Motor control circuit for Solar tracker

[(unknown)]

Greetings, I completed the drawing for motor control for the solar tracker. It is bidirectional if the input photo variable resistors are fabricated into a sensor correctly. A and B are one set and C and D are the other set the sets must be placed back to back and then mounted perpendicular to the tracker so it is only possible for the  sun to activate only one set at a time.

A voltage divider is used to trigger a comparator which will activate a 4011 nand oscillator causing the a voltage doubler to turn on the power fets. I tested this circuit back in 2002 and found that it will operate a DC motor up to about 8 amps. I plan on using wind shield wiper motors to control the axis of the tracker.

Feedback welcome.    

[Junkie]

I found wind screen wiper motors to be quite weak and have a lot of movement in them (they shouldn't but...). I only tried a few though in my tracker.

[KilroyOdin]

Greetings,  thanks for heads up about the motors. What type of motors are you using? I took a quick look at your web site and your thermal unit looks very interesting. I found out from others about a free software download called ExpressPCBs and I am using it layout the motor control circuit. From there I am using TurboCad to draw the traces and after that the .dxf file can be used to create the g-code to fabricate the pcbs using a cnc router. It is a bit laborious but should help when fabricating multiple circuit boards. If you have any other ideas please let me know. Thanks again and best regards.

[ghurd]

I hate to be a party pooper, but I strongly suggest you make a perf board version first, before ordering boards.

Photo variable resistors are astoundingly fickle.

Their resistance (even in the same lot) can vary with the light intensity.

They are not exactly predictable.

Hard to explain.  Like one has a lower resistance in high humidity, while the other has a lower resistance in low humidity?

I have a felling it will operate erratically.

I strongly suggest a fuse for the motor before the H bridge fets.

G-

[KilroyOdin]

Greetings, Thanks for heads up. Back 2002 I tested the main part of circuit using a micro interface, worked well. I still have to do some testing using  the light sensors.  I am using a cnc router to make the pcb's.  I viewed a video on you tube where a bike chain and sprocket is used to create a gear set for the motor interface.  This will make fabrication very easy and is what sparked my interest in this project, well that and the cold weather. Cabin fever. Thanks again and best regards.

[KilroyOdin]

PS> The back to back and vertical than placement of the sensor sets should allow for smooth tracking.  

[Junkie]

Hi,

  I tried a few different ones from ford and fiat, mine were used but I believe even new ones will have too much slack.

Also I agree with Ghurd about LDR's, the one in my tracker is proving to be unreliable, it seems to need constant tweaking, though I accept this is probably not helped by poor circuit design on my part.

Hope this helps, good luck with your project  - please post photo's when it's finished.

[joestue]

Fets Q1 and Q2 need to be P type or the gate needs to be fed from a charge pump to be at lest 5 volts higher than Vdrain.

What is to prevent Q1 and Q3 from turning on at the same time?

[KilroyOdin]

Greetings, the back to back and then vertical placement of the sensors sets is what should allow the circuit to work. A project in Berkeley is using the technique. The video shows how to mount the sensors far better than could possibly explain it.  

http://www.youtube.com/watch?v=iH49Xd_NV3A

I still need a simple design for the sensor mount to allow for tracking adjustments to fine tune the focal length of a dish or lens.