how to test a capasitor

[dunny123]

Hi,could someone please tell me the proper way to test a capasitor please.Also when you change a comp and its a diffrent model and pins on comp are diffrent,how do you tell which is star winding and which is run.I know how to test resistance across windings,is the higher number the start winding,and the lower number the run winding?When i say number i mean the number on tester when testing resistance.Thanks

[Kp3]

ur start and run windings should be the most. start and common, run and common should add up to your start and run windings number. my meter (robin) has a cap tester on it. if you havent charge it with a meggar then put a screw driver across terminals to see if it sparks (old school days) sorry oldies

[frank]

The way to test a compressor for Start/Run windings is quite easy and one of the basic things to learn.

The terminals will be marked C S R (Common, Start, Run)

If you understand the basics of electricity, it is quite simple. The higher the resistance, the lower the current. If you had a direct short between live and neutral, loads of current would pass and the MCB (protective device) would trip instantaneously. If you had a massive resistance (to current flow) the the electric current would struggle to flow. This would result in a small current flow.

With a compressor, the start windings draw a large current for a short period of time and then the run winding take over with a reduced current draw. Logic tells you that if you had a compressor that draws little current to start but lots of current while running, something would be amiss.

So, we have a common terminal on the compressor that is connected to both the start and run windings then pins dedicated to either the run or start windings.

If you put your Ohm meter on the common and Start winding pins, you would get a reading. The same can be said about the Common and Run terminals. As the Start winding draws more current than the Run winding, it is expected that the Start reading would be lower than Run winding (more toward direct short circuit and lots of current draw)

If you put your Ohm meter across the Start and Run terminals, you would expect to get a sum of the Start and Run readings.

i.e. Typically

Common to Start = 4ohms
Common to Run = 8 ohms

Start to Run = 12ohms

That's how simple it is.

[dunny123]

Brilliant replys,thanks.
The reson i ask is i fit a compressor today and there where no crs i could see on the pins,and the pins was diffrent to the previous comp.So i thought you could tell which winding is which by testing across the windings.And you have give a great example that you can.Thanks

[frank]

You are welcome. Just click on my scales and add to my reputation......:D

[chemi-cool]

Here is some useful info,

http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html

{ and don't forget to click on Frank's scales......}

[marc5180]

You are welcome. Just click on my scales and add to my reputation......:D




Rep whore:D

[dunny123]

What do you mean click on franks scales?

[Yuri B.]

Hello Dunny123.
As I see on the bar bellow you are currently viewing your thread - I'll tell you how I successfully (learned from someone to) test a cap.

Turn it to the line through automatic switch (for safety) and measure current. Multiply by 14. So, if it draws 1A then it is +/- 14mF. That for 220V, however, am not sure about 110V, 127V nets.

(Only remember that start cap-s - they are black coloured - cannot be energized for more than few seconds: otherwise ba-bach! Run ones - white coloured - can be for any time)

[Yuri B.]

Have to reformulate my above post.
To find out whether a capacitor is good, A^14 = mF. Thus, the good 45mF rated capacitor should draw about 3A, 30mF capacitor - about 2A, etc.
(That for 220V, dont know what the factor is for the nets with other voltages.)

[ptsac]

Quote:

The way to test a compressor for Start/Run windings is quite easy and one of the basic things to learn.

The terminals will be marked C S R (Common, Start, Run)

If you understand the basics of electricity, it is quite simple. The higher the resistance, the lower the current. If you had a direct short between live and neutral, loads of current would pass and the MCB (protective device) would trip instantaneously. If you had a massive resistance (to current flow) the the electric current would struggle to flow. This would result in a small current flow.

With a compressor, the start windings draw a large current for a short period of time and then the run winding take over with a reduced current draw. Logic tells you that if you had a compressor that draws little current to start but lots of current while running, something would be amiss.

So, we have a common terminal on the compressor that is connected to both the start and run windings then pins dedicated to either the run or start windings.

If you put your Ohm meter on the common and Start winding pins, you would get a reading. The same can be said about the Common and Run terminals. As the Start winding draws more current than the Run winding, it is expected that the Start reading would be lower than Run winding (more toward direct short circuit and lots of current draw)

If you put your Ohm meter across the Start and Run terminals, you would expect to get a sum of the Start and Run readings.

i.e. Typically

Common to Start = 4ohms
Common to Run = 8 ohms

Start to Run = 12ohms

That's how simple it is.




http://www.refrigeration-engineer.com/forums/showthread.php?t=12956&highlight=single+phase+motor

I'm normally dealing with three phase, but I seem to remember that the start winding is of the higher resistance. hope this link to a previous post by Brian helps.