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Unread 11/17/2014, 05:03 PM   #6
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Join Date: Jan 2012
Location: Lancaster,PA
Posts: 1,720
Got the relay box switching circuits built today. Just need to solder the base wires to the D-sub that will connected to the pump/control box, and wire the AC into the relay box.

The 2N2222 transistors get a bit warm during operation even though there's only about 100 mA collector current (rated at 1A). I'm going to do some burn in testing during the remainder of the week to make sure they'll be reliable.

Here's a crude schematic of 2 of the switching circuits in the relay box. It has a total of 8 relays, 7 normally open and 1 normally closed (so 8 total transistors). The load of the normally closed is in series with one of the normally open. This is for redundancy for the ATO. The ATO has 2 float switches. If the bottom switch fails and/or the normally open relay sticks, the normally closed relay and top float switch (which is controlled by a separate arduino pin) will ensure that the ATO doesn't overflow the tank.

I cut the connecting tab between the terminal of 3 of the outlets. The 4th I left intact.

As far as the heater goes, I'm going to continue to allow the internal thermostat to work as designed. The relay (in combination with the ds18b20) will only be used as a fail safe to cut power to the heater if the tank exceeds a certain temperature.

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