Can a capacitor start a toy car?

[pug]

Hi, I am trying to build a solar powered toy car. And no its not for my son, its for my own curiosity. The problem I am having is that...while the solar panel is sufficient to rapidly turn the (4) micromotors 6 inches away from a lightbulb it isn't sufficient to even turn the wheels when I put it in the full Virginia fall sun light on level ground. So...rather than get a bigger solar panel my thought was to add a capacitor between the panel and the motors. My hypothesis is that the capacitor will store a sufficient charge to allow the car to slowly rotate its wheels. I am prepared to experiment with different types of capacitors but before I do that... is this plausible?

 

[anorlunda]

Yes, that's possible. But more practical may be to let the panel's charge batteries instead of capacitors. The reason is that when you have used 50% of a capacitor's energy, the voltage has dropped 50%. Batteries hold higher voltages longer in the discharge cycle.

 

[CraigHB]

Capacitors have poor energy density compared to batteries. They're designed to store energy for a different purpose. It would be possible if load can be reduced enough, but you can get into a situation where the power required to propel the weight and size of a capacitor increases faster than the energy it can store. There's actually a video around of a guy that used a capacitor to power an ultra small and light model airplane. It worked pretty well actually, but the load on that would be a lot lower than a model car powering wheels.

There are Li-Ion capacitors that might do a better job as they have higher energy density than standard capacitors. Otherwise you could use a Li-Ion battery around fifty mAh to do the job assuming the car is ultra light with very low drag. You can find them readily and cheaply from hobby shops. I actually have a ittle Lithium Polymer battery like that sitting in my box of electronics odds and ends. Just be a bit careful with them since they can catch fire when abused, just don't over-load, over-discharge, or over-charge.

 

[Vanadium 50]

I think the whole premise is problematic. If there's not enough power, adding a capacitor won't help it.

 

[CraigHB]

It might since electric motors draw peak current on start-up. Once the car is rolling motors are spinning at some rpm where they waste less power. It also takes less power to keep the car moving when it's not accelerating. The premise is still problematic if there's not enough power, but a charged capacitor may provide the extra bump to start it moving where it would not before. Obviously a charged battery would make much more power available. In that case solar cells would only charge the battery and extend run time some amount.

 

[anorlunda]

The other thing not mentioned is that if the car is powered by charged batteries (or capacitors) then the solar panels don't need to be mobile. Put the panels on the roof of your house, and move the charged batteries to the car. In your mind, is that still a solar powered car?

You should also do some research on the Mars rovers. The ways they manage energy could be applied to toys.