Constant Torque 1000:1 vs. 2000:1

[moosetracks555]

I am selecting a vector motor for an application, and one motor has a 1000:1 constant torque and the other is 2000:1. What does that ratio represent, and which one is better?

 

[jraef]

The ratio is the speed turn down ratio within which you can expect the motor to operate without running into problems with temperature. So if you have a 4 pole 1750RPM motor rated for 1000:1 CT, it means that you can turn the speed down to 1.75RPM and expect it to still perform to spec. with full torque and without overheating (provided adequate cooling is provided) when using a vector drive. The one rated for 2000:1 would then be able to be run at .857RPM.

The difference represents the accuracy with which the motor is constructed, especially the laminations, air gap and bearings, plus the heat dissipation capability. By having better designs, there are less iron losses (eddy currents) and so the motor runs cooler to begin with. They they also design the heat transfer capabilities to not rely upon fans, because at those speeds you have no fans anyway. The difference between those two motors is, however, kind of like spitting hairs IMHO.


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[ozmosis]

moosetracks555
What does your application need? If your application only needs 3:1 constant torque then both motors may be overkill and overly expensive for your needs.

 

[DickDV]

As jraef mentions, whether the motor is spec'ed at 1000/1 or 2000/1 is probably meaningless. You can expect either of these motors to operate successfully at full rated torque down to essentially zero speed without overheating.

 

[jraef]

Yes, meant to say that too, thanks Oz. I just helped someone with a project where the Engineer specified 100:1 rated motors on pumps. But when you look at the pump performance curves, the VFDs will never turn down below 50%. So the extra expense of 100:1 rated motors vs 10:1 or even 3:1 rated motors is a waste.


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[moosetracks555]

This is a lifting application, and I need the vector motor to stop the load from back driving the gearbox. I have tried a standard motor with no luck. I have a 1000:1 vector motor that works great, but the 2000:1 is cheaper, and I have 10 more to purchase. Thanks for explaining what the ratio means.

 

[jraef]

Don't forget that cheaper is not always necessarily better. There is no free lunch, so unless the first motor supplier is trying to bite off a disproportionately higher profit margin, I would be at least initially suspicious of a motor claiming to be rated higher yet costing less. Sometimes manufacturers do what I call "Targeted Specsmanship" where they target specific specs that they know customers look for or are industry buzzwords, but make cutbacks on other important yet unfamiliar design considerations in order to sell for predatory prices. Major motor manufacturing costs are primarily in materials and workmanship, and material costs are essentially based on commodities.


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