Lithium battery BMS questions

[mechman600]

Originally Posted by P-hack

I have to mention that manually bottom balancing a 18 cell pack once a month (if it even needs it) can be pretty trivial.

The hard core bottom balancing advocates (the loudest of whom is Jack Rickard...just Google him) are claiming that it only should be done once a year, and even by then they are still very close. Just drive the car till it's nearly dead and then slowly drain each cell individually to 2.7V. Charge it up. Bam! Finished. Of course it is tedious and would probably take a whole day, but hey, you get to tinker on your car!

[P-hack]

Yah the muxshield probably wouldn't work. I was thinking since you had one at 72v it might, but no.

I'm sorting out a distributed bms (lots of notes, some parts on order) for cheap per cell and probably something more than an arduino for a controller (i.e. olimex). But it isn't at the top of the list currently, gotta sort out one of them $200 or less chargers and put my controller kit together first.

I get where jack is coming from, he knows what you can do with electronics and he isn't seeing it. Cell level monitoring and inductive balancing and easy installation and warnings before cutoff and charger/controller integration doesn't have to be expensive though, at least not in hardware, at least it looks that way on paper And the relatively dumb op-amp based boards beat the intelligent node boards to market. I think a lot of hardware only guys are stuck, but for less costs they could have had a lot more functionality and less bad rap.

I am definitely going to experiment with a cheap bluetooth adapter and android torque too, though I wouldn't put any critical controls or alerts over bluetooth only, still want hardwired idiot lights methinks. But you could open a terminal application on your android and configure the bms controller as well.

[TurnNBurn]

So an ardiuno wont work. Hmm. What about the gamber BMS stuff? GamberBMS

I've been watching his stuff on youtube for a while now. Good series of videos.

Looking for a BMS to handle 18 cells is quite hard. I've been googling all evening.

-edit-
These leaf batteries are pretty awesome and they're local to me available to pickup. But with all this BMS crap, it's looking like it may be easier to go with GBS or another Lifepo4 battery.

[mechman600]

Originally Posted by TurnNBurn

So an ardiuno wont work. Hmm. What about the gamber BMS stuff?

That's not what I said. An Arduino will work great. The amount of resolution you desire will determine how many Arduino boards you will need. A single Arduino with a Mux Shield will give you a 0.1V resolution on a 72V car and three will give you a 0.035V resolution. Not difficult to set up. I am going to change my tune and say that even 0.1V resolution is good enough, especially if you keep it conservative and don't try to charge/discharge to the limits.

Gamber's system is very very good. I met up with him when I was in Calgary a couple of months ago and saw his system on his motorcycle. You can adjust shunting voltage with the menu screen. All voltages are displayed. Fully customizable. However, it is a top balancing system, which I feel is fundamentally flawed to begin with. Like all other top balancing BMS, it is always shunting current at the top of the charge, trying to keep everything even. Completely unnecessary if you bottom balance.

[P-hack]

gaa, the nano's are 3 for $10 (and 8 adc a piece) (something about a regulator?!?)
multi-cpu communication/coordination is a little more challenging, aside from optos. Simplest is to pull down a pin on one from the master (via opto) and it streams the volts out its tx port (through another opto) back to the rx port on the master, with a known start and end string, in case communication gets out of wack. With the main board controlling who turn it is to send there should be no conflicts.
EDIT: no obvious usb port, would have to adapt an arduino to program it.


still the serial lcd is nice though, keep the boards and wires by the battery.

Turn, I grabbed 3 of those modules for my scooter, was planning on taking them apart for 45volts 32ah, till I watched a kid do it on youtube. Well, I'm still planning on taking them apart, just not looking forward to it He doesn't appear to have a lot left in stock by the website.

[TurnNBurn]

Originally Posted by mechman600

That's not what I said. An Arduino will work great. The amount of resolution you desire will determine how many Arduino boards you will need. A single Arduino with a Mux Shield will give you a 0.1V resolution on a 72V car and three will give you a 0.035V resolution. Not difficult to set up. I am going to change my tune and say that even 0.1V resolution is good enough, especially if you keep it conservative and don't try to charge/discharge to the limits.

Ok. I must have misinterpreted when I read the "muxshield probably won't work" and lost hopes.

What sort of items would I be looking for to compile a shopping list for an Arduino setup? Is there any soldering required?

[P-hack]

Mech, this is also worthy of consideration:
20x12 bit adc, 256 KB Flash, 16 KB RAM, arm m3 core $7.88 at mouser

32L100CDISCOVERY for STM32L100RCT6, $7.88 at mouser



EDIT: they also have an arduino looking thing ($11) that might be easier to get started with, *should* have like 40 ADC pins, but arduino may not have caught up with that sort of expansion:
http://www.mouser.com/Search/Product...-NUCLEO-L152RE

[kennybobby]

Man that stuff is low cost, but it seems like the complexity of firmware development for a 32-bit processor kinda blows away the concept of a microcontroller just to read and report some voltages. i'll probably get one to play with, just to compare assembly language programming with the simple 8051...

[P-hack]

The have really simplified things with the nucleo, it plugs into your usb port and they have a web based development environment, you just give 'em an email address for access. When you compile, it all happens on the server, where they control all the setup and versions of tools and whatnot, and you save the downloaded bin to your usb device, where it automatically loads.

$10 for 40 12 bit adc pins in an even easier (and more predictable) than arduino to set up environment.

Development Platform for Devices | mbed
Don't expect anything like assembler though, You will have to "baremetal" it as the plebes say

i.e. https://launchpad.net/gcc-arm-embedded <- which is gnu C++ and being supported by ARM developers directly (and isn't scared of some asm). Probably your first option for the discovery boards too, or olimex boards.

[mechman600]

Wow, those are indeed low cost. Unfortunately I am dumb if it's not Arduino.

What I had figured out is multiplexed cell warning signals with multiple Arduino boards, but not actual voltage reading of each cell. Example, you could get a warning that cell #1 is low voltage (a PWM signal from that cell's board to the main board) but not actually know what the specific voltage was.

I am going to play with the I2C communication side tonight to see if I can make it do the latter.

Yes, TurnNBurn, you will need to solder. I picked up a 35W soldering gun at Princess Auto yesterday for $15. It even came with solder. Start practicing and do some YouTube tutorials. It's really not hard.