Charging current max for cells: 16s1p 50ah lifepo4 is most common battery type, but it varies for operator to operators. Theoretically 1c charging would theoretically allow 50amps of charging.
Then you could safely do 50A of regen current. Keep in mind as cells age they can do less and less discharge or charge current (their resistance grows, so votlage sag or rise and internal heating increases; also their capacity grows less and less at the same time)
How much braking force that gets you depends on the torque the drivetrain and motor produce with that much drive current--however much torque that is at the wheel is how much torque you get when forcing that much current back into the battery.
If the batteries are close enough to full then the current they'll accept is less than that, so braking will be less. As they get closer to empty they'll more easily accept that much current, and the easier it is to generate it by the voltage difference between the generated votlage at the motor/controller and the battery's lower voltage.
The BMS is something I’m trying to get more information on about max charge rate. Back in the day (2018 to 2020) I helped oimported a few hundred of these types of 16s1p 50ah lifepo4 batteries. The BMS has a common charge / discharge. They were originally used in solar storage applications, but with some modification to the packaging worked great for pedicabs. Continuous discharge is 50 amps, with bursts of 100amps. I’ve contacted our supplier about charge max and am waiting to hear back.
Best guess is charge is more like a tenth to a fifth of that--that's a common ratio, since ti's also a common ratio for cells' capabilities.
Depending on the charge current needed for the braking force required,
Currently the controller does no regen, and the motor chain drive has a freewheel. I’m wanting to let people get away from the motor freewheel and replace with a solid sprocket for added reliability,
Those are both easy enough to change. Does the pedal drive have a separate freewheel? If not, you might want to add one.
with the added benifit of regen braking. I am hoping to find the “best” i.e. most powerful regen controller and BMS (if necessary) in the 50 to 100 amp output range. Of course, lower price is better, and the fewest pieces (points of failure) that have to work together to be functional is best.
Keep in mind the controller probably needs to be one that can handle high ERPM as well; many are suitable for hubmotors but not always for middrives, especially with high motor RPM and number of pole pairs.
I also do highly recommend the variable control vs the on/off control, both for controllability of the braking force and for reducing stress on the drivetrain from shock loads.
Most FOC controllers would be suitable, as long as they can do the current and voltage required. VESC variants, maybe the Phaserunner or various other ASI variants, or if you don't mind the hefty DIY, even the Lebowski brain chip / board (which you'd have to build a controller around) or various other opensource FOC projects.
Which one is most suitable will also depend on the traction capabilities required, as well as what else is needed (like throttle, PAS, any display or other features, etc).
