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I have salvaged a motor from a treadmill to make a stationary bike generator.

Motor Specs: 180 VDC -4500 Rpm 1.3 Hp 6 amp

I mocked up a bike trainer and using the rollers from treadmill and was able to output 100-160 VDC unloaded, and using a 50 cm piece of Nichrome wire I was measuring 20-30 VDC @ 2-3 amps. But the current fluctuates.

I am trying to work out what I would need to safely charge a deep cycle battery which I understand I will need a controller or circuit to reduce voltage and manage battery charging, but not sure what that would look like.

The generator will be placed in a communal space for people to help power the campsite, so it would need to be idiot proof.

Thanks

Edit: 1: Battery hasn't been finalized most probably a 120 Ah 12v AGM Deepcycle Marine battery

2: Disregard what load will be coming off the battery as it should not interfere with what can be put into the battery

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    \$\begingroup\$ You haven't mentioned the specs of your battery that you need to charge. \$\endgroup\$
    – Chetan Bhargava
    Commented May 8, 2017 at 2:58
  • \$\begingroup\$ remembering the "exercise bike demo" at a hydro power plant hurt's my legs; you had to pedal like mad to get a tungsten bulb to light up... fridges and pumps are some of the most power-consuming items too... \$\endgroup\$
    – dandavis
    Commented May 8, 2017 at 4:18
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    \$\begingroup\$ Does anyone know if something like this aliexpress.com/item/… (intended for 100 VAC - 240 VAC) could be used with a 30 VDC - 180 VDC input and still work? I'm not sure what the internals of these things look like. \$\endgroup\$
    – Jeremy
    Commented May 8, 2017 at 4:42
  • \$\begingroup\$ The bike to power at shows/showroom at nuclear power plants and what have you, does not actually use the power from the bike to power the various appliances connected to them, at least not the ones I've lifted the hood on. If you can modify your battery charger so that the ouput current depends on the input voltage from your generator, you should be able to get decent behaviour. If you have a fixed current limit, you need to pedal until you simply "get there" and then keep the rpm and torque up to maintain it. \$\endgroup\$
    – winny
    Commented May 8, 2017 at 6:58
  • \$\begingroup\$ The motor is too strong for a bike generator. You don't need 1.3 HP, about 0.5 HP or less will do. \$\endgroup\$
    – Uwe
    Commented Jul 8, 2017 at 19:59

4 Answers 4

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Please confirm how you are going to rotate the motor. And at what speed/rpm? The motor is of quite high power & you can get the desired voltage range by rotating it slowly also. My suggestion is to use a 24v battery or 2x12v as the nominal voltage is touching 30volts. I suggest to use a solar charge controller of 10A which supports both 12 & 24 volts (can be used for multiple applications if not giving desired output). Be sure to check input voltage range before buying charge controller or try to add a LED voltmeter/rpm meter for input so that you can avoid over voltage. If you can share what is going to run in the battery, i can suggest better solution. How much watt is the load or how much current the load required? Edit: You can use dummy load (search online) so that over voltage can be avoided. Or hook up a LED with zinner diode & some resistors so that light will glow if the voltage is exceeding charge controller's input range & you can stop pedaling. Best option is to choose a charge controller which has auto shutdown feature for your ease & project safety.

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What you need is a converter that can accept, as input, the voltage range that the generator can produce and provide a constant output voltage that is appropriate to charge the battery. If you are charging a 12-volt battery that would be a buck converter / charge controller that will reduce the voltage to about 15 volts. If you have a battery that could be damaged by the maximum current that anyone can generate, the charge controller would need to be designed to limit the current. You may want to experiment with a variety of loads to see if you have the optimum speed ratio between the pedals and the generator shaft. That would be a pedal speed at which most people can perform well.

It is unlikely that you can power fridge, pumps, lights, etc. with just human power. However, without actual load power requirements, and usage times, that is impossible to estimate. It is also impossible to determine much about the charging system without the battery voltage and Ah capacity.

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    \$\begingroup\$ I didnt say i was going to power a fridge from the generator i am just wanting to charge the battery, I also understand that the voltage needs to be reduced but i have been unable to find something that has a variable input to constant output \$\endgroup\$
    – Melvin000
    Commented May 8, 2017 at 4:30
  • \$\begingroup\$ At some point, you need to consider how many hours per day of charging will be required with nothing but human power. There are variable-input converter / charge controllers made for wind turbine, solar, and hydro-electric use. If you want to buy something you need to research that elsewhere. This site is limited to design questions. \$\endgroup\$
    – user80875
    Commented May 8, 2017 at 10:50
  • \$\begingroup\$ Re, "... and provide a constant output voltage that is appropriate to charge the battery..." Really? is constant voltage ever appropriate to charge a battery? Battery chargers that I have used provide constant current until something* happens, and then maybe apply constant voltage to "maintiain" the battery. *The "something" could just be, voltage comes up to some level, or could be a combination of voltage and temperature. \$\endgroup\$
    – Solomon Slow
    Commented Jun 17, 2017 at 22:38
  • \$\begingroup\$ Yes. I made reverence to a charge controller, but "constant output voltage" is not appropriate.I am not going to bother to clarify it. The question doesn't deserve more than a few general directions is guidance to further research. \$\endgroup\$
    – user80875
    Commented Jun 18, 2017 at 2:38
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Your current at 30V was 2A, so the current into a 12V battery will be... what? If, as seems likely, you can maintain that same power into the generator, it'll be 5A and will work just fine. A 120 A-h battery can take 12A and only achieve full charge in ten hours, so you have lots of safe margin.

Connect it and go! The only issue, really, is overcharging (and that can be corrected by monitoring the battery charge, and the output, with energy meters).

If the stationary bike has gears, it's best to keep the tempo of pedaling at about one revolution per second (a good athlete might manage twice that), for comfort and efficiency.

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  • \$\begingroup\$ Thanks i guess then the question would be what would i use to change the 30v to 12v and when there is no load (battries full ) is it a problem when some one gets on and it would see 100v+ ? would a cheap solar charger work? \$\endgroup\$
    – Melvin000
    Commented May 8, 2017 at 10:34
  • \$\begingroup\$ Because the 'no-load' voltage was 60V, and 'with-load' was 30V, the 'with-battery-as-load' will be 12 to 13.8 until the battery is fully charged. It might be useful to switch off when the battery is overcharged, but there's no need to do much more. Just short across the generator output terminals ( the pedaler will feel the pedals lock, even if the 'charge full' indicator doesn't come to his attention). The choice of 'batteries full' causing loose pedaling, or hard stop to pedaling, is open. \$\endgroup\$
    – Whit3rd
    Commented May 8, 2017 at 22:27
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An average cyclist should be able to keep up about 150 watts continuously. (125 W for an eight-hour shift is 1 kWh - the amount of work you can get out of a servant in a day.) Factor in the efficiency of your drive chain, generator and charger losses and you'll be lucky to get half that into the battery.

I mocked up a bike trainer and using the rollers from treadmill and was able to output 100-160 VDC unloaded, and using a 50 cm piece of Nichrome wire I was measuring 20-30 VDC @ 2-3 amps.

P = VI = 30 x 3 = 90 W max. You were getting 60 to 90 W which agrees with my comments above.

I am trying to work out what I would need to safely charge a deep cycle battery which I understand I will need a controller or circuit to reduce voltage and manage battery charging, but not sure what that would look like.

Possibly very little is required. Your generator power is limited by human effort and will be intermittent.

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  • \$\begingroup\$ Something like this will be limited in possibilities, but with decent engineering should still be sufficient for a few phones and flashlights, which tend to be key to keeping modern humans happy. \$\endgroup\$
    – Chris Stratton
    Commented Jul 9, 2017 at 3:49

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