What governs how hard it is to turn a dynamo?

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Discussion Overview

The discussion revolves around the factors influencing the difficulty of turning a dynamo, particularly in the context of attaching it to pedals for generating power. Participants explore the roles of physical configuration, electrical load, and methods for adjusting resistance to change the physical difficulty of turning the dynamo.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants suggest that the difficulty of turning a dynamo is primarily influenced by the electrical load attached, with heavier loads requiring more work to generate current.
  • Others describe the dynamo's physical configuration, including the arrangement of electromagnets and stationary magnets, as a factor, but to a lesser extent.
  • One participant proposes that adding resistors can allow for adjustable difficulty in turning the dynamo.
  • There is a discussion about the availability of dynamos and the specific purposes they are designed for, with some participants noting the challenge of finding a suitable dynamo for experimentation.
  • Participants note that motors and generators are mechanically similar, suggesting that a motor could be used as a generator by running it in reverse, although one participant cautions against running it backwards and instead recommends increasing speed.
  • Suggestions for sourcing dynamos include scrap yards and specific types of automobile motors, with details on their potential current output and suitability for DIY projects.

Areas of Agreement / Disagreement

Participants generally agree that the electrical load significantly affects the difficulty of turning a dynamo, but there is no consensus on the extent to which physical configuration plays a role. The discussion includes multiple competing views on sourcing dynamos and the methods for adjusting resistance.

Contextual Notes

Participants express uncertainty about the specific ratings and purposes of different dynamos, indicating a lack of clarity on how to select an appropriate dynamo for their needs. There are also unresolved questions about the mechanics of motors and generators, particularly regarding the implications of running them in reverse.

Who May Find This Useful

This discussion may be useful for individuals interested in DIY projects involving power generation, those exploring the principles of electromagnetism, and beginners seeking practical applications of motors and generators.

samsonmustang
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Say I wanted to attach a dynamo up to some pedals or something - what factors would affect how hard the shaft would be to turn?

Is it governed by the physical configuration of the dynamo (windings, etc)? Or is it the (electrical) load attached that matters - and how does that work?

If I wanted to be able to alter the resistance (as in physical difficulty) of the pedals up and down in steps, how could I do that? What kind of steps could I get? And how would that affect the power/voltage/current/physical-electrons-coming-out-of-the-dynamo?

I feel like I know a lot of terms and 'theory', but I have very little instinct for how things go together in practice.
 
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hi there
welcome to PF :smile:

samsonmustang said:
Is it governed by the physical configuration of the dynamo (windings, etc)?

to a very minor extent

samsonmustang said:
Or is it the (electrical) load attached that matters - and how does that work?

that's the one :wink:

the heavier the load ie. the more current required by the load
the more work you have to do to turn the dynamo shaft to generate that current

power in = power out minus losses in the system

Dave
 
samsonmustang said:
Is it governed by the physical configuration of the dynamo (windings, etc)? Or is it the (electrical) load attached that matters - and how does that work?
Welcome to PF!

A dynamo or motor is basically a cluster of electromagnets and stationary magnets rolled into a cylinder. The magnets and electromagnets oppose each other and in dynamo mode, the magnets quite literally push the electrons through the wires.
 
Okay, that's brilliant. So that sounds like I can 'step' the difficulty up and down just by adding in more and more resistors?

I don't suppose either of you gentlemen would be able to recommend a good place to buy a dynamo so I can have a play with this at home? (Google just shows me lots of portable diesel generators or those little bike things, nothing in between.)
 
an automobile heater or radiator fan motor is a dynamo.
I

SO is an old fashioned automobile generator
http://www.ebay.com/itm/9060-Generator-Delco-Remy-Chevy-Car-/151994166265?hash=item23638eebf9:g:gMYAAOSwNgxWC~tw&vxp=mtr
 
Okay, thanks.

I think I need more voltage than a little bike generator can give me - but not as much as the car one would provide. It seems that dynamos are generally made for a specific purpose - you can't just come up with a rating and buy them off the shelf from somewhere?

(Makes me wonder where those bike/car companies are sourcing them from.)
 
...I've just realized, motors and generators are mechanically the same thing, aren't they? So if I know what wattage I want out, I can just buy and motor and run it backwards. Right?

Nidum: thanks. It may sound silly, but when you're this new to a subject, you don't even know what words you should be Googling. That vocab (simple as it is) is often just as useful as the search results.
 
  • #10
samsonmustang said:
..I've just realized, motors and generators are mechanically the same thing, aren't they? So if I know what wattage I want out, I can just buy and motor and run it backwards. Right?
dont run it backwards, just speed it up.

So long as you don't get into brushless DC motors, yes they're the same .

Get a small brushed motor and spin it with an electric drill to experiment.

samsonmustang said:
I don't suppose either of you gentlemen would be able to recommend a good place to buy a dynamo
For the man on a budget scrap yards are handy. I buy electric motors for thirty cents a pound.
Windshield wiper motors abound and are good for a few amps. Older Ford ones are three brush - an interesting variant to look up should you encounter one.
Automobile radiator fan motors are popular among DIYers , good for perhaps ten amps. Get a single speed one with only two wires for starting out, they're simpler.
Automobile heater fan motors are surprisingly powerful, some approach twenty amps.
A permanent magnet dynamo makes voltage in direct proportion to speed, no regulator required.After you've got your feet wet you can advance to something with a field ?
 
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  • #11
Thanks, Jim.

The only think I've really played with are little stepper motors, which won't do at all. I shall take all this on board.
 

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