LiPo Discharger
A Discharger for 3S Lipo Packs
I wanted a discharger that I could use for my flight packs that I did not use while at the felid. I found a old article on rcgroups.com for a circuit designed by Dan Bowman.
I ordered the parts from Digi Key for the schematic below. I substituted the 520 ohm resistor for a 510 ohm as that is what I had on hand. I also used the recommended STP55NF06L Mosfet in place of the IRF520.
The load is two 3 Ohm 50 watt wire wound resistors I had on hand. With a 3S Lipo and 1 3 Ohm resistor that gives me about 38 watts of power to dissipate as heat. I added a switch so I could switch between 3 Ohm and 6 Ohms. The LED Meter is a $3.00 unit from Hobby king.
I ran into a little problem when I built the unit in that it would not disconnect the load all the time. I was using lightbulbs for the load when I first built it and it worked great, But once I switched the 3 Ohm resistors the circuit would not disengage at the proper voltage. It took me a while to figure out what was going on. It turned out that the wire wound resistors were acting like inductors, so I needed to add a diode across the load just like you would with a relay. See the schematic below for diode placement. I used a common 1n2007 that I had on hand. Once the diode was added the circuit acted like it should with the wire wound resistors.
I am very happy with the circuit. It draws about 3.5 Amps on High, and half that on Low. When I find some higher wattage resistors I will build another that handles 1s, 2s, 3s, and 4s.
I ordered the parts from Digi Key for the schematic below. I substituted the 520 ohm resistor for a 510 ohm as that is what I had on hand. I also used the recommended STP55NF06L Mosfet in place of the IRF520.
The load is two 3 Ohm 50 watt wire wound resistors I had on hand. With a 3S Lipo and 1 3 Ohm resistor that gives me about 38 watts of power to dissipate as heat. I added a switch so I could switch between 3 Ohm and 6 Ohms. The LED Meter is a $3.00 unit from Hobby king.
I ran into a little problem when I built the unit in that it would not disconnect the load all the time. I was using lightbulbs for the load when I first built it and it worked great, But once I switched the 3 Ohm resistors the circuit would not disengage at the proper voltage. It took me a while to figure out what was going on. It turned out that the wire wound resistors were acting like inductors, so I needed to add a diode across the load just like you would with a relay. See the schematic below for diode placement. I used a common 1n2007 that I had on hand. Once the diode was added the circuit acted like it should with the wire wound resistors.
I am very happy with the circuit. It draws about 3.5 Amps on High, and half that on Low. When I find some higher wattage resistors I will build another that handles 1s, 2s, 3s, and 4s.
