pff7 said:
Instead of the regen going to to the battery,which everyone seems to think is just a waste, I wonder if the regen is enough to charge a separate small battery for a bike light? And could it be possibly be wired for such?
Run your light off the main pack. This way - even if the pack runs out of power, your motor will generate enough power from you pedaling forward to light the bulb; it might not be very bright though :|
Correct me if I'm wrong, but this would mean without moving light goes off,no?(especially if the main pack runs out of all power)----going to a (small)battery would still give me light when stopping at intersections,ect.
I have a DC-DC converter that creates 12V and 5V for my external lighting; the 12V is used for LED turn signals and brake lights, and the 5V runs my High-powered LED headlamps and Blinkies.
Example 1: Ideal Condtions
Imagine I am in deep space between two galaxies where the effects of gravity are close to nil, and also not affected by solar wind or any other distractions. In this void of cold space there is billiard ball with a thruster attached, the object is at rest. Let’s add 50W of power to achieve a velocity of 50 kph (31 mph); Acceleration and velocity begins at zero, and when we reach our terminal velocity we shut off the power: Acceleration goes to zero, though velocity is held constant. Because there are no resistances in the deep void, the velocity going forward remains constant and consumes no energy to maintain. Now let's come to a stop: We rotate the object 180* and then fire the thrusters using 50W of power: Acceleration goes negative, and velocity reduces up to zero – and we shut off the power.
Regen in this model is zero because we also did not have traction upon which to generate power when reversing. However I used 50W of power to go forward, and 50W of power to stop. Ideal and efficient use of power.
Example 2: The perfect ride
We're at sea level, standard temperature & pressure, windless day at Noon, and the road is brand-spankin’ new and quite level. The Ebike has just broken in and the bearings are rolling smooth as perfect as possible, as are the new perfectly pressurized tires having the least rolling resistance possible. The bike & I are at rest. Let’s add 1000W of power until we achieve a velocity of 50 kph (31 mph). The losses on this system are:
- Controller, harness wiring, and motor design
- Effects of Inertia upon the wheels rolling forward
- Resistance & slippage induced by traction of the tires against the asphalt
- Wind resistance at velocity
- Finally – the actual amount of power, including the inertia of the entire ebike & rider used to raise the speed from zero to 50 kph.
Other than the last item, the rest is wasted energy, also called “drag”.
Now that the bike and I are moving forward, our velocity immediately begins to degrade due to resistances within the system, what we call "drag". Unless we use throttle to maintain our velocity, the bike & I will slowly come to a stop. Therefore we apply throttle to hold our speed constant… for many miles.
We approach a stop sign ahead. Instead of mechanical brake, I invoke regen which turns the motor into generator/electric brake. The wheel resists changing speed in the same manner as when applying power to accelerate. Presuming the controller has the same efficiency using battery power to create forward motion as it does taking motor-generated power and pushing it back into the battery, and all other forms of drag remain the same, the bike will come to a stop much sooner than coasting. Let’s forget we have to use mechanical brakes to stop the last 5 kph.
Regen can only hope to recover 100% of the power used to provide forward motion. Because we are not in free space, because we have drag, all power used to hold the velocity constant
is not recoverable. Therefore on long trips the positive contributions of regen are very small. However, the situation is actually even worse than that because we have losses when trying to go forward from zero that have no hope of recovery, compounded by losses during regen/braking that also cannot be recovered. Let’s say the system is 60% efficient in forwards and braking. If I used 1000W to go forward, 400W was lost to drag, and 600W was used to propel the ebike forward. Now we brake: I can only hope to recover 600W, but because my system is 60% efficient, we only get back 360W because 240W was lost to drag.
There’s also another problem with regen: Unless the controller has been modified to convert high potential, the amount of instantaneous conversion is capped and shunted off as waste heat.
Imagine I had a dam that was just below my height and holding back a stream of water so that only a trickle came over the top. Regen attempts to capture energy and put it back into the battery. So, I bend over and with a drinking cup – scoop up some water, then lift lift lift the cup over the height of the dam and then dump the water back in. Lifting that cup of water
takes work,
takes energy. I didn’t get very tired from it cos it’s only a cup of water. But what if I’m dumping a lot of water, similar to an ebike going very fast down a hill: Lots of power there! My little cup can’t handle the flow. Let’s grab a bucket. I race like mad trying to capture all that flow and dump it back behind the dam. Pretty soon I’m real hot from working so hard, and I can’t capture all the flow.
Therefore, Regen can’t add significant range to an ebike because of inherited losses either by design, or by poor manufacturing quality, or by elements of weather, or by the riding conditions. The best that it can do is recover some of the energy used to accelerate the bike, and the source of that acceleration can also be from going downhill. If you start your journey from a tall hill and end up at the bottom, there’s a chance you could wind up with more energy in your pack than when you started. But the reality is that most people wind up with a lot less.
We’re not in space. There’s no free lunch. Regen works best for braking, and nothing more. And a well-maintained bike with proper tire pressure, along with good aerodynamics will have the best effects against drag.
Wired or straight-jacketed… my responses are the same.
KF
