4 ms·

It's basically impossible with our current electronics to only charge the battery to 95% and leave headroom for regen braking. We could let the battery charge

by skdoo 12y ago

It's basically impossible with our current electronics to only charge the battery to 95% and leave headroom for regen braking. We could let the battery charge to 100% and then bleed off energy slowly, but most users keep it charging and then start riding immediately after unplugging it. The other option is to divert braking energy to heat instead of recharging the battery. But on steep hills, braking energy can reach hundreds of watts, which would quickly overheat the electronics or motors without regen. This is an issue that affects a very small subset of users, almost all of whom live at the top of a hill - definitely a unique corner case to design for. We tell them to discharge the battery by running it uphill or on flats briefly to discharge the battery enough to allow some regen headroom.

mik3y 12y ago
Naively I would have guessed you include something like a 1kW resistor + heat sink package, and divert to that. Assuming such parts exist, are they just cost prohibitive, or is there more to it? (Thanks for taking questions!)
- skdoo 12y ago
  Yes, but the added weight of something as large as a 1kW resistor compromises the portability of the board. We're looking into how to do this without adding weight.
  - tomsaffell 12y ago
    Would it be possible to arc it over an air gap? I.e. allow the energy be dissipated over the resistance of the air? I have no idea whether the power numbers work out, and maybe you'd need to step up the voltage, which adds complexity. Just a thought..
    - skdoo 12y ago
      Interesting idea. I think you won't be able to dissipate enough heat this way, but I'm not sure.
  - mikeyouse 12y ago
    A bit of a higher price point, but some Formula 1 teams went through similar issues with their KERS system in regards to performance and weight. I think everyone converged on extremely high speed flywheels, but there was a fair amount of work into ultracapacitors. I'd imagine a 1,000F ultracap could handle the ~20-30 seconds of 100W braking power at well under a pound? I know nothing of their reliability or availability and I'm sure you guys have done your own research but just thinking out loud.
    - skdoo 12y ago
      There are some excellent cells out there developed for KERS. One example: http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells
  - beambot 12y ago
    Random thought: Would it be possible to incorporate a resistor directly into the board stackup -- eg. the "board" part itself becomes a large carbon resistor?
    - skdoo 12y ago
      Cool idea! I'm not sure about the conductivity or thermal properties of structural carbon fiber, but it may end up being a good option.
btbuildem 12y ago
what about charging the onboard laser?
- skdoo 12y ago
  One of my cofounders worked on this before we started Boosted. http://en.wikipedia.org/wiki/Boeing_YAL-1 http://en.wikipedia.org/wiki/Boeing_YAL-1

by skdoo 12y ago

mik3y 12y ago

Naively I would have guessed you include something like a 1kW resistor + heat sink package, and divert to that. Assuming such parts exist, are they just cost prohibitive, or is there more to it? (Thanks for taking questions!)

skdoo 12y ago
Yes, but the added weight of something as large as a 1kW resistor compromises the portability of the board. We're looking into how to do this without adding weight.
- tomsaffell 12y ago
  Would it be possible to arc it over an air gap? I.e. allow the energy be dissipated over the resistance of the air? I have no idea whether the power numbers work out, and maybe you'd need to step up the voltage, which adds complexity. Just a thought..
  - skdoo 12y ago
    Interesting idea. I think you won't be able to dissipate enough heat this way, but I'm not sure.
- mikeyouse 12y ago
  A bit of a higher price point, but some Formula 1 teams went through similar issues with their KERS system in regards to performance and weight. I think everyone converged on extremely high speed flywheels, but there was a fair amount of work into ultracapacitors. I'd imagine a 1,000F ultracap could handle the ~20-30 seconds of 100W braking power at well under a pound? I know nothing of their reliability or availability and I'm sure you guys have done your own research but just thinking out loud.
  - skdoo 12y ago
    There are some excellent cells out there developed for KERS. One example: http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells
- beambot 12y ago
  Random thought: Would it be possible to incorporate a resistor directly into the board stackup -- eg. the "board" part itself becomes a large carbon resistor?
  - skdoo 12y ago
    Cool idea! I'm not sure about the conductivity or thermal properties of structural carbon fiber, but it may end up being a good option.

btbuildem 12y ago

what about charging the onboard laser?

skdoo 12y ago
One of my cofounders worked on this before we started Boosted. http://en.wikipedia.org/wiki/Boeing_YAL-1 http://en.wikipedia.org/wiki/Boeing_YAL-1