Is it safe to connect inputs of two Power modules in series?

Question

I need to convert a 600VAC to 24VDC in the most compact way possible to put on a PCB. Is it a promising idea to connect the inputs of two or three of the following modules in series to achieve it?

https://mx.wiautomation.com/mean-well/fuente-de-alimentacion/IRM205

I'm more concerned with your concept of *600VAC to 24VDC* AND *compact*. — StainlessSteelRat, Apr 19 '22 at 11:29
@StainlessSteelRat, I say compact because it is a portable device that I want to make. — SKGadi, Apr 19 '22 at 14:23
I do understand the meaning of compact, but based upon the nature of your question, I am not sure you understand the implications of main voltages and isolation, which is dangerous! — StainlessSteelRat, Apr 19 '22 at 14:26
@StainlessSteelRat, I am thinking of making a PCB, then applying conformal coating, then placing it inside a plastic enclosure. — SKGadi, Apr 19 '22 at 14:43

score 1 · Answer 1 · answered Apr 18 '22 at 21:37

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No, you will need to find a converter that will run off of 600VAC or, more likely, use a transformer to step 600V down to something an off-the-shelf converter will be able to use.

answered Apr 18 '22 at 21:37

vir

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What is the reason? Why is it different from a passive element like a resistor, capacitor, or inductor which I can use in series? Or Am I wrong with the passive elements as well? – SKGadi Apr 18 '22 at 21:55
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I'm sure others can add more reasons but off the top of my head, the input to each of the converters goes through a rectifier and you are essentially connecting each of them in series. For diodes in series to share voltage drops equally, you need to add components across them (resistors, Zener diodes, etc) to account for reverse leakage current. Without these extra components, it's possible that one or more of the diodes would experience an inverse voltage in excess of its rating. The normal failure mode in this case is short, which would cause a cascading failure of the remaining diodes. – vir Apr 18 '22 at 22:09
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@SKGadi The power modules are designed to adjust their input current to deliver the required amount of output current. If one of them tries to demand less current, it will get more voltage, and then probably reduce its current even more until it gets way too much voltage and blows up. Connecting resistors or incandescent lightbulbs in series would be fine, but it's a bad idea with complex electronic devices. – user253751 Apr 19 '22 at 11:12

hacktastical · Answer 2 · 2022-04-19T19:05:59.897

tl; dr: no, it isn’t safe.

Say you do what you’re proposing: modules with their primaries in series. One of them has a max load, one has no load. What do you think will happen? Answer: very likely the one with no load will see nearly the full line voltage and blow up.

In other words, PSU ‘input resistance’ varies with load. Were you thinking to tie the outputs in parallel? That’s not workable either, regardless of what you do with the primaries.

Even if somehow you could wire the outputs together, the voltage rating from primary to secondary isn’t able to withstand 600VAC (peak voltage about 850V.) It would likely fail, arcing over to the secondary.

So, hell no.

You need a transformer to step the primary voltage down to a range this PSU can work with. It needs to be rated for 600V, which means it will be somewhat bulky due to the stronger insulation it needs to handle that voltage. It can be located off-board, which is a good idea anyway to keep 600V away from your sensitive stuff.

Is it safe to connect inputs of two Power modules in series?

2 Answers2