This has come up and I searched the archive but am still confused and challenged electrically.
I want to lower my voltage for one vibrotor accessory without affecting the other accessories coming off of the same transformer. I would like to lower by two volts. Resistor? Diode? What’s right for the job. Rating and specific Radio Shack woud be really, really helpful.
You can do it either way if the accessory draws a steady current when it is running.
To find the right resistance, you need to know how much current the accessory will be drawing at the voltage at which you want to run it. Then divide two volts by that current (in amperes) to get the resistance value. Then you need to calculate the power (in watts) that the resistor will dissipate as heat, which is the product of two volts and the current. Then get a resistor rated at at least twice that power.
To do it with diodes, you will need about 8 rectifier diodes rated at about the current that the accessory draws. Wire them into parallel pairs, with the anode of one diode connected to the cathode (the end with the stripe) of the other, and vice-versa. Then connect all four of these pairs in series.
To do it with bridge-rectifier modules, connect the + and - terminals of each module together. Then connect two modules in series, using their ~ terminals.
Unless it’s a very big accessory, yes. You could probably use its smaller 3-ampere cousin, remembering that the current flows in each diode only half the time.
When you get it going, don’t trust your voltmeter to tell you how much you have reduced the voltage. The waveform is no longer sinusoidal, so the meter reading will have some error. However, the important thing is that the accessory behaves the way you want it to. So, you can add or remove diode pairs until you are happy with its operation, even though you don’t know exactly what the true (RMS) voltage is.
Got the 3amp diodes. Used 4 pair and my fork lift loader works nicely. I might add another pair to slow down even more. Thanks a lot. Your electrical knowledge is a great asset here!