I recently moved into a new home that is on a hill, which means that I always need to ride downhill when I take my ek8 out. First 200m is quite steep and then it gets gradually flatter.
I would like to avoid overcharging the batters and prevent over-stressing it so I am not charging it 100%. Currently I stop when the voltage of individual cells is around 4,08V. This gives me plenty of slack but I also loose a bit of range. Any thoughts on where the sweet spot would be?
First time when I rode downhill with an almost full charge I noticed that Davega showed battery voltage that was slightly higher than the maximum voltage of the pack (50,4V/12S) while breaking. I freaked out and stopped and the voltage obviously dropped back under the max. In terms of over-charging - is the short term spike (while breaking) the important one or the state when the battery is idle? With other words - is it a problem if the battery sees higher voltage than max during breaking or it becomes a problems only after the cells would go over that voltage when not under any load?
Dude these are awesome questions. I have no idea other than guessing about the answers so I won’t- but I’ll be watching for the community wisdom. Love the forums! Good luck.
You definitely want to avoid going over max voltage. I would suggest charging to 85-90% and use your first hill descent to get a few extra battery % and be safe.
I think people will often overcharge to maybe 4.25 when charging fast and the cells will drop back down when off the charger.
Jamming in high amperage when already almost at full charge is not the best time to do it. What current do u see passing? If u don’t know that would be worth finding
Maybe feel the cells at the bottom of the hill and see the temp
This is a horrible problem to have; I’ve dealt with it.
You can make what I call a brake burner, or you can not charge all the way, or you can ride uphill a bunch first (if you’re not at the very top) and then turn around and go all the way down. Any of those 3 will work.
maytech used to sell some overvoltage burner
edit found it :
note : never tried it, no idea if it does actually work, also it says up to 10s
I thought Maxkgo sold one, but now I can’t find it
Spintend sells one. I have it but never used it.
Oh, that’s why I couldn’t find it! It’s Spintend not Maxkgo.
I have one of these in Chortl.
This one is 10S to 20S configurable, and not locked at 10S like the Maytech one.
This module is only part of the solution, though. You’ll also need a big heatsink and some chonky resistors… and you need to know how much current you’ll need to burn off, to drive the design of that part.
You can get the energy produced from your descent (the gravitational potential energy) in Joules by MGH=J where M is your mass in kilograms, G is 9.8m/s^2 (acceleration of gravity) and H is the height of the hill in meters. To convert Joules to watt hours its J/3600=Watt _Hours. You could fully charge so you’re balanced and then use some type of external load to drain the battery by this amount before you head out so you have some room in the cells for your regen braking.
did you ever see it actualy do something ? (genuine curiosity)
Yes, I also connected a buzzer as well as a resistor, so you can hear when it starts burning off energy, and also so you can check to make sure the heatsink isn’t getting too hot, because it can in a hurry.
It’s not a binary on/off though, the Spintend one uses a duty cycle that increases as the overvoltage situation intensifies.
I no longer live on a huge hill though…