e-beach said:
But here is the thing, and please let me be perfectly clear....I am not looking for free anything! Only looking to harvest what is already there.
That's the thing-- if you harvest it to move it to another place, it is no longer in the place you harvested it *from*. If you take it from the motor's rotation (BEMF or otherwise), it's not in the motor anymore, and the motor will slow down.
The only way i can think of that you could take any energy from the motor without slowing it is to take the waste heat away from the motor and use that to do whatever you want. Such as putting Peltier junctions within the motor, and tapping the voltage across them. While they are very inefficient, at least taht would not cause the motor to slow down by taking that energy away.
So I hung an 18" x 5' piece of tin foil from a book shelf in a second story bedroom where I live. The foil hung about 10 inches away from a window of about the same size. The window has a venetian blind in it that blocks the sun most of the time. I soldered a thin hookup wire to the center of the foil and then attached the other end to the positive lead of a small capacitor. I then attached a wire to the negative end of the capacitor, ran it out the window and attached it to a short piece of iron re-bar that I had pounded into the ground. Much to my surprise, the capacitor started filling. It didn't fill very fast until I put a diode in line with the positive lead. (apparently cosmic energy is AC)
Almost certainly, what you're picking up is not "cosmic energy", but rather just radio waves--stray RF that is everywhere nowadays, because of power lines, radio stations, tv stations, and the bajillion devices we ahve that transmit radio power. All of those things would be AC power. You can make the receiver more efficient if you use separate frequency-tuned antennas, like the old common roof antennas for tv before satellite and cable became so common. Find out what the highest power frequency bands are in your area, then build antennas suited to each one. Then use a half or full-bridge rectifier rather than a single diode, and use (IIRC) germanium ones as they have the lowest voltage drop, and you will harvest (probably) more energy than with the single diode (whcih basically rejects half of the energy coming in).
Hook up a piezo speaker or headphone earbud (because it's high resistance and doesnt' need much current, so should be louder than a coil-type speaker in this case) to that instead of a battery and you'll probably hear some of the radio noise that is from AM transmissions.
Some of that radio noise is actually "cosmic" in origin, such as that generated by the sun's magnetic field interactions, and that of Jupiter, Saturn, and even Earth itself. (and other stars and whatnot)--but that energy is pretty faint compared to all the RF junk we generate ourselves.
Many people have accidentally "discovered" this source of energy, and come up with various ways to harvest it, but they ultimately come down to still requiring an external source of energy to harvest, and it is one with a fairly low energy density.
If you take a fluorescent tube light, not connected to anything, you can make it light up by holding teh tube and walking under some power lines, especially near a substation. This is another source of "free power" but really you are tapping the field off the wires, and the power company frowns upon that, because it takes energy from their system--sure, its' nto much, but that's the source of the energy to light the bulb.
It may also be a bit of energy from the earth's magnetic field itself, which is different from daytime to nighttime, as it si more compressed by particle radiation from the sun during the day. Depends on exactly what the foil is doing and probably even how it is aligned. But that would be a DC component, and would require the field lines move to be cut by the foil in order to generate a current, so I expect you would see more of this component during the twilight and dawn hours as the local field is pushed around more, and probably not very much (if any) unless you are either near the magnetic poles, or one of the various magnetic anomalies where field polarity is reversed from normal.
It is an easy experiment I encourage anybody out there to try it and post your results. Some time in the new year I am going to fly a tin-foil kite to see if the current is stronger at altitude.
I suspect you will find it is weaker the farther away from a city you are.
Anyway, the point being is this. There is plenty of energy out there that we just don't know how to harvest yet.
Probably true--the question becomes, "how do you harvest it in a way that is cost-effective, useful, or worth it in whatever other terms you choose?".
So back to the regenerative motor concept. Consider the simple bi-filer coil. If you pulse current through one set of leads, the primary coil, then a voltage can be harvested from the second set of leads, the secondary coil. The question, as obvious as it is, becomes, how does one the harvest the back EMF from the secondary coil without creating a load on the primary coil which would "slow the motor."
If you transfer energy from one winding into another, you lose some of that energy. If the process could be 100% efficient, it still wouldn't do what you want, because anythign that takes energy from the motor's rotation, will slow it down. (the BEMF is specifically created by the motor's rotation, thus anythign taht takes energy from teh BEMF takes it from the motor's rotation, slowing it down).
It is less efficient to steal energy from the motor (because you now have to convert that energy back into the battery, with losses) than to simply have a larger or more efficient battery.
You can always take energy from the motor, but to maintain it's speed you then have to put more back in. To do that, you now lose a little more than before because the energy being put back in goes thru the conversion of battery thru wires thru controller thru wires into motor, all of which stages lose a little energy. Better just to leave it in the motor until you need to slow the motor down.
If the slowing is imperceptible, then the energy removed is simply very low. Either way, it's still doing it. (despite many websites and YT vids that purport to say otherwise, but can never seem to make it work when people with measuring instruments are around,
From my cursory experimentation i have found that it might be possible to fill a bank of small capacitors, by quickly switching amongst them, in between the square wave of the controller, (assuming a square wave controller) to fill a larger set of capacitor that can either fill back into the bms or a battery or be used as the primary source of power via a larger capacitor bank to put the motor into motion before the battery pack kicks in. Wouldn't it be nice to always have a set of caps quickly get you moving before you use battery power?
While this might theoretically work, it still uses energy taken out of the battery in the first place, then converted up to several times, with losses at each stage, so that essentially you are throwing away a lot of energy. Possibly more than half of what you harvested. It is more efficient to take it directly from the battery and leave it in the system.
Also, the caps are going to be very much larger than a battery, for the same Wh, and only a small percentage of the energy in them can ever be used, unless you add an inefficient DC-DC converter wiith a very high voltage input range. They're not worth using on something that has to be small and light and move around, like a bike or a car. Might be fine for a stationary application.
If you have a controller on an ebike it has a certain voltage range it is useful in. Let's be generous and say you have a 48V nominal system, and the controller uses a 24V LVC (to protect it's own electronics, rather than the battery), and the battery has a generous nominal range of 44-56V from LVC to HVC. This would let you use a bit more than half the energy from the caps, perhaps, but it is also optimistic, and assumes you don't need speed from the voltage on the caps, or htat the motor will ever get faster than what 24V would drive it to, before the caps run out and battery kicks in.
Then there's the problem that the capacitor takes a lot of energy to fill it up to that 24V, and *none* of that energy can be put back into the system. It's wasted, because the controller will shut off to protect itself at that voltage. It can't be put into the battery either, becuase the voltage is too low. You can add a DC-DC that still runs from a very low voltage (say, 2-3V) to upconvert that to a voltage still usable by the controller and/or battery, but you may lose 20-50% or more of the energy in the conversion.
You run into a the same problem with the small bank of caps taht is charging the larger cap--once the larger cap has reached the same voltage of the smaller caps, nothing happens anymore. You would have to again need a DC-DC to upconvert the voltage, and lose more energy. It would be better to leave out that entire stage, but it still wont' help the system be efficient. Just less inefficient.
The size of the capacitor is also a problem. As you go up in voltage, you go down in capacity, for the same size, and to get one that is high enough capacity to be useful in the very-high-energy moments of ebike startup or acceleration (the part you're talking about where it would be used before hte battery kicks in, I presume), it would have to be larger than your battery pack.
For just a few seconds runtime, if even that.
So while you can certainly build what you're talking about, it isn't going to do what you want, unless what you're after is to reduce the effficiency of the system as a whole, make it use more energy, and make it weigh more and be physically larger.
I would love to be proven wrong, but AFAIUI, that's simply how these things work.
Thanks for reminding me. And, yes a full bridge rectifier works way better then a single diode. That is how I realized that cosmic energy was ac.
