how to measuring a capacitor(230-380)

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100kwh-hunter

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Just like the title.
It is about a capacitor of a electro engine, 1 phase "food" to threephase "need"(to get the phase shifting going)
it is a 3 phase (380v) engine that must run on one phase (230v)
I have a strong suspicion that due to time (and Abuse)and frost the capacitor is not capable to do its job anymore.
How can i measure it...just to be sure.

I am not willing to haul my oscilloscope(yes the old type, the boat anchor), only my good multimeters. :cool:

Thanks in advance
 

daromer

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Pick a multimeter that can meassure caps. Or perhaps i dont understand the question?
 

100kwh-hunter

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image_sgfeob.jpg
This is my best multimeter


The motor is used for a transporter beld.
The storage is in a shed where the temperature has free play, but its dry.
About 10 years of age.

It kinda lost its power when running.
 

ajw22

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Nov 16, 2018
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In case you don't know what a VFD drive is:
eg.
https://www.aliexpress.com/item/32987238577.html

Takes AC (1phase in this case, but many take 3phase) as input power, converts it internally into DC, then outputs 3 phase AC as output (just like an inverter) for the motor. The fun part is that you can adjust the output frequency (ie. motor speed), voltage, ramp up/down speed slowly, reverse rotation, etc. It's also very easy to connect it to sensors and various controllers.

I use one to control the speed of a cooling tower fan. A temperature sensor feeds data to the VFD, and it adjust the fan rotation speed to keep the temperature in a certain range. Saves a us lot of power/money.
 

Korishan

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ajw22 said:
I use one to control the speed of a cooling tower fan. A temperature sensor feeds data to the VFD, and it adjust the fan rotation speed to keep the temperature in a certain range. Saves a us lot of power/money.

Can you make a new thread with info on this build? I'm curious as to what you've done and how you did it. Saving power is always a good thing :)
 

100kwh-hunter

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I had a idea what i should be.
But this thing is very good looking altou i dont think its practical.
A similar alternatief was over 300 euro's from one to three phase.
Can i measure the capacitor in a way with my multimeter posted above?
Or is there a alternative?

thanks
 

Redpacket

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If the capacitor is one that came with the motor, it is either a "motor start" or "motor run" capacitor.
A "motor start" cap is only connected briefly during start & centrifugal contacts in the motor disconnect it once running.
A "motor run" cap is connected all the time.
Both cap types cause a second coil winding to get a different phase (timing) of the AC current to increase torque (twist force) of the motor.
This type of electric motor are not three phase, more like two phase.
Both caps types do degrade with time & use.
My dishwasher motor wasn't starting properly & the wash (if it did start!) seemed weak.
I bought a replacement cap for $5 & all good again. Original one was about 8 years old.
They are available cheaply from appliance repair companies or large electronic chains.
Make sure it is rated for motor run/start use and the same uF value and voltage as the original part.
They usually have several hundreds of volts on them when running & are made of "self healing" stuff to be safer & last better.
To test one, power off, remove it from the motor, connect it to a multimeter on the uF capacitance range. It should be within about 20% of the label value.
 

100kwh-hunter

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@ redpacket....
Clear as spring water, thanks.
The capacitor was original on the motor, i had a idea it was getting to old, judging by your story it is a running capacitor and not start up, i did not know that, this difference on run and start, i thought only start or phase shift(timing).

But all my multimeters don't have a uf position, is there another way to measure?just curious.

Btw i am going to buy a new capacitor anyway,.11 euro.
 

Korishan

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For testing those types of capacitors, set to Ohms, 10k or 100k, and probe. If the meter just keeps going up to infinity fairly rapidly, then the cap is good. If it takes it's sweet time or tops out at a value, then it's basically dieing.
 

Korishan

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The probe is the exposed metal tip that's connected to the DMM. And 'to probe' is to use that tip and connect to the terminals of the capacitor, in this case. ;)

Being an AC capacitor, it doesn't matter which probe connects to which terminal. If the capacitor has 3 terminals (start and run built into 1) then you should get continuity between the common and one of the other terminals.
 

Korishan

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Redpacket said:
The cap needs to be disconnected from the motor or the meter will just see the windings (=short or low ohms)

Yes, this would be important. Thanks Redpacket, I forgot to mention this as being needed in the testing. The cap needs to be out of circuit for sure.
 
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