Bike Light That may Improve Cycling (Features List)

I’m working on a bike light for improving cycling. Its features include:

  • Low beam brightness controlled by speed for longer battery life
  • Inactivity timer for improving battery life
  • Daytime running lights
  • Side visibility LEDs
  • Turn signal lights
  • Brake¬†light with brake status LED
  • LED strips
  • Tip over alarm for alerting road users of a crash
  • Horn
  • Bell
  • Low power modes
  • Adjustable modes for different riding conditions and power levels
  • Easy to locate switches
  • Li-ion batteries

What do you think? Do you have any suggestions?

APR18650M1A Batteries Internal Resistance Measurement

The APR18650M1A LiFePO4 batteries are high powered and low cost. They have a rated capacity of 1100 mAh, a rated voltage of 3.3V, and a rated current of 30A. 10 pieces cost $36 on eBay. I measured their internal resistance with the SKYRC B6AC V2 Charger.



Enter a caption The battery pack was soldered to power and charge balance connectors. It’s very important to get their polarities correct or you’ll damage the charger.

I bought them because they’re lighter than the 1.3Ah 12V SLA battery used for the car horns on my bicycle, quite safe, and long life.

Possible applications of the batteries include battery pack rebuilding, power tools, flashlights, battery backups, and e-bikes. Note that they’re 3.3V which is lower than the 3.7V cells commonly used in electronics. They also need a charge voltage of 3.6V instead of 4.2V.

To test them, I installed them into a custom built 4 cell 18650 battery pack and connected it to the charger.

The battery pack’s total internal resistance was 268mR. If you draw 30 amps, the pack voltage should drop to 5.16V.
Individual cell internal resistances being displayed.
Individual cell voltages being displayed.
Battery total voltage being displayed.

Compared to other LiFePO4 batteries bought from DealeXtreme, the APR18650M1A batteries have a low internal resistance. Those from DX have an internal resistance of about 0.18 ohm, or up to three times higher. If your applications are high current such as electric vehicles and power tools, you’ll need a lower internal resistance.

I have tested the batteries with a pair of car horns. With two horns, they should draw 10 amps which means the battery pack voltage drops to 10 to 11V. Unlike other 18650 batteries I used before, the horns didn’t click.

If you’re interested in a battery that’s lightweight, high powered, safe, and long lasting, I would recommend the APR18650M1A batteries or something similar.