USB Load Discharger

This is a very useful device to have at home for electronics hobbyists, it helps to discharge power banks and batteries to cycle them, but you could also use it to measure a battery's capacity using a USB doctor in addition to this setup.

When you have so many batteries and power banks like me it is difficult to keep them in top shape. Lithium batteries need to be top'd up once in a while roughly 3 months is what I do and todo that, the fastest and easiest way is to have a Discharger like this one, simply connect it and let it suck away all that juice, then charge it back up to store it for a couple of months.

For me though its best use is to measure capacities of 18650 batteries or old power banks that are given away from friends and family to reuse them in what ever way I can. Less toxic trash in the bin and a couple bucks saving for me.

Its a simple design, let's get started

• 5W or 10W load resistors
• small perf board
• 3 x Red LED
• 1 x 200 ohm resistors
• Male USB breakout board
• 3 x switches
• small fan (optional)

Very basic connections here .

Start with the USB breakout board, solder the V and Gnd contacts to the main perf board and solder well because you apply force when pushing the device into other components and also pulling from here so you can solder all 4 contacts on the breakout to give it extra strength or add super glue.

If you do not have this breakout board you can simply get one from old USB pendrives or USB cables.

Next place all the other components and solder their terminals onto the perf board so they stay secure. Please follow the circuit diagram for the connections between the components.

One end of the resistors connects to Gnd, connect the middle leg of the switches to the V pin on the USB breakout board, the first leg is not important it can be left open or connected to V itself. The last leg on the switches connects to both the +ve terminal of the LED's as well as the other ends of the load resistors, finally connect the -ve terminals of the LED's to Gnd through a 200 ohm resistor.

(Optional) - I've added a small fan which is not shown on the circuit but shown in the video, to keep things cool. The 5W load resistors can dissipate about 1A of current and that will generate some heat, considering that our device is designed to dissipate up to 3A so that's a lot of heat. If you are interested then simply add a male pin header to the perf board one pin for V and another for Gnd

As shown in the video the resistors pull about 1A current, since the power bank is only able provide about 2.84A maximum the USB the discharger cannot pull more than that. Adding the fan has reduced the peak temperature by at least 35%.

Thank you.