DIY LiPo Battery Discharger with 12V Halogen Light Bulbs

Just a quick and easy DIY project how I built a LiPo Battery discharger with some 12V halogen light bulbs. In theory, it works for 2S, 3S, 4S, 5S and 6S LiPo.

We discussed how to dispose LiPo batteries before, using salt water solution is easy but it takes a long time to discharge your battery completely, if the battery had plenty of charge left.

So I built this light bulb discharger to accelerate the process. I can now hook this discharger up with a LiPo battery and it would only takes less than an hour to discharge a 2000mAh 3S LiPo battery.

LiPo Discharger Circuit Diagram

I am throwing 6 light bulbs in this discharger, and probably a on-off switch too.

There will be an option for 12V/24V discharging mode: 12V is for 2S/3S LiPo, 24V can be used for 4S, 5S and 6S.

The bulbs are rated at 20W, so at 12V, each will be drawing 1.67A of current. 3 of them will be drawing  a total current of 5A (3 in parallel), in theory that means it can drain a 2000mAh 3S battery in 24 minutes.

However the current draw decreases as voltage drops, so the discharge will slow down gradually. Therefore it will take much longer than 24 minutes. There is also a cut off voltage about 1 or 2V, which means it won’t completely discharge the lipo, but there is only very little charge left any way.

lipo-discharger-light-bulb-build-circuit-schematics

Components for the Battery Discharger

I am trying to keep it as simple as possible, all the parts are from eBay. The whole build costed less than $10.

  • 6 x 12V Halogen Light Bulbs (20W)
  • 4 x 3-way PCB screw terminals (or you can use 6 x 2-ways terminals)
  • 1 x on-off switch
  • 1x PCB (circuit board)
  • Some wires enough for your max discharging current (my max discharging current is 10A, so 22AWG or larger should be fine, Check out this Wire AWG Chart to find out)

lipo-discharger-light-bulb-build-components-parts

And here are the parts for my 12V/24V mode switch.

  • 1 x male XT60 connector
  • 1 x male 3.5mm bullet connector

lipo-discharger-light-bulb-build-discharge-mode-plugs

Building the LiPo Discharger

PCB screw Terminals

I am using screw PCB terminal, because it makes light bulbs swap out much easier, as you know light bulbs do break and stop working sometimes.

It also allows you to connect the exact number of bulbs you want to run, making things a bit more flexible.

Maybe later on, you want to connect some other types of load, such as high current resistors instead of light bulbs. Thanks to the terminals, it is possible. :)

lipo-discharger-light-bulb-build-PCB-socket lipo-discharger-light-bulb-build-PCB-solder-bottom

12V/24V Discharging Mode Switch

These light bulbs are rated for 12V, so if you are discharging 4S or higher, you need to put these bulbs in series.

This mode switch allows this. It basically just a bullet connector, either connects to the ground (12V), or to another array of bulbs in parallel to increase the max allowed input voltage (24V).

lipo-discharger-light-bulb-build-discharge-mode-plugs-solder

On Off Switch and Discharge Cables

The on-off switch isn’t really needed at all. But I just like to make it a bit more convinient, in case there is something wrong with the discharging battery, and I am unable to unplug it, I can just flip the switch to interrupt the discharge process.

You can actually just unplug the 12V/24V switch connector to turn the thing off. :)

Not that I used pretty long discharge wires, so the battery can be some distance away from the discharging device.

lipo-discharger-light-bulb-build-on-off-switch lipo-discharger-light-bulb-build-on-off-switch-solder

Future Upgrades

These bulbs get very warm! I think it might be a good idea to put a fan on top to help heat dissipation. A fan runs off 5V powered by a step down voltage regulator maybe.

Testing

I tested the unit with just 1 bulb connected. When turning on the light bulbs, note that there is a current surge (2.6A when power up), and it stabilizes at 1.6A. Once they are warmed up, the current surge doesn’t happen any more when you turn them on again later on. It doesn’t affect me, just found it interesting. :)

These bulbs are rated at 20W, with my 11.9V battery the actual power is 19W so it’s pretty close.

Using 24V discharging mode, the power drops almost half (as expected as resistance increases when you put loads in series). So it’s a good idea to switch to 12V discharge mode, once you have discharged your 4S battery below 12V.

lipo-discharger-light-bulb-build-testing-result

5 thoughts on “DIY LiPo Battery Discharger with 12V Halogen Light Bulbs

    1. Oscar Post author

      depends on why you want to discharge it… if for storage, best to discharge them to 3.8V per cell.. if you want to disposal them discharge them as close to 0V as possible.

      Reply
  1. Catio

    Hi Oscar
    that’s too simple!
    Please add an Arduino / µc with auto voltage detection to the discharger which switch the bulbs with mosfets. ;-)
    Thanks.

    Reply
      1. Catio

        Hi Oscar,

        sure, it would be more a challenge for “because it is possible”.
        I’m going to buy* an electronic load, so it will be useful for this too.

        (to less time and knowledge to built it)

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