3-192S Arduino BMS (using BQ76PL536A)

[grindz145]

To be honest, I don't have anything in that configuration at the moment, but I could build to suit

I run mostly 20s, and I have one pack at 7s. Just outside of that window. I could reconfigure my trek to support 10-15s, which would work out very well.

EDIT: I just Rememebered an EV team I'm working with has an electric moped running 12s. That would be a perfect beta, and the kids are already using a Arduino based BMS that they're designing with a LTC eval board.

 

[dmwahl]

Definitely would be a good beta test, I'll keep posting the status here, but obviously my life will become quite busy shortly. Hope to have a working board available early 2014. I haven't used the LTC boards but I've heard they work well, although a bit buggier than the TI chips. That's just hearsay though, never used them myself. Methods did a design with them a while back, he might be a good one to contact. My goal is to have something easier to use with Arduino than the eval boards for less money.

 

[winzEracer]

Any updates? I am interested as I am running an Arduino based ev computer on my eKart. It would be for a 36s setup.

Thanks,
Brock

 

[dmwahl]

Any updates? I am interested as I am running an Arduino based ev computer on my eKart. It would be for a 36s setup.

Thanks,
Brock

I've been doing some consulting work on a project using the same chip, so I haven't had the time to spend on this one. I still intend to produce a design for the community as well, but obviously paying work has to come first

That said, do you have specific requirements for your project (size, charge current, other features, etc)? It helps when designing a project that will ultimately be open sourced to know what people want to use it for.

 

[akelly]

Wow, I started designing a battery monitor a few days ago and was torn between this chip and the LTC6804 when I discovered the projects on this forum using both! I want more features than either shield has, such as a voltage regulator, current sensor, buzzer, and Micro SD card slot for logging, so I think I'll make my own board, but I'll definitely watch this thread. Good luck!

 

[dmwahl]

Wow, I started designing a battery monitor a few days ago and was torn between this chip and the LTC6804 when I discovered the projects on this forum using both! I want more features than either shield has, such as a voltage regulator, current sensor, buzzer, and Micro SD card slot for logging, so I think I'll make my own board, but I'll definitely watch this thread. Good luck!

I would highly recommend starting simple and adding features later, the BQ76 (or LTC680x) chips have a lot of features to figure out. Once you have the basic communication worked out though it's not too difficult.

Good luck, they're fun parts to work with.

 

[jumpjack]

Rather than a full BMS, I'd need just a cell logger, which I could build using an Arduino board.
Can BQ76PL536A be used for such a project?

 

[dmwahl]

Rather than a full BMS, I'd need just a cell logger, which I could build using an Arduino board.
Can BQ76PL536A be used for such a project?

Yes, definitely. The balancing portion of the chip is not used unless you explicitly choose to use it. It would work very well for logging voltages. In my experience cell voltages are generally within a few mV of my fluke DMM.

 

[jumpjack]

Yes, definitely.

Great.
And... how much would it cost to me to get from you a BQ76PL536A soldered on a PCB? Probably I can add by myself further needed components, but I have no tools for making PCBs and soldering SMDs.
If you were able to setup a PCB in standard arduino-shield shape, we could build a nice project also for other people!
How many pins do I need to bring from BQ76PL536A to Arduino to log data?
And what else do I need besides a level shifter (maybe) and a voltage regulator to get a BQ76PL536A working in pair with an ATMEGA?

 

[dmwahl]

I already produced and built about 8 Arduino shield boards (see about half way down on the first page of this topic) and sent them out to a few people. At the moment though it's just not worth my time to build more of them since demand is pretty light and it takes a good amount of time to build each one.

The only connection needed between the BQ76 and the ATmega is the SPI lines, so 4 pins plus ground. No level shifting is required as long as the microcontroller ground is at the same level as the BQ76.

I have the schematic done for an 12-18S version with a built in microcontroller that is compatible with the Arduino interface and programming and have started layout, but due to light demand here it's kind of on the back burner for now. Once complete, scaling up to 24S or higher is easy to do, the only reason I went with 12-18S is that's what will work on my bike.

Once the project is complete I plan on releasing the whole thing (schematic, layout, software, etc) as open source.

 

[jumpjack]

It's good news!
Anyway I was not talking about a full BMS shield, but just a bare PCB with a only BQ76PL536A soldered, so I could do some experiments.

 

[dmwahl]

There's not much useful you can do with just a BQ76PL536A chip, for proper operation it requires a fair number of added parts. The shield I made was a bare bones application and still had about 80 parts.

 

[jumpjack]

There's not much useful you can do with just a BQ76PL536A chip, for proper operation it requires a fair number of added parts. The shield I made was a bare bones application and still had about 80 parts.

When you wrote this:

The only connection needed between the BQ76 and the ATmega is the SPI lines, so 4 pins plus ground. No level shifting is required as long as the microcontroller ground is at the same level as the BQ76.

I thought you meant it was all I need to connect the chip to the arduino... :-(

So I can't just connect the cells to the chip and the chip to the arduino?

 

[dmwahl]

So I can't just connect the cells to the chip and the chip to the arduino?

Nope.

I will consider building another batch of Arduino shields for dev use if there's enough interest here. The only conditions would be that it would be 1-2 boards per person (3-6S each), any software written would need to be shared back with me, and once the software is in a good working state it would be released as open source (GPL or something similar). Thoughts?

 

[eBikeJunkie]

I would be willing to purchase a few of them is possible. I would be looking for 30S though, can you do that as well?

Thanks !!!

 

[dmwahl]

I would be willing to purchase a few of them is possible. I would be looking for 30S though, can you do that as well?

Thanks !!!

I don't have a schematic for 30S at the moment, but once software is done for the smaller version is scales up easily. Are you able to help with the software development?

 

[Jojack]

Hi dmwahi,

I'm currently building out a 24S pack for my own ebike. Really interested in what is going on here, I have to do a little more homework but I could possibly be interested in 4 boards. A few of us engineering students are doing it as a side project to cut out taking transit, most of our work thus far has been on the pack itself but we would be able to share our work scaling it to 24S if your interested.

 

[dmwahl]

Hi dmwahi,

I'm currently building out a 24S pack for my own ebike. Really interested in what is going on here, I have to do a little more homework but I could possibly be interested in 4 boards. A few of us engineering students are doing it as a side project to cut out taking transit, most of our work thus far has been on the pack itself but we would be able to share our work scaling it to 24S if your interested.

Right now I'm looking for help with the software side, I have the communication basics all completed but need someone to work out things like automatic detection of connected cells and managing the balancing. Is that something you're interested in helping with?

 

[Jojack]

Sorry, I've been away without reliable internet connection. Yes we would be interested in helping you guys with that if we get that far in our dev. process.

 

[dmwahl]

Sorry, I've been away without reliable internet connection. Yes we would be interested in helping you guys with that if we get that far in our dev. process.

Which product are you using for your system?

 

[Jojack]

In terms of cells? We are building ours using Samsung ICR18650-22PM. As for BMS, We have been experimenting with the AD7280A and AD8280 chips so far. We haven't made bucket loads of progress with them though, and would be willing to swap over to your system and assist in code developments.

We also kinda want a working prototype in a reasonable time frame, so thats incentive to switch.

 

[GiantEV]

Any updates?

I might be interested in helping, but 24S is important for my setup. How much for the hardware?

 

[dmwahl]

Not sure on price yet, but probably in the 150-200 range for a fully assembled board. Despite the lack of updates here, I have been working on it somewhat regularly, it's just been slow going since my wife had a kid about 9 months ago. The schematic is totally laid out for a 24S board, with balance resistors included. I also plan on adding headers to add a secondary board with extra balance resistors for higher balance current.

I decided to make it a 24S board by default, since I figure most people who would use something like this are not running an off the shelf 12S pack, but are going to be in the 16-24S range most of the time. For smaller cell counts you just divide them up evenly between sections and short together unused cell terminals.

The main thing I'll need help with is firmware, there was someone helping me with that a while ago and he had a good start, but I haven't been able to get in touch with him so it's back to the start. I have all the basics worked out, but need someone with the ability to create a complete firmware. I plan on offering the board to anyone who can help with software at cost.

 

[dmwahl]

Here's a quick update on the status of this project. I've been busy with a new son (9mo) so my free time has been cut down substantially, but still finding time here and there to work on it.

1. As the title implies, I'm designing the system to handle anywhere from 12 to 24 series cells, which covers the majority of configurations.
2. Cell balancing will be optional via an add-on board. This will minimize size, and move the heat generating parts away from the rest of the board.
3. Rather than being an Arduino shield, the microcontroller will be built into the board. It's still "Arduino compatible" meaning you can use the Arduino development environment to program it, but it will not look like an Arduino board. I may include the Arduino style headers so the various shields can be used, but I haven't done so yet.
4. Instead of using a linear regulator and/or drawing power only from the first few cells like many similar products do, it incorporates a switching power supply rated up to 250mA at 5V. The input can handle up to 140V, well above a fully charge 24S lipo pack, and draws power equally from all cells in the string. Another advantage of this is that it lowers the current draw from the pack. For example... a constant load of 5V/5mA from an 80V pack will only draw around 500uA from the cells.
5. I added an XBee header for wireless pack monitoring, and possibly later board control.

Schematic is for the most part complete, there may be a little rearranging during layout, but otherwise it's finished. I'm hoping to have layout complete within a month or so, and then I can get some built. For those of you watching this, I appreciate your patience.

 

[dmwahl]

Very interesting link I just ran across on Tesla's battery packs: http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack

Also interesting that they're using the same battery management chip as my project, very cool 8)