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dynamo's

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boobesque | 15:45 Thu 10th Nov 2005 | Science
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anyone know where i can get one? i have been hunting on search engines but can only find dynamo powered torches/radios.


do different sized dynamo's give different levels of power?

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A bicycle shop
Question Author
no, i dont want it connected to anything. A bicycle shop would sell dynamo powered bike light.

But the dynamo bike light sets usually consist of


A. the front light, B. the back light, C the DYNAMO, just buy a complete set and chuck out the lights+wiring+switch if you only want the dynamo.


Well a dynamo is really just a permanent magnet excited generator, the bigger the unit the more power it will produce.

Question Author
ok. lets imagine that i wanted to power something bigger. does anyone know where i could purchase a large dynamo
(Posted in 2 parts):

Just how big is your definition of large, Boobesque? And what is going to be used to power the dynamo. The wind perhaps? Or turning by hand?

A dynamo, in essence, is only an electric motor running in reverse. e.g. if you take a small electric motor, like the ones used in some Lego sets, and connect a battery to the terminals, the motor turns. If you take the same motor, however, and force it to turn by, say, connecting it to a small windmill, then you'll be able to connect a bulb across the terminals and get it to light. So, the same device can have two names. If you put electricity in and get rotational energy out, it's called an electric motor. If you put rotational energy in and get electricity out, it's called a dynamo.

You can buy dynamos from about the size of a thimble up to the size of house. The smallest ones are used in educational kits, the biggest ones are used in power stations. So, unless you tell us a bit more about your needs, it's hard to point you in the right direction!
(2nd Part):


It's perhaps worth mentioning that 'dynamo-powered' products (such as torches and radios) contain more than just a simple dynamo. A dynamo only produces electricity while it's actually turning; you probably wouldn't want to have to continually turn a handle while listening to a radio or using a torch. These type of devices use what is basically a clockwork motor to store up the energy provided by turning the handle, so that the dynamo continues turning after you've ceased turning the handle. They also include electronic circuits to 'smooth' the electricity generated by the dynamo.

Nearly 40 years ago, I took the clockwork motor from an old model railway and used it to run an electric motor, from a Meccano set, backwards (i.e. as a dynamo). I then used the power produced to power the amplifier of a small radio. It was an interesting experiment but I thought no more about it. After all, I thought, who'd be interested in a clockwork-powered radio. Years later, Trevor Baylis had the same idea and rapidly became a multi-millionaire. C'est le vie!

Chris
Question Author
i do indeed intend to use the wind to power my dynamo. and from what i know about ups systems i can make a ups battery out of a battery charger or something so the clockwork motor isnt needed. lets imagine that i wanted to power my tv with this dynamo. what sized dynamo would accomplish this? i imagine that the faster you turn the dynamo the more energy it creates per second but is there a limit? one more question. if i had a windmill of x size and connected it to 2 dynamos. one dynamo was the size of a fist and the other the size of a person. if the wind was turning the dynamos very slowly would the larger be less efficient?

If you want to charge a battery then the simplest way would be to get a 12vdc car alternator (still a dynamo by definition) and turn that with a wind turbine, the alternator has all the control system built in for regulating the charge on the battery etc... its much the simplest way to do it. It could run all day and charge the battery slowly say at 1amp x 24hrs = 24amp/hrs and then you could use it to get more power output over a short period to run the TV say at 10amps for 2.4hrs = 24amp/hrs


Your question about size is a bit more difficult, rotating electrical machines become more efficient the bigger they are, thats why power stations have a few big machines, but if you are running them slowly below their correct operating speed the values become meaningless.

qapmoc's suggestion of using a car alternator is an excellent one. It's also a very inexpensive one (�15, perhaps, from a breaker's yard?) As soon as you start looking at purpose-made products, prices start to rocket:
http://www.unlimited-power.co.uk/Aerogen_wind_turbines.h tml

(For further links, search for "wind generators" or "wind turbines").

Whether you go for DIY or purpose-made, don't forget that your windmill will require planning permission.

Chris
Buenchico - that site is really quite annoying because there are NO PRICES!

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