# capasitor



## RIVETER (Sep 26, 2009)

zrul said:


> someone can tell me function capasitor 840C4(20uF 450V) at diagram


It is a bypass capacitor.I blew up the schematic, now I changed my mind on what it is.


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## John Valdes (May 17, 2007)

Google it. It's spelled capacitor.
Its in the motor power circuit, so thats about all I can get from your drawing. In the US we usually use motor capacitors on the motor and do not show them on the schematic. Honestly I do not know. Sorry.


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## zrul (May 17, 2010)

it look like static converter rite..


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## ElectricArcher (Feb 25, 2010)

What is this schematic of? Is it controlling a sychronous motor?


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## MDShunk (Jan 7, 2007)

I have a feeling it's just to increase torque.


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## John Valdes (May 17, 2007)

I think its a remote start cap. Wheres Rob when you need him?


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## RIVETER (Sep 26, 2009)

John Valdes said:


> I think its a remote start cap. Wheres Rob when you need him?


That is why I changed my mind about it. When the circuit is expanded you can tell that it is in series with one of the windings, but I can't tell if, or when it drops out.


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## micromind (Aug 11, 2007)

It's obvious that it's a 3 phase motor, and looks a lot like a synchronous one. But I don't see any control for the DC injection.

It's equally obvious that it's reversible. It's possible that the capacitor is there to introduce a phase shift, and cut back on torque when it's plugged (thrown in reverse when it's still turning forward). 

It's hard to tell without the rest of the drawings though.

Rob


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## RIVETER (Sep 26, 2009)

micromind said:


> It's obvious that it's a 3 phase motor, and looks a lot like a synchronous one. But I don't see any control for the DC injection.
> 
> It's equally obvious that it's reversible. It's possible that the capacitor is there to introduce a phase shift, and cut back on torque when it's plugged (thrown in reverse when it's still turning forward).
> 
> ...


Peter D. said he knows the answer but he is starting his own web site and use it as a draw.


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## John Valdes (May 17, 2007)

micromind said:


> It's obvious that it's a 3 phase motor, and looks a lot like a synchronous one. But I don't see any control for the DC injection.
> 
> It's equally obvious that it's reversible. It's possible that the capacitor is there to introduce a phase shift, and cut back on torque when it's plugged (thrown in reverse when it's still turning forward).
> 
> ...


Thanks Rob, As usual you did make some sense of it all. :thumbsup:


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## zrul (May 17, 2010)

it use for webbing up tape for printing...like cassate tape or old video tape VHS,when motor rewind 1 motor use 3 phase to rewind tape and the same time one motor use 2phase (like digram) for support or some thing...i dont no...what effect the motor torque,speed when motor running 2 fhase like that...


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## micromind (Aug 11, 2007)

If a 3 phase motor is connected to single phase power, it will develop zero starting torque and maybe 20% running torque. 

A capacitor in an AC circuit will cause a phase shift, but not complete loss of a phase. 

If a 3 phase motor is connected to two good phases, and one that's shifted from normal, it'll develop less starting torque as well as less running torque. How much less depends on how far the phase is shifted from normal.

I suspect that the capacitor is only in the circuit during starting, then it's shunted out when the motor is up to speed. Its purpose is to reduce starting torque. If full starting torque is applied, the machine might start too fast, and break the tape.

Rob


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## Mr.C (Dec 20, 2009)

I agree with you Rob that they are using the contactor on the right to reduce torque possibly for starting and that the cotactor on the left is a cross the line contactor for full speed or torque, though I don't think they are reversing this motor (at least not with the circuit shown). It kind of reminds me of a dipper trip on a shovel only insted of having a resistor bank in line with each phase to reduce torque this tape machine is using 2 phases with 1 phase cap shifted to supply the third leg. Now on a shovel the reason you would use a resistor bank in line with each phase is because you want the motor to always spin applying a little torque to keep its load under constant torque until you need more torque then you shunt them out for full torque. It's interesting that given the type of application this is used on that there not using a dc motor. Now ZRUL you got everybody curious about this circuit and I would like to see more of the schematic, could you please show us some more of it?
Rob have you seen this 2 phase caped third phase used in industry before and if you have whats the application? If you have not do you think that this would work reliable on something like a 10hp motor? I would like to try this perhaps it would be easier on the motors versus the resistor banks.


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## micromind (Aug 11, 2007)

I've seen the phase shift capacitor used on very old cranes. It's pretty rare, usually the older ones have a wound-rotor motor and resistors to weaken the field and thus reduce torque.

I got the idea that it could reverse from the 845K2 contactor (in the center of the drawing), and the contactor on the far left and center. It's hard to tell though, to know for sure you'd need to see the rest of the drawing.

Rob


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## Electric Al (Mar 13, 2010)

Sorry. I can't remember which thread it was, but I asked about phase protection for 3 phase motors. I found the piece of equipment I was looking for. 


CONTROLAB INC. D.S.P. 1 L

Thanks again guys....  Is anyone else familiar with this product ??


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