My reaction should have been expected. Everyone else who designs a BMS reports significant temp increases during use, which is expected. You report that there is essentially no temp rise and expect everyone to just think thatâs nothing to comment on or inquire about?
You are taking temperature readings across a thermal insulator in freezing cold weather. That has an effect on your readings and, IMO, should have been mentioned. The temps of your FETs, sense resistor, and balancing resistors will be much, much higher than the board average type temp reading you are taking now.
Board average temps are fine to note but the thermal fatigue of components and solder joints, and possible damage, comes from the actual temp of the components themselvesâŚa critical part of reliable circuit design.
I am not saying your component temps are too high. You are reading beyond my statements. I am saying a lot higher than the 26°C you reported. If this is not a concern for you then no problem.
That is not an indictment of your design or testing methods. It is merely an observation of what happens in these circumstances. My inquiries were merely born of curiosity, not malice.
I am in awe of the work you have done and congratulate you on having created this BMS! But extraordinary claims often lead to questions. I would hope every hardware designer would recognize that and be eager to answer those questions. Especially from those who are considering which product to buy and are comparing test results.
Sorry, I was just saying wait a minute/hold your horses/donât get too excited. Better datas will come along the way, but cold weather from canada is all I have at the moment for testing. Iâm kind of happy to get the unit working fine will all the new improvements done on botu hardware & software.
I will try to stick a thermistor on the fet directly for the next discharge for more accurate datas on that topic.
AhhâŚmy apologies, I misunderstood.
Looking forward to your continued testing!
If you can, epoxy down the thermistor or use something to thermally couple the thermistor to the FET. The rounded thermistor and flat FET means that there is very little heat transfer between them. Add that onto the thermistor having a very slow thermal response and you end up with a temp reading that is much too low.
Burying the thermistor in epoxy helps to spread the heat all around it and makes for a much more accurate reading as long as the heat continues for a long time and the surface reaches thermal equilibrium (which it will for a long test here). A thermocouple, the tiny type-k or similar, makes accurate reading of temps a lot faster and easier but you need a meter that can use thermocouples.
After many charge/discharge cycles @ 70A continuous discharge completed, I feel confident enough for starting the shipment of the 15S version this week. Some bugs were corrected during testing and some new features implemented with the small I2C display (larger fonts, all datas now available & user can shuffle between shown datas with the power push button)
I should receive the 18S boards (SS & SS-LITE) this week and will start testing them.
Next on my to do list:
Finalise the 24S version and order PCBs for testing
make the QT mobile bluetooth app works on android (the QML code seems to work fine on build mobile windows, but Iâm struggling with android deploy ABI X86 config stuffâŚ) maybe someone here is a QT specialist and could helpâŚEBMS-tool repo is all on github and available.
-update NRF51 repo for use with EBMS packets ID instead of VESC
Validate + improve CAN implementation between EBMS & VESC
Implement throttling (max. allowed current & regen control) into VESC code over CAN bus.
Here is a pic of the 18S-LITE PCB. This thing is quite small, maybe not as small as the 12S FlexiBMS, but not exactly the same thing. This BMS can manage up to 18 serie cells, up to 9 temp sensor monitoring, should be able to manage charging rate probably a bit above 20A and has large robust main connectors which take a lot of surface area:
It does run on my phone at the moment. Iâve been able to build the NRF51 & NRF52 firmware with EBM comm_packet_id yesterdayâŚi must now try to upload tge firmware to the NRF IC with openOCD. I have an early version below of the SS-18 that had an NRF chip at the back for testing thisâŚ
Good to know you received it.
You mean not soldered perfectly? It is possible, I have one employee doing the assembly, Iâm doing the final QC, but a lot of things to look out for so I have to improve on that. Things are getting better more we build boards and he is getting better as well with the build process.
I will move to outsourcing the PCB assembly once Iâm 100% sure everything is optimized to the max. on the hardware side.
Those are TVS diodes for extra safety on the balance IC. They might not be necessary, but I thought it is better to have more safety than not enough. Just sad that they have not been soldered properly.
Firmware & software are there on github, follow the links on the website for pinout, user guide & block diagrams, but schematics & PCB files wonât be released for SS lineup.
