Snap on pro mig 187 low on power ?

[johnny]

Hi i bought myself a second hand snap on pro mig 187.
I have been having a go of it and found that it dosent seem very powerful...its ment to go up to 180amps but its struggling on 3mm steel on its highest setting.
My old clarke 150en is more powerful than the snap on.
Surely there must be something wrong with it..?
Ive thoroughly cleaned the earth clamp..but still not any better.
Any ideas would be appreciated.
Or has anyone else got one of these welders who could tell me how they perform on thicker metal?
Thanks

 

[baldy]

selector switch or rectifier not working correctly?

 

[qwakers]

or you've got it plugged into a wimpy power supply?

 

[123hotchef]

I use to have a snapon pro mig it was a great machine I welded 10mm steel with it no bother.

 

[eddie49]

Check the DC voltage between the torch tip and the work return clamp. From the lowest to the highest setting on the power selector switch, it should rise incrementally from 23 to 37 volts.
Disconnect from the mains, open the case and inspect all the connections in the high-current path - the transformer secondary, the rectifier, the inductor, the Eurotorch and return sockets. Look for loose, corroded, or burned joints. If in doubt, open, clean, and re-tighten the joints.
As baldy suggested, the contacts on the power range switch may be burned, limiting the current in the transformer primary, or one of the rectifier diodes could have gone open-circuit.

 

[johnny]

Ok ive plugged it into a very heavy duty extension lead and that made no difference.
I then checked the power selector...it does go up in increments from 23 to 37.
I have taken the side off and checked for sparks while i used the welder...nothing sparked inside...
It all looks pretty clean inside there.

 

[johnny]

Also ive noticed that the fan starts as soon as the machine is turned on...i dont know if thats normal for this model...?

 

[123hotchef]

Do you have it on a 13amp plug

 

[AndersK]

My old Esab suffferd the same. I went over all electrical connectors, taking them apart and reconnected them. Some of the screw connectors were quite loose. What a difference that made...

 

[johnny]

Yes its on a 13 amp plug...ie just had a look at that and its ok.

 

[eddie49]

You are right, the machine does look really clean and tidy inside. Still, no harm in gently trying to check all the connections - especially the push-on ( car-type ) tags, to make sure that they are tight.

[ It has a centre-tapped secondary on the main transformer, with just two effective diodes to provide full-wave rectification ( rather than 4 diodes in a bridge rectifier ). I think these "Snap-On" machines are made in China. It does have a smoothing capacitor on the DC welding output, which is nice.]

Yes, it's OK that the fan runs as soon as you power-on, some machines do that.
It is good that the DC output voltage rises steadily as it should, from 23 to 37v. That implies the secondary, the rectifier, the capacitor, and the range selector switch are all OK. Any faults would have made that voltage too low, or intermittent, or jumpy.

I would suggest that you need to test it on-load. That's not really possible whilst welding, but one method is to take 3 x 12v car headlamp bulbs ( e.g. 60 watt H4 bulbs ) and wire them in series. That gives you a 36volt load that will pull 5 amps. Join this contraption to the torch tip and the Earth clamp, set the welder to the highest power setting, and switch on. Turn the gas off at the cylinder and slacken the wirefeed pressure roller. Press the torch trigger switch, and put a cable tie around it to keep it on. Put your voltmeter across the full string of bulbs - i.e. MIG torch tip to Earth. The load is only drawing 5 amps, not 180, so the welder output voltage ought not to drop much, if at all, so it should be very close to the no-load 37 volts. If it drops a lot, you need to move the positive probe of the meter back up the current path. Keep the negative probe on the Earth, move the positive probe to the brass block at the back of the Eurotorch socket. Then try the positive of the large red capacitor, and the positive of the rectifier. Be aware that there is mains voltage exposed in the cabinet, and that the capacitor may hold a charge even after you have switched off.

If the 37v does drop under load, we need to find where in the high-current path the voltage is being lost. If it does not drop, but the welding power is still weak, it means the car bulb load is not enough to show the fault. We'll have to think of a way of testing with a heavier load.

 

[qwakers]

Yes its on a 13 amp plug...ie just had a look at that and its ok.

hmm, after some research i find it should be ok on a 13 a plug, which surprised me, but i wouldn't bet on it being ok on a extension, have you tried plugging it directly into the supply?

 

[johnny]

Yes i plugged it into mains its still the same.
I tested the ac from the transformer...its pulling 26 volts...that was on a extension lead.
I checked the rectifier again for blown tails but they all seem fine...with no evidence of burnt connections..
It looks to have had very little use and im pretty sure there is a date of may 2015 on the transformer so its not that old.

 

[johnny]

Its a bloody nuisance...

 

[johnny]

Ive orderd a clamp meter...apparently you can get someone to measure the voltage as you weld..?

 

[eddie49]

Ive orderd a clamp meter...apparently you can get someone to measure the voltage as you weld..?

With a clamp-on meter you can measure the actual welding current as you weld; putting it over the return cable will show that.
You need to be sure that the typical "AC/DC Clamp-on meter" will actually measure DC amps. The AC part is easy - it's just a coil on the laminated steel jaws, that acts as a transformer. For DC, the meter needs to have a Hall Effect sensor. Check the detailed small print for the meter to be sure that something like "DC Current 0 - 400 A" is listed.

After setting the meter control dial to DC Amps, you may have to press a "Zero" button. There may be a Manual vs. Hold function. In Manual, the meter will show you ( or your mate ) the actual current in real-time. In Hold, it will freeze the reading, so you can do a weld and then look at the meter yourself. Best of all, this Manual/Hold option may also have a choice of Min or Max, which means the meter will lock-in the display of the highest current reading.

Checking the current with a clamp-on DC ammeter will confirm your suspicions that the welder power is too low. To diagnose the fault further needs checking for lost voltage along the circuit.

 

[johnny]

Thanks eddie...

 

[johnny]

Ok i got a clamp meter and the machine was only hitting around 70amps when welding...i then fitted a new rectifier and it made no difference...still hitting around 70 amps..?
What on earth could be wrong with it..?

 

[123hotchef]

have you checked the power selector is actually working? ie the pot behind the selector dial?

 

[paulo1974]

réad the ac amperage output of the transformer