NOTC relay

[MikeMl]

...
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.

What is the contact rating on the relay?
What voltage is connect to the inductive load?
Is one end of the load connected to the supply voltage, or to ground?
How many times per second is the load switched on/off?

 

[BlackSportD]

I'm not sure of the questions. I'm not trying to transmit the PWM signal through a transistor. The origin of the delay circuit request was to delay switched on power from powering up the PWM circuit because the other product I'm using to deliver the 0-5vdc signal to that PWM circuit to control it's PWM output has a voltage "spike" upon startup- making the DC motor the PWM circuit powers jolt for a second.

So I went in search to find an economically priced delay relay to replace the current relay to the PWM's (and motor's) power source.

Then after looking over your circuit and it's relay's resistance requirement, I figured I'll use it instead with a smaller relay (will satisfy the resistance requirement) and be an open to the control part of the circuit open power up, stopping the voltage spike problem. And heck as everyone knows I'm not the king of electronics (hence being a member of a forum such as this), it might give longevity to the control circuit as I have no idea what a 1volt spike to the control circuit would do when the rest of the circuit (12vdc) is de-energized.

Then I figured hell, the control voltage for the PWM circuit is hardly any current flow, something like a transistor (but I thought those are more for current and not for voltage) or MOSFET would be better than a bulky relay.

But as previously stated, its gone far over my head. I will stick to the original circuit. thanks again for providing it.

 

[truck man]

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.

MikeMl, I know this thread is over 6 mth old but I was looking for a relay delay cct and the one you posted seemed suitable. I needed to vary it slightly to suit my application and had to use a 2n7000 FET as it was the only one I could get locally. BTW, the relay coil is 400ohms.

I built it as per the attached cct but unfortunately it's not working, and with my limited electronic knowledge I don't know why - hopefully someone may be able to tell me.

The output of A1101 is high and goes low when it's activated. BC327 is switching and providing 12v to the 2.2meg resistor, however the volts at gate of the FET begin to increase but only get to .67v and stop there.

What could be the problem?

 

[mneary]

If D1 is connected to GND instead of +12V, this could cause exactly what you see.

The next most likely problem is the CAP could be backwards. It's probably an electrolytic, and the (-) should be to GND.

 

[truck man]

Thanx for the suggestion. I was hoping it would be something as simple as that but no, everything was installed correctly.

I decided to put the diode across the coil and moved the anode from the gate to the drain. This got the circuit to work - it delayed the relay turning on by approx 5 - 10 secs. When it finally did switch on, it wasn't a "clean" switch, it seemed to take maybe .5 sec or maybe longer. Not sure if it would hurt anything, I just haven't heard a relay do that before.