USB-C PD 3.1 - Charging at 240W 48V

[Username1]

It seems this hasn’t been broadly discussed here. So from what I’ve gathered so far (correct me if I’m wrong)…

The standard supports 5a at up to 48v. It also supports 0.1v increments between 15-48v (with a minimum accuracy requirement of 0.02v).

This seems suitable for charging 11s batteries (46.2v @ 4.2v per cell), or even 12s (48v @ 4.0v per cell). The BMS would just need to communicate with the charger to request the appropriate voltage as it charges.

Imagine being able to charge your e-bike fairly quickly using USB-C, via a small gallium nitride charger. Is there any reason this can’t be done in theory?

 

[harrisonpatm]

Imagine being able to charge your e-bike fairly quickly using USB-C, via a small gallium nitride charger. Is there any reason this can’t be done in theory?

In theory? No, it would certainly work in theory. 48v is 48v.

In practice?

The BMS would just need to communicate with the charger

That's the sticking point. There's too many different BMS's out there, w different manufacturers. I could imagine (again in theory) that a single ebike manufacturer could develop an ecosystem of batteries w a bms that would have a USBc port, and sell/package it with a charger that could also charge your phone.

But then I come to the reason why I really think this wouldn't work, and why I wanted to respond to the post. If you make an ebike battery with a USBc port, some idiot is going to try to charge it with a cheapo dollar store charger that has insufficient protection and catch something on fire.

 

[Username1]

But then I come to the reason why I really think this wouldn't work, and why I wanted to respond to the post. If you make an ebike battery with a USBc port, some idiot is going to try to charge it with a cheapo dollar store charger that has insufficient protection and catch something on fire.

I thought the whole thing with USB is that it’s basically fool proof. The charger and device must communicate before any power is exchanged. When have you ever heard of even cheap USB chargers causing problems?

If anything I thought this was a safer and more fool proof solution. Commercial e-bikes almost always instruct to only use the stock charger, because there’s a real risk that a layman uses a different voltage charger (or even too many amps for a small pack). I’m not sure if most BMS even protect against that user error.

 

[Steakbroetchen]

It is totally possible to do it safely. An intelligent BMS could determine the charger capabilities and/or stop charging if a charger can't provide the right voltage.

It would be even possible for 13S or higher, if it does not need to be superfast: At ~3.7V a common 18650 is already about 60% full and charging current is already decreasing.
AD LTC4020 standalone charge IC for example is limited to 500mW power dissipation, which should manageable inside a battery, maximum currents can be set and thus power dissipation can be lowered, charges batteries up to 55V, and takes variable input voltage from 4.5V to 55V, the higher the input voltage the better the efficiency and maximum charging power.

Or TI BQ76972 for up to 16S, either standalone or host controlled by an MCU.

Combined with a 240W sink, like shown in the REF_ARIF240WS3 reference design, which is made for such an application:

The reference design board REF_ARIF240WS3 further extends existing power sink capabilities of the EZ-PDTM PMG1 MCU family of high-voltage microcontrollers from 140W to 240W, making it ideal for such power demanding and fast charging applications as: Light electric vehicles (eBikes, eScooters and personal mobility devices),[...]

I've seen this board at the embedded world conference this year, quite impressive.

To summarize, from a technical view it's possible, but it is quite challenging and probably too complex and difficult for most battery suppliers.
And with this solution there are more electronics in the battery itself, instead of the charger.

But if one settles with something more moderate than 240W, I think it would be even possible to DIY it.
I've ordered an empty battery case together with the regular battery, after building and setting up the bike I think I'll look into building a lightweight battery with USB-C input for travelling. Maybe in the ballpark of 60W charging.