Lately I’ve been building some custom battery packs and I’ve been unlucky with the cheap BMS boards.
That’s why I’ve decided to build my own – something that could work stand alone and provide basic protection.
For that I chose the BQ77904 and BQ77905 from TI.
They have all the functionality that I need and they can be chained to create up to 20S packs.
Hello,
This post is about a new project that i’m using as a start-point for a bigger one.
The final target will be a BMS system for a 10S or 15S battery, like the one that’s used in electric bikes / push-bikes
After checking the datasheets and the available parts, I’ve decided to use the following system setup:
I’ve decided to start with a 5S chip for 2 reasons: I had a 4S pack available to play with (a pack used for a modified car vacuum cleaner) and because I wanted to limit the amount of available energy and potential damage if something went wrong.
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I was bored while waiting for some other things to finish and I remembered I had some high voltage transformers pulled from some scrapped laser printers.
They have two coils, one at around 100uH, the other at over 40H. I’ve always wanted to try the MOSFET based push-pull resonant converters and they where the ideal candidates
Some time ago i got an ADSM302 digital microscope to replace the aging metallurgical microscope I’ve been using for the last 10 years.
Here are some links about it, and some short clips of my own:
Several days ago a friend gave me 3 defective displays that were in the dumpster at his office. They where complaining that the image was unstable, they where shutting off, etc.
That made me curios if the CCFL’s where dying or they had some power supply problems, as all 3 are very old monitors with a lot of run hours
Disassembling them revealed that at least the power supply had better days. Most of the low voltage capacitors where faulty.
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After disassembling my Inokim Light for a spring-clean-up I’ve found out that it has severe water damage inside, after running on wet roads all autumn, and getting submerged once in a deep puddle.
It looks like, because of the shape of the frame, front lid placement and the synthetic sponge used to secure the battery, water pooled on the bottom of the unit and remained there for a long time.
Also, no care was given for connector protection.
Incepand cu 2015 m-am ocupat de primele generatii de hardware pentru proiectul Ao-to, descris aici: Ao-to
In link-ul respectiv gasiti o descriere detaliata a modului in care Razvan a ajuns la cerintele specifice proiectului si link-uri catre toata documentatia proiectului, impartita pe etape.
Proiectul e bazat pe un microcontroller STM32F407V, un accelerometru LIS302DL si ceva electronica de suport: drivere pentru servo-uri, LDO si toata reteaua de filtrare, cateva switch-uri discrete ca decupleaza alimentarea extensilor nefolosite, etc.
Intreaga “magie” e in codul si modelele matematice facute de Razvan.
Intregul proces de dezvoltare a fost iterativ, pe masura ce am descoperit probleme sau Razvan a avut idei noi.
De asemenea, nu toate variantele de design au avut si implementare practica.
Pentru primele 2 generatii rolul meu a fost de schematic + pcb designer si constructia / depanarea prototipului la nivel de HW.
Pentru a 3-a generatie Razvan s-a ocupat de design, eu am avut doar partea de review si montarea prototipului.
Generatia asta a fost faza de validare a intregului concept hardware si software.
Tinta a fost sa includ toate functiile cerute de Razvan si sa reduc cat se poate de mult suprafata cablajului.
A trecut prin cateva iteratii in care am redus dimensiunile, rearanjat componentele si imbunatatit informatiile de pe silkscreen.
au devenit
Aceasta varianta a fost folosita pentru a monta primele prototipuri:
Cu ocazia asta am gasit si cea mai serioasa problema de design: footprint-ul tranzistorilor alesi pentru a comanda canalele de servo nu se potrivea de nici un fel cu tranzistorii cumparati.
Am decis sa fac un mic hack si sa montez tranzistori in SOT23-5 “dead-bug”:
Nu arata frumos, dar a fost suficient pt a valida intreaga idee.
Acest set de placi este cel care a fost inclus in proiectul de pe kick-starter ao-to-one
Modificarile majore: modificata partea de comanda sa utilizeze doar tranzistori in capsula SOT23-5, rearanjat conectorii si aranjarea componentelor pe placa.
Acest set de documentatie a fost folosit pentru a realiza primele prototipuri oficiale, cele folosite pe kickstarter:
Din pacate proiectul de pe kickstarter nu a avut succes.
Aceasta iteratie a fost o varianta “mini” a intregului proiect, cu un pcb mai mic si doar o parte din functionalitate.
A fost conceput ca un “main-board” care contine microcontroller-ul si electronica de baza.
Pe main-board se conecteaza placa cu senzori.
Pcb-urile produse arata asa:
Proiectul a ramas in aceasta faza datorita lipsei de timp.
Sper ca documentatia sa fie indeajuns pentru reproducerea proiectului de cei interesati.
Eventual o sa incerc sa raspund la comentariile de pe aceasta pagina.
The 3’rd in the series is the control board.
It’s purpose is to allow easy interface from a single-board computer that has one SPI and one I2C port.
Also, it provides a common reference clock and a synchronous update signal to the two DDS boards, as required by AN-587
The SPI port is level-shifted to a MCP23S17-E/SP SPI to parallel expander.
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The second board in the VNA is the phase / frequency detector.
For this one I chose an AD8302 chip.
It will measure in the range I’m interested in.
It might not be the best part for this, but for the initial design it’s enough, as it works out-of-the box.
The board contains:
The signal generator is based on the AD9851 DDS chip
The board contains:
