I know little about engineering electric vehicles, but I was riding in to work and it occurred to me that when I stomp the gas I am deep drawing the battery, and when I am emergency braking with the motor I am generating more electricity than the battery can take. Would it not make sense to use one of those SuperCaps that can hold all the electricity generated by the braking to reuse during the acceleration?
I guess the computer would need to know about it, and has been calibrated to understand the batteries only. The voltage going WAY up when initially braking and slowly charging the battery pack would really confuse the computer.
Just curious what others think about the use of capacitors in an electric vehicle...
-Randy
The controller is set for what is appropriate for the pack, so if you changed the pack to supercaps/lithium/whatever-comes-next, you could get more acceleration and regen capability, but you would have to have access to the controller's programming. As it is, Vectrix does not allow full current from a dead stop - I don't know when the limitation cuts out, but it is at a level that they felt you wouldn't be able to break loose the tire.
The only issue with this is the power density of lithium batteries is higher than "super" caps
you're better off just putting more battery in.
additionally - the vectrix can't regen more than the battery can take - it isn't that powerful (most I have seen is 110A @ 140v, braking at 100kmh). you're also limited by traction on regen
Actually, the vectrix does allow full current from a stop - it's limited by the 300A IGBT module
It could be improved with better firmware (mainly doing field strengthening to increase the back emf, to increase low speed acceleration), but the MC is the bottleneck here
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Hmmm.... I thought I read, here or elsewhere, over the years, that originally the bike let you pump all the power you wanted, but people were killing their battery packs, so they had changed it in firmware where now I can barely drop my wife off the back as I accelerate out of a light. I don't even bother moderating my acceleration usually as my bike just appropriately moves out at full throttle. I thought it was related to the updates (2) that I have had over the years from the original 2007 firmware. Perhaps the battery packs are just aging or I am getting fatter.
-Randy
______________________
I also own a 2018 Tesla Model 3 and a 2012 Mitsubishi iMiev
Actually, the vectrix does allow full current from a stop - it's limited by the 300A IGBT module
It could be improved with better firmware (mainly doing field strengthening to increase the back emf, to increase low speed acceleration), but the MC is the bottleneck here[/quote]
Hard to believe I have a full 300A on tap! I read in some analysis (granted, online) about limitation at takeoff, and I believed it because, from a stop, the Vectrix is no better than an Xtreme XM3000, but it "winds up" soon after that.
The only change was the min battery voltage was raised from ~104v (I forget the actual value) to 108v
If your battery is/was marginal, this would result in reduced acceleration.
If not, then no difference
They did back the acceleration off slightly at high speed, but I haven't been able to produce a measurably different result between the two firmware versions (on my lithium bike)
there's a myth that all electric motors develop peak torque at 0 rpm
basically they don't (This is only true for DC motors used without a motor controller, and certain types of induction motor operated direct online/no controller)
in the case of both the vectrix, and the extreme scooters, they both used permanent magnet synchronous motors.
so basically acceleration is proportional to *average* phase current.
the trick part is heat buildup in the wiring (and to a lesser extent the motor controller, specifically the gates/IGBT) is proportional to the real mean square current (I'll get back to that in a moment)
the thing is you are limited in *peak* current by what the gates in the motor controller can handle.
the motor inductance determines how fast the current rises when the controller puts the full battery voltage across it (2 henrys means it takes 2V 1 second to increase the current by 1A)
so, a simple example with a 300A motor controller and motor with 0.00013333 henries of inductance and negligible resistance and pretending it's DC (because AC will just make the example too complicated) :
just starting off, the motor is at 0A with 0V back emf (motor is stopped), and the controller is set to full throttle.
the controller turns on and puts 120V across the motor.
at 15000 Hz, by the time the controller turns off, the motor is at 300A.
the contoller turns off, and current starts to fall.
given the low speed acceleration is so low, it is likely the current has fallen back to 0A again before the controller turns back on.
for easy of calculation, we will say this happens as the controller turns back on.
so in that situation, the peak current is 300A, the controllers limit.
The *average* current is only 150A - so not so great acceleration.
The RMS current is 225A - so stuff is getting hot
now say we are operating at the max power and torque point (70kmh in the case of a stock vectrix with a good battery)
the motor back EMF is around 115v and the controller is still cutting off when current reaches 300A.
*but* because the effective voltage acting on the inductance is now only 5V (120v battery voltage - 115V back emf), the current does not rise nearly as fast. what this means is the controller doesn't turn off, meaning the current doesn't fall.
so 300A peak, means roughly 300A average, which means good acceleration.
now, you can improve upon the low end acceleration, without increasing the phase current, by either increasing inductance, or increasing back emf.
not much you can do with inductance (without adding some seriously heavy bits)
but with some different firmware, the back-emf can be increased, by way of field manipulation.
the Vectrix controller already does this by weakening the field above 70kmh, to hold the back emf at around 115v.
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks, that was informative, and explains why the Zero X with PM DC system had so much kick with 300A and 48V (that, and a third of the weight).
It really was informative, but not being adept in motor theory I was left lacking understanding. Perhaps I'll have to wait for the movie...
Did you say the Zero X is 1/3rd the weight of a Vectrix? Wow! That might be the bike to hang off my RV when I road trip!
-Randy
______________________
I also own a 2018 Tesla Model 3 and a 2012 Mitsubishi iMiev
My other EV project is a 2009 Zero X - it may had its "compromises", but it did use a readily-available PMG-132 PM motor and AXE 48V/300A controller, so no complex programming like the Vectrix or proprietary software anywhere, and true rubber-burning traction (actually, you usually wheelied off the back).
Originally meant for off-road, mine had the road legal minimum add-ons...but not a speedometer/odometer, or a very accurate capacity meter. The pack was under 50# and the rest of the bike just over 100#. Unfortunately, the pack itself was another horror story of engineering near-sightedness, and I have made a rough replacement with 14s3p of Nissan LEAF cells that recently got its snug insertion, but little else as I contemplate high and low voltage rewiring and more useful instrumentation. I hope to turn down its massive torque with a a larger sprocket on the motor in exchange for a higher top speed (>70mph if nothing dies a glorious death).
But despite their complexity, the Vectrix are easier to play with using the scooterdiag to access the firmware.