Pedal generator from scratch...a couple of questions.

[JChris]

First off, I'm new to the board, but I've been reading for a month or two and have enjoyed every minute so far. Initially, wind power is what has brought me here, so a wind turbine is the ultimate goal; however, in the interim I thought playing around with a homebuilt bicycle/pedal generator would be an interesting means of gaining some background knowledge in addition to what I've read thus far.

First, is there a basic calculation for the required mass of neo magnet material required for a desired output level. My understanding is that typical capabilities of human power output are on the order of 75 watts continuous (for reasonable amounts of time) and 150-200 watts for short durations. Similar to a lot of the wind turbines here in the states, I was thinking dual rotors with 12 magnets each and 9 coils (3 phase). I've reviewed some of the other postings on here about pedal generators and it seems that some use quite a bit of magnet material (approaching that used in some 1kW wind turbines), which seems to be more than necessary given the intended 200 W max output. Any direction here would be appreciated.

Secondly, is there a realistic way of conditioning the power output for direct feed into my home? I'm on the grid and don't really have any interest (at this point) in dealing with charging batteries to watch TV, etc. Ideally, I'd just like to get a workout with my creation while feeding power back into my house so that my efforts will offset some of my usual power consumption.

I'm also open to other ideas at this point, but that was where I thought I'd start and see where the journey leads.

Thanks,

Josh

[Flux]

Your estimates of power level are reasonable. What you get out depends ultimately on the alternator efficiency.

If you want an efficient low speed alternator you need a lot of magnet and copper, the comparison with a 1kW wind turbine alternator makes sense for direct drive. You will not be able to pedal as fast as a 12ft prop.

For pedal power where you are not looking for extreme efficiency at low power levels, chain gearing makes a lot of sense and that will let you reduce the quantity of magnet material very considerably.

Personally I consider grid tie of something as small as this completely crazy, the inverter cost will never be recovered in your lifetime.

There is no reason why many devices such as TV, radio computer or others of low power consumption cant be driven directly from dc with a suitable regulator but you would need to be able to build it. May be simpler to just float over a virtually scrap car battery as a crude regulator ( it would not see a significant charge/discharge cycle and even a nearly knackered one would work well enough.

Flux

[Norm]

David Butcher gives a very realistic viewpoint,

also you don't have to make electricity to save

electricity! You can hook up a pedal machine to

run a small compact washing machine even a small

clothes dryer run by you and heat provided from

hot air in your attic.

Well anyhow here's his link ...this may deflate

some of your ideas about making electricity to

cut down on your electric bill....remember it's

at least 10 times easier to conserve than it is to make.

http://www.los-gatos.ca.us/davidbu/pedgen.html

   ( :>) Norm.

[ghurd]

That sounds like typical `Norm'.

Reducing everything to reasonable, usable, simplicity.

I'd say get the biggest friggin' PM DC motor you can afford, then proper gears and a battery.  My experience says the larger the motor, the less the internal losses.

It would be hard to physically keep up with a 60W solar panel, and a 60W PV makes no sense monetarily to purchase a gridtie inverter.

Like Mr. Flux said, we won't live long enough to pay for the 1st gridtie inverter, let alone the 2nd one when the first one fails.

G-

[JChris]

You are definitely correct, the unit would have some sort of chain drive and gearing to allow the generator to run at a higher RPM.  Since pedal power would be more consistent and higher start-up torque would certainly be available, cogging shouldn't be an issue, so I thought the use of gearing went without saying.  Hence my confusion as to why some of the other examples to date use a seemingly high amount of magnet material.  Given a suitably high RPM via gearing, is there a rough calculation for mass of magnet material that can get me started?

Obviously, I'm not familiar with the intricacies of inverters and grid-tie systems, but I have seen inverters on ebay for less than $100 that have 2 115V outlets and are powered via a 12V battery.  Based on this, it would seem that if the power was rectified to 12V DC, it could then be inverted through a similar device and fed back into the grid.  I guess my initial desire to avoid a battery is not an option, but is a set-up such as this feasible or would it just make sense to use one of these off the shelf inverters to power small devices.  The units I've seen are rated at 1250W (2000W peak), which is well above what I'd need; however, perhaps these are not quality units, which would explain the relatively low cost.  As you can tell, this is the area with which I have the least experience.

I certainly appreciate the feedback.

[Flux]

If you use a chain drive then you can use a smaller and cheaper generator. If you can accept low efficiency the generator can be quite small. As others have mentioned the simplest option may be a decent pm dc motor if you can find something suitable. This will have an acceptable efficiency. If you want the highest possible efficiency then a decent dual rotor axial will probably be best but to obtain that high efficiency you will still need a lot of magnet and wire. If you cut corners you can still get results at lower cost but you will get far less for your physical efforts. If I had to pedal the thing I would want to extract the highest possible efficiency but if you just want the exercise and a bit of extra power then you may be able to get 50% efficiency at a far lower first cost. To get over 80% you would still need something comparable to a 500W wind alternator even with gearing.

The cheap inverters are not compatible with grid tie and you will get a spectacular bang and little else. You can use them from a battery source but you will need decent batteries, which tends to defeat your original idea. To use your low power level effectively you would do better to choose loads to match your pedalling ability and try to use it directly as dc at low voltage. You will not want to pedal for hours to charge a battery flattened by an inverter driving too big a load.

Flux