constant to momentary

It may be ok with the 1000 mic capacitor.  A larger cap will yield a longer pulse.  I am concerved about the length of the pulse when power is removed from circuit. 

It works exactly like you said. Hard to tell the both pulses seem the same to me.

Thanks a million.

Luca

Hello, Im new to this forum and I need to make a constant to momentary relay but would like to get a diagram or at least a parts list of what I need in place of the ones in the diagram above for my specific application. What I need it to do....

I have a terrarium with tree frogs and they are from a rainforest and need lots of humidity. I have an electric water mister that runs on 3v (2 AA), but I will replace the batteries with a 3v power adapter. I need this sprayer to turn on for aprox 4-5 seconds and stay off for a couple hours. I already have the means to cycle the several hours part via an outlet timer and that will operate the constant to momentary relay which will hopefully give 4-5 sec of 3v power to the mister. I think I need a different capacitor than shown, what size will I need for 4-5 seconds of 'ON' operation? Will this relay STAY off after this initial ON cycle? My outlet timer is only capable of providing 30min intervals of on and off and I only want 4-5sec of spray.

One more question, Aside from using the required 12v supply to operate the relay....Can I use 3v fused through the relay instead of 12v shown in the diagram? I dont think thats a problem but Im not sure and wondered why it specifies 12v fused if not all applications use 12v.

Thank you for your time,

You will have to try this with a 10,000 microfarad capacitor.  How long does your timer keep the power off?  Every time the timer turns on, it should have output for near 5 seconds.  As long as the off time is at least a minute, it should reset just fine and be ready for the next cycle.  Yes you can run 3 volts through the contacts of the relay. 30 and 87. 

Constant to Momentary Output ( link)

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.

Thank you for the fast reply. My timer will cycle on for 30 minutes then cycle off for the next 3 or 4 hours. Its one of those wall outlet timers that has a round dial that has pegs in it each indicating 30 minutes of time and you either press them in or pull them out for on or off.

Out of curiousity, After the relay is used for 4 or 5 seconds, Will the relay still be drawing 12v current? It seems that the 12v current is fed into the capacitor the entire time you send current to 86. If thats the case, how much current is the fully charged capacitor drawing? Is there a risk of overheating the capacitor? The shortest ammount of time I can send power to 86 is 30 minutes and I will be using a 12v power adapter between 500ma to 1amp. Is this too much or not enough?

Thanks again.

I went shopping for the parts I needed today and put it together. I could not find a single capacitor over 3500 uF or so. Instead I bought a capacitor kit with several sizes upto to 3500 uF and I used 6 different ones to total around 7400 uF I think. This makes the relay stay closed for about 10 seconds! Could this longer than expected time be due to using a "light duty", low coil draw, pc relay? I may cut one off if I decide 10 sec is too long. I put the capacitors in parallel, not in series. I wasnt sure which was correct but it seems to work fine like this. I wasnt even sure if cobbling a bunch of random caps together would even work. I took pics of the project if your curious how it looks. This is actually my first electronic build from scratch I guess, I never built anything on a blank electronic board before.

I have one main concern yet. When I energize the board and the relay does what it should, it takes at least 30 minutes or more to drain the caps down before resetting. This really isnt a problem in the real world use of this relay since it will only need to power up maybe 3 times a day, but for testing it I cannot power it up more than once an hour or so. I have several extra 10k, 1/2 watt resisters. Can I add 1 more resister to drain the caps in half the time or will that be more detremental in the long term use? Again, its only desired for 'seeing' it work sooner while testing. Heres the pics. BTW, in the pics you will notice I have 2 diff power adapter jacks. 1 is for powering the relay, the other is the power supply for the water mister. Also you will see 2 wires attached to the board, these go to the water mister. There was probably a better way to wire it up but I am pretty noob at it.

Thanks so much for helping me!

https://i49.tinypic.com/20sd192.jpg

https://i49.tinypic.com/2gv66qg.jpg

https://i48.tinypic.com/2yknyc3.jpg

https://i45.tinypic.com/2gx0h1s.jpg

https://i45.tinypic.com/33xkbk5.jpg

After testing it again I was unable to get the relay to actuate and close. So I added another resistor next to the first one in parallel and after an hour or so it still wont reset. I did some research and found one source that says 'increasing the resistor size increases the recovery time or discharge time of the capacitors'. Is this true? If I want the recovery time shortened, I need a smaller resistor? Im so confused about the part the resistor plays and how it works that I must ask...... What would be considered "smaller"? I have 10k Ohm resistors now. Is 5k Ohm smaller? Or does less Ohms mean larger resistor? As it is, Im sure it wont reset soon enough because when I test it I plug the power source into the relay for only a couple seconds and it still takes forever to reset. In the real world scenario it will be powered up for 30 minutes before disconnecting power, so I need it to reset alot faster.

My setup so far.... Same as diagram except I am using 7440 uF cap. And I recently added a 2nd resistor < color=#2200cc>parallel with the first one. If I need a weaker resistor, can I use 2 of my 10k resistors in series, effectively making a 20k resistor? I believe what I did was make 5k Ohm resistor. Can you clear up my confusion? Thanks alot.