My uBMS PCBs Finally Arrived!

uBMS Frontside Unpopulated

After weeks of planning, designing, researching, testing, and then routing, my first ever 4-layer PCBs for my uBMS project have arrived from JLCPCB! I was really impressed at the speed of shipping, especially considering the ongoing pandemic. It only took 4 days from the day it shipped to the day it arrived at my doorstep!

The uBMS project is really exciting because I’ve taken all that I have learned over the past few years working on my independent electric vehicle projects and my college’s electric vehicle project and have been able to put that knowledge into a package that is only slightly bigger than a credit card. 😃

Comparing Differences

uBMS Compared with my previous BMS prototype and a credit card

I was really able to miniaturise this design (sacrificing few features) compared to the previous design due to a few major differences:

  1. Surface Mount All the Things - By keeping parts using surface mount, I can save a lot of space since they generally have a smaller footprint
  2. Using small package sizes - For all resistors and diodes I’m using the 0603 package, for my thermistors I’m using the 0201 package, and decoupling capacitors I’m using the 1206 package
  3. 4 Layers (fancy right?) - Being my second ever PCB, it was a little ambitious to use a 4-layer PCB, but it was definitely required to get the feature set and size constraints that I set myself for this project. It was especially tricky without the help of blind and buried vias, but that will keep the costs down.
  4. No Development Board - The previous design used a socketed ESP32 dev-board which took up huge amounts of space and wasted away too much power
  5. Smaller Connectors - This board uses 1mm pitched pinouts for sensing and balancing compared to the 2.54mm of the last design. I really want to 3D print connectors to save cost here…
  6. Simplified Balance Architecture - This is one of the major design enhancements over the previous generation. I no longer have dedicated “bleed” resistors with MOSFETs but now only use MOSFETs and without the need for bulky and expensive optocouplers for control (don’t worry!).

Once I get the board soldered up I’ll be writing another post going into more of the architecture’s unique design choices. I’m just waiting for a late Digikey order (no worries though!) :)

As soon as the board is soldered up, which I expect to be quite the challenge (it’s around 200 parts in a 60mmx90mm area), I’ll begin work on nailing the firmware down and then beginning on the board that will partner with this one ;). Hopefully these will work well and I might be able to sell them someday! For that I’ve been looking into open-source Pick ‘n Place machines and software like OpenPNP which is really cool stuff.

Stay tuned!

P.S. Here are some additional cool images to check out

Back of my uBMS board feat. my name

All four layers of my PCB. I think it shows the mayhem pretty well lol

The smallest component I will have to solder 4 times on my board, the 0201 NTC Thermistors