LiPo Battery Discharge Hack
We have all returned from our favorite flight field from time to time with some fully charged LiPo batteries or some that have not been discharged to the proper storage voltage of about 3.8 volts per cell. My balance charger has a discharge cycle, but it's slow. Real slow.
Here's a simple hack that will allow you to safely store your batteries for extended periods of time at the proper storage level. You can discharge your batteries in just a few minutes using the method below.
CAUTION: Never leave LiPo batteries in an unattended state. They are highly volatile and can cause a fire. This hack also will generate heat from the automotive light bulbs that are used. Be sure to put the light bulbs on a non-flammable surface or a piece of tile to help dissipate heat.
What you will need:
- Four automotive brake light bulbs (1156 or equivalent)
- Your favorite LiPo battery connectors -- XT60, Deans, JST, etc.
- LiPo Battery Voltage Meter with Alarm ( http://tinyurl.com/kf9yy2c for example )
- Some copper wire: rigid for wiring the bulbs in parallel and stranded for attaching your connectors.
- Soldering iron and solder
How to do it:
- This setup is ideal for 2 or 3S packs of 1300-2200mah. See below for a setup for smaller packs. Don't use for larger than 3S packs as you will burn out the lights.
- Solder four of the brake lights in parallel. This means wiring all four batteries so that they each draw 12 volts. See the illustration below:
- Solder on your favorite connectors. In the picture you will see that I have two different connectors attached.
- Attach your battery meter to the balance lead on your battery. Set the alarm for 3.6 volts. Why 3.6 volts? When the alarm goes off when the battery pack reaches 3.6 volts per cell, when you remove the load (the lights), the battery will rebound to approximately 3.8 volts per cell -- perfect for storing your batteries.
- For a fully charged 2200mah LiPo pack, your batteries will discharge to a storage level in about 5-7 minutes -- about the same time that you would fly most planes.
This setup is designed for the discharge of 3S packs (nominal fully charged voltage of 12.6 volts per pack). You can also use this setup for 2S packs, but packs larger than 3S will burn out the lights.
Discharger for smaller packs
I also have created another discharge setup for some of my smaller 2S and 3S packs. You can simply solder just one light, like the ones used above, or pick up a 12V halogen lamp from your local hardware store. The one shown in the picture is one used from the Malibu style low voltage outdoor lights and is simply soldered to a JST or other connector.