ESAB MIG welder output thyristor control

Thread Starter

jeka616

Joined Jan 14, 2009
131
Good day folks!

It has been a while since my last visit in this forum, so hi to everyone I knew few years ago..

I've recently been given (as a gift, could not have been better:) ) a MIG welder, Esab 502, internals..i.e. power transformer, and output diods+thyristors I believe)

Please see the pictures attached.

I was hoping it had taps on primary side, but not. The control is done on secondary side.

There are black and red wires sticking out, I think these are for thyristor control. Also 2 grey one, I guess for thermo signal

Question is, can I drive this monster by just adding PWM based on 555, and 1 IRF540 (may not be even needed).?

Logic is to have thyristor open for period of time, which should control the volts and amps

I've got the circuit diagram, but it does not show details, i.e. it just says "control board"
 

Thread Starter

jeka616

Joined Jan 14, 2009
131
And here is the schematics,

there are no details of actual components..I would not guess to have one either on instructions manual
 

Attachments

Thread Starter

jeka616

Joined Jan 14, 2009
131
It seems pretty straight forward..secondary, + power diods 3 phase bridge, and thyristor control of output

what factors should I consider while bulding PWM for thysirtor? I've been reading around forum, and have info about gate drive voltage, should not exceed +3 volts. And it takes about 80-100mA to hold open the thyristor (therefore I don't think irf 540 is required, 555 should be able to drive gate)
 

Thread Starter

jeka616

Joined Jan 14, 2009
131
Gents

Ive taken apart the output stage, and this is what stands at the heart of rectifiers/regulators. Seems like some type of power thyristor/SCR.

There is no name or part number on it. Can't find similar even looking subjects around the www, so I can compare

It has 4 leads sticking out, red/black- pretty heavy, I bet this is control leds. And 2 grey ones, pretty skinny, have no clue what they are for


If anyone knows what these are called exactly so I can get datasheet, please let me know.

Regards

J
 

Attachments

shortbus

Joined Sep 30, 2009
8,043
Maybe try giving what you are wanting to do with this, with your add on "circuit". The part you are wanting to know about in the last post, where is it on the schematics you showed in earlier posts? Some things like that are not "off the shelf" things, but a proprietary part only used by that manufacturer for their product.
 

Thread Starter

jeka616

Joined Jan 14, 2009
131
It is V1 , on the schematics on post #3

Its a power thyristor to control the output voltage/amps. Pretty simple to understand, but just dont have any part numbers or etc to know exactly what it is, in order to get a drive circuit built for it
 

Alec_t

Joined Sep 17, 2013
11,737
Looks to me like the part in question is a potted array of parallelled power devices (SCR or whatever). I'd guess the heavy red/black wire pair are for driving the gates and the grey pair are for sensing the voltages at the device terminals. I doubt a 555 would have enough oomph to drive that!
 

shortbus

Joined Sep 30, 2009
8,043
Its a power thyristor to control the output voltage/amps. Pretty simple to understand, but just dont have any part numbers or etc to know exactly what it is, in order to get a drive circuit built for it
How do you know that is what is bad? Are you sure it isn't the controller its self? You still didn't say what your trying to do, is this a repair of a nonworking machine or a modification?
 

Thread Starter

jeka616

Joined Jan 14, 2009
131
Looks to me like the part in question is a potted array of parallelled power devices (SCR or whatever). I'd guess the heavy red/black wire pair are for driving the gates and the grey pair are for sensing the voltages at the device terminals. I doubt a 555 would have enough oomph to drive that!
Im on the same page, the heavy wires are for driving.

I've got IRF 540 at the output of the 555, so basically it is a simple PWM for DC motor control. I guess it should be enough to drive em.

Originally red somewhere in the forums that power thyristors need about +3v to drive em. So I had 7805 to power the PWM, thus limiting max output voltage to around 4.8v

And the found that some power thyristors are driven between +4v till 32v.

So next step is to get rid of 7805, and increase voltage

Will come back with results soon
 

Thread Starter

jeka616

Joined Jan 14, 2009
131
How do you know that is what is bad? Are you sure it isn't the controller its self? You still didn't say what your trying to do, is this a repair of a nonworking machine or a modification?
Im trying to revitalize welding machine. which has power transformer, power diods for rectifying current, and power thyristor to control output. the missing part is thyristor drive

bad news is the thyristor does not have any damn part number nor details..so I have no clue what type or model it is.
 
Top