Weller TCP junk-box mod.

[FRANK.C]

My Weller WTCP 51 iron stopped working, cleaning the magnastat contacts restored operation, but I remembered reading a thread by Kat Manton suggesting it would be a good idea to take the heavy current away from the magnastat by using it to control another switching device thereby prolonging the life of the magnastat .
I thought now was a good time to try and do something along those lines while there is still some life left in the magnastat.

I found a 24V DC relay in the junk box and made up a bridge rectifier from some IN4007 diodes to provide DC to it. This simple circuit was mounted on a PCB along with a snubber for the relay contacts. There are some plastic clips on the inside of the front to accept a PCB and the PCB was cut to suit these. The circuit worked well but the noise from the relay was objectionable with a click every 10 seconds or so.

Another rummage in the junk box was called for this time I found a BT139 Triac and a 330 resistor for its gate. The PCB was reused to mount these components on. It's working away now nice and silently. The only downside of using the Triac is that there is approximately a 1.5V drop across it, but this hasn't made any noticeable difference when using it.

Frank

[davegsm82]

Thats a really good idea, I like it.

I'd be tempted to connect one side of the heater element to the earth and use that feed as the earth return, then use the actual earth wire as the switched feed back to the triac as you've done in the picture.

Sometimes the element can fail such that there is leakage between the earth and heater, in this case that would mean the triac could start to fire continuously.

Dave.

[FRANK.C]

Hi Dave
That's a very good point, I will swap them around.

Frank

[love kt3]

hi,my weller is wired like that but thrugh a solid state relay,with the 3 wires as com, element and switch and a brige and resistor and zener accrose the ssr input.since 1996 i replaced the magnetostat once only,before that evry year.(i think i posted the idea in Kats thread)

[FRANK.C]

Hi love kt3
It's good to know that it dose extend the life of the magnastat.
I seen your post in Kat's thread but I am not familiar with solid state relays and I used just what I had to hand. Indeed at 800V and 16 amps a BT139 is a bit OTT for this application.

Frank

[love kt3]

hi,a solid state realy is a block with a triac controled by an opto isolator,with current limit on the input.the one i used was from an industrial psu,input 3 to 30 v,output 250 v at 25 amp with zero crossing switching.i had it on hand and it simplyfied the circuit.youre circuit is just as good.

[FRANK.C]

Thanks for explaining, never came across one. Sounds like a handy device.

Frank

[McMurdo]

I've done this mod this week to my TCP. At £25 trade for a new magnastat, I'd got through 3 or 4 in the space of a month, (after years of using the factory-fitted one). I tested the element, the transformer, current consumption etc, and decided the magnastats were simply a bad batch. Examination showed the fault was the plastic actuating plunger being made of a soft plastic that allowed the circlip to fall away when they got hot due to the contact current.
The last (warranty) magnastat that RS sent me was faulty out of the box (read o/c before use with bit fitted) so I gave it up as a bad job.

I used the SSR method, using the earth wire as the switch wire. I haven't earthed the element at all, since the PSU is a double insulated version (including split bobbin transformer with 2-core mains lead) and when you ordered the power supply, you could get them in 2 versions: one with element earthed to mains (and 3-core mains lead) and the other with the element just connected to an ESD point on the front panel. Since Ive never used this point, I utilised the earth wire in the lead for the switch signal.
If you have the ancient type power supplies with non-double insulated transformer then for safety the element should be earthed of course.

This is the diagram of my mod.
It's worth mentioning that the iron power supply is physically split by a plastic barrier into mains and isolated sections and so the mods should be contained in the isolated section and regard taken to making sure the barrier is not breached under possible fault conditions eg detached wires or melted components.

[evingar]

Originally Posted by McMurdo

The last (warranty) magnastat that RS sent me was faulty out of the box (read o/c before use with bit fitted) so I gave it up as a bad job.

I have to confess that I've developed an anti Weller bias since Cooper Tools quit the UK. Had a lot of trouble supporting some not very old equipment at my last place, both in respect to getting parts and also having to deal with poor quality replacement when we could actually get them !

[McMurdo]

My replacement parts all came from RS and they were only too happy to replace them ad-nauseum until the inconvenience in a busy workshop demanded a permanent solution.