I am trying to decide which relays I should purchase for my AC Power supply.

Thread Starter


Joined Sep 27, 2016
I am in the process of designing an AC Power Supply. My team and I have decided to go with a Multi tap Transformer to tap the 7 voltages that we need (240, 380, 400, 480, 600, 690, and 1,000VAC). At each of these 7 Voltages we are 4 current levels of 0.5, 2.5, 5.0, and 10Amps. We are in the process of ordering a Variable Resistive AC load bank that will automatically give us the resistance values at each voltage to reach the currents that we need. My manager had informed me that I will need switches within the power supply for the transformer and the load bank to properly operate. I have never had to order relays before but I was wondering based off of the information that I have given what switches would I need for the AC power supply and how would they function within the supply. Such as high powered relays and solid state relays. Thanks to anyone who can help.


Joined Jul 18, 2013
Although applicable to DC relays, one thing I would refute in the above link is

As a power source for DC relays, a battery or either a half or full wave rectifier circuit with smoothing capacitor is used.
In the case of ripple included in the DC power source, if the smoothing capacitor is too small, humming develops and unsatisfactory condition is produced, due to the influence of the ripple.
This ripple is calculated using the formula described in Fig.4 and it is necessary to give consideration to use of a power source with less than a 5% ripple.
I have conducted empirical testing on several different relays using unfiltered DC and taking the voltage down through the hysteresis point, where ripple effect would be expected to be seen.
No adverse effect or humming was seen to occur.
There are many examples where other contactors, clutches, brakes and solenoids are fed this way with no ill effects.