Inrush current for 775 motor and power supply

Thread Starter

r2m

Joined Aug 8, 2018
3
ECFD5291-5F0C-4ECB-B531-F71D25F1A24C.jpeg I have two power adapters and, this may be a dumb question, but one of them is triggered off because of a high inrush current of a 775 dc motor, and the other has just a smooth start and is working ok. The power supply that works ok is 2A and the one that shuts down rated as 4A
So... what’s the deal?.. is one switching power supply the the other is not?

8CF474F8-EBE7-4C89-9E7B-6A88C8BEBBF6.jpeg
 

Hymie

Joined Mar 30, 2018
721
Both are switch mode power supplies – this is evident from the input voltage range 100-240V~.

It is likely that the motor inrush current is sufficient to cause a momentary overload condition which is causing the 4A output rated unit to shut down.

You could confirm this by adding a small resistance (say 2Ω) in series with the output.

You might find a low resistance NTC device that you could wire permanently is series with the output that would not compromise the motor performance.
 

MaxHeadRoom

Joined Jul 18, 2013
19,463
Bit ridiculous rating for that motor if it is the RS-775 at 43.9amps stall current!!
Easy to check by applying low voltage to locked rotor and measure the current.
Check different spots for lowest reading.
Max.
 

Thread Starter

r2m

Joined Aug 8, 2018
3
Thanks for the answers.
I tried, of course, with both, 2ohm resistor and NTC, just to verify, both worked well, resistor is taking too much power and the NTC getting hot because the one I have is not suitable for these currents, but what amazes me is that I also tried with a 38A power supply of an old IBM workstation, and it also going into current load safe mode! So I really don’t understand what is so special in the small PS?
 

MaxHeadRoom

Joined Jul 18, 2013
19,463
Maybe goes into a type of current limit mode until motor starts to rotate, the faster this happens the lower the current.
Max.
 
Top