[Djunk]

Hello,

I am working on a project where I am using a stepper motor to control a valve(open/close). Normally the motor will be connected to a constand power supply*plug*, but incase of energy malfunction I want to implant a battery that will shut off the valve (so that the valve will not be stuck in open position)
I was thinking about connecting a battery to the system where a pulse runs trough. The moment there is a energy malfunction the battery feels no pulse and then sents energy towards the motor to close it. * how exaclty this is going to work I dont know, but that is for later worries when I start talking whit the electro engineers*

For now I have sellected a motor and was wondering what sort of battery could work.
The required run time is extremely low, since it will only need to run for a maximum of two secconds when there is an energy malfunction (once a month would already be a lot). The battery does need to have a long lifetime, since the system will need to be working for atleast 10 years.

Sellected motor:
2 phase
1.5A
2 ohm
3.2 mH
0.45Nm ( 1 to 3 gearing of 1.2Nm)
required RPM: 90RPM (30RPM after gearing)

The rated voltages would then be: 2 *1.5 = 3V

Required Power becomes (KW) = 0.45 x 90/ 9.55 = 4.24 Watt

and MaxVolts ~= SQRT( 3.2 ) * 32 = 57 V

example choice of battery

TLP-91111/A/SM Flying leads 91111
3.6 V
2.40 Ah
3 A

power (watts) = voltage * current
power (watts) = 3.6 * 3 = 10.8 Watt
Run time of motor will be 2.4(aH battery)/1.5 ( ampere motor)= 1.6 hours (can I just assume the run time will be longer, because of the higher voltage its delivering, 3.6V compared to 3V)

I think I am making a lot of mistakes in this part of the project, since I have no knowledge in batterys.
Therefor I was wondering if someone could give me some guidelines of how I could choose a battery for my system. What am I overlooking at this moment and how can I determine the minimal required battery (voltage / current /aH)?

Any given help would be greatly appreciated.

[springlakecnc]

U said any help is appreciated, so here goes: first of all, I don't think any battery will last 10 years, so you may have to change out the battery in a few years. A battery is DC voltage, a stepper motor takes DC voltage. run the stepper motor from the battery, as its power supply, and always have the battery charger hooked up! when you lose power to the battery charger, the motor will still work until the battery goes dead................its Miller time!

[Torchhead]

Few observations from a worn out old Engineer:
Steppers take a wave form (steps) though a motor driver . No steps signals from some external circuit, no motion.

3.6V will not be enough to do much of anything (okay, you can flash an LED) But not to run a stepper driver. Usually takes about 12VDC to at least power the stepper deriver electronics.

Steppers may not be the best fit to do simple actions like turn on/off a valve. I won't even ask why you need a motor to turn a value on/off instead of using a solenoid valve BUT a simple DC motor and some limit switches or a small DC gearhead motor would run off JUST DC and something as simple as a relay. You could even make it so that a relay is held "in" (active) with the external power on and have a set of Normally closed contacts that are open when active and closed when it is off and that would trigger the motor and have the limit swtich (tripped when the valve is off) in series so it stops. So power goes off the realy closes the NC contacts and the battery powers the DC gearhead motor. Diode isolate the circuits so the battery is trickle charged when power is on but it supplies the DC motor power when the power goes off.

TOMcaudle
www.CandCNC.com

[dmalicky]

How about a spring return for the valve? ~Infinite life, extremely reliable, low cost. The only disad is the motor has to supply constant torque to keep it open, but with proper sizing, that's no problem.

I'm assuming yours is an infinitely-variable valve application. If it's just an on/off valve, use a solenoid as Tom said.

[Djunk]

@Torchhead: Thanks for your response. Its not a simple on on/off valve, but a flow control valve. A proportional solenoid valve could work, but these are really expensive. Therefor I am designing with a stepper motor.
The system is working already controlling a flow and temperature control valve, but now I was trying to find out if its possible to connect a battery on it to make sure that even if there is a power failure the motor can close the system off. This could be done by adding a solenoid valve in the system, but this seems overly expensive, since the on off function is already in the flow control valve. So by simply adding a battery you could save yourself buying a solenoid valve to make the system save during a energy malfunction.

I am aware of the 12V (or 24V) needed to run a stepper motor,but then what can u do with the information of rated voltage (current times resistance), which gives 3V. And would a simple 10 pack of AA bateries 1.2V be enough to power the stepper. In other words what statistics of the motor / battery do I need to use to come to a workable solution?

@dmalicky: thanks for your input, but the valve choice has been on a ceramic cartridges due to their caracteristics. Long life, low torque, small size, allot of manufactureres.

@springlakecnc : thanks for your input, I was hoping batterys where capable of surviving 10 years if they only require to work a few times a year for a few seconds. This is indeed something I have to keep in mind.

[Djunk]

A ok the 3V calculated is the phase Voltages and thus not interesting for this matter. 12V is minimal but 24/30 is possible aswell, so at 12V I should be able to turn the motor if the battery can deliver 1.5A.
So a batterypack of 12V with 10Ah will work and can give me up to 6.5 hours of battery life? Not that battery life is that much of a concern if the battery dies it will be because of age and not because of being empty (being charged full time and only required to turn the motor 180 degrees during power failure).
What is the lifetime of a battery generally? What other things do I need to keep in mind?