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Growroom design and set-up

Why has my timer switch failed and what should I do?

Why has my timer switch failed and what should I do?

Contributed by: skunkaroo
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Editors safety note:
Skunkaroo's instructions below, failed to include a common ground.

It would be much safer to use three conductor cord so that a common ground could be incorporated into this project. Tie all the grounds together using either a four post terminal block instead of the three post block skunkaroo used below, or else tie all the grounds together using a large wire nut. It would also be benifical to tie this to a dedicated ground close to the grow, this can be as simple as a piece of pipe or ground rod driven in the earth with a piece of #8 tied to it.


Normal household timers are not designed or rated to deal with the inductive power load used by horticultural lighting. There are 2 ways around this, you could go to your local Hydro shop and buy a contactor all built and ready to go along with a hefty price tag. Or you can get yourself a suitable change over Contact Relay switch, this will only set you back a few $$ ££. A contact relay switch is required so that the timer turns on the contactor which then turns the light on.

Almost all new growers will experience this failure. The reason for this is the contacts in these timers are not sufficient for the job. Household timers are rated for a RESISTIVE load, ballasts present an INDUCTIVE load, (a very large surge at switch on) this fuses the timer contacts together = Timer failure.


What is a relay switch?

An electro mechanically operated switch.


What follows?

Complete instructions (including photos) on wiring a contact relay switch to replace your timer contacts.


What parts are needed and where can I buy them?

The following parts can be purchased at any good online electrical store ie maplin.co.uk rswww.com

In my case I run 1 x 400w HPS, I know the INDUCTIVE load is 3.15 amps at switch on. Ask the manufactures of your light for this info. I am also running 5 x PC fans and a 1 x PC power supply unit. I have chosen a 240 volt, 10 amp contact relay switch from maplin code JG60 & JG54 this particular Relay switch has screw-terminals for easy wiring, and a push fit, easy mount base.

You will also need a 3 way terminal block, 2 x 3 pin mains plugs, 1 x 3 pin female mains socket, 1.5 meter of 2 core mains wire, sharp wire cutters/blade, an electrical screwdriver, and a cross head screwdriver.



Wiring a relay switch.

Note: mains voltage can kill you! So please exercise caution when wiring electronics of any kind!

1. Cut your 2-core wire into 4 measures the same length. Now pre-pair the wire ends, cut 2” from the outer sheath, then cut 1 cm off the inner sheath to expose wire. *Optional - solder all wire ends*
2. Fit mains plugs to 2 of the 4 pieces of wire, and then 1 of the remaining pieces of wire to the female mains socket.



3. Select one of the pieces of cable terminated with a mains plug, and connect to the relay base as follows: - Connect the live wire (Brown) to terminal 7 on the relay base. Connect the Neutral wire (Blue) to terminal 2 on the relay base. These connections are used to energise the relay coil. Now label the mains plug “Timer” (Plug 1).



4. Select the second piece of cable terminated with a mains plug, and connect to the terminal block as follows: - Connect the live wire (Brown) to terminal 1 on the terminal block (see diagram for terminal block numbering sequence). Connect the Neutral wire (Blue) to terminal 3 on the terminal block (see diagram). These connections are used to operate the grow room light (via the relay contacts). Now label the mains plug “Power” (Plug 2).

5. Select the third piece of cable terminated with a female mains socket, and connect to the terminal block as follows: - Connect the live wire (Brown) to terminal 2 on the terminal block. Connect the neutral wire (Blue) to terminal 3 on the terminal block.

6. Select the final piece of wire and proceed as follows: -Connect one end of the Brown wire to terminal 1 on the terminal block, connect the other end of this wire to terminal 8 on the relay base. Connect one end of the Blue wire to terminal 2 on the terminal block, connect the other end of this wire to terminal 6 on the relay base. Note: under operating conditions both of these wires become live.





7. Now take the relay unit and plug into relay base. (Plug 1) plugs into the timer. (Plug 2) plugs into a separate power socket. The female mains socket will supply power to your grow room lights.



Principle of operation.
When the timer switches on it will provide power to the relay coil. This in turn closes the relay contacts and bridges the terminals 8 & 6 on the relay unit thus providing power to female mains socket.

Total cost = £10. Time taken = 30min. Total saving = £25-30.