any relay do this?

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stupidpig

Member - Posts: 31

Joined: February 17, 2009

Location: California, United States

Posted: May 08, 2009 at 2:59 AM / IP Logged

Parts finally arrived, and it works great . I tried 2.2K, 20K, and 220uF cap, which gave me about 5s delay-on and 4s delay-off. I'm still playing with different combinations to decrease a little bit on delay-on and increase a lot more on delay-off. My goal is to have about 3s delay on and more than 30s delay off (I guess the delay off part probably impossible). I do found one problem, which is if I keep turning the input on and off, it will still switch on the relay after a couple times. May be the cap keep adding charges and stored it.

i am an idiot

Platinum - Posts: 13,716

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: May 08, 2009 at 6:04 AM / IP Logged

stupidpig wrote:

Thanks. 3s just an example, I think anything more than 1.5s should work for my needs.

Good thing we opted for the transistor.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: May 08, 2009 at 7:54 AM / IP Logged

If you want to adjust the delay on time independently of the delay off time, just use a parallel combination of diode-resistor in series.

In place of the 20k resistor picture, put a resistor in series with a diode facing forward, and then in parallel with that, put a resistor with a diode facing backwards.

This allows each resistor to be adjusted to change one time without affecting the other.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: May 08, 2009 at 8:02 AM / IP Logged

stupidpig wrote:

I do found one problem, which is if I keep turning the input on and off, it will still switch on the relay after a couple times. May be the cap keep adding charges and stored it.

That's perfectly normal, since the voltage isn't starting from zero if you don't allow it time to reset to the starting condition by charging or discharging the cap fully. You'd need a different circuit to have it reset immediately on a transition for a new timing cycle.

stupidpig

Member - Posts: 31

Joined: February 17, 2009

Location: California, United States

Posted: May 08, 2009 at 2:19 PM / IP Logged

I tried a 330uF cap and replaced the 1K on picture with 20K, and it increased the delay-off to about 10s, not as much as I want but I think that's good enough. The problem with the 330uF is it increased the delay-on also. I think by decreasing the 20K on picture should shorten the delay-on. Time to get a couple resistor with different ohm for try...

Oh, any suggestion on how to drain the cap if I just pulse the input? A relay to ground the cap when input is off sounds overkill.

stupidpig

Member - Posts: 31

Joined: February 17, 2009

Location: California, United States

Posted: May 09, 2009 at 12:59 AM / IP Logged

OK, here is what I used finally. 1K in picture replaced by 47K, 20K in picture replaced by 15K, and 330uF cap. About 5s delay-on and 17s delay-off. Originally I want to use 10K instead of 15K, which give me 3s delay-on and 16s delay-off, but the relay will switched on after I pulse the input for 4 times only. With the 15K, the relay only switched on after pulse the input for 12 times, sounds acceptable.

Thanks for all the help :)

stupidpig

Member - Posts: 31

Joined: February 17, 2009

Location: California, United States

Posted: June 05, 2009 at 4:21 AM / IP Logged

Unfortunately, this thing die after 3 days. I checked the spec for 2n6488, and found that the max emitter-base voltage is 5v, and we are following 12v to the base to turn it on. Will that be the cause of the death?

i am an idiot

Platinum - Posts: 13,716

Joined: September 21, 2006

Location: Louisiana, United States

Posted: June 05, 2009 at 4:34 PM / IP Logged

Have you checked to make sure the transistor is the defective device?

stupidpig

Member - Posts: 31

Joined: February 17, 2009

Location: California, United States

Posted: June 05, 2009 at 7:07 PM / IP Logged

Nope, but will try once I back to home.

i am an idiot

Platinum - Posts: 13,716

Joined: September 21, 2006

Location: Louisiana, United States

Posted: June 05, 2009 at 7:27 PM / IP Logged

I didn't go back and read what you wound up using for the capacitor values. What about the 20K resistor, did you change that to a different value?

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