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Help with timer circuit and relay

G

Grenge

Jan 1, 1970
0
I am having some trouble with a electronic circuit that I have built and
wondering if anyone can help me.
I built a timer circuit from a Dick Smith kit "K-2813 555 Timer Circuits". I
made circuit #1 shown here
http://members.ozemail.com.au/~tizza/timercircuit.jpg I added extra
resistors in series with VR1 to extend the time.
When I finished it, I tested it with a lamp connected to the output and it
all worked fine. The timer ran for 17 seconds before switching off. Then I
connected a relay to the output, because the relay would then switch a
flasher circuit that is working in combination with it. With the relay
connected, the timer will turn the output on but it won't turn off. I have
tried disconnecting the relay and all works fine again so the relay must be
causing some problem. The relays number is KU1T-A
Is there any way I can get the timer circuit working with a relay?

Thanks
Grenge
 
L

Lord Garth

Jan 1, 1970
0
Grenge said:
I am having some trouble with a electronic circuit that I have built and
wondering if anyone can help me.
I built a timer circuit from a Dick Smith kit "K-2813 555 Timer Circuits". I
made circuit #1 shown here
http://members.ozemail.com.au/~tizza/timercircuit.jpg I added extra
resistors in series with VR1 to extend the time.
When I finished it, I tested it with a lamp connected to the output and it
all worked fine. The timer ran for 17 seconds before switching off. Then I
connected a relay to the output, because the relay would then switch a
flasher circuit that is working in combination with it. With the relay
connected, the timer will turn the output on but it won't turn off. I have
tried disconnecting the relay and all works fine again so the relay must be
causing some problem. The relays number is KU1T-A
Is there any way I can get the timer circuit working with a relay?

Thanks
Grenge

What is the exact part number of the 555? I'm trying to determine if it is
a
CMOS version or if it is the standard version. The output might need a
transistor driver to work with the relay. You will need to place a diode
across the relay to protect the preceding circuitry from the inductive
'kick'
when the relay is switched off.

What voltage are you applying the timer / relay circuit and what is the
resistance
of the relay coil?
 
H

Harvey

Jan 1, 1970
0
Grenge said:
I am having some trouble with a electronic circuit that I have built and
wondering if anyone can help me.
I built a timer circuit from a Dick Smith kit "K-2813 555 Timer Circuits". I
made circuit #1 shown here
http://members.ozemail.com.au/~tizza/timercircuit.jpg I added extra
resistors in series with VR1 to extend the time.
When I finished it, I tested it with a lamp connected to the output and it
all worked fine. The timer ran for 17 seconds before switching off. Then I
connected a relay to the output, because the relay would then switch a
flasher circuit that is working in combination with it. With the relay
connected, the timer will turn the output on but it won't turn off. I have
tried disconnecting the relay and all works fine again so the relay must be
causing some problem. The relays number is KU1T-A
Is there any way I can get the timer circuit working with a relay?

Thanks
Grenge

The coil current of that relay seems to fall well within the output
specs of the 555 so it shouldn't be overloading the chip.
Have you fitted a diode (1N4148 signal diode) across the relay coil
(connected backwards) to protect the 555 from the voltage spike created
as the coil is switched off?

It is possible that your circuit is re-triggering itself as the coil is
switched off so it's a good idea to also connect another diode (1N4001
rectifier diode)in series with the coil.

You could also drive the relay via a transistor circuit.
http://www.eleinmec.com/article.asp?1
 
G

Grenge

Jan 1, 1970
0
Harvey said:
The coil current of that relay seems to fall well within the output specs
of the 555 so it shouldn't be overloading the chip.
Have you fitted a diode (1N4148 signal diode) across the relay coil
(connected backwards) to protect the 555 from the voltage spike created as
the coil is switched off?

It is possible that your circuit is re-triggering itself as the coil is
switched off so it's a good idea to also connect another diode (1N4001
rectifier diode)in series with the coil.

You could also drive the relay via a transistor circuit.
http://www.eleinmec.com/article.asp?1

It was the two diodes that it needed.
Thanks
 
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