Why has my timer switch failed and what should I
MedMan Last edited by:
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Why has my timer switch failed
and what should I do?
skunkaroo Images archived
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.
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 =
What is a relay
An electro mechanically operated
Complete instructions (including photos) on
wiring a contact relay switch to replace your timer
What parts are needed and where
can I buy them?
The following parts can be
purchased at any good online electrical store ie
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
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
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
Total cost = 10. Time taken = 30min.
Total saving = 25-30.
Last modified: 19:18 - Dec 12,
faq:1190 "Why has my timer
switch failed and what should I