Tuesday, 9 June 2015

Battery testing





Here are the 42 battery cells I'm re-homing from the scrap pile at work. They're 4,400 mAh, 3.7V, Li-Ion batteries, with a protection circuit built in. They're not the fanciest battery in the world, but at the price I got them at (free), they're pretty unbeatable!

The first thing to do was to find out the maximum current they could put out. The protection circuit in these units effectively limits the amount of current the battery can discharge. The reason being, if these things let out too much current, they will heat up, and become quite dangerous. The downside is the current limiting circuit chokes the maximum power limit of the bike.

According to the battery datasheet, the maximum discharge current is 2.4~4.5A. I decided I better test this out, and see how much juice I could pull out of these suckers. I bought some high current load resistors from Trademe for a few bucks, connected them to a few batteries, and started measuring the current with a multi-meter, and an oscilloscope.

High current resistors (3 and 5 ohm)

Turns out the current limit kicks in at 3.6A. Now I understand the current limit of these things, I can go ahead and tailor the battery pack for the power output I want. I could potentially disassemble the battery pack, and remove the protection circuit, but as the pack will be sitting quite close to my girlfriend's butt, I figure I'll leave it connected for now, until I understand the system better.

Battery specs:

Manufacturer: Golden Cel Battery Co. Ltd.
Model: CELALB18650-PCM
Max discharge current output: 3.6A
Nominal voltage: 3.7V
Capacity: 4400mAh

1 comment:

  1. Yuhoo you have done with the battery testing of all the 40 batteries successfully!! This is an achievement itself indeed. Wishing you a best of luck for the rest of the task.

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