Power Factor Correction Help 230V AC

Thread Starter

cells

Joined Oct 19, 2008
34
So a switch connects the compressor to the power. Is that switch so different from a thermostat that current does not flow through its contacts? And when that current does not flow, it can not weld the contacts together during a start surge into the capacitor because current doesn't flow through the switch contacts. I don't believe that is true.

You stop the fan and the machine uses more power. Hmmm...do you think the pressures increase and the compressor works harder for lack of air flow?

As far as I am aware the machine works by regulating the working gas to the freezing chambers. So the switch (mechanical) allows the gas to flow to one of the three cambers or not depending on the thickness of the slush. That seems to be how it regulates the temperature.

The compressor (and cooling fan) does not turn off unless I switch them off. Unlike a domestic fridge which clicks on and off the compressor to maintain temp this machine seems to always be on. The power draw does vary. On start up it draws more power and once the slush is frozen a few hours later it continues to draw power but at about 2/3rds of what is was while trying to freeze it up. There are no complicated microchips or anything like that (not counting the LED lights etc) so I'm not sure how it regulates how much power to draw. I assume one the product is frozen the compressor has less real load and of it is an induction motor compressor less load sjoipd draw less power.

I am concerned about what you say but I don't think I understand it. Are you saying that the addition of the run capacitors across the compressor can cause a current surge when I switch the compressor on/off? Why would there be a surge due to the addition of the cap I thought the cap reduced the real current drawn? Is it a real concern I should investigate and how could I look into this.

When the switch is closed (compressor and cooling fan turned off) the compressor and fan do have some momentum but I am talking about a second or two until they come to rest.



'You stop the fan and the machine uses more power. Hmmm...do you think the pressures increase and the compressor works harder for lack of air flow?'

That's a very good point. I did think of that myself my guess was probably not that because the measurements we're taken very soon after start up maybe just a few seconds. The thermal mass of the condenser should I believe have kept the working gas cool for a brief period even without airflow. However its the beat guess and probably correct. Maybe my recollection of how quickly I read the meter is wrong or maybe the working fluid heats up far quicker without the fan than I am assuming.
 

Thread Starter

cells

Joined Oct 19, 2008
34
It is possible. For this reason I mentioned avoiding over compensation earlier. But at that time, the cap was to be installed to extension cord outside the machine and as tcmtech wrote, there is no over compensation issue in that case. This site has more information,

http://www.electrical-installation.org/enwiki/Power_factor_correction_of_induction_motors

From that, page:
How self-excitation of an induction motor can be avoided
When a capacitor bank is connected to the terminals of an induction motor, it is important to check that the size of the bank is less than that at which self-excitation can occur

More info is on the same page.

Can you help me out with that I've spent a couple of hours trying to understand it but I don't know enough about the topic

Is over sizing the cap really a potential problem or risk here? I Mean it is not a generator it has some momentum when turned off but comes to rest within 1 second probably less definitely under 2 seconds.

Also why would the capacitor across the compressor be any different from the capacitor in the plug just outside the machine. Isn't it effectively exactly the same circuit bit with the connection just a meter or two further from the compressor terminals?
 
Can you help me out with that I've spent a couple of hours trying to understand it but I don't know enough about the topic

Is over sizing the cap really a potential problem or risk here? I Mean it is not a generator it has some momentum when turned off but comes to rest within 1 second probably less definitely under 2 seconds.

Also why would the capacitor across the compressor be any different from the capacitor in the plug just outside the machine. Isn't it effectively exactly the same circuit bit with the connection just a meter or two further from the compressor terminals?
I think it's time for you to have a "refresher" educational moment about "leading" and "lagging" power factor and what causes the changes and shifting of power factor. See the "Education" tab at the top of this web site and concentrate on Vol. 2, Alternating current. There is a good section on Power Factor.

Regards,
 

tsan

Joined Sep 6, 2014
116
Also why would the capacitor across the compressor be any different from the capacitor in the plug just outside the machine. Isn't it effectively exactly the same circuit bit with the connection just a meter or two further from the compressor terminals?
If the capacitor is inside the machine but before the switch that supply the compressor, there is no difference. The circuit is the same. Earlier you wrote, that the capacitor alone takes 6,5 A and I thought that you have connected the capacitor behind the switch.
 

Thread Starter

cells

Joined Oct 19, 2008
34
I have discovered a problem

With the capacitor inside of the machine when the switch is turned off the capacitor discharges into the compressor and fan motor as expected. However the discharge into the fan motor seems to be dislodging the fan from the fan motor. This took me a few hours to figure out. My guess is as the cap discharges into the fan motor it reverses the direction of the fan motor (or tries to reverse it) which creates a very large torque in the opposite direction to the fan motors normal operation which seems to dislodge/loosen the bolt connecting the fan to the fan motor.

I will have to go back to the original idea of having the cap outside the machine with a bleed resistor.
I probably wasted 10 hours of time putting the caps inside the machine and now taking them outside again
 
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