Capacitor esr

[Joebiker2011]

Hi, I'm building a resonant tank and need a high current capacitor. So Ive found that I can use a multiple of polypropylene capacitors.
15nF 2000VDC 700VAC https://www.electro-tech-online.com/custompdfs/2011/12/mkp385.pdf

Now I will be creating a bank of either 200 or 300 in parallel to make a capacitance of 3µF or 4.5µF. The bank will be running at about 500Vrms at 500Arms, frequency range 30 to 100kHz. My question is, how much will they dissipate in heat.

I have found the tangent of loss angle in the PDF of 0.0005 at 10kHz and 0.0015 at 100kHz. Now ive found out that tan(θ) × Xc = ESR

Now this is the part I'm confused at. does 0.0005 = tan(θ) or is it tan(0.0005).
What powers do people get at 10 and 100kHz at 3 and 4.5µF

Thanks

 

[unclejed613]

reading the pdf, it looks like tan(θ)=0.0005

i get 0.5305 ohm at 10khz for the 15nf cap, and 0.1575 ohm at 100khz. divide these values by 300 (the number of caps in parallel) for total ESR of the bank. with this many caps in parallel, the wiring resistance will be a bigger concern

 

[Joebiker2011]

Those are the values that Ive been getting. I have sorted the wiring out and it shouldnt be too much of a concern, the long boring part is soldering them together and water-cooling the whole thing.

Thanks for your help, much appreciated.

 

[unclejed613]

so for a ballpark figure, it looks like each cap will dissipate 0.5W or less in ESR losses. how are you generating 250kW at 30khz? did you find an old Alexanderson alternator in your barn or something?

 

[RCinFLA]

I would not use a metal film polypropylene capacitor for such high current. They are basically plastic sheet with thin metal deposited on the surface. The metalization has relatively high sheet resistance that is causing the poor dissipation factor.

Use a metal can, sealed motor run capacitor.

 

[The Electrician]

You don't want to use a large number of small capacitors wired in parallel; get larger capacitors, such as found in the links below.

https://www.electro-tech-online.com/custompdfs/2011/12/MKP_B32774_778.pdf

For the size and current you describe, you would be better off to use capacitors specifically made for high ripple currents, such as:

**broken link removed**

**broken link removed**

 

[Joebiker2011]

Hi, its an RLC resonant tank, my input power will only be about 5kW.

Motor run capacitors are far too large, the inductance and resistance will be too high because I would need very long bus bars. Its for an induction heater, the large industrial heater caps are infact polypropylene - just too expensive unfortunately.

@ The Electrician - I'm trying to keep cost minimal and those larger capacitors are a bit too expensive although I will keep looking.

Thanks

 

[unclejed613]

my grandfather always drilled into my head "the right tool for the right job", and that usually applies to electronics too..... especially with anything running in the "KILL-O-WATT" range..... any mistake you make with components here can be disatrous.....

 

[ronsimpson]

https://www.electro-tech-online.com/custompdfs/2012/01/WIMA_MKP_10.pdf Look at the picture on the first page.
wima.com
I have used wima capacitors for high voltage high current applications with good luck. They have application notes on using these parts in CRT monitors, they show current and voltage graphs.