Hi All,
previously posted on the Stan Curtis 60W Class a Thread.
I'm pretty new to this, so would like to ask a few questions:
I'm going to make a pair of these and in relation to smoothing caps in a PSU, the example above uses 2x 15000uf 'Sprague 36D' caps rated at 50V. These are obsolete, although there are new versions available and similar caps also available from other manufacturers. So I have a couple of questions if I may:
Whats the effect on a transformer feeding two of these giants as opposed to say 8 x 4700uf in parallel? in regards to the rectifier, is the charging time for the smaller caps quicker?
As a reference PSU, my Electrocompaniet EC25's have 4 x 4700 uf for one side feeding one set of rails (I think) and two 2200uf on the other.
I hear references to ripple current and ESR, the larger value caps do have higher ratings for both Ripple and lower ESR - certainly in the examples I'm looking at. Ripple is quoted at 100Hz. But what is the effect when smaller caps are in parallel? Do they smaller caps values add, multiply or neither? So if the ratings do add or multiply - this is better?
I have plenty of space in the chassis I'm using so either is viable, but I'd be interested in your thoughts.
Kind Regards
Joe
previously posted on the Stan Curtis 60W Class a Thread.
I'm pretty new to this, so would like to ask a few questions:
I'm going to make a pair of these and in relation to smoothing caps in a PSU, the example above uses 2x 15000uf 'Sprague 36D' caps rated at 50V. These are obsolete, although there are new versions available and similar caps also available from other manufacturers. So I have a couple of questions if I may:
Whats the effect on a transformer feeding two of these giants as opposed to say 8 x 4700uf in parallel? in regards to the rectifier, is the charging time for the smaller caps quicker?
As a reference PSU, my Electrocompaniet EC25's have 4 x 4700 uf for one side feeding one set of rails (I think) and two 2200uf on the other.
I hear references to ripple current and ESR, the larger value caps do have higher ratings for both Ripple and lower ESR - certainly in the examples I'm looking at. Ripple is quoted at 100Hz. But what is the effect when smaller caps are in parallel? Do they smaller caps values add, multiply or neither? So if the ratings do add or multiply - this is better?
I have plenty of space in the chassis I'm using so either is viable, but I'd be interested in your thoughts.
Kind Regards
Joe
2x15000=30000
8x4700=35600
Capacitors in parallel add in capacitance value and don't change in voltage or ripple current rating. ESR is resistance and so reduces in parallel according to r1*r2/(r1+r2).
8x4700=35600
Capacitors in parallel add in capacitance value and don't change in voltage or ripple current rating. ESR is resistance and so reduces in parallel according to r1*r2/(r1+r2).
couple of youtube videos to check out from eevblog:
"caps in parallel" #742 and "psu ripple filtering" #1116
"caps in parallel" #742 and "psu ripple filtering" #1116
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The 8x4700 will likely have lower ESR overall, meaning sharper current pulses from the transformer, more potential for ringing and transformer saturation. If your transformer can handle it though, and if you use a snubber for any potential ringing, the 8 parallel caps with lower total ESR would likely have better high frequency filtering as a benefit. You could also add resistance between the transformer and bridge rectifier to slow down the current pulses, with the benefit of less sharp current pulsing, and better high frequency filtering. Negative of this is that those resistors drop a bit of voltage, so your rails wouldn't be as high voltage (may be a good thing or a bad thing). The lower heat generated in the 8 parallel caps may also prolong their life in comparison to just a pair of 15kuF caps.
Many thanks for the replies. I shall take a look at those videos. I'll also have a look at whats on the EC PSU board to see if it has anything novel between the BR and Caps, but I know there's nothing between the ( Huge ) transformer and Bridge Rectifier.
Joe
Joe