Saturday, August 29, 2015


With but a few weeks left in summer, I decided that it was a good idea to start designing a sort of universal battery pack for silly EVs.

The goals of the project are to incorporate the following features:
  • Integrated BMS 
  • Output protection 
  • "Hot-swappability"/fancy latching holder mechanism 
The integrated BMS would likely come from one of those newfangled Chinese BMS boards flooding eBay, and a fuse integrated into the output port would prove a nice alternative to a hot, smoky death.

To elaborate on hot-swappability: the concept of having an easily removable battery unit in an EV has always been an attractive feature that is almost always countered with "I'll do it later." More seriously, doing it well involves adding some mechanical latching mechanism to hold the batteries into the vehicle along with a backplane of sorts to mate with the battery. Further, packaging becomes more important as I can no longer just shove some wires to the side and call it a day.

The idea is that I'd have at least two of these modules in parallel in any given application, allowing the system to stay on as one pack is replaced after the other (how necessary this is in a derpy vehicle is another question), as well as allowing for the increase in capacity so long as there are empty backplane connectors.

Taking a cue from modern cylindrical cell based EV packs, I started with a modular frame structure.
Buttery holders
Slots were included above and below for balance leads and space was included for the battery tabs. Holes for M2 fasteners are also there for insulation mounting.

A few test prints later, this appeared:

It fits!

Buck, buck, buck, boost
I finally got around to tuning and laying out the hysteresis controller for the buck converter.


  • FOD8314 gate driver w/optocoupling and desaturation detection
  • Totem pole output capable of providing 30A of gate drive. 

One of the reservations I have about this board is the implementation of the gate drive power.

After looking to the ends of the earth for fancy DC-DC bricks, and inverting regulators beefy enough, I finally decided to cut my losses and go with a pair of isolated bricks since, well, it's easy. Further, it would cost me all of $0 instead of whatever Vicor or Murata want to charge.