I have an SMPS which takes input of 220-240V, 50Hz single phase AC supply and gives an output of constant 12V DC.Its current rating is 20A. I needed constant 24V for a PMDC motor which works on about 2A current. So, I connected the outputs of 2 SMPS in series. It showed 24V but when I connected the motor across it wasn't supplying the motor any power. In the above case I was connecting both the SMPS in same phase of the main supply. Then I connected the two SMPS in different phases(just suppose one SMPS in R-phase and other in Y-phase). Now the circuit was working and supplying power to the motor. I know the results but I don't know the physics behind it. Can someone explain?
Electrical – Connecting two SMPS in series
acpower supplyswitch-mode-power-supply
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Best Answer
Your 12V DC supplies are not 100% equal. Another starts sooner than the other. Please draw for yourself a connection diagram of the outputs and the load.
See it in a new way: One power supply feeds another with reverse polarity voltage through your load. Maybe that's noticed by the safety circuits and considered as a proper reason to stay quiet.
Few millisecond delay between the mains voltage phases gives the right head lead for the slower.
Probably your system works from one phase too, if you let the PSUs start in the peace and connect the load thatafter.