Help welder not working

[stevo65]

Thank you I will be back with it on Sunday and will remove it for testing. From reading through on the tests advised I will be in the same boat of is it worth replacing the rectifier with a generic unit or would it just be easier to replace the welder with a new unit.
Sorry if I am asking the same questions again

 

[eddie49]

This SIP welder is one of their early industrial-quality models, and it is definitely worth saving.
If the rectifier is faulty it can be replaced at a reasonable cost:

Pardon our interruption...

and the welder will continue to be a simple, reliable, maintainable unit.

 

[stevo65]

I have looked at these but was dubious as to whether it would be suitable as the physical build of the original is larger than this with more heat sink fins

 

[eddie49]

The eBay Seller "Yorweld" is TecArc of York, makers of the respected Oxford and Portamig welders. If they rate a rectifier at 170 Amps, it will definitely be up to the job. For car bodywork repairs you are unlikely to need more than half of that anyway. They do also sell a 230 Amp version.

 

[SipMerlin150]

Loosing the arc and the plug blowing fuses.. did you notice the arc sounding any different?

If you have a multimeter that can test diodes and capacitance you should be able to test each component and compare it to data information sheets available from manufacturers on the web.

As a general rule, i would check the most stressed components first,

The large electrolytic capacitors, usually rated a few hundred volts, for shorts, swelling, lack of rated capacitance, burned connections, but i advise leaving the unit a good few hours from being plugged into the mains before going near the capacitors as they will hold a lethal charge for some time after unit it powered down.

Output rectifier, check for shorts, and test with the meter in diode mode, test in both directions should yield a volt drop one way and reverse bias voltage the other way or show 'OL' open lead. A rectifier is basically a one way valve converting AC current in DC to charge them large capacitors.

Transformers can be checked via a basic continuity test, but these transformers are generally very hard to hurt.

The other area of failure are the mosfets on the pcb, most likely voltage regulators and timer IC for spot welding modes, these can be checked for shorts, then of course the rest are resistors, check for open or shorted resistors. If you are okay with soldering, the components are pretty cheap.

 

[stevo65]

Hi all
Thank you all for the replies, I have now removed the rectifier and tested it and it all ( as far as I can see) tests OK with consistent readings of 0.50 one way and OL the other way.
I have checked the capacitors on the PCB and they all appear to be good. There does not appear to be any large capacitors any where else. Am at a total loss now.

 

[SipMerlin150]

Hi all
Thank you all for the replies, I have now removed the rectifier and tested it and it all ( as far as I can see) tests OK with consistent readings of 0.50 one way and OL the other way.
I have checked the capacitors on the PCB and they all appear to be good. There does not appear to be any large capacitors any where else. Am at a total loss now.

Take a few close up photographs of the main pcb with its components, let me have a look,

How did the transformer test out?

 

[SipMerlin150]

Hi all
Thank you all for the replies, I have now removed the rectifier and tested it and it all ( as far as I can see) tests OK with consistent readings of 0.50 one way and OL the other way.
I have checked the capacitors on the PCB and they all appear to be good. There does not appear to be any large capacitors any where else. Am at a total loss now.

One additional question, the contactor takes a huge brunt, they are powered by a small magnetic coil that when energised will pull in some heavy duty contacts that initiate the welding current, they can burnt out or weld together, when you squeeze trigger you should hear a 'thunk' and the center of the contactor should pull in, and when trigger is let go it should come out again, its quite a robust snappy action, try to trigger it without welding so you dont blow a fuse. If its arcing and making a poor contact it could overcurrent and blow a fuse as the current through here isnt controlled by the power settings on front of unit, it takes full mains voltage. Best of luck!

 

[stevo65]

Hi all
The transformer tested out OK and the contactor is working properly pic enclosed of the circuit board

 

[eddie49]

The circuit board looks fine, like new. To blow a 13A fuse you need to pull about 4kW, and there is nothing on that PCB that could take that power.
When you tested the rectifier, there should have been a total of eight results - four with "500" or "0.5" indicating conduction, and four with "OL" or "1. " showing blocking.
With the rectifier disconnected from the secondary of the main transformer, if you power up and press the torch trigger now, does the 13A fuse no longer blow?

Considering what could be causing a weak arc and blowing the fuse if not the rectifier:
Have you been able to measure the AC output across the transformer secondary? It should start at about 15 volts and rise to about 32v as you step up the voltage on the rotary switch.
Does the switch action feel smooth, with equal mechanical resistance at each step?
The primary of the main welding transformer on a MIG rarely shorts, but it is possible. To check the primary resistance, unplug the welder, set your meter to the 200 Ohms range and connect the test leads across Live and Neutral at the 13A plug. Turn the welder power switch on and go to the lowest setting on the rotary switch. This connects to the greatest number of turns on the primary, and therefore the highest resistance - but that will only be a couple of Ohms, or less. Press the manual operating button in the centre of the contactor firmly, and the meter should show that resistance value. Then step up the voltage settings on the rotary switch. At each higher setting the primary resistance should drop, in roughly equal steps. It may show as low as 0.3 Ohms, but should not be zero.
More details in Post #7 of this thread:

E

Post in thread 'Sealey 180 supermig v3'

Jan 14, 2019

I've found that any attempt to rewire or dismantle those rotary switches results in much confusion and blown fuses!
If this helps, I have made some resistance measurements on the primary of my Eland 175 MIG. It is a 200 Amp machine, with 8 power ranges. The range switch is a very simple 1-pole 8-way switch.
At the lowest power setting ( which is the highest transformer turns ratio, with all of the primary winding in circuit ), the primary resistance is 1 Ohm. Increasing the power setting decreases this resistance progressively, down to 0.3 Ohms at position 8.

Those measurements were made...

• eddie49

 

[stevo65]

Hi thank you again I will try to get back there this week and check the other settings, the switch action does feel smooth though