FlexiBMS Lite - Flexible Configuration BMS w/ CAN-bus

[SimosMCmuffin]

Yo,

Been busy at work with overtime working on the military project we got (got new things to learn on it) and developing a FOC-motor controller for another customer, making the FOC-control algorithm from scratch and really learning its fundamental workings. Note, not planning on entering the esk8 market with my controller at his point .

Sorry I’ve been unreachable during this time. Situation may get better in the following weeks.

Project update,
Due to the Covid-19 virus outbreak my 0.5 HW PCB order was delayed by about a month, so it has been in essence frozen for the past month and I’ve therefore focused more hours on my workplace projects, other personal backlog projects and future plans. Fortunately the PCB fab house has been able to now complete the board order and I should be receiving them this week (week 10).

The action plan for the upcoming days/weeks is to get a couple of 0.5 boards assembled, tested and verified. Once I’m satisfied with the results I’m now planning on doing another tester batch with a dozen or so boards. I have couple of new testers already lined up, such as @Chricious (you’re on the list), couple others and a couple of the old testers who are helping with the development and feedback. I have 15 boards coming, but I’m not necessarily assembling all of them and I’m not planning on opening another official tester application form at this point. I’ll let you guys know when I’m looking for more people to send test boards to, so please don’t go spamming my inbox at this point. I know you guys are interested and I appreciate it.

Note. Covid-19
All upcoming plans might get affected by the Covid-19 as a force majeure influence, so at this point I can’t promise anything scheduling wise, but rather just milestone steps that we get to and pass as we go forward.

In Helsinki, capital of Finland, we now have confirmed cases of infection among the general populace and recommendations to self-quarantine are starting to be enforced.
In all likelyhood, from what I have gathered from following the situation. The incubation period can be up to 27 days while being asymptomatic and able to transmit the virus via aerosol and droplet transmission. The virus has also been reported to survive up to 9 days on surfaces. This will cause economic slowing/downfall, as the infection will very likely slowly spread through the populace, with the self-quarantine acting more as a method to slow the speed of spread and help the infrastructure services (food, medical) to absorb the impact by spreading it timewise out.

Stay safe out there.

Off-topic
I’ve been planning up the crazy trip idea to travel over 2000 km on a esk8 during the summer to Lapland or up north of Finland. I ordered some camping equipment and tested them out last weekend, a daytime trial-run so to say. Got even a work colleague to join up and grill some sausages. (pictures show correct orientation on computer, but for some reason they get rotated ).

I also need a pretty beefy charger to take with me on the trip. I’ve had this one benchtop lab supply project on a backlog just forever and finally got working on it and after some 3D-print iteration it turned out pretty well. It’s made with a DPS5015 chinese DC-DC buck-regulator mated to a Meanwell LRS-350-48. It’s about 80-90 euros for a 350 Watt power supply, which is pretty good value IMO. The 3D-print case also allows them to be stacked vertically on top of another unit. Not the sleekest form factor, but more pragmatic and functional.

I’m gonna do at least one test unit with Meanwell’s SE-600-48 600W PSU that is around 90-100 euros, that might actually be the one I would take with me to the trip for faster charging.

[Zach]

@SimosMCmuffin

making the FOC-control algorithm from scratch and really learning its fundamental workings.

Wow, Well done! That shit is awesome!

@SimosMCmuffin

I’m not planning on opening another official tester application form at this point.

Shucks, oh well, Maybe next time. Really anticipating getting my hands on one of these so i can finish my pack off.

@SimosMCmuffin

n Helsinki, capital of Finland, we now have confirmed cases of infection among the general populace and recommendations to self-quarantine are starting to be enforced.

I hope you and your loved ones manage to stay safe. This damn virus is popping up everywhere.

@SimosMCmuffin

I’ve been planning up the crazy trip idea to travel over 2000 km on a esk8 during the summer to Lapland or up north of Finland.

You absolute Mad man. Are you not worried about ride fatigue at all? Otherwise, i think it’s gonna be a blast! Looking forward to when that comes around

[PixelatedPolyeurthan]

@SimosMCmuffin

from what I have gathered from following the situation. The incubation period can be up to 27 days while being asymptomatic and able to transmit the virus via aerosol and droplet transmission. The virus has also been reported to survive up to 9 days on surfaces. This will cause economic slowing/downfall, as the infection will very likely slowly spread through the populace, with the self-quarantine acting more as a method to slow the speed of spread and help the infrastructure services (food, medical) to absorb the impact by spreading it timewise out.

Finally someone who actually tries to understand the situation…

I really pity those who think this virus is nothing.

Don’t want to derail so stay safe and thanks for this great update!

[Chricious]

Thanks Simos for not forgetting and taking care of us!

@SimosMCmuffin

I’m gonna do at least one test unit with Meanwell’s SE-600-48 600W PSU that is around 90-100 euros, that might actually be the one I would take with me to the trip for faster charging.

I can recommend you the Meanwell HLG-480H 8.9A 480W. Its about 100€-120€ and completely passive cooled .

[Creavenger]

Nice write up, thanks for the update. The camping looks fun! I want to go camping in the snow sometime… but this year we didnt really get any unfortunately…

And If you need more testers, I’d gladly sign up. I would test it in combo with the new v6 neobox samples ill receive soon.

[Darkie02]

@SimosMCmuffin

DPS5015 chinese DC-DC buck-regulator

Might be interested in this topic

SmartCharger - One to rule them all

Hi dear builders, I’d like to present you a project that took me few weeks of work. The SmartCharger [IMG_20190912_122445] [IMG_20190912_122457] Origin The project came from few statements : On events we have all our own charger leading to a messy charge area and a car full of different chargers We barely can’t borrow a charger to someone due to the difference of voltage/current/connector Having different boards at home means differents chargers (6S, 10S, 12S). Money and mess. I can’t put …

[SimosMCmuffin]

@Zach

Are you not worried about ride fatigue at all?

Plan would be to travel from camping site to camping site. Charge and rest there for the nights and ride during daytime. Need to carry some camping equipment with me though. Packing might prove to be a challenge.

@Chricious

I can recommend you the Meanwell HLG-480H 8.9A 480W. Its about 100€-120€ and completely passive cooled .

I’ve been using the HLG-150H-48A and it ain’t bad. I just personally like having access to the voltage and current values graphically and being able to use the power supply for benchtop use.

[Zach]

@Creavenger

And If you need more testers, I’d gladly sign up. I

Second this! A modular battery await it’s flexibms

[Pimousse]

@SimosMCmuffin

Plan would be to travel from camping site to camping site. Charge and rest there for the nights and ride during daytime. Need to carry some camping equipment with me though. Packing might prove to be a challenge.

Get in touch with the banana Riders. They did the same kind of trip last year (or 2 years ago).

Banana Riders

@Darkie02

Might be interested in this topic

Ahah yes, this reminded me something too.

[SimosMCmuffin]

I got the 0.5 HW boards this week, haven’t gotten around starting assembly on them yet. Probably gonna start tomorrow (Sunday).

Spent a couple more iteration rounds on the Benchtop power supply 3D-printed parts to optimize it’s airflow for cooling, it can now handle continuous 330 Watt pretty easily (PSU rated for 350W, so maybe actually a bit overloaded with 330W going to load through the buck converter), while staying moderately cool (warm, but not burning to hand). The problem was that the warm air moved by the PSU’s fan, kept circulating inside the 3D-printed enclosure, so I added a wall inside to stop it from being able circulate inside and it now pulls in fresh air from the front air ports and exhausts it from the back. I integrated the wall into the 3D-printed mount DPS-buck converter later (no pic).

On saturday I finally got back to building my DIY reflow oven that has been sitting on my kitchen table for at least 6 months. Planning on making a little production line… with a pick-n-place machine…

Couple test runs without any extra control electronics, just measuring temperatures from the thermocouples inside the oven (only upper TC in the first pic, both in the second one) with the heating elements wired straight into the wall plug. X-scale is time in seconds and Y-scale is temperature in Celsius. It has a pretty decent temperature curve, as these show the fastest possible heating time.

[SimosMCmuffin]

Update

I have partially assembled one 0.5 board to test the new buck IC and it’s layout. So far it seems promising, as it’s outputting voltage, and that voltage is what it should be, but I will do a noise and thermal test with an external load to test/stress it a bit more.

I’m taking inventory of my current component wares as well as ordering the necessary parts for the upcoming hand-assembly batch.

I’m also designing my production testing jig, which is gonna be a bed-of-nails type of deal with a clamping connection for the battery and charger pads. Idea is to break out all the connections from the board by placing it in a jig and having all the testing equipment connected to the jig. Board doesn’t need to have any connectors on it to test it.

Point is to make sure that everything essential on the board has been tested and verified to work before shipping to them customer to reduce amount of DOA or defective items. This is also because battery equipment related malfunctions have the potential to be catastrophic. I’ll also probably ship the testing result certificate paper to show that the board has passed testing.

Here’s a list of the planned things that will be tested in order (questions/conversation welcome):

• Short-circuit test
• Flash production testing firmware
• 5V buck output voltage
• 3V3 linear output voltage
• Status LED
• TX/SCL and RX/SDA pins
• CAN-comms
• Cell voltage measuring
• Cell voltage balancing
• Battery and Charger voltage measurement + calibration
• Charging current test + calibration
• USB-connectivity
• If all tests passed up to this point, write board HW version in one-time-programmable memory
• Flash application/user firmware
• Print test result and calibration verification

This test procedure should be able to detect the majority of defective boards while they are still in my hands. I can then set them aside, diagnose, fix and run them again through the procedure.

Most likely this will be a semi-manual test at the beginning that I will automate further with time, as the volumes increase.

[Darkie02]

@SimosMCmuffin

Cell voltage measuring

What the Accuracy tolerance you looking for?

[SimosMCmuffin]

@Darkie02

What the Accuracy tolerance you looking for?

The cell voltage measuring is done through via the LTC6803-3 battery stack monitor IC and referring to
it’s datasheet, the cell voltage measurement error should be within a couple ± milliVolts and the whole stack’s voltage error within ± ten milliVolts and I have seen and verified the cell readings to be within a couple milliVolts with external measuring equipment. So it is a pretty dang accurate chip (and better be for it’s price…). I personally run the balancing on my packs so that the cell voltages are within 5 mV between the bottom and top cells at top SoC.

680313fa.pdf

[SimosMCmuffin]

Got some measurements done on the buck regulator.

Thermals were ok at about 45 C at full load with 20 C ambient.

Noise measurements
Yellow trace is battery input (my 10S pack, fully charged, ~41,5V). Blue trace is 5V output from the buck regulator. We’re measuring AC ripple on the voltages.

Input (battery side) capacitors are 1µF 100V + 100nF 100V ceramics.

10µF 16V output cap:
No load.

290 mA load.

22µF 16V output cap:
No load.

290 mA load.

47µF 6V3 output cap:
No load.

290 mA load.

test setup:

Summary:
10µF output cap, no load ~175 mV noise, full load ~100 mV noise
22µF output cap, no load ~125 mV noise, full load ~70 mV noise
47µF output cap, no load ~90 mV noise, full load ~40 mV noise

22µF output cap is what I have specified in the schematic and with it the output is pretty decent in terms of ripple. What it actually needs is a bit more capacitance on the input side, as can be seen with the relatively large ripple voltage, but currently all 63V high capacitance ceramic caps are absolutely out of stock everywhere, so you have to jump to 100V rated ones to find more stock and then you are much more limited in the capacitances available in the 1206 package size. And then the costs start to go increase… The next capacitance size from the 1µF is a 2.2µF and it’s almost double the price of the smaller one. I’m thinking of ordering a couple of the 2.2µF ones to test what the performance would be with them and maybe upgrading to them.

The ripple performance is very close to what is shown in the datasheet with just the single 22µF output cap, whereas the datasheet measurements have 2x 22µF ceramics on the output. Also we do have a much higher input voltage, but it doesn’t seem to matter that much with how this IC regulates the output.

[PrivacyDoctor]

I am excited about every update - keep it up!

Just a crazy idea: As we are talking 100V components - Have you thought about making a version for up to 20s? Or would it be possible to intelligently combine two for a 24s BMS? That would make these really versatile!

[Mainflow]

Can bus.

[SimosMCmuffin]

@PrivacyDoctor

As we are talking 100V components - Have you thought about making a version for up to 20s?

I’ve been thinking of a concept design for a 6S-18S BMS with that would support daisy chaining the BMS-modules for higher S-packs, but I need to focus on getting this project first out of the vaporware realm.

@Mainflow

Can bus.

If you’re thinking of using CAN-bus for high voltage pack setups, then you need to design the CAN-bus system around galvanic isolation and isolated power, but if you’re going for dedicated isolated communication bus then you can essentially use any communication bus for that matter.

True isolation is of course better and will be able to support to hundreds of S-packs.

[Mainflow]

It was just for the communication.

[SimosMCmuffin]

@Mainflow

It was just for the communication.

Communicating from the bottom pack to rest of control system and not the other series’d up packs? Or for communication between the series’d up packs.

Normal CAN-bus ICs have a maximum common-mode (voltage to GND) voltage that the ICs can handle. There are then the special ones that support isolation, but usually need a dedicated isolated power supply for them.

[PrivacyDoctor]

@SimosMCmuffin

I’ve been thinking of a concept design for a 6S-18S BMS with that would support daisy chaining the BMS-modules for higher S-packs, but I need to focus on getting this project first out of the vaporware realm.

Yes and Yes!