Jabe24

Hej,

Due to the low quality of the PAS that came with my ebike conversion kit, I haven't installed the PAS yet and have used the thumb throttle instead.

Basic info on my setup: 500W front hub driver with a 48V 20mAH battery. Speedcap of thumb throttle is set at 25km/h.

My question:
Would the engine consume less energy with pedal assist than with thumb throttle, given that I apply the same amount of torque while also assuming the speedcap w
ith pedal assist is set 25km/h?

Follow-up question:
If there is a strong decline and my bike is going 30km/h without using the TT, would the energy usage be significant if I use the TT (which would give no benefit as I am already going faster than 25km/h). I am asking because I have tried it, and I can hear the motor working, so there must be some energy wasted, right?

Thanks

OldRailfan

Using PA is probably more logical/battery frugal (but it depends on the set-up) than just using the throttle. My e-MTB doesn't have a throttle, but my equal-half's e-bike does. I get more kilometres with the e-MTB set up than with her generic e-bike. Tested on the same terrain/course!

Doc_Wui

The past week, I ran the same 17 mile route with my usual habit of throttled starts, level 1 assist, and throttle help on hills. Then I did it a few days later without touching the throttle, and downshifting more. I used a wattmeter to measure the amp-hours used. The savings with PAS only was 20%, What this showed is how lazy I had become in my riding habits, falling back on throttle whenever the going got tough,

On the other hand, I think that shutting off PAS and using throttle only will save more battery than PAS alone, if one wants to get exercise when riding. That;s because with a cadence assist and moseying along at 12 mph, my controller puts out a constant 100W, or about 2-3AH per hour depending on battery voltage, I could do that w.o the motor on the flats,

linberl

My system lets me pause the PAS so when on flats I flick it off, and just button push it back on for inclines or headwinds. I don't use the phone app very often, but it does show my output in wh as well as the motors so I can see who is doing the work. I find I use less battery by turning on the PAS when needed rather than using the throttle as I can't quite keep it exactly at the equivalent of level 1. Bumps tend to cause me to push a bit more and I just can't hold it precisely for long periods. but that's just me....

chas58

No.
There are a lot of variables, but if everything is the same (power from the motor and power input from you), there is no difference. Now if you ramp up power faster with the throttle, and get lazy with your legs, sure that is different.

No.
Again, it depends on a lot of variables. But these motors have a torque peak, then power falls off very, very sharply. once you go beyond this saturation point (peak), the motor starts to use less and less energy. Sure, you are using some, but probably not a lot. One way to know is to measure the wheel speed with no load (spinning in the air). once you go beyond that point, you aren't using much energy at all. Even if you are within 2-3kmh of that, you aren't using much.

Here is a chart to help visualize power vs speed:

mpetry912 

Chas, interesting chart, where did you get it ? and what are the units for the Y - axis ? you're point about torque vs speed makes sense to me.

what I see a lot of ebike riders do is ride everywhere on the highest assist, and in 9th or 10th gear So for most of their riding they are on the steep part of the torque curve. that does not result in the best range generally speaking.

As a long time road bike rider, I ride my e-bike very much like a roadie, I start off in a low gear and shift up with speed, shift down for hills. I think this technique is easier on the drivetrain and leads to improved range.

/markp

mclewis1

That looks like it's taken from something like Grin's motor simulator tool - https://ebikes.ca/tools/simulator.html

Long term road rider here too. I ride a cadence PAS (power) setup and tend to leave it in one of just a few power settings and continue to use the gearing to vary my speeds/effort. For example it's at 100w for most of my flat riding. I turn it off on downhills and I might go up to 200w with sustained head winds. Then it's 500-1000w depending on the up hill characteristics. With a geared hub motor setup I try and ride the hills as fast as practical (a little different than when it was just me powering the bike). This keeps the motor in a better (more efficient) rpm range but it's not something I can maintain for too long. If I use anything around 1000w I will overheat the motor in a few minutes, but I can climb for quite a while with just 500w.

2old

Not quantitative, but I tend to leave my PAS bike in some setting and ride, while with the "throttle only", I ride without assist most of the time, then power on when I feel like it. Accordingly, less power usage with throttle, although it doesn't matter since I always have enough power to finish the ride.

chas58

Yes, take a look at "Grin's motor simulator tool - https://ebikes.ca/tools/simulator.html"
It is an amazing tool for designing and building ebikes.

Being a strong rider, it took a little design work to get my bike where I wanted it - basically just a top end boost (like riding a tandem with my brother, or riding in a pack). It adds about 5mph to my solo cruising speed (used mostly for commuting).

The x axis is speed, The y axis (on the full chart) is torque, power (and efficiency).

One of the key things I learned is that for most ebikes - pedaling does nothing at speed . The power drops off, and the wind resistance increases faster than most people can make up for by pedaling. With a 750 watt motor, the power drops off like dropping off a cliff.

Ideally, you want to design a motor to hit its power peak around its top speed so that the inflection point in the power matches the power required to go at that speed.

Most good long term riders do 100rpm. When I see someone doing 25mph at 60rpm, its pretty obvious they are on an ebike. I don't think mid drive motors really let you do 100rpm at peak power.

Interestingly, I ended up with a bike geared like my track bike - 90 gear inches
on the track, cruising speed is 25mph, race speed is over 30, and sprinting is about 40mph.

on the road ebike, I just have a full throttle switch, that I really don't need to use until I'm up to 20mph - the throttle makes it efficient to cruise at 25mph.

i have a mountain bike too, but a good light drop bar road bike with good tires is impressively efficient with a small motor (as opposed to a 60lb mountain bike with heavy inefficient tires).

mpetry912 

thanks for sharing Grin's site, lot of information there.

I genuinely learned something from this post ! thank you

/markp

mschwett 

A well designed one should! Specialized’s SL, for example, peaks at 100RPM. Of course, that peak is only 240w watts at the crank (300 watts of battery)…