![]() ![]() Rather than use that monster 4.7 uF capacitor, it might be cheaper to If you put the switch rightīefore the cap, it could conceivably be charged up to 165V, which would meanĦ4mJ of energy stored across the cap, enough to wake you up. Has been off for 2 hours and you pick it up. This will keep you from shocking yourself when the circuit One last thing, I'd put a 1MEG 1/4 W resistor in parallel to the 4.7uF cap That at goldmine, I believe.) You could also use a cheapo hot glue gun toĬover all the wires in goop. Users, and encase the wires and leads in heatshrink tubing (you can also get Inside the case, make sure NOTHING, including the relay, can be touched by ![]() If you are going to build this, mark HIGH VOLTAGE clearly somewhere on You can get both of these, and a sandstone 10 ohm 5W resistor mailorder from Should go 50V just to be safe and to extend the life of the cap. You need something that'll handle a high enough voltage, like a 25V cap. Ground (which is the bottom line) in the circuit. The 4700uF cap is a big electrolytic cap (you probably can't get anythingĮlse that big.) The minus on the cap (it'll be marked clearly) goes to the The voltage rating is marked on the cap, or you specify it when you buy it.ĭon't use anything with a lower voltage rating! The 4.7uF cap is a big fat non-polar 250V cap. It is hard to beat and it could also be a nice fit for your amp. To the circuit, but for initial experimentation with RC timing, The timing is not important, so even if the timing varies with For a turn on delay for your amp, precision in Power that the relay coil needs and an appropriate zener and To select (or make) a darlington that can easily handle the This is a nice experiment, and the parts are cheap. Resistor in series, you would have a nice adjustable The 33K ohm resistor with a 50K ohm pot, and added a 4.7K In turn this will cause the darlington toĬonduct and the relay will transfer. InĪnother second or so, it will reach 9 volts, and the zener The cap charges to ~7.5 volts in ~ 3.3 seconds. The series RC made of the 33K resistor and the 100 uF cap, What happens? When power (12 volts DC) is applied across (NPN) circuit by connecting the emitter to ground and theĬollector to the relay coil, while the other side of the In series with the 33K ohm/ 100 uf cap junction,Īnd stuff the other end of the zener into the base Some specific level? Well, we can do that by puttingĪ zener diode between the high impedance circuitĪnd the cap. The voltage at all, until it reaches (or exceeds) Suppose we prevent that high impedance from seeing Much of an effect on the time constant - but it will beĪble to "see" the voltage rising on the cap. Times higher than 33K ohms) across it? It won't have However, suppose instead of placing the relay coilĪcross the cap, we place a very high impedance (many Resistor is trying to charge the cap, the 330 ohm The trouble with that occurs when you connect the Make the resistor 33000 ohms, and the cap 100 uf You could get the same time constant with a muchīigger resistor, and a much smaller capacitor. The rest of this post goes into some light theory andĮnds with a description of a nice circuit you canĮxperiment with and possibly use in your amp. You'd need a large C to get a few seconds delay - aboutġ0000 uF to reach 63 percent of full voltage across In rough terms, a resistor in series withĪ capacitor will charge the capacitor to about 63 % ofįull voltage in a time equal to R times C. Lets set aside the other issues, and just address theĭelay time. Resistor (or, if I've miscalculated that value, with the proper valueĪny observations, suggestions, corrections (I'm getting used to these!!) are Value of the capacitor be to give me a 1 or 2 second delay with the 500 ohm Since I need to delay the relay's turn-on, I'll be adding a capacitor,Īnyway, whether I use this relay or a true DC-rated type. How complex would it be to run this relay with mains voltage? Is it as simpleĪs a diode followed by a resistor? Would this resistor be 120/0.071/2 = ~500Īnd a fundamental question: can a relay with an AC coil function properly & Nice new relay with properly-rated contacts sitting on the shelf with a coil ![]() Ideally, a relay with DC-rated coil would be most appropriate, but I've got a I realize that this means getting DC voltage (via I need to power a relay from 120 vac such that its action is delayed for aįew seconds after power-on. ![]()
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