I actually did some research before posting, and found a lot of threads mentioning supercaps indeed. From what I gathered, the consensus is that supercaps are no match for li-ion in terms of energy storage. Yet the idea to limit their application to capture break power and give a boost during startups keeps resurfacing as viable. hence me question. Has there been any field test ?amberwolf wrote: ↑May 11, 2018 4:58 amFor some existing info, theres a number of threads discussing the basic idea, such as this one
finding the others may require a bit of poking around, mostly they shoudl be findable by a search on titles or first posts of threads, displayed by topic, search terms of supercap* or ultracap*, possibly in combination with regen* (but not always).
That assumes the cap bank can be drained to 0V to extract all the stored energy, which isn't the case without a powerful DC-DC converter. So you need to recalculate for the voltage range actually used.
In general, I think resizing batteries and/or choosing the right battery specs are an easier way to accomplish this. The electronics to selectively route energy to supercaps rather than batteries is fairly complex, and supercaps have their own issues (i.e. voltage range.)
No you wont be limited by the current rating of the charge input, as the regen current flows through the same wires, only in reverse direction.
So how does balancing work in regen mode ? Not at all ?
Regen pushes back about 2% in my average ride and I would not be solving an in-existent problem of balancing cells at regen (which occurs anyway, because BMS does not care where the current comes from, is it charger or controller). You must be living on peak pike to care where to put excess regen energy in. I live on the hill already and just have mediocre regen the first sloop, because my cheap Xiechang controller has regen limit voltage set, then I hit throttle for 30 meters and next sloop of 200m is not enough to limit my regen by overvolting to set point.qwerkus wrote: ↑May 12, 2018 8:11 amSo how does balancing work in regen mode ? Not at all ?
Also it doesn't change the fact that i'd need a programmable controller - or an additional device between the controller and the bms - to regulate regen bursts.
I'm going to have a closer look at the open source VESC. There is a post where user Addy says he successfully implemented progressive regen on a VESC. Maybe that config could be tweaked into a "fast-charge" regulator.
See earlier post: working on a gear hub with regen. Wondering if it is possible to recover the energy from short bursts in a stop and go config. The manufacturer claims power levels are too high for the battery to handle it. Hence this investigation.
In a literal analysis I think the manufacturer is correct. The average ebike pack is often low-powered, maybe only 3 or 4 parallel low-discharge rate 3400 or 3500mAh cells with a maximum charge rate of 1C (~3.5A) on the datasheet, so any more than 10-12A of regen (entirely plausible) looks like too much.qwerkus wrote: ↑May 12, 2018 11:32 amThe manufacturer claims power levels are too high for the battery to handle it.
I've been doing some maths: if I drive 8.5m/s (30.6km/h) with a combined bike + driver weight of 100Kg, that's roughly: 3612.5 J of kinetic energy. (KE=1/2*m*v^2) If the generator (motor in regen mode) and the loading circuit has an (optimistic) efficiency of 50%, that's 1806J to cope with over 1s (averaged brake time) this means a burst of 1.8KW
My impression is that manufacturers try to reduce warranty cases as much possible and save on every end.