Linear voltage regulator?

[SwollenUvula]

I am currently trying to attach a small generator to my bike (dumb side project) I have a small DC motor I am going to be using to do so. It has a 24vdc output at max RPM, but when it's not spinning at max rpm (which will be most of the time) the voltage it output drops. I need something that can regulate the motor/generator to 14vdc at any rpm. It can output up to 350W, so a decent amperage. Any help would be appreciated.

 

[ronsimpson]

Are you charging a 12V car type battery?
I think a person can only produce about 100 watts.

 

[AnalogKid]

A linear regulator will not work in this application for two reasons.

1. At low speeds, when the generator output voltage is below 14 V, a linear regulator cannot boost it up to 14 V. There are switching regulators called "buck-boost", that can move seamlessly between boosting an undervoltage and bucking (regulating down) an overvoltage. Linear Technology (now a part of Analog Devices) is big in this arena. Know that this is not a trivial design project at low power. At 350 W it is a difficult design project.

2. If the generator can produce 350 W at 24 V, regulating that down means dissipating 146 W. That's a lot.

Please add some details to your question. At what bike speed does the generator output drop below 15 V? When producing 15 V, how much current is available?

ak

 

[Nigel Goodwin]

Are you charging a 12V car type battery?
I think a person can only produce about 100 watts.

I seem to recall that a fairly fit man can only generate about 60/70W for any decent period of time, with 100W been more of a short time peak. The simple 'test' was usually powering a 60W bulb

Top cyclists can generate more for long periods though - and the guy who cycled over the English Channel on a pedal powered plane was particularly impressive

A 350W alternator would seem pretty pointless, and produce less power than a more sensibly sized one.

 

[Tony Stewart]

10W load will feel like a significant drag on your speed and likely make you not reach your goal.

Even the friction of trying to spin it to max RPM with pulleys will be a challenge to your strength and be an uphill battle.

 

[ronsimpson]

With out knowing what is powered by the 14 volts we cannot say what to do. Charging a battery is very different than a heating element or running a car radio.
At this point, we all agree you will never get 350 watts. Not close.
We mostly agree "linear regulator" will waste power.
I cannot comment more because we don't know enough and guessing adds confusion.

 

[AnalogKid]

I seem to recall that a fairly fit man can only generate about 60/70W for any decent period of time, with 100W been more of a short time peak.

50 to 150 W for us mortals. To get the Gossamer Albatross across the English Channel took around 1/4 horsepower continuously for over two hours.

Human power - Wikipedia

en.wikipedia.org

ak

 

[Tony Stewart]

14 yr old boys can possibly charge up a flashlight with one hand for hours after 15 minutes of vigorous exercise.

However your concept is not sufficiently thought out.

 

[Papabravo]

In my former city there was a museum exhibit with a hand crank AC generator and gearbox with three 20W light bulbs in parallel as a load. The idea was to crank the generator up to some comfortable speed and switch the lightbulbs on one at a time. When the third one was switched on there was noticeable difficulty in continuing to crank. It was very difficult to continue for more than a minute. Legs might be better than arms but there are still enormous obstacles to using human power to generate electrical power.