09 April 2006

Solar/capacitor powered RC car.

As you can see in my previous post, I believe that the super capacitors are possibly the way to go with the future cars. To test my theory, I've moded a very small RC car to use a capacitor instead of a battery.

The results are pretty good, and the car moves for an estimated 20 meters. I can play with it for about 2 minutes before it runs out of juice, while not in the sun.

Except for the smaller run time, the capacitor version is much better than the battery equivalent, because the battery was 1.2V @80 mAh.
This capacitor, while rated at 2.5V, the open circuit voltage it can store is over 3.6V . So basically it provides (in the beginning) 3 times more voltage than the battery. I was a little afraid this might burn the motor, but since the cost of that car is about 10 USD or less that was an acceptable risk.

It turns out that the motor was quite happy with 3.6 volts, and the car was so fast that it could even climb on the kitchen carpet (I was running it on linoleum). With just a battery, it can't really do that.
The turns are very abrupt, and the can can stumble over itself, and turn upside down. Since this won't cause any damage, I think it's kind of cool.

One thing worth mentioning is the fact that a capacitor, unlike a battery, will drop it's voltage linearly. Which means, after half the power was used, the voltage is also halved.
A battery, on the other hand, doesn't drop it's voltage (much) until it's drained.
That means that only 2/3 of the capacitor power can be used, after the voltage drops under 1.1 volts the car it's not going to work.

Ok, enough for the theory, now let's go into the construction details.
What you will need:

a. A small RC car. You can find them in a local toy store, Radio Shack, eBay, etc. For example, you can get 4 of them and free shipping for 29 USD, from this guys.
b. A super capacitor, preferably 10 Farads or more. They are kind of hard to find, I got mine from a broken digital camera, but this company has some nice selection for affordable prices: www.alliedelec.com
Notice how my capacitor is flat, and the capacitors here are round. A minor inconvenience, but shouldn't affect the performance of the car.
c. A 3V solar panel. I highly recommend a flexible one, they are very lightweight, and being flexible you don't have to worry about them being damaged if the car crashes. Some good source is this company, although you might be able to find them cheaper on eBay.
d. Soldering gun/iron, soldering supplies, and some wires.
e. Glue, some screwdriver, wire cutters, etc.

Getting started:

1. Take the RC car cover off. It's just getting in the way.

2. Open the battery compartment (bottom) and remove the battery. You might want to put it aside for other projects that need small batteries.

3. Solder two wires on the bottom, where the battery terminals were. The polarity should be marked on the bottom.
4. Glue the capacitor on the back of the car, and connect the wires from the battery compartment to the capacitor. Pay attention to the polarity of the capacitor.
5. Glue the solar panel[s] to the capacitor, and connect another set of wires from the solar panel[s] to the capacitor.

After everything is completed, turn on the RC remote (some car models will leak a lot of voltage while the RC remote is off) and place the car in such a way so that the sun shines on it. If no sun is available, you can try to recharge it from a light bulb, but be careful, if you place an incadescent light bulb to close it might damage your solar panels.
A multimeter would be very useful to determine when the car is fully charged (a voltage of over 3 volts it's good, 3.40 is better, but some capacitors might not be able to charge that much).
With one flexible solar panel (3v, 25 mAh) it should fully charge in about 20 minutes, under the sun.

That's it, now you are ready to play with your car.

The reason there is no diode between the solar panel[s] and the capacitor is because the car itself will drain all the voltage if idle, as they do not have a on/off switch. Another reason is that a diode will lower the voltage by about 0.6V, and you want the capacitor to be as charged as possible.

Let me know if you have any comments, questions, etc.


Blogger Donny said...

I might have to goto radio shack one of these days and pick up a remote controlled car and give it a try, I think i have a soldering Iron somewhere.

I wonder if there is a better way to make the capacitor store energy for a longer ammount of time or maybe using more capacitors to lengthen the amount of time the car will run for. I think that will be the only major problem with a brake through like this. Sounds very easy to do but for a car that isn't already electric it would take some work. I wonder would it be possible to take away some of the energy the car is using from the capacitor so it doesn't drain as fast since the car doesn't need so much energy anyhow? I'm not much of an electronics person myself I do know some things but not much. Too bad there wasn't a way to make the car recharge the capacitor from its motion. I know this is being done with breaks in many cars now but what if you could use its energy it was using to create motion and convert that into a slow charge that would make the capacitor run out of juice as fast.

Very cool invention I must say.

9/4/06 22:35  
Blogger Radu said...

Well, actually from what I heard, new hybrid cars might use a capacitor to store the energy not only from breaking, but also when going downhill for example.

9/4/06 22:52  
Anonymous Anonymous said...

Even modern non-hybrid cars use that technique.. they call it 'regenerative breaking'. I think the new VW Passat has this for example.

11/4/06 08:03  
Blogger Radu said...

The older cars use a battery, not a capacitor to store the energy from the braking.

11/4/06 14:40  
Anonymous Anonymous said...

You could stabilize performance with a Voltage Regulator. Google for "Regulator_for_High_Efficiency_Voltage_Conversion" and you'll find a tiny adjustable VR chip that's designed for SMT but that you can solder directly to.

27/4/06 12:19  
Anonymous Anonymous said...

a zener diode can be used to regulate the voltage consumption of the car. Also the energy in a capacitor is E=C*V^2 so increasing the voltage across the capasitor increases the stored power more than increasing the capacitance, though that helps too.

26/5/06 03:18  
Anonymous Anonymous said...

A zener diode wastes power to regulate.

Anything but a very carefully built switching regulator is going to waste more power than it saves.

Regenerative "breaking" (sic) again, you can't get back more than you put in and the energies here are so low, the circuitry would likely waste more power than it would save.

Back to the original topic... this is very cool!

8/7/06 00:52  
Anonymous Anonymous said...

what would you have to change to put solar power on a much larger RC car (2 feet in length)

21/1/07 20:14  
Anonymous Anonymous said...

How about running it in the sun? It seems that all you want to do here is leave it charging in the sun and take it out of the sun before using it. does it work if you run it at a fraction of the maximum power so that it would run nearly continuous (apart from when the sun goes away)?

1/11/07 23:34  
Anonymous Anonymous said...

your experiment is exactly the same as the one i wanted to do for school! I thank you because i was trying to use a solar powered K'nex car vrs. a regular Zip zap. As you can see the differences causes problems! Thanks again this was awesomely helpful.

24/2/08 17:27  
Anonymous Anonymous said...

How about using electricity from the capacitors to seperate the hydrogen out of water, and then use the hydrogen to run an engine to charge the capacitors? Then you could run the car on water.

21/6/08 05:20  
Blogger Unknown said...

won't work it will always take more energy to create the hydrogen "and the o2" then you could get from running the engine to charge the capacitor.

you might as well try using the capacitor to power a motor that turns a generator to charge the capacitor.

if 100% efficency was possible it would work but in the real world its just not..

28/10/08 15:10  
Blogger Edward Robins said...

There are actually two major kinds of solar panels namely the traditional photovoltaic panel and second type is the thin film panel.

solar energy
solar power
solar hot water
solar panels

28/10/10 01:53  
Blogger Unknown said...

Your posted was well informative, that every person who read or see this will get knowledge about you posted. you made a great job for this and thank you for sharing your taughts on us..More power! Earth4Energy build solar power.

15/1/11 06:45  

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