Scaled-up Solar Tracker – proof of concept part 7: Nearly there..

see part 6

In this post:

  • Ongoing test runs
  • Various parts arrived
  • Reduced height of lift-and-twist pole
  • Next steps

Ongoing test runs

Everything is working fine except that the motor is too quick. When the sensor solar cells detect the sun such that the lift-and-twist needs to happen, the solar panel frame overshoots where it should stop.

Various parts arrived

Over a couple of days, parts I’d been waiting on to take the project forward arrived:

  • Pole / frame clamp
  • Solar panels
  • Step-up buck converter (for more motor torque)
  • Solar charge controller (for 12V motor-driving battery)
  • EcoFlow River 600

Pole / frame clamp

The pole / frame clamp’s purpose is to allow the angle of the solar panels to be adjusted so they can point higher in the sky during summer and more towards the horizon in the winter.

Here it is installed:

As you can see, the clamp fits around the bottom of the pole-top mount tube and is connected to the frame via a tie and slotted bracket.

The angle of the frame and solar panels can be adjusted as the year progresses by a combination of adjusting the position of the clamp on the pole and changing the position of the tie in the slotted bracket.

It really needs a much longer bracket and slot and then the required angle could be set without moving the clamp. But for the life of me I can’t find one online, so it’ll have to do as is for now 🤪

Solar panels

a photo solar panels mounted on the frame
solar panels mounted on the frame

After mounting them on the frame, I used MC4 Y-connectors to connect the solar panels in parallel and then to connect the output to the EcoFlowRiver 600 as per the photo:

a photo showing the Y-connectors connecting the solar panels in parallel and then being hooked up to the EcoFlow River 600
showing the Y-connectors connecting the solar panels in parallel and then being hooked up to the EcoFlow River 600

EcoFlow River 600 portable power station

This is a power station with a lithium ion based 12V 288Wh battery capable of delivering a sustained 600W, with an x-boost mode that delivers 1200W (but only one of the ac outlets can then be used).

It uses MPPT to maximise the power take-up from the solar panels and has an inbuilt inverter to give a pure sinewave 240VAC (UK / Europe model)

In the UK / Europe, if it’s being used to power AC appliances that are earthed, then the provided earthing screw needs to be connected to earth to maintain electrical safety.

Outdoors the earthing screw gets connected via an earthing (aka grounding) cable – literally a stake that you drive into the ground.

If using the River 600 inside a house (UK / Europe), then connecting the mains charging cable to it (but not switching it on) will do the earthing job equally well.

Even when not switched on, the earth coming in on the charging cable remains connected, so providing an earth route for any appliances plugged into the three pin power sockets on the River 600.

As the EcoFlow River 600 will be inside my house, a 15m PV extension cable run is needed. I’ll be using 6mm² (10 AWG) cable.

Ideally I’d use 10mm² (7 AWG) to keep losses at 10A – the maximum input current the River 600 can take – to an acceptable 5%. Unfortunately the cost of that cable is prohibitively expensive. To work things out, I used the DC Cable Sizing Tool here.

Solar charge controller

Before I can connect up the solar charge controller for the motor-driver battery, I need a way of connecting its input to the solar panel ouptut.

I’ll tap into and solder a short length of twin core cable to the positive and negative MC4 cable branches – the ones that come from the output of the Y-connectors that connect the panels in parallel. I’ve got some vulcanising rubber tape so I’ll use that to tightly cover the connection points and so make them weatherproof.

I’ll need a diode in the positive line feeding the charge controller so that it’s isolated from the River 600. A Schottkey 5 amp one will do the trick nicely. See the block diagram below.

Step-up buck converter

In the last post I explained how I decided to use a cradle with a counterweight because the motor didn’t have enough torque to do the lifting on its own.

It wasn’t a solution that I was really happy with, making access to the innards of the box rather cumbersome.

So after another brainwave, I decided to use a step-up converter to up the voltage supplied to the motor and so increase the torque that way. After some playing around, I found that 18V did the trick. So I’ve now removed the cradle.

Block diagram

Here’s a block diagram showing how the various blocks interconnect. Note that D2 (a 5 amp Schottky diode) prevents the solar charge controller and the EcoFlow River from interefering with each other:

a diagram showing how the various blocks are connected
diagram showing how the various blocks are connected

Reduced the height of lift-and-twist pole

The pole height was too great – even in a gentle-ish breeze the whole lot was just too unstable. The solar panels really caught the wind and the long pole, acting like a lever, put a lot of strain on the box.

So I reduced the length of the lift-and-twist pole so that the frame, when fully vertical, just cleared the top of the box.

That made a big difference and I’m happy with the result. That’s not to say the whole assembly won’t need anchoring, just that I’ve minimised the amount needed.

I was worried that in a strong wind, the pole could bend or be torn off its mounts insde the box. I’m less worried now 🤞

Next steps

Strong-ish winds (36mph) are forecast for tomorrow – fingers crossed that everything holds up! 🤞

Waiting for the replacement motor..

The existing motor rotates just too quickly, overshooting where it should stop.

So I’ve tracked down and ordered a 12V 2.2rpm motor with a torque of 90kgf.cm (8.8Nm). It should have more than enough power to lift the solar panel frame assembly and will definitely be slow enough to stop the overshoot.

It also helps a little that the weight has been reduced by around 0.5kg due to the shorter the pole length.

Mounting the whole structure

I’ve ordered a 1.2m 35mm diameter aluminium tube with a wall thickness of 2mm and bought a stainless steel one from a local marine supplies store. It’s 28mm diameter and also has a wall thickness of 2mm.

Whatever solution I go with for locating the tracker in my garden, at least I’ve now got the poles to mount the box on. I’ve also ordered some extended u-bolts and cradles to mount the box on the poles.

Scaled-up Solar Tracker – proof of concept part 6: First run…

see part 5 :: see part 7

photo showing the first run of the solar tracker (minus the main solar panels but with the equivalent weight in water containers)
first run of the solar tracker minus the main solar panels but with the equivalent weight in water containers
(click for large image in new tab / window)

Pole-top Mount arrived

Well.. most of it. I’m still waiting for the clamp that will let me angle the solar panel frame to point higher in the sky in summer and lower in winter.

photo showing the details of the pole-top mount
pole-top mount details

The clamp will go around the bottom of the pole-top mount tube and be connected to the frame via a tie and slotted bracket. That way the angle of the frame and solar panels can be adjusted as the year progresses.

Motor driver circuit – actual

In the previous circuit I emulated the sensor solar cells and the motor. I’ve now fitted them so I’ve got a working prototype.

Here’s the circuit now:

schematic showing the motor driving circuit with the emulated parts replaced with actuals
motor-driving circuit with sensor solar cells
(click for large image in new tab / window)

Wiring it up

While waiting for the pole-top mount to be completed, I made it easy to connect and disconnect the wires from the motor-driver circuit, housed near the top of the frame, to the parts in the main box:

  • 12V battery
  • Motor
  • Microswitch

The microswitch is on the output of Comparator-2 and, at dusk, stops the motor when the solar panels have reset to their dawn start position. It’s mounted on the wooden block holding the motor and is activated by the bolt the rod end bearing is attached to.

I used EC5 connectors for the 12V supply from the battery and half an EC3 connector for the power to the motor from the MOSFET’s drain.

I then routed and hot glued the wires in place inside the main box.

First run

I transported everything into my back yard, put the pole-top mount and frame in place and plugged the various connectors together.

I connected the 12V battery first and used my multimeter to double check that all was good in the motor driver circuit.

With that showing ok, I plugged the rest of the connectors together – no smoke or flames – always a good sign, hehe!

Weighting

I weighted the lift-and-twist pole with containers of water as a stand-in for the solar panels.

Next I filled the counterweight cradle with a house brick and just enough small pebbles so that the motor was able to lift the pole – but not so much that it prevented the pole from dropping again when the motor had rotated past the half-way point.

The run…

Luckily the day turned out sunny with the odd cloud or two. This meant I was able to do the fine tuning to get the sensor solar cells to work as intended.

All I had to do was to adjust the trimpot so that when the main sensor solar cell was in direct sunlight the combined sensor solar cells’ voltage was only just enough to switch on power to the motor.

Finally, when it turned to dusk and there wasn’t enough light to keep the sensor solar cells above the lower voltage threshold, the motor came on and allowed the reverse twist-and-drop to point the frame towards the sunrise position.

When it reached that position, the microswitch on the output of Comparator-2 was activated, removing power to the motor ready for the next day to dawn.

It was a bit windy and even without the wind resistance of the main solar panels, I had to weight the box down even more. I knew in advance that I’d need a way of fixing the whole structure so it could withstand the wind but I was a bit surprised that it was an issue without the main solar panels.

The next day dawns

Everything is working as intended 😊

There was no sun until mid-morning and the secondary sensor solar cell did its job when the sun finally appeared.

Next steps

Second solar cell..

I’ve probably still got some tweaking to do with the secondary solar cell. That’s the one that makes sure the solar tracking still happens even if the morning was cloudy and no lift-and-twist happened.

Right now I’ve got it pointed around 60° from the main one in the direction the sun takes across the sky.

It seemed to be doing the job when I was setting things up and manually turning the frame this way and that to monitor what happened but only a real test will tell.

So here’s looking forward to a cloudy morning with the sun coming out in the early afternoon. The first run gave it a partial test but I’ll have to wait for a full one.

Mounting the whole structure

I’m not yet sure where I want to put the box in the back yard. Wherever it goes, I’m going to need to fix a pole in a concrete block and then attach the main box to it with u-bolts.

Do I dig a hole to take it? My garden is a bit on the small side so that’s a last resort.

More cogitation needed…. 🤪🤯

Getting and using the solar panels

Due to the weight constraints, I’ve designed for two 120W flexible solar panels, coming in at a total of 6.2kg

I’ve also got to decide how to go about making use of the power generated by them. I’m thinking of getting an Ecoflow River with 288Wh battery and 600W power output.

The main reasons for going that route are:

  • it takes solar panel power using MPPT as charging input
  • it has an internal inverter to provide 240VAC power as output
  • 600W is ample to power my computer, TV and various bits and pieces

This way it’s a little cheaper than buying / building the individual modules and avoids the associated headaches.

Scaled-up Solar Tracker – proof of concept part 5: The heavy lifting…

see part 4 :: see part 6

a photo of the guts of the solar tracker showing the new counterweight cradle
guts of the solar tracker showing the new counterweight cradle

In this post:

  • working with the new motor
  • I still got the torque wrong – I stupidly ignored friction
  • Introducing the counterweight concept to make up for it

So the motor arrived

I got quite excited! I had to get a block of wood cut to mount it on and a quick trip to my local supplier got that sorted.

I mounted the motor and gave it a quick try on progressively heavier loads tied onto the lift-and-twist pole.

It was nowhere near able to lift the required weight due to frictional losses. Alas, alack, woe is me! And then I realized I’d been stupid (again!)

Counterweight Cradle

From the outset, all the design needed was a counterweight so that the motor wouldn’t have to lift the whole lot by itself.

So a quick rejig and I had a cradle mounted via pulleys to take the counter weight. I attached its cords to the lifting eyelets at the same place as the motor cords are attached. I’ve made a short video (25s) without any loads so you can see it in operation:

Note that as the counterweight cradle goes down, the pole twists and goes up, driven by the motor. When the cradle goes up, it’s the weight of the pole going down that lifts it, as the motor relaxes its pull on the cords.

Counterweight in action

Here’s a video (58s) showing how it works under realistic loading:

  • Weight on pole: 12.5kg
    I’ve used containers filled with water and tied them to the pole as a substitute for the frame (3.5kg), top mount (1kg) and two flexible solar panels (6.2kg) – with a little extra as a fiddle factor
  • Counterweight: 6.5kg
    For the counterweight I’m temporarily using the 12V battery that drives the motor and a lump of rock – it’s actually half a polished stalactite I picked up on a dig of a collapsed passage from my caving days, but that’s another story…
  • Frictional losses on motor lifting path: 6kg
    These losses mean that the maximum lifting power of the motor (around 13kg at 45mm from the shaft as used here) is almost reached with the above loadings

Observations

  1. As the weight on the pole increases, so the counterbalance weight has to be increased to help take the strain from the motor
    • Uh oh! As the weight on the pole and the cradle increases, so do the frictional losses
    • There’s a limit imposed by this beyond which the motor can’t supply enough power to lift the pole and the weight on it.
    • Increasing the counterbalance weight when this happens (to assist the motor’s lifting force and so be able to lift the pole and its weights) means that the combined weight of the pole and the weights on it aren’t enough to allow the pole to drop down when the motor relaxes its lift – the counterbalance weight together with the frictional losses are just too great to allow the pole to drop
    • Luckily this happens at a (slightly!) greater weight than the combined weight of the pole, the pole-top mount, the frame and the solar panels
  2. The motor I’ve used has a small amount of backlash (Wikipedia definition)
    • When the cord that’s attached to the rod end bearing on the motor plate goes over the top, there’s a clunk as the backlash kicks in.
    • Without the counterweight and with a more powerful motor, I’d be concerned that the repeated shock it would give the motor’s gears might eventually lead to gearbox failure
  3. If I was starting the build again from scratch, I’d use a different approach to the lifting:
    • I’d use a linear actuator (Wikipedia definition) with a similar or slightly better torque rating
    • It would need a double pole double throw switch / relay so that when the top of travel is reached, the actuator motor’s positive / negative could be reversed to bring the pole down again (drop and reverse twist)
    • A similar arrangement would be needed for when the pole reaches the bottom of its travel, swapping the actuator motor’s positive and negative again so it would lift the pole once more.
    • (it would still need another switch to cut power entirely when things have returned to their dawn starting position at dusk)
    • The cost of the linear actuator and switches / relays would come out about the same as the current motor and pulleys I’ve used.
    • It would also give a simpler build and one that could easily be scaled up even further to lift more than the two solar panels

Next steps

I’m waiting for the pole top mount to be made by a local supplier. As soon as it arrives I’ll fix it to the frame and then mount it on the pole.

I’ll still need to attach a couple of containers filled with water (6.2kg) to the pole to act as a substitue for the solar panels. I’m not ordering them until I’ve proved everything – just in case!

Upwards and onwards 😎