How hot does the motor on your mill/lathe run?

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, you need to take into account the insulation class of the motor to know if your motor is overheating or otherwise. take a look at **LINK** and **LINK** My old Chester Champion mill, the motor will get too hot to keep your hand on it even for a moment, after being used for about an hour. This has a class E rating, which equates to 120 C at its windings and assuming the temperature difference of 30 C will still allow the casing to reach 90 C. Stopping and starting a motor will elevate the temperature faster.

The plate above is on my Chester Champion Mill. Motors will always feel hotter for awhile, when they stopped after a reasonable time of running.

Regards Nick.

Edited By Nicholas Farr on 28/08/2019 07:42:23

[Dave HalfordParticipant @davehalford22513]

Nicks second link is most interesting when you find the power & current tab.

Simply doubling the current for 230V 1ph gives you 2A for a modern 1/2hp motor compared to my 1980's Brooke Crompton budget drill motor which is plated the same as Nicks Chester at 4A.

How standards have moved on.

[BazyleParticipant @bazyle]

The original post asked about 'continuous rated'. Your mill is not continuous rated. It is probably intended for 50% or even 30% duty cycle with maximum period of less than an hour.

When getting a new motor first run it for just 5 minutes so the internals don't warm up but check the bearings. They may well run hot too initially but look out for one being way hotter than the other.

Rating plates can be misleading. On electrical items like computers PSUs and radios they are the maximum possible for fuse selection not the running power. For example we use a 25W PSU on a device taking 13W-15W. The previous model took 21W so in the new model we estimated getting below 18W. Too close to risk ordering a 20W PSU so went for 25W but it still takes less than 15W owing to improved final design.

[Harry WilkesParticipant @harrywilkes58467]

Another factor that shouldn't be over looked is the number of starts per hour and the time between starts

H

[SillyOldDufferModerator @sillyoldduffer]

Posted by Bazyle on 29/08/2019 13:18:09:…

Rating plates can be misleading…

Very true! The numbers given in adverts lack all the detail needed to give more than a rough idea of a motor's performance. While rating plates are much more useful, they too fail to provide the data needed to really understand how good or bad a motor actually is.

To get that information, you need some kind person to measure the motor's behaviour over it's operating range on a dynamometer. This results in a graph that discourages advertising gloss. Manufacturers seem reluctant to publish performance graphs; presumably they think ordinary consumers don't need to know. (Which is probably true.)

However, this seller does provide Performance Graphs from which I pinched this example, a golf-cart motor:

As can be seen, the graph shows the performance of the motor varies considerably. Torque tends to drop as the Power Output rises. Peak power output occurs at about 4000rpm. Current and power output are related but do not track exactly. Although efficiency isn't measured directly, it can be inferred that motor efficiency peaks between 3500 and 4000rpm, and while running the motor slow reduces efficiency, running it much faster is even worse.

One important fact not captured in this example is temperature. Although far more informative than a few numbers stamped on a plate the graph gives no clue as to whether this particular motor is continuously or intermittently rated. As the motor is intended for a golf-cart, I guess it's intermittently rated, perhaps 60 to 80%. It's probably expected to work hard pulling a couple of chubby golfers between holes but then has several minutes to cool while they putt and tee off. Nor is there any information about vibration or expected life.

A great deal depends on the type of motor too. The AC/DC motors used on old sewing machines behave very differently from a 3-phase motor on a lathe, which is different again from a brushless motor. Perhaps the worst electric motors are the single-phase types but even they do a decent enough job as proved by many satisfied Myford owners.

Fortunately it can be assumed most motors operated in their comfort zone will be – very roughly – about 80% efficient. Big motors tend to be more efficient than small ones and modern motors are usually better than older ones. This is partly because designs are better optimised and partly because superior materials are available. Superior materials can mislead. Improved insulation means motors are run a lot hotter than was possible before. You can't just stick your hand on a new motor and decide it's too hot. It might run hot by design and heat need not mean the motor is inefficient.

Or it could be faulty. Magic smoke is always bad news…

Dave

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