Can an E-Bike Power a Cinema?

Why the stock drivetrain cannot generate

Mid-drive motors — Bosch, Shimano STEPS, Yamaha, Brose, and DIY kits such as the Bafang BBS02/BBSHD and Tongsheng TSDZ2 — apply assist at the bottom bracket through one-way clutches, so the rider never drags the motor. Grin Technologies' controller manual states the consequence: regenerative braking on these systems "won't be able to help slow the bike down due to the intrinsic freewheel" ¹⁹. Builders document two to three one-way clutches stacked between crank and rear wheel in a mid-drive path, and a specialist mechanic documents both a crank-freewheel sleeve and an internal sprag-clutch bearing inside a Bosch Gen4 drive unit ^20,21. Stock geared hub motors fail at the wheel for the same reason: "Almost all of the geared hub motors on the market have a freewheel inside … it eliminates the possibility of regenerative braking," a conclusion an independent academic study of e-bike drivetrains also reaches ^22,23. On a stand, either drivetrain produces nothing, because no mechanical path runs from pedals to rotor. The single documented commercial exception is Grin's GMAC hub, which replaces the usual freewheel with a locked clutch so that it can generate ¹; at least one vendor describes aftermarket clutch-locking modifications of other hubs, which are modifications, not stock behaviour ²⁴.

Specifications

What do these labels mean?

Field	Value	Confidence	Sources
Grin GMAC locked-clutch hub	the only documented commercial geared hub able to generate (locked clutch replaces the usual freewheel)	Documented	¹
Direct-drive hub voltage-to-RPM relationship	370 rpm produces about 48 V open-circuitBuilder-documented; voltage is proportional to rotational speed.	Documented	²
DIY direct-drive hub conversion efficiency	roughly 50–60 % end-to-end (hub, rectifier, DC-DC converter, battery)Practitioners' own forum-reported estimate; medium confidence, not independently verified.	Estimated	³
2013 stationary direct-drive build, design target	50–100 W, for a laptop and small sound systemA builder's stated target, not a logged result.	Operator-stated	²
December 2025 stationary hub-generator build, measured charge power	116 W (15.92 V at 7.3 A, via MPPT controller, into a 16-cell LiFePO4 pack)Instrumented with controller telemetry and screenshots; not independently replicated.	Measured	⁴
Same build, regen-controller mode	up to 200 WAn upper bound from one strong, motivated rider, not an event average.	Measured	⁴
Phaserunner V6 peak regen phase current	up to 90 AManufacturer manual; regen current setting directly sets peak braking torque.	Documented	⁵
Hub motor stationary cooling penalty	12 km/h of airflow gives about 3× better heat dissipation than still airGrin Technologies' own instrumented controller tests.	Measured	⁶
Two-wheeler hub motor winding temperature, low-speed use	up to 170 °C; torque limiting above 130 °C, demagnetisation risk above 150 °CPeer-reviewed measurement.	Documented	⁷
CycleCinemaClub Vienna system draw	roughly 250 W to projector and amplifier	Operator-stated	^8,9
CycleCinemaClub per-rider contribution and rider count	about 50–60 W per rider; 10–12 active participants	Operator-stated	^8,10
Battery-as-source DC-DC plus inversion loss	roughly 10–20 % conversion loss (reported from 48 V e-bike packs)DIY practitioner reports of running laptops and small televisions, not instrumented measurement.	Documented	^11,12
London Fire Brigade e-bike/e-scooter fires, 2025	206 total, 171 involving e-bikes (record high)	Documented	¹³
UK product-safety fire-cause attribution, 2024	45% post-market conversion kits, 39% while charging, 93 % battery as ignition source	Documented	¹⁴
Schaeffler Free Drive crankset generator	3.5 kg, 250 W total drive output, up to 60,000 km maintenance-freeFleet production since February 2023; no documented cinema deployment.	Manufacturer rating	^15,16
CIXI PERS range-extension claim	up to 25 %Research correction:A vendor promotional figure, not an independent measurement; no pedal-cinema deployment of this hardware is documented.	Promotional / press-reported — not verified	¹⁷
Mando Footloose pedal-charging contribution	judged "negligible" by reviewers; unrideable with a dead batterySold roughly 2013–2017; now discontinued.	Documented	¹⁸

What can generate

Direct-drive (gearless) hub motors have no clutch: the magnets pass the stator windings continuously, so any rotation of the wheel produces three-phase AC whose voltage tracks speed — about 48 V at 370 rpm in one builder's documentation ². The DIY path is hub, three-phase rectifier, DC-DC converter, battery, at an estimated 50–60% end-to-end efficiency ³. A 2013 stationary build targeted 50–100 W for a laptop and small sound system ²; a December 2025 build measured 116 W of charge power into a 16-cell LiFePO4 pack, rising to 200 W in a regenerative-braking mode, from one strong rider in a single session ⁴.

The hazards of forcing it

Regenerative-braking firmware is tuned for short deceleration events, not continuous generation. The Phaserunner V6 manual sets a peak regen phase current of up to 90 A and warns that at low motor speeds this current "can be many times higher" than what the battery sees ⁵; peer-reviewed literature confirms the low-speed boost effect, which uses the motor's own windings as an inductor ²⁵. Run continuously, the December 2025 builder found it "impossible to maintain proper rpm," because crank position determined how much torque reached the motor ⁴. The battery carries the sharper risk. Grin Technologies founder Justin Lemire-Elmore: "If a controller doesn't have a maximum regen cutoff, and you do regen and then either unplug the battery or have the battery BMS circuit trip, then the voltage will keep on increasing as the regen current has nowhere to go until something gives (usually the mosfets)" ²⁶. Batteries with separate charge and discharge ports fail the other way, unable to shut off regen current at all ²⁷; a repair forum documents a Sabvoton controller needing its MOSFETs replaced after a battery-disconnect spike of this kind ²⁸. Heat is the third limit. A stationary stand removes the airflow a hub motor relies on — Grin's tests found 12 km/h of moving air gives roughly three times the heat dissipation of still air ⁶ — and peer-reviewed measurements record hub-motor winding temperatures reaching 170°C in low-speed, high-current conditions, with torque limiting above 130°C and demagnetisation risk above 150°C ⁷, the regime that 100–200 W of sustained stationary generation occupies.

Cutaway comparison from Grin Technologies: a direct-drive hub motor beside a geared hub motor opened to show its planetary gears — Image: Grin Technologies (ebikes.ca) — via ebikes.ca

The one fielded lineage

Vienna's CycleCinemaClub, in its fourteenth season in 2026, is the only fielded pedal cinema documented here that is built on e-bike hardware. Three to five workshop-converted e-bikes run their motors as bare generators into a battery bank sized so that output "does not drop while one rider dismounts and the next mounts" ⁹. The rig draws roughly 250 W for projector and amplifier at about 50–60 W per rider, so ten to twelve rotating participants suffice ^8,10. The conversion replaced the stock control architecture with the direct-drive path above; no mid-drive or geared-hub e-bike was used as purchased.

Battery as source

E-bike hardware helps as a charged, silent energy carrier rather than as a generator. DIY builders report running laptops and small televisions from 48 V e-bike packs through DC-DC conversion and inversion at a conversion loss of roughly 10–20% ^11,12. The same community's documented practice is never to draw power from a battery's charge port, because "if you short it by doing that, the bms will not cut out and could start a fire"; discharge belongs on the discharge terminals, where the protection circuit is live ¹¹. London Fire Brigade recorded 206 e-bike and e-scooter fires in 2025, a record high, 171 of them e-bikes ¹³, and UK product-safety notifications for 2024 trace 45% of such fires to post-market conversion kits, 39% to charging, and 93% to the battery itself as the ignition source ¹⁴. The documented use is an undamaged, OEM-grade pack discharged through its own discharge terminals into a correctly sized inverter — not a modified pack, a charge-port tap, or any improvised path around the battery's protection.

Three documented absences

As of September 2026, no documentation had been located of a stock original-equipment e-bike battery being recharged by stationary pedalling; no commercial bidirectional charger existed that pushes power from an e-bike battery back out as a source; and no pedal-cinema system in this record uses regenerative-braking-mode generation ⁴. These are limits of what was located, not proof that no such thing could exist.

Commercial bike-by-wire products

Purpose-built "bike-by-wire" e-bikes design out the chain rather than retrofitting one. Schaeffler's Free Drive is a 3.5 kg crankset generator feeding a rear hub motor and battery buffer, rated at 250 W total drive output and 60,000 km maintenance-free, in fleet production since February 2023 ^15,16. CIXI's PERS markets "Pedal backward to slow down and recharge the battery"; its "up to 25%" range-extension figure is a promotional claim without independent measurement ^29,17. The Mando Footloose, a series-hybrid e-bike sold roughly 2013–2017 and since discontinued, was unrideable with a dead battery, and reviewers judged its pedal charging "negligible" ¹⁸. None of these products has a documented cinema deployment.