FlexiBMS Lite - Flexible Configuration BMS w/ CAN-bus

SimosMCmuffin · October 3, 2019, 11:12am

Well for the american start-up that I’m developing it for is going to be using it for a 96S setup consisting of 8 modules; 1 master, 7 slaves, 12S each. Each module supports 3-12S and they can be then daisy-chained via real isolated comms. Bottom of the stack module will be master module and all above that will be simpler slave modules. Master module will have the comms to connect to the rest of the electrical system and has isolated contactor control, CAN, DAC-outputs, USB.

I don’t know what the upper limit for the amount of modules chained is, but limiting factor is the communications through the modules.

Is there newer HW schematics available of VESC 6 than the 6.4, which dates back to 2016? My understanding is that he hasn’t released the later version schematics?

Pimousse · October 3, 2019, 11:18am

SimosMCmuffin · October 3, 2019, 1:14pm

I’m gonna be closing the application form this week’s Friday and I’ll be selecting the testers. I think I’ll be able to announce the confirmed testers during this week.

Didn’t know he had released newer HW schematics, thanks for linking to them. I’m not opposed to sharing the schematics at some point, but I really want to get this closed release testing done first and the FW in releasable state.

SimosMCmuffin · October 4, 2019, 5:58pm

Tester Application Form - Now Closed

Participants will be informed of the selected testers this weekend.

Boards have been shipped

I should have them on Wednesday or Thursday of next week.

FlexiBMS Lite FW github repo under construction

Once SW documentation and code formatting has been completed, I’ll post a link to the repo. Testing with a closed group have shown so far 100% compile success after following a written setup guide.

SimosMCmuffin · October 5, 2019, 8:09am

Testers have been chosen

I had a total of 14 responses with 10 people selected to receive one or two boards out of the allotted 14 boards. All applicants were notified of the results via email.

Below are the selected testers and number of boards allotted to them.
@mackann - 2
@rpasichnyk - 2
@Friskies - 2
@ducktaperules - 2
@Wisp - 1
@annihil8ted - 1
@M77 - 1
@Pedrodemio - 1
@hexakopter - 1
@glyphiks - 1

glyphiks · October 5, 2019, 9:46am

Yeeewwww! Excellent! I will be taking the diebiems out of my current diy and replacing it with a charge only… when do you expect that these will be ready to send out @SimosMCmuffin

SimosMCmuffin · October 5, 2019, 12:03pm

If I get them on Wednesday or Thursday of next week (9-10.10) I’ll first assemble one for quick check up that everything looks ok and I’ll then start assembling them in bigger batches. I expect that I’ll have most of them assembled by the end of next week assuming that everything goes smoothly and then start shipping them out the next week after that.

So let’s just say I’ll be able to ship in two weeks.

glyphiks · October 5, 2019, 12:36pm

I reckon I can hold out til then excellent work mate!

SimosMCmuffin · October 9, 2019, 6:09pm

Wisp · October 9, 2019, 8:28pm

Is the connection order typical for BMS’s? Never heard about it. Or is it typical for the flexiBMS design?

SimosMCmuffin · October 10, 2019, 2:58pm

I can’t say. I have never used other BMS’ for my own packs so I can’t say if it’s typical for example for the chinese ones. All I can say is that connecting pack first and balance second is safer and that’s what I recommend doing.

I once burnt couple components from the balancing circuit (couple resistor and diodes, I changed them) and that was when I connected balance connector first not thinking much about the connecting order back then, so all I could assume it was something to do with that, as it hasn’t happened again when connecting pack terminals first ever since.

Hit a bit of a snag when I started doing batch assembly for the tester boards today. I ran out of solder paste… The syringe in the picture is bottomed out.

Luckily, earlier I had ordered more solder paste from digi-key, as I was starting to run low so I was kind of glad when I got the order and looked into the pack and… Well let’s just play a little “find the inconsistency in the picture” with the image below and figure out what went wrong… I have already contacted their customer support about this.

Guess I’m gonna make a little visit to the office this evening and “borrow” their non-leaded paste from the lab’s fridge, so I can continue the assembly during the weekend and likely finish all the 14-15 pieces of tester boards.

hexakopter · October 10, 2019, 3:09pm

Why would you name both paste and flux starting with SMD291…
Thanks for the update. Looking very good.

SimosMCmuffin · October 10, 2019, 3:47pm

Sitting in the bus now, so I havetime to do another more on topic and off-topic post.

I found a little beneficial update to the hw design. I had done a little reading error on the MAX 5v buck dataheets, misunderstanding the behavior of the MODE pin, which toggles between pwm and pfm running modes for the converter, or so I had thought.

Currently the MODE pin is tied to ground, causing the chip to always operate in pwm mode. There isn’t anything wrong with this per say, but at light loads is not very efficient and results in multiple mA quiescent current consumption even at no-load. Pfm is intended for light load use and greatly reduces the quiescent current at no- or light-loads (~120 uA @ no-load). Now I had thought the mode pin toggled between these modes exclusively, but turns out the other MODE pin setup allows the chip to automatically to change to pfm mode at light loads, reducing current consumption anf then back to pwm mode when load increases over 50 mA. Luckily this doesn’t require any sort of code change, but works purely as a hw change, so there is gonna be 0.5 hw iteration.

I’ll wait and see if more needed changes are discovered with the 0.4 boards in tester hands.

I was thinking more of the flexibms variation naming and thought of having FlexiBMS and FlexiBMS Lite as two base products, with the Lite being smaller and supporting 3-12S configurations and FlexiBMS would support higher configurations up to 18S. These models would be charge-only. Then as a variation to both would be the Pro-variant, which would also support discharge path and extra features.

The normal versions could then be smaller size wise, cheaper and then have Pro-versions which would end up bigger and more expensive.

Thoughts?

I’m finally upgrading my smartphone. I’ve been using a HTC One m8 that I bought back in 2015 used and has served me well, but the battery is finally starting to die very early if exposed to cold/cool weather.

After some pain and groan of looking at many different phone manufacturers and models and not finding one to my liking I ended up with a Xiaomi Mi A3. Now the relevant part to this topic is that the phone has a USB type-c connector.

With this I have decided to upgrade my custom powerbank’s charge controller that I designed myself to support Qualcomm’s Quick Charge 2.0 and 3.0 alongside USB PD upto to the normal 60 Watt limit.

Once I get that going and working I can start looking at possible charger uses for esk8 environment.

What an absolute pain this was to write on a smartphone screen!

annihil8ted · October 10, 2019, 3:55pm

Love the idea of having different tiers of the BMS. I feel that ways, you cater more to the masses. Given that people have different preferences for charge/discharge BMS and also different budgets, having more variations will give people more options. As long as the tooling/assembling the different BMS doesn’t cost too much, I feel this is the better way forward. Also, since this is the first batch, you can see demand and adjust accordingly later.

Oooh that would be amazing! PD at 60W or maybe 100W would be beautiful! At 100W, you could have a fully charged board (250Wh) in about 3 hours which is perfect. Even at 60W, a 5 hour charge is pretty good. Peoeple can get to work, plug their boards in, and have it topped off for the commute home or even for lunch.

I absolutely have writing long posts on a smartphone screen. It’s so small and why I always opt for the bigger screen if I can.

M77 · October 10, 2019, 5:53pm

USB PD would be awesome Really like the idea with different versions of the BMS so you have different choices depending on budget and what you are building.

Pedrodemio · October 10, 2019, 5:58pm

If you manage to support them and make the firmware somewhat interchangeable would be great to have various versions for different goals

You could also make the pro be a add-on board for the lite modules, I don’t know if this make things simpler or more complex

Or maybe have a range of add on boards, lets say I want just to be able for the BMS to monitor the discharge, so I could connect a shunt to the Lite and be done with it

SimosMCmuffin · October 10, 2019, 6:16pm

USB PD is a bit problematic to integrate well/easily into the esk8 electronics as the battery side voltages are much higher than the normal use ones. Most of the “easy-to-implement” SMPS converters meant for USB PD use are buck-boost capable in both direction, but they are usually meant for battery packs between 2-5S for the 20V max output voltage on the cable side.

I did some component searching in digi-key and couldn’t find a single IC that could support buck-boosting for that high voltage with a serial interface that you need for the voltage output and current limit configuration. Now it would be doable and much easier, if you only need to do the charging in only one direction, either into the battery pack or out of the battery pack to a device, but bi-directional support is tricky and would need a lot of development and testing to make sure it works properly.

For now I’m gonna be first implementing it for my powerbank as I need to get more experience with the PD communication protocol first. Once I have a better understanding of the nature of the beast in question I can make a more informed look adapting it to the esk8 environment.

Well let’s just say it certainly doesn’t make it more simple, to put it, dare I say, simply.

annihil8ted · October 10, 2019, 6:20pm

@SimosMCmuffin, yeah that makes sense but I’ll remain hopeful Do you have links to your powerbank btw?

@Pedrodemio I like modular but that usually comes at cost and size. Could also require custom protocols when communicating between the chips. Not to say modular is bad but may not be that simple.

Pedrodemio · October 10, 2019, 6:31pm

PD would be awesome, but I think it’s at least a while until USB-C really becomes mainstream

SimosMCmuffin · October 10, 2019, 6:55pm

Now, when I say my “custom powerbank” it doesn’t necessarily mean that it’s anything nice, neat or special.

It’s more of a testing development platform as can be seen from the picture below. Have been planning on printing an enclosure for it for a long time, but just haven’t bothered. But with the planned QC and PD support for my new phone, I have a good project to re-make it into something special. This was my first ever USB device charging capable device however, so even when I designed these boards it was another development/learning experience back then and I have not iterated it since the first version.

On the other hand… it’s almost dead simple… and it works…

But yea for the PD, I plan on making it support the Dual Role, so you can charge your device from single USB-C and charge the pack from the same connector using external PD chargers. I might make it dual C ported though…