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I know that normally devices are wired in parallel on AC mains, lights, power sockets. Even in multi-adapter power sockets, things are generally in parallel.

Is there any reason the following layout will not work?

enter image description here

Here, the PSU in each device would be a small 5 V/2 A switching PSU, and the devices may be something like an ESP8266. The PSUs I'm planning to use are happy with 100..240 Vac as input.

I understand that if one of the PSU's primary coils would fail, both devices will be affected, but what else here could go wrong or be a concern?

Does the fact that these devices are quite low power devices help?

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    \$\begingroup\$ This won't work. The power supplies won't have equal input current and due to positive feedback loop on increasing input current with falling input voltage, one will end up with basically all the voltage and the other with too little. Please run them in parallel as intended. \$\endgroup\$
    – winny
    Commented May 30, 2023 at 12:38
  • \$\begingroup\$ Does this answer your question? Is it viable to connect multiple ESC units in series? \$\endgroup\$
    – winny
    Commented May 30, 2023 at 12:39
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    \$\begingroup\$ this may be an XY question ... asking for help with your solution to an unspecified problem, even if the solution is misguided ... what problem are you trying to solve? \$\endgroup\$
    – jsotola
    Commented May 30, 2023 at 14:30
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    \$\begingroup\$ 100-240 V won't help. One will (start to) pull more current than the other and the voltage will drop more and more until it restarts. What are you trying to solve that a straight up parallel connection won't? \$\endgroup\$
    – winny
    Commented May 30, 2023 at 14:33
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    \$\begingroup\$ If you stablise the centre voltage with either two, large, ordinary loads like heaters, or with a centre-tapped transformer primary, then this will work. However, you probably don't want to use those extra components. The zero-component way to do it is to connect them in parallel. \$\endgroup\$
    – Neil_UK
    Commented May 30, 2023 at 14:39

2 Answers 2

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Theoretically you could do this if your loads were let's say a couple of 110V light bulbs.

However, Switching power supplies are a non-linear (and non-constant) load so you can't assume that 220V voltage will split 50/50 between them. It could even lead to a runaway effect where for example one PSU sees a little less voltage than the other which causes it to take more current (to maintain the same power) which leads to the voltage sagging even more and so on, until it stops working due to undervoltage.

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Switching regulators with a constant output load have a negative input resistance (the current increases as the voltage drops in order to maintain approximately constant input power) so connecting them in series will quickly lead to something bad happening.

Probably one will take most of the voltage and the other will oscillate between undervoltage lockout and attempted start-up.

Connect them in parallel, as intended.

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