On my Minnie Mambo build thread over on RCGroups.com, we were discussing what kind of battery that should go into the plane to power the receiver and servos. A normal sized flight pack is way too heavy for this size of plane, so one guy suggested using a BEC and a 2s Lipo battery. A BEC is a Battery Eliminating Circuit. It takes a voltage over 5 volts and it will drop it down to a constant 5 volts to power the receiver and servos. For example, a 2s lipo is a little over 8 volts when fully charged. A BEC will take the 8v and drop it down to 5v for the RX and servos. Well, you can buy one of these for like $10 or so, but like many things, I made my own.
Building the BEC was surprisingly easy. I am not an electronics expert by no means, so I just Googled it. I found a simple schematic on how to build one, but I had none of the parts it called for. I called my brother who is currently studying to be an Electrical Engineer and asked him if there were any substitutes. It turns out that I could substitute what the schematic called for with what I had. I ended up using a 7805 voltage regulator, two 47uF capacitors, a servo lead, and a JST connector. If you would like to make a BEC for yourself, I have attached a schematic below that you can follow.
When making the BEC, I didn’t have any perf-board on hand, so I just soldered every thing up loosely. After soldering everything up, I put some electrical tape around all of the solder joints. I then took a large piece of heat shrink and slid the soldered components into it, but I left the voltage regulator sticking out. Then for protection, I pumped some hotglue into the large piece of heatshrink and then I shrunk the heatshrink while the glue was still melted. This was to protect my solder joints and the capacitors. I left the voltage regulator sticking out because when there are a lot of servos hooked up to the receiver and they are all moving, the voltage regulator can get hot. For this reason, I slid a heat sink onto the exposed voltage regulator.
I hooked up my RC gear and tested it out. It worked! On my airplane I will only have 2 servos, but as a test I hooked up 6 servos to my receiver and moved them all simultaneously. When I did this, the voltage regulator did get quite warm, but quickly cooled down because of the heat sink. The voltage regulator did not get hot when I had just two servos hooked up to it. One thing that makes me happy is the commercial version of the BEC weighs 9 grams and my homemade version weighs 10 grams! I’m only 1 gram off!
Here are some pictures and a video!
(I forgot to take a picture of my solder joints. . . )
