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# What's inside an electric motor tester dynometer, CAN I BUILD ONE?

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#### Electro nS

##### Full Member level 6
whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

hello guys

i basically understand the idea of a dynamo meter , input power and output power from an electrical motor to determine its characteristic curve . now i can measure input voltage and current , and output speed , but the problem is output torque ! how can i measure the output torque ( or braking torque ) without stopping the motor , and what type of brake is used to apply torque on the motor in actual dynamo meters .

i want to build one , since they are expensive , the motor size is 200w to 2000w
thanks for any help , if you think the post should be moved somewhere else please advise

Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

The following method might not be safe to use with your motor size, but it illustrates a concept for measuring.

In a mechanical engineering class we attached a clamping device around the turbine shaft. The clamp was made so it could apply greater or lower pressure to the shaft. This was done by an adjustable spring in the clamp.

Either we tightened the clamp so the turbine could just barely rotate, or we made it run at a certain speed. At that moment we read the spring pressure. That gave us a measurement of torque. It was not in the correct units, but it did give us a number, so we could compare one turbine's performance to others.

You may need to test torque by attaching various loads, and observing motor rpm. It is risky to stall the motor by attaching an immovable load.

Electro nS

### Electro nS

Points: 2
Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

thanks . that device could work ,
i want to measure the performance from no load speed all the way to stall , collecting about 15 points of speed/torque to draw a curve .
i am thinking of a similar method but instead of the clamping device i wound attach to the shaft a bicycle brake and measure the toque with a dynamic contactless torque sensor , what do you think are these sensors cheap ?? ( my range is from 2N.m to maximum of 30N.m )
what do you think guys

Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

what do you think are these sensors cheap ??
Unlikely.

A more basic method is a torque weighing mechanism, mount the motor or the brake rotatable around an axis aligned with the shaft, use an arm to apply the force to a balance.

Instead of a mechanical brake, an AC or DC generator with variable load resistor can be used.

Electro nS

### Electro nS

Points: 2
Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

Unlikely.

Instead of a mechanical brake, an AC or DC generator with variable load resistor can be used.

can you give more info or reference on this method does this method eliminate the need for torque sensor ??

Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

"can you give more info or reference on this method does this method eliminate the need for torque sensor ??"

With this method the amount of power the generator makes is the torque sensor. The problem is calibrating it. If this is in house only for comparative force between different motors you can just use the power generated as a torque number.

Electro nS

### Electro nS

Points: 2
Re: whats inside an electric motor tester dynometer , CAN I BUILD ONE ??

Primarly, the generator is used as a variable load. For precise torque detreimination, you still need a separate measurement. The torque of a DC generator is basically proportional to output current, but there's an error caused by friction.

Electro nS

Points: 2