Westwood2006

iTrader: (1)

I'm trying to find a couple of power factor correction (PFC) capacitors but I can only buy them in bulk!

Depending on what values I can get I'm after:

Scenario 1
78uF
468uF

Scenario 2
88uF
538uF

Can anyone help please?

kingofturds

iTrader: (1)

Have you tried ebay? I picked up a few on there a couple of years back for a rectifier circuit.

I still remember what they taught us at college, Black b******s rape our young girls but virgins go without. I doubt they would get away with that these days.

Westwood2006

iTrader: (1)

Yeah. I can only find one on there at the moment and it doesn't have the right numbers.

Lol.... I don't remember the resistor colour code being so controversial at the time. Funny how things change.

AndyC_772

iTrader: (2)

Lol I thought I was the only one that learned the sequence that way...

Can you post the voltage rating and any other details you have?

I trust you've already tried the obvious: RS, Farnell, CPC, Digi-key. I think Future Electronics now also has a site you can buy from direct in small quantities.

AndyC_772

iTrader: (2)

stupid f**king double post bug

Westwood2006

iTrader: (1)

Only has to be 110 VAC current 15A and of course 50Hz. I'm modifying the air conditioning motors on my new RV to run on 50Hz (60Hz in america)

I have a power factor of 0.62!

Haven't tried digi-key and future electronics. I'll check them out now.

Cheers.

Westwood2006

iTrader: (1)

No luck with digi-key and future electronics. Good websites though. Thanks for that!

AndyC_772

iTrader: (2)

Do you have a specific manufacturer and/or part number in mind? If so, the CIE Distributor Directory is a good way to find who sells it: http://www.ciedirectory.co.uk/site_2008/default_j.asp

Another site to try who will sell in 1's and 2's: http://www.rapidonline.com

Failing that I think you might have to sweet talk one of the bulk distributors into letting you have a small quantity; for power and passives Flint Distribution are pretty good.

The Chief

I'm a buyer in electronics, send me the manufacturers part and i'll see what i can do.

Westwood2006

iTrader: (1)

Great, thanks for the offer. I'm looking at EPCOS film capacitors - Power Factor Correction.

I can email you some data sheets if you PM me your address. These are as close as I have got so far.

50uF
Part Number: B32340C2002A830
Quantity: 12 pieces (box quantity and MOQ)
Price: £9.50 each (ex-VAT)
Availability: TBA

457uF
Part Number: B25667B2457A175
Quantity: 6 pieces (box quantity and MOQ)
Price: £66.20 each (ex-VAT)
Availability: TBA


It occurred to me. Does anyone fancy helping me to double check the calculation for capacitor values? I didn't do it my self so a double check would be great.


Here are my measurements:


Running from Generator 60Hz
Voltage – 115v
Current – 14.82A
Power factor – 1.0

Running from Mains 50Hz
Voltage – 115v
Current – 25.14A
Power factor – 0.62


The existing capacitors are 10uF for the fan motor and 70uf for the compressor.... hence the two scenarios above. One to supplement the other to replace.


70 to 538 uF seems like a big jump for 50Hz to 60Hz!!

The Chief

And i take it you only want one of each?

Westwood2006

iTrader: (1)

Yes please. That is my challenge.

The Chief

These are looking like they are quite tough to get and are a long leadtime (at least 12-14 weeks) but i'd speak to the UK branch of Epcos 01344 381510 and ask if any UK distributors are carrying these in stock, If not then ask if they carry an alternative as these may have been made obsolete, if there is not a lot of call for them they will make them to order and like you said will incure a moq.

If you would rather call or e-mail the distributors yourself here is the link to them...

http://www.epcos.com/web/generator/W...locale=en.html

Another route is to call a hard to find supplier try Phoenix Components and speak to Luke, Nice chap and will help you whereever he can.

http://www.phoenix-components.com/CONTACT.aspx

Let me know how you go on.

Westwood2006

iTrader: (1)

Coooool. Thanks so much for your time. I'll get back to you and let you know what happened.

AndyC_772

iTrader: (2)

Something's not right here. It's a long time since I did anything to do with PFC, so bear with me, and grab yourself a copy of LTSpice. It's free

Here's what I think your equivalent circuit looks like, having worked backwards to get the correct RMS current with both voltage and current in phase - and frankly there's almost no difference between how it looks at 50Hz vs 60Hz. Do you really need to change the caps at all?

Version 4
SHEET 1 880 680
WIRE 272 -32 16 -32
WIRE 416 -32 272 -32
WIRE 544 -32 416 -32
WIRE 272 16 272 -32
WIRE 544 64 544 -32
WIRE 16 144 16 -32
WIRE 416 160 416 -32
WIRE 544 192 544 144
WIRE 16 416 16 224
WIRE 416 416 416 224
WIRE 416 416 16 416
WIRE 544 416 544 272
WIRE 544 416 416 416
FLAG 272 16 0
SYMBOL voltage 16 128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 162 60)
SYMBOL ind 528 48 R0
SYMATTR InstName L1
SYMATTR Value 600n
SYMBOL res 528 176 R0
SYMATTR InstName R1
SYMATTR Value 7.76
SYMBOL cap 400 160 R0
SYMATTR InstName C1
SYMATTR Value 80µ
TEXT -18 426 Left 0 !.tran 200m

Westwood2006

iTrader: (1)

Interesting chat with Epcos. Only 12 of the 50uF are on order from a German company so I'll need to call them to blag one.

The 457uF has never been made! And anyway the factory is just being moved from Spain to India so thay have a very long lead time!

Turns out they specify capacitors in data sheets and then see if they can sell them to order!

Soooooo. I reckon this one is a blind alley. I guess I'm after suggestions for any power factor capacitors... the Epcos ones just came up in Google so I assumed they would be easy to get!

Any suggestions for make & models??

AndyC_772

iTrader: (2)

Also worth a look: http://www.allaboutcircuits.com/vol_2/chpt_11/3.html

Westwood2006

iTrader: (1)

I'm downloading LTspice now.

Originally the 115v 20A breaker kept popping on over current so I did some digging around. I thought it might be a frequency issue so to prove a point:

I have a 60Hz gen knocking around and got these readings:

Running from Generator @ 60Hz
Voltage – 115v
Current – 14.82A
Power factor – 1.0

Running from Mains @ 50Hz (via transformer)
Voltage – 115v
Current – 25.14A
Power factor – 0.62

So my conclusion was it doesn't like running on 50Hz!

Westwood2006

iTrader: (1)

Here is the electrical diagram of the a/c unit.



Here in the id sticker showing other info.

Westwood2006

iTrader: (1)

I managed to get your circuit open. Basically you are correct but there are 2 motors! I'll have to spend more time learning how to use it!

AndyC_772

iTrader: (2)

Have fun then BTW I think the inductor should be about 5mH - not that it makes much difference. I'm really struggling to see how 50Hz vs 60Hz could change the power factor quite so much...

Westwood2006

iTrader: (1)

Update:

So I managed to get hold of a proper power factor guru who pointed out that even if I corrected the power factor back to unity and brought the apparent current down to say, 18 amps or so, the current flowing through the motor would still be 25A… which means it would still be over heating and could still catch fire.. because the breaker would no longer see the dangerous over current condition!

Then I found this website http://www.lmphotonics.com/motor_50Hz_60Hz.htm which introduced me to the idea of “Voltage / Frequency” ratio. Basically, you need to reduce the voltage of a 60Hz motor on a 50Hz supply and vice versa.

The sticker on the AC unit shows 115v and 60Hz giving a voltage to frequency ratio of 1.92. Will this theory fly I wondered? Seemed too simple to be true.

Soooo, in order to prove the theory I found a 20A variac on eBay and set to doing some measurements. The results are interesting if you are into this kind of thing.... it weighs 20kg!





Volts....Current....Voltage / Freq ratio.....Power
80V..........7.1A................1.6.............. ..568W
90V..........7.1A................1.8.............. ..639W
95V..........8.1A................1.9.............. ..769W
100V........9.9A................2.0............... .990W
105V........11.5A...............2.1..............1 207W
110V........13.8A...............2.2 .............1518W
115V........16.5A...............2.3..............1 897W
120V.........21A................2.4............... 2520W
125V.........25A................2.5............... 3125W

From these results you can see that increasing the voltage from 115 to 120 increases power consumption by more than 600W!

It seemed happiest running at about 100v which by coincidence is close to the theoretical 1.92... also because of the magic of flux and stuff that I don't really understand properly power consumption is down to about 1000w from 3000!

It was then I realised the transformer I have been using gives out 130v when it should be 115! I called the people who wound it today and they are going to rework it for me and also give me 4 taps off it so I can set the voltage how I want.

Loooooong journey great result. I'm now waiting for a hot day so I can check the performance of the A/C at various voltages. I managed to blag a proper electronic thermometer that also does air flow.

I'll still correct the power factor but at least now everything is running safely and more importantly coolly.

The microwave (which is also 115v / 60Hz) is almost silent at 100v and works much better. It buzzed really loudly at 130v!

To be continued .....

AndyC_772

iTrader: (2)

OK, I think I need to openly admit that I clearly don't understand motors very well... you have a system there where the measured power increases as almost the 4th power of voltage. That's a bit scary.

I think I'll stick to designing communications equipment instead