Stepper motors consume power when stationary in stepper-valve system?

[treez]

Hello,
This shower operates by the hot and cold pipes being regulated by valves which are operated by stepper motors
**broken link removed**

The stepper motors (one for hot and one for cold) are bipolar stepper motors and the current in the coils is regulated by a switch-mode type of operation of the full bridge stepper motor drivers.

When the customer has selected the shower temperature by moving the stepper valves to the right place, will the stepper motors be consuming power when the valve is just stationary in the required position?

 

[barry]

Yes. Current is always flowing in stepper motors.

 

[albbg]

Yes. Current is always flowing in stepper motors.

I don't think so. Why the current should continue to flows after the position has reached ?

 

[treez]

if the current stops, then the magnetism stops, and the stepper is unable to hold position?.....but I am thinking they designed the valve with friction and inertia such that relatively high power is needed to move the stepper valve, and then it just sticks there unless the stepper is again activated to move it...what do you think?

 

[FvM]

Yes. Current is always flowing in stepper motors.

Not necessarily. Stepper motors have a certain holding torque without phase current caused by the permanent magnets, gears may be self-locking. Depends on the mechanics and controller design.

 

[barry]

Not necessarily. Stepper motors have a certain holding torque without phase current caused by the permanent magnets, gears may be self-locking. Depends on the mechanics and controller design.

Fair enough. Maybe I should have said: every design I've done (maybe 10) has had continuous current to provide holding torque, as the detent torque was insufficient.

But, more importantly, who could POSSIBLY need a digitally controlled shower?

 

[treez]

I see, but I think that with the aqualisa showers they have sufficient stiction in the valve such that it doesn't move unless the stepper is on full power , trying to move it.
Digital showers?.......well, for some, shower time is quality time, and they want the exact temperature of shower...so hence the mixer valves.

 

[FvM]

I see, but I think that with the aqualisa showers they have sufficient stiction in the valve such that it doesn't move unless the stepper is on full power , trying to move it.

Have you seen the valve mechanics? Otherwise it's just a guess. You might even want self-closure in case of power-loss as a feature. Or need additional solenoid valves.

 

[albbg]

To increase holding torque a reduction gear box can be used (I don't think a high speed is required to operate the shower) furthermore the windings can be shorted during stationary state. Otherwise you should supply current also when you want to stop the water flux, unless there is an on/off valve that, however, will increase the power consumption.

 

[FvM]

Shorting the windings does not increase the holding torque, only the braking torque when the motor is rotated.

 

[albbg]

Shorting the windings does not increase the holding torque, only the braking torque when the motor is rotated.

I don't think this is completely true for stepper motors. Although you'll have more detent if DC current is applied also shorting a winding you should have an additional detent torque (or coggling torque) depending from the actual geometry of the internal magnets.
I tried by myself to short a winding of some stepper motors I have and manually rotate the shaft. It has been more difficulte to rotate it with respect to the condindition with the wires left open and the "steps" are felt much more by my hand.

 

[treez]

You might even want self-closure in case of power-loss as a feature.

.....youre quite right, there is an enormous storage capacitor to close the valves in the event of power failure

 

[Analog Ground]

Fair enough. Maybe I should have said: every design I've done (maybe 10) has had continuous current to provide holding torque, as the detent torque was insufficient.

But, more importantly, who could POSSIBLY need a digitally controlled shower?

From the Aqualisa site: "Use your remote control to switch your shower or bath on and off, or to divert between the two from up to 10m away, putting an end to getting splashed with cold water." It is obviously meant for those concerned with the toxicity of cold water.

 

[treez]

I believe that water above a certain temperature damages hair...such that hair is not a stylable.....so you need a shower which can very accurately regulate the shower temperature, right from the start, as even small time exposure of hair to higher-temperature-than-wanted water can damage the hair........I am being serious about that........I mean if you step into a electric shower the temperature can be tooo hot.....and your hair will go bad........I am serious, its mainly for women, but men too.

 

[barry]

I believe that water above a certain temperature damages hair...such that hair is not a stylable.....so you need a shower which can very accurately regulate the shower temperature, right from the start, as even small time exposure of hair to higher-temperature-than-wanted water can damage the hair........I am being serious about that........I mean if you step into a electric shower the temperature can be tooo hot.....and your hair will go bad........I am serious, its mainly for women, but men too.

What a bunch of nonsense. What is the temperature spec for YOUR hair? I specifically mean storage temperature and operating temperature.

 

[treez]

it sells though, your actually correct, it is nonsense.

 

[Tunelabguy]

I don't think this is completely true for stepper motors. Although you'll have more detent if DC current is applied also shorting a winding you should have an additional detent torque (or coggling torque) depending from the actual geometry of the internal magnets.
I tried by myself to short a winding of some stepper motors I have and manually rotate the shaft. It has been more difficulte to rotate it with respect to the condindition with the wires left open and the "steps" are felt much more by my hand.

It depends on what you mean by "holding torque". The resistance that you felt to turning the shaft with the windings shorted was the resistance to motion. The slower the motion, the less the resistance (except for the residual magnetic cogging that would have been there anyway, even without shorted windings). The additional resistance to motion due to shorted windings goes to zero as the speed of the shaft goes to zero. But true holding torque is something that can be measured, even at zero speed. For this kind of holding torque, FvM was correct. Shorting the windings does not increase holding torque at extremely low speeds.

 

[albbg]

It depends on what you mean by "holding torque". The resistance that you felt to turning the shaft with the windings shorted was the resistance to motion. The slower the motion, the less the resistance (except for the residual magnetic cogging that would have been there anyway, even without shorted windings). The additional resistance to motion due to shorted windings goes to zero as the speed of the shaft goes to zero. But true holding torque is something that can be measured, even at zero speed. For this kind of holding torque, FvM was correct. Shorting the windings does not increase holding torque at extremely low speeds.

OK, I don't insist since I'm not a true expert in motors.
Sometimes I used stepper motors where the position where held by irreversible gear box. Trying to move the shaft of a motor, shorting a winding, my feeling was that the torque to rotate it was greater than that required when the windings were left open. Probably I'm wrong.

 

[FvM]

Trying to move the shaft of a motor, shorting a winding, my feeling was that the torque to rotate it was greater than that required when the windings were left open. Probably I'm wrong.

You'll feel an additional torque when rotating the shaft at a certain speed, but not chance to keep the motor from slowly creeping off position if you exceed the small holding torque of the rotor magnet.

 

[treez]

I now think inside the product, they use the gearing that was spoken of, to prevent the motor going off position, as well as the rotor magnet.