FAQ
TL;DR: For a 200 W, 24–36 V target, plan ~140% shaft power and prefer a 30–90 V permanent‑magnet DC motor as generator; “The magnets contain no potential power.” [Elektroda, Steve Spence, post #21669282]
Why it matters: This FAQ helps DIYers pick realistic parts and wiring to power a 24–36 V, 200 W load without wasting effort.
Quick Facts
- Expect ~40% conversion losses; plan about 1.4× mechanical input for your desired electrical output. [Elektroda, Steve Spence, post #21669269]
- A fit rider sustains ~100 W; bursts are higher, so 200 W electrical may require multiple riders or storage. [Elektroda, Steve Spence, post #21669282]
- Car alternators need a few thousand RPM and their field coil eats power; PMDC treadmill/lawnmower motors (30–90 V) work better. [Elektroda, Steve Spence, post #21669282]
- Flywheels store energy; they are not energy sources, so you must supply torque first. [Elektroda, Steve Spence, post #21669273]
- Chaining alternator→alternator compounds losses (~40% per conversion), leaving far less usable torque. [Elektroda, Chuck Sydlo, post #21669277]
What’s the best alternator or generator to power a 200 W 24/36 V DC motor?
Use a permanent‑magnet DC motor (30–90 V) as a generator, not a car alternator. It produces voltage at human‑achievable RPM and avoids field‑coil losses. A car alternator wants thousands of RPM and wastes your limited pedal power. [Elektroda, Steve Spence, post #21669282]
How much mechanical power do I need at the shaft to get 200 W electrical?
Budget roughly 1.4× your electrical target. For 200 W out, plan about 280 W into the shaft to cover typical alternator losses and inefficiency. That overhead comes from load‑dependent drag and heat. [Elektroda, Steve Spence, post #21669269]
Do alternators cog, and what resistance will I feel at 200 W load?
Automotive alternators don’t cog like permanent‑magnet machines. Drag rises with current draw and inefficiency, so resistance is light at no‑load and noticeable under 200 W. Expect significant load‑proportional torque. [Elektroda, Steve Spence, post #21669269]
Can a flywheel be my energy source?
No. A flywheel only stores energy; it does not create it. You must supply torque first, then the flywheel smooths power and bridges short bursts. “A flywheel is a energy storage device, like a battery.” [Elektroda, Steve Spence, post #21669273]
Can I drive one alternator with another to boost power?
Avoid alternator‑to‑alternator chains. Each mechanical↔electrical conversion loses about 40%, so two stages compound losses and waste most of the input torque. It’s a classic efficiency trap. [Elektroda, Chuck Sydlo, post #21669277]
Will a car alternator work for human‑powered 24–36 V output?
It’s a poor match. Car alternators need high RPM and their field coil can consume much of a rider’s power. A PMDC motor used as a generator is simpler and more efficient for pedaling. [Elektroda, Steve Spence, post #21669282]
How many amps can a human realistically produce at 12 V?
About 10 A is realistic for short periods; 60 A at 12 V from human pedaling is not. Human sustained output is around 100 W, so current is limited by both voltage and rider stamina. [Elektroda, Steve Spence, post #21669282]
What RPM should I target?
Automotive alternators expect a few thousand RPM to reach rated current, which is hard by pedal. PMDC generators produce voltage roughly proportional to RPM, making them workable at modest speeds. [Elektroda, Steve Spence, post #21669282]
Are magnets themselves a power source?
No. Magnets enable conversion but don’t provide energy. “NO, you cannot produce work with magnets.” You must input mechanical work to get electrical output. [Elektroda, Steve Spence, post #21669280]
Do I need a transformer or DC‑DC converter for 24–36 V systems?
Transformers only work on AC. DC cannot be transformed directly, so use a DC‑DC converter to change DC voltage, accepting about 10% conversion loss in the process. [Elektroda, Steve Spence, post #21669271]
How should I couple a 30 cm, 15 kg flywheel to hit a 200 W draw?
Set gearing so the generator spins in its efficient range while you can sustain cadence. Drag rises with electrical load and inefficiency, so adjust pulley ratio to maintain cadence under about 200 W. [Elektroda, Steve Spence, post #21669269]
Quick How‑To: Build a 24–36 V pedal generator that can deliver ~200 W
- Select a 30–90 V PMDC motor as your generator and gear it to comfortable cadence.
- Rectify/regulate as needed and feed a 24–36 V battery or motor controller.
- Add a flywheel only for smoothing; it won’t increase net energy. [Elektroda, Steve Spence, post #21669282]
Could ferrofluid or iron filings inside a coil boost output?
Focus on proven PMDC‑generator designs instead. The core message: your legs are the energy source; magnets and materials only shape conversion. Prioritize low‑loss generators over exotic coil fillers. [Elektroda, Steve Spence, post #21669282]
Why does resistance feel low when the alternator is unloaded?
With no load, current is minimal, so mechanical drag is small. As electrical draw rises, copper and conversion losses grow, increasing shaft torque demand and the pedaling effort you feel. [Elektroda, Steve Spence, post #21669269]
Can an alternator also act as a motor out of the box?
Automotive alternators are not motors without modification. Treat them as generators only; if you need motor function, use a proper motor or a modified unit. [Elektroda, Steve Spence, post #21669278]
