You are here

brake switch/brake regen question

3 posts / 0 new
Last post
smallbikefun
Offline
Last seen: 7 months 3 days ago
Joined: 2024-02-13 04:46
Posts: 3
brake switch/brake regen question

hi im wondering if someone can answer some braking questions about an ebike project im working on. im using a flipsky 75100 on a 14" bike that has disc brakes. i built a batt pack for it from sony vtc4s (16s8p). i dont have any brake switches hooked up.  the disc brakes work ok and i was planning on upgrading to hydraulic brakes eventually. but in the meantime my concern is if the voltage created from the motor during regen could damage the controller.  i have motor max brake and battery max regen currents set to -80 amps, but i dont feel any regen braking when letting off the throttle. i only have the conventional ebike throttle hooked up in current mode.  i imagine its necessary to have the brake switch or another hall/brake lever installed for this option?  with my current setup with no active electric braking, should the excess voltage when letting off the throttle or going downhill still go back into the battery?

vadicus
Offline
Last seen: 2 months 1 week ago
VESC Free
Joined: 2018-08-17 07:26
Posts: 431

vct4 cells have the max safe charging currents of 2A without auxiliary cooling. 8P x 2A = 16A max charging current per battery pack. If you push 80A (more than 4x) into the battery pack, you should carry a good fire extinguisher, although, I am yet to see any extinguishers that actually work against lithium cell thermal runaways. It continues to burn even fully submerged under water. 

So, you want to set you negative battery current to less than 16A, ideally somewhere below that. For the motor current, you can set whatever but generally, 70-100A would be good values. 

If you want the bike to brake when you release the throttle, you need to set up your ADC input to Current No Reverse Brake Center and set throttle voltage correspondingly to activate brake when you release the throttle. However, for the bike application, what works best is to have two separate ADC inputs, one for the accelerator and one for the brake, so you can modulate the amount of braking power. You can also connect your brake input to the analog sensor on your brake lever, so it activates regen before it activates disk brakes. A well designed and configured controller should not blow up on regen. It comes down to how much reverse current you battery can absorb and how well the DC link capacitor bank is designed to prevent voltage spikes.  

 

 

 

NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)

smallbikefun
Offline
Last seen: 7 months 3 days ago
Joined: 2024-02-13 04:46
Posts: 3

thank you for the input vadicus. i think i had the actual electrical braking force and braking regen mixed up in my head.  i did end up finding the option for Current No Reverse Brake Center explained in a youtube video, but heres another question for you:  if i used the Current No Reverse Brake Center option and kept my brakes mechanical, wouldnt it consume less battery in comparison to adding a hall brake lever or thumb throttle for braking with Current No Reverse Brake Adc 2?  it is my understanding that with the adc input 2 used its just accelerating the motor in reverse and would consume the battery just like acceleration would.  so my decision would have to be based on whether i want to use more battery or replace brake pads more often