component values in circuit shown here?

I'm looking at building one of these circuits: https://www.the12volt.com/relays/relaydiagram22.html. My electronics knowledge is fairly basic, so I have a few questions: - what type of capacitor is the 10K uf cap... and what voltage rating is needed? - what's the wattage of the resistor (and how would I calculate that with Ohm's law in this instance?) - is the diode on the feed side (inbound from the turn signal on left) a 1N4001 type or could I use a 1N4004 there as I need in the relay? Bonus question: the instructions mention changing the cap value to get a "longer output" ... am I correct in assuming that the output it's referring to is once the turn signal input is cut off and it does a final discharge? Or do I need to play with the cap value to make sure it doesn't drop the output even while the turn signal continues to send a pulse? Thanks!

Electrolytic caps cover that 10uF range. Though available as 16V, I'd suggest a 25V (or higher) rating. You needn't worry about the resistor - it is in parallel with the relay coil and has negligible effect. (If anyone disagrees, please chime in - eg, to dampen any oscillation?) But for future ref, the power dissipated from a resistor V*V/R or I*I*R. EG, in this case assume 15V hence 15V x 15V / 10,000R (R = Ohms) = 225/10000 = 0.0225W. Hence a common 1/2W (0.5W) is fine. Even a 1/4W resistor is 0.25W which is 10x more than required. BTW - the above formulas come from Ohms Law V=IR and Power P = VI. You could either calculate I from V=IR => I = V/R = 15V/10k and then substitute that into P=VI, but you might see that's the same as V*V/R as I used directly. And yes, the output or delay time is the time ON after power (+12V) is removed. The cap discharges thru the relay's coil (probably around 250R). The bigger the cap, the more the charge and hence the longer time thru that same (coil) resistance. The relay will turn on as soon as the next +12V pulse arrives (ignoring any cap charge-up delay caused by the LHS input diode). Be wary of relay chatter that might occur.

10K microfarad = 10,000 microfarad

Yeah, sorry - my Bad. I was thinking 10mF. Thanks ye that thinks he's the idiot! But yes, it's 10,000uF

Thanks... I did that calc on the resistor wattage but it came out so small I thought I must have done it wrong. When you mention relay chatter... you're suggesting that it might open when the cap discharges if the next pulse from the turn signal doesn't get there soon enough to keep the cap charged? Can I use a 1N4004 diode in both spots or does the LHS one need to be a 1N4001?

The only difference between a 4001 and 4004 is the rated voltage. For any application here, they are identical devices.

x2 on the calcs. But after a while you realize 10k "big" & 12V "small". And rough sanity checks like 10x10/10000 = 1/100 & 20*20/1000 = 4/100. The chatter occurs if the voltage "bounces" between the relay's drop out & pull in voltages - say 5V & 8V. The bounce can occur because of the nature of LC or RLC circuits which typically oscillate. (L is the inductance from the relay coil.) It's not always a problem - it depends on the relay characteristics and component values involved. Plus that spike suppression diode (across the coil) reduces the negative spike (caused when current is cut to the coil). And Dang! I forgot the diodes. Yes, use 1N4004. Or 1N4007 - both are common, and both are rated for 1A. (1N4004 is rated for 400V "PIV"; 1N4007 for 1,000 PIV.) The 1N4001 has a 1A 50V rating and though okay for the "series" input diode, it is probably under-rated for the RHS "parallel" spike suppression diode - de-energisation spikes are typically 100V or more (try it and see!). Besides, the IN400x range has generally been reduced to the 4004 & 4007 - it's a 2 sizes fits all production philosophy. A higher 1N400x end-number exceeds lower numbered ratings.

Thanks all... I think I'm all set to build this now.

Standardise on 1N4004, it's the most commonly available and the PIV withstands coil spikes on relays. This will also protect solid state equipment, mandatory on alarms IMO.

If I understand correctly: when you cut the power, the energy in the coil can cause a reverse spike into the circuit back into other components... and that's why we need a diode? Thanks,