HV soft start

[Trileru]

Well, I don't know... you didn't specify how much ripple is required, and apparently you haven't been consistent about what current draw is required, because I now see that the maximum requirement is up to 350mA! 😱 😱 And you've been showing considerable worry over this inrush issue, while at the same time, you haven't asked the important question: how much inrush is actually tolerable?

Indeed I haven't mentioned mentioned the needed current. The amp will draw a max of 350mA, with an idle of 200-250mA.

FWIW, the fusing current of copper is a great many times the steady-state rating, and that still requires a sustained second of fault current before it finally opens up.

Indeed, the location shown is not the most likely failure spot. It's open to air, and is connected to a large metal lug, which provides additional heatsinking. The most likely spot is deep within the winding, where wire is surrounded by wire, all of it very rapidly heating up if a short circuit occurs. So any given piece of wire, down in the center, only has to heat itself up, and doesn't have to overcome any heat conduction to its neighbors, because they are all heating up as well.

But an ampere peak, and tens of milliseconds? Your worries are misplaced. You can go more like tens of amperes and whole seconds before that thing smokes! 🙂

This is good info, lack of experience doesn't help me. It's good to know this.

The limiting elements are probably the capacitors (which are rated for some amount of surge voltage and current) and rectifier diodes (which are rated for exactly this kind of surge, usually around 20A for diodes this size). You should worry more about your power switch, because it will spark a little bit, each time you turn this on; but that's just a matter of getting a big enough (5 or 10A?) switch, no worries.

Tim

The current surge rating of the caps is something I worry, and that's why I found it unfeasible to use a small cap for the first position. Couldn't find any with a high enough rating.

Thanks once again for the info, it's been good learning!