About 12 years ago ,I made a few auto toppers based on an ac float switch,for a few of my tanks and a few of my friends tanks,out of all the ones that I made only one failed,because the man I made it for plugged in a power head that required 25 watts of power,and I told him to use a maxi-jet 400,but he knew everything and did not listen...The one I made costs around 20.00 You plug your pump in it,it has a light [red] that tells you that there is power on the unit,also a friendly reminder to turn it off when working on the tank,It has a push button to cut the power to the unit,It has a [green] light to let you know when the switch has been activated,What messes them up is the load on it ,If you use a 5 watt or under pump on one it will last for years and years with no problem,The size of the switch that is inside the float valve is so small that it can not fail in the closed position,The reason why i know this I have purposely plugged the valves into straight 120v with no resistance,just to bust them to see if I could get one to fail and still conduct electricity and I have never had one fail in the closed position a lot of people have bad mouthed the hvac float switches online,I,Found that out just recently because i started doing a little research on a few things, I am learning how to use the computer [what can I say,I finally decided to buy a computer,and actually use it..If I could figure out how to send a picture,that was transferd from a camera by my nephew to this area,I could show you how to make one,and also how it looks.......I will have to get my nephew to show me how.....