As an example: I was looking at a 10000 μF, 50 V capacitor with a ripple current rating of around 5 A at 20-120 Hz.
My transformer secondary is rated for 24 VAC, 20 A.
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3\$\begingroup\$ Perhaps you can form a rule of thumb for reasonable values of secondary capacitance. My recommendation is that you simulate your worst use case. \$\endgroup\$– winnyCommented Sep 15, 2022 at 16:10
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\$\begingroup\$ @winny not sure what you mean. can you please explain to someone who doesn't work in the electronics/electrical industry on a daily basis? :D \$\endgroup\$– mrjayviperCommented Sep 15, 2022 at 16:40
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\$\begingroup\$ Where is this capacitor going to be placed? Right across the secondary windings? Is there rectifier (half wave, full wave, bridge) in there someplace? \$\endgroup\$– SteveShCommented Sep 15, 2022 at 17:11
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\$\begingroup\$ There is a relationship between how much capacitance you need for a given voltage and power, hence you could come up with a reasonable rule of thumb value for capacitor ripple current rating to output current. Please simulate it. \$\endgroup\$– winnyCommented Sep 15, 2022 at 19:08
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1\$\begingroup\$ Upvoted because question is interesting, but OP should provide more information and a schematic. \$\endgroup\$– PStechPaulCommented Sep 16, 2022 at 0:56
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1 Answer
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Here are simulations for a 24 VAC 4 A transformer having 260 mOhm secondary with 10,000 uF capacitor and 8 ohm load. I ran it at other values as well. Your transformer would have less internal resistance so output would be higher. K factor (leakage inductance) will also affect output.
Note: Values in first column are with 1000 uF.
(edit2) Adding a 30 mH inductor in series with the input seems to be equivalent to 0.998 coupling factor. And a 47 ohm + 100 nF snubber takes care of the oscillations.
As an answer to the OP's question, there does not seem to be a great deal of a relationship between ripple current and transformer secondary current rating. Ripple current seems to be about 70% more than output current, but adding a bit of leakage inductance makes the two currents about equal.
answered Sep 15, 2022 at 21:36