[Syphonics]

Hi guys as above.
I have an old 420v 3 phase motor rated 4.2A 2200W lying around. As my power supply currently is only 1 ph, I would like to convert the 3 ph motor to run using only 1ph.
I have seen before some 3 ph motor coupled with a hugh capacitor to run the 3 ph motor using 1 ph power supply.

How do I calculate the capacitor rating?
I have a 12uf 450VAC capacitor is it sufficent?

And how do I actually connect them?
Is my circuit correct?


THanks

[jeffrey001]

Cap should be around 70uF for each HP

Should give you about 2/3 of the actual motor HP rating.

But if you can afford it, sell the motor and get a single phase motor, lot easier.


Just my tough

Jeff

[mike_Kilroy]

you have 420v 1ph available? wierd voltage.... even tho you can do stuff like this, you still need nameplate voltage and freq for the motor to work.... is this a 50hz motor? you can't just stick a different voltage on it....

[Al_The_Man]

A similar principle to a rotary convertor, you may want to tune it with caps to each phase to improve the power factor, as is done in a RPC.
AC Motor run rated capacitors are a must.
A RPC will 1 phase at first and blow the fuse/breaker if no way of starting the rotor to move is not carried out.
Check out the RPC files here http://metalworking.com/dropbox/_1998_retired_files/
With FRWx suffix.
Al.

[Syphonics]

you have 420v 1ph available? wierd voltage.... even tho you can do stuff like this, you still need nameplate voltage and freq for the motor to work.... is this a 50hz motor? you can't just stick a different voltage on it....

oh the 3 phase motor is rated 420V 50Hz
Instead of purchasing an inverter to power this 420v 3 phase motor, I intent to use a capacitor as in my attached drawing. But I did not know what size of capacitor is needed for such a motor.

[Al_The_Man]

An induction motor must when started obtain run speed within a second or two. If not it can overload fuses or breaker as I mentioned previously.
Normally to do it with a Capacitor, you require both a start and run cap.
The start cap is usually up to 10x and up larger than the run cap.
This must only be in circuit for the period of that the motor obtains run speed and immediately disconnected and the run cap is left in circuit at this point.
The start capacitor can be motor start rated as it is only in circuit briefly.
Various Capacitors values for both start and run have to be experimented with to obtain the optimum values while taking current readings.
Al.