Imagine cruising through the streets without ever having to worry about charging your ride. Sounds like a dream, right? Well, thanks to some ingenious minds
If a 100kg person + bike was going 50kph and came to a stop in 5 seconds, the average power generated would be 2kW.
I consider that to be a fairly extreme circumstance and requires 100% efficiency. A typical e-bike battery is around 500Wh, so that’s a 4C charging rate which isn’t really that extreme especially if it’s only maintained for a few seconds.
Now in a more sustained situation, it might be helpful. If you’re trying to maintain a comfortable 30kph while descending a 45% grade, that’s a continuous 4kW that needs to be shed. I suspect a lot of it would go to wind resistance, but if 100% of it went into your battery, a standard lithium pack may struggle to keep up.
So maybe it’d help in extremely hilly situations, but I’d still like to know what it weighs. Supercap specific energy per wikipedia is around 90Wh/kg vs 270Wh/kg for lithium ion. So a cap weighing the same as a 500Wh e-bike battery would have a capacity of around 160Wh.
In the above descending example, it would be fully charged in 2.4 minutes.
So I guess it depends on the scenario.
The other thing to consider is comfort. It’s generally more comfortable to coast to a stop on a bike (burn off energy to wind resistance), and assuming the bike has conventional brakes, I wonder what it would feel like switching from regen to friction braking.
The current a battery can accept/provide tends to scale with the size of the battery. So rather than measuring it in Amperes, it’s usually measured in C. 1C means that the battery will be full charged or discharged in 1 hour. 4C means it’ll be charged in 1/4 hour. The charge rating tends to be lower than the discharge rating though it depends on the cell.
Basically, you take the battery capacity and divide it by the charge rate. If you exceed the C rating of the battery, it could cause it to overheat or even catch fire.
When it comes to higher performance requirements (like in drones), you can get insanely high C rates like this though those batteries aren’t typically designed to survive too many charge/discharge cycles.
Interesting point. Did some napkin math on that:
If a 100kg person + bike was going 50kph and came to a stop in 5 seconds, the average power generated would be 2kW.
I consider that to be a fairly extreme circumstance and requires 100% efficiency. A typical e-bike battery is around 500Wh, so that’s a 4C charging rate which isn’t really that extreme especially if it’s only maintained for a few seconds.
Now in a more sustained situation, it might be helpful. If you’re trying to maintain a comfortable 30kph while descending a 45% grade, that’s a continuous 4kW that needs to be shed. I suspect a lot of it would go to wind resistance, but if 100% of it went into your battery, a standard lithium pack may struggle to keep up.
So maybe it’d help in extremely hilly situations, but I’d still like to know what it weighs. Supercap specific energy per wikipedia is around 90Wh/kg vs 270Wh/kg for lithium ion. So a cap weighing the same as a 500Wh e-bike battery would have a capacity of around 160Wh.
In the above descending example, it would be fully charged in 2.4 minutes.
So I guess it depends on the scenario.
The other thing to consider is comfort. It’s generally more comfortable to coast to a stop on a bike (burn off energy to wind resistance), and assuming the bike has conventional brakes, I wonder what it would feel like switching from regen to friction braking.
Can you explain what is meant by a “4C charging rate”?
The current a battery can accept/provide tends to scale with the size of the battery. So rather than measuring it in Amperes, it’s usually measured in C. 1C means that the battery will be full charged or discharged in 1 hour. 4C means it’ll be charged in 1/4 hour. The charge rating tends to be lower than the discharge rating though it depends on the cell.
Basically, you take the battery capacity and divide it by the charge rate. If you exceed the C rating of the battery, it could cause it to overheat or even catch fire.
When it comes to higher performance requirements (like in drones), you can get insanely high C rates like this though those batteries aren’t typically designed to survive too many charge/discharge cycles.
Thank you!