Best set-up for range minded individuals

[dogman dan]

I don't know that answer. Usually the lower voltage motor will be slower, and then go further due to less wind resistance. The more typical thing would be to have controllers of similar amps, and the voltage is the variable. I would guess, though, that if WOT on both the 24v 20 amp and the 48v 10 amp were producing the same speed, they would both be equally efficient at WOT. What happened between start and full speed might be better with one of em but I can't even guess which it would be.

 

[rearengine]

My first post..

I just mounted a 36v , SLA 12ah, 50amp controller, 600w motor, 20" front wheel, on my Rans V2 recumbent bike.. It is a WE Aotema motor.. I have about 80 miles on it, runs fine so far.. I haven't gone far enough on one charge to know my range.. the longest was 12 miles..
I am just wondering what you guy's think of this set up, and if there is anything I should know, pros or cons.. Or what any of you would do with it if you had it .. Thanks.. Bill

 

[dogman dan]

Depends on how far you need to ride. For shorter rides, like 70% of the capacity of the sla's or less, the lead is fine. But for longer ranges, or just for not having to worry so much about depth of discharge, any other battery is better. I just got some old school nicad for my recreational bikes and am quite impressed with it. Sure it's a bit heavy, but the shelf life for a weekend bike was more important for me than the weight. For my commuter though, lifepo4 is the bomb. Long range, no voltage drop, high expected cycle life, really light weight. You could get 10 ah or more of lifepo4 and be set for some long rides.

 

[StevenR]

I get 25 miles at an average of 20 to 25 MPH (depending on wind and if I ever get that 30 MPH tailwind it will go way up) from a 5303, 48V40A controller and 48V20aH Ping pack.

The Ping is at/beyond its limit and occasionally cuts out if throttle is applied to quickly but otherwise this seems to be right in the same range ballpark as the super efficient systems. I am running faster than most are describing here which would put the X5 in its efficient band. I regularly run at 30MPH on the flats and usually hit 45 somewhere on a downhill along the route. I practice wind management and try to tuck whenever possible. This seems to reduce power consumption by around 20% at 25-30 MPH. If I am running at 1000 watts it will drop to 800 or so. A fairing, aero bar extensions and a tail cone are in the dream/planning/acquisition stage. I want to get 60-80aH at 48V and shoot for 150+ mile range at 25+ average.

 

[icecube57]

Depending on how fast you want to go is the main issue. Can you pre plan to set aside some time to go slower. Or do you need to get there right away. My fat butt consumes about 1 AH a mile on my set up WOT@ 25 to 30+mph. But yesterday I did. 52 miles and consume 14.55 AH @ 14.2 wh per mile.. Over the entire trip it was about 3.5 miles per AH sometimes 4 miles got squeezed in on certain sections of the trail. All I did was reduce my speed to 15-18 mph and pedaled along with the motor. Not even putting any effort in. Almost play pedaling. I stayed below 3-400watts or about 5-6A. You can make any bike a hyper miler. Just by playing with the throttle. If you are trying to get range with WOT. I honestly think you have to get a slow wound motor that has a low top speed. Once that motor reaches its top speed. (near freewheel speed) the amp consumption will fall to your 10A or less but a faster wound motor could do the same thing you just dump alot of power trying to get to that free wheel speed . I think slow and steady wins the race. Especially if you factor in hills. You get a high turned clyte on some hills and compare it to a 406-408 AH start to add up fast. on the lower wound motors.

 

[Russell]

I think many folks are confused by the simulator curves at ebikes.ca with regards to the efficiency plots. The motors most folks use are efficient over a wide range of speeds, not just at a high speed. What the curves show you if you don't change the throttle setting down from 100% is that yes the efficiency is high at some high speed and then if you hit a hill or encounter a headwind which causes you to slow down the efficiency of the motor will decrease dramatically. However this does not mean the motor is inefficient at low speeds because they aren't. All you have to do is reduce the throttle setting on the simulator and you'll see the entire efficiency curve moves with it so yes you can go slow and the motor will be very efficient and of course since you're moving slower the overall efficiency will be far greater also because of reduced drag due to rolling resistance and dramatically less aerodynamic drag.

-R

 

[dogman dan]

Well said and exactly right. I didn't understand that till recently. I can climb a hill or ride into the wind slower on my brushless motor. The old brushed one would simply stop if you tried to ride half throttle up a hill. So stalling the motor, I would get horrible efficiency going slower. But if the motor is happy at a slower speed, it's very efficient.

 

[spinningmagnets]

I don't want to sound experienced...I'm not. But I have been doing some research for a while. My range needs are short, but if range is important, I have some thoughts I'd like to share.

I'm reading good things about the effieciency of the 9-Continents hubmotor from ebikes.ca It is a hub-motor with a high pole count, this also allows the option of a sensorless controller, but what caught my eye was the reliable hub-motor configuration got measurably better range from a higher pole-count. It is more expensive than some of the more common affordable hub-motors.

Another thing is, if you are willing to go slower on a steep up-hill, having gears will always increase range efficiency in a non-hub set-up. I drive an 18-wheeler, and with my 14-speed trans I am very familiar with the design philosophies behind pulling heavy loads up steep hills without over-heating.

I have read about two non-hub set-ups that were very enthusiastic about how they extended range without adding Ah to the battery pack size.

First is the well-known Cyclone kit. It is pricey, but it allows the motor to use the bikes gears to allow good hill-climbing and also high top-speed without overheating. Enthusiasts who like this often discuss how to upgrade the kit-parts weaknesses. Pricey...

Chas over at VisforV has a trike with a 500W cylinder motor that uses a 3-speed bicycle internally-geared hub as a transmission. 1st is hill-climbing, 2nd is normal driving, and 3rd is high-speed. He could afford a bigger motor and battery pack, but the smaller motor helped him get the best possible mileage. he sacrificed raw acceleration, and speed during hill-climbing, but he got GREAT range from a small battery. It was a 24V motor that was run at 36V.

There is also another option I recall. One E-biker has a small hub-motor and also a free-wheeling cylinder-motor set-up. During accelleration, both motors help get great acceleration (if desired) but when just cruising, he only uses the small (just adequate) cylinder motor to get best possible mileage. If this dual-motor set-up interests you, there has been a lot of work here recently with the tiny ultra-high-RPM RC motors...

 

[julesa]

I think many folks are confused by the simulator curves at ebikes.ca with regards to the efficiency plots. The motors most folks use are efficient over a wide range of speeds, not just at a high speed. What the curves show you if you don't change the throttle setting down from 100% is that yes the efficiency is high at some high speed and then if you hit a hill or encounter a headwind which causes you to slow down the efficiency of the motor will decrease dramatically. However this does not mean the motor is inefficient at low speeds because they aren't. All you have to do is reduce the throttle setting on the simulator and you'll see the entire efficiency curve moves with it so yes you can go slow and the motor will be very efficient and of course since you're moving slower the overall efficiency will be far greater also because of reduced drag due to rolling resistance and dramatically less aerodynamic drag.

-R

Yeah, and the real efficiency of power->motion goes through the roof if you take the throttle down to zero. :lol:

The motor efficiency does actually go down as the bike slows down, electric motors are generally more efficient at higher speeds, or at least the speed the motor was designed for. Try moving the throttle slider around, you'll notice the PEAK efficiency does get lower as the throttle gets reduced. But the simulation graph makes it look worse than it really is. Anyway you're right - decrease in aerodynamic drag will easily overshadow the decrease in motor efficiency.

 

[Russell]

The motor efficiency does actually go down as the bike slows down, electric motors are generally more efficient at higher speeds, or at least the speed the motor was designed for. Try moving the throttle slider around, you'll notice the PEAK efficiency does get lower as the throttle gets reduced. But the simulation graph makes it look worse than it really is. Anyway you're right - decrease in aerodynamic drag will easily overshadow the decrease in motor efficiency.

Yeah of that I'm aware but it's only a few percent. What I was referring to is when folks look at the efficiency curve for 100% throttle and then assume from that plot the efficiency at say half speed is something like 50% when in fact be 79% compared to 83% at 100% throttle.

Another problem happens when people look at the plots for a high rpm motor (the ones intended for a 20" wheel) in a 26 or 700C wheel and see they go really fast however that's only on paper. In reality they don't reach the projected speeds because they don't make enough power. In that case the motor is always run lower down the efficiency curve. There's a reason vendors offer certain motors in certain wheel sizes and to go too far away from those standard pairings can cause disappointing performance.

-R

 

[Russell]

Oh and one more thing; hub motors aren't designed so much for a certain speed as they are designed for a certain rpm/volt. People run the same motor at various voltages which is essentially the same as running at various throttle settings since all you're really doing with the throttle is changing the effective voltage to the motor. You can see this if you vary the battery voltage for a specific motor on the ebikes.ca simulator. The same motor will have slightly less peak efficiency when run at 24V compared to 36V and 36V compared to 48V and so on. This slight drop in efficiency is similar to what you see when you are running a 48V battery and reduce the throttle setting to achieve a lower speed.

-R

 

[OneWayTraffic]

I don't know that answer. Usually the lower voltage motor will be slower, and then go further due to less wind resistance. The more typical thing would be to have controllers of similar amps, and the voltage is the variable. I would guess, though, that if WOT on both the 24v 20 amp and the 48v 10 amp were producing the same speed, they would both be equally efficient at WOT. What happened between start and full speed might be better with one of em but I can't even guess which it would be.

Just going to elaborate here.

Watts are watts. Unless the motor has different efficiencies at different voltages, then it really doesn't matter how you put the watts in. Having said that, I played with the ebikes.ca simulator and there does seem to be slight differences in overall efficiency at different voltages, with lower voltages being slightly more efficient. I'd guess it's due to internal resistance in the batteries. Playing with the simulator is the number one way to get a feel for performance without spending money. That simulator is a fantastic traffic pull to the ebikes.ca website.

The main reason people usually say that volts=speed and amphours=range is very basic. If you have the speed, you're more likely to use it. Unless you are deliberately choking your throttle, then you're going to see more range at lower voltages and higher capacities. If you're riding deliberately for range, then there will be very little difference. It's also much easier to pedal along at lower speeds unless you have that godugly but awesome 58 tooth chainwheel that Dogman has.

The single most important thing for range is wind resistance. It's a cubic. So going twice as fast burns 8 times as much energy to cut through the wind. The effective range differential between 15mph, 20mph and 25mph is huge.
Then there's hills. The most efficient way to climb a hill is at a speed where wind resistance drops off to negligible values compared to the work required to gain gravitational potential energy (less than 15mph), but not so slow that your motor stalls. So look for a throttle value that gives you good efficiency and output energy at less than 15mph and stick to it.

Play around with the simulators and you'll get a good feel for it.

http://www.me.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc1.htm

http://www.ebikes.ca/simulator/

 

[OneWayTraffic]

OK maths graduate mode on:

Exponential a^x.
Cubic x^3. ( A subset of polynomial.)

Wind resistance is a cubic, not exponential.

It may seem picky but the difference is huge.

Credit card interest is exponential. Most things in the basic physics of ebikes are not.

It's a cubic due to the 0.5mv^2 relationship of kinetic energy multiplied by the linear relationship between speed and the amount of air that hits you. So a doubling of speed=twice as much air containing four times the kinetic energy.

 

[Miles]

It's a good job that you get there in half the time when you double the speed, or the energy required for the journey would go up by the 3rd power, too....

 

[swbluto]

Another mathematically aware user. I think I like OneWayTraffic's perceptiveness (Fechter's comment that wind resistance as being exponential in the FAQ section seems a particular blunder, but it's a good enough approximation for the laymen just starting out).

(I'll be using the term "Equilibrium" to denote values at the top-speed you'll attain under a set of specified conditions)

Anyways, if you reduce the throttle, it has two effects.

1. It decreases air drag and (Power loss is cubic to speed)
2. It decreases the current going to the motor at the "equilibrium speed" since the "equilibrium speed" is lower and so the "equilibrium torque" is lower, which decreases the energy lost to the motor's internal resistance. (Power loss is square to current)

So, in essence, it doesn't really matter how you cut it... in regard to wh/mi, lower throttle is the way to greater range within a reasonable range. I.e., don't expect to go too far when you're not pumping enough current to go anywhere. But, in terms of Motor Efficiency, a different concept, the peak efficiency does tend to go down since a greater ratio of the current is used to overcome the "cogging torque" of the motor as opposed to actively pushing you forward/providing useful torque but the "equilibrium efficiency" peaks at a given throttle value(It seems to be at about 80% throttle on my ebike according to my simulator). Cogging torque seems to decrease with rpm, however, and... uhhhh.. it's going beyond my comprehension at the moment.

So, basically, differentiate between "motor efficiency" and "traveling efficiency".

 

[swbluto]

So going twice as fast burns 8 times as much energy to cut through the wind.

Hate to be pedantic, but I thought I'd share your style: going twice as fast burns eight times as much energy per unit time to cut through the wind. It actually only burns 4 times as much energy per unit distance so the total energy usage for a given distance would be quadratic to velocity.

 

[Miles]

So going twice as fast burns 8 times as much energy to cut through the wind.

Hate to be pedantic, but I thought I'd share your style: going twice as fast burns eight times as much energy per unit time to cut through the wind. It actually only burns 4 times as much energy per unit distance so the total energy usage for a given distance would be quadratic to velocity.

Like I said...

It's a good job that you get there in half the time when you double the speed, or the energy required for the journey would go up by the 3rd power, too....

 

[OneWayTraffic]

So going twice as fast burns 8 times as much energy to cut through the wind.

Hate to be pedantic, but I thought I'd share your style: going twice as fast burns eight times as much energy per unit time to cut through the wind. It actually only burns 4 times as much energy per unit distance so the total energy usage for a given distance would be quadratic to velocity.

Like I said...

It's a good job that you get there in half the time when you double the speed, or the energy required for the journey would go up by the 3rd power, too....

You know I never thought of that.
I was thinking of power, not energy.

Still using four times the energy for each doubling of speed. (And once you get to say car or motorbike speeds, this absolutely dominates) is significant.

The other thing where power matters would be with the C rating of your batteries. Cutting speeds a little would both increase range and battery life.
The best thing to do for commuters, imo, is to pick a speed that will get you there on time and in range, and stick to it. It's better to leave ten minutes early rather than pedal the last 5miles.

 

[swbluto]

Like I said...

It's a good job that you get there in half the time when you double the speed, or the energy required for the journey would go up by the 3rd power, too....

Miles, I think you know your brain operates on a higher plane than us mere mortals. :wink:

 

[JennyB]

Still using four times the energy for each doubling of speed. (And once you get to say car or motorbike speeds, this absolutely dominates) is significant.

The other thing where power matters would be with the C rating of your batteries. Cutting speeds a little would both increase range and battery life.
The best thing to do for commuters, imo, is to pick a speed that will get you there on time and in range, and stick to it. It's better to leave ten minutes early rather than pedal the last 5miles.

For ultimate range it also matters how fast you can recharge, because total travel time= time on the road + recharge time. In GB, using a single domestic socket, you are limited to 3Kw. Given that limit how fast can you actually restore, say 1KwH of capacity?

Some goals to shoot for:
500 miles in one day
800 miles in two days
3000 miles in ten days
200 miles a day for a longer period.

That represents the absolute limit for ultramarathon cycling, or about as far as a sane person would want to go on a motorbike tour. Is it possible for ebikes?
The latest electric sports cars have a max range of about 200 miles (3 hours?) and recharge in 7 hours. Given charging points in the right places, the 2-day target would be possible, but 500 in one day would be out of reach, even starting on a full charge.

Now consider a streamlined e-bike that could maintain an average of 30 mph on 500 watts. That could travel the distance in just under 17 hours on the road, leaving seven hours for recharging (and sleep). Not easy - but possible?

 

[swbluto]

If you have the opportunity to recharge, look at Hyperion G3 CX lipo! They can be charged upto 5C meaning a recharge in under 15 minutes! Complying with under 3kW, it seems that you'd be limited to 3kw/5 = 600 wH or slightly longer charge times for higher watt-hour. At a range-oriented 20wH/mi(@20 mph), that implies a 30 mile range before recharging or recharging for 15 minutes every 1.5-2.0 hours of riding.

They're not as cheap/wh as low-c lifepo4, but nothing on the market that can take fast recharge times are.

 

[JennyB]

If you have the opportunity to recharge, look at Hyperion G3 CX lipo! They can be charged upto 5C meaning a recharge in under 15 minutes! Complying with under 3kW, it seems that you'd be limited to 3kw/5 = 600 wH or slightly longer charge times for higher watt-hour. At a range-oriented 20wH/mi(@20 mph), that implies a 30 mile range before recharging or recharging for 15 minutes every 1.5-2.0 hours of riding.

They're not as cheap/wh as low-c lifepo4, but nothing on the market that can take fast recharge times are.

I guess there's only one way to find out. Anyone on for trying Lands End to John O'Groats in two days?