New Project: Compact 3.7kW charger & configuration

After installing TW560’s latest battery pack and testing it thoroughly, one of the points I definitely want to address is reducing full-charge time. With a potential maximum of 18.9kWh having to go into the batteries, my current setup with 6.8kWh peak charging capacity means I’m charging for at least 3 1/2 hours.

Adding chargers is simple, but there are some limitations to consider:

  • Weight: my current chargers are at about 12kg each, adding more isn’t really an attractive option
  • Price: Each charger cost me CHF 960, extra chargers will not be substantially cheaper if I insist on a hardened automotive type.
  • Complexity: More connectors mean more points of failure
    …and, last but not least, the most important point:

  • Maxiumum charge rate: What is allowed/recommended for my cells?

My current setup with 12A from TW560’s inverter and 2x10A from my trusty wide-range Chinese automotive chargers gives me a total of 6.8kWh true charging capacity.

My 35E cells allow for a maximum charge at 0.59C. Given my setup, I could charge at a maximum of 10.6kW without permanently damaging the cells. The documentation explicitly says that 0.59 is not for cycle life. Since I will not be fast-charging on a regular basis, this isn’t a problem.

I raised this with Dreifels and they then told me that there is a newer generation of the chargers I have in my TWIKE available. The charger is half the size and weight and outputs up to 3.7kW, finely controllable via a CAN bus.

They added that they hadn’t had the time to look into this for the moment and more specifically, how to control and configure the charge via the CAN bus.

Since I’ve got an idea how to do this (years ago, I was flipping bits in my electric Kangoo’s ECU’s via the OBD2-port), I volunteered to have a look into how we could get this working for a TWIKE including designing simple stand-alone electronics and user interface. After making sure that this wasn’t a high-priority project for them – I’ll be off to the US for over a week and traveling regularly during the next few weeks – I took the charger with me and started the project (…one more πŸ™‚ )

Ah, my trusted CAN bus shield

Ah, my trusted CAN bus shield

With my Arduino and a CAN bus shield, I started sniffing the bus, just to discover that it communicates at a strange speed with strange packet lengths.

RTFM, then πŸ™‚

I'm a sucker for chinese technical documentation

I’m a sucker for chinese technical documentation

The Chinese documentation is written in the usual Dadaist manner and not always without ambiguity πŸ™‚

Welcome to my lair :)

Welcome to my lair πŸ™‚

As always, debugging these things take time … which I unfortunately don’t have much of. (And since I, nowadays, sleep very well, my nights aren’t available anymore for complex projects πŸ˜‰ )

I’ll post updates on this project as they occur.