Electronics for Dogs III · 11 October 05
Before we turn over the chalkboard to the critters let’s talk about relays a bit.
Relays are electro-mechanical switches powered by a small voltage applied to the coil of the relay. The coil is just a bunch of wire wrapped around an iron core, kind of like the electro magnet we made as kids by wrapping wire around a nail and hooking it to a D cell.
Same thing with the relay: power to the coil turns it into a small magnet that pulls on a piece of metal. The piece of metal is a lever that closes (or opens) one or more switch contacts.
The average car has in the neighborhood of a two or three dozen relays that look just like the one pictured here. Relays are used to turn on wipers, turn signals, brake lights, starters, you name it.
One reason relays are used is to cut down on prices and keep the size of wires down. When you flip on the windshield wiper you are closing a relatively low amperage switch (cheaper) which is connected via a small wire to a relay, either under the dash or in the engine compartment. The relay has heavier duty contacts and wiring, able to turn on and off the higher current to the wiper motor.
An EV uses a few small relays and one or more HUGE relays. The big relays are still powered by the car’s 12vdc, but they switch hundreds of volts and amps.
Now on to Electronics for Dogs Part IV