A little bit of knowledge needed

[Spinalot]

Can anyone explain to me in plain English why there are not regenerative ebikes. I know there are regen brake systems, although from the posts I have read on here they are not widely liked. But in my mind the wheels go round as does the crankshaft. Why can this movement not be transfered to electricity? After all, we have dynamo lights.

Thanks in advance for your insights.

 

[banbury frank]

There Are Regen Bikes They are fitted with the Bionx System

You set it to give you a workout so it turns the motor into a generator so you have to pedal on the flat with NO assistance but like you are going up a steep hill makes you sweat on the flat like a exercise bike with electronic braking they call it training mode


Technology - BionX - Intelligent Mobility Systems

Frank

 

[mike killay]

Are you sure that you are not asking for a perpetual motion machine?
You mention dynamo lights, but when you switch them on, you have to increase pedalling effort. You probably won't notice this because the amount of electricity you genarate in very small.
Get hold of a wind up torch and try winding in 500 turns, then you will appreciate that it takes effort to make electricity.

 

[Artstu]

Then when you get home you can use the battery to power the TV

 

[eddieo]

The best e bikes in my opinion are those that are as close to a normal bike in weight/handling etc...as possible.
More resistance is the last thing you would want or need.....it would be horrible to ride.

 

[Spinalot]

So its just because it takes too much effort to generate electric? How much are we talking? Wind turbines go round pretty easy I thought it was just magnets passing near each other surely this is not that much resistance?

 

[Scottyf]

The resistance question is one no one seems to know on the forum. I asked the same question.

The reason most Ebikes currently have no regen is becasue they all have a freewheel gear ability where by the clutch disengages when no power is passing through the motor.

I have actually had my clutch lock on once or twice usually when going off curbs.
Now when it was locked on it didn't feel that bad in my honest opinion. It felt a little bike the tires where a bit low rather than being flat.

Most direct drive hub motors offer regen as they are always engaged.

 

[flecc]

Energy cannot be had for free. Getting energy out of any system means putting energy in. Since all energy conversion loses efficiency, more work is put in than is got out, the rest lost in various ways, mostly as heat.

The energy used to complete a journey is what's necessary for that journey with a given performance, there is no spare for other purposes. Anything taken out for other purposes results in a lower performance journey.

 

[Mitch1960]

Spinalot, Those magnets spinning by one another act as an electromagnetic brake when the sysytem is on load..ie charging. Did you ever disconnect an alternator on a car when working on it? When you reconnect it (while engine is running by the way) the engine slows.very noticeably. Dont do this on modern cars M

 

[electric_avenue]

Wind turbines go round pretty easy

Just give me time to recover. Wind turbines take a huge power to turn them.

 

[oigoi]

The amount of power it takes to turn a generator is proportional to the load connected to it.

The more useful work you are asking a generator to do the more effort it takes to turn it around.

In the case of wind turbines there are those that turn very easily but do not generate many watts of power, at the other end of the scale there are wind turbines than generate hundreds or thousands of watts and so they need much bigger blades to turn them.

How much power you would capture from a regenerative motor would depend on how you configured it. If you configured it to have quite a powerful braking effect you would recapture a lot more of your kinetic energy as it is turned back into electrical energy.

I think one of the main reasons there are not more regenerative ebikes is because of the issue of riding a bike with a flat battery. A hub motor or crank drive with a freewheel as part of the drivetrain allows the bike to be pedalled along with a flat battery in the same way a normal bike rides.

However having a freewheel as part of the drivetrain makes it difficult to have regenerative braking. At the moment the only systems I am aware of with regen are direct drive hub motors with no freewheel

 

[Jimod]

I've been asked by 2 people why you can't fit a hub dyno to the front wheel to charge the battery as the electric motor drives the bike. I tried explaining the laws of physics and electric generation and power losses during such generation to them. They didn't believe me. I told them both, if they could invent a small hub generator which produced more power than the hub motor which is driving the bike and therefore turning their hub dyno, that they would soon become the richest people in the world.
Now I know most people in the world don't know much about what it takes to produce electricity compared to the amount of electricity generated. However, the 2 gentlemen in question BOTH work in a power station.

 

[Mitch1960]

lol jimrod. . . .perhaps they should feed juice back to the prime mover. . . and free leccy for us all. M

 

[Spinalot]

Hmmm, I am still not getting it. I think your missunderstanding me. I am not talking about a perpetual thing, just a system that uses the wheels and crank to make leccy that goes back in. Even if it was say 5% it would still increase the range before the leccy runs out on the battery.
Please can someone explain in real simple terms. Imagine I am a 10 year old and not 45

 

[piotrmacheta]

The way to look at this is that for every 100 watts of work (pedalling or motor drive) you will generate approx 70 watts of power back to the battery (for a 70% efficient dynamo) the remaining 30% is wasted as heat. This is on top of the power you need to use to move you and the bike. SO you end up loosing energy by doing this.
I recall reading somewhere that a bike was made where you pedalled a generator and it converted it to electricity which powered a hub to drive you along. Apparently rubbish due to the low conversion efficiency.

 

[johnc461165]

I guess it's a case of you don't get anything for nothing, when you consider the time it takes to recharge your batteries, the amount of time that you can regen power is minimal. So for me it's a no go situation sounds good in theory but in practice it's a no go situation at the present until technology improves.

 

[mike killay]

Hmmm, I am still not getting it. I think your missunderstanding me. I am not talking about a perpetual thing, just a system that uses the wheels and crank to make leccy that goes back in. Even if it was say 5% it would still increase the range before the leccy runs out on the battery.
Please can someone explain in real simple terms. Imagine I am a 10 year old and not 45

One way to explain it is this. Imagine you are trundling along on the flat under throttle only. You are using the full 250 watts.
Also, you have a 250 watt generator in the front hub, so you switch it on. Now you have an engine pushing forwards with 250 watts and a generator pushing backwards with 250 watts, so the bike comes to a halt. The problem is that the generator is not 100% efficient, so you don't get back what you have put in.
So, if you settle for a generator making only 20 watts, the bike will still go forwards only slower, but it is still using 250 watts and maybe, because of the losses, only recovering 15 watts, so rather than extending range, you reduce range.
Regenerative braking is used going down hills when you are freewheeling, in this case, instead of continually speeding up, the bike goes as if the brakes are lightly applied. Because of losses, the amount of electricity recovered is minimal. Worse still, if you are crossing a valley and the downhill is followed by an uphill, you will have lost velocity.

 

[oigoi]

Hmmm, I am still not getting it. I think your missunderstanding me. I am not talking about a perpetual thing, just a system that uses the wheels and crank to make leccy that goes back in. Even if it was say 5% it would still increase the range before the leccy runs out on the battery.
Please can someone explain in real simple terms. Imagine I am a 10 year old and not 45

The most simple way I can explain it is this:

For the extra effort you or the bike's electric motor would have to exert to propel the bike forwards as well as generating power, you would travel further and faster just using that effort to travel forwards without generating power.

For example:

You attach a small dynamo to your ebike so that makes power and charges your battery as you ride along. This dynamo takes 5W of power to make it rotate and it is 80% efficient so it gives you 4W of power out. Say you put that power directly back into the motor so you are giving the motor an extra 4W on top of what it is drawing from the battery. But you are taking 5W from the battery to rotate the dynamo so overall you are 1W down in power.

 

[Spinalot]

Many thanks to all for your attempts at making me understand.

Can you see a time when something could be done, or do you think the only way forward is to make batteries better?

 

[tappy]

Good morning fellow enthusiasts.

The Storck Raddar system does offer up to 10% regen back into the battery on freewheel automatically. You don't need to activate a switch when braking or anything like that. The system will regen as soon as you stop pedalling, coasting, freewheeling downhill etc. There is no drag or noise. This does help provide a very useful 100klm battery range.

Cheers,
Ian