I am making a Christmas project where a kid can crank a dynamo and it will light up stages on a tree the harder they crank. The design is done and bread-boarded, but I seem to be having problems finding bulbs that would look nice and would eat up enough power to make it increasingly difficult to crank (due to the increased load).

So I am looking for a light that run on 12-15VDC. I can have up to 10 levels of output, and I am planning on using somewhere on the order of 7-12W total, so that is my wiggle room to play with.

I could burn off some power through a power resistor, but I was hoping to have the user use all of his generated power for the lights (so minus the inefficiencies in my rectifier, boost/buck, etc, all the power would be for the lights (to show how hard it is to generate enough power to light up a little bit of lights.

Any suggestions of what to use that would be colored and not be like the sun when cranked up (I guess this is the downside to using LEDs, they are so darn efficient!!!!)

 

I am making a Christmas project where a kid can crank a dynamo and it will light up stages on a tree the harder they crank. The design is done and bread-boarded, but I seem to be having problems finding bulbs that would look nice and would eat up enough power to make it increasingly difficult to crank (due to the increased load).

So I am looking for a light that run on 12-15VDC. I can have up to 10 levels of output, and I am planning on using somewhere on the order of 7-12W total, so that is my wiggle room to play with.

I could burn off some power through a power resistor, but I was hoping to have the user use all of his generated power for the lights (so minus the inefficiencies in my rectifier, boost/buck, etc, all the power would be for the lights (to show how hard it is to generate enough power to light up a little bit of lights.

Any suggestions of what to use that would be colored and not be like the sun when cranked up (I guess this is the downside to using LEDs, they are so darn efficient!!!!)

One option is automotive light bulbs, except that they are fairly expensive and also mostly clear. You could use a LOT of LED lights and make a fair load, depending on the dynamo that you are using. Knowing how much power will be generated will help with deciding what kind of lights to use.

 

One option is automotive light bulbs, except that they are fairly expensive and also mostly clear. You could use a LOT of LED lights and make a fair load, depending on the dynamo that you are using. Knowing how much power will be generated will help with deciding what kind of lights to use.

I was thinking of having a 2D Chrismas tree with the lights going up in a staggered line. Then the lights would turn on one at a time until it got to the star at the top, but it is seeming like single bulbs will just be too darn efficient.

I think that I would want to be generating about 7-12W total across all the bulbs as full on.

 

Ebay- long strips you can cut to size- look in the boy racer section.

 

The really big challenge will be the sequential switching circuit to deliver the rising illumination from bottom to top. The obvious way to do it is with a bar-graph IC, but most of those are for log-type volume displays, while it seems that your application would need a more linear scale. AND, using one of those would then require external transistors to switch the higher currents, if you used incandescent bulbs. An interesting possibility would be LEDs of different colors, which have somewhat different forward voltages, and then have enough filtering on the dynamo output so that the DC voltage would rise smoothly as the cranking effort increased.
Now the other question is about the "dynamo" being used to generate the power. That term covers a wide variety of devices, from hand-cranked phone generators through automotive alternators and windmill generators. Is the intended device a DC or AC output type, or something possibly not yet selected? Knowing that would help point toward a more specific set of illumination things.

 

Thanks for the feedback guys! I like the underbody lights idea, I hadn't thought of them before, and they are designed to bee outdoors, so that is good.

As doe the sequential switching, I am using an LM3914, which is linear (the LM3915 is the log version). The output of the LM3914 is open collector, so I am using a weak pullup and driving that into the gate of a P-channel MOSFET to do the switching. So I am not too worried about the current right now.

This is the dynamo I have: https://www.ebay.com/itm/2015367765...c6e859caf58&bu=43186072801&cp=1&sojTags=bu=bu

I have it running into a bridge-rectifier that is then smoothed out by a big cap. I sort of expected the voltage to be between 0 and 36ish Volts. I then use that to drive vmy boost/buck to give me a constant 15V (it is adjustable, so I can tweak that). I use the 15V to drive the LM3914, then I have a voltage divider divde the signal by 3 to give me a 0-12V input the LM3914 to decide on which LEDs to turn on. I might have to adjust some of the voltages a little and figure out the right wattage to make it usable, but the overall design seems to work out fine (in simulation and in bread-boarded practice).

My end goal is to be able to have a kid light up at least have the lights, but need an adult to work hard to get all of them to come on. That is the part that I still need to work out (what are the wattages at each light to make this a reasonable goal).

 

OK, it seems that you already have come up with what seems to be a good scheme for the system. I am guessing that the biggest challenges will be in the mechanical portions of the project, since somebody will be putting a fair amount of mechanical work into driving that dynamo.

 

So I ended up buying some 4 color SMD LEDs and associated heatsinks on Amazon. They run at ~1W per color, so I will hardcode the different colors and try to use 7-10 outputs (depending on how hard it is to crank them all).

Yeah, the mounting concerns me. There are mounting holes on the dynamo, so that is a plus, but I need to mount it to a stand that gets put into my yard for a season. I haven't figured that part out yet.....

 

My guess is that mechanical design assistance is beyond the scope of this website, especially when it comes to creative solutions based on observation and understanding. Or possibly not.
I wonder what the moderators would have to say.

 

My guess is that mechanical design assistance is beyond the scope of this website, especially when it comes to creative solutions based on observation and understanding. Or possibly not.
I wonder what the moderators would have to say.

True, I'll keep those thoughts to myself. Thanks