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[January 7, 2011]


I have read many articles and heard some first and second hand stories about how leaving a sump heater plugged in all winter can lead to corrosion in the engine. Someone at the airport swears their engine was ruined because of it. One of the mechanics which builds a lot of the ECi kit engines for the RV'ers at KDMW says he can always tell an engine that has been plugged in all winter when he pulls the mags because of the excessive corrosion. The Reiff heating pads instructions warn against it, and also there have been many articles warning against it.

My problem is if I want to go flying, I have to drive 20 miles (40 miles round trip) to the airport the night before to plug in the heater. And for some reason if I can't go flying, I will have to unplug it. That inspired me to do some research to see if there was any way I could remotely turn on my engine sump heater.

There are three main types of remotely controlled switches. If you have internet access in your hangar (I don't) there are models which turn on and off via a web browser. The other two models work by subscribing to a cell phone provided and either calling the number or sending a text message. The solution I created works on the latter two methods. I can call the number of my switch, or send a text message.


This is the brains of the switch right here. It is a GSM Remote Controlled Switch, purchased through http://gsm-auto.com/ for about $180. It has two relays on it for controlling up to two outputs. It works on GSM based carriers (AT&T and T-Mobile are the main ones I know about in the states). I purchased a pre-paid T-Mobile SIM card from a T-Mobile store for $10, and it came with about $5 worth of credit on it. I set up this device so that if I call it from my cell phone or house phone, it will turn on an outlet for 18 hours. Additionally, I can send text messages to it to turn it on for a specified period of time, and turn it off. The nice thing about sending it a text message is it will send a confirmation text message back, letting you know the outlet is turned on.

Since this device sends and receives texts, it costs $0.15 ($0.05 to receive a text message and $0.10 to send a text message from t-mobile) every time you turn it on by a text message. That's a lot cheaper than the gas I spend driving to and from the airport! Plus it saves an hour of commute! One limitation of the T-Mobile pre-paid card is it needs to be filled up with $10 every 3 months. So it really costs $40/year to run this device. Turns out to be $3.34/month. Not too shabby.


Here is how I designed the remote switch. The power input is fused by a 10A fuse, and then goes to the 12V power supply (to power the GSM-AUTO) and also to the relays on the GSM-AUTO. The Relays then feed into two outlets. I bought the enclosure and outlets at Home Depot (largest one). The fuseholder was purchased at Radio Shack. The power input connector and power supply were surplus from work. Total cost was about $250.


I wired up both relays just in case I wanted to add something in the future.


It used a standard computer power cable.


In the lid of the enclosure I put a piece of plexiglass to see into the box once it is closed. Why? Well there are LED's on the power supply and GSM-AUTO board which indicate the status of everything. The power supply has a green light indicating that it is on. The GSM auto has a red LED indicating it is getting power, a green led indicating a relay is closed (i.e. activated) and a blue LED indicating the device is connected to the cell phone network, or searching for it, depending on its blinking patter.


Finally it is all assembled. I installed it in the hangar tonight and gave it a quick test. It seemed to work great. I am very excited about not needing to drive out to the hangar to plug my RV in, and saving the engine too!

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Last Modified: September 4, 2017