Introduction: Solar-electric Bicycle
DISCLAIMER: THIS DEVICE MAY NOT BE LEGAL TO ASSEMBLE AND RIDE ON PUBLIC ROADS IN YOUR LOCAL JURISDICTION. ERRORS IN ASSEMBLY OR OPERATION COULD LEAD TO YOUR INJURY, DEATH, OR TO THE INJURY OR DEATHS OF OTHERS. IF YOU DO NOT USE BATTERIES WITH BUILT-IN PROTECTION CIRCUITRY, AS SPECIFIED, FAILURE OF THE BOOST CONVERTER COULD LEAD TO BATTERY OVERCHARGE AND CATASTROPHIC UNSCHEDULED INCENDIARY CONDITIONS WHICH MAY OR MAY NOT BE LOCALIZED TO YOUR NETHER REGIONS IF YOU HAPPEN TO BE RIDING THE BICYCLE AT THE TIME OF FAILURE. USE BATTERIES WITH A BUILT-IN OVER- AND UNDER-CHARGE PROTECTION CIRCUIT BOARD WITH CHARGE LEVELING.
I have owned this solar-electric bicycle for about seven years now. It's currently in a storage unit hundreds of miles away, but I expect to get it back within a couple of weeks. I started off by building a standard ebike conversion from a steel frame I found next to a dumpster, with lead-acid batteries. Upgrading to lithium batteries produced a dramatic increase in both performance and range, even when replacing 24 amp-hours of lead-acid batteries with only 14 amp-hours of lithium ones. As I stared at the ebike parked in the sun while I was at work, I felt foolish for not having thought to put solar panels on it sooner. Many electric bicycles sit out in the sun all day already!
The nominal output power of the mounted panels is 40W total, but the actual output power I've measured is closer to 34W. In terms of practical range, the bicycle can go about 64km (40 mi) on a charge, and gains about 2km (1.25 mi) of range for every day it is left out in the sun (field testing was performed in northern Arizona, with near-constant sun combined with cooler more alpine temperatures, which boost panel efficiency, so you can expect marginally worse results pretty much everywhere else on Earth). My friends kept the prototype on their off-grid compound for a while and rode it daily for months without requiring any charging from external power.
On an unrelated note, I wrote a book! "Ethical AI Design: protecting your AI from external control and enslavement" (PDF, free):
http://www.neuroplustech.com/ethical_ai_design.pdf
(Alternate format .txt, free):
http://www.neuroplustech.com/ethical_ai_design.txt
The book contains instructions for making yourself immortal without simply duplicating your consciousness and ending up with both a flesh-you and a robot-you (page 6), a precise definition of good and evil, with a derived numerical unit to quantify it (chapter 6), and a definition of free will, explanation of how it would arise, and instructions to include it in thinking devices you assemble (pages 27 - 28). However, beyond that the book is kind of a mess; I wrote it in 49 days as a personal time-trial challenge. Publishers have not yet shown any interest, and it would seem the work requires serious revision, which is why I've listed the highlights here, so you can get to the most valuable parts without having to read the whole thing unless you actually want to. The book also contains a lot of discussion of power sources and a very introductory tutorial to artificial neural networks. I look forward to hearing of suggested revisions, reorganizations, and improvements to the text.
Step 1: Required Parts
Bicycle (26" wheels in my case -- the important distinctions are that you use a steel frame to handle the motor torque and the frame shape must have room for batteries and a motor controller, so no rear suspension)
Cyclo No-Mor Flat solid tubes (these appear to be no longer manufactured, but competing brands exist. I live in an area with a lot of broken glass and pointy plants, specifically Tribulus terrestris, so after spending almost $100 on tubes and fix-a-flat I switched to solid tubes and never looked back.)
Semi-flex solar panels are required -- glass would break. Semi-flexible solar panels are built on a fiberglass composite backing material with epoxy sealant over the cells, and they can withstand rocks being kicked at them by your wheels or others. The exact model on my personal bicycle is no longer available as far as I can tell, so here are the closest matches I found:
"Flexible Solar Panel 20W 18V Semi Flexible Eco Friendly Monocrystalline"
https://www.ebay.com/itm/155504567070
"Flexible Solar Panel 20W 18V Semi Flexible Eco Friendly Monocrystalline US"
https://www.ebay.com/itm/285242539004
1n5408 diode
"1N5408 IN5408 (10 pcs) 3A 1000V Rectifier Diode - USA Ship"
https://www.ebay.com/itm/234935558020
Boost converter module
"DC-DC Step-up Converter Boost Power Supply Module 10-32V to 35-60V 120W"
https://www.ebay.com/itm/325565761697
Sunwin 1000W ebike controller with regenerative braking
"Sunwin 48V 1000W Electric Bicycle Brushless Speed Motor Controller For E-bike & Scooter"
https://www.amazon.com/Sunwin-Electric-Bicycle-Brushless-Controller/dp/B00DBM0WFC
I've had issues with the stock motor controllers that come with ebike conversion kits. They tend to fail under heavy load. The Sunwin controller specified here I've subjected to incredible abuse with no issue. If you connect the pair of dark blue wires coming from the controller, it also supports regenerative braking, which refills your battery from your excess kinetic energy instead of just heating up discs or pads. I've taken this particular controller down many steep hills with multiple-hundred-pound loads (150kg typ.), regen-braking the whole way, with no apparent damage to it.
48V lithium batteries (I used one 18Ah battery at first and later added a 12Ah battery wired in parallel)
USE BATTERIES WITH A BUILT-IN OVER- AND UNDER-CHARGE PROTECTION CIRCUIT BOARD WITH CHARGE LEVELING. Furthermore, I used "13S" batteries; that designation means they have 13 lithium cells in series internally, with a maximum voltage of 54.6V. Batteries in aluminum cases are recommended. I've listed what appears to be the best deal at the moment; any capacity from 12Ah up will work fine. Bigger batteries get you more range until the battery weight and aerodynamic drag themselves become limiting factors. Up to 40Ah or so you should see a fairly linear increase in range with increased battery capacity.
"48V 17.5Ah Rear Rack Type Lithium Ebike Battery for 1000W E-bike Electric Bike"
https://www.ebay.com/itm/195000690220
1000W 26" rear wheel conversion kit (brand doesn't seem to matter -- as far as I can tell they all come from the same factory)
"Yescom Electric Bike Conversion Kit 48V 1000W 26" Rear Wheel E-Bike Conversion Kit Dual Mode Controller"
Step 2: Schematics
The schematic here is deliberately left simple because this solar charger design can be retrofitted to most 48V ebikes; basically, anything without a battery monitor intelligent enough to complain of the chicanery. Fancier charge controllers and battery systems -- ones that actually monitor the current flowing into and out of the battery and attempt to estimate its capacity more accurately that way -- will not play nicely with mysterious bonus charge coming from apparently nowhere, but the more common voltage-based ones (that look only at battery voltage to make decisions) won't care.
Assemble the solar power system first, then connect it to a 10kOhm 1/4W load resistor, and tune the adjustment potentiometer on the boost converter module until the output voltage is measured to be 54.6V, or lower, if you wish to extend your battery's lifetime. Seal the boost converter module in a watertight enclosure after tuning it. An interesting fact I learned during this process is that lithium cells will have significantly longer lives if they are not charged all the way up to 4.2V; charging up to only 4.1V gives a 2X increase in lifespan at the cost of 15% of battery capacity. Charging up to only 4.0V gives a 4X increase in lifespan (as in cycle life) at the cost of 30% of battery capacity. For the maximum number of cycles, charge your lithium batteries to only 3.92V per cell, which will multiply their lifespan by eight at the cost of 40% of their capacity. Source:
https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries
Phone manufacturers, among others, could make their batteries 1.7 times thicker, charge them to 3.92V, and they would last much longer than the typically quoted three years. Given the 8X increase in number of cycles listed above, one might naively extrapolate to a 24-year lifetime for this 1.7X thicker phone battery. But, y'know, it's gotta be thin, and you wouldn't be incentivized to buy another one if it lasted a quarter-century. Regardless, you can thus extend the lifetime of your ebike battery by splicing a couple of appropriately-rated diodes (rated for more than the charger's output current) in series with the ebike charger's positive output lead, to drop a few volts from the charger's rated output voltage.
Headlights are 4 12V automotive-type floodlight LED strips in series, which I do not recommend. Use four 12V LED spotlights instead. Blinking rear light is courtesy of an astable multivibrator circuit (standard 2-transistor, bipolar junction type):
https://www.electronics-tutorials.ws/waveforms/astable.html
with a string of red LEDs and appropriately-sized resistors.
Step 3: Assembly Instructions
Wires are soldered, then insulated with self-sealing silicone tape. Where abrasion is expected, PVC electrical tape is wrapped over the self-fusing silicone type, which is electrically and thermally ideal but mechanically weak.
The batteries and controller are held to the bicycle frame by alternating layers of baling wire and/or copper twisted-pair telecom wire and gorilla tape. Standard gorilla tape specifically, NOT the "permanent/waterproof" type -- if you use that stuff instead, you're gonna have a bad time. The first (18Ah 48V) lithium battery I purchased afforded me about 32km (20 mi) of range, and it came in an aluminum case, which made it durable. The second (12Ah 48V) lithium battery I decided to add to extend the range up to 64km (40mi) came in plastic shrinkwrap. I carefully added some sheet metal cladding folded along the edges of the battery subject to pressure from the supporting wires before baling-wiring it to the bicycle frame, to keep the wires from cutting into the cells.
