Determining motor size when not accurately stated 1

[Johnnkc]

I am a purchasing agent, and trying to verify the size (in watts or horsepower) of electrical motors that are used in power tools. They are typically 500 watts or less.

I suspect that our vendor is not giving us what is specified, but am having a difficult time figuring out how to gauge the size of an electric motor.

Any instructions would be really helpful. I know how to get the motor out of the product, but then what?

Thanks

John

 

[ScottyUK]

If you want a definitive answer, you need a dynamometer test. You'll need to send it out to a specialist - some of the bigger motor overhaul shops might be able to help.


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Sometimes I only open my mouth to swap feet...

 

[Johnnkc]

Is there any simple (weight-mesaurement-multimeter) test that can get you resonably close?

 

[BJC]

"I suspect that our vendor is not giving us what is specified"

If there not giving you what you specified -don't pay them. I learned a long time ago to treat required documentation just like any other part of an order. If they didn't send it, don't pay for any of it. If they don't want to pay send it back. Your PO should state what documentation is required and state payment is contingent on arrival of ALL of the order.

 

[CJCPE]

Make the vendor prove they are providing what is specified. Require the vendor to perform tests and allow you to observe. If that is not practical, evaluate the performance of the tools in typical use. Compare with competitor product and purchase the ones that do the job. Let the vendors know your intentions and expect them to act accordingly. Let the vendors know that you expect to be notified of any change in design that might effect the performance of units purchased in the future.

 

[oftenlost]

Unfortunately, a lion's share of power tool manufacturers use breakdown torque or stall torque when describing their motors. If the unit is corded in the US, it is covered by UL so the amperage will probably be right but everything else is subject to the manufacturer's desire to sell the motor. A motor which develops .75 HP at breakdown cannot operate continuously at anywhere near that value. Many power tools have this breakdown value listed as the horsepower of the tool. While technically accurate insofar as available horsepower, this figure is misleading as the tool cannot sustain such treatment and survive. The simplest method of testing small motors without a laboratory setup involves manufacturing a shaft mounted disk or cylinder, an abrasive brake, a lever arm, a voltage and current meter and a scale of some sort. I have manufactured these utilizing plywood, brake disks from an auto parts house and wingnuts to adjust load. The torque can be determined by calculating the measured load and the length of the torque arm.
These brake pads are often asbestos so care must be utilized in their use or you create another type of problem.