When to use a motor vs a dynamo?

Thread Starter

toozie21

Joined Oct 4, 2012
59
Just like the subject says, I am not sure when you would use one over the other for generating a DC voltage. I am working on a prop for next Christmas where a user turns a crank which would then ultimately drive a series of lights (I haven't decided how I want to handle that part yet).

I had thought that a dynamo was the way to go, but there was a similar prop at a children's museum I went to and supposidly they used a DC Permanent Magnet Motor, DC Speed Control (0 to 24/VDC Voltage Output,10 Max. Amps), and a prop controller: http://www.efx-tek.com/php/store/index.php?main_page=product_info&cPath=1&products_id=2

OK, the prop controller makes sense, it is probably what they are using to drive the different 12V LED bulbs they were using, but I don't see what they used a motor and motor controller vs a dynamo.

Any thoughts?
 

nsaspook

Joined Aug 27, 2009
9,436
Sure a DC motor (maybe cheaper and readily available than a proper DC generator) can be used as a DC voltage source but the output voltage can vary greatly with crank speed and the current load. The DC Speed controller acts as a voltage regulator (DC in from the generator aka motor, DC out to the load) for the prop controller and lights.
 

Dodgydave

Joined Jun 22, 2012
10,233
A dynamos output can be controlled by it's field winding, a motor can't.

If you just want to illuminate leds, like on a bicycle use a permanent magnet dynamo or motor.
 

MaxHeadRoom

Joined Jul 18, 2013
24,979
The cheapest is the P.M. DC motor, a BLDC motor will output 3ph AC.
The greater the load (current) the greater the effort needed to rotate it.
Max.
 

dendad

Joined Feb 20, 2016
4,110
If it is low power, try a stepper motor.
If you use a 25V one from an old printer, and a 3 phase bridge rectifier fed into a filter cap and maybe a regulator is needed, that will power the LEDs ok. I had a wind generator in the back yard driving LEDs as an ornament. It ran for a few years until a storm broke it.
 

Thread Starter

toozie21

Joined Oct 4, 2012
59
Thanks for reading and chiming in folks! I guess some more info from me would be helpful.

I was planning on having something like a wooden Christmas tree cutout with staggered bulbs going up. As the user cranked the arm, they could light the bulbs up sequentially (think like a bell ringing strong-man prop at a fair with a sledge hammer). I haven't thought through how I plan to turn on the "next" bulb or what "turning on" means (a micro controlling a relay, or let the bulbs turn on in a more organic fashion), but I am open to suggestions.

I am looking to not overcomplicate this (which I tend to do), but to learn some in the process. I am a digital guy, so some of this is new concepts to me.

Thanks again!
 

Dodgydave

Joined Jun 22, 2012
10,233
Thanks for reading and chiming in folks! I guess some more info from me would be helpful.

I was planning on having something like a wooden Christmas tree cutout with staggered bulbs going up. As the user cranked the arm, they could light the bulbs up sequentially (think like a bell ringing strong-man prop at a fair with a sledge hammer). I haven't thought through how I plan to turn on the "next" bulb or what "turning on" means (a micro controlling a relay, or let the bulbs turn on in a more organic fashion), but I am open to suggestions.

I am looking to not overcomplicate this (which I tend to do), but to learn some in the process. I am a digital guy, so some of this is new concepts to me.

Thanks again!
For sequential bulb/led lighting up, you can use a LM3914 chip in bar mode, they can light up 10 leds, as long as the dynamo gives out 5 to 12v.
 

Thread Starter

toozie21

Joined Oct 4, 2012
59
This sounds like a good approach, and mirrors somw things I've see elsewhere. What would you do if the dynamo ends up putting out more than 5v?
 

dendad

Joined Feb 20, 2016
4,110
What would you do if the dynamo ends up putting out more than 5v?
Feed the dynamo you via a 1K resistor to a shunt 4.7V or 5.2V zener to limit the volts. That will help protect the input too if they turn the handle the wrong way (if you use a DC motor).
 
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