Build a Bicycle Dynamo Power Bank: Charge Radios Off-Grid with a Spare Wheel

A week after the storm, the generator’s cans are dry, the solar’s buried under gray sky, and the only reliable voice is the one coming from your handheld radio—until its battery icon starts blinking. You’ve got a spare bicycle wheel leaning in the shed and a stack of parts you’ve meant to tinker with. Ten minutes later, you’re spinning rubber and hearing the reassuring beep of a charging pack. It isn’t magic; it’s watts—your watts—turned into a steady trickle of off-grid power.

I’ve built and field-tested three iterations of a bicycle dynamo power bank for comms and lighting, teaching this setup in backcountry comms workshops and refining it during real outages. The sweet spot isn’t sprinting for grid-level output; it’s sustained, safe, quiet power you can make in a living room. With a modest permanent-magnet DC motor or hub dynamo and a sane regulator, an average rider can produce 10–15 watts continuously—enough to add roughly an hour of receive time to a typical 7.4V HT in about 10–12 minutes of pedaling.

In this guide, we’ll turn a spare wheel into a dependable charger built for radios. You’ll get a precise parts list and sourcing notes, options for the generator (hub dynamo vs PMDC motor), and the exact rectification and regulation chain: bridge diode choices, smoothing capacitors, buck/boost settings, and why we prefer LiFePO4 or high-cycle 18650 cells for the buffer pack. We’ll build a compact wheel stand you can assemble with scrap lumber, dial in gearing for comfortable cadence, and add a flywheel for steadier voltage. Then we’ll test under real loads—handhelds, AA/NiMH chargers, and USB—and solve the gremlins: overvoltage spikes, RF noise in your receive, hot diodes, and slipping tires.

By the end, you’ll have a quiet, durable power bank that turns calories into comms—no sunshine, no fuel, no drama. Let’s spin up something reliable.

Define the Mission First: Power Requirements for HTs and What a Spare-Wheel Dynamo Can Really Supply

You’re two hours into a storm net, the grid’s down, and your HT battery is sliding toward empty. In the truck is a spare front wheel with a bottle dynamo you’ve used for bike lights. Can that wheel keep your nets alive? It can—but only if you match what your radio needs to what the dynamo can actually deliver.

What Your HT Actually Needs

Battery size and charge rate: A typical dual-band HT (think UV-5R/FT-60 class) runs a 7.4V Li-ion pack around 1800–2200 mAh—about 13–16 Wh. A healthy charge rate is 0.3–0.5C for Li-ion packs, but most desktop cradles are conservative: roughly 0.3–0.6 A at 8.4V (2.5–5 W into the pack).
Charger input reality: Many OEM drop-in chargers take 10–12V DC at 0.3–0.6 A (3–7 W in) and do the CC/CV internally. Some newer HTs accept 5V USB-C at up to 1 A (5 W). Actual wall-warts often read 10V/0.5 A for Baofeng-style cradles and 12V/0.35 A for Yaesu/Kenwood.
Direct pack charging: If you bypass the cradle and charge the 2S Li-ion pack directly (with a proper CC/CV module set to 8.4V), expect 0.3–0.5 A = 2.5–4.2 W into the pack.

Why it matters: Your charger is a power sink. If it wants 5 W steady and your generator can only provide 3 W clean, you’ll brown out the regulator or stall the wheel—wasting effort and risking your electronics.

What a Bicycle Dynamo on a Spare Wheel Can Supply

Nameplate vs. reality: Standard bottle or hub dynamos are rated 6V, 3W at around 15 km/h. On a 700C wheel, that’s roughly 120 rpm at the rim. Hand-cranking or foot-pedaling a mounted spare can reach 90–150 rpm sustainably.
After rectification/regulation: A full-wave rectifier and DC-DC converter cost efficiency. Expect 70–85% end-to-end. So a “3W” dynamo yields about 2–2.5 W usable DC continuously, 3–4 W if you’re really cranking.
Voltage behavior: Unloaded, the dynamo voltage can spike high—tens of volts. Under load it sags. That’s why you must rectify, smooth, and regulate before touching anything electronic.

Translation: Think of the spare wheel as a reliable 2–3 W trickle source, not a wall outlet.

Matching the Two: Realistic Expectations

Time-to-charge: A 14 Wh pack at 60% depth of discharge needs ~8–9 Wh back in. At 2.5 W net, you’re looking at ~3.5 hours of spinning, plus conversion losses—call it 4–5 hours. Topping off 20–30% is a one-hour task, not an all-day ordeal.
Strategy: If your cradle demands 10–12V at 0.5 A (5–6 W), it’s too hungry. Either:
Charge a 5V power bank first (buffering and smoothing), then run the cradle or a USB-C equipped HT from the bank, or
Skip the cradle and charge the 2S pack with a CC/CV buck-boost set to 8.4V at 0.3 A, matching the dynamo’s sustainable output.

Common Mistakes and Quick Tests

Mistake: Trying to transmit while charging off the wheel. A 5W HT draws 1.5–2 A at 7.4V (11–15 W). Your dynamo cannot cover that. Charge during listen-only periods.
Mistake: Feeding AC dynamo output straight into a USB module. You’ll kill it. Always rectify and buffer first.
Test your load: Put your charger on a bench supply and note the input current at its minimum working voltage. If it needs >3 W continuous, plan on a buffer battery.
Monitor with a multimeter: Verify your regulated output doesn’t dip below 4.8V for USB or exceed 8.4V for a 2S CC/CV charger.

Key takeaway: A spare-wheel dynamo is a steady trickle charger, not a fast charger. If you right-size your load—aim for 2–3 W continuous—and use a buffer where needed, you can keep HT batteries topped through extended outages. Next, we’ll turn that spiky 6V AC into clean, regulated DC your radios and power banks will accept without complaint.

Select Proven Components: Hub vs. Bottle Dynamo, Rectification, DC-DC Regulation, and Safe Lithium Storage

Picture this: you’ve got a spare 700c wheel on a stand, a handheld radio that’s hungry for electrons, and time to kill during a grid-down evening. The difference between a frustrating trickle and a reliable charge comes down to the components you choose. Here’s how to spec parts that actually work together—no smoke, minimal wasted effort, and usable power at the end.

Hub vs. Bottle Dynamos

Hub dynamos (6V/3W nominal at ~15 km/h) are efficient, quiet, and weatherproof. They produce steadier power with less slippage and are ideal if your spare wheel already has one laced in. Expect 60–75% overall system efficiency after conversion, translating to roughly 300–500 mA at 5V under realistic spin rates.
Bottle dynamos clamp to the tire sidewall or rim. They’re cheaper and easy to add to a spare wheel, but they slip when wet, wear tires, and add noise and drag. Choose proven models with grippy drums (e.g., AXA HR, B&M Dymotec 6) and set firm contact pressure. If you plan to spin by hand or with a strap, bottle dynamos are the fastest path to power—but mind alignment and tire pressure to reduce slippage.

Troubleshooting:
– Slipping bottle dynamo: roughen the contact patch slightly, use a clean, dry sidewall, and ensure the roller hits squarely.
– Sharing power with lights: most dynamos are 3W total. If you keep the headlight on, your charger gets what’s left. Use a switch or prioritize charging.

Rectify and Smooth the AC

Dynamo output is low-frequency AC (30–100 Hz) that rises with speed. You need a full-wave bridge and a buffer.

Rectifier: Use a Schottky bridge rated 3A/40–60V (e.g., four SS34 diodes or an MBR3045 bridge). Schottkys run cooler and waste less power.
Smoothing: Install a low-ESR capacitor 2200–4700 µF, 25V across the rectified output. This reduces ripple so your DC-DC converter doesn’t drop out at low RPM.
Protection: Add an 18V TVS diode (e.g., SMBJ18A) across the rectified DC to clamp overspeed spikes, and a 1A resettable polyfuse on the dynamo line.

Common mistake: skipping the capacitor. The converter will chatter, your radio will see resets, and charging will stall.

Regulate for Useful DC

You need stable 5V (USB) or a selectable output for radios.

Converter: Use a buck-boost (SEPIC or 4-switch) module with wide input (6–40V DC) and at least 15W rating. Set USB to 5.2V to overcome cable loss. MP1584 buck modules work only once input stays above ~7V; a true buck-boost (e.g., LTC3115-based or quality XL/DF series) handles variable speeds.
Filtering: Add an LC filter (100 µH + 1000 µF) on the converter input to cut alternator whine and RFI that can desense receivers.
USB signaling: For phones or smart devices, add 49.9k pull-downs for USB-C 5V or Apple/BC1.2 resistors on USB-A so they actually draw current.

Troubleshooting:
– Converter resets at high RPM: your input is spiking. Upsize the cap, confirm TVS, and check that the module’s max input isn’t being exceeded.
– No charge on certain radios: their docks expect 9–12V. Use a selectable buck output or feed a proper charger cradle instead of raw 5V.

Store Energy Safely in Lithium

Buffering with a lithium pack lets you charge while pedaling and use gear later.

Pack: A 1S (3.7V nominal) 18650 bank (2–4 cells in parallel for 5–12 Ah) is versatile. Use a proper 1S BMS with overcharge (≈4.25V), overdischarge (≈2.5V), and short-circuit protection.
Charging: Feed a dedicated CC/CV charger (e.g., TP4056 with protection) with stable 5V from your converter. Set charge current to 0.5–1.0A; the dynamo will usually be the limiting factor.
Outputs: From the 1S pack, use a separate boost module to 5V/9V/12V as needed. Fuse both the pack (2–5A) and outputs, and use 20–22 AWG silicone wire.
Enclosure: Ventilated, IP54+ rated, with cell holders (not loose cells), thermal pad under the charger, and strain relief. Keep the battery physically isolated from the rectifier/converter heat sink.

Common mistakes:
– Charging bare cells directly from 5V or, worse, from the dynamo. Always use a charger IC and BMS.
– Packing cells tight with no fuse. A shorted 18650 can ruin your day—use a pack fuse and protected cells.

Key takeaway: Pick a reliable dynamo, rectify with low-loss components, regulate with a robust buck-boost, and store energy behind a proper lithium charger and BMS. With parts chosen, we’ll assemble the stand, mount the dynamo, and wire the first test loop next.

Turn a Spare Wheel into a Generator: Stand, Fork Mount, Drive Choices, and Ergonomics for Sustained Use

You’re parked under a trailhead pine, the net check starts in 20 minutes, and your handheld’s battery is sagging. Out comes the spare front wheel with a hub dynamo, a scrap fork, and a compact stand. Ten minutes of smooth foot power later, your power bank is climbing. The difference between “neat idea” and “usable generator” is in the mounting, drive, and ergonomics. Build for stability and comfort, and you’ll actually use it when it counts.

Build a Stable Stand

A wobbling wheel wastes energy and eats hands. Start with a 3/4-inch plywood base about 18 x 24 inches. Glue and screw a pair of 2×4 uprights to the base, spaced to accept a standard front fork (100 mm dropout spacing). Add rubber feet or set the base on a camp mat to stop skittering; a 10–15 lb sandbag on the rear of the base locks everything down.

Set axle height 11–14 inches above the base. That gives room under the tire for a belt or roller and keeps the rim clear of your knuckles. If you’re using a salvaged fork, bolt it through the uprights with 3/8-inch carriage bolts and fender washers. Align the fork so the wheel plane is square to the base; even a few degrees off causes side-load heat and can make a hub dynamo growl.

Why the fuss? A stable, square mount reduces friction, prevents the tire from “walking” off any drive roller, and keeps your cadence transferable to the generator rather than the stand.

Fork Mount and Alignment

Drop the wheel in with a quick-release or axle nuts. Spin it unloaded first. Watch the gap between rim and brake pads (or a fixed pointer); lateral wobble should be within 2–3 mm. True the wheel if needed. For hub dynamos, keep the connector facing away from your drive to avoid snagging. If you’re using a bottle dynamo instead of a hub unit, mount it to the fork leg so its roller hits the rim sidewall squarely and firmly; expect to increase spring pressure slightly to avoid slip at lower RPMs.

Troubleshooting:
– Scrape or shudder under load: check fork squareness and ensure the axle is fully seated in both dropouts.
– Wheel slowly shifts sideways: add a hose-clamp “keeper” around each dropout and the fork blade as a stop.

Drive Choices: Hand, Belt, or Roller

You’ve got three practical options:

Hand spin (emergency): With gloved hands, you can hold 60–90 wheel RPM for short bursts—enough to wake a power bank—but fatigue hits fast. Use only when you must.
Belt drive (best field option): Wrap a smooth V-belt or 3/4-inch flat webbing around the tire. Route it to a small 50–80 mm pulley on a simple treadle crank (a 2×4 lever with a pedal). A 70 mm pulley to a 700c tire (~680 mm OD) gives roughly a 1:9.7 speed increase; at a comfortable 70 strokes/min you’ll see ~110–130 wheel RPM—right where most hub dynamos make their rated 6V/3W. Tension so you can deflect the belt 10–15 mm mid-span with one finger.
Contact roller (shop build): Press a 100 mm wooden or aluminum roller on bearings against the tire, driven by a hand crank or pedals. It’s efficient and quiet, but fabrication is more involved. Ensure the roller axis is exactly parallel to the axle to prevent the tire from climbing.

Common mistake: over-tensioning belts. It chews sidewalls and drags. If the belt squeals, add a bit more wrap angle or lightly scuff the tire sidewall—don’t just crank down tension.

Ergonomics for Sustained Use

Aim for 90–120 wheel RPM. With a belt ratio that lands you there, you can produce the hub dynamo’s 3W continuously for 20–30 minutes without smoking your quads. Sit on a stool with hips slightly above knees, knee angle near 120 degrees at the bottom of the stroke. Keep your ankle neutral; pointing toes wastes effort. If using a treadle, add a light return bungee so the pedal comes up without lifting your leg.

Why cadence matters: Power is torque times speed. The dynamo’s sweet spot is at speed; forcing high torque at low RPM feels punishing and yields less energy. Smooth, circular strokes beat stomping.

Safety and comfort:
– Gloves prevent blistering if you hand-spin.
– Keep clothing clear of the belt. Guard the roller if kids are around.
– Take 60-second breaks every 10 minutes; your average output will be higher than grinding nonstop to failure.

Key takeaway: A square, heavy stand plus a simple belt or roller drive turns a spare wheel into a generator you can run for the length of a radio net. With the mechanics dialed, we’re ready to route that 6V AC into clean, regulated DC for your power bank and handheld—up next.

From Spokes to Stable Volts: Wiring the Rectifier, Filtering, Protection, and Smart 18650 Power Bank Charging

Picture the front wheel humming on a work stand while your DMM jitters between numbers. That’s your cue: the dynamo is alive, but radios and lithium cells don’t tolerate jitter. This stage turns that lumpy AC from spokes into stable DC your charger understands, with filtering to smooth surges, protection to save components, and a smart path into 18650 cells.

Rectify and Smooth: Turning AC Into Usable DC

Bridge rectifier: Feed the hub dynamo leads into a bridge (the two “~” terminals). For efficiency, build one from four Schottky diodes like SS34 (3 A, 40 V). You’ll lose ~0.3–0.4 V per leg versus ~1.0 V with standard silicon—worth it at low power.
Reservoir capacitor: Across the bridge’s + and – terminals, add a 2200–4700 µF, 16 V low-ESR electrolytic and a 0.1 µF ceramic in parallel. The big can reduces ripple at low RPM; the ceramic kills high-frequency noise that upsets DC-DC converters.
Why it matters: Hub dynamos are roughly 6 V AC, 3 W at ~15 km/h. Without smoothing, your downstream regulator sees a sine wave and will latch, reset, or dump heat. This cap gives the converter a “flywheel” to ride between peaks.

Troubleshooting: If the converter chatters (LEDs flicker, USB devices connect/disconnect), increase capacitance or speed, and keep the wiring short. If the cap runs warm, you’ve reversed polarity or used too low a voltage rating.

Protection: Because Open-Circuit Voltage Can Spike

Polyfuse: Put a 0.75–1.0 A resettable fuse (PTC) in series with one dynamo lead. It trips on shorts and self-resets.
TVS clamp: Across the DC bus (after the bridge, across the capacitor), add a TVS diode such as SMBJ15A (standoff 15 V). Open-circuit hub dynamos can hit tens of volts. The TVS eats spikes and protects your buck converter.
Bleeder: A 10 kΩ, 0.25 W resistor across the cap slowly discharges it and tames minor overshoot.

Common mistake: Skipping the clamp and feeding a cheap buck (20–24 V max) directly. One downhill sprint and you’ve bought smoke. The TVS + polyfuse combo is cheap insurance.

Regulate and Limit: Feed the Charger What It Wants

Use a CC/CV buck module (XL4015-based works well) set to:
– Constant current: 0.4–0.6 A. This matches a 3 W dynamo and prevents bogging at low RPM.
– Constant voltage: 5.1–5.2 V. Slightly above 5.0 V helps overcome cable loss.

Why CC first? The current limit keeps the dynamo in its comfort zone; without it, the converter hunts, torque surges, and everything pulses.

Set CC by shorting the output through an ammeter and dialing to 0.5 A. Then set CV to 5.2 V with no load.

Smart 18650 Charging: Do It Right or Don’t Do It

You’ve got clean 5.2 V. Now hand charging off to a proper Li-ion charger/BMS:
– Single cell: A TP4056 board with protection (DW01A + 8205A) is ideal. Change RPROG to set current: 2.0 kΩ ≈ 580 mA, 3.0 kΩ ≈ 400 mA. For dynamo use, 400–500 mA is the sweet spot.
– Multi-cell power bank: Use a reputable 1S power-bank PCB that handles cell protection and balancing (if parallel cells) and accepts 5 V input. Mount cells in holders, use spot-welded tabs or proper nickel strip, and keep leads short.

Troubleshooting: If the TP4056 overheats, your input sags or airflow is poor; reduce charge current or add a small heatsink. If charging cycles on/off, lower the buck’s CC limit or increase the reservoir capacitance.

Key takeaway: Rectify with low-loss diodes, smooth generously, clamp the bus, and deliver a current-limited 5.2 V into a smart 18650 charger. Do that, and your “spokes to volts” pipeline stays steady from walking pace to downhill sprint. Next, we’ll mount and weatherproof the electronics so this rig survives real trail grime and rain.

Prove It in the Field: Output Testing, Load Matching, RF Noise Control, and Protecting Sensitive Radios

You don’t know a power system until you’ve ridden it. Picture this: you’ve laced the spare wheel with a hub dynamo, clamped it in a repair stand, and spun it up with a drill or quick pedal strokes. Your handheld is on scan, a power bank is connected, and you’re watching numbers. Field validation is where theory meets terrain.

Validate Output in Real Conditions

Start simple: test at three speeds—walking pace (4–5 mph / 6–8 km/h), cruise (10–12 mph / 16–19 km/h), and sprint (16–18 mph / 26–29 km/h). A 6V/3W hub should deliver ~3 watts near 12 mph. Use a USB inline meter and a multimeter on the rectified DC bus.

Open-circuit: you might see 8–12 VDC after rectification. That’s fine. What matters is loaded performance.
Under load: aim for 5.0V at the USB port with 0.5–0.7A at 10–12 mph (2.5–3.5W). If the voltage sags below 4.8V or the converter resets, you’re overdrawing at that speed.

Actionable setup: add a 2–3Ω, 10W dummy resistor across the bus for quick tests, or use an adjustable USB load set to 0.5A. Check that the buck/boost holds output steady and doesn’t oscillate.

Common mistake: bench-testing only at one speed. The dynamo is speed-sensitive. Validate across your real riding profile.

Match the Load to the Dynamo’s Curve

Why: a dynamo is a current-limited source; overloading it collapses voltage and wastes effort. Your DC-DC stage must sip, not gulp.

Use input current limiting. Many quality buck/boost boards let you cap input to ~0.5A at 6–8V (≈3W). Set it so the dynamo never stalls. If your board lacks this, add a series current limiter or choose a module with pseudo-MPPT behavior.
Buffer the input. A 4,700–10,000 µF low-ESR capacitor on the rectified bus smooths pedal pulses and prevents converter dropouts at low speed.
Stage the load. Charge a small buffer battery/power bank first, then run radios from that. Radios see stable voltage; the dynamo sees a forgiving charge controller.

Troubleshooting: if the converter “hunts” (ticking, periodic resets), lower the load or add more input capacitance and a modest series resistance (0.5–1Ω, 5W) to tame surge.

Control RF Noise Before It Kills Your Reception

Switching converters are noisy. Your receiver will tell you fast.

Filtering: add an LC filter on both input and output. Start with 47–100 µH inductors and 470–1,000 µF low-ESR caps. Snap-on ferrite chokes (mix 31 or 43) on the leads and USB cable tame common-mode hash.
Layout: twist input leads from the dynamo, keep the converter in a metal enclosure (bonded to ground), and physically separate it from radio/antenna cabling.
Field test: tune an AM radio around 1 MHz near the setup; loud buzzing = noise. Improve filtering until it’s faint. Check VHF/UHF by watching your S-meter and squelch behavior while charging.

Common mistake: plugging the radio directly into the converter without filters. Expect birdies across HF and harmonics into VHF.

Protect Sensitive Radios from Spikes and Oops

Overvoltage: clamp the bus with a TVS diode (e.g., 15V bidirectional for a 12–13.8V rail; 6.8V for 5V USB). It absorbs surges when you abruptly unload the system.
Reverse polarity: use an ideal-diode MOSFET or at least a Schottky diode on each rail.
Fusing: inline 1–2A fuse on the DC output to radios. If something shorts, your dynamo and converter survive.
Clean power for radios: feed radios from the buffer battery or a low-noise linear regulator off the battery, not straight from the switching converter.

Field note: if your HT hums while charging, switch to “charge-when-pedaling, RX-when-coasting,” or run the charger 2–3 meters from your operating position with extra ferrites.

Key takeaways: test at realistic speeds, cap input current to respect the 3W limit, add serious LC filtering and ferrites, and protect against spikes and polarity errors. With output proven and noise tamed, you’re ready to package the system for hard miles and fast deployment in the final build-out.

Push the Build Further: Gearing, Flywheels, Supercaps, and Hybrid Solar/Bicycle Charging Strategies

Picture this: you’re riding out a three-day storm in a backcountry cabin. The folding panel on the porch limps along under heavy cloud. Your spare wheel generator is the constant you can count on—but with a few strategic upgrades, it becomes a quiet, efficient powerhouse that smooths pedal effort, buffers bursts, and plays nicely with solar.

Smarter Gearing: Hit the Sweet Spot

Most dynamos and small PM alternators have an efficiency “happy place.” If your wheel turns 200 rpm on the stand and your alternator prefers 1,500–2,000 rpm, you need a 7–10:1 step-up. A simple way: a 60T chainring driving a 12T cog (5:1), then a second stage with a 48T to 16T (3:1), for a combined 15:1. Belts work too: a 120 mm pulley to 20 mm on the alternator yields 6:1; add a second stage to fine-tune.

Why it matters: running in the sweet spot reduces wasted heat, cuts drag, and stabilizes voltage for cleaner DC conversion. Watch for over-gearing—if you’re grinding at 50 rpm cadence to hold voltage, you’ve gone too far. Aim for comfortable cadence (70–90 rpm) and adjust ratios so your generator sits where it’s most efficient.

Troubleshooting common mistakes:
– Belt slip under load: increase belt wrap with an idler, roughen the small pulley, or bump tension slightly.
– Bearing heat at high RPM: add a drop of light oil or swap to sealed bearings rated for >5,000 rpm.
– Voltage spikes when you stop: use a load dump diode and a TVS across the generator.

Add a Flywheel: Smooth the Pedal Pulse

Human power is lumpy. A modest flywheel makes your alternator “feel” like it’s driven by a small engine. A 1 kg steel disc at 150 mm radius has I ≈ 0.0225 kg·m². At 300 rpm (31.4 rad/s) it stores ~11 J—enough to ride out half-second cadence dips. Mount it on the alternator shaft or an intermediate shaft; shield it for safety.

Why it matters: inertia flattens torque pulses, reducing voltage sag that can crash buck converters or glitch radios. Keep it balanced (static balance with two knife edges) and don’t oversize—heavy flywheels make starting painful and can overstress mounts. If you feel “runaway” at high RPM, add a simple mechanical brake or an electronic dump load tied to bus voltage.

Supercapacitor Buffer: Instant Surge, Fast Recovery

A supercap bank turns staccato human power into a steady DC bus. Example: six 2.7 V, 50 F caps in series (8.3 F effective) rated to 16.2 V. Energy = 0.5 × 8.3 × 12² ≈ 600 J—enough to cover radio transmit bursts or absorb short pedal lulls without dragging RPM down.

How to do it right:
– Balancing: use 2–5 mA active balancers or 10–33 kΩ passive resistors across each cell.
– Precharge: add a 10–20 Ω resistor and bypass MOSFET to avoid inrush that can weld connectors.
– Low-ESR wiring: short, thick leads; ring lugs; crimp, then solder. Add a 5–10 A fuse near the bank.

Common missteps: linear regulators on a supercap bus (they’ll cook), no reverse protection, and mounting caps where they see vibration—use foam standoffs or a strap cradle.

Hybrid Solar + Pedal: Auto-Priority Without Babysitting

Let solar lead and legs assist. A practical layout:
– Solar: 50–100 W panel into a small MPPT set to a 12–14 V DC bus (or straight to a 12 V LiFePO4 pack via a proper BMS/charge controller).
– Bike: rectified generator through a buck-boost to the same DC bus.
– OR-ing: Schottky diodes work, but an ideal-diode controller (e.g., LTC4412, LM5050) drops only millivolts, maximizing every watt.
– Output: your USB-C PD buck lives off the bus or the LiFePO4. The bus also feeds your radio.

Why it matters: the sun carries the base load; you pedal to top off or cover clouds. With OR-ing, sources don’t backfeed each other. Add a voltmeter and a 0–10 A shunt display; train yourself to pedal to a bus voltage target (e.g., keep 13.4–13.8 V) instead of chasing current.

Troubleshooting:
– MPPT hunting with pedal assist: slow the MPPT sweep rate or put a small (5–10 Ah) LiFePO4 buffer between MPPT and bus.
– Shadow flicker causing PD drops: enable power-good hold-up with 470–1,000 µF at the PD output and set USB triggers to conservative profiles (5 V/3 A before stepping to 9–12 V).
– Hot diodes: move to ideal-diode controllers or parallel Schottkys with proper sharing resistors.

Key takeaways: gear for your generator’s sweet RPM, add a modest flywheel for smooth torque, use a well-managed supercap bank for surge and stability, and let solar lead while your legs fill the gaps. With these upgrades, your spare-wheel charger transforms from “it works” into a dependable microgrid component ready for real-world field use.

If there’s a single lesson here, it’s to think like a radio op first and a tinkerer second: define the load, then build only as much generator as you need. A spare wheel, a proven dynamo, and a well-behaved DC path can reliably feed HTs when the grid goes dark—provided you respect the limits. Aim for sustained, clean 5–10 watts into a battery buffer, not headline-grabbing peaks, and you’ll keep comms alive without burning yourself—or your cells—out.

Your next moves are simple and actionable. Inventory your radios and chargers; note charge voltage and typical current. Select a quality 6 V/3 W hub or bottle dynamo, low-loss rectification, a CC/CV regulator set for your target (5 V USB or 8.4 V for 2S packs), and a protected 18650 bank. Build a rigid stand with comfortable cadence, then mark the “sweet spot” RPM where voltage and effort settle. Wire in protection (polyfuse, TVS), add low-ESR capacitance for ripple, and choke RF with ferrites and an LC filter. Field-test under real loads; log watts vs. cadence; key a radio while charging and listen for desense. If the charger hunts, increase capacitance; if RF sprays, shorten leads and add ferrites; if power sags, gear down or add flywheel mass.

From there, iterate: integrate Andersons, OR in a folding panel, and pre-stage a laminated charging SOP with the rig. Build it, practice monthly, and you’ll own something better than gear—you’ll own an energy advantage you can make on demand.

Build a Bicycle Dynamo Power Bank: Charge Radios Off-Grid with a Spare Wheel