Too Busy For Words - the PaulWay Blog

Thu 2nd Dec, 2010


I just thought of an idea for the E-bike. Have an RFID tag sensor in the bike and one or more RFID tags with things like the keys, my wallet, etc. The bike will still turn on with the key, but if the correct RFID tag isn't sensed nearby it will limit its top speed, acceleration, etc. So if something goes wrong with the sensor it's still driveable, but only to get to repairs. But if it's stolen it's near useless even if hotwired.

I've also worked out how to set up the switches on the bike. For cars, the key switch has four positions - lock, accessories, on and (momentary) start. A bike has three - lock, off and on; but a bike also has a separate motor kill switch (usually near the right thumb) and a (momentary) starter switch as separate things. A bike also has a footpeg switch - if you put the footpeg down and the bike is not in neutral, the motor will switch off (because taking off with the footpeg down is a sure way to have an accident). For combustion-engine vehicles, there is one electrical system - the 12v system; for EVs there is a separate (high-)voltage system to run the motor. (You're crazy if you try to run an EV on twelve volts, because the amperage the wires will have to carry to get the same amount of power will mean huge cables or things bursting into flame.)

So I have the key switch turn the twelve volt system on and off. This allows the headlight, signals etc. to work, and also provides 'system' power to the motor controller. The 'motor kill' switch then engages the contactor, a whocking great relay capable, in my case, of carrying 400 amps. This connects the battery to the controller and everything is ready for take-off. The 'ignition' switch is useless, but I'm tempted to repurpose it to cause a roll of thunder to be emitted from the onboard speaker, or flash the LED strip lighting menacingly, or activate the tesla coil, or shoot lasers or something. Or something useful, like put the motor into 'reverse' mode so that I can have power-assisted reversing.

There are a couple of criteria here. I want to make sure that the systems remain as 'standard' to a regular bike as possible, so I can lend it to a friend without a half-hour tutorial and so that I can hop from it to a regular bike without nuking the engine or something. This means the clutch lever might be dropped but I won't repurpose it (whereas on a scooter it's the rear brake and, when one goes to change gears, can result in amusing and health-endangering stopping). I also need to make sure that the lights and emergency indicators can remain functional even if the main 'motive power' battery is dead (or at least completely unusable - e.g. fuse blown) - this is for the Australian National Code of Practice for building electric vehicles.

Unfortunately for me, I bought a DC-DC converter that outputs 12V in the mistaken belief that I could simply wire that up to the power battery and have power to drive the lights even if it was too low to drive the bike. It turns out that I have to have lighting as a separate circuit so that even if something goes horribly wrong - one cell dies, a cell interconnect fuses, a bit snaps off somewhere, or even just the main fuse goes - I can still be illuminated at night. So I do need a (small) separate 12V battery; and because 12V lead-acid (and similar) batteries charge at 13.4V, the 12V that the DC-DC converter outputs is not enough.

Anyone want to buy a barely used 150W DC-DC converter with an input from 84 to 120 volts?

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