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Old 28th Dec 2017, 12:25 pm   #1
David G4EBT
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Default Odd ripple rating of Rubycon capacitors?

Just looking to order some of the miniature high ripple rated Rubycon capacitors which I've used for some time now for stuffing can type electrolytic reservoir and smoothing capacitors. (So compact that three will often fit in a can). Not only are they compact and with a high ripple rating, they're modestly priced too. I've not noticed before, but the ripple rating as stated in the makers own data is at 120Hz and 100 kHz. Surely that's a typo which should read 100Hz - not 100kHz? Hence, the two ratings would be for full wave rectification of 60Hz (for the US) and 50 Hz AC, for the UK etc, or am I missing something?

http://uk.farnell.com/rubycon/450bxw...73390001133238

The data sheets state: Rated Ripple Current (A r.m.s./105℃) @ 120Hz and @ 100kHz

http://www.farnell.com/datasheets/21...8aAj19EALw_wcB

Huh?
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Old 28th Dec 2017, 12:36 pm   #2
MrBungle
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Default Re: Odd ripple rating of Rubycon capacitors?

It is correct. Some of these are expected to be used in switching supplies which run much faster. 25KHz+.

If you look at low ESR vs non low ESR ones, the ripple current rating is higher and the ESR is lower at the higher frequency. Normal ones don’t do so well at higher frequencies.

If you look at the BXW series they are diameter constrained as well and generally change in length. These tend to be used in switching converters in televisions where thickness vs cost is a big thing. See: https://spares2repair.co.uk/images/s...0Rev%201.3.jpg

Nice capacitors!
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Old 28th Dec 2017, 12:52 pm   #3
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Default Re: Odd ripple rating of Rubycon capacitors?

Yes they are correct, the data sheet gives a multiplier for the ripple current rating for different frequencies including 60(50)Hz (Bottom LH side of 1st data sheet):

Eg: 450v 10uf @ 120Hz = 0.13 Amps.

Multiplier for the above @ 60(50)Hz = 0.8 = 0.104 Amps.

Lawrence.
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Old 28th Dec 2017, 1:29 pm   #4
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Default Re: Odd ripple rating of Rubycon capacitors?

The mains input creates a ripple current component at 50 or 100Hz depending on the type of rectifier.

If it's the reservoir for an SMPS, then the switcher TAKES ripple current at its operating frequency. Switchers have got faster over the years. One of my designs is a SEPIC type running at 600kHz and can take a DC input of 8-60v and convert it to 50v regulated. At 600kHz you need to be sure of ESR and ESL in your capacitors. Switchers over 1MHz are getting common.

So good capacitors have specs at a range of frequencies.

David
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Old 28th Dec 2017, 2:29 pm   #5
David G4EBT
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Default Re: Odd ripple rating of Rubycon capacitors?

Thanks for the info - I was in 'steam radio mode' - never thought of SMPS!
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Old 28th Dec 2017, 2:36 pm   #6
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Default Re: Odd ripple rating of Rubycon capacitors?

Ah, just think of SMPS as ways of making efficient longwave verging on medium wave transmitters, then they fit firmly into the radio world. They just need proper screening if we want to keep the bands for radio.

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Old 28th Dec 2017, 10:13 pm   #7
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Default Re: Odd ripple rating of Rubycon capacitors?

If you are ever concerned that the ripple current seen by the first filter capacitor may be exceeding that datasheet rating (eg. for small capacitance, high voltage caps that replace vintage values of say 8uF), then I can highly recommend the software PSUD2 by Duncan Amps (http://www.duncanamps.com/psud2/) as the easiest way to simulate the current levels within typical valve power supplies.
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