Bicycle Generator for Emergency Electricity


[Hackett's] back at it, this time with some practical advice for the next power outage to hit your city: why not prepare for the worst by building your own bike generator? You’ll no doubt recall that hurricane Sandy devastated New York City’s grid, even flooding substations and causing massive explosions. [Hackett] experienced the Sandy outages first-hand, and knows the value of having this simple build ready to roll.

The project uses a permanent magnet DC motor (around 250 watts), which you can find in electric wheelchairs or other mobility scooters. His setup’s gear reduction spins the motor 50 times for each revolution of the bike wheel. The apparatus [Hackett] built to press-fit the wheel to the motor’s spindle is particularly clever: a threaded rod adjusts the position of the motor, which is bolted onto a hinged platform, with the other part of the hinge welded to a larger frame that supports the bike wheel.

The motor is connected to a home-built charge controller based on Mike Davis’s design, which monitors the deep-cycle batteries and both kills the charge when it’s full as well as turns charging back on after it’s reached a set level of discharge. The rest is gravy: with the deep cycle battery connected to a power inverter, [Hackett] can plug in and keep phones charged, music playing, and even (some of) the lights on. If you’re a fan of [Hackett's] straightforward, practical presentation style, check out his tripod build and his demonstration of stripping pipes of their galvanization.

[Thanks Becky!]


  1. hue says:

    I love his tongue in cheek critique of preppers here. So funny. :)

    The generator design is also pretty neat, and his presentation is simple and effective. I like it.

  2. Augur says:

    I wonder if this could be modified to be placed under a car tire?

    • abe says:


    • J E Carter II says:

      Funny. Because we wouldn’t just use the cars electric system to charge a battery, that would be too easy… no geek cred for easy. Except then there’s gas and that’s a finite resource… but then again so are calories.

    • fartface says:

      Yes, because this is a better idea than using the power made by the car’s larger alternator.

      • Mulvane says:

        You are correct. But, if you are already running the engine at idle, why not also put it on a ramp and grab power from the wheels while its in drive vs park to reclaim more useful power out of the already running engine.

        • abe says:

          Yes! Because it’s free power!

          The alternator is in each car for some reason.

        • Augur says:

          Exactly what I was thinking of Mulvane!

          Fartface is so cute when he tries to be sarcastic ;-)

        • So you don’t think that by putting an additional load on the idling engine will make it consume more gas? If you don’t think it’s so, then I suppose that you probably also believe that a car going uphills at 100mph won’t use more gas than an idling engine either…

          • Kerimil says:

            If you have a car you pretty much have a gas generator… add an inverter and you can power mains powered appliances with it. Sure gas is a finite resource but if all you need is to get by for a few days or a week then it’s actually the cheapest option of all. Just buy 50L of petrol and store it somewhere…. aaaaand it can be used both for driving or producing electricity.

            As someone has pointed out calories are finite too. If you’re seriously into having a sustainable power source then build a small wind turbine and/or buy solar panels & some 12V batteries. This hack isn’t really practical. Not trying to be mean just stating the obvious.

          • Kevin says:

            No no no… you’ve got it all wrong, we’re going to have the car going DOWNHILL… we’ll collect the power from that, then go back to the top of the hill, and do it all again :)

        • KleenexCommando says:

          Um because the rules of physics and thermodynamics and all of that sciencey stuff say there is no such thing as “free” energy. It costs fuel to power an engine, so if you are drawing power off of the alternator with a load, the loads current draw causes the engine to use more fuel because under load, the alternator is harder to turn. If you add another load, like strapping something to the cars wheels, or setting the turning wheels on a dynamo like device, it will cause the engine to use even more fuel… Also, it takes even MORE fuel to turn all the stuff between the engine and the wheels, like the transmission…. It would be the most energy efficient to just tap all the electrical power you need directly from the alternator and bypass all of the mechanical friction of the drive train, which is waste. I reallllyyyyyy hope you guys were just kidding and I just typed all of that for no good reason… STEM indeed.

          • Mulvane says:

            The alternator has a max power output though. If you need to go above that, you could do it in tandem by using a generator tied into being turned by the wheels. It’s not about getting free or somehow magic energy, but a way to achieve MORE power.

          • Coligny says:

            or put a heavy duty alternator… like on most offroads or RV’s

        • static says:

          Ramp? More like leaving on drive wheel on the ground and jacking the other off the ground being mindful that the on off the ground is goint to turn in the apposite as to what the gear shift indicates direction.

          • Willis75 says:

            Except as soon as you put a significant load on the jacked-up wheel, that load becomes “traction” which in turn causes an equal amount of force to get routed to the wheel on the ground, moving the car off the jack. Not to mention the terrible stress put on the CV or universal joints which aren’t designed to be used constantly at the full travel of the suspension.

      • York says:

        This gives me an idea. I notice that there have been many comments on this, including, why not just get a generator. Well that’s no fun. Alternators natively generate 3 phase AC right? Rig up a control system for the engine’s speed (for 3000/3600 RPM depending on your power standard), leave it in neutral. All you need then is some voltage regulation.

        I imagine this wouldn’t be especially practical of course, such an engine speed would be woefully inefficient without significant load.

    • cheeseslices says:

      If you have gas for a car, then you have gas for a generator…negating the need for this device.

    • Hirudinea says:

      What, you guy’s never seen Predator? Watch the first 30 seconds then enjoy the firefight!

  3. Jason says:

    Very nice. Any estimate on the time to charge a battery to 90%?

    • rgoiejgroigj says:

      About ten hours or so for a 150lb male in decent shape.

      Typical alternator efficiency is 50%. Coulometric efficiency for lead-acid batteries is ~70%. I’m being generous in not counting the resistance of the tire-roller interface.

      Given even a fairly-in-shape person will struggle to put out more than about 1W per pound of body weight for an hour (and seriously, this is a LOT harder than it sounds if you’re doing it for an hour)…We can figure that they’ll get about 57Whr in electrical output. Your average car battery is 500-600Whr. So…ten hours. Ish?

      However, most people have at most 2 hours glycogen stores, and once those are exhausted, their output drops appreciably. Don’t forget that humans are about 25% efficient at turning calories into work, too, at least on a bike.

  4. Dave says:

    I too would like to know how long it takes for the battery to charge.

  5. Dynamo Dan says:

    I used a car alternator which contains its own charge controller and is very commonly available. I’ll shamelessly post the link.

  6. Orange says:

    newbie here. Is there any way to drop the excess voltage without overloading components? Must this be some sort of ‘force feedback’ on the bike wheel?

  7. dALE says:

    Wicked cool, I’ve got an old sit down lifefitness stationary exercise bike that could even house the batteries and all inside its case.

  8. Chris Krug says:

    he’s an opportunist. human powered generators have been around and there’s noting special about his. The opportunity is all the low power consumption devices now make this viable.

  9. Trui says:

    I’d simply get a gas powered generator. Sure, you need gas to run it, but for the bike you need similar amounts of high calorie food.

  10. static says:

    On would have to find an alternator that with a rated output that closely resemble your estimated power consumption, as not to waste input energy. To to mention alternators typically have to be spun faster. An alternator is equipped for a belt drive so that a point in there favor.

    • dynamodan says:

      True, true! Probably shouldn’t use a big semi-truck alternator, good advice for folks who accidentally buy the real big expensive one, rather than keeping their eyes open for the smaller, more common cheap / free ones. The one I used on my excercise bike is from a Chevy Cavalier, and spins the correct speed(s). It’s interesting to feel its torque curve change with pedaling speed, as a higher rpm requires less effort, at the same wattage output.

  11. static says:

    That’ too broad a brush, not all foods in the US are high calories foods. That many consume too much of the higher calorie foods would be the better statement. More likely that not several in a family or in the neighbor hood has stores of calories that could last for a way, until the stored food calories need to be consumed. Hopefully by that time relief in the form of food delivery are coming into the area as well.

  12. Manuka says:

    SPOILER: Us humans are pretty feeble creatures energy wise & although high output bursts may be briefly possible, most of us max at only ~50 Watts on a bike style system such as this. Even generating 50W will become tiring & dead boring after a while…

    Cheap solar PV (photo voltaic) panels can readily generate 10s of Watts under even overcast conditions, allowing us in emergencies to better use our nimble hand skills & brain & sense to rustle up food, organise shelter.or protect our loved ones.

    • KleenexCommando says:

      On the prepper side of things: Who you gonna call? not many people are going to be smart enough to build something like this to keep their phones and gadgets charged anyway… When disaster strikes, the first thing to go down (besides – insert someone you don’t like or said persons mother here), is CELL SERVICE due to the insane amount of calls to people that likely cannot or will not help you anyway. Let alone the fact infrastructure like that isn’t going to stay up for long anyway ( like -insert someone you don’t like here or their father here) so it’s pointless. Even ham radio is kind of pointless because those guys aren’t going to save your either… Which brings me to my biggest point (insert “thats what she said joke here”): Why the hell do you want to live through armaggedon anyway!? You’ll be stuck in dystopia with a bunch of people that will ALWAYS want to murder you for what you have that they don’t, and there will be no stopping them seeing how there is nothing keeping them from it, or you have to kill them first, which may or may not be a good time. ALL FOR WHAT? Just to die anyway…? No matter what you do, you gonna die… So you prolong your ultimate suffering and assured demise a few years, maybe less? Lame and pointless…

      • Richard says:

        Well, there are different kinds of disasters. Sure, I can imagine a hypothetical global collapse that wouldn’t be much fun to live through, and if that happens, getting a little electricity to charge a cell phone would be kind of pointless.

        But there are common regional disasters involving floods, earthquakes, wildfires, storms, and similar, where almost everyone survives but a lot of infrastructure is damaged for a while. Our power grid is one of the most fragile bits of infrastructure we have. I’ve personally lived through two events that caused week-long power outages, neither of which got much national news coverage. These weren’t major disasters; they were inconveniences. That’s the kind of situation where having some ability to make your own electricity could be handy. Probably not lifesaving, but handy.

        • TheAlchemist says:

          Not just handy, but amazingly comforting and morale preserving. It’s easy to take for granted what a little electric light on demand, being able to send/receive a text message or play a dvd for the kids can do for people living through an event and waiting for the power to come back on can do.

          I don’t care about these civilization-ending global disaster scenarios; they’re pretty much a secular gloss of the christian apocalypse mythology. But I am interested in localized systematic failures and what can be done to mitigate the impact.

      • static says:

        But who mentioned Armageddon? I don’t recall either Josh or Hackett doing so. I know there are plenty on web who believe they will be that king of that hill of bodies. That why I put out of mind the, thought that preparedness, would be a great reoccurring Hackaday topic as fast fast it entered my mind. Having said that I wouldn’t mind more preparedness related hacks presented. As in hacks that help make living through the aftermath a run of the mill disaster event more comfortable and safer, after surviving it in the first place

    • tony says:

      This is pretty much what I was thinking. It’s better for demonstration purposes than to practically generate electricity.

  13. CoolMod says:

    Lame… Plus needs a hair wash and a cut

  14. echodelta says:

    There is a picture in an old National Geographic that shows a scene during a crises in the 70′s. A bicycle is set up in filling station line, bike rim belted to the gas pump to pump fuel in measured amounts to customers. Those pumps had mechanical metering! They would have limited you to a couple of dollars though.

  15. Dax says:

    The description in the video is wrong, you do not get 250 Watts out of a 250 Watt motor – you get exactly as many watts as how hard you pedal because once the voltage goes up enough that it exceeds the battery voltage, the battery starts drawing current and the voltage stops rising. From there on, the motor starts to resist being spun faster.

    So once the voltage exceeds the battery voltage, the battery will clamp the voltage down to what the state of charge of the battery is, plus a little bit more depending how much current you’re pushing into the battery, which depends on how forcefully you pedal. The internal resistance of the battery is quite low, so a small increase in voltage over what the battery already has results in a large increase in current going into the battery, and since power is current times voltage, you need to pedal much harder to make the Watts to keep the charge going.

    The charge controller he’s using is a bit wrong for the purpose. It’s designed to switch to dumping power when the voltage exceeds 14.9 volts and go back to charging only when the voltage falls below 11.9 volts, which means that if you even temporarily exceed the set point it will not re-start charging the battery unless the battery is empty, or you disconnect the battery, or reset the circuit. I’m not even sure it works correctly for its original intended purpose, as it will not start charging batteries that were previously charged and then discharged to half full unless you manually reset the circuit.

    The full standby float charging voltage per cell for SLA batteries is 2.23 volts, for AGM batteries 2.25 and for flooded (car) batteries 2.32 volts. For a one-time non-continuous charge the voltage goes up to 2.37 volts per cell for all types. There’s six cells in a 12 Volt battery. That means the lower set point should actually be at 14.2 volts or else the controller won’t let you fully charge your batteries, since towards the end of the charge when the battery is getting full it’s easy to push it over the limit by pedaling slightly too hard.

    A better controller would not disconnect the battery but simply connect the dummy load in parallel to the battery to dump the excess and maybe give you a beep that you’re doing more than enough.

    • Dax says:

      That said, to fully recharge a regular 60 Amp-hour car battery from empty to full with 100 W you need to pedal for 7 hours straight. That’s because 60 Ah times 12 Volts = 720 Watt-hours.

      That’s why bike chargers are not a very reasonable response to power outages. Average adults can sustain about 75 Watts continuously and that’s about as hard as shoveling gravel for a job, and you lose some power in the mechanical setup, so you have to be prepared to pull several hours overtime just to get one battery charged up.

      • dynamodan says:

        Agreed. A bike alternator is *one more* option. Whether or not it’s a good one, we all find out after pedaling it for a few minutes. My alternator-bike is more useful as an exercise machine than a practical power source. But it’s better than the useless air blowing fan it was made with.

      • static says:

        In the event you are trying to charge up a flat battery with human power you are doing it all wrong. The battery is kept on a float charger until backup power is needed. From there you manage your power consumption, so it doesn’t take a lot of effort to top off the battery. Hints you don plan to use an inverter for lighting loads use the battery directly to power LED lighting. Get an absorption refer the fueled by kerosine or propane, that or dig a hole in the ground to keeps items cool. Hackett should keep back issues of Hustler around, unlikely the internet is going to be up anyway. Maybe if you have DSL & are hooked directly to the central exchange you may get your daily fix of fresh internet porn. My WISP evidently doesn’t have backup power at the tower site, lights go out in town I don’t have internet out of town even if I have power.

  16. Paul Bruno says:

    moar [Hackett] plz

  17. static says:

    One cellphones, don’t expect to use them much. One researching Radio Amateur Civil Emergency plans I came across this interesting tidbit. In an emergency Public safety organizations will have priority access the the cell phone system. We civilians when we get access will be limited to time slots that could be as little as 5 minutes. Meaning everyone should be planning ahead by by coordinating with family & friends so when get a such a call we know there is no time to waste get the import information to be forward with others outside the affected area conveyed YMMV if this is something that may be in force where one lives. Though I believe the closer you live to a major metropolition area the more likely this will be the policy

  18. It Hertz says:

    How many squirrels would it take to power this?

    Is there a Squirrel Power Factor?

  19. FastEddy says:

    The more Soylent Green you eat, the faster you pedal…

  20. While the set up behind this is cool, if you *really* need power, you’re better off with a generator and some deep cycle batteries. And by *really*, I mean save your refridgerated food, keep your house warm, cook food, and boil water.

    Get yourself a decent generator and a couple deep cycle batteries with an inverter and a 120V charger. I have a 5500 W generator that will run for about 12 hours at 50% output when full. I keep enough gas on hand to stretch that to about 36 hours. But I don’t need to run it constantly. A fridge/freezer will keep food safe for up to 24 hours if you don’t open it a lot. I’d just have to run the generator a few hours/day to run the fridge/freezer. I’d only need to run it for an hour or so to power a toaster oven/heating pan to cook. Assuming natural gas is still working (a big if, true), I only need to run a few hours a day to power the furnace fan. Even if gas is not available, I could run a space heater in a single room. By doing this, I can stretch out my gas supply out to a week (easily) and maybe longer.

    Use the deep cycle battery and inverter for continuous stuff like a light/radio/computer/internet. If you have the capacity, run everything at once to be efficient: fridge, furnace, charger, etc.

    Also, get yourself a 20 lb propane tank and a burner to heat/boil water. If you don’t have access to safe water, you can at least boil it.

    Obviously, these all require space/money. But if you can swing it, do it. Heck, you can buy a 900 W generator from Harbor Freight for probably the same amount of money for Hackett’s setup. Add in a 5 gallon gas tank, and you’ve got 25 hours of run time at 450 W. That’s easily a week of equivalent power with the added benefit of you doing something besides pedaling.

    Now, if you’re planning for the end of the world, then, yeah, prepare to pedal.

  21. JimBob says:

    Solar power isn’t free. Neither is wind power. Any power you harvest is no longer going where it originally was. Look at it this way: if the entire planet was covered with solar panels, no solar energy would be hitting the earth’s surface. All plant life would die, the surface would cool, etc. Solar energy (& wind) is finite, too. Ever hear of the heat death of the Universe? TANSTAAFL.

    • static says:

      I’d rather buy as many 1930-1950 era Briggs &Stratton 1 kilowatt farm power plants I could find to rebuild for what a Harbor Freight power plant would cost. some models had load sensing & auto start. Just like the Windcharger they where made obsolete by the REA. I knew a man who grew up with them. Locating them to restore was on of his retirement pastimes

    • Pete says:

      This is impressively bonkers. Of course if you have a planet entirely covered in panels, there’s no room for plants, but panels make very little difference to the temperature of the earth’s surface because the electrical energy ends up as heat after it’s done useful work.

  22. lastchancename says:

    OK, the solution to everyone’s needs.
    A mobility scooter jacked up onto a car alternator arrangement – feeding into a rectifier/charge controller – and on to the deep-cycle batteries – which can in turn be used to power/sustain the mobility scooter!
    You can sit down and create perpetual motion and energy until your ass gets sore, or the blackout ends (either in darkness or a return to city power!)

  23. J Merton says:

    This is sounding like the comedy channel. Comments should really be on-topic or they’re a time waster to wade thru.

    • TheAlchemist says:

      This must be your first day on the internet. Perhaps you’d like to volunteer to organize a comment police force, or maybe if we all scowl hard enough the miscreants will shape up and act like proper netizens.

      I’d say that the majority of the comments are relevant, even if there is a significant fraction that are tangential to the presented topic.

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