OK, threw together a 3-phase generator using an LM324. See the attached.

It's output frequency is about 19.2kHz, which is way too fast for your motors. But I did it that way so that it would be easier for you to see the pseudo-sine wave output.

If R5 through R7 are removed, the outputs become square waves and the frequency drops to around 250Hz, which should work fine with your motors. However, the opamp alone won't likely have enough current to drive the motors.

Note that R4 sets the voltage level for the + inputs of all three opamps. This is to allow adjustment for the duty cycle of the outputs; I wanted 50%. In this simulation, I wasn't worried about getting it exact; ballpark was enough. It really needs a 0.1uF cap to ground to eliminate noise.

Note that there should be a 0.1uF (100nF) bypass cap across the supply pins. This goes for just about any IC.

Thank you for this circuit i do it and it work
Please advice me how to operate with this circuit motor in with delta connection
and can i work the motor in star connection all the time
this is my email <snip>
i hope to here from as soon as u can

 

You are trying to run a 2hp AC 3phase motor from this circuit?

 

OK, threw together a 3-phase generator using an LM324. See the attached.

It's output frequency is about 19.2kHz, which is way too fast for your motors. But I did it that way so that it would be easier for you to see the pseudo-sine wave output.

If R5 through R7 are removed, the outputs become square waves and the frequency drops to around 250Hz, which should work fine with your motors. However, the opamp alone won't likely have enough current to drive the motors.

Note that R4 sets the voltage level for the + inputs of all three opamps. This is to allow adjustment for the duty cycle of the outputs; I wanted 50%. In this simulation, I wasn't worried about getting it exact; ballpark was enough. It really needs a 0.1uF cap to ground to eliminate noise.

Note that there should be a 0.1uF (100nF) bypass cap across the supply pins. This goes for just about any IC.

OK, now we're on the same page (literally!)

I modified the circuit I put up earlier to (mostly) agree with what they have in the schematic. Differences to note:
1) Instead of a fixed R12/R13, I'm using a pot (R4) (*See below)
2) Instead of a fixed R1/R2, I'm using a pot (R11)
3) I'm using 10v instead of the 6v shown. I'll change that later.
4) A minor difference is for C5 I'm using 1uF instead of 10uF. Little consequence.

The big difference between this circuit and the one I put up before is that the previous one was designed primarily to produce square waves 120° apart, whereas this design is for producing sine-like waves 120° apart, although there is significant clipping going on.

If you look at the simulated O-scope trace below, you'll note that the frequency of the output will be roughly 0.518Hz - very slow indeed! That's OK though - it can be sped up later. Your mission, Mr. Phelps, is to get the thing working.

(*) On that very subject, I suggest that instead of the fixed R12/R13 combination, that you use a potentiometer as I did in 1) above. Initially, set it for equal resistance from the wiper to both 'ends'. You can use a 10K, 25K, 50K pot (pretty much whatever you have) but it should be a linear pot, not an audio or log taper pot. This will enable you to adjust the symetry of the waveform, but more importantly will also provide an adjustment in case the oscillator won't start on it's own - although if you've assembled things properly, it should.

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I make it thank you very much but i replace LM324 with 741 and C1, C2, C3 with 11nf it give something like 50hz
Can you advice me how to take these three phase to work motor in delta connection and this is my mail <snip>
Best regards
Osama Gaballah

 

Stop posting your E-mail address. Nobody is going to E-mail you except for "spam bots" that scour the Web for E-mail addresses.

The circuit is just an example of how to generate an approximate 3-phase sine wave using a quad opamp. It is not suitable for driving a large 3-phase motor.

 

thank you
can we replace PNP and NPN with mosfet N and P channel
i have N-channel 20N60 do u know P-channel for it