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Author: Subject: Broken Stirrer & Motor Replacement
weegit_Raven
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[*] posted on 23-12-2020 at 15:13
Broken Stirrer & Motor Replacement


Like the title has said, I have a hotplate with a broken stirrer motor. It is a Corning PC-320
I would like to know what are the option i can use to replace the said motor?
Aside from normal DC brush motor (They create sparkes so i dont want to use them in the lab), what are my options?
Otherwise are there any procedures i could follow? Any suggestions and ideas are welcome.
I do have access to soldering irons and such, so they are not a problem.
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valeg96
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[*] posted on 23-12-2020 at 15:30


Can you send a photo of the broken part and the inside of the hotplate?




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aromaticfanatic
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[*] posted on 23-12-2020 at 16:15


The magnetic stirrer function is just a magnet on a motor. The difficult part is making sure the magnet can withstand the heat and the motor can too. You have also already mentioned the spark issue. I recommend looking into brushless motors that operate in your hote plate's voltage and amperage range and can tolerate the heat. Getting a brushless motor shouldn't be too difficult as they are everywhere nowadays.

If I were you I'd research high temp magnet compositions and make sure you get a magnet that 1. fits onto your motor and inside the hot plate and 2. falls into the temperature rating.

Maybe look on Ebay or similar sites for broken hot plate stirrers that are being sold to be scavenged. I would be certain that there are many with the heating function broken but the stirring function working. You could use that hot plate as a donor for parts.




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monolithic
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[*] posted on 24-12-2020 at 12:18


The PC320 uses a shaded pole motor (induction motor) so there are no brushes to spark. Have you determined why the motor died? It might be rust since Corning uses unshielded/unsealed motors. You might be able to replace the bushings or bearings and have a functioning motor. If the windings shorted out/melted you could just rewind it yourself, just measure the wire diameter and count the number of turns as you unwind it.

Shaded pole motors are used in appliances, fans, and small blowers. If you can't find the replacement part on eBay or repair the motor yourself, you could try salvaging one from one of the above sources. Box fans are probably a good starting point. You can't easily replace your PC320 motor with a brushless motor since there are a number of considerations you would have to address, mainly the integration of a brushless motor controller and adapting a high RPM brushless motor (10k+ RPM) to the required speeds (probably through mechanical gearing.)

[Edited on 12-24-2020 by monolithic]
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Dr.Bob
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[*] posted on 24-12-2020 at 12:27


I likely have a motor for a PC-320, it might take me a few days to find it, but I will look.

I have lots of various parts and pieces from trying to fix a few. Send me a note if you can with where you are located, are you in the US?
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earpain
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[*] posted on 28-4-2021 at 11:03


Quote: Originally posted by aromaticfanatic  
The magnetic stirrer function is just a magnet on a motor. The difficult part is making sure the magnet can withstand the heat and the motor can too. You have also already mentioned the spark issue. I recommend looking into brushless motors that operate in your hote plate's voltage and amperage range and can tolerate the heat. Getting a brushless motor shouldn't be too difficult as they are everywhere nowadays.

If I were you I'd research high temp magnet compositions and make sure you get a magnet that 1. fits onto your motor and inside the hot plate and 2. falls into the temperature rating.

Maybe look on Ebay or similar sites for broken hot plate stirrers that are being sold to be scavenged. I would be certain that there are many with the heating function broken but the stirring function working. You could use that hot plate as a donor for parts.


Greetings! Judging by your response you've got a knack for fixing hotplates and stirrers. And, like Dr. Bob, you understand how lab equipment works on a deeper level than most that use them.

At this point, I have been able to repair, or repurpose/transform every hotplate/stirrer I have come across. A lot of junked old ones found their way into my hands over the years.

I'm looking at a "broken, for parts only Corning PC-320. Actually the stirring is said to be working, but not the heating. I'm better at heating circuits than motor circuits for now.

Would anyone happen to know by which method the heating is controlled? bimetallic strip, triac, simple PWM duty cycle, or one of those plus a feedback circuit?
Considering buying a bunch of these things, fixing, and reselling. There's so many of them and similar on ebay.
ty!
also: Dr. Bob - also I recall you mentioning you had broken hotplates and mantels. If that's still true, would love a price quote or a brief chat.
-e
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