start single phase capacitor

[dear.mr.davidov]

hi
i have fan motor (230 V) without label how i can select capacitor for it.

[paul_h]

What does it do, CF motor, ducted evap motor etc?
Was this motor just laying around, or is it in a system with a capacitor already in there?
Depending on size and duty, most fan motors have 5uF to 20uF
Got any testing equipment and spare capacitors?
Normally small motors are 5uf or less (so 5uf would be fine), small ducted motors are 10-15uf, and the large 4amp twin shafts are 20uF. But most of the larger units have stuff stamped on rather than a sticker. How many wires does it have going to it?
Capacitors don't have to be exact, they are rated at +-10% from the factory anyway. But without a clue of it's size or what it does, no one can help you better.
edit: Also fans don't have a start relay, so they generally don't have start capacitors, they have a split capacitor setup.

[duarte]

Plug the motor to mains, start it by hand and mesure the current (amp's). Get another motor with the same AMP's, and get the capacytor value.

[nike123]

hi
i have fan motor (230 V) without label how i can select capacitor for it.

What is motor power? Measure current of that motor with capacitor of 20microF!
Then, you could find catalog of similar fans and by current find similar motor power, and then read what capacity have capacitor for that motor.

[kinz]

There should be a uf rateing on the motor data plate, or ring the manufacture

[rachid toufik]

hi, kinz there book called kotza, if you look page 347 ,you found how to size capacitor for motor .it is rating current x 14.+-10%. correct me if i am wrong.

[sachin230]

hi
i have fan motor (230 V) without label how i can select capacitor for it.

Basically motor capacitors perform two functions. The first function is to start the motor and the second function is to run the motor. Some motors only require a run capacitor others require both a start and a run capacitor.

You'll have to tell us the wattage or horsepower rating of the motor for us to better answer your question. Any other information regarding the motor's former use would be helpful such as ;was it used in a fan, was it used to drive a compressor, etc.?

In these two instances a fan only needs a run capacitor because the starting torque requirements are low whereas a compressor motor usually starts against a load and needs a start capacitor to increase the starting torque.

[B G Scott]

hi
i have fan motor (230 V) without label how i can select capacitor for it.

In general terms capacitors for most motors can be calculated using the formula below.

(2650 x Amps) divided by the Voltage
= Micro Farads.
Do consider the type of motor it is, capacitors are used for different reasons, dependant on the starting characteristics of the motor