STFA20
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Replacing Stirrer Motor Corning PC-320
I've had this workhorse for 15 years and I'm not ready to give up on it. After replacing the triac and the pulse generating IC, I realized that it was
the stator windings themselves that had fried.
I've got the magnet and fins sitting in pentrating oil, trying to free the piece that is keyed to the motor shaft, but I've torn apart almost all my
appliances looking for a shaded pole motor with a matching shaft diameter.
Can someone assist in finding a suitable replacement motor? I'm sure only a few dimensions and specs are used to describe these things to
manufacturers but I don't know enough about this to know how custom this motor really is... certainly not worth the price from Corning.
Thanks for your help, brothers and sisters!
It's a brilliantly simple PCB, and in my mind, simplicity is elegance.
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Heptylene
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Have you considered rewinding it yourself? You can buy enameled copper wire of any diameter online. If you can count the number of turns you can make
an identical coil.
You could also buy an identical broken hotplate on ebay, and scavenge the part you need from it. This https://www.ebay.com/itm/Corning-PC-320-Laboratory-Ceramic-Stirrer-Hot-Plate-Portion-Does-Not-Function/123736395689?hash=item1ccf438fa9:g:OwIAAOSwj39c
tLEQ for example lists the heater as non-functional but the stirrer works.
[Edited on 9-1-2020 by Heptylene]
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STFA20
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Now why didn't that come up when I searched for it? That's exactly the thing i've been after! Still a bit dear, though, for a shaded pole motor (SPM).
I mean, is there something about the slip configuration that makes stirrer motors special in some way? something that makes them less prone to
decoupling?
I had considered rewinding, but the windings are put in as a press fit in the laminated stator stack and I cant remove the windings without either
cutting the stator stack and replacing it with another similar winding from same stack thickness SPM or threading each loop of wire through the gap in
the stack by hand, which seems like a massive PITA and likely to be a crap result.
With respect to to first option, has anyone tried welding the stacked stator plates together? It would be the only way to reattach a new winding
(without the doing the threading thing), and I suspect that fusing the plates together will interfere with the induced field.
Having met a lot of SPM's lately, I can't see enough difference between either the build quility or the motor itself to justify the price of stirrer
motors, and was hoping we could figure out the language for getting a drop-in replacement for stirrer SPM's... possibly put a repair database
together, who knows.
Most of the variation between SPMs is in shaft and rotor diameter, with build quality showing up in shaft run-out. The stack thickness doesn't vary
significantly, neither do the mounting holes. I want to believe there is a $5 SPM out there that shares the same shaft/rotor diameter as the stirrer,
with a stack close enough that the magnet isn't scraping the bottom of the plate.
Thanks for the link, btw!
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Nitrous2000
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do you have any details/pictures of the circuit board?
I'm looking at a PC-320 with functioning stirrer but no heat.
How difficult to rebuild these things?
Thanks
Doug
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Nitrous2000
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Has anyone rebuilt the ceramic heating plate?
Is it even possible? IS there a fuse anywhere? 
Doug
(Does anyone have time to take a photo of the bottom (solder side) of the PC-320 board? Mine has been pretty much ‘resoldered’ by the person I
bought it from…. Not clear if there are any solder bridges I need to address). Tnx
[Edited on 27-9-2022 by Nitrous2000]
[Edited on 27-9-2022 by Nitrous2000]
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Rainwater
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Google found this https://www.ebay.com/itm/124675568530
Whats the numbers printed/stamped on the motor?
Pictures?
Winding ohms?
Total ohms?
small motors like that often have a diode or thermal fuse inline with the windings.
Its the first to go. Easy to replace.
If there is a diode, then you will have brushes too.
May need cleaning or replacing. Parts are cheap, but finding the right one is impossible.
They're easy to fab with a file and stick of graphite. Little super glue
the first time will take hours, second time minutes.
If the bearings are stuck just replace the unit.
https://www.google.com/search?q=50B2+motor
Looks like a general purpose motor, standard form factor. These prices are outrageous.
Edit:
Rebuilding the heater plate depends on its construction
If it's a thin film heater, trash it. A thin film of metal is applied to a ceramic substrate and once cracked is difficult to repair. Conductive ink
works for a time but is not a long-term solution and messes up the wattage
If it's a laid trace( looks like a PCB board) on ceramic, repairs are easy
you need to ohm out the trace until you find the break, then bridge the circuit.
For small breaks, less than 2mm
(Electroplating pen works best). High temp solder does work but is unreliable.
An electroplating pen can be made from household items and copper sulfate solution with 2 d cell batteries. 1mol solution works well. A few mL is all
that's needed. 3v, .5amp 5~10 seconds, then test the break, repeat until <.1ohm is present.
For large breaks, I will need more information to assist
[Edited on 27-9-2022 by Rainwater]
"You can't do that" - challenge accepted
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Gammatron
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These small induction motors, specifically known as shaded-pole motors, are super cheap and common and they are pretty much all the same, the only
thing that would differ is max RPM and the size of the core. They are used in bathroom fans and microwave cooling fans, if you can find one with the
same dimensions then chances are it'll work.
[Edited on 9-28-2022 by Gammatron]
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arkoma
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Glad to see this info in case mine goes south. My Corning hotplate is a wonderful piece of gear, and if it quits, our members in Oz are liable to hear
me wail out loud, and I'm in the US 
*edit* @nitrous--you don't find a pic of that PCB, holler at me, I might could be convinced to drop the bottom of mine and get that photo for you.
[Edited on 9-28-2022 by arkoma]
"We believe the knowledge and cultural heritage of mankind should be accessible to all people around the world, regardless of their wealth, social
status, nationality, citizenship, etc" z-lib
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Dr.Bob
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I just found parts of a broken PC-320, if you still need a motor, I am happy to let you try to salvage the one from it. Just let me know if you want
it.
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