Thinking of a controller board for 120v Swamp Cooler

[BrentNewland]

I've been considering building a controller board for a swamp (evaporative) cooler to interface with any standard programmable thermostat.

I've been having a hard time finding information on what voltages a thermostat works with, but I've been able to determine the basics (I think):

Power feed is 24v A/C from air conditioner
Some thermostats support 2-stage air conditioning (a two stage compressor setup)
--I don't know when the two stages kick on, or if both are active at the same time; I am assuming that the second stage comes on when extra cooling is needed, but it may be for a fancy start-up sequence
A single wire is sent to the air conditioner to turn on "cooling"
A single wire is sent to turn on circulation fans
Power is constant from the signal line when the feature (cooling or fan) is turned on
--According to here

And how a Swamp Cooler controller is wired:
**broken link removed**

Here is my thought:
Would need to have a 120v a/c to 24v a/c converting circuit (I'm sure I could find one on google)
--Not sure of the amperage needed
24v a/c gets sent on a wire to the digital thermostat
First and Second stage cooling wires and fan wires are run to the controller (near the manual swamp cooler controls)
Fan line is connected to a 120v relay that is connected to the low-speed motor connection
Stage 1 cooling is connected to a 120v relay that is connected to the low speed motor connection and a second relay (in series?) that is connected to the pump connection
Stage 2 cooling is the same as above but with the high-speed connection

That should allow a digital thermostat to control a swamp cooler, I think.


The only areas of concern I have are:
Starting amperage of the motor and pump
--I read the motor can draw between 5 and 15 amps while running, I'm worried starting voltage could be much higher
Type of relay
--I was looking at Solid-State Contactor relays and Latching relays, not sure what the best and most affordable would be
--Also, where I would even find one (are they all really $80+?)
Manual controlling of a hooked-up swamp cooler
--might make circuit more complicated by having 2 24v sources and not being able to have them hooked up to the same relay (since you can't send voltage to the thermostat over the signal line, it might fry it)
Possibly needing to wait a few minutes for the pump to run (and wet the pads) before starting the fan
--Saw a few sites mention time-delay relays


So, does it seem feasible? See any flaws, or have advice? I don't dabble in electronics very much, so forgive any rookie mistakes.

 

[Boncuk]

Hi,

I'm using an "IMARFLEX" evaporative cooler.

It has a three speed fan and a submerged water pump.

The fan speed is controlled via pushbuttons and the water pump can be activated only if the fan is running.

The pump supplies water to the top of the device, where it is used in a "spray bar" to wet the multi layered evaporation area consisting of special paper.

Excessive water flows back into the reservoir via a divider.

I suggest to use two push buttons (permanently closing) and design a logic circuit which allows for one fan speed only.

For fan power I suggest two solid state relays (Sharp S102) which can switch loads up to 8A.

All you need is a 5VDC power supply for the logic circuit and relay control.

A delay circuit is not necessary since cool air is already produced with the first evaporating water drops.

Boncuk

Attached is the Sharp data sheet and a circuit suggestion for fan control.
Current limiting resistors for the SSRs must be selected according to the data sheet. All unused gates (inputs) must be connected to circuit ground and decoupling caps of 100nF should be used for each chip.