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Hand Crank Generator IKEA Hack

23
Jun/14

We are always thinking about ways to improve our circuit boards activity set so that there are interesting components that can also survive the wear and tear of the museum floor in a semi-facilitated environment.

One kind of component that we really like are hand crank generators. These are geared down motors with cranks that can subsitute for batteries and show how rotational motion can be transformed into electricity. We usually use something like the ones above for workshops, but they tend to not be robust enough for the museum floor. Also at 30$ to 60$ we cannot afford to continuously replace broken generators.

 

But yesterday I went to IKEA and saw a huge-o bin of these LJUSA hand powered emergency flashlights. I bought one and at $4.99 and figured it would be worth seeing if I could hack it to make a hand crank generator to try out with our circuit board set.

IMG_8153

I started by prying off the top of the flashlight with a utility knife and a tiny screwdriver. I cut off the button and attached the two protruding wires to alligator clips to see what would happen.

When we cranked the flashlight it did power the component! However, once we stopped turning the handle, the light or mechanism kept working, although dimmer and dimmer or slower and slower. We realized that this was because the flashlight was meant to be spun and then powered on for a set period of time. We figured there was some sort of capacitor or other circuit board inside the bottom half making it do that.

While this was an interesting phenomenon to us, we thought that it would be too confusing for someone just starting out learning about electricity. So I decided to see if I could remove the circuit and find out how to make the crank directly power one of our outputs.

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I was nervous that prying off the bottom part with the handle would wreck the device, but I went ahead and tried it anyways and was relieved to see that the handle was just press-fit on the gears with a hexagonal connection. I also discovered that there was a little circuit board with a battery (rechargable?) on it and some other components that looked like resistors and capacitors.

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One thing that I was confused about was that the motor had three wires coming off of it and the circuit board somehow turned that into just two wires (labeled positive and negative). I color coded the wires and tested it out with a light bulb and figured out which two of the three worked together to power the bulb.

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So I soldered the wires together and then put everything back together. I ran the two wires out little holes that I drilled in the clear cover and added alligator clips to the ends. We tested it out and it seemed to work great.

IMG_8176 However, once we tested it with a wide variety of circuit boards, we noticed some strange things. It wouldn't power any motor or mechanical toy part. It also seemed to work either way with the piezo buzzer (which usually only makes a sound when connected in one direction. We hooked it up to a multimeter and although we don't completely understand all the bells and whistles it seems to give us a value when its on AC current and nothing when it's measuring DC current.

 
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This makes a bit of sense to us (although none of us as a solid grasp of how electricity really works) because a light could be powered with pulses in each direction, but a motor couldn't spin if it was constantly getting equal pushes in opposite directions.

The next step may be to add a diode to the system which may limit the current to only going in one direction. We're not sure how this might affect the generation of electricity but we'll find out!

So, there is still potential for the LJUSA to be a part of our circuit exploration set, but more experimentation is required to make it work the way we want it to and interact well with all of the other conponents.

Hi Ryan this is really nice - I'll head out to Ikea to see if our local one has these - I'm wondering if the thing that looks like a battery might be a super capacitor... ? Asia and I have used them to power small geared motors. So it may be ac current to power how many LED's?

Hey Keith,

sounds good! let us know what you guys discover in your experiments. I think with what we learned from experimentation and other commentators you are right, it's a super capacitor. Without the circuit board it's churning out AC. I wonder if there's some way to reconfigure the other elements so it works on DC but doesn't remain on after being spun.

More messing around is needed!

R

Hi Ryan, just one suggestion, we used this solution in our energy i-lab for more then one year and we have learned that this crank don't support too high mechanical charges , lighting a more then 3 W lamp in 4 weeks we have damaged lethally the mechanical structure, probably because it is designed just to charge the super-cap...
this is a picture of the cranck:(
https://lh4.googleusercontent.com/-5EIPU0z--jg/U6rRkEDPWBI/AAAAAAAAEHk/a...

fabrizio

Hey Fabrizio!

Good to hear from you! So funny that we're working with the exact same device on different continents. Yeah I also wondered how robust the mechanism would be over time with the kids at the museum but I didn't think about how it would withstand different levels of current.

R

Hi Ryan,
i reappear on this post because we are going to test a new generator ikea derived
http://lavorincorso-museoscienza.blogspot.it/2014/08/lavvitatoreo-della-...
our post is in italian, but i can try to translate if you think can be interesting

Yes, that thing is obviously a supercap. There is one resistor in the circuit (the gray thing behind the cap), maybe there to limit the charging current. Diodes D1 to D4 are equally obviously a classical rectifier circuit, and one of the other diodes will probably be a Zener to protect the supercap against overvoltage (they are quite sensitive to that). I am not quite sure what the remaining diode is for, maybe to protect the cap against reverse voltage from the output terminals.

If you want a DC source, you should just unsolder the supercap (and keep it for other things, they are not cheap). Or just live with the fact that generators usually generate AC and develop your activities around that. Handing kids a generator that outputs DC sort of trains then not to understand generators and use them as a prefabricated magical devices instead. Then they will be surprised if they encounter a real, bare generator and it cannot drive a motor, like the author of a blog post I read recently.

Hi Florian,

Thanks for the explanation. It wasn't obvious to me, but I'm glad that I could use the materials around me to come up with a similar conclusion. I think we'll get a couple more of the IKEA generators and experiment with just de-soldering the super cap. It would be nice to have a couple different types of generators available so that visitors can see that they're not all the same and test out the difference in behavior.

Our gallery is next to a collection of electricity exhibits designed to teach different concepts and after reading your comments a few of us went and checked out an exhibit on hand cranked generators.

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It would be nice to have that close by if we do have generators with hidden parts in the Tinkering Studio so that if people get interested in the idea we can show them the inner workings of the model. I think kids being surprised, playful, and excited with new ideas is part of the activity, but I agree that it's nice to have resources available to follow up if people want to continue their investigation.

I'll do another post if we continue to experiment with the IKEA generator or other devices...

r

The generator might actually output 3-phase AC, I'm not sure though. But as Florian said, if you want direct feedback from the crank just remove the capacitor (and save it for something else). Then use the +/- output normally going to the LED lamps.

Had to take mine apart and check after writing my last comment:
Indeed it's a three phase brushless generator/motor, therefore three wires. 2 diodes for each AC phase to rectify it into DC. DC is then fed into the super capacitor (5.5 v, 1 F) via the large (20 ohm) resistor, presumably to limit the current. The capacitor is then connected via a smaller 2 ohm resistor to the 3 white LEDs that are connected in parallel. It's very simple but it's nice for the price.

The big resistor will burn about a third of the power, with the rectifier and small resistor it becomes about half the power, the rest is used by the LEDs. So a bit less than half of the "crank power" is turned into light (since generator and leds are not 100% efficient either). That's not so bad for such a cheap item though.

If you only want the DC output without the resistors and capacitor you can remove the capacitor and short out the resistors (replace the resistors with a piece of wire).

Hi Ryan,

Sorry to hear that you are going through hand crank generators so quickly. (I am a member and really enjoyed that exhibit when I was there with my sons recently. There favorite station was the pin-ball machine. It has a great combination of acceleration and sound.)

I work at PASCO. We developed a durable hand crank generator to address the issues you are seeing. (http://www.pasco.com/prodCatalog/EM/EM-8090_hand-crank-generator/index.c...).

I can get you a couple or so of these for free if you are interested.

Kind regards,

Joe

Here is the link. The one posted above appears to not work. http://www.pasco.com/prodCatalog/EM/EM-8090_hand-crank-generator/index.cfm

Hello Joe!

Thank you for the kind offer, we would love to field test a couple of your generators if you're willing to part with them! Write us at our email address to figure out details, and thanks again!

You could just use a motor with a crank on it as a generator.

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