Help from elec. experts

Lew

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Trying something new.  I have a unit that uses a Lamson PIR and Ramsey timer to fire the camera.  Now I want to add a second Ramsey timer to give me a several minute delay between pictures.  I was thinking if there is such a thing as a normally closed relay, then I could run the PIR through that to the two timer.  The one firing the camera and the second to open the relay and prevent a second picture.  Qustion is there such a relay and what do I look for or ask for,  to get what I  need  ??  If you know of a specific normally closed relay that would handle 9v's that would even be better.  Thanks.   Lew
 



Guy Wire

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Yes, there IS such an animal as a Normally Closed.

Relays come in both flavors...no and nc.
 

Lew

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I talked to the people at Mouser Electronic today and they recommended I try relays 653-G6B-2114P-DC5 and DC12.  The Lamson system operates on a 9v battery, therefore I am concerned that the 5v relay may get burned out and the 12v may not get switch with just 9v.  I plan to get them and give them both a try.  I suppose a second option is to use the 5v and use a risistor to bring down the voltage from 9v to 5v, if needed.  Any idea how much resistance would be needed to cut the voltage by that much??  If I get this whole thing to work I will share the information for what it is worth.  Lew
 

Tinhorn

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Lew,

Here's the formula to calculate the resistor value.  You will have to plug in the coil voltage and coil current values based on the relays you bought but I used these values for example.

Batt Volts = 9
Coil Volts = 5
Coil Current = 20ma's which is .020 amps

9v - 5v = 4v (to drop)
4v / .020amps = 200 ohms

Resistor to use is 200 ohms

Tinhorn
 

Lew

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Thanks Tinhorn,  I knew you would have the answer.   I think with that piece of information I get the system working regardless if the relay is unable to use a 9v current.  This has been a fun project and I have learned a lot from you guys.  Lew
 


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