# Need Help! Solar tracker design

Joined Mar 18, 2017
15
Hey guys, I'm new here, and need some help! I'm pretty wet behind the ears when it comes to building circuits, no prior education, but a decent understanding of electronics. I'm trying to build a single axis solar tracker. I've got 2 small solar panels that produce 1.2watts peak and current is about 10ma. I would like to trigger a normal 5 pin spdt 12volt relay coil tested at 85ohms. Would a transistor be able to do this? And if so, how would I go about figuring which transistor would have the optimum parameters? I realize these could be loaded questions, but any help I could get would be greatly appreciated! Thanks in advance

#### dl324

Joined Mar 30, 2015
15,406
Welcome to AAC!

Will the relay be powered from the solar panels? The relay will require about 140mA.

What conditions will trigger the transistor/relay?

1.2W and 10mA gives a voltage of 120V; that can't be right.

What voltage are the panels? How will they be connected? Series? Parallel?

#### late_bloomer

Joined Feb 22, 2017
21
I think it's 100mA, then math adds up to 12 V panels..

Joined Mar 18, 2017
15
Sorry, meant to say 1.2volts peak on the small solar panels... They're tiny little things ripped off of dollar store patio LED lights

#### WBahn

Joined Mar 31, 2012
27,853
What is going to power the tracker?

Joined Mar 18, 2017
15
I'll be running a 12volt line to a small 12volt motor.... And at least in my head I am going to have the 2 of the automotive SPDT relays switch the motor polarity depending on which of the two solar panels are producing

Joined Mar 18, 2017
15
Welcome to AAC!

Will the relay be powered from the solar panels? The relay will require about 140mA.

What conditions will trigger the transistor/relay?

1.2W and 10mA gives a voltage of 120V; that can't be right.

What voltage are the panels? How will they be connected? Series? Parallel?

#### AnalogKid

Joined Aug 1, 2013
10,170
Are you saying that the two small cells are what you are using to make the differential light measurement that drives the tracker position relays and system?

A garden variety small signal transistor can drive your relay coil. NPN: 2N4401. PNP: 2N4403. If they look too small to you, NPN: TIP29. PNP: TIP30.

ak

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
One typical trick for tracking, is to use a tube and two solar cells for two axis. When they both have the "same normalized" current, your in the right position. The problem with this approach by itself is hunting with respect to clouds. There are also effects with dust, snow, rain etc.

4-axis tracking can use 4 cells. Wedges even work. What diameter? - don't know.

Joined Mar 18, 2017
15
Are you saying that the two small cells are what you are using to make the differential light measurement that drives the tracker position relays and system?

A garden variety small signal transistor can drive your relay coil. NPN: 2N4401. PNP: 2N4403. If they look too small to you, NPN: TIP29. PNP: TIP30.

ak
Yes! I was hoping I was on the right track lol... Once again going down the rabbit hole, I've read you must have a resistor on the base of the transistor... How would I go about figuring out the value I would need?

Joined Mar 18, 2017
15
One typical trick for tracking, is to use a tube and two solar cells for two axis. When they both have the "same normalized" current, your in the right position. The problem with this approach by itself is hunting with respect to clouds. There are also effects with dust, snow, rain etc.

4-axis tracking can use 4 cells. Wedges even work. What diameter? - don't know.
I know this is a crude system lol, but I'm very new to electrical circuits, I'm a gas technician by trade and work on motor homes, so that should give you the extent of my knowledge. But for the time being, this project sounds fairly robust and cheap until I can learn more about circuits... Gotta start somewhere

#### WBahn

Joined Mar 31, 2012
27,853
I'll be running a 12volt line to a small 12volt motor.... And at least in my head I am going to have the 2 of the automotive SPDT relays switch the motor polarity depending on which of the two solar panels are producing
One of the things you are going to have to contend with is what happens when you are positioned correctly. If you approach things naively what can happen is your system sits there and chatters as it oscillates back and forth. I can think of a few ways to deal with this, but it depends on the basic approach you have in mind.

#### AnalogKid

Joined Aug 1, 2013
10,170
I'm sure there is a ton of solar tracker information on the web, but going in cold it sounds like you need a 3-state system: too far left, too far right, and a good-enough zone in the center where the motor is off. At the system level this is called hysteresis; at the circuit level it is a form of a window comparator. Two opamps or comparators (or one dual part), two SPDT relays. Think perf-board the size of a business card.

Many solar trackers use what is called an H-Bridge circuit instead of relays, but there's nothing wrong with relays while you get you feet wet.

https://images.search.yahoo.com/sea...Gl2cw--?p=solar+tracker+schematic&fr2=piv-web

ak

Joined Mar 18, 2017
15
One of the things you are going to have to contend with is what happens when you are positioned correctly. If you approach things naively what can happen is your system sits there and chatters as it oscillates back and forth. I can think of a few ways to deal with this, but it depends on the basic approach you have in mind.
I get what you're saying... My approach is to build it as simple as possible with components easily accessible in the bush... I do have lots of the small solar panels, relays, and broken electronics I can harvest parts from lol... I'm open to suggestions and will keep trying to learn, it seems with each suggestion, comes a couple hours of research to wrap my head around everything...

Joined Mar 18, 2017
15
I'm sure there is a ton of solar tracker information on the web, but going in cold it sounds like you need a 3-state system: too far left, too far right, and a good-enough zone in the center where the motor is off. At the system level this is called hysteresis; at the circuit level it is a form of a window comparator. Two opamps or comparators (or one dual part), two SPDT relays. Think perf-board the size of a business card.

Many solar trackers use what is called an H-Bridge circuit instead of relays, but there's nothing wrong with relays while you get you feet wet.

https://images.search.yahoo.com/sea...Gl2cw--?p=solar+tracker+schematic&fr2=piv-web

ak
I completely agree, but some of what you said sounds like Latin to me lol and I don't quite yet know all of the symbols in those schematics let alone understand them... I'm really happy to have all this great input from everyone here, I truly appreciate it... But it's like a bunch of rocket scientists trying to teach a neanderthal how fire works lol

Joined Mar 18, 2017
15
I would like to avoid using micro controllers/555 timers etc (beyond my comprehension at the moment).. I don't need it to anything fancy, I can over ride it come bad weather. But yes, I would like to avoid chattering relays, the motors bouncing back and forth would suck as much power as I'm gaining tracking the sun

#### AnalogKid

Joined Aug 1, 2013
10,170
There is no way to avoid some electronics, but they should be pretty minimal if you stick with relays for the power switches.

The way you prevent the hunting or chattering is to create a dead zone, a defined state where both direction relays are off. In this state the panels are pointed so close to dead on that no correction is needed. The more narrow this space is, the more often the motor will run, but it will run for shorter periods of time. As you have said, there is a point of diminishing returns. Life is choice.

The left half of this schematic is the starting point. http://www.eltronicschool.com/2015/04/simple-circuit-schematic-solar-tracker.html

We'll add a couple of resistors to make it chatter less. What are the relays you want to use to drive the motor? Manufacturer, part number, photo, website where you got them, anything.

ak

Joined Mar 18, 2017
15
Sounds good! The relays I have kicking around are a 12 Volt Bosch style 5 pin SPDT rated at 40Amps, pretty standard amongst most cars. The coils inside them ohm out at around 85ohm, so I guess it'd be around 140ma? And I looked up the LM324 IC in that schematic, it's not as intimidating as I thought, just gonna have to do some reading.

Joined Mar 18, 2017
15
I'll test one of the PV panels tomorrow and get an exact measurement of voltage and amperage I get out of them, I do have a few LEDs kicking around if you think they would work better, but I'll be damned if I know the technical specs for them... I'm hoping I can scavenge everything I need for this, I live pretty far out in the bush most of the time lol