Stepper motors or something else

HI,
Do stepper motors use power all the time ?
I want to control solar panels and direct them towards the sun all day, will they use power all day even at idle ?
If so I will have to think of something else…
Thanks.

Good project to tackle these days (greenenergy). Yes, stepper motors use constant current to hold the rotor in place even when they hold instead of running. Regular dc motors don't need power when they don't spin. On the other hand, both types of motors will not hold their position when power is cut so sometimes the position is held by balancing the object they rotate so that even when no motor is engaged the object will not rotate, and a gearbox system will be able to hold the object with its friction. The key is to balance the object to be rotated, to rotate it around an axis that goes through the center of mass of the object.

Yes, stepper motors use constant current to hold the rotor in place even when they hold instead of running.

And, they use lots of current, so, stepper motors are not really compatible with solar panels, unless you are talking large solar panels generating kW of energy.

PaulS:

Yes, stepper motors use constant current to hold the rotor in place even when they hold instead of running.

And, they use lots of current, so, stepper motors are not really compatible with solar panels, unless you are talking large solar panels generating kW of energy.

Like Paul said, I would not use stepper motors, and use dc motor and work on balance the rotation stage to minimal torque. Plus, stepper motors require more electronics to control. You can control a dc motor with one arduino pin and a transistor (with resistor on base).

Steppers do actually have a small amount of holding torque when power is removed. It isnt a lot, but if the rest of the system is balanced and does not have high wind loads(small panels indoors) it could be sufficient. But otherwise a spring applied holding clamp or tight pivot joint may be required. The fact that a stepper rotates a known fixed distance each pulse and the sun moves at a known rate may be quite useful as no sensors are required. The processor can sleep most of the time with only the 32kHz clock running. Wake up, pulse the stepper one time, calculate how many clock ticks till it should wake up again(maybe overnight), then go back to sleep. The higher current required to turn the stepper would be offset by having to turn it less often and requiring less correction and monitoring. Dustin Maki

Well I would suggest you research telescope drives that automatically track with the earths rotation, for ideas you could use for your solar arry. They tend to use small low power motors with large gear ratios. As the speed of rotation is a constant (so in theory you only need a motor on/off control) the only real software interface required to to insure the starting position is correct before starting the days tracking and at the end of the day sometime the array is positioned back to the starting point for the next sunrise.

Lefty

As slomobile said, Stepper Motors have a known "holding torque" when the power is off. Rotate a stepper motor by hand when it's turned off and you will feel it "cog" or have many positions where it naturally stops, in between magnetic pole maximums. This is more obvious on larger motors, which you are probably talking about for this application.

Since the rotation rate of the solar panel is only 1 revolution per day and no panel needs to be aligned to better than 5 degrees (unless it has a lens or reflector) you only need to actually re-aim the collector 30 or 40 times a day. If the collector has a "equatorial mount" where a single axis movement tracks well, and it is well balanced it should not need a lot of stepper motor power, but it might be necessary to accelerate and decelerate the move due to the mass of the collector.

Some collectors have a manual setting for latitude and seasonal month. The angle changes plus and minus 23.5 degrees in one year, so it's about 4 degrees per month (but it's not linear: it's a sine wave and so that angle changes very slowly in mid-winter and mid-summer and changes fastest at the spring and fall equinoxes.) Just a little Arduino math :)

Stepper motors often are used for this purpose, normally with a large gear reduction ratio.

Once a day the collector needs to be cycled all the way back over to sunrise position, and you would have a limit switch or sensor to "start the day" in a known position. Stepper motors would be able to be moved a calculated number for each move, and no other position sensors would be needed.

Let us know what you finally do and how it works out...

Regards, Terry King ...In The Woods In Vermont terry@yourduino.com