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What Capacitor to be Used?

06/04/2011 5:40 PM

I'm using a gear-motor with the following specs:

3-phase, 200v to 220v, 0.2Kw (200 watt), 28 rpm, 50-60 Hz, Amp 1.1 to 1.2, continuous, 4 poles.

What should be the U.F and volt of the capacitor to be used with this motor?

current capacitor is of 12UF and continuous but the number of volt is not printed on it.

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#1

Re: What capacitor to be used?

06/04/2011 6:17 PM

Why use a capacitor at all on such a small 3Φ motor? (The power factor correction it might provide would be pretty small.)

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#12
In reply to #1

Re: What capacitor to be used?

06/05/2011 12:14 PM

they say..in Japan...3 phase 220volt is equilant to Asian single phase 220volt.

please check the description for volt in the answers. at #3

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#2

Re: What capacitor to be used?

06/04/2011 6:37 PM

It's a three phase motor and doesn't use a capacitor. Three phase motors generally show the volts in star connection and also the volts in delta connection. It's possible that this is 415v/220v or maybe 220v/127v .

It's possible on smaller motors to simulate a single phase capacitor run type of motor by connecting live and neutral direct to one winding and the capacitor in series with a second winding. Some circuits show a three phase motor say U,V,W with L to U, N to V, and L through a capacitor to W. The 12 MFD capacitor looks to me to be used in this way, a capacitor run motor would be nearer to 2 or 3 MFD, there are circuits via google.

The value of the capacitor is not critical as the phase difference is never what it should be, the volts rating is important and I personally would go for 400vac rating.

I would go for it with the capacitor you have, perhaps with a 5 amp fuse in series, as well as circuit breaker/overload relay for the total current. You could test the capacitor & fuse across 220vac without the motor to see if it holds up, then go ahead with the complete circuit.

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#11
In reply to #2

Re: What capacitor to be used?

06/05/2011 12:09 PM

I've given detail of rmp for the motor only(without gear). at #3

Go through it and decide what volt and uf capacitor to be used.

currently its on 12uf BUT has not been checked under load, was checked to see that the motor starts. The motor is used, good condition.

Basically, the capacitor seller has asked me these question and he does not understand the answer by my given information.

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#3

Re: What capacitor to be used?

06/04/2011 6:54 PM

To know the most performing value of the capacitor you need to communicate the speed of the motor before reduction. You'll need this for the calculation.

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#10
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Re: What capacitor to be used?

06/05/2011 12:03 PM

O.k

the speed of the motor, under different conditions, is as follows:

v 200 200 220

Hz 50 60 60

Amp 1.2 1.1 1.1

rmp 1410 1700 1720

is this of help??

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#4

Re: What capacitor to be used?

06/04/2011 6:59 PM

4-pole = 1800 rpm (less slip) @ 60Hz, 1500 rpm @ 50Hz.

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#5
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Re: What capacitor to be used?

06/04/2011 9:54 PM

The motor he has is a 3-phase type.

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#6
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Re: What capacitor to be used?

06/04/2011 9:58 PM

Already acknowledged in Post 1.

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#8
In reply to #6

Re: What capacitor to be used?

06/04/2011 11:09 PM

Sorry, but thanks

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#13
In reply to #4

Re: What capacitor to be used?

06/05/2011 12:18 PM

check #3 for volt detail....then let me know the answer; what volt and uf capacitor?

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#16
In reply to #13

Re: What capacitor to be used?

06/06/2011 4:03 AM

It doesn't need one.

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#7

Re: What capacitor to be used?

06/04/2011 10:15 PM

Check "Steinmetz"

Here the formula:

C= P X 10^6/ 2 Pi (=3.14) X f X 0.87 X U^2 X n

C= capacity in MicroFarad

P= Power supplied (rated) Watts

10^6 = (6 zeros)

f= frequency in Hz

U= voltage in volts

n= efficiency (rendement)

in this formula you don't need the RPM figure.

enjoy.D

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#14
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Re: What capacitor to be used?

06/05/2011 12:24 PM

looks great

but....whats steinmetz? and rendement? how to calculate n (efficiency)?

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#18
In reply to #14

Re: What capacitor to be used?

06/06/2011 6:54 AM

Just use a 20μF with a 400V rating and save everyone the trouble.

Efficiency is not calculated but measured unless given by the maker: You can conduct some trials and estimate it and then this is another story...

This motor looks like a dual speed or something like that... Because if it is a proper 3phase, you would not need a capacitor to run it. The number of wire terminals coming out of the motor does not necessarily mean it is a 3 phase.

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#23
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Re: What capacitor to be used?

06/13/2011 12:34 AM

Steinmetz is the "intellectual owner" of the principle and schematic to connect a 3 phase electro motor to a 2 phase net (in some countries called single phase net)

The third phase gets its power through capacitor, connected to one of the phases.

Rotation can be switched using phase 1 or phase 2.

Normally the rotation field in a 3 phase motor requires a 120 degrees shift between the phases. The capacitor provides a shift, but not one 120 degrees. In principle 90 degrees when a "perfect" capacitor is fitted. For this reason the motor will also NOT perform equal to as used on a 3 phase net.

The original Steinmetz method had been developed for motors with 2 coils, the formula has also the relation of the numbers of the work- and resp. starter coil.

for n in your application take a value between .93 and 1.

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#9

Re: What Capacitor to be Used?

06/05/2011 10:16 AM

It's a three phase motor.

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#15

Re: What Capacitor to be Used?

06/05/2011 10:46 PM

A capacitor in a 3phase motor can reduce starting current surge if connected during starting only and correct pf as well as reduce starting current if connected permanantly.

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#17

Re: What Capacitor to be Used?

06/06/2011 6:53 AM

He has three wires and one capacitor.

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#19

Re: What Capacitor to be Used?

06/06/2011 8:44 AM

I know what not to use.. a light bulb..

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#20

Re: What Capacitor to be Used?

06/06/2011 3:13 PM

How can a 3 phase motor have 4 poles? It should have some multiple of 3.

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#21

Re: What Capacitor to be Used?

06/06/2011 5:17 PM

Wow!

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#22

Re: What Capacitor to be Used?

06/07/2011 3:26 AM

Hi Bob, I am not sure that the motor, that you have is a three phase motor!

Have you been able to run the motor, even for a breif time? What current was it drawing per Phase? Have you attempted to dismantle the motor to see if it have a start centrifugal switch?

I have heard of motors such as you describe but I have never seen one, the only motor that I have heard of that implements this kind of wiring was a refergent compressor motor but I have never seen one (so i have put them down as an urban mith).

Have a look at the motor terminal connections, there is 6 connections?

1.Are only 4 of the terminals connected by 2 links?

2.Or are there 3 terminals connected by 2 links and 3 terminals by themselves, or is their three links connecting 2 terminals each?

If the answer is 1 then it is single phase

If the answer is 2 the motor is 3 phase, and does not require a capactor.

Cheers

Joe

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#24
In reply to #22

Re: What Capacitor to be Used?

06/13/2011 11:17 AM

its a 3 phase G. motor by nessie, Japan u can check it on net. I have not opened it yet but will open it once my mechanic gets time. will let you know what is inside of it..will try to post its pics tooif possible.

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