[Arduino #13] LED helmet research #2

From my dear friend Heikki I heard that Lipo batteries explode. I googled and yes it does explode.

I find this article very helpful. According to what I’ve read, Lipos explode under following circumstances

  1. Shock
  2. Heat
  3. Overcharge
  4. Discharge under 3.0V
  5. Use of budget Lipos.

Nobody would put a bomb behind their head I guess.(At least not me.)

About not discharging below 3.0V:

The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.

Electric power(Watts) = Voltage * Current

How fast will a battery be discharged?

How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).

Lithium batteries are weak to both high and low temperature. This is a problem because I’d use the LED helmet mainly during winter time. Finnish winter can be quite cold…..

I should check this http://www.batteryuniversity.com later. Now time to work 😦

Here’s another Adafruit video about LEDs. They use ordinary Li-ion batteries here. cool

Here’s what I did today

I made the following circuit according to one Adafruit tutorial. Knowing transistor’s pins were crucial in this exercise. Otherwise it’s easy.



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