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NOTC relay

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BlackSportD

New Member
I'm trying to find a small economical 12vdc delay relay. I initially looked for a mechanically delayed relay like a pneumatic dampened relay as I do not need range adjustment, just a few seconds of delay, but those all seem to be dated and bulky.

Are there any small 12vdc relays that have a compact delay circuit integrated into it, possibly a fixed delay (to save cost). Couldn't find anything really attractive on the internet.
 

MikeMl

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BlackSportD

New Member
^^ Yes please.

I found this circuit that seems simple enough, and also read of even simpler capacitor/resistor based setups but I'm scratching my head searching google because there MUST be a relay somewhere on God's green Earth already built to do this, mass produced and dirt cheap.
simple delay
 

arunb

Member
a capacitor could be used to delay the relay contacts, the value of the capacitor would depend on the current used by the relay though..
 

KMoffett

Well-Known Member
What are the current/voltage requirements for the relay contacts? How many contacts...SPST?...SPDT?...DPST?...DPDT? How many relays do you need?

Ken
 

MikeMl

Well-Known Member
Most Helpful Member
^^ Yes please.

I found this circuit that seems simple enough, and also read of even simpler capacitor/resistor based setups but I'm scratching my head searching google because there MUST be a relay somewhere on God's green Earth already built to do this, mass produced and dirt cheap.
simple delay
Here is my version. I do not like the one you posted, because it is overly complicated, and it takes too long to discharge the timing network if the power is momentarily interrupted. Mine resets in less than 1s. I intended it to be used with a 12Vdc relay that has a coil resistance of 100Ω or more. The parts cost per Digi-Key is less than $1 not counting the relay. If you need a longer delay, I would say that an upper limit on R1 is 4.7megΩ. C1 should have low leakage.
 

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BlackSportD

New Member
I have an 85ohm SPDT relay just sitting around, all I need is one relay, a SPST at that.
Actually a DPDT relay would be nice

Anyway to try and cheat w/ your circuit to run the 83ohms?

B.
 
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MikeMl

Well-Known Member
Most Helpful Member
Use a higher power NFET, like an IRF530.
 

BlackSportD

New Member
Will do. I think I will go with your original design and get a smaller more adequately sized relay for this project, which in turn should have a higher resistance value.
 

MikeMl

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Hero999

Banned
Here is my version. I do not like the one you posted, because it is overly complicated, and it takes too long to discharge the timing network if the power is momentarily interrupted. Mine resets in less than 1s. I intended it to be used with a 12Vdc relay that has a coil resistance of 100Ω or more. The parts cost per Digi-Key is less than $1 not counting the relay. If you need a longer delay, I would say that an upper limit on R1 is 4.7megΩ. C1 should have low leakage.
D3 is connected incorrectly, it should be connected across the inductor, not from the gate to +V.
 

KMoffett

Well-Known Member
I think D3 is there to rapidly discharge C1 through R2 when power is removed. There probably should be one across the coil, as you say.

Ken
 

MikeMl

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Hero999,

the diode is placed where it is to discharge the timing capacitor through R2 when power is removed from the circuit. No snubber diode is needed on the relay coil because the Fet turns off slowly enough (τ=C1R2) precluding a large voltage spike at the FET's drain.
 

MikeMl

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Most Helpful Member
I think you are asking is there such a thing as a transistor? :D
How much current do you want to switch?
What is the nature of the load? Resistive? Inductive?
Do you want to switch the 5V lead or the ground lead?
 

Mikebits

Well-Known Member
I think you are asking is there such a thing as a transistor? :D
How much current do you want to switch?
What is the nature of the load? Resistive? Inductive?
Do you want to switch the 5V lead or the ground lead?
Based on the Op's earlier question, do you really think he could answer your questions?;)
 

BlackSportD

New Member
Yes Mikebits, not all people rush out of the womb an EE. I get along w/ what the Navy taught me, as much as I'd like to take it further God had a sense of humor with my math abilities and here I am, entertainment for you. I don't mind though, everyone needs an ego boost.

I'm assuming the control circuit is an inductive load.
Its a PWM driver that uses a 0-5vdc (not 0-20ma) input for 0-100% duty cycle. I was afraid a transistor would distort the signal a bit. If not I suppose a 10K at the base and I could replace the relay.
 

Sceadwian

Banned
If it's PWM it's already nothing BUT distortion (that's what square waves are) 10k at the base for how much current? 1k is usually more sensible depending on what the transistor needs to draw for current, unless you're using a darlington pair or some super high gain transistors, or very low pass current.
 
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