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Author: Subject: magnetic stirrer problem
soma
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[*] posted on 23-6-2017 at 02:01
magnetic stirrer problem


I've got 2 magnetic stirrers. They both heat up after being on for over an hour. This is a problem because I want to run a reaction for over 12 hours stirring at room temperature and this would raise the temperature beyond what I want.

Is it normal for mag stirrers to heat up like that?

One of them is a combination stirrer hot plate and the other is just a stirrer.
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alking
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[*] posted on 23-6-2017 at 07:01


How hot are we talking? Mine will sometimes generate electricity with prolongued stirring but never any heat. Is it possible to work around, say insulating the base of your flask with something with poor thermal conductivity? You could also put it in a water bath to help maintain the temp and switch it out if it gets warm.
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soma
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[*] posted on 23-6-2017 at 14:11


I had been thinking of using insulating material. The stirrer gets to around 40C. The stirrer/hotplate gets to over 50C. Hopefully, the wires inside the stirrers aren't going to melt.
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[*] posted on 23-6-2017 at 15:03


I wonder why it gets so hot. I can't imagine it's simply from friction alone, or at least not by design, that seems so wasteful. That's a substantial amount of heat generated simply from rotating a small piece of metal.
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[*] posted on 24-6-2017 at 00:50


I'm thinking of taking it apart and oiling it.
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[*] posted on 24-6-2017 at 09:12


You don't have it on any kind of dimmer circuit by chance do you? Or is it a sketchy power source supplied to your work space?

The stirrers often use shaded pole induction motors, which are built with an intended frequency and voltage in mind. Dimming them with circuitry not built in or specific to the motor can be problematic = heat or lack of torque. Likewise, I assume if your work shop is an out building with a long extension cord or under rated standard wiring, there may be too much voltage drop.

Other than that, I'd say something's wrong. Pretty darn hot for a stirrer or shaded pole motor. They are usually just laminated core with a diecast pot-metal ends for holding the rotor. Not much to heat up by friction. But lubrication isn't a horrible thing. Some have an oiling point built in, others have sealed bearings and won't help. have seen a bronze looking babbit bead trapped in oiled felt as a bearing, others have standard roller bearings and more of course. They are in things like bathroom fans, microwave exhaust, oven hood and more for many years... Lots.

Good luck




Sauce
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soma
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[*] posted on 25-6-2017 at 02:22


I took it apart and it doesn't seem to need oil. The motor looks like a small standard fan type. It's not on a dimmer and the outlet it's plugged into is 20A 110V 3 wire.

I think the problem with it (this is mag stirrer without a hot plate), is that they didn't put any vent holes to cool it. (And, of course, there's no vent fan on the bottom of the motor either.)

I'm thinking of drilling some holes in it at some point.

It's a Fisher Scientific stirrer. Seems fairly old. Got it from ebay for $25.


[Edited on 25-6-2017 by soma]
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