Open Source 18650 Lithium Battery Characterization System

A place to list links to sources for EV related parts and services.
Post Reply
dcambron
1 µW
1 µW
Posts: 1
Joined: Dec 08, 2016 9:12 pm

Open Source 18650 Lithium Battery Characterization System

Post by dcambron » Dec 08, 2016 9:45 pm

Hi Everyone,

I'm a long time reader, but today I'm a first time poster! I would like to introduce you to my start-up's first kickstarter campaign. Our product, the "Batlab" fills a need in the hobbyist/small-professional markets for use in characterizing lithium ion cells (18650 form factor). The Batlab does a complete characterization of each individual cell (capacity, ESR, etc etc) and provides reports for the user to utilize in battery pack design. For anyone that uses these cells, or likes to recycle them from drill batteries, laptop batteries, and the like, in order to build an ebike/eV, this product will be useful for your projects. By characterizing each cell, one can determine which cells are worth saving and which ones should be recycled. Additionally, it will advise the user on the optimal cell configuration for battery pack construction. A single Batlab can characterize 4 cells at a time. However, we have designed it so that multiple Batlabs can be daisy-chained together to measure many cells at once. The video on the kickstarter page provides a good overview of the system.

Image

Because our team (I'll introduce "us" down below) are big fans of hobby electronics, "tinkering", etc, we are proud to say we are mostly creating this product open-source. We will release the full schematic, BOM, and every bit of code used on the device (both the embedded firmware and the PC software). We plan to release all of our code on github for easy use. Pretty much the only thing we don't plan on releasing (for now at least) is the raw CAD files and gerbers. However, we want to encourage people to alter and develop the functionality to meet their specific needs (if necessary) and to facilitate hardware modification/repair. We also are creating a "developer's guide" which will provide information such as circuit theory-of-operation, code descriptions, etc to aide in the personal modification of our device.

About me and our team
Our team is made up of 5 recent graduates from the University of Kentucky in Lexington, KY. 4 of us majored in EE (with myself and one of my partners getting our MSEE degree), and 1 in ME (currently pursuing PhD in ME). We worked together in all of our classes and assembled our team for our start-up. We each bring a skillset to the team that we hope will help us be successful. My partner Joshua generally does all of the PCB design and DFM work, I handle embedded firmware, and my partner Alex handles PC software, Hayden manages scheduling, purchasing, and "sales", and Chris handles system integration, thermal design, and DFM work. All of us were heavily involved in the University of Kentucky Solar Car Team (we build and race solar powered race cars) during our years of study, with all of us holding technical leadership roles on the solar car team. During my tenure on the team, I served as both the Electrical Team Lead (managing all electrical aspects of the solar car) and overall Team Manager (managing all technical and non-technical aspects of the team operations). The UK solar car team is primarily student-managed with occasional faculty advising.

While working on the solar car team, we designed and built multiple custom lithium battery packs for racing, and a variety of custom electronics such as Battery Management Systems, Data Collection Systems, etc. I probably designed and built upwards of 20 different system boards during my experience on the team.


These are some good links for the UK Solar Car team if you're interested in seeing what it is about. I know I consulted this forum many times when looking for ideas, advice, and parts while on the team.


Twitter: https://twitter.com/UKSolarCar
Instagram: https://www.instagram.com/uksolarcar/
Facebook: https://www.facebook.com/UKSolarCar/?fref=ts


You can see multiple pictures and footage of the battery packs we designed and built on both our kickstarter page and at those links.


When we built these lithium battery packs, we would spend a lot of time characterizing cells for optimizing the pack design. The latest pack, for example, is comprised of 420 cells (35 modules in series, each module having 12 cells in parallel). We purchased roughly 650 cells, fully characterized each of the 650 cells (using circuitry designed for this task) and selected the best 420 cells and determined which cells to put in which modules. It was through this process we realized that a similar system can be used by other people. That's how we came to design this system.


I'd love to hear any feedback you have on our design or campaign. We are definitely a start-up (formally started over the summer) so a lot of this is new to us. We have the engineering experience to make a successful project technically, but are brand new to the sales/marketing side of things. Any technical or non-technical comments/concerns/questions would be greatly appreciated!

Cheers,
Daniel

User avatar
justin_le
1 MW
1 MW
Posts: 1997
Joined: May 28, 2007 3:27 am
Location: Vancouver
Contact:

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by justin_le » Jan 10, 2017 8:36 pm

Congrats on meeting your funding goal on this and hope that the initial production and release phase is going well.

I've been long looking for something like this that is reasonably affordable, not so much for testing and matching cells for pack assembly, but for doing long term cycle life testing on different cell types and under different usage conditions. So tests cycling in verious SOC windows (40-100% vs 20-80% vs 0-60%), and at different 'C' rates and temperatures, and witnessing firsthand the exact effect of these conditions on the life cycle degradation. There's so much now that is anecdotal and self referencing info in lithium battery life span optimization and a gadget like this could facilitate getting independent and quantitative original data.

Right now your description on the product doesn't seem to indicate clearly the maximum charge and discharge rates of the device. Can it do 2C (ie 5-6A) discharge currents and 1C (2-3A) charge currents on each channel?

GIven the open source nature of the software I would imagine that adapting it for life cycle experiments as opposed to characterization/matching tests would be pretty easy to accommodate, so long as the hardware can handle the power levels where we want to see this data.
Big Dummy Frame (yes This One, thanks ES!) with prototype 26" Grin all-axle front hub, Phaserunner controller, and 52V 11Ah Cellman triangle pack
My website: http://www.ebikes.ca
Please contact via email, info@ebikes.ca, rather than PMs, which are disabled

User avatar
PaulD
100 W
100 W
Posts: 180
Joined: Aug 28, 2008 5:42 pm
Location: Ashland, OR
Contact:

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by PaulD » Jan 11, 2017 12:06 am

justin_le wrote: Right now your description on the product doesn't seem to indicate clearly the maximum charge and discharge rates of the device. Can it do 2C (ie 5-6A) discharge currents and 1C (2-3A) charge currents on each channel?
Hey Justin, Luke and I asked some of these questions on the kickstarter comments page, and got some answers. Click the link above to see. The current looks quite low (3A), but that's sufficient for my cycle life testing needs..Can't wait to get mine!
p.s. - check your email when you have a chance!

User avatar
liveforphysics
100 GW
100 GW
Posts: 14481
Joined: Oct 29, 2008 1:48 am
Location: Santa Cruz, CA, USA

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by liveforphysics » Jan 11, 2017 1:21 am

I'm excited for mine to arrive too!
Each carcinogen vapor exposure includes a dice roll for cancer.

Each mutagen vapor exposure includes a dice roll for reproductive genetic defects in your children.

Each engine start sprays them into a shared atmosphere which includes beings not offered an opportunity to consent accepting these cancer experiences and defective genetics life experiences.

Every post is a free gift to the collective of minds composing the living bleeding edge of LEV development on our spaceship.

User avatar
justin_le
1 MW
1 MW
Posts: 1997
Joined: May 28, 2007 3:27 am
Location: Vancouver
Contact:

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by justin_le » Jan 11, 2017 3:03 am

OK very sweet and glad to hear that two of the most competent people here have them on order with similar intents :-)

I thought I read through all the kickstarter comments but I see that I missed the one where this was addressed. He seems to imply that the current limit is mostly just thermal dissipation from the metal enclosure, so I'm imagining with fins and forced air cooling that it should cope with more like 5A without any change to the board layout or components. That said, even 1C will be adequate for some of the most pressing questions to me which are 1st hand measured data on cycle life vs. SOC dependencies over various brands of cell.

I'm not really on kickstarter but Daniel if you are visiting this page on ES I'd be interested in signing up for a few units too if there are extras available. I've looked a lot at the chinese cell testers whenever I've been overseas but they are always so ungainly in size. I like my lab equipment cute and tidy whenever possible and this fits the bill perfectly.
Big Dummy Frame (yes This One, thanks ES!) with prototype 26" Grin all-axle front hub, Phaserunner controller, and 52V 11Ah Cellman triangle pack
My website: http://www.ebikes.ca
Please contact via email, info@ebikes.ca, rather than PMs, which are disabled

User avatar
liveforphysics
100 GW
100 GW
Posts: 14481
Joined: Oct 29, 2008 1:48 am
Location: Santa Cruz, CA, USA

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by liveforphysics » Jan 11, 2017 4:15 am

An option to parallel units may also be a good way to handle higher current discharge levels.

I bought a handful of cell testers from Banggood, none have been more than ~45mAh repeatable and none do over 2A, this unit should be a useful step up.
Each carcinogen vapor exposure includes a dice roll for cancer.

Each mutagen vapor exposure includes a dice roll for reproductive genetic defects in your children.

Each engine start sprays them into a shared atmosphere which includes beings not offered an opportunity to consent accepting these cancer experiences and defective genetics life experiences.

Every post is a free gift to the collective of minds composing the living bleeding edge of LEV development on our spaceship.

User avatar
justin_le
1 MW
1 MW
Posts: 1997
Joined: May 28, 2007 3:27 am
Location: Vancouver
Contact:

Re: Open Source 18650 Lithium Battery Characterization Syste

Post by justin_le » Jan 11, 2017 5:33 am

liveforphysics wrote:An option to parallel units may also be a good way to handle higher current discharge levels.
Yeah I saw that comment on the kickstarter page. It's a simple approach that he might as well implement since there is really nothing to it other than a hardware jumper, but then it reduces the number of cells that can be simultaneously tested during the long term cycling. So I'm still interested if there's a way to get all 4 cells going at 2C discharge.

If it is just thermal limiting from the casing too, and not local thermal limits from the transistor acting as a load, then it may also be possible to manage the higher amperage by alternating charging cells with discharging cells. So you would have cells 1 and 3 on the charge cycle, while cells 2 and 4 are on the discharge cycle, and visa versa. That way the worst case load (2 cells at 2C discharge) is the same casing watts as the current design (4 cells at 1C discharge).

-Justin
Big Dummy Frame (yes This One, thanks ES!) with prototype 26" Grin all-axle front hub, Phaserunner controller, and 52V 11Ah Cellman triangle pack
My website: http://www.ebikes.ca
Please contact via email, info@ebikes.ca, rather than PMs, which are disabled

Post Reply