Generating electricity

Dlogic

Dlogic

1 kW
Joined
Oct 18, 2010
Messages
379
Location
Germany
I know it probably sounds stupid, but has anyone ever tried to generate electricity while pedaling and using this power to directly drive the bikes motor? I know that you won´t get thousands of watts out of this setup. However you might save yourself the chain and gear shifting system. Like the german Erockit, but without the battery to boost your effort.
 
It's been tried, but it is very, very lossy. Here are some ballpark numbers to illustrate the problem, compared with a conventional chain driven bike.

Sustained pedal power input from an average cyclist ~100W (Lance Armstrong can reputedly hold around 400W for maybe an hour, but he's exceptional)

Chain drive losses ~ 1% to 3%, depending on state of chain, relative size of sprockets and type of lubrication used

Generator losses ~ 15% for an 85% efficient generator, which is typical. The best generators maybe just over 90% efficient, but only over a narrow range of load conditions and speeds.

Motor losses ~ 15% for an 85% efficient motor, again this is typical. Permanent magnet motors and generators are reciprocal machines, so the same rules pretty much apply to both.

Let's assume that the other mechanical losses, from bearings etc, are the same for both chain drive and generator/motor drive, so cancel each other.

Let's also assume a perfect electrical system, with no wiring or other I²R losses.

Here's the comparison:

Chain driven bike with 100W input to the pedals will deliver around 97W to 99W to the rear wheel and waste around 1% to 3% of the rider power as heat.

Pedal generator/motor driven bike with 100W input to the pedals will deliver around 72W to the rear wheel and will waste about 28W as heat. If run at the generator/motor best efficiency point all the time (around 90% for both) then the power to the rear wheel increases to around 81W, with losses of around 19W as heat.

The bottom line is that the relatively poor efficiency of the generator/motor set up makes it a poor choice. Chains are surprisingly efficient, and waste very little power, which is why bikes have stuck with them for so long.

Jeremy
 
http://www.hupi.org/HPeJ/0015/0015.html
 
There is also a thread here on ES about a hybrid bike that does this, where his pedals are not connected to the drivetrain except electrically. I can't find the thread at the moment, nor can I remember who was doing the project, but it had quite a bit of detail on the project. The motor itslef was being driven by a 3-phase converter, powered by an inverter from large lead acid (I think) batteries. The pedals ran a generator that could help charge the system.

Searching for Serial Hybrid (the type of drive system you're talking about) on ES
http://www.endless-sphere.com/forums/search.php?keywords=%22serial+hybrid%22&terms=all&author=&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search also finds one I hadn't seen before:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=3423&start=0
 
I remember seeing the photo, it was a trike, with square tubing, using a converted alternator (permanent magnets placed in the rotor) that would normally be used as a wind generator unit, I never saw the completed trike. An easy way out if one did not want to run a chain from the sprocket to a cluster/rear wheel system, and maybe get under the wire, as a legal electric bike/trike peddle no license/insurance unit.
 
Peter ("fitek") made a SWB bent:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=3423

His personal blog-page on the build is down, but the video linked in the thread is still active.
 
Thanks for the feedback guys. A few month ago a friend sent me a link of some guy in Switzerland that claims to have built what i´ve written about. Well, i´ve lost that link but will ask him for it again. Sounds quit logical what you´ve written. It´s like the comparison of the chain vs the hub gear shifting systems. As soon as more then 2 sprockets are used to transmit power to the rear wheel, the thing becomes inefficent. I really like the Rohloff hub, but somehow always think that in the lower gears, were all 3 planetary gears are used, the setup eats a lot of the pedal power i put into it. That´s the thing with mechanics. Some solutions are just perfect. Like the invention of the wheel. I bet no one will ever come up with something more ingenious. :)
 
Dlogic said:
I know it probably sounds stupid, but has anyone ever tried to generate electricity while pedaling and using this power to directly drive the bikes motor? I know that you won´t get thousands of watts out of this setup. However you might save yourself the chain and gear shifting system. Like the german Erockit, but without the battery to boost your effort.
Click to expand...

You wrote: ..."I bet no one will ever come up with something more ingenious".


I am sure that I can bet on you!!!
No,the idea isn't stupid! I'd realised my bike with this system before half year!
In the front I'm pedaling an alternator, from this source I can get about 3AMPs at 40VOLTs = 120WATTs.
More power with my muscles over a considerable time is not possible.
Additional I've got a solar roof, this gets me about 0.5AMPs at 40VOLTs = 20WATTs.
And there's for braking the recouperation, that's the most difficult thing, because there can flow up to 15-20AMPs
in a short time. That can blow up your BLDC motor, your MosFETs and your battery!!!
Of course every part has got loss, in all cases the loss changes into heat. The parts which gets really warm are the MosFETs
from the controller. The MosFETs are mounted on a tunnel heatsink and I use it for the air heating.
In summer I'll blow the warm air outside and for very very cold days I can turn a seperate heating on.

Here in europe is the regulation, I must pedal and then I ride. If I stop pedaling, the motor stops and I cannot ride!
I shift my gears only with buttons, there's no bowden cable and no gear box or derailleur!
So it doesn't matter if you have a hill, a mountain or just straight ahead, the shifted speed is nearly always the same!!!
From the first motor rotation the power and transmission is excellent, just sometimes the tire smokes.....

I can explain you soooo much, just look the video:
http://www.youtube.com/watch?v=U3SAFnheRJo
[youtube]U3SAFnheRJo[/youtube]

And the battery: LiPO 37V/27Ah/66C/1000Wh
http://www.youtube.com/watch?v=Zl9ACAbocZ0
[youtube]Zl9ACAbocZ0[/youtube]

I hope, I could help you now!!!
 
Hey folks, the "guy in Switzerland" is actually two people. Their names escape me at the moment, but at least one was a professor and they for a time had a business to commercialize the idea.

I migrated my website, you can find the serial hybrids here:
http://hybridmojo.com/evolution/serial-hybrid/
[Edit: for some reason that page is all broken. Here are the links which are supposed to appear:]
http://hybridmojo.com/evolution/serial-hybrid/short-wheelbase-serial-hybrid/
http://hybridmojo.com/evolution/serial-hybrid/full-suspension-short-wheelbase/
http://hybridmojo.com/evolution/serial-hybrid/short-wheelbase-tandem/

The system is extremely lossy without electronics, and not useful for charging until a certain RPM is reached. Building electronics for this has been an ongoing project for me... I did last year finally manage to build something, but there was something wrong with the circuit and, although it boosted the voltage from all but the lowest input up to pack voltage, the losses in the circuit were quite bad.
 
fitek said:
Hey folks, the "guy in Switzerland" is actually two people. Their names escape me at the moment, but at least one was a professor and they for a time had a business to commercialize the idea.

I migrated my website, you can find the serial hybrids here:
http://hybridmojo.com/evolution/serial-hybrid/
[Edit: for some reason that page is all broken. Here are the links which are supposed to appear:]
http://hybridmojo.com/evolution/serial-hybrid/short-wheelbase-serial-hybrid/
http://hybridmojo.com/evolution/serial-hybrid/full-suspension-short-wheelbase/
http://hybridmojo.com/evolution/serial-hybrid/short-wheelbase-tandem/

The system is extremely lossy without electronics, and not useful for charging until a certain RPM is reached. Building electronics for this has been an ongoing project for me... I did last year finally manage to build something, but there was something wrong with the circuit and, although it boosted the voltage from all but the lowest input up to pack voltage, the losses in the circuit were quite bad.
Click to expand...



Hi!

I'd take alook into "hybridmojo.com", cool page and cool pictures!
You have the same 24VDC alternator as I used in my LowracerHybrid. But I needed the double voltage to charge the battery!
Ok, I need a higher speed of the alternator, so I need another chain ring http://www.youtube.com/watch?v=cOZ-_ClKRmg
You wrote extremely lossy. I had changed the cable of the alternator from 2.5mm² into 6mm². I can only pedal 3AMPs, there a 6mm² is nearly 10times oversized, but the alternator should lose only a minimum. In the (+) of the alternator line I have got a freewheeling diode, here I'd taken 6 schottky diodes/TO220 parallel. With a schottly diode you lose only 0.3VOLTs, with a normal silicium diode you lose 0.7VOLTs. That's a big difference, 0.3V@3A=0.9W loss, 0.7V@3A=2.1W loss.
I've mounted 6diodes parallel on my aircooled tunnel heatsink so the diodes never run hot, if diodes run hot the loss is ascending more and more!!! On the tunnel heatsink are also the controller and an auxiliary heating(2 power resistors).
All loss is used to heat up the cockpit. Now in autumn and winter I could ride with a T-shirt!!! :lol: :lol:
 
Chris, I don't think I'd have the patience to make a chain ring with an angle grinder, hehe. I like the idea though!

I used the biggest bicycle chain ring I could find, which was not that big-- 48T, or something like that. Tom Kabat from WoodenBikes.com has been able to find large sprockets on old exercise machines.

I also connected multiple diodes paralleled to the generator motor, but I think I used regular diodes. You are overstating the loss however. I can pump about 5 amps into the batteries. 0.7V drop x 5A = 3.5 Watts loss. Not significant.

This system is sufficient for ebikes which would simply not be able to exist otherwise.
 
fitek said:
Chris, I don't think I'd have the patience to make a chain ring with an angle grinder, hehe. I like the idea though!

I used the biggest bicycle chain ring I could find, which was not that big-- 48T, or something like that. Tom Kabat from WoodenBikes.com has been able to find large sprockets on old exercise machines.

I also connected multiple diodes paralleled to the generator motor, but I think I used regular diodes. You are overstating the loss however. I can pump about 5 amps into the batteries. 0.7V drop x 5A = 3.5 Watts loss. Not significant.

This system is sufficient for ebikes which would simply not be able to exist otherwise.
Click to expand...


HI!

The chainring creation is very easy, so you can create chain ring up to 99T! :roll:

You have a 24Volt system, then 5AMPs is a good value. You pedal 120WATTs!!! 8)
Well, the last but not least, I've created a 32W solar roof. I can get the lost (loss) power back!
Additonal, with the solar the bike "knows" if it's day or night. I can loop-in these conditions in the system control!
But I don't show the solar roof in YouTube, the chinese should create their own solar sytems!!! :lol:

Now I install new brakes to my hybrid bike, MAGURA GUSTAV M with a 210mm disc:
[youtube]iYvzdP3r2A8[/youtube]
 
Jeremy Harris said:
It's been tried, but it is very, very lossy. Here are some ballpark numbers to illustrate the problem, compared with a conventional chain driven bike.

Sustained pedal power input from an average cyclist ~100W (Lance Armstrong can reputedly hold around 400W for maybe an hour, but he's exceptional)

Chain drive losses ~ 1% to 3%, depending on state of chain, relative size of sprockets and type of lubrication used

Generator losses ~ 15% for an 85% efficient generator, which is typical. The best generators maybe just over 90% efficient, but only over a narrow range of load conditions and speeds.

Motor losses ~ 15% for an 85% efficient motor, again this is typical. Permanent magnet motors and generators are reciprocal machines, so the same rules pretty much apply to both.

Let's assume that the other mechanical losses, from bearings etc, are the same for both chain drive and generator/motor drive, so cancel each other.

Let's also assume a perfect electrical system, with no wiring or other I²R losses.

Here's the comparison:

Chain driven bike with 100W input to the pedals will deliver around 97W to 99W to the rear wheel and waste around 1% to 3% of the rider power as heat.

Pedal generator/motor driven bike with 100W input to the pedals will deliver around 72W to the rear wheel and will waste about 28W as heat. If run at the generator/motor best efficiency point all the time (around 90% for both) then the power to the rear wheel increases to around 81W, with losses of around 19W as heat.

The bottom line is that the relatively poor efficiency of the generator/motor set up makes it a poor choice. Chains are surprisingly efficient, and waste very little power, which is why bikes have stuck with them for so long.

Jeremy
Click to expand...

-------------

Very lossy?? No, I don't think so! Ok,I've got a big battery. Of course every system has got loss, but I need
loss to warm up my cockpit! I understand all your calculations. For every deflection pulley I can calculate about 2% loss.
Some people would say, that's not much. But I say that's a big difference! I've tested different materials, polyamid plastics, aluminum, steel.
The steel chain rings and steel deflection pulleys are the best choice against loss!

In the Lowracer Hybrid I am the charger, and I know, with an empty battery I don't need to ride!
If I wanna reload the whole power(1000Wh) of my battery I can pedal about 9hours in the parking position.
So all my muscle power is limited to about 120Watt constant..... God save us the LiPO-AMPs! :lol:
 
LOWRACER said:
Very lossy?? No, I don't think so! Ok,I've got a big battery. Of course every system has got loss, but I need
loss to warm up my cockpit! I understand all your calculations. For every deflection pulley I can calculate about 2% loss.
Some people would say, that's not much. But I say that's a big difference! I've tested different materials, polyamid plastics, aluminum, steel.
The steel chain rings and steel deflection pulleys are the best choice against loss!

In the Lowracer Hybrid I am the charger, and I know, with an empty battery I don't need to ride!
If I wanna reload the whole power(1000Wh) of my battery I can pedal about 9hours in the parking position.
So all my muscle power is limited to about 120Watt constant..... God save us the LiPO-AMPs! :lol:
Click to expand...

Yes, very lossy. No question, no doubt. You lose about 10% to 20% in the generator (due to I²R, magnetic hysteresis and frictional losses) and then lose about another 10% to 20% in the motor (due to the same I²R, magnetic hysteresis and frictional losses, but in the motor). If you add a battery to the system you also lose another small amount of efficiency due to charge/discharge losses; batteries usually take more power to charge than they give out during discharge.

Chains only lose a tiny amount, maybe 2% to 3% if well-adjusted and lubricated, so are massively more efficient than a pedal to generator to motor system, especially with a battery added to the mix..

If you add an extra power source (pre-charged battery, solar panel or whatever) that does not change or reduce the losses, it simply compensates for them by adding extra power, which has to come from somewhere.

Getting best efficiency (total power in from all sources versus total power out) is tough. I've spent a lot of time and effort optimising efficiency during development of my solar charged electric boat and was amazed at the amount of time and effort it took to eliminate excessive losses, from just about every component.

Jeremy
 
What about the cool factor?
I have been looking at this and a chain is basicaly impossible to beat for making a system practical!
BUT... I was wondering about haveing a generator from the peddle producing 3 phase ac and feeding it directly to the drive wheel? Then Using the generator and having it switch from series to parrellel and WYE to Delta in steps for the different speeds Keeping the battery out of the system??? Now might not want to feed this power to the main drive motor so maybe having the peddles feed a second motor on the bike?
The other though was it would be handy to be able to peddle to partialy recharge your bike,
Or imagine working out in your house charging your e-bike then using the energy to race to work when you dont have the time to ride slow and or get swetty.
In the end it is a cool concept but hard to make practical. I think a mountain biker type who wanted to backpack across an island like were I live or something could benifit from this it would be nice to be able to charge the bike while you are stopped camping somewere!
 
There is an advantage in being able to even out pedal power demand by being able to pedal to recharge during low power demand periods. This would work better on a trike, as you could pedal the generator while stuck at lights or whatever. I've been looking at doing something like this as an emergency power source on the boat. If I can generate around 60 to 80 watts then that's enough to get me out of trouble if the weather gets bad enough to not give me enough solar power and the battery starts to go flat.

Whether the gain from being able to pedal harder during low load periods makes up for the extra losses is debatable, but it might make sense if you ride in a mainly flat area with a lot of traffic, where you don't need much speed but could do with some battery-boost acceleration on a fairly frequent basis.

Jeremy
 
Jeremy- Since the self-discharge is so low, perhaps just a little 6s5Ah brick or two that is stowed charged in a vacuum-locked bag somewhere for use in an emergency? Kinda like the of equilivant of carrying a spare gas can for use in the event Murphy get's extra feisty.
 
liveforphysics said:
Jeremy- Since the self-discharge is so low, perhaps just a little 6s5Ah brick or two that is stowed charged in a vacuum-locked bag somewhere for use in an emergency? Kinda like the of equilivant of carrying a spare gas can for use in the event Murphy get's extra feisty.
Click to expand...

Yea, you're right. There comes a time when you need to stop worrying about backing up the backups..............

Jeremy
 
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