Help! Can't buy power factor corrector capacitors!
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? |
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. |
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. |
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. |
stupid f**king double post bug :mad:
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Originally Posted by AndyC_772
(Post 9420550)
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. I have a power factor of 0.62! Haven't tried digi-key and future electronics. I'll check them out now. Cheers. |
No luck with digi-key and future electronics. Good websites though. Thanks for that!
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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. |
I'm a buyer in electronics, send me the manufacturers part and i'll see what i can do.
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Originally Posted by The Chief
(Post 9420618)
I'm a buyer in electronics, send me the manufacturers part and i'll see what i can do.
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!! |
And i take it you only want one of each?
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Yes please. That is my challenge.
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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. |
Coooool. Thanks so much for your time. I'll get back to you and let you know what happened.
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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 |
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?? |
Also worth a look: http://www.allaboutcircuits.com/vol_2/chpt_11/3.html
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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! |
Here is the electrical diagram of the a/c unit.
http://lh5.ggpht.com/_-7yvTt9T-Mc/S_...00/Diagram.JPG Here in the id sticker showing other info. http://lh3.ggpht.com/_-7yvTt9T-Mc/S_...ing%20info.JPG |
Originally Posted by AndyC_772
(Post 9420686)
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 :)
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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...
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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! http://lh3.ggpht.com/_-7yvTt9T-Mc/TB...800/Variac.jpg http://lh5.ggpht.com/_-7yvTt9T-Mc/TB.../The%20Rig.jpg 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 ..... |
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 :) |
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