Backyard Aquaponics
A place to discuss aquaponics

NOTE: INFORMATION IN THIS SECTION IS THE OPINION OF THE POSTERS ONLY, DO NOT ATTEMPT ANYTHING YOU READ HERE UNLESS YOU HAVE A CLEAR UNDERSTANDING OF ELECTRICAL PRINCIPLES, ARE AUTHORISED TO CARRY OUT ELECTRICAL WORK AND ARE COMPLYING WITH LOCAL REGULATIONS
Steve


Ok, Steve here is the formula.


The top formula is for calculating resonate frequency. The bottom formula is for solving the capacitor value. Please note in solving for the capacitor value you must use enter the frequency in thousands of hertz; kilohertz. This is for two reasons. 1, it makes the output value = the cap size in uF. Second, it makes the numbers fit on the calculator screen.

The most dramatic examples of how a resonate tank circuit can reduce power draw by resonating locally and not through the meter is with a fan/blower motor. You can often reduce amp draw my 75%. I am going to work an example here using windows calculator. I will use brackets [] to denote key press other than numbers.

First, I measured the inductance of my well pump. It measured .022 H or 22mH.
Second, Enter the inductance in henry. .022, press sqrt button (0.14832396974191325897422794881601)
Third, [*] 2 [*] 3.14 [ent] (0.93147452997921526635815151856457)
Fourth, [M+]
Fifth, [C]
Sixth, .060 [1/X button] Line Frequency in KHz (16.666666666666666666666666666667) 50 in other countries
Seventh, [/] [MR] (17.89277766622192373265633430033) [ent]
Eighth, [MC][M+] [*] [MR] [ent] (320.151) This is the Capacitor value in uF or .000320 Farads so we would use a value of 320 uF. Now in the example given here for my well pump I was able to reduce amp draw by 20%!

You can now use the top formula to double check the values; only the frequency value will be in Hertz. Always a good idea in case you hit a button wrong.

To wire the capacitor to the motor simply place in parallel to the two power input wires on the motor, BEHIND the switch that controls the motor so the caps are not always powered up. If you are running more than one motor at once then you can wire them all together and measure the total inductance and calculate accordingly.

Use run capacitors. Start caps will blow out as they are not rated for continuous duty. Air conditioner supply house or any supply house that sells electric motors will have capacitors. I always like to get the 440 volt caps because they seem to laster longer, but if all you can get is 330 volt then go for it. Most likely you will not have a single capacitor that has the value you need so you will need to wire several in parallel. If you dont know what than means then PM me. The common cap sizes here at my supply house are 5, 7.5, 10, 12, 15, 20, 25, 40, 45, 50, and 80 uF. The most space saving way would be to use 4 each 80uF caps, but the 80 uF cap cost a lot more than the very common 40 uF caps; $36 vs $8. So, being cheap as I am I opted for 8 40uF caps on my well. Also check ebay for run capacitors. Now if you need some odd value just get as close as you can. The closer to the correct value the less power will be drawn. Now, about power draw. If the motor is fully loaded then the power saving will be less. The 75% power reduction of the fan motor is because its not loaded. Just like a bell that is ringing the more you dampen it, or load it the more you have to strike it to keep it ringing. Same thing with a tank circuit. My air conditioner for example is pretty well loaded down so I can only save about 10% amp draw on the compressor. So, basically what Im saying is, you mileage will vary... For you blokes on 50 Hz power grids, sorry but you will require bigger caps than those of us on 60Hz so you will have to pay more to do this trick; 50 Hz on my well would have required 461 uF, for example. So you may want to consider salvaging for a source of caps just make sure you have them tested with a capacitance meter.

*Footnotes:
*1) This is not power factor correction per say. Its setting up a resonate tank circuit that, like a bell, will ring locally and not pass full load back and forth between your motor and the power company's generators (through your meter). There will also be some measure of power factor correction.
*2) Measure your inductance as accurately as possible.
*3) You can switch in and out small capacitors to fine tune performance. Just watch your amp meter. The further you get from perfect resonance, on either side of the value, the more power will be drawn. This is, of course, dangerous if you do it live with the motor running.

after reading that a few times i actually understand it!

Good thing that you put in the not power factor correction but tank cct, made it much clearer along with the unloaded comment.

i have done much reading on resonance. i love N. tesla

If forgive you for the wiring caps comment its surprising how many in the trade dont know how to work out series and parallel caps

thanks dan

What kind of motor could this be used on?
(i'm assuming it isn't ye olde squirrel cage motor)

Dan would be the one to answer 100% but i'd be leaning to answer any type of single phase motor configured as permanent split phase (run capacitor) and possibly split phase with the best savings on motors that are not "loaded" heavily such as blower motors for ducted heating units.

how did i go, dan?

mmm, that was my next question - about the loading of the motor.

just saw the prices you posted for caps

i'm fairly sure last time i bought a 50 uF it cost about $48 trade.
25uF are about mid $20's ............will have to check now

You did good steve. This can be used with any AC motor single, double or tipple phase. I just bought some 30 uF caps for $5 at my local trade supplier.

something wrong here. picked up 20uF two days ago for $12.......................

might have to start using D-D-M as a import source............

Yes, it seems my supplies are exploiting some poor country to sell us caps at a price that could not cover the cost of shipping. Best of all due to planed obsolescence they will fail at the first lightning storm or after so a year or two of hot summers as does any good mexican or china made product. Non-the-less I'll give them a try.

gotta say, i'm happy with our 440V ones. much better than the shite ones in the Chinese import a/c's that fail after a few 40C summers.

picked up a beefy 50uF for $40 today. wish they all had 4 terminals x2..............8am jobs gonna need bp connectors and some splicing......