Service Factor Less Than 1

As the manufacture, they / we can say or do anything. But, with that type of service factor (if correct), it would not make me want to install one.

Never heard of such. To me that would mean that the motor can be safely run at 1/2 of the rated amp draw/output of the motor.

Actually there are, and thats when to get the desired output, the ratio either compromises the gear box or motor SF.

It does happen.

Spot-on. I'd say that it can meet the customer's requirements of speed & torque, but only at half power input. Presumably the supplier has nothing else to offer (at a reasonable cost).

Intermittent duty?

I once worked on a 500HP motor that was rated on the nameplate to be started no more than once per day, for no more than 15 minutes run time. It was custom designed for a very specific paddle type exhaust fan application originally, my customer bought it used for $500 and wanted to put it on a Banbury mixer. 500HP motor, 1-1/2" shaft!

I had a hard time explaining to him why he had been able to buy that at such a bargain basement price but couldn't use it. It really was only worth the copper in the windings.

at 500 Hp, he should have gotten his money out of it?

I think so, but he was not willing to scrap it, he kept insisting that if it was rated 500HP it was 500HP and he wanted to use it. He believed that intermittent duty rating was a lie to get people to spend more money than they needed to, because HP is simply a torque speed relationship. I was trying to explain it to him by equating this to those consumer tools where they say "develops 3HP" on something like a cheap compressor but when you look at the nameplate it says the motor is 1500W. It will put out that high torque momentarily, but that doesn't mean it can sustain it.

I walked away, I didn't want to be around when that shaft broke or the motor smoked.

ahhhh, I see..... you lips are moving but nothings coming out attitude.

There are plenty of small motors in satisfactory service with a service factor less than 1. However, the manufacturer needs to specify the duty cycle in absolute terms (example only, 10 minutes ON / 10 minutes OFF) because the time to heat the windings to maximum acceptable temperature must be specified.

Many small German motors have the vague notation "AB 10/10" but the user may be unaware of that meaning in the standards. Such a motor will overheat the windings if run for 30 minutes, and if it survives, will not cool satisfactorily in another 30 minutes, even though 30/30 is just 0.5 duty cycle.

So, 30/30 duty will kill a motor with service factor 0.5 but with maker's spec AB 10/10.

Motors designed for compressor service also will have a service factor less than 1 and should also specify the maximum starts per hour. Your ratio of air storage to air demand will control the frequency of starts. Your air demand alone will control possible conformance to the service factor.

Mark Bingham
Relativity PL

Why don't you give us the name of manufacturer and full nameplate information as well as the type and power of machine driven by it.

The service factor for a geared motor gives you an idea how "strong" the gear box is build.

If I'm building a gear box and I have to transmit a given torque, I can design the output shaft in different diameters (20 mm, 25mm or perhaps 30mm). The same with the gear wheels and the bearing size.

If chosen right, all the combinations will work.

But if you have an APPLICATION

• that needs a lot of starts / stops per hour,
• that has severe momentary variations in the desired torque,
• that even can make the gear motor work as an generator (lot of inertia during deceleration).
• that has a combustion engine drive.

One can imagine that the "lightest" built gear will fail the soonest.

The service factor gives you an idea of how the gear is built. It has nothing to do with the duty cycle of the electric motor. (continuous duty, intermediate duty ..)

Service factor for gear boxes :

----------daily work ---- less 0.5 h ---- 0.5 till 2 h ---- 2 till 10 h ---- 10 till 24 h

type of load: normal ---- sf 0.8 -------- sf 0.9 --------- sf 1.0 -------- sf 1.25

------ light overloads ---- sf 0.9 -------- sf 1.0 --------- sf 1.25 -------- sf 1.5

----- heavy overload ---- sf 1.0 ------- sf 1.25 --------- sf 1.5 -------- sf 1.75

This means that a gearmotor with sf 1.25

• if used in an application 24h/day with a normal load or
• if used in an application only 2 h/day but with heavy overloads,

will have the same 'life time'

If in you application, the gearmotor 0.75kW 40 RPM is choosen much to strong, and the application is running very smoothly, than it is possible to use it.

Related...

In the EV world it has become common to specify motors by peak HP, because that gives a better comparison to engines which are also rated for peak output. In a practical sense this works well, because Tesla, with its 225 hp motor accelerates like a car with a 225 hp motor. The same motor in industrial use would soon overheat, if used at 225 hp.

Used as an industrial motor, the Tesla motor would have a sf of perhaps .3... or even less. Some EV motors are rated for 1 minute peaks.

Earlier in my career, I did a stupid mistake of sizing servo motor by HP than by torque.