Selection of SMPS with correct wattage

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Hi all,

I don't know whether this is the right category to post this question. I need to build a panel which is controlling stepper motors and has some controllers and sensors. It must be powered using an SMPS which will give you a 24V DC ouput. The confusion is how to select SMPS(Specification) for this kind of system.
If the stepper motor is rated for 4A and if we are using a chopper driver to drive it, i think motor wont need a constant 4A inorder to operate. So it there are 2 4A motors and one controller which is rated for1.5A at 24V. How to select smps with correct current output?.
Is it like 2*4 + 1.5 = 9.5A, 24V?
 

Hi,

SMPS are problematic when overloaded. The voltage drops almost immidealtely.
Therefore you need to avoid overload.

If the motor draws 4A or less ... we can´t say. YOU have to decide.
Usually a stepper has a couple of windings, be sure to take care of the overall current. And take care about worst case cenarios.
I´d try to avoid voltage drops that may cause a system reset.

Klaus
 


Motors can be thought of an LR circuit . If my motor winding resistance is 2.4ohms and inductance is 9.5mH, then time constant is L/R = 3.95. Circuit will take 5*3.95 = 19.7ms to reach its maximum current (24/2.4 = 10A). Since we are using a chopper drive, it will cut the circuit when it senses 4A.
In this case the power source(SMPS ) has to provide only 4A for a little amount of time(< ms).

So do we need to select 4A SMPS to power this motor in this scenario?
 

Hi,

So do we need to select 4A SMPS to power this motor in this scenario?
Click to expand...
if you can be sure that your application doesn´t draw more current (we don´t know) ....

Klaus
 

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