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Unread 08-08-2013, 10:41
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Re: Battery powered raspberry pi

Quote:
Originally Posted by Nathan4567a View Post
As referred in C2, what do you mean by super capacitors? Why would these super capacitors cost $25? That is a lot of money for a capacitor. In Houston I can grab a handful of these guys (picture) for $5-10. That should be enough to stabilize the power input.

Like you said there are some drawbacks to having a capacitor bank, but the issues don't strike me as major ones.
Super capacitors are generally a class of capacitors using double layers and gold to produce a large capacitance with a high internal resistance. They are suitable to provide power to digital circuits. They are not so suitable for things like locomotion.

In this case many of these capacitors are $5 and many rated at less than the voltage required by the load. So you need to put them in series. Putting them in series works like resistors in parallel so your capacitance divides. Then you need more capacitors because your capacitance is being divided down to reach your voltage requirements.

If this is legal then there a few people that have spoken to me in the past that have been asked at inspection to remove capacitors incorrectly.

The risks of a bank of capacitors are that the current to charge it when discharged can be high. If you limit the input current then it takes a while to reach the target output voltage. Plus if you turn off the robot with a large capacitance there the power will remain.

All of this can be eliminated with a good circuit design.
However between the cost of the capacitors and extra circuitry the cost as a whole will climb.

Keep in mind that large capacitances like this were not available at these prices until recently (last few years).
It's a big problem when people say....just put some capacitors in parallel on something.
You could have 82F capacitors....are you sure you want hundreds of Farads sucking power from your battery hard when discharged?
There really is such as thing as too much or too little with this.

Last edited by techhelpbb : 08-08-2013 at 10:52.