Transformer repair

[prepman]

I've recently bought a 2nd hand faulty welder off eBay to repair, a Draper MW151AT.

I've found that the external windings of the primary transformer are damaged. But only 2 turns. It looks as if the the set has fallen over on to it's side whilst powered up and a foreign metal body has got impaled in the windings as it shifted against the internal centre panel (the one carrying the wirefeed assembly). I reckon the mag field has pulled the panel onto the windings each time it was under load, from the description of the seller. Only blew fuses when attempting to weld.
The question is? Best way to repair. I've thought of splitting the core and rewinding the damaged tapping. But there's only 2 turns on the surface broken all the rest are fine and meter out OK.
The easiest/cheapest way would be to re-join the turns, tape and re-lacquer. I can machine copper barrel connectors or whatever on the lathe.

Question......
Has anyone done this before? If so how did you re-join? Butt solder? Lap solder? Crimps? Rewind?

 

[rtbcomp]

You're probably better unwinding the top layer an connecting the "good" end to the terminal post.

You may be able to do this without dismatling the transformer, just feed the end of the wire between the windings and the core.

 

[prepman]

The zapped bit is mid winding-ish. Not sure how many turns I'd loose to unwind damaged bit.
I found out the hard way that it's aluminium wound. Once I started using the aluminium solder I started having some success. However pulling on the joint parted the solder. Not sure if ally solder is very weak or the joint hasn't flowed. Resistance however was good (low) < 0.01 ohm. I machined 2 ally links and recessed the ends.

 

[R BEADLE]

im not been cheeky , but is it really worth going through all that trouble on a draper welder . i can understand if it was a miller or the like but come on a draper . by the time you add all your time up messing about you could have bought a new one or a good second hand one . there again you might like projects like this a challenge . good luck

 

[prepman]

im not been cheeky , but is it really worth going through all that trouble on a draper welder . i can understand if it was a miller or the like but come on a draper . by the time you add all your time up messing about you could have bought a new one or a good second hand one . there again you might like projects like this a challenge . good luck

No it's not cheeky. I understand what you mean. I retired early (58) and have a lot of time on my hands. Only want it to repair the chassis on my Trooper (My old Clarke 90 is no match). Only repairing the chassis because of the previous sentence. Trooper is SORN'd so no rush there. Might starting work again, so I'll scrap the lot and buy a new 4x4.
But back to the Draper. Are they really that bad.? I've read the comments about mig makes on the forum with great interest. I was amazed to see Clarke reviewed so well. I bought it 20yrs ago to repair a Triumph Dolomite, then a Triumph 2000 MK1.
Only bought a MIG because I was sick of setting Minis on fire with the oxy back in the 60-70's.
http://www.mig-welding.co.uk/forum/images/smilies/whistle.gif

 

[R BEADLE]

draper

draper and Clarke are still only hobby migs built with cheep components , the better welders have copper transformers with the exception of esab . but for what your doing a hobby mig is fine . they probably do a neat weld its just they wont weld all day long 7 days a week like the professional makes . good luck with the trooper

 

[prepman]

So far so good?

Managed to joint out the damaged windings, by making ally barrel connectors and soldering. Have separated joints using f'glass tape to re-tighten windings. Windings and joints are now resin coated to anchor/insulate. Stopping the windings 'dancing to destruction' is the main concern.
Biggest problem was getting the ally solder to flow. As someone else said in the forum somewhere. 'clean,clean, clean, shiny, shiny' for ally'
Looking at the rest of the machine while the resin sets. It's obvious it's had a chequered past. The spade connectors to the tappings switch have been bodged. Someone may have juggled the windings to get around the 'blown' one. This is where a diagram would speed things up.
Does anybody have one of these units? A picture of the switch/wire connections would do.

 

[prepman]

Job finished all's well.

Repairs have held and welding fine. Had to re-site transformer to accommodate hernia on windings. Added insulation plate to stop a re-occurence.

 

[R BEADLE]

Repairs have held and welding fine. Had to re-site transformer to accommodate hernia on windings. Added insulation plate to stop a re-occurence.

well done that man .

 

[prepman]

Thanks.

I must be part Womble? Weeks work + £40... saved £200 maybe? Can't get over the improvement on the Clarke 90. It has steel liner + a lot more 'ooomph'. The feed motor assembly is equivalent to the Clarke. The overall construction is pretty poor. i.e chassis and component location. Should be more bracing for the TX. The plastic ends are a pig to re-fit. I've added insulation panels to the side walls to protect the diode assembly from touching and the dividing wall for the tx.

Bit shocked to see that the main power-on relay is rated 8amps 250vac and is circuit board mounted. http://www.mig-welding.co.uk/forum/images/smilies/speechless.gif. I thought it was the pilot relay at first. Makes a nonsense of fitting a 16A 'blue-plug' ????
But it works on all settings and doesn't blow 13A fuses.

Need some 0.8mm wire, 4mm plate and some co2. My scrapped industrial co2 fire extinguisher has finally run out!
Using my 0.8mm ss wire to test it. The rollers don't like the 0.6mm.Think they're sized for gasless wire

 

[rtbcomp]

........
Using my 0.8mm ss wire to test it. The rollers don't like the 0.6mm.Think they're sized for gasless wire

Are there 2 grooves on the driving roller? There is usually a 0.6 groove and a 0.8 groove, simply remove the roller and fit it the other way round.

 

[prepman]

Are there 2 grooves on the driving roller? There is usually a 0.6 groove and a 0.8 groove, simply remove the roller and fit it the other way round.

Yes...stamped 0.8 & 0.6. Neither groove likes my 0.6 mm wire. Wire sits too deep and pressure roller doesn't contact it. Probably worn out. It was an ex-demo machine. Wire OK in the Clarke 90. I'll make a new roller if necessary and knurl the groove. Or simply buy one?

 

[prepman]

Wanted to add this but no means to. So done as a reply.
The unit is still going...the onboard relay was substituted with a SSR (Mosfet), bolted to plate and the then given away to a relative. But it's still in use! (12yrs)
Bought a Stahlwerk MIG/TIG as a replacemnt and can't fault it (10yrs ago). Have now bought a Sherman AC/DC TIG set as Stahlwerk don't ship to UK after Brexit.
That's coming from Poland. 2yrs waranty as opposed to 7 yrs. After seeing a detailed Youtube video my only concern is that the boards are mounted horizontally.
Make nice litlle shelves for dust blown in.

 

[Barking Mat]

Fair play mate !