battery management system

9 Articles

Make or buy lithium ion battery pack

Comparing Making To Buying A Lithium Ion Battery Pack

May 1, 2018 by 31 Comments

At Hackaday we’re all about DIY. However, projects can have many components, and so there’s sometimes a choice between making something or buying it. In this case, [GreatScott!] wondered if it would be cheaper to make or buy a lithium-ion battery pack for his new eBike kit. To find out, he decided to make one.

After some calculations, he found he’d need thirteen 18650 cells in series but decided to double the capacity by connecting another thirteen in parallel. That gave him a 5 Ah capacity battery pack with a nominal voltage of 48.1 V and one capable of supplying a constant current of 40 A. Rather than connect them by soldering the nickel strips, he purchased a kWeld battery spot welder, adding to the cost of the build. He charged his new battery pack using his bench power supply but being concerned about uneven charging of the cells over the battery pack’s lifetime, he added a Battery Management System (BMS). The resulting battery pack powers his eBike motor just fine.

After adding up all the costs, he found it was only a tiny bit cheaper than prices for comparable battery packs on eBay, which were €24.4 per Ah (US$29.5 per Ah). The only way it would be cheaper is if he made multiple packs, spreading out the one-time cost of the battery spot welder. So that means it’s really up to your preference. See his video below to judge for yourself if you’d rather do it the DIY way. And then let us know what you’d do in the comments below.

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Refurbishing Armored Tablets

July 4, 2016 by 10 Comments

Who can resist the insane deals on bizarre hardware that pop up on auction websites? Not [Dane Kouttron], for sure. He stumbled on Armor X7 ruggedized tablets, and had to buy a few. They’d be just perfect for datalogging in remote and/or hostile locations, if only they had better batteries and were outfitted with a GSM data modem… So [Dane] hauled out his screwdrivers and took stuff apart. What follows is a very detailed writeup of the battery management system (BMS), and a complete teardown of this interesting tablet almost as an afterthought.

First, [Dane] tried to just put a bunch more batteries into the thing, but the battery-management chip wouldn’t recognize them. For some inexplicable reason, [Dane] had the programmer for the BMS on-hand, as well as a Windows XP machine to run the antiquated software on. With the BMS firmware updated (and the manufacturer’s name changed to Dan-ger 300!) everything was good again.

Now you may not happen to have a bunch of surplus X7 ruggedized tablets lying around. Neither do we. But we can totally imagine needing to overhaul a battery system, and so it’s nice to have a peek behind the scenes in the BMS. File that away in your memory banks for when you need it. And if you need even more power, check out this writeup of reverse-engineering a Leaf battery pack. Power to the people!