Nominal Power misunderstood?

trex

Esteemed Pedelecer
May 15, 2011
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You add them , they ain't compounded..
X squared plus x squared is 2x squared ...
Flud, you misunderstood my post. F is the drag force, the equation or drag force is:
F = 0.5 * Ro * V * V * Cd * A
Ro is the air density roughly 1.223kg/cubic m
V is speed, in m/s
Cd is the drag coefficient, for a bicycle + rider, between 0.7 for a racer to 1.2 for an average e-rider.
A is the area (or profile) of the bicycle + rider, in square meter

P is the mechanical power required to propel the rider and bike at V. P = F * V

Therefore:

P = F * V = 0.5 * Ro * V * V * V * Cd * A

P is proportional to V cube.

resource:

http://www.cyclingpowerlab.com/CyclingAerodynamics.aspx
 
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wp_ss_20160404_0004.png wp_ss_20160404_0003.png

???

So according to this untrained cyclists ( which is group I,d put myself in) can achieve 1.5 w per kg..I,m 105 kg so I,m looking at around 160w ??? When working hard???
Again from wiki...
and
Bike so efficient we can pedal along at 9 3 mph using less energy than walking at 5 ???

So giving your average cyclist ( who will only weigh around 75 kg) another 250w is way over doubling their available power...

But flec, very well written and good post...

But I,m inly referring to CD bikes and legal ones as described elsewhere.. Yes ungeared hub motors will have to draw way more than 250w...but isn't that the whole point of cd drive units ???

Trex
Your calculations and explanation are spot on. I stand corrected over calculations for total power required..They do go up extremely quickly with advancing speed, its even steeper than I,d estimated..but since legal pedelecs shouldn't be powered above 15 mph its a bit superflous..
Power required at 15 mph is not such a great deal..sub 100w..
 
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flecc

Member
Oct 25, 2006
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But I,m inly referring to CD bikes and legal ones as described elsewhere.. Yes ungeared hub motors will have to draw way more than 250w...but isn't that the whole point of cd drive units ???
It used to be the point of CD, especially in the early strict 200 watt days, but more recently they've got into a power race.

To give some idea of the situation, back in 2001 Panasonic's new CD unit was a true 250 watt one, not very powerful by today's standards and with an increasing power limiting system from 15 kph (9.4 mph) upwards.

In 2006 they introduced a new unit with higher efficiency but which operated similarly and became very popular with a number of European manufacturers of pedelecs, especially in Germany. Their only rival in Germany was the small company Daum with a more powerful CD unit.

It was then that Bosch woke up to the possibilities and produced their first unit which understandably perhaps had some faults. Among them that it was so high powered that it was destroying bike chains very quickly, leading to Bosch calming it a little. However they still became a subject of complaints from Shimano, since the unit still exceeded the loading limits of Shimano's hub gears and SRAMs for that matter. The Bosch answer to that was to slightly downrate the units supplied for hub gear bikes, the derailleur ones remaining the same.

Of course customers liked all that power and the Bosch units swept the market, knocking Panasonic right out. Panasonic who had always used 24 volt systems belatedly retaliated with a very powerful 36 volt one and also removed the power phase down on the 250 watt ones, but it was too late and they remain virtually absent from the European market.

Meanwhile German bike company Kalkhoff who had been using Bosch after dropping Panasonic units bought the Daum unit rights and developed it as the Impulse 1 unit to rival the Bosch power. Take off for them was quite good, but they then brought out the Impulse 2 which was even more powerful. The outcome was that started to chew up and destroy it's internal gears, causing the new introduction of a replacement model called the Evo, still powerful but hopefully no longer destroying itself. There's threads in here about the Impulse 2 troubles.

I think from all this you can appreciate what we are saying about the power of modern units, 250 watts is not going to destroy bike chains in two or three hundred miles or chew up gears that had previously always been ok at 250 watts. It's been obvious for a long time that the Bosch and Impulse units have been far in excess of 250 watt capability and German sources reckon the Bosch has an easy 500 watt capability.

In support of that is that Bosch make the one unit which they rate as 350 watts when supplying for the high speed 45 kph S class or to the US market. For the legal pedelec market they call it 250 watts and set the speed limiting to 25 kph instead of 45 kph. The power is unchanged, only the speed limiting is changed. As a result there are "dongles" on the market to override the speed limiting so legal pedelec owners can unleash the speed potential by spoofing the signal the unit gets from the rear wheel rotation speed, illegal of course since it makes 50 kph assist possible. A similar dodge is possible on the Impulse units.

Another indicator of the excess power is the introduction of automatic power easing during gear changes to alleviate the problems the high power was causing during changes.

Incidentally, all these units are torque sensing, the power depending on the rider input. The full power is only unleashed with sufficient rider input, so your admitted lower inputs are probably not releasing the potential.
.
 
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soundwave

Esteemed Pedelecer
May 23, 2015
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if you get a dh pro you can rip the de railer in half:eek:
 
D

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Flud, you don't seem to be getting it. Let's try and put you in the picture. Going back to the old Panasonic 26v crank-drive system, some people took measurements of the power leaving the battery. I guess Flec will be able to post a graph from his archives to show that the power was round about 400w from the battery. Most motors are around 70% -80% efficiency, say 75%. Add another loss of say 10% for controller and primary drive efficiency brings the power down to 252w at the output sprocket. That motor was absolutely gutless by todays standards. Go and try one to see what I mean.

I made a measurement on the first Woosh crank-drive, which showed 14 amps from the battery, so that's 560w to the controller and 365w at the drive sprocket. You could feel that that motor was a lot more powerful than the Panasonic, but still some way behind the Bosch. Since then, Bosch increased their torque, which one would assume also increased it's power because at the same speed, power is proportional to torque. Although I haven't taken any measurements, my information is that Woosh increased their maximum current to 20 amps to get similar power to the Bosch, which would make it 800w from the battery and 500w at the drive sprocket.

I've experimented a lot with crank-drives and hub-motors over the years, taking actual measurements of the current from the battery with a wattmeter. After a lot of tests, you get a feel for the relationship between maximum current and the perceived power of the motor. I would say that the Bosch is running at at least 18 amps - maybe 20A. That would mean around 750w from the battery and about 500w at the drive sprocket.

Don't forget that the legal requirement is for a motor to be a maximum of 250w nominal continuous output power, not peak power, for which there's no regulation as such.

In your example of Lance Armstrong on his 8 kg bike producing 450w to go up a hill, don't forget that he and his bike are something like 40kg or more lower than one of us riding a Bosch/Yamaha MTB. We'd need closer to 675w in the same circumstances.

Here's an example of logging data from my present bike that shows the actual current coming from the battery whilst riding. I would say that this bike has approximately the same power as the latest Bosch/Yamaha. The steps are where I change the power level on the display. the controller, fixes the maximum current at each level:

 
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flecc

Member
Oct 25, 2006
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Here's a journey graph of the second series Panasonic unit from 2007 when the unit was well below Bosch and Impulse power levels. It can be seen that it almost reached 500 watts at times and routinely to 400 watts. From this graph you can see that this relatively low powered unit averages 250 watts, rather than that being its maximum:

panasonic_power_graph.jpg
 
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Great replies all of you..
I,ll read them all again, do some more research and peddaling!!!


I have said all along motor/ controller are capable of way more than 250w...Putting bike into a situation where it demands it is quite different ,but I haven,t the evidence to substantiate anything ,whereas your graphs etc speak for themselves. Points accepted....
Thanks for patience. Apologies for pedantic attitude, no offence meant to anyone..
Great thread tho...
I promise to try harder to flatten my battery quicker...and start a new argument afterwards.!!!!

The bike is superb..Couldn't recommend it more highly.
Take care.. Good cycling...

WP_20160330_002.jpg

Me and bike top of Neulous. The Alberes..not bad for a pup???
Picture taken at around 3600ft. Climbed up from 198..Took 1hr 48 mins..(and 92%) to just over 4000ft.( top was in cloud as village (Laroque Des Alberes) was when I left..
 
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soundwave

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danielrlee

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May 27, 2012
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Great replies all of you..
I,ll read them all again, do some more research and peddaling!!!


I have said all along motor/ controller are capable of way more than 250w...Putting bike into a situation where it demands it is quite different ,but I haven,t the evidence to substantiate anything ,whereas your graphs etc speak for themselves. Points accepted....
Thanks for patience. Apologies for pedantic attitude, no offence meant to anyone..
Great thread tho...
I promise to try harder to flatten my battery quicker...and start a new argument afterwards.!!!!

The bike is superb..Couldn't recommend it more highly.
Take care.. Good cycling...

View attachment 13591

Me and bike top of Neulous. The Alberes..not bad for a pup???
Picture taken at around 3600ft. Climbed up from 198..Took 1hr 48 mins..(and 92%) to just over 4000ft.( top was in cloud as village (Laroque Des Alberes) was when I left..
Your inability to drain your battery quicker than you do is testament to your ability to keep your motor running extremely efficiently. Whatever you're doing, it's clearly a good riding style and a great position to be in.
 
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Your inability to drain your battery quicker than you do is testament to your ability to keep your motor running extremely efficiently. Whatever you're doing, it's clearly a good riding style and a great position to be in.

Cheers Dan...Going home in morning..back to Derbyshire/ Lady Bower/ Howden Res.. Just as stunning..
Do think bike promotes better technique..noticed on slippy technical bits pays dividends to keep backside on seat/ wheel weighted for traction..so much easier with a bit of help to keep pedals turning..
Take care...

Ps. Mountain in background of picture is Mt Canigou..just over 9000ft... Highest in region, will be snow capped til mid May...then again mid Oct..

Its strange doesn't look much higher than where photo was taken, its actually 3 times higher..
 
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Your inability to drain your battery quicker than you do is testament to your ability to keep your motor running extremely efficiently. Whatever you're doing, it's clearly a good riding style and a great position to be in.
That's an interesting point. Theory says that if you keep the crank rotating at about 2/3 the maximum RPM, you get the highest efficiency and longest range; however, it's not as simple as that because there's so many other factors that come into it. It would be closer to the truth if the controller didn't change the maximum current. The sophisticated algorithms in the controllers are constantly changing the PWM to the motor, varying it with pedal pressure, bike speed, LCD setting and crank speed. The 2/3 rule only applies when power is at maximum.

I did some tests with a crank-drive bike with a Nuvinci CVT fitted so that I could keep the crank turning at the optimum speed, which I monitored on a LCD. It showed that there was little difference whether I kept the crank speed at optimum or just rode the bike in the normal way.

From all the tests I've done, I found that there's two ways that you can get increased range from your battery: Turn the power down or pedal harder. Apart from those, there's no magic formula yet.
 
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I don't think about doing anything different to normal but I have found light pedal pressure gives far lower current shown on graphic. For example pedalling at 60 cadence but then increasing pressure sees,s similar graphic rise to at lower cadence..Keep pedal pressure low at any cadence is what I tend to do..
Its easier on legs too.( and better for repaired knee)
Infact I,d go as far as saying with mine help from motor simply correlates with pedal pressure, irrespective of cadence..Your pedal pressure automatically falls with increased rpm, so it stands to reason generally bike would be more efficient with us pedalling faster.?

So I,d agree for ultimate long range pedal hard in low setting...but for getting best compromised range pedal gentle on highest setting ???
 
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memac

Finding my (electric) wheels
Mar 21, 2016
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0
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Hi there new to all this and this may not be the correct place to post this. I seem to have made a complete mess of buying a motored wheel.I am 56 and unfit I work as a private hire driver my neighbour offered me an older ebike with a 250w motor however due to the fact that I am about 30 kilos over the max load capacity it struggles even on very slight inclines.So silly me thought a bigger motor would help so I bought a 500w motor then on doing some research (yes I now know I should have done this first) I find I cannot fit this to the bike as it is not legal in the UK and it would basically be a moped and would need to meet all the same requirements otherwise I would be putting my driving licence at risk of points or a ban which would not be very good I feel that if it is not legal to use the wheel then it should not be legal to sell said wheels in this country.
 

D8ve

Esteemed Pedelecer
Jan 30, 2013
2,142
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I hear you memac.
It is legal if you happen to have access to fenced private land.
And some people take the risk and ride them anyway.
If you are careful and behave unless you have an accident the risk is low.
But as you note if something happens then the **** that follows could cost you your job.
It's not one to take chances with.
Me I am three years from an accident and the lawyers will soon be agreeing a payment. If my bike had been illegal then I could have suffered injury, and been prosecuted because of a 4*4 on a cycle path.
 

Alan Quay

Esteemed Pedelecer
Dec 4, 2012
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Hi there new to all this and this may not be the correct place to post this. I seem to have made a complete mess of buying a motored wheel.I am 56 and unfit I work as a private hire driver my neighbour offered me an older ebike with a 250w motor however due to the fact that I am about 30 kilos over the max load capacity it struggles even on very slight inclines.So silly me thought a bigger motor would help so I bought a 500w motor then on doing some research (yes I now know I should have done this first) I find I cannot fit this to the bike as it is not legal in the UK and it would basically be a moped and would need to meet all the same requirements otherwise I would be putting my driving licence at risk of points or a ban which would not be very good I feel that if it is not legal to use the wheel then it should not be legal to sell said wheels in this country.
There are lots of things can be done to increase power AND stay legal. If you start a new thread we can help you.

Sent from my HTC One_M8 using Tapatalk
 
D

Deleted member 4366

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Hi there new to all this and this may not be the correct place to post this. I seem to have made a complete mess of buying a motored wheel.I am 56 and unfit I work as a private hire driver my neighbour offered me an older ebike with a 250w motor however due to the fact that I am about 30 kilos over the max load capacity it struggles even on very slight inclines.So silly me thought a bigger motor would help so I bought a 500w motor then on doing some research (yes I now know I should have done this first) I find I cannot fit this to the bike as it is not legal in the UK and it would basically be a moped and would need to meet all the same requirements otherwise I would be putting my driving licence at risk of points or a ban which would not be very good I feel that if it is not legal to use the wheel then it should not be legal to sell said wheels in this country.
Post pictures of your bike. We will then be able to suggest ways to solve your problems.