Trek Cytronex - First Impressions.

[flecc]

As somebody who designed and built my own off-grid low voltage system (24V, 610 Ah storage) and has run it for the past 20 years, I think I can lay claim to a little technical understanding........

Then as someone who was doing similar years before you, I don't need an explanation of Ohms law and am surprised you haven't noted the difference I highlighted. Viewing the power expression watt/hours in isolation is far from the whole story, as these two extreme examples of 120 Wh systems show:

24 volts 5 Ah, suitable for powering an e-bike for an hour.

12000 volts 0.01 Ah, suitable for providing a powerful ignition spark for a fraction of a second.

Clearly the lower voltage system is more suited to providing moderate power over a long time, which in the present context makes Panasonic's choice of 24 volts with higher Ah preferable to the 36 volts with lower Ah of the Cytronex for a longer range design. The latter is a better choice for a higher power and shorter range design and does not have overall equivalence to the former.

Now I know of your design experience I will be able to see that any further detail omissions in the Cytronex favour should they occur will not be accidental.
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[Orraman]

An interesting discussion but given the relatively high currents involved, is it safe to reach conclusions while ignoring I squared R losses when comparing systems at different voltages?

Dave

 

[Jeremy]

Far be it from me to add further controversy to this exchange, but there is an element here regarding power, voltage, current and battery amp hour ratings that seems to be less than clear, at least to me.

A bike will require a certain amount of energy to move it a given distance at an particular speed. This will obviously depend a great deal on the terrain, wind speed and direction and to a lesser extent on the type of bike. The energy it requires should really be expressed in joules (watt seconds) but it's become common practice to use watt hours when discussing electric vehicles.

A common rating for vehicle efficiency is the number of watt hours it needs to travel one mile in nil wind on level ground at a particular, constant, speed. This is a pretty good indication of maximum likely range. A reasonable figure for an electric bike would be around 10 to 15 watt hours per mile, at normal bike speeds.

The energy stored in any battery is a function of both it's voltage and it's amp hour rating; neither rating is much use in determining range without the other. For example, a 24 volt 10 amp hour battery has the same amount of stored energy as a 48 volt 5 amp hour one. The battery amp hour rating is not an effective or accurate indicator of stored energy or range on it's own. The key measure is the usable watt hour rating of the battery, with the stress on usable. Drawing high currents from any battery will result in less usable capacity - the lower the current drawn, the greater percentage of theoretical capacity will be usable.

A pulse width modulated ebike motor controller is a very effective and efficient voltage/current transformer. It's perfectly possible to run a 24 volt rated motor from a 48 volt battery (provided that the controller is adequately rated) as the controller can be set to only deliver 24 volts to the motor, by limiting the throttle range. One advantage of such an approach is that the current drawn from the battery is halved, when compared to a 24 volt battery. This has two advantages, in that it allows smaller gauge (lighter) battery wiring, plus results in better battery efficiency, as Peukert effect losses (due largely to battery internal resistance) are lower.

One plan for a really efficient electric bike, now that we have high cell voltage, low Peukert constant, LiFePO4 cells, would be to have a high voltage (say 60 volt) battery, with a modest amp hour capacity of perhaps 5Ah. The reduced losses, from using a much lower battery current, would make for a useful increase in range, from a pack with around the same weight as existing packs of similar capacity. Of course, the controller would need to be limited, otherwise any advantage would be lost to the temptation to use the extra voltage to travel at much greater speeds.............

Jeremy

 

[Chris_Bike]

First of all, can I say to Flecc that I am sorry my previous post irritated him and that I do not intend to take offence at his remarks above.

Then can I thank Jeremy for his very knowledgeable comments and also admit that, whilst I did 1st year Physics before becoming a Biochemist, I did not follow all of them.

I was going to post that Flecc's example of the ignition spark vs. a low voltage motor was not really relevant to the comparison of two low voltage motors running at very similar voltages (24 and 36). I am sure that differences in performance here (both in top speed and range) are mostly down to motor/controller design - a point that Jeremy has made more eloquently than I and is exemplified by the use of faster rpm motors for the races at Presteigne. It seems to me that the main advantage of increasing volts is that the motor will run on a lower current and the voltage drop in the cables running to the motor (which are usually quite small) will be minimised (this is Ohm's law, whilst my last post was not).

Of course, the other big difference between the Panasonic unit and the Tonxin is that the former delivers its power through the drive chain and gears whilst the latter does not. This will radically affect their characteristics. In the former, you will get a level of assistance (defined by the setting you choose) that is related to how much you peddle up to the maximum (cut out) speed. If the assist is 1:1 the motor will match your effort up to about 15 mph. In contrast, the Tonxin will try to take you to its maximum speed whether you pedal or not. If you pedal reasonably hard, the motor will do less work and the range will be higher. If you don't pedal at all, the motor will do all the work and the range will be lower. The disagreement on this thread arises because contributors are speculating how much effort you need to put in to get a reasonable range. The point that John and I are trying to report is that this effort is rather less than some have implied. I think we both suggest that prospective buyers try the bike and see - I think that you will be pleasantly surprised but, if you try it and disagree, by all means come on this thread and tell us all.

 

[Andrew harvey]

Apology To Flecc

Thank you for your promt response, I confess I hadn't meant to stir the debate so much.
I do actually have a Lafree in my garage,( but alas no Lafree battery I was under the impression that they were supposed to be 8Ah) it sits next to the Curry Drive, Tongxin, Suhou Bafang (8Fun), and assorted spare motors, mainly Crystalytes.
The Lafree I must confess does not actually run very well, the electronics are shot and the rotor bearing ( out board I think) twists out of the socket whenever you wheel the bike backwards causing the rotor to rub on the stator. I have managed to get it to run using a Tongxin controller from EGOGB, but you have to be careful not to let it roll backwards. Using a throtle on a Lafree makes it a completely different machine, but not likely to be legal of course, just more fun while it lasts. The bike had spent a considerable period in the river before I aquired it.

I am well aware of the finer points of the panasonic control sytem, I just didn't no that anyone else knew them. I have somewhere at work an old data sheet descibing the sytem as you do in your link.
The point here is that I first came across a Lafree outside the Queens Head in Wolverly near were I live. The owner a more senior gentleman, had given up driving because of failing eyesight, he had been sold the best electric bike in the world, but hadn't ridden since he was a lot younger. He was not however sure it was working as it should, I tried the Lafree expecting a little to much from it, I had previously made a couple of spectacular failures of gear drives bikes, and was dissapointed, hence I dug up the information, my very first web search.
I have tended as a result to the opinion that these bikes were better suited to cyclists than non cyclists.
Why? You need to know how to pedal, for instance my wife, an inexperienced cyclist likes the pedals under her instep not her toes, how does she produce any real power?
This is the same concern you feel for the Cytronex, if I was to say a few things more on the subject, my wife who is reletevely fit for her age has followed me up a short (about 75yrd) 1 in 5 hill and a much longer 1 in 12 on her 160 rpm Tongxin (Nano) assisted bike, a lower geared version. I riding her bike can cover over 20 miles on a 6Ah lithium with no sign of it dying, and finally electric motor currents fall as the motor speed increases, (I'm ignoreing current limiters for simplicity), any well engineered electric bike that allows you to ride it fast allows you to ride it economically, this includes the Lafree, Kalhoff and I feel the Cytronix, but you do need to put some effort in.

I've been throught some more of this forum, and you obviosly know more than I gave you credit for, I'm sorry for this. If I may say so , if you are 72 and can still average 12.5mph on a bike your as fit at your age as Chris Bike is at his, may you have many happy years of pedaling still to come.

Could I recomend that anyone who doesn't know the site and wants a better understanding of how electric motors work check out ebikes.ca
If any one cares to look it has a motor simulator, which gives power/speed curves for various Crystalyte motors with different batteries ,controllers and wheels sizes, the're fairly accurate , I have in the past spent a few afternoons with some of my old motors a set of batteries and an oscilorscope.

Now everyone stop bitching and enjoy the good weather, sorry spoke to soon it just started to rain.
Andrew

 

[Matt]

For some reason the word 'patronising' springs to mind

 

[john]

It seems to me that the main advantage of increasing volts is that the motor will run on a lower current and the voltage drop in the cables running to the motor (which are usually quite small) will be minimised

Only a fraction of a volt will be dropped by the cables, far more (up to several volts) can be lost in the motor windings, as I think implied by Orraman...

is it safe to reach conclusions while ignoring I squared R losses when comparing systems at different voltages?

 

[Jeremy]

The other place where you can get a significant voltage drop with increasing current is the battery, particularly with sealed lead acid cells. Peukert losses from battery internal resistance will often significantly exceed the copper losses in the wiring and motor and form one of the most serious total energy losses.

For example, when testing my bike with three 12V SLAs (with the Tongxin motor), I found that the controller would cut out at full throttle after a minute or two. The battery voltage was dipping from around 37V off load to less than 29V at about 14 amps, purely as a result of the high internal resistance of the particular cells I was using.

Increasing battery voltage and reducing current is a very effective way of reducing this source of loss, although some types of lithium cell are much better in this regard anyway.

Jeremy

 

[Miles]

Only a fraction of a volt will be dropped by the cables, far more (up to several volts) can be lost in the motor windings, as I think implied by Orraman...

But the only gains to be made, in this case, are in the connecting cables......

 

[john]

But the only gains to be made, in this case, are in the connecting cables......

Given the same motor, that is true. Adding more copper to the motor would save a lot of energy, but there would be no space to do that (so not practical). Adding more copper to the wire would be practical but save only a very small amount of energy.

Jeremy's point about battery resistance is the more practical one.

(PS Jeremy, I sent you a PM)

 

[Miles]

Hi John,

The only point I was making was that there's nothing to be gained in motor efficiency, by raising the voltage and changing the number of winding turns to match. This was something that confused me when I first started learning about electric motors.

 

[flecc]

Chris_bike, Jeremy, Andrew harvey

Thank you for your responses on the voltage systems issue. Please don't think I'm ignoring you but busy with other things for the moment and will post a response later.
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[flecc]

If I may say so , if you are 72 and can still average 12.5mph on a bike your as fit at your age as Chris Bike is at his, may you have many happy years of pedaling still to come.

Andrew

Hi Andrew, absolutely no call for that apology, but thanks anyway.

It's odd about my cycling speed, since I always think it's not very good!
I've never been involved in cycle sport, any sport for that matter, and back at 65 years old I decided my fitness had gone too far downhill and in my typical impulsive way resolved to do a year's more intensive cycling, August to August, every day to get back into form. Started with a new decent bike of course, a Trek would you believe!

I stuck it out with the fitness and range increasing over time, and in the latter months was frequently doing trips of 50 to 55 miles within four hours. I was happy with my general fitness and endurance, but was always dissatisfied with the average speed of just over 12.5 mph feeling it was slow.

Maybe it was because we have a huge amount of sport cyclist every day training going on in the area where I cycle, professionals amongst them, and even the Tour de France guys training with the local club some years. When the start was in London, some of the famous names stayed in the nearby Selsdon Park hotel and I was often passed by them training with our best locals. Talk about making one feel useless, perhaps little wonder I was unhappy about my 12.5 mph!

You've cheered me up though, and so has the information of others decades younger doing only the same with electric help. One thing that may boost my averages is that I cycle in the hilliest parts of the North Downs and belong to the school that thinks braking downhill is for wimps, so am quite happy to top 40 mph where possible, which more than compensates for the loss climbing up the other side.
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[flecc]

At last back again on the "volts for performance" and "amps for endurance" issue. (They sound like good slogans for marketing batteries don't they?)

The odds here are too overwhelming so I surrender (sort of).

Of course I know the theory reasonably well, but as long term members know, I tend to make up a porridge of theory, practice and experience and apply it liberally over issues in question, much to the irritation of purists of course.

Certainly the volts/amps ratio doesn't alter the power rating, though as my deliberately extreme example shows, it can affect the usability for differing purposes and thus make the theoretical same, practically different. Chris himself earlier questioned why according to accepted theory, top cyclists do what is theoretically impossible, illustrating the value of considering real world experience as I always do and never just theory in isolation. In part I do this because I know I don't have all the answers so add in what others do and know about anything.

In this instance I look at what happens in practice, and overwhelmingly the examples of performance e-bikes and many other electric prototypes opt for the high voltage approach. Examples of the converse are difficult to come by, since long range electric vehicles are as rare as hens teeth, but there are some useful instances.

Panasonic have never designed for high performance in their various e-bike versions due to Japanese law, always aiming for good range, and they have always adopted the lower 24 volt option to achieve that.

More intriguing is the example of Giant though. Having dropped the Panasonic unit on cost grounds, they produced a 36 volt e-bike, a utility style bike with front hub motor and rear of seat tube battery. Completely conventional and much lower price than the Panasonic unit Twist model, it sold quite well as the "Suede" and with minor changes as the "Argue" on the continent.

They then decided to opt for a long range model based on the Suede, and to do that using the same motor, they converted the system to 24 volts with much larger battery capacity. They don't appear to have made that choice for any specific battery design reason, since the bike is marketed as the Twist 1 with Li-Polymer and the Twist 2 with NiMh. Equally it wasn't on battery cost grounds, since they opted for an expensive realisation by using twin batteries on the bikes. Equally it wasn't to keep the bike price down, since it's marketed at around twice the price of the Suede.

So why did they do that? I doubt it's a case of the world's largest cycle company by a huge margin, not knowing what they were doing in their fourth e-bike design. That would be a bit like saying Toyota doesn't know how to make cars.

So there's the conundrum I've set you guys. . Over to you.
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[Jeremy]

I think there is an element of working with components that are available, Flecc, plus the strong influence of value engineering.

To get any significant advantage from using a high voltage, low current, system, the controller would need to have the facility to limit power to the motor, irrespective of input voltage. Most controllers only limit current, using a simple shunt measurement system. As far as I know, nobody has yet produced a readily available power limited, high voltage controller. I'm sure it will come, but we are still in the realm of lead acid thinking, even with regard to battery voltages being in multiples of 12 volts, which doesn't fit well with Lithium cell voltages.

From what I've read, few manufacturers seem to make controllers specifically for the UK/EU power limits. There are units aimed specifically at the Japanese market, like the Panasonic, but most seem to be aimed at the relatively unrestricted Chinese market.

One or two, like Bionx, seem to have had a go at making something a bit more intelligent, but I guess that, until interest picks up, the UK is just not a big enough potential market to support a neat custom design of controller.

It's pretty easy to add power limiting - I'm sure that something like the Cycle Analyst could be modified to do this (it currently provides speed limiting). The CA already measures power, so changing the firmware to use a set power limit to turn off the controller would be very straightforward.

One aspect of switching to a low amp hour capacity, high voltage system is the smaller size of the cells. It might well be feasible to fit the cells inside the frame tubes, for that truly stealthy look.

Jeremy

 

[flecc]

Thanks Jeremy, that Cycle Analyst approach looks as though it could be a useful way forward.

Your last paragraph content is what makes me question just why Giant dropped the voltage to 24 in that way, since higher voltage and smaller cells would have given a lighter end product than the present one with twin 9 or 10 Ah batteries.

Alternatively they did after all have a proven 36 volt setup which could merely have had some extra capacity added for longer range, as Wisper and others have done with light 14 Ah batteries.
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[john]

It's pretty easy to add power limiting - I'm sure that something like the Cycle Analyst could be modified to do this (it currently provides speed limiting). The CA already measures power, so changing the firmware to use a set power limit to turn off the controller would be very straightforward.

The Cycle Analyst already has an adjustable current limit, so, knowing your battery voltage you can set this to the input power limit you want. Or am I missing something?

 

[felix]

Another first impression

Hi All,
I have been meaning to post for a while now but with so much discussion here, each time I've caught up it's been past my bedtime!

Anyway, these are my honest impressions. Here goes:

Picked up my Treck Cytronex twelve days ago.

Background Stuff:

I'm 54 years old, 14.5 stone, put 2 stone on while suffering two consecutive frozen shoulders over the course of 5 years. I invested in this bike for two reasons:

1. To improve my fitness and

2. To be able to leave my car at home.

I live in the shadow of Kinver Edge, South Staffs. which I regard as a gravity well, whatever direction you choose to escape involves great expenditure of energy. When I was a younger and fitter man I would jog or cycle around but even then it was a struggle. They don't put gradient signs up round here, but some hills are the "out of saddle, legs burning, get off and push" type.

Bike Impressions:

My first ride was in Purley as I had done a "Round Robin" to pick up the bike and visit my daughter for the weekend.

As the battery needed to be charged, I took the bike out for a run without it. This was on a flattish stretch. I was immediately impressed with the smoothness and how easily the bike rolled. My thinking at that time was "This is great, why do I need a motor?

I crossed the main road into the hilly part (Don't know the area very well.) and realised very quickly that I was in the torture zone. I soon headed back to my daughter's to recover.

A couple of hours later, I felt better and took to the hills with the battery in!
What a difference! I clocked 8 miles up and down the hills with ease. Experimenting with easing right off and letting the motor take the strain at low speed on a long steep hill produced no problems. There was no controller cutting out or screams of protest from the motor’s internal roller drive.

Since then, battery range has increased, and after 5 conditioning cycles, the battery is lasting 18 miles back in the Kinver area, commuting to work, this is with moderate effort and coping with steep hills.

I am very happy with the bike, my fitness has increased already and my car is stopping on the drive so it’s all coming to plan! I have some accessories on order, rack, panniers and (apologies to some) mudguards. Will post some pics when they’re fitted.

All the best
Mike

 

[flecc]

Hi Mike, I've been watching and waiting for your report ever since you said you were going down to Purley that weekend. The weather wasn't too clever then was it, though not quite as bad as forecast.

Good to hear the bike is doing the job for you in giving relief on those hills and that you're pleased with it.

P.S. I think the mudguards make perfect sense, it is Britain after all.
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[keithhazel]

P.S. I think the mudguards make perfect sense, it is Britain after all.
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oh Flecc you have lost loads of street cred by joining my "mudguards make perfect sense" club.........would you like a "fuddy duddy" badge like mine too ?...lol