Page 229 - Robot Builder's Bonanza

198 ROBOT POWER SYSTEMS

Power leads

15 20
15
20

Wires to block
accidental hookup
20
15
15 20
Figure 19- 7 Use guard wires in a solderless breadboard
Plug in here
to help prevent accidentally connecting the power plug to the
wrong column of tie points.
Polarized connectors and wiring harnesses with polarized connections are available at local
and online R/C model stores.

ELECTRONIC POLARITY PROTECTION
When you can’t use mechanical means to avoid physically connecting the batteries backward,
you can turn to some simple electronics that will protect the rest of your circuitry.
The simplest method is to put a diode inline with the incoming + connection from the bat-
tery. Diodes restrict current flow to one direction only. If you reverse the power leads from the
battery, the diode will stop current from entering the circuit. Nothing will work, but your circuit
won’t be damaged.
Diode Choose a diode with the current- carrying capacity for the circuit. The 1N4001
silicon diode handles up to 1 amp; the 1N5401 diode, up to 3 amps.
The downside to this method is that there is a voltage drop across the diode. For
To circuit
silicon diodes the drop is about 0.7 volts. For Schottky diodes the drop is only
about 0.3 volts. See Chapter 31, “Common Electronic Components for Robotics,”
for information about different kinds of diodes.

On the Web: How to Solder a Barrel Plug onto
a Battery Holder or DC Wall Transformer

Check out the RBB Online Support site (see Appendix A) for a step- by- step soldering guide
on how to solder a barrel plug onto a battery holder or DC wall transformer. Make your own
polarized power connectors.

Adding Fuse Protection

Big lead- acid, NiMH, and NiCd batteries can deliver a most shocking amount of current. In
fact, if the leads of the battery accidentally touch each other, or there is a short in the circuit,
the wires may melt and a fire could erupt.

19-chapter-19.indd 198 4/21/11 11:49 AM