Im doing a long time discharge test on my 10S5P (600 Wh) battery pack with my old BMS proto, which has standby current of ~9 mA from the battery, here’s the current graph of it’s effect
It has almost been 30 days in standby mode. Then consider slowing this drain over 10 times for the deep sleep mode for 300+ days for the equivalent capacity. I think it’s good enough. Could the deep sleep mode discharge be smaller? Yes, but this is already looking good enough approach.
After looking closer at the Battman’s RTC wake-up implementation and figuring out the logic behind it, it’s pretty smart and I hadn’t before realized how it exactly worked. But yes, it’s a very good design that allows for very low quiescent current. Essentially only the LTC6803.
the MCU in sleep mode is not enough to reduce the input current a lot, because the buck regulator has such a high no-load current. Battman’s implementation gets around this by completely cutting off the regulators from the battery via Q7, which causes the MCU to also shut off, but the RTC is using the Cell1 from the battery pack to power itself and periodically then enables the regulators back up.
I feel like I was beaten in 4D chess game I didn’t realize I was even playing At least I learned something new.
I’m gonna look at the possibilities on how to possibly implement something similar considering that there is hardware difference between the boards.
EDIT: Note, that the Battman’s implementation does depend on having the balance connector on, so that the Cell1 is actually available. Mine implementation works with just the battery pack connected.
I’m considering this. There is the LTC6803 5V output, which could be used to power just the MCU via a small LDO, the MCU (STM32L433CCT6) supply pins didn’t seem to accept 5V directly after looking the datasheet. Then the MCU could power up the buck regulator directly if it needed to enable other circuits needing higher power.
I personally like this approach more then an external RTC IC. I’m gonna check the datasheet to see if the MCU has internal RTC capability, or if it needs an external 32kHz rock + does it need a high speed crystal for USB, or does it have an internal oscillator for that.
Direct quotes from the STM32L433 reference manual. RCC chapter
HSI48 clock
The HSI48 clock signal is generated from an internal 48 MHz RC oscillator and can be used
directly for USB and for random number generator (RNG) as well as SDMMC.
LSI clock
The LSI RC acts as a low-power clock source that can be kept running in Stop and Standby
mode for the independent watchdog (IWDG), RTC and LCD. The clock frequency is 32 kHz.
It seems that it wouldn’t actually need any external crystals or oscillators to run USB and the RTC in low power mode.
@okashira I’ve been doing some measurements and comparisons between the Battman and Flexi 0.1 design and based on my tests I would say that the Battman has at least about 200 µA input current at 40 V battery voltage even at deep sleep mode.
Here’s my evidence based on purely schematic design.
The boost charger resistive divider will have with 40 V battery voltage:
40V - 0.7V (FET body diode) = 39.3V
39.3V / 207kOhm = 190 µA
There is also going to be some leakage through the FSV10120V schottky in the boost charger block to the LTC3873 boost controller. So I would say from design viewpoint, that there is no way for the Battman to have sleep drain of only 10 µAmps. Period.
Most of my quiescent currents also comes from voltage dividers, eliminating those somehow would have a decent effect on the deep sleep quiescent current.
I have had multiple people contact(PM) me about the interest towards the FlexiBMS project, so I am compiling this message as a general reply in relation to the current project status at this point of time (22.3.2018).
Thank you for showing interest towards my project, I’m honored and also appreciate the outreach from the community in both user and vendor side. At this moment in time I’m planning on continuing the development of the project under my own control, but I welcome all feedback and discussion towards and about the project, preferably in the FlexiBMS forum thread itself (FlexiBMS - First prototype board assembled and firmware development started! - Flexible configuration and charging BMS). I’m neither accepting or refusing any possible collaborations or other offers at this time or for the perceivable future. For now the project is so WIP that I don’t want to tie myself down yet. I’ll continue working on it and updating the thread as things progress.
I am in thinking on changing the license of the project to something that would allow:
Allow people to make their own derivative, based off of the files in the GitHub. I don’t want to stop innovation and want to enable the designs to work, as a launchpad toward their own unique/distinctive project/product.
Allow the use of the Github files to make a copy of the hardware for their own personal use.
To protect myself from someone who would link the Github repository directly to a chinese PCB fab and start flooding the market without receiving compensation.
If/when this product becomes available. If I can’t meet the supply demands I’m open to allow other vendors to produce their own 1:1 batches with a reasonable license fee, so I can get compensation and people be able to get their product.
Personal message:
I want to do this for a living and make a living with it. I find this to be enjoyable and rewarding. I want to give people good products. I want to allow people to make their own derivatives based off of my work and be able to sell those. I want to protect myself from somebody flooding the market using 1:1 clone of my product without receiving compensation. In the case that I can’t supply the demand, I will allow for other vendors to produce their own batches under a reasonable license fee to help ease the possible supply problems (what good is a product you can’t get?).
Nothing has been set in stone yet, but these are my current thoughts, so I’m posting this here if people want to have a discussion.
In case you’re wondering about how the license fee would work. I mean it as a small compensation per board (5-15 €). Maybe I see there is a supply problem and I can’t meet the demand so I decide to allow the production of 200 boards with the aforementioned fee. Vendor X takes up the offer and we make a contract, they pay me license fee and then they are free to produce those 200 boards directly with the files available on github, they are also free to sell those boards at the price they see fit. I personally see this being the fairest to all sides on this issue: Me, Vendor and the end-user.
Require certain levels of QC to be met in order to use the license. Some of the east Asian factories just pump stuff out without even testing to see if it works, hence the super low prices. A bunch of junk on the market just looks bad on your design, even if it was the manufacturer being negligent. Shipping defective units revokes licenses.
Good idea and point altogether. This can be bundled into the contract for the license fees.
I plan on doing my own visual check on the soldering job and then make an automated function/sanity check for the electronics that can quickly be run to test the circuitry.
I’m not asking for donations/money at this point in time, because that is not the current limiting factor in the development. It is time.
I work at a local engineering firm doing hardware, software and a little bit of mechanical design. I Work 8 hour days, 10 hours when you count in travel. Continuing doing the same thing when you get home is a bit rough and usually during the work days the progress is not huge every evening. Usually managing to test one specific thing. Weekends are much more productive. The pay is good, considering I graduated last year from university with bachelor’s degree in embedded systems, but I have always been active on my free time, doing interesting projects while trying to incorporate new technologies into them and develop my skill and experience through that.
Here’s a run down on how much an hardware iteration costs:
4 layer PCBs, 5-10 pcs - 38€
SMD stencils for bottom and top - 20€
Shipping PCBs and stencils - 55€
Components for a single test board ~ 70€
So I can do a whole round of iteration for around 200€, which is very cheap all things considered. The bigger loss in productivity is the turnover time for the PCBs, which is around 3 weeks, but at least now I can write firmware meanwhile I wait for the new boards to arrive.
I order my PCBs and stencils from SeeedStudio and components from Digi-key.
I certainly hope those extra 2 hours are spent on top of an esk8. I hadn’t truly lived life until my commute was on top of an esk8. No, seriously. I thought I knew what life itself was. I didn’t.
I wish, but Finland isn’t really the ideal esk8 country during the winter, especially with a single wheel drive (grip and torque limited) + the real possibility of turning into a human icicle. pic related.
But I’m working on a new board iteration as well. Custom deck, dual rear drive, 10S6P watertight/resistant battery pack. And I have been prioritising more ruggedness and all-terrain capability more. Here’s the raw board out of the mold. It’s shape is based on the Trampa’s HolyPro 35, but it’s made out of finnish birch veneer, which also has it’s contour limitations in the mold, AKA can’t do super tight radii, so it’s bit more rounded. It was made by one the mechanical designers at the office. You can find him @ https://www.instagram.com/pabloboards
Found a weird glitch in the hardware while debugging the BMS and it’s making this very weird noise. I don’t know what’s causing this, so I’m just posting a short video of it in case you guys know where it might be coming from?
At least I learned something new.
Gonna have to make it rain on him!
