Page 59 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

R3 10 ohms, 2 W
1
R4 220 ohms, 4 W
Wall transformer (see earlier in this chapter)
Building a solar-powered battery charger
Once you have designed a battery charger for a rechargeable bat-
tery pack, you can convert it to a solar-powered battery charger.
You need to replace the step-down transformer (or wall trans-
former) with a combination of solar cells that will equal the power
delivered by the transformer. Points to keep in mind when plan-
ning a solar power system are
1. The average illumination received by the solar panel
2. Hours of illumination needed to recharge power supply versus
work period

Fuel cells—batteries with a fuel tank

Fuel cells and batteries are both electrochemical devices that
convert chemical energy into electric energy. In the battery, the
chemical reactants are stored internally. When the reactants are
38 exhausted, the battery is replaced (or in some cases recharged).
Fuel cells use reactants (fuel) that are stored externally. As long
as fuel is supplied to a fuel cell, it will (in theory at least) continue
to generate electricity.

When a fuel cell starts running low, it can be simply refilled with
fuel, much like today’s automobile. A fuel cell–powered robot will
be able to get back to work quickly as compared to another robot
that will be out of service while its batteries recharge.

Figure 3.10 is a schematic of an alkali fuel cell. This is the type of
fuel cell used in U.S. spacecraft. The first thing you may notice is
that the anode is labeled ( ) and the cathode is labeled ( ).
When I first started looking at fuel cell schematics, I found this
confusing. Actually I though it was a mistake, but after looking at
a few dozen schematics with the same error, I realized it couldn’t
be a mistake. Accordingly, I checked the definition of cathode in
the Oxford Dictionary of Current English. It reads: “Cathode: 1.
Negative electrode in an electrolytic cell. 2. Positive terminal of a
battery.” I only bring this up so that you don’t become confused
when studying other schematics of fuel cells, since all the
schematics I’ve seen so far follow this convention.

Team LRN
Chapter three