Cool down a mini-mill motor.

[Jeff DaymanParticipant @jeffdayman43397]

Good job Johan, well done.

Remember though – if you ever have plumbers working in your home or shop, put a cover over the mill or they may connect that fitting to a "working" pipe!

JD

(Seriously, the white parts look fine on the motor)

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Johan, pretty neat job I reckon.

Regards Nick.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Heat conduction between the armature and stator/casing of a metal cased electric motor is usually quite good . The metal construction, very small air gap and constant air movement all contribute very effectively to heat transfer .

With metal cased motors cooling the casing certainly helps cool the armature – simple heat sink effect . This is why many motors have ribbed casings and why some specialist motors have casings with proper designed in heat sinks using large area fins .

Heat transfer is mostly by simple conduction . Thermal Inertia effect is very small – time constant can't exceed 90 seconds and settling times must be of order of a few minutes at most .

Wound armatures do sometimes fail by bulk heating of the whole thing causing insulation failure and then shorting out but a far larger number of failures are caused by local defects in the windings . Most common of these local defect failures occurs when a length of the winding wire is in poor thermal contact with the rest of the windings . This separted length doesn't lose heat as well as the rest and runs hotter . With modest current flow this doesn't usually matter but with higher current flows ( and especially when motor is being run above its rated power ) the separated length gets very hot and fuses .

Using randomly chosen motors for dead slow plus high torque applications is always likely to cause heating problems . At dead slow speeds current drawn by DC motors is only limited by the winding resistances .

Properly designed electronics can improve matters a little but not really very much if motor is completely wrong for the application .

Older type permanent magnet motors ran hotter the older they became . This was due to gradual loss of field strength caused by magnets getting weaker with time . Modern magnetic materials are much better .Weak magnets were the primary reasons why early Hornby and Triang OO motors failed so often – magnets became weaker , current went up and sooner or later burn out happened .

When I worked at Mtu I often went over into Switzerland and that was a wonderful place to see electric motors . Many on the cable lifts and railway engines were 1930 to 1950 vintage and semi open frame with everything visible and beautifully constructed and maintained .

Michael Williams .

[Michael Cox 1Participant @michaelcox1]

Hi Johan,

That is a very neat solution and an ingenious repurposing of a WC connector.

Mike

[Thor 🇳🇴Participant @thor]

Hi Johan,

Your solution to the cooling problem of the mini-mill is very nice. Is the extracter fan very noisy?

Regards

Thor

[Johan CrousParticipant @johancrous15881]

Ultra quiet. As soft as the sound of a notebook / PC.

[Johan CrousParticipant @johancrous15881]

I have run a long dovetail cut with my homemade dovetail cutter with a single carbide tip. The motor is not getting hot, only moderately warm.

[AndyfParticipant @andyf]

Johan,

You said earlier "I am too lazy to make a big project yet, as I would like to evaluate first before I do the mod permanently, and only if it works." It seems to work very well, so don't fix it unless it falls off!

Thanks for showing such an ingenious adaptation of hardware store items..

Andy

[Author]

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