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timer Relays

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alarm_guy1

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Hi guys, I'm new to this forum and a bit of an electonics newbie, I need to buy (pref ) or build a timer relay, unfortunately I need a 10 min switch time but non latching. i.e. I need it powered 24/7 i need the timer to change the relay state but only briefly every 10 or so minutes. any help or direction greatly appreciated
 

MikeMl

Well-Known Member
Most Helpful Member
I have one of these. You can program it to do what you want. You will need a small 120Vac relay if your application requires a contact closure.

Added: oops, on rereading your post, I see that you want a reoccurring output every 10min. The timer referenced above will only do it 8 times per every 24hours.

What voltage do you want to operate the timer on?
How long does the output need to stay on?
How accurate does the timing cycle need to be?
How much are you willing to spend?
 
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alarm_guy1

New Member
Operating Voltage 12Vdc
The output needs to stay on for a fews seconds only with a 10 or so interval
Not particularly Accurate
Very Little

cheers
 

Willbe

New Member
Operating Voltage 12Vdc
The output needs to stay on for a fews seconds only with a 10 or so interval
Not particularly Accurate
Very Little

cheers
Perfect for a 555 timer with a very short duty cycle.
 

MikeMl

Well-Known Member
Most Helpful Member
Timing for 600 sec (10min) requires that the product of the timing resistor and timing capacitor values be about 480. If you use a 20megΩ resistor, the capacitor has to be about 25uF. As the capacitor charges toward the 555's upper trip point of 2/3 Vcc (8V) the timing resistor has only 4V across it, so it can only source 200nA. The 200nA has to exceed the input bias current of two inputs to the 555, the leakage of the timing capacitor, and there has to be some current left over to charge the timing capacitor.

That is why you have to use the CMOS version of the 555. Trying to get a 10min delay out of a Cmos 555 is a very marginal design, which might stop working at elevated temperatures....
 
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