Control pump speed with 120 VAC?

Here’s a good question: “Your iSolar™ controller literature says the relay outputs are 120 VAC and it also says the output can control pump speed. How is pump speed control accomplished with 120 VAC?"

The iSolar semiconductor (Triac) outputs source 120 VAC. In the controller settings, minimum pump speed - nMN - is adjustable between 30% and 100%. If set to less than 100%, the 120 VAC output is “conditioned” and the sine wave varies to control pump speed. The controller program will reduce pump speed, based on the temperature sensor values and the differential temperature program settings, to save pump electrical energy when it makes sense. The circulation pumps provided with Caleffi solar pumping stations are compatible with this kind of “poor man’s modulation” signal.

If using the output to control a load other than a pump, such as a valve or pilot duty relay, always set nMN to 100%. The output will not vary and control is simple on/off. Relays and valves are typically not compatible with a conditioned sine wave and they may “chatter”.  VERY IMPORTANT: The iSolar Triac outputs are rated for 1A maximum current; DO NOT EXCEED!  If your load is greater, use a relay with a 120 VAC coil. For speed control, go with a solid state relay such as Caleffi’s NA15012. If on/off is all you need, use a common pilot duty relay (and don’t forget to set nMN = 100%). Double-check your electrical ratings!

Thanks for the read,
Kevin Freidt