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tylernt 11-15-2012 04:07 PM

1/2HP motor: start on low, or high?
I'll be installing a two-speed (1750/1150RPM) 1/2HP motor in my roof-mounted swamp cooler in the spring. This motor will be controlled by a "smart thermostat" and when the thermostat calls for cooling, it has the option to start in either high or low for a few seconds before switching to the appropriate speed based on cooling demand.

I've noticed that ceiling fans and wall fans usually come with a switch configured for off, high, medium, low. I assume this is deliberate -- by forcing the user to switch to high first, it presumably helps the motor start more reliably. Will a 1/2HP swamp cooler motor benefit from starting on high in the same way, or are they wired differently such it doesn't matter?

An argument for starting on low would be to cause less arcing and wear on the relays (the smart thermostat only switches 24V, separate RIB2401B relays do the heavy lifting), and to help avoid blowing fuses / tripping breakers / dimming lights with a smaller inrush current.

I notice that the typical 6-position swamp cooler dial switch lets you go straight from "off" to "low vent", so this suggests starting on high is not strictly necessary.


Missouri Bound 11-15-2012 07:47 PM

Let it start on the low speed and ramp up if needed. I believe that is the purpose of the smart controller.:yes:

micromind 11-15-2012 08:01 PM

That type of motor doesn't care in the least which speed it is started on.

I it makes any difference, the transition from low to high will be smoother than from high to low. Other than that, it just doesn't matter.

tylernt 11-16-2012 11:48 AM


Originally Posted by micromind (Post 1053123)
That type of motor doesn't care in the least which speed it is started on.

Awesome, thanks!

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