Background: I have an undersink 3-canister filter in my kitchen and wanted to monitor the amount of water going through the filter. I purchased a Digiten DFC15 water flow controller and a Digiten DV12V normally open solenoid.
Problem: I intended for the controller to supply 12 V to the solenoid when it reaches the set limit. Instead I found that it was supplying power (closing the solenoid) in run mode and stopping power when it reaches its limit. This is the exact opposite behavior to what I need.
Troubleshooting: I contacted the manufacturer and they said that it only works with a normally closed solenoid which I can't use because it would be on 24/7 and generate a lot of heat. They did not place this information in the documentation.
Idea: What I want to do is flip the behavior of the controller so that when it stops providing 12 V to the wires, my solenoid closes. I think if I wire a relay to the 12 VDC wires (positive and ground) and have an external 12 V power source I can achieve this, but it's unclear to me what kind and spec relay I need.
The solenoid is 12 VDC and 4.8 W, so 0.4 A. If there's a better way, please share that too. The power brick for the controller supplies 12 VDC, so with a splitter pigtail, I can draw my 12 VDC to power the solenoid when the relay closes. The other thing I'm not sure about is whether the relay solution will generate a lot of heat as well, since that's what I'm trying to avoid.