Motor HP – Unusual Value on Label

[Andy_HParticipant @andy_h]

I've been looking at an electric motor. In the HP section of the motor plate it says "25M" (yes, it is "M" and not "W&quot.

Any idea what that really means?

Andy

[Andy_HParticipant @andy_h]

[bernard towersParticipant @bernardtowers37738]

Manufacturer and model plus case size might help

[Andy_HParticipant @andy_h]

This is the label. Not sure it really helps – there's no manufacturer and the model no does not yield anything on Google.

I'm wondering if it's an odd decimal notation that signifies 0.025 HP – which would be ~18W

Andy

[noel shelleyParticipant @noelshelley55608]

50Hz 1425 rpm 230v ccw rotation, continous duty cycle.. 0.53a is odd and does not tally with .25Hp ? 180watt would be .25 Hp. Could it be ex military ? Noel.

[Andy_HParticipant @andy_h]

Posted by noel shelley on 05/09/2023 12:44:20:

0.53a is odd and does not tally with .25Hp ? 180watt would be .25 Hp.

I agree.

And my thought about being notation for 0.025HP doesn't stack up either!

Andy

[SillyOldDufferModerator @sillyoldduffer]

Posted by Andy_H on 05/09/2023 16:02:15:

Posted by noel shelley on 05/09/2023 12:44:20:

0.53a is odd and does not tally with .25Hp ? 180watt would be .25 Hp.

I agree.

…

But it's about right for .125 HP (Metric)

My guess is a stamping mistake – the plate is missing a decimal point and a 1

I expect an apprentice did it!

Dave

[duncan webster 1Participant @duncanwebster1]

Just multiplying volts by amps gives 122W. O. 125hp is 95W.this implies 80%efficiency, which is on the high side for a fhp motor. BUT we've forgotten the power factor, real power isn't volts * amps for a reactive load.

I've no idea what 25M means.

[Andy_HParticipant @andy_h]

Posted by duncan webster on 05/09/2023 17:25:57:

Just multiplying volts by amps gives 122W. O. 125hp is 95W.this implies 80%efficiency, which is on the high side for a fhp motor. BUT we've forgotten the power factor, real power isn't volts * amps for a reactive load.

I've no idea what 25M means.

I think I've worked it out.

I believe the "M" denotes metric horsepower.

That's the units sussed. As for the value I conclude it must be 0.25 but with the decimal point missing.

The quoted voltage and current product is 122W which implies about 66% efficiency.

Andy

[noel shelleyParticipant @noelshelley55608]

metric Hp is Ps I think ? And a horse is a horse imperial or foreign ! I would fall for 0.125 Hp then the rest is about right. Noel.

[duncan webster 1Participant @duncanwebster1]

Metric hp is only very slightly less than imperial, so this doesn't sound right to me

[Andy_HParticipant @andy_h]

Posted by noel shelley on 05/09/2023 22:24:21:

metric Hp is Ps I think ? And a horse is a horse imperial or foreign ! I would fall for 0.125 Hp then the rest is about right. Noel.

I think PS is probably more common but, according to Wikipedia:

Metric Horsepower: hp(M) – also PS, KM, cv, hk, pk, ks or ch

Andy

[Michael GilliganParticipant @michaelgilligan61133]

So we have a 25 Metric Horsepower motor, in a surprisingly compact and efficient package

MichaelG.

[noel shelleyParticipant @noelshelley55608]

Yes Michael ! And they also manufacture free lunches ! Oh, They also build perpetual motion machines as well. Noel.

[Michael GilliganParticipant @michaelgilligan61133]

… which was the point of my

[not done it yetParticipant @notdoneityet]

It looks, to me, likely to be a synchronous induction motor of about 90 Watts? Just working on current, assumed power factor of Cos Theta = 0.8 and likely heat losses.

A pic of the motor might help. A usual 1/4 horse power induction motor would consume rather more than 1/2 an Amp and not be of fixed rotation.

As to the HP – maybe it was supplied by Hewlett Packard? (Joke)

[duncan webster 1Participant @duncanwebster1]

Surely a synchronous motor would be 1800/1500 rpm.

[Ian ParkinParticipant @ianparkin39383]

The slower speed duncan is because of slip its still a sychnonous motor

[duncan webster 1Participant @duncanwebster1]

Not according to this

A synchronous motor has magnets attached to the rotor (typically permanent magnets, but could be electromagnets and slip rings) and runs at some fraction of mains frequency, in this case it would be 1500 rpm.

An induction motor by definition cannot be synchronous

[not done it yetParticipant @notdoneityet]

Synchronous/asynchronous. Point taken. I meant the type of motor on the typical scavenge pump on a dishwasher/ washing machine. Can’t remember what they are called. Fixed direction, cheap and also found on cooker oven fans.

[duncan webster 1Participant @duncanwebster1]

Main dishwasher pump motor 3000 rpm (nominal) induction motor, I recovered one and used it on a drill grinding thing. Not well guarded, so I had to make up some covers.

[Mark RandParticipant @markrand96270]

Washing machine pump motors tend to be shaded pole synchonous motors, with a separate, dry, stator and a ferrite magnet rotor running directly in the 'efluent'. Bitter experience of such, because they get completely seized when you wash shop rags or overalls that have any cast iron powder on them. I got quite good at swapping out the saized one for a cleaned spare…

[not done it yetParticipant @notdoneityet]

Washing machine pump motors tend to be shaded pole synchonous motors

That’s the type of motor I was thinking of. Yes, pretty well synchronous, so I wad fairly accurate in my previous posts?

None of my pumps, fans, etc have run in ‘effluent’. The rotors are all in fresh air. The chinese bearings in the Meaco dehumidifiers are the worst, IMO.

[duncan webster 1Participant @duncanwebster1]

Shaded pole come in three varieties, if it has a magnetised rotor it is synchronous, if it has an unmagnetised squirrel cage rotor it is an induction motor, and isn't synchronous. An induction motor relies on having some slip to generate current and hence magnetism in the squirrel cage, and so cannot be synchronous.

The third type have rotors which have both a squirrel cage and permanent magnets. The squirrel cage gets them going, but when close to full speed, the magnets take over and it becomes synchronous. Common low power shaded pole are likely to be pure induction, no need for running at exact speed. 

Edited By duncan webster on 07/09/2023 13:01:25

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