speed at position 10 ?
    Wire speed calculator: https://www.mig-welding.co.uk/calculator.htm

    You will reach a higher welding current with thicker MIG wire, i.e. 0.8mm runs more Amps that 0.6mm.

    What thickness of metal are you using, and what do the welds actually look like?
    Memmeddu likes this.
  9. paulo1974 Member

    hi there eddie49
    I have bought the material to do the conversion but i havent do it because i has searching to transform the unit to eurotorch with a gas valve also. But in light of the measures i toke i think i wont touch the unit. i call a person that fixes the welders cause i tought that was something wrong with the welder i told him about the readings. He ask me if the welder melts the wire and it did.The thinks that my multimeter is wrong, i have to test on my other welder a 250 amp one to see if the readings are correct. He ask me what brand was the welder and told me that those welder only weld on max and badly (he works with industrial grade machines).

    As for multimeter acurrancy i toke measures from 2 diferent multimeter and the voltage when i press the triger was around the same. the other one doesn´t have dc amperage. i did not test on max wire speed i weld on 7 more or less.

    Wire speed i think it goes to beyond 9ms but only at plus 7

    i have to make another video where i film the piece to be weld, take is tickness.

    i set the machine for 0.6 mm(0.24) wire
  10. paulo1974 Member

    Change my mind and i decided to try again.
    So in this first run i converted to euro conector and add a 24vdc gas valve.
    I decided to wire the valve directly to the leds (dinse 25) not sure of the wire conection on the pcb board, on the 2 wires from the torch i only measure 16vdc. Any problem with this wirering setup?
    I try to see if this setup will do( not sure about wire speed) could solve it by cutting the potenciometer in half (from 10k to 5 k) or a more drastic measure, put a pwm for motor control, with a transformer from 220 vac to 24 vdc and a relay. it would have to reconfigure the connection so that the relay is in charge of the operation. I don't know where I have space to put the transformer :(.
    put some pictures soon.
  11. paulo1974 Member

    Similar to my welder, mine hasn´t got warning lights, but you can see the wirering of the welder.
    Can anyone tell me were to cut the motor and the potenciometer from the pcb so i can get another 24vdc power supply with the pwm to control speed?
    as i see i cut all the wires 1,3 and 4.