Thermal arc 250 problems

[irondarren]

Having a little trouble with my thermal arc 250, its about 10 yrs old (Australian built). Its not putting out the power it should do, i guess its been getting worse over the last year or so, i just havent noticed it until now. I have messed around with the earth cable connection, and replaced the cables and connectors, with a bit of improvement.
On the inside of the machine is a power setting verses wire speed setting for different thickness of material. To be honest i havent looked at that for years, i just set the voltage and turn the wire speed and weld, adjusting the wire speed if need be. Having used the setting chart and set it to 24-29volt course and setting 2 on fine, it should run at a wire speed of 12.5mtrs per minute. Now this just produces massive amounts of cold edges, reduce the wire speed to 10mtrs per min and its fine, no cold edges on the weld bead. But 10mtrs per min wire speed should be 19-23volts course setting and 2 on the fine.
I have been having a little trouble with the wire remain live after the wire feed has stopped. run out about 6 inches of wire without actually welding, then earth it out without touching the trigger and there is enough power in the wire, to produce a heavy spark. (weldequip tells me this is possibly the contactor at fault). I have noticed tonight a slight buzzing sound (only because i decided to give the inners a real good clean out) which seems to be comming from the contactor, its a little difficult to tell because of the fan, but im 90% sure its the contactor buzzing. What i really need to know is can the contactor be responsible for the powerloss in welding output.
If i can restore it to 95% of output again i would be quite happy but if not then it looks like a new welding machine, with a portamig 350amp with swfu looking favourable, but at the moment im trying to save a few quid so don't really want to spend out if can help it.
any ideas?

 

[Mikey D]

well not knowing a great deal about the internals of your machine ,but i do know a bit about electrics ,its sounds like the contacts on your er contactor may be burnt or pitted not allowing the full current thru ,or sticking on ..... try testing the continuity thru the contacts with a multimeter

you may be able to get a relacement from an electrical wholesaler locally ,obviuosly making sure the coil voltage and contactor ratings are the same tho ..

cheers mike

 

[Robotstar5]

I would agree with Mike, sounds like a contactor problem. I use City Electrical Factors (CEF) and Newey & Ayre, don't know if they are countrywide. Give them the details of your contactor and they should be able to match it, just double check the coil voltage as 48V is common but most welders use 42V.
Just repaired a Murex with a Danfoss contactor and CEF supplied a Telemecanique one that was exactly the same spec and size, worked fine.

 

[Welderpaul]

Mate, your a welding business, if its 10 years old and given you good service, are you throwing good money at repairing something that is going to fail again. Buy a newwun??
Just my 2p! Wait for the next big job to come in and price in a new welder - then its paid for itself? Thats how i've bought my Murex sets!

 

[murex400]

daz you got 3 phase there if so pm me

 

[irondarren]

Single phase only Murex, which is a real royal pain in the bum lol.

welderpaul thats what i was wondering 10yrs use isn't bad going really, if its the sake of 50 quid for a contactor then i don't mind, but much more than that and its probaly not worth repairing. chuck it in for a nice 300amp portamig with swfu

 

[Welderpaul]

I picked up a nearly new 260A Murex mig for 700 quid - single phase. I know it aint cheap but you have to draw the line some where - 10 years is good going. If you bodge it up, you know it will pack in in the middle of a rush job and cause you no end of bother - there are enough problems without having to worry about your kit as well!

 

[Wozzaaah]

portamig 350amp with swfu

a nice 300amp portamig with swfu

Dropping 50 amps a day Darren? It'll be a SIP 150 by the end of the week

 

[murex400]

Them portamigs can you have a separate wire feed unit on them ?

My miller I got only cost me £150 quid from an auction though I had a bargain till realized I needed a wire feed unit that was another £200

 

[irondarren]

Dropping 50 amps a day Darren? It'll be a SIP 150 by the end of the week

roflmao. Wozzaaah. At the minute a SIP 150 is looking good. As long as i can botch this together until after xmas i will be happy to shell out on a 350 swfu

This fault gets stranger and stranger, just chucked a multimeter across the contactor, there are 4 connections on each side. 3 of the top and 3 of the bottom are mains 240volts. the other connection top and bottom seem to be 36volt, obviously the switching voltage. I couldn't get a reading without pulling the torch, once the torch trigger was pulled the 36volts was there, but once let go and the contactor opened, it remained at 36volts, and began to slowly go down, perhaps 0.1 volts per second. I am sure once the contactor opens the voltage should drop away almost immediatly.

 

[irondarren]

Murex they do up to 400amps on a swfu on single phase and 500 amps on 3 phase. Sensibly priced as well about 1200 quid for the 350amp plus vat, which for a machine that has 60% duty cycle at full power isn't bad price

 

[Welderpaul]

Murex they do up to 400amps on a swfu on single phase and 500 amps on 3 phase. Sensibly priced as well about 1200 quid for the 350amp plus vat, which for a machine that has 60% duty cycle at full power isn't bad price

Get Mrs daz to buy you one for xmas.

 

[shenion]

This fault gets stranger and stranger, just chucked a multimeter across the contactor, there are 4 connections on each side. 3 of the top and 3 of the bottom are mains 240volts. the other connection top and bottom seem to be 36volt, obviously the switching voltage. I couldn't get a reading without pulling the torch, once the torch trigger was pulled the 36volts was there, but once let go and the contactor opened, it remained at 36volts, and began to slowly go down, perhaps 0.1 volts per second. I am sure once the contactor opens the voltage should drop away almost immediatly.

Sounds like there are capacitors on the supply. A meter will take a long time to discharge them. Normal welding would draw them down almost instantly.