# Light bulb!

#### benkoostra

##### New Member
OK, here's a crazy idea I had last night while riding my spin bike in the livingroom:

If I hook a generator to the bike and rig it up to illuminate a 100-watt light bulb, I'm generating at least 100 watts, when friction is taken into account, right?

So a series of bulbs will give me a rough approximation to my power output, or am I missing something critical?

benkoostra said:
OK, here's a crazy idea I had last night while riding my spin bike in the livingroom:

If I hook a generator to the bike and rig it up to illuminate a 100-watt light bulb, I'm generating at least 100 watts, when friction is taken into account, right?

So a series of bulbs will give me a rough approximation to my power output, or am I missing something critical?

wouldn't using a strain gauge somehow interfaced with a small computer be a better way of doing this?

<post circa 1985>

mr_mojo said:
wouldn't using a strain gauge somehow interfaced with a small computer be a better way of doing this?

<post circa 1985>
Yes, it would be more accurate, but my question is this: instead of using a special hub, or measuring the deflection of the chain or some other technique, isn't the raw output of the machine, i.e. the human body, just as well measured in this simple way? The bulb requirs 100 watts to function, so if I can light it up, I am producing the necessary power.

Not to mention I can build this for well under \$100.

benkoostra said:
Yes, it would be more accurate, but my question is this: instead of using a special hub, or measuring the deflection of the chain or some other technique, isn't the raw output of the machine, i.e. the human body, just as well measured in this simple way? The bulb requirs 100 watts to function, so if I can light it up, I am producing the necessary power.

Not to mention I can build this for well under \$100.
Now I'm not a EE, so maybe I'm missing something. Your average everyday light bulb is an AC device yet a generator outputs DC current. And then there is the issue of whether the lit 100 watt bulb is really taking 100 watts, because if you provided insufficient current, the bulb would still glow, just not as brightly.

joule said:
Now I'm not a EE, so maybe I'm missing something. Your average everyday light bulb is an AC device yet a generator outputs DC current. And then there is the issue of whether the lit 100 watt bulb is really taking 100 watts, because if you provided insufficient current, the bulb would still glow, just not as brightly.

There are electronic ways to provide AC current to a series of lamps that would light up as long as power supplied reached a specific threshold. You'll have some inefficiency in the devices but you could build yourself say, 4-8 lamps that would light up in sequence according to the power supplied.

If you make 200 watts you get one lamp. If you make 250 watts you get to watch TV. If you make 300 watts the DVD player will show your Tour videos. If you make 199 watts or less your TV will show "American Idol", from the first season...

WarrenG said:
There are electronic ways to provide AC current to a series of lamps that would light up as long as power supplied reached a specific threshold. You'll have some inefficiency in the devices but you could build yourself say, 4-8 lamps that would light up in sequence according to the power supplied.

If you make 200 watts you get one lamp. If you make 250 watts you get to watch TV. If you make 300 watts the DVD player will show your Tour videos. If you make 199 watts or less your TV will show "American Idol", from the first season...
HAHA!
This is exacly what I'm talking about! A series of bulbs that light up in sequence as a wattage threshold has been reached. I have no doubt that such a device could work, but........
Am I correct in thinking that by providing enough power to light a 100 watt bulb, I am generating that much wattage with my legs (plus what is lost in friction)? The machine would need some fine tuning, but why wouldn't this work similarly to a powertap in measuring output? Power is power, right?

benkoostra said:
HAHA!
This is exacly what I'm talking about! A series of bulbs that light up in sequence as a wattage threshold has been reached. I have no doubt that such a device could work, but........
Am I correct in thinking that by providing enough power to light a 100 watt bulb, I am generating that much wattage with my legs (plus what is lost in friction)? The machine would need some fine tuning, but why wouldn't this work similarly to a powertap in measuring output? Power is power, right?

Well, depending on how sophisticated your device is you could be losing 20-30+% in efficiency so it might take 130 watts to make 100watts AC. You could just use LED's on a bar graph to indicate the current coming out of your generator.

Remember those old generator lights that had a wheel rubbing against the side of your tire as your rode? When you were going slow the light was dim, but it got bright once you were going a certain speed. I'm not sure if your device could really measure power, as much as it would be merely measuring the speed of your wheel or whatever part of your drive train was connected to the measuring device.

WarrenG said:
Well, depending on how sophisticated your device is you could be losing 20-30+% in efficiency so it might take 130 watts to make 100watts AC. You could just use LED's on a bar graph to indicate the current coming out of your generator.

Remember those old generator lights that had a wheel rubbing against the side of your tire as your rode? When you were going slow the light was dim, but it got bright once you were going a certain speed. I'm not sure if your device could really measure power, as much as it would be merely measuring the speed of your wheel or whatever part of your drive train was connected to the measuring device.
hey why not just get one of those lights do they still sell em??

No need for a series of lights. Just hook the ouput of the generator to a watt meter. Radio Shack sells them.

Rick

benkoostra said:
Am I correct in thinking that by providing enough power to light a 100 watt bulb, I am generating that much wattage with my legs (plus what is lost in friction)?
Not really, no. As has been mentioned, a 100w bulb will light with less than 100w. It's rated to draw 100w based on a 120V 60hz AC input, but it will produce light under other conditions as well.

http://www.otherpower.com/otherpower_experiments_bicycle.html
http://users.erols.com/mshaver/bikegen.htm

The funny thing is that if you were to generate electricity for you home using a bike powered generator, the food costs alone would probably make the electricity more expensive than if you were to purchase it from the electric company (depending on the utility rates where you live). Strange but true.

benkoostra said:
OK, here's a crazy idea I had last night while riding my spin bike in the livingroom...

You aren't the first:

a whole science class project around the concept

shawndoggy said:
I remember long ago seeing a news story about some unfortunate kids with a sadistic ******* for a father They had to ride a bike in order to power a TV. No exercise... no TV.

Personally, I'd have killed him in his sleep then watched all the TV I wanted.

frenchyge said:
Not really, no. As has been mentioned, a 100w bulb will light with less than 100w. It's rated to draw 100w based on a 120V 60hz AC input, but it will produce light under other conditions as well.

The funny thing is that if you were to generate electricity for you home using a bike powered generator, the food costs alone would probably make the electricity more expensive than if you were to purchase it from the electric company (depending on the utility rates where you live). Strange but true.

This last paragraph is specious, because it fails to take into account that you would be getting in shape, NOT buying electricity from a coal burning plant with its concomitant waste and effluent, and lastly, THAT YOU WOULD BUY AND EAT FOOD ANYWAY. Strange but false, in this case.

You know, anyone with fingers can Google humorous pictures of bikes with quaint old light generators, et al, but I'm not talking about that. What I want to know is this: can anyone tell why this wouldn't work and be just as effective at measuring my wattage output as the powertap, or walletdrain, or whatever it's called?

benkoostra said:
What I want to know is this: can anyone tell why this wouldn't work and be just as effective at measuring my wattage output as the powertap, or walletdrain, or whatever it's called?

I see the big problem as setting up the resistance.

If you knew the efficiency of the generator (or motor... they're the same thing) throughout its range of RPM (if I remember my E&M correctly the torque required to turn an electric motor decreases with RPM) and you purchased a meter (electo-mechanical or digital) of sufficient accuracy then you could replace the PowerTap. But...

I can't see how you'd create enough resistance to get a real-world estimation of your power. In your plan you'd be limited by cadence more than anything. Generators have minimal mechanical resistance and any other form of resistance you added to give you a workout (fans, friction, etc) would just make your measured power (at the generator) drop.

What you propose is the beginning of how some non-portable power meters work but with a difference... they measure the amount of current required to resist your pedalling force and derive power from that.

How about getting a PowerTap (maybe the wireless one) and putting it out of sight? Then have an assistant monitor your power output and switch on a combination of lightbulbs representative of your power output? For example, if you're doing 250, he or she will switch on two 100W bulbs and a 50W bulb.

benkoostra said:
This last paragraph is specious, because it fails to take into account that you would be getting in shape, NOT buying electricity from a coal burning plant with its concomitant waste and effluent, and lastly, THAT YOU WOULD BUY AND EAT FOOD ANYWAY. Strange but false, in this case.
Nothing suspicious (or false) about it; it just says what it says. If you want to assign a monetary value to the rest of that stuff for additional analysis, then go ahead. Yes, you'll need to eat food anyway, but the point was that the extra calories burned simply as a result of generating the electricity on a bike would cost more than just buying the electricity. It struck me as interesting that the electric company can produce and sell power cheaper than a seemingly 'free' source of power like a bike generator.

benkoostra said:
What I want to know is this: can anyone tell why this wouldn't work and be just as effective at measuring my wattage output as the powertap, or walletdrain, or whatever it's called?
I believe I did. Did you read the *first* paragraph I wrote?

you could always crack an egg and smear it on your quads...when it starts cooking you've hit 1200w. Stick an english muffin and some canadian bacon down your chamois and voile...powerMcMuffin.

Squint said:
How about getting a PowerTap (maybe the wireless one) and putting it out of sight? Then have an assistant monitor your power output and switch on a combination of lightbulbs representative of your power output? For example, if you're doing 250, he or she will switch on two 100W bulbs and a 50W bulb.
sorry, slightly different topic. Do they make a wireless powertap? Honest question. I was actually annoyed when I looked at their website and doenst mention anything. Is the SL wireless?

netscriber said:
sorry, slightly different topic. Do they make a wireless powertap? Honest question. I was actually annoyed when I looked at their website and doenst mention anything. Is the SL wireless?

A wireless PT is due later this year. Phonak (among others) have been testing it since last season.

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