Stepper Motor operated valves ....and max. power?

[schnell]

hello

apologies for length of this post.

it is nothing complex, it is just that i am trying to find out what is the maximum power drawn by stepper motors in my system.
The system is like a domestic shower, where valves in the hot and cold pipes are moved with stepper motors.

There is one valve in each pipe...
-and one stepper motor for each valve.

The stepper motors are as follows:- (UBB1/5, 6V, 18.5 Ohms per phase)

http://www.auf-vertrieb.business.t-online.de/pdf/UBB.pdf

We will be driving the stepper motors with this driver (NJM2673)

http://www.cn.njr.com/PDF/NJM2673_E.pdf

..its an efficient switch mode stepper driver.

Currently, the steppers are running from power provided by a 50Hz transformer based PSU.
-it is my job to replace this 50Hz transformer based PSU with an SMPS.

-However, first i must know what maximum power the stepper motors draw.
-then i can design the SMPS.

The engineer who spec'd the 50Hz transformer based PSU has left the company, and we do not know if he calculated the necessary power properly.

There is an added complication............

supposing that the steppers draw a very high peak power for a very short time in their operation.
-it could be argued that the SMPS would not need to be rated for this peak power, because the energy stored in its
output capacitors could (if they were big enough) supply this short interval of high power.

...however, this is not the case for us......our output capacitors must stay at least at 36V and no less at all times,
because otherwise they will not have enough energy in them to allow the steppers to close the water valves in
the event of a mains power failure.

-so our SMPS must not suffer transient drops in output voltage when the steppers endure their maximum power operation.

i.e. whatever is the steppers peak power draw...that is the power at which the SMPS will be rated.

So, ....i am getting nearer my question...................

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QUESTION 1 :-

Out of these following stepper motor operations in this system, which one will result in the stepper motor needing to draw the highest peak power?............

(-in all cases , please assume that water under the maximum pressure is trying to flow through the pipe........)

1.... Moving the valve with the stepper at constant angular speed whilst closing the valve
2.... Moving the valve with the stepper at constant angular speed whilst opening the valve

3..... Accelerating the valve at with the stepper at maximum d(angular speed)/dt whilst closing the valve.
4.... Accelerating the valve at with the stepper at maximum d(angular speed)/dt whilst opening the valve

5.....Moving the stepper motor from stationary to open the valve, when the valve was initially fully closed
6.....Moving the stepper motor from stationary to close the valve, when the valve was initially fully open

7.....Moving the stepper motor from stationary to open the valve, when the valve was initially half open
8.....Moving the stepper motor from stationary to close the valve, when the valve was initially half open

9....Holding the stepper motor stationary, whilst the valve is half open
10....Holding the stepper motor stationary, whilst the valve is fully closed
11....Holding the stepper motor stationary, whilst the valve is fully open

12. ..."Pinch-Off"...that is, that instant in time when the valve is just about to completely close the valve

13...some other operation

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QUESTION 2:-

At the moment , i am thinking of putting the stepper through all of the above actions, and continuously monitoring the
Voltage Rail that supplies the stepper motors, and continuously monitoring the current that flows in the stepper windings.

I am just hoping that i don't miss the peak power instant.

Do you know of any good oscilloscopes with data logging facilities so that i can save the voltage and current data
such that i can pick out the maximum power?

 

[gerhardl]

I see that you have got no answer yet, so please allow me some suggestions and comments:

(Note:I dont know what a SMPS is and have mechanical-not electrical background)

a) The important thing for normal, and larger, electrical actuators is to dimension the power supply (wires and fuses) for the ampere peak at maximum torque for the actuator. You also have to have an adeqaute power supply (effect over time) if you have a UPS system. At the same time you have to protect for peaks when motors are turned on/off.

b) If the motors are rigged to work both at the same time (in the same circuit) you have to add the electrical impact for both.

c) a and b taken care of it should be possible to guess at the maximum average effect necessary over time, max power both motors - adeqaute time.

d) Sometimes (as you suggest) theoretical considerations can be involving too many variables, and cheapest and fastest way is to test practically.

Good luck!

 

[cloa]

I'd say question 2 considers part d- he is testing practically but needs the right equipment to see what's going on.