So I have an ERV (energy recovery ventilator) in my shop that provides fresh air and removes the stale air from the workspace. It's essentially two squirrel cage fans, and a small motor turning an entropy wheel. The thing is on a timer, and comes on at preset times (which can be changed, of course).
The problem is that we'd like it to come on in response to certain conditions. First, we still want it to turn on at the preset times. Second, we'd like it to run whenever the humidity in the shop rises above some value. Third, we'd like it to run for awhile whenever we ask it to.
Currently, functions 2 and 3 are not possible. So I got to thinking, I can have an arduino do all this for me. Replace the timer with an SSR, and the arduino can be configured to handle all three functions.
Well, at this point I have the arduino side all figured out, and have tested it with an LED as the output. Humidity was a rough one to get the settings right, but was able to do so (used adafruit's DHT22, fwiw).
Anyway, now I'm trying to spec out the SSR, and I ran up against some knowledge barriers. The ERV has 2 0.5HP motors. It appears to spin them up at the same time, but I can't be sure without taking it apart and running it. (The wheel motor is only 0.1HP, and it is on a delayed start, so I'm not worried about it). So I'm assuming a 1HP inductive load. Based on the inrush current, I should be looking at a 75-90 Amp rated SSR. Also, based on what I've read, for motor loads, random start is better than zero-crossing.
Of the myriad options available, SSRs which are roughly equivalent in spec will vary wildly in price, often an order of magnitude. (See this FOTEK-SSR-75DA-H (~$9) vs this Crydom CWD2490-10 (~$95)). And that is before the heatsink.
Is the Crydom worth the extra $86? What am I missing here? How important is random-start?
Thanks for any help.