Light box wiring exercise - ECN Electrical Forums

From Kenbo:

Quote

I am trying to resurrect an old wiring exercise and wondering if I have got the diagram correct. (seen this before but had to work out the wiring diagram myself)

It consists of a 12V transformer, one 12v 8 pin relay, two one way switches, one double pole three position switch, and two banks of lights.

The idea is 3-position switch in middle all lights off, up allows you to operate one bank of lights, down the other. The relay is used as an inter-lock.

I have ordered the parts and awaiting delivery so have not constructed it myself yet

I know this is more complicated than needs to be but the idea is it introduces students to working from wiring diagrams, and once they have built it I can then introduce faultfinding using a multimeter.

A DPDT switch and a DPDT relay to do what could be achieved with a SPDT switch is certainly the "Steamroller to crack a nut" school of design, but effective as a demonstration! [Linked Image]

The circuit looks fine to me, assuming a standard pin-out octal relay:

Coil on #2 & #7.

First contact set:
Common #1, n/c #4, n/o #3

Second contact set:
Common #8, n/c #5, n/o #6.

With the DPDT switch in the up position (up with respect to the tags as drawn) there's no power to the relay coil, and you have a circuit completed to the series lamps via the n/c contacts on relay pins 1 & 4.

With the DPDT switch down, the relay is energized and the circuit is completed to the parallel lamps via n/o contacts on 6 & 8.

Thanks Paul

It is a standard 8 pin octal relay (I could not think of the correct name for it)

I got the stuff to build it today and it did not work [Linked Image]

Then realised I had bought 12V DC relay instead of 12V AC.

But only noticed my mistake after I re-worked the wiring diagram. [Linked Image]

This time I drew it on the white board using different colours for the different circuits.

The students are goiong to hate me for this [Linked Image]