Author Topic: motor as a generator question  (Read 1127 times)

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toozie21

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motor as a generator question
« on: January 10, 2018, 04:26:47 PM »
Howdy. I stumbled onto yourall's great sight while doing some research on motors as generators.

I have a similar application to you guys, but on a MUCH smaller scale. What I am looking to do is create a "tower of power" Christmas display for my yard for 2018 (I like to have a homemade mechanical Christmas display). My vision is of a wooden cut-out of a Christmas tree with some staggered 12V bulbs going up it. I then was going to use bicycle parts to create a hand-crank that drives a generator/dynamo. As the user cranks harder, I want more and more lights to light up (think the ringing-bell sledgehammer prop at fairs).

I am a digital electronics guy, so my power background is pretty limited. Based on my research on this and other sites, I think I know what I need, but I am having trouble finding something that fits the bill that doesn't cost a fortune (since this is a prop that is going to sit in a yard for a month out of the year and subject to weather/kid's abuse). I should only need low wattage since I just want to power a couple of bulbs (not sure if I am doing 12V light bulbs or maybe LED C7 sized Christmas bulbs), maybe something on the order of 50W - 100W total power budget.

I was hoping someone could maybe guide me in the right direction (I still am not 100% sure why a motor generator is preferred over a dynamo, whose purpose I thought was to do this sort of thing....). Correct me if I am wrong, but I am thinking I need a 12V permanent magnet DC motor (why not a dynamo?). Then I need to make sure it can supply somewhere on the order of 4A - 8A (to get me my 50W to 100W range). Lastly, I think it needs to supply the 12V at a low RPM, say ~100RPM since this is going to be a hand-crank operation. Does this sound like the requirements for this sort of project?

If I am on the right track, can someone point me in the right direction of a motor that can handle this? I either find things that are rated for very high wattage (like what you guys need for your wind generators (and would be overkill for this application), or it is stuff in the $100+ range, which is where I didn't want to get into. I don't mind using used/reclaimed motors if that helps drive the cost down, I am just not sure where to go from here (been spending most of my time looking for motors on Amazon and eBay and some on random Google searches).

Thanks again folks

SparWeb

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Re: motor as a generator question
« Reply #1 on: January 12, 2018, 12:59:16 AM »
One simple choice at the beginning will decide if this is easy or hard:  Will the mechanical work of the crank supply all of the energy the system uses?
Bear in mind that kids aren't very dedicated pedallers when they aren't going somewhere on a bike, and by hand they can get about ~100 Watts for a few seconds before their arm gets tired.  I tried it myself once doing a science demo at my kid's school, and the kids had fun but they hardly got a glow out of three 40W light bulbs.
You can consider having multiple kids cranking at the same time to get brighter lights, or make it a contest... sky's the limit there!

Perhaps a place to start are the in-wheel bicycle motors.  Normally they're used to drive the bike from a small battery, but most are quite simple and can be driven like a generator to develop the kind of power you are looking for, and won't overtax the kids arms.  The other advantage is they run at a speed range that neatly coincides with the cranking speed you're looking for.  In fact, you might want to NOT dismantle one from the bicycle and instead leave it all together, flip the bike upside down, and crank the pedal.  Simple starting point and the bike wheel contributes a flywheel and the crankset already has a clutch that will keep spinning when the kid stops cranking.

LED's use very little energy, but they burn out easily.  Strings of LED christmas lights are fairly tough and can be cut according to your needs.
« Last Edit: January 12, 2018, 01:26:13 AM by SparWeb »
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

hiker

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Re: motor as a generator question
« Reply #2 on: January 12, 2018, 02:34:21 AM »
Old battry powered hand drill...make a simple crank that will fit in the drill chuck...take power from the motor leads...go to your local electronic shop and pick up a cheap 3 leged voltage regulater..get your string of L.E.Ds  and crank away.....should be real easy to crank..at a super low RPM..  Picture of regulator...they come in a variety of voltage..
« Last Edit: January 12, 2018, 04:32:57 AM by hiker »
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hiker

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Re: motor as a generator question
« Reply #3 on: January 12, 2018, 02:40:22 AM »
Or you could do this ..exersize bike alt
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toozie21

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Re: motor as a generator question
« Reply #4 on: January 17, 2018, 10:37:39 AM »
Wow, very sorry I dropped off there, I am back now!!!!  ;D

Thanks for all the help.  Reading here and elsewhere and thinking about it on long commutes, I think the easy way is the right way to go.

I am thinking of using the generator to be a tip-off to either a micro, or potentially, the LM3914.  My head was originally about power the LEDs directly, but I am thinking that that is too hard based on SparWeb's nice write up.

One thing I really want to do is make sure that  I use something like a freewheel from a bike so that when a kid stops turning the crank really hard, it doesn't keep whipping around and snapping some kids wrist or something.  Besides the freewheel, I am not sure what the other options are.

hiker

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Re: motor as a generator question
« Reply #5 on: January 17, 2018, 04:54:01 PM »
A drill would stop instantly....simple set up..? Should easly power up a string of LEDs
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toozie21

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Re: motor as a generator question
« Reply #6 on: January 18, 2018, 02:41:01 PM »
A drill would stop instantly....simple set up..? Should easly power up a string of LEDs

So I have been mulling this option over some.  Wouldn't a drill require a very high RPM to produce any noticeable voltage?  I assume if the drill had a speed setting, the lower speed would require less RPMs, but would the clutch settings come into play somehow?  I am just trying to envision this a bit better than I currently can.

toozie21

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Re: motor as a generator question
« Reply #7 on: January 18, 2018, 03:07:45 PM »
I should have thought first that YouTube probably had the answer to my above questions.....  Here is one guys video that goes over some of it (I am not allowed to post links yet, so you will need to piece the link together yourself):
wwwDOTyoutubeDOTcom/watch?v=PJFAXxV2ME8

JW

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Re: motor as a generator question
« Reply #8 on: January 18, 2018, 03:44:15 PM »
Hi toozie21

Your links wont work until you have made 10 posts after that everything will work right :)

I think your link is ok, but this is done automatically sorry about that. We have to do this because some people just become members to spam us.

toozie21

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Re: motor as a generator question
« Reply #9 on: January 18, 2018, 04:01:14 PM »
No worries, I completely get it.

Hi toozie21

Your links wont work until you have made 10 posts after that everything will work right :)

I think your link is ok, but this is done automatically sorry about that. We have to do this because some people just become members to spam us.

hiker

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Re: motor as a generator question
« Reply #10 on: January 18, 2018, 10:55:24 PM »
Should be more than enough voltage for low voltage LEDs ..hook a string in paralle...just make a simple crank and put it in the chuck.....take the power from the motor..add a regulater if needed..crank away..by hand
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toozie21

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Re: motor as a generator question
« Reply #11 on: February 01, 2018, 02:11:13 PM »
Should be more than enough voltage for low voltage LEDs ..hook a string in paralle...just make a simple crank and put it in the chuck.....take the power from the motor..add a regulater if needed..crank away..by hand
Sorry guys, I had the flu and dropped this thread for a little bit.  I think I have an angle on a drill to play with, I just haven't had time to dig into it yet.

While driving to/from work, I've been giving the lighting of the "tree" some thought.  I was originally thinking of an LM3914 to create a bar-graph that controls some relays, but now I am thinking that won't work with the drill approach unless I add an external power source to set the LM3914's set points while running.

So that leads me to think I should drive the lights directly.  So that leads me to ponder how I can drive lights in stages, anyone have some thoughts on that?  I know that as they crank and draw more current, it will get harder and harder to turn, so I am trying to think of a novel way to have the lights turn on in sequence so that if you can only turn on half the "tree" it can do that.  My current ideads would only give me all-or-nothing lights, and I don't want that effect.

I have been tossing around the idea of cutting up a string of mini-lights (the incandescent ones run on 2.4V) so that I have individual bulbs and wire them up somehow to do my sequential lighting, I just haven't figured out the best way to turn them on in that order.....

hiker

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Re: motor as a generator question
« Reply #12 on: February 01, 2018, 08:12:20 PM »
https://www.youtube.com/watch?v=AwX0nmOh__U          simple hook up straight from the dc motor;;;;ac conversion for lights,,, 6 amp draw on saw.. just showing you whats possible.....have fun
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