Building my understanding of the issue from (First PSU - need help with capacitor size) (especially the comments/ripple wiki/several capacitor sizing webpages) the calculation for rectifying a full wave bridge rectifier at 50A 16V should be:

$$\frac{50A}{2 * 60Hz * 2V (Ripple)} = .208333$$ Converting from F to uF, I get $$.208333*10^6=208,333uF$$

So I should get a filter capacitor close to 0.21000uF at greater than 30V (Peak/rounded/safety margin)? This is my first time doing such calculations, are there any glaring errors? I know that the person several people struggled with some of the complexity, and I'm not sure if my interpretation of some of the variables (particularly dV) is correct.


1 Answer 1


Err, no, I think your last step there is off.

$$ \frac{50\text{A}}{2\cdot 60\text{Hz}\cdot 2\text{V}} = 0.2083\text{F} = 208333\mu\text{F} $$

That's a huge capacitor. Or, more likely, huge bank of capacitors. (Edit: as it turns out, there are plenty of capacitors > 200mF and > 35V. However, they are expensive, and about the size of a Mason jar.)

Are you sure you want to be designing a 50A bridge rectifier? There are likely better ways to design a 50A AC-DC converter.

Also, how crucial is the 16V output? I'm guessing the 16V accounts for voltage drop on a regulator, so does 15V regulated out work? Because there are power supplies that can provide 15V @ 50+ A (see this XP Power PSU for example).

  • \$\begingroup\$ Yeah, I just noticed that it was one more digit off than I thought. That sucks. Order of magnitude difference. I'm not sure what method is best for AC to DC conversion at that high of a current. I can increase the ripple size to 5V & decrease the current to 40A which makes the system more manageable at 66,666uF. \$\endgroup\$ Apr 7, 2016 at 3:59
  • \$\begingroup\$ Does it absolutely have to be a monolithic supply? It'd be a lot easier to build a few ~25A power supplies. Also, see my edits. \$\endgroup\$
    – uint128_t
    Apr 7, 2016 at 4:12
  • \$\begingroup\$ Actually, I've finagled together a microwave oven transformer (rewound for 16V) and am using it with a bridge rectifier to run 40-50A DC through various electrochemical projects. (Which depend critically on current) So far, I've only paid $10 for the bridge and about $5 in connectors. (I found the MOT on the street) It works rather well (for about 5 minutes before it gets too hot), but doesn't produce a reasonably constant voltage, and currently only uses the absolute value of the sin function. \$\endgroup\$ Apr 7, 2016 at 4:45

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