Spot/ resistance welding machine

[OllyO]

Can't get continuity between any cable entering isolator block. As far as I can see three phases enter, one terminates in fuse block and the other two continue on into machine.

I have continuity across the slydlok fuses and across the wire leaving the fuse labelled no2 but not across no1.

This might be going over my head (electrics not my strong point) but surely a machine cannot work on two phases and no Earth or neutral?

 

[Robotstar5]

Can you post a couple of pictures?, one showing the blue panel above the top arm on the front of the welder and another showing inside the back of the welder (cover plate removed).

 

[OllyO]

Sorry meant to attach these pics to last post

Will take picture of timer tomo. It's a W6 model, British federal are sending me some info they have on it so will post that as well.

 

[OllyO]

Inside machine

 

[Wendelspanswick]

If you think of each of the 3 phases supplying 240v when measured on its own to neutral and if you want a higher voltage you connect 2 of the phases together to give you 415v.
3 phases still gives you 415v but it's balanced (each of the phases is an equal amount out of phase to the other phases) so a 3 phase motor runs smoothly.
It's easier when you see the waveforms drawn out than trying to describe it.

 

[Wendelspanswick]

2 phases

3 phases

 

[OllyO]

Thanks for the explaintion (and patience) Jon. It's slowly starting to sink in.

 

[OllyO]

Timer

 

[OllyO]

Just had a spark round who has isolated the problem to the transistor which is bad news. Going inside was beyond his experience but he felt it could be a reasonably straight forward job for someone with this kind of knowledge.
Anyone know of anybody like this in the Bristol area?
Am looking at scrapping the machine or spending 1.5k on having a new timer fitted so any help appreciated.

 

[Robotstar5]

A transistor replacement is fairly easy once you work out a modern equivalent, but if it's the thyristor pack that's failed it's going to be expensive

 

[OllyO]

Fingers crossed then!

Hopefully it's not junk. It's a Very nice machine. My other thought was to by pass timer completely and time welds manually. Not sure how possible it is, depends on the length of time the machine needs to make a weld.

 

[Robotstar5]

Had to wait until I got a PC as I couldn't see any detail on the phone. The last picture looks like the timer module, is that where the transistor was found by your sparky?. The Thyristor pack will have large mains cables connected to it going to the welding transformer and is normally mounted on an Aluminium heatsink (metal plate with fins on?) and possible a water cooling pipe fitted to it, have you seen anything like that? (may be inside machine casing somewhere).

 

[OllyO]

That's right, he followed the live to the timer/ transistor and whilst he couldn't tell me what was wrong he believed the issue was in this area.
Two lives come into machine, run through fuses then into the loom that leads to the contactor. He initially thought the later was at fault but found it to be working.
The gubbins inside the time was where he lost the live I believe.
I'll have a look for the thyristor on weds when back in the shop.
Cheers

 

[Robotstar5]

Just had a thought, it may be a very basic/old industrial welder with no thyristor pack, the welding transformer will be connected to the arms on the front with heavy gauge wire/copper and the smaller wires from the other end of the transformer could go to the small contactor you show in the pictures.

 

[OllyO]

There's certainly some monster copper wires in there going into the arms. I'm on site now but they certainly come from the direction of the transformer from memory.
Think the machine is poss early 1970s

 

[OllyO]

Can't see anything like the thyristor you describe. Tried to get a pic of the cables running to the arms from transformer.
As far as I can see there is a contractor, transistor/ timing unit, transformer and nothing else.

May take a look inside timer to see if there are any obvious loose wires that could have been dislodged during transit

 

[OllyO]

Cables

 

[Robotstar5]

The thick cables will go to a big transformer, if the thinner cables coming form the same transformer go to the contactor there is no thyristor pack fitted. A basic set up will use the timer to close the contactor sending mains voltage to the big transformer and a lower (15-20V) voltage but much higher current comes out of the other side to the welding electrodes.

 

[OllyO]

That's certainly seems to be the case following the wires entering and executing the loom.

I've given the timer to a mate of mine who's optimistic his mate can make sense of it

 

[Robotstar5]

That's certainly seems to be the case following the wires entering and executing the loom.

I've given the timer to a mate of mine who's optimistic his mate can make sense of it

It should be a fairly basic/simple circuit, no modern chips & processors to worry about. Modern ones are packed with PCB's full of chips and even communicate via ethernet!.