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Comment by tim333 | Hacker News Reader

I'm looking at a 2nd hand ebike for sale and the battery on it talks to the computer on the handlebars and reports its charge level. It's not like a car battery which is presently just a battery.

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It's probably using SMBus -- a standard protocol for exchanging information like state of charge: https://en.wikipedia.org/wiki/System_Management_Bus

If it's not, then I agree that the proprietary shit has to go.

Ah - thanks. I'm new to ebikes.

It’s most often a custom protocol, every now and again it’s CANBUS.

Quite often it also needs an activation code or the BMS will kill output on a draw >5-10A after a few seconds

It is still just a battery. The battery on that ebike like every other ebike on the market is actually exactly the same: an array of common 18650 batteries packaged into a plastic “pack”.

It’s been shown that we can write standards for these things. In fact you would build on an existing baseline like i2c. they almost certainly already do already

The CDC (charge-discharge controller) of many BMS (battery management system) devices can already communicate the charge state. My home built e-bike uses a one-wire protocol, newer ones use a serial protocol. Even the plugs have become standardized these days. There are so many manufacturers selling components and kits, and 99.9% of them interoperate with components and kits from other manufacturers. Pick the bike computer you like, the form factor of the battery pack, size of battery pack (they all use 18650 cells anyway), BMS, CDC, wiring harness, motor. It is no more complicated today, and actually far easier so long as you size the motor to the bike frame and the battery to the motor, than assembling a desktop computer.

I've gotten really into commuter biking, and I have a nice frame sitting there. I can solder, build power and BLDC motor controllers, and do light machining. but somehow the idea of learning wheel building is just too involved for me :-)

do you have some references? I would love a little hub motor for the hills.

You don't need to do any wheel building yourself. You can buy the hub motor pre-installed in a wheel. Simply purchase the proper diameter wheel for your frame. The only aspect to keep in mind is to get the right sized motor for your frame. Too many people chase the "big number" hub motor wheel, picking up a 3KW or 5KW motor, and installing it on a frame that will shake itself apart, or a frame that isn't made to travel at 40MPH/60KMH with brakes incapable of handling that speed. If you do end up purchasing just a hub motor, and want to fit it to your current wheel, find a good bike shop that does wheel rebuilds, and have them put the motor in for you and tension the spokes. Takes like an hour of their time. My old motor is 500watt, which gets me a top speed of around 18MPH/30KPH on the flat and a 15 mile range. I am contemplating going to a 1KW motor. Eventually. Maybe.

Many cars require that the battery is coded to the car. The reason (excuse) is auto-stop/start.

BMW have been doing this for over 20 years.

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