Light bulb!

[beerco]

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?

Well, it would sort of work but not quite how you think. Adding a generator to your trainer setup would be like adding another resistance unit with a linear increase in resistance (not considering start up current in the lightbulb) as speed increases.

So, let's say you've got the lightbulb up to it's regular brightness so you've got 100w pumping through there. This means that you're making much more than 100w due to the inefficiencies of all of the equipment as an earlier poster mentioned. You'd have to use some other means to calibrate how much power you're making when the lightbulb is at 100w.

Finally, this would only work on a trainer because the generator is simply a "flat tax" on your power related only by wheelspeed. e.g. it wouldn't see the extra power you're making to get up a hill at 8mph, it would only see the power needed to go 8mph under any circumstances.

 

[sidewind]

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.

If you can build it, why not just build the system and report the test results here rather than repeat your questions wether it is feasible approach at all...

 

[Squint]

A lot of people claim to be able to build a powermeter for less than $100 in their garage after a trip to Radio Shack. My response is the same as yours: go do it.

Building a powermeter might just be more difficult than one thinks. Some manufacturers have found this out too.

If you can build it, why not just build the system and report the test results here rather than repeat your questions wether it is feasible approach at all...

 

[MichaelB]

When I broke my arm I got some shitty old bike I had lying around and welded a car alternator onto it. Not easy with one arm let me tell you!

It seemed kind of a pity that with an alternator you only get an output when you connect the field terminal to a battery so it wasn't totally human only power (although that will be a few watts only).

Anyway it was bloody hard work just getting a 60 watt car headlamp to light and even harder when you hooked both the main and full beam up to give 115W.

Being such a crappy bike didn't help and also you could smell the rubber from the tyre because it was slipping and getting hot. Also the inefficencies in the alternator took a little power (the diodes, reg, windings...). Having said that alternators are very efficient devices - at least 80% if working well.

Take it from me this was one crappy generator mainly due to the fact I had a broken arm, wanted immediate results (hence bodged it up in half an hour or so) and put no effort into design etc... You could probably do a good job of this and if you got a low capacity storage device like a 1 to 3 Farad capacitor you could have a useful system.

The AC DC issue isn't one if you onyl want to light a light bulb. They aint fussy and 240VAC is actually the same as 240VDC for something like a light bulb. In fact the stated voltage and power on a light bulb will be the Root Mean Square (RMS) value which is the effective DC heating value. The AC voltage will vary bettween ~ 350V to +350V in the UK and about +/-170 V in the USA. The RMS value tells you what the equivalent DC value would be for the same heating effect.

You might even get a TV to work off 250VDC/120VDC because they have switch mode power supplies which convert the AC straight to high voltage DC and then make it AC again to get it down to low voltage. Therefore it mightn't be bothered that it was DC all along but you might blow it up if it in fact does not have a switch mode PSU in it and instead has a transformer - like VCRs tend to.

 

[tuney]

What you guys are missing here is NOT wether you can light a 100watt bulb with the right intensity..amps...voltage...blah blah... its that you could be storing the power and then reducing your electric bill...

OR SELL IT BACK TO THE NATIONAL GRID (UK) I think we in the UK buy at 12p per KWH(i dont know what they buy at), so a good 4 hour ride on a turbo could make you in the region of 12p!

Just think how hard you would have to pedal in the ad breaks!

MAN... Im gonna be rich... hmmm maybe not.

 

[jetnjeff]

What you guys are missing here is NOT wether you can light a 100watt bulb with the right intensity..amps...voltage...blah blah... its that you could be storing the power and then reducing your electric bill...

OR SELL IT BACK TO THE NATIONAL GRID (UK) I think we in the UK buy at 12p per KWH(i dont know what they buy at), so a good 4 hour ride on a turbo could make you in the region of 12p!

Just think how hard you would have to pedal in the ad breaks!

MAN... Im gonna be rich... hmmm maybe not.

Yeah but will it download into Cycling Peaks software?