Mini How-To How I built a 200W LiPo Discharger

[Yowzilla]

I built this today and the first test was better than expected without the use of Thermal epoxy. I have the two part epoxy but wanted to see how the temps were going to get before committing.

It uses 4 each 4ohm 50 watt resistors mounted to two large extruded aluminum heat fins I found on EBay. The resisters are soldered in parallel using 12 AWG black and red wire with nice silicone coating. I used a quality 140mm computer fan powered by 12v of my power supply that is also powering the 308Duo. This is theoretically a 1 ohm resistive load with 200 Watts power handling. The reality is it was a 1.6ohm load measured.

Setting Resistive load at 150 watts heats the base mounting of aluminum extrusion to 170 F while the resistors only measured 135F on the top. This brought 2 - 3S packs down from full charge to a 3.86v storage charge in 4 minutes....Then some balance time.

I will epoxy the resistors in place and test with my Logo600SX 10S packs as soon as I need to....

Most will say....To discharge batteries put something in the air!!!!....
The reason I built this was because of the Texas wind. During this time of year down south the wind will rise throughout the day. If it gets to the normal 30mph before I make all my flights I need to bring my LiPos to storage when I get home....

I also measure my 2 - 2S packs for the 92" Edge just below 4 volts after 4-5 flights, so I regularly need to bring them down as well.

So far I think it works perfect and fast enough without stressing the fragile discharging of the 308Duo.

Let me know if you have any questions and I will see if I can help...
Yowzilla

 

[gyro]

Really cool Yowzilla, definitely a must for the showing up at the field with a bunch of packs. The wind here is so unpredictable, and it's worse down where you are.

Hope to see you at the Austin 3DBash next weekend. Shouldn't be toooo far of drive

 

[AtomicFlyer]

I built this today and the first test was better than expected without the use of Thermal epoxy. ...

Thanks for posting that Yowzilla. I actually didn't even know there were chargers available that allowed the use of an external dummy load.

My most common reason to discharge a battery is a crashed plane instead of the wind though.

I've been using this 50 watt car headlight to discharge. But it requires keeping a close eye on it with a timer so it doesn't over discharge. I think I'm going to start shopping around for a new charger that allows an external dummy load.

Marc

 

[Yowzilla]

The best in my opinion is the newer version of mine with more amps per channel ( 40 vs 30 amps). It is the 408 duo I get my chargers from progressive RC. Discharging without is dangerous and leave cells un balanced. The Duo chargers provide the most info in an easy read way with arguably the most control.