Problem with Solar Tracker circuit

[TheEngineer]

Hello,

For a project I am attempting to make a solar tracker that tracks the sun throughout the course of a day from east to west. I will have circuitry to sense the sun and then use a motor and linear actuator to adjust a PV panel to face directly at the sun.

The circuitry uses photoresistors (along with an LM339 comparator) that will change resistance depending on the amount of sunlight. Therefore, when the West sensor sees more light than the East, it will have less resistance and allow for more current to flow and activate a motor relay to turn the panel towards the West. When the panel is directly under the sun, both sensors will see equal light and the panel is not moved. At the end of the day, when both panels see equal darkness (high resistance), the panel will move back to the East.

I found several schematics online for the control circuitry but am having trouble getting the design to simulate correctly (using MultiSim). I can configure the circuit to work correctly for one instance (i.e. pointed directly at sun or with the West seeing more sunlight), but it does not work when I change resistances.

Basically, when the circuit sees equal light, the photoresistors will have a value of approx 10k. In order for the panel to stay where it is, the voltage at the base of each of the transistors needs to be high (the actual motor relays will connect to the collector of the xistors).

Similarly, the base voltage of the EAST_DRIVE xistor needs to be high when the WEST resistor is 10k and the EAST is 100k (dark) so that the panel will turn towards the West.

The problem I am seeing is that since the outputs of U3D and U3B are tied together, that node will only be high when both outputs are high. For whatever reason, I cannot get the values to come out right.


I am attaching a jpg of the schematic as well as the MultiSim file (in zip folder) incase anyone can maybe run the simulation and see if they can find out what is wrong? I have been racking my brain trying to troubleshoot this.

Thanks!!

 

[BrownOut]

Quote from TheEngineer:
The problem I am seeing is that since the outputs of U3D and U3B are tied together, that node will only be high when both outputs are high. For whatever reason, I cannot get the values to come out right.

Yeah, that's kind of the point. This keeps both motors from running at the same time, and tearing up the mechanical components.

 

[Boncuk]

What happens if one is high and the other one is low?

Use two switching diodes at the outputs.

 

[BrownOut]

Diodes aren't needed, and would defeat the safety feature. Also, the OP's writeup is wrong; in order for the thing to NOT move, the transistor bases have to be low. If they are both high, then the motor will get confused.

 

[Boncuk]

If they are both high, then the motor will get confused.

what will happen exactly if U3B and U3C are high.

 

[BrownOut]

what will happen exactly if U3B and U3C are high.

Then "East" relay energizes, and the safety feature prevents the "West" relay from energizing. Safety featuer could be made much better, I'm sure.

 

[TheEngineer]

Then "East" relay energizes, and the safety feature prevents the "West" relay from energizing. Safety featuer could be made much better, I'm sure.

Thanks for your input, sorry about the delayed response.

I guess I am a little confused. If the base of the transistors is High, then the multimeter attached to the collector sees a Low voltage. It was my understanding that I want a Low value in order to keep the relay, which will be where the multimeter is, from activating. Thus, when I want the panel to turn towards the West, I want a High value on the multimeter XMM1 and a Low value on the multimeter XMM2. Is this correct?

 

[BrownOut]

If your relays are modeled by the 10K ohm resistors, then it's just the opposite. You have one side connected to VDD, so it takes a "Low" on the collector side for any current to flow, and energize the relay.

 

[TheEngineer]

If your relays are modeled by the 10K ohm resistors, then it's just the opposite. You have one side connected to VDD, so it takes a "Low" on the collector side for any current to flow, and energize the relay.

Ahh, that makes perfect sense. Thanks!

On another note, I am having a hard time figuring out the purpose of the 1M feedback resistors (I did not create this circuit originally). Taking them out doesn't seem to affect the output node on the comparator. Do you know what they might be there for, especially when their value is so high?

 

[BrownOut]

It's called "hysterisis" and it prevents the output from oscillating at the switch point. Leave them in.

 

[TheEngineer]

It's called "hysterisis" and it prevents the output from oscillating at the switch point. Leave them in.

Ok. Any specific reason why U3D doesn't need one?

 

[BrownOut]

I'm not crazy about the way U3D is connected. I would probably not connect the way it's in your drawing. But without at least simulating it, I would't feel comfortable telling you to change anything. IMO, you can connect a 1M feedback or not.

 

[TheEngineer]

I'm not crazy about the way U3D is connected. I would probably not connect the way it's in your drawing. But without at least simulating it, I would't feel comfortable telling you to change anything. IMO, you can connect a 1M feedback or not.

I believe it is set up that way so that both relays can never be on at the same time. Do you have any suggestions as to a better configuration?

 

[BrownOut]

I believe it is set up that way so that both relays can never be on at the same time. Do you have any suggestions as to a better configuration?

You're right about that. I just think it's not optimal, but if it works, then go with it.

 

[TheEngineer]

I have this circuit working now and am looking for some advice on a driver unit to turn the panel. Currently, I have the panel mounted on a lazy susan-type turntable that will be rotated by the use of a linear actuator. I am planning on making this linear actuator myself by mounting a bolt on the motor shaft, similar to this: Quick and easy "electric linear actuator" prototype ...

However, I have run into the issue of my motor running way too fast (~2500 RPM) and would like to use a stepper motor with a 555 timer as a controller. In reference to the circuit that I posted earlier in this thread, when the "west" photocell receives more light than the "east" (and the panel should turn west), I'd like the motor to step towards the west, then recheck the signal, step, recheck, etc until both photocells are receiving equal light and the panel does not turn too far.

Can anyone point me in the right direction of how to set this up?

 

[Boncuk]

Hi,

the motor should not run at that high revs. There are small geared and powerful motors on the market.

I use small motors (12mm dia) with a gearbox of 14mm dia (used for robots) connected to an M6 threaded rod which moves the panel for azimuth and elevation.

If the panel "overtakes" the sun you'll have a problem.

Boncuk

 

[TheEngineer]

Hi,

the motor should not run at that high revs. There are small geared and powerful motors on the market.

I use small motors (12mm dia) with a gearbox of 14mm dia (used for robots) connected to an M6 threaded rod which moves the panel for azimuth and elevation.

If the panel "overtakes" the sun you'll have a problem.

Boncuk

I see. Could you describe this system in a little more detail?

 

[Boncuk]

Hi,

I use telescopic aluminum pipes normally used for bathroom (floor) cleaners. When taken apart the two pipes will have a usable length of 16 to 20". The inner pipe takes the ball bearings for the threaded iron, the nut and the motor with reduction gear. (The thread is directly driven by the motor with reduction gear.)

A 6mm thread requires 6,667 rotations for 10mm of stroke, resulting in further rpm reduction and increase of torque.

That pipe must be slotted for the nut for two reasons: First, the nut is not supposed to rotate - but slide along the thread and secondly the nut is bolted to the outer pipe which then slides along the inner pipe giving double length if fully extended.

To prevent jamming in case the limit switches malfunction remove part of the thread (big enough to have the nut + a pressure spring in the gap). When reaching one end the nut will not be driven anymore, regardless of the continuously running motor.

When the motor is reversed the nut will be pressed onto the thread again and move the outer pipe which is connected to the leverage of the solar panel. For easier "finding" of the thread machine the end slightly conical. (Just a few file strokes suffice.)

Since you are using the drive outdoors remember to put the slot of the inner pipe facing ground. (Otherwise you'll have to do a lot of grease jobs.) For initial greasing use lubricant along the thread richly.

Those pipes are shaped in wave form and are pretty stable withstanding a lot of vertically applied force. They break if shear force is applied, proved by my wife who manages to break one of them every month.

Boncuk

P.S. For an accurate fitting of the motor drive axle (normally flatened) I suggest to heat the thread red hot and ram a steel axle (same dimensions as the motor drive shaft) into the hot rod. You can do it most accurate using a lathe.

 

[mbarazeen]

why dont you use another circuit with a single comparator connecting both sensors to one of its input. and compare? it will drive only one motor but in both directions. i have used such a circuir long before using LDR instead and worked good, also to turn it completely after sunset and to position next day to the high sunlight the same worked excellent. just before the sensors you have to use some guide tubes(a pice of pipe to direct the light only from certain angle) for good operation.

 

[TheEngineer]

Different aspect...

Hello all,

I have this project complete and it is working! I have one question though...

I can't figure out the purpose of the voltage divider connected to the gate of MOSFET Q1 is in the attached picture. Is it simply for current limitation? Anyone know?

Thanks!