3M Thermofax Bulb Conversion... attempt.

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Absolutely the right choice. I'm actually glad that I was able to mount the resistor - this machine will be seeing daily (professional) use in my friends shop, so a half-arsed fall-aparty solution would be no good. I took care of all lead dress and made sure all the new wires were firmly secured to the chassis before buttoning her up.

Now this guy uses $20 bulbs instead of $270 bulbs. I think he'll be OK that I spent $4 on a resistor

Mike
 
It's the 15amp "Secretary" model - it looks like this:
**broken link removed**

Can you let me know, when running yours, do you get some noisy arcing out of the switching/terminal box in the back of the unit? Mine has been doing that, but it appears to be designed to do this... the way the cover is designed on that box leads me to believe that this is normal operation. I'd like confirmation if you wouldn't mind.

Mike
 
Hey Mike,

The link you included isn't working though I'm fairly sure we have the same machine. I'm including a photo.

I hear a small click when I insert a carrier sheet into the machine. It seems like it's coming from the little mechanism that is pushed down when inserting the sheet into the front. It's not noisy at all and it's literately just a small quick "dink". Would you mind telling me which bulb you purchased and how you hooked the relay and resistor up? I would love to do this in house without sending it out. I'm happy to pay you for your time as well.

Thanks,
Doy
 

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No need to pay for my time, Doy... I'm "paying it forward"!

Yes, that's the same machine. The relay and resistor were hooked up similarly to the schematic I posted above:
-Old lamp connection (~300vac) -> 15k power resistor -> one side of relay coil. The other side of the coil is connected directly to the neutral AC line (white)
-Hot AC line voltage (black, 120vac) -> one side of relay switch. The other side of the relay switch is connected to side of the bulb that used to be fed by the 300vac line. Leave the other end of the bulb hooked into the neutral AC line (no change).

My buddy got the bulbs from interlight.biz. I've not dealt with them, so I can't say much about the company. I think there are several suppliers - the key is to look for the 115v thermofax bulbs.

The noise I'm getting is from the small white-capped box near the terminal block at the rear of the machine. When the machine is powering up, it makes quite a racket and arcs a bit. I'll check the connections... not sure if it did this before my modifications. Everything works well, though.

Mike
 
Thanks Mike.

If you don't mind, I just want to confirm the relay part number is 255-1639-ND and the resistor part number is 696-1424-ND?

Was your bulb the same length? This is the only bulb I'm seeing on interlight is this one and it's longer - https://www.interlight.biz/light-bulb/QIH115-1350/L

If you still have the machine would you be willing to send me a few more photos of the wiring setup? Sorry, I don't have a ton of knowledge on the electrical side.
 
Hey Doy - I don't have the machine anymore... sorry. Those are the correct part numbers.

The new bulb I installed was slightly longer than the old bulb, but it did fit in the bracket with the bulb springs removed.

Get the bulb first to make sure it fits in your machine, and then order the rest of the parts. You'll also need a soldering iron, solder, shrink wrap tubing and some 600v hookup wire if you don't already have all that stuff.

Careful - 300vac isn't fun voltage. Be careful in there.

Mike
 
Thanks so much. I've ordered everything and I look forward to taking it on. If it's ok I'll reach out with any questions once I get the materials.
 
 
Hey guys, so glad I found this thread. I've been fixing thermofaxes for several years now and this will be my first attempt to modify a 15 amp model. The one I've got now is the 45CG. I was wondering if you had to modify the mounting brackets since the 12amp lamps are smaller in diameter?

Not sure if you have figured out your noise problem yet rave in but if you have any questions I can look at the model I have right now and see if I can help you.
 
Good stuff Rob - thanks for chiming in. I did NOT have to modify the brackets - the bulb fit by removing the springs that held the old bulb in place.

The arcing noise I was getting came from the covered box towards the back of the unit, next to the terminal block. It would happen when the unit was starting up and pulled a lot of current, but everything seemed to work properly other than that. The box seemed designed to isolate those connections for just that reason, but I'm not sure the function of the box.

Mike
 
Hmmm, I must have a different model. I don't see the covered box you are referring to.
 

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Nope, yours doesn't have it. Mine is right between the terminal block and the transformer. Must be a slightly different model.

Mike
 
The thread lists the Digikey part numbers for the relay and resistor. Take the existing 300V power (used for the 15A lamp), run it to one side of the resistor. From the other side of the resistor, run a wire to one side of the relay coil. Run the other side of the coil to neutral. Find a 115V source from the transformer and run it to one side of the relay switch. Find the hot side of the lamp circuit and run it to the other side of the relay switch.
 
Hey Robb81 - I could use your help here. I've got a problem with the motor control circuit on mine. Right now, the motor runs at full tilt every time we run a sheet through. The speed control pot doesn't vary the motor speed at all.

I did replace the electrolytic can for the MC, and the .1uf wax cap on the board since it looked a little suspect. Everything appears to be wired correctly, and the pot checks out.

Any thoughts on where to start?
Mike
 
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