Does PEdal Assists Save battery with constant starts & stop?

[tomtom123]

I live in NYC and basically riding and ebike would means of stop and starts, which would kill battery life.

Then i saw this pedal assists, item and it states under the description:
"Extends battery life – Avoid power wasted by inconsistent acceleration (example: accelerating with a throttle, only to waste power by braking soon afterwards"

Is that true? or just BS marketing? If it's true then how come?
cause even with pedal assists don't the motor stop when you stop and still have to turn on again? can anyone explain how the motor and controller works with pedal assists and without pedal assists?

Also are pedal assists just more trouble then they're worth? should i even bother?

 

[mlt34]

Full disclosure: I hate PAS.

With that out of the way, I believe it is actually backwards, PAS wastes energy with constant starts and stops. With PAS, most systems just check if the crank is turning and if so, give gas. That's the equivalent of always giving a hand throttle 0% or 100%. But we know that by feathering the throttle on starts and not just twisting it to wide open throttle when the light turns green can save a lot of energy. A CA or other watt meter illustrates this well. If I go WOT I pull up to 40 amps until I get up to speed. If I feather it, I can keep it below 15 A and it only takes a few more seconds to get up to speed. PAS on the other hand is like flooring it all the time or totally releasing the throttle - there is no feathering ability.

Some people might say if you are ACTUALLY pedaling hard to help the bike, then PAS helps you save energy. Most people I know with PAS just pedal enough to make the sensor start giving gas.

 

[d8veh]

Pedal assist can only save your battery when you provide the energy by pedalling that the battery would otherwise have given. Some pedal assist bikes don't have throttles, so you have to pedal to start them, which would save a reasonable amount of battery, but at the expense of your tired legs.

PAS systems have moved on a lot recently. You can get decent controllers with LCD displays where you can adjust the amount of assistance either by current control or speed control. This makes the bike very comfortable and easy to ride. They still have independent throttles, so you get the best of both. Normally, you can switch off the PAS at the display if you want.

You need to check a few more details about that bike's PAS system; No display is normally bad; LED display is not bad; LCD display is good; No throttle is not as good as an independent throttle, but not bad with LCD display type.

I've detailed the common Chinese systems above. There's many other more sophisticated systems particularly on European bikes, but they normally don't have throttles.

Can you give a link to the bike in question?

 

[dogman dan]

I think a good right hand on the throttle can be much smarter than PAS. To be honest, I have never tried a pas. I come from years of both bikes and motorcycles, and throttles come natural to me.

But I have a bad right hand on the throttle most days.

The best way to ride to extend range besides simply riding slower is this.

Pedal the first 10-15 feet, then throttle up. Set a speed, then keep pedaling so you go 2 mph faster. If you have a wattmeter you can watch while riding, you will see between 100 and 200w less than motoring the same speed. Typically 20 mph takes between 400 and 600w. You can pretty easily make that 300-500w, or even 200w if you pedal hard. That can be a big savings.

Much of the wasted power on an ebike is when the motor struggles to get going, from 0-10 mph. The faster the winding of the motor, the longer that struggle takes and the more heat is made.

Another way to make the struggle short for a fast winding motor is to add more power. In that case, you get going very fast, and don't make such a big percentage into heat. But you don't get much more efficient, since you use more power to get going faster, and in general end up going faster the whole ride.

With the slower winding motor, you also feel it get going 10 mph faster, without adding more power, and experiments with a thermometer in the motor confirm that the motor stays cool longer.

My real world ranges in city riding and limiting top speed to 20 mph with a fast motor was about 20 miles, same route with a very slow motor was nearly 30 miles. That was with no pedaling till moving 15 mph. Much closer to the same range with both motors if I pedaled to get going, then throttled. But that meant shifting down every stop sign, every 300 feet. Ugh.

 

[dogman dan]

One more comment. Both fast and slow windings are nearly identical in range once cruising 20 mph. I got the same results with both dd and gearmotors, including fast and very slow winding dd motors, if tested on a run with nearly no stops at the exact same speed, exact same route, exact same weather. Makes sense, once at 20 mph, all the motors are running in an efficient rpm.

The big difference was in how the motor did with lots of starts and stops.

For that, the worst was a fast wind dd motor. Both the gearmotor in a middle range winding, and the slow winding dd motor did about the same in stop and go riding. The middle range dd motor did better than the fast dd, but not as good as the middle speed gearmotor or the slow dd.

So with the gearmotors, you can use a faster winding and get good efficiency in stop and go. That's the benefit of the planetary gears, and why they invented that kind of motor.

I did not find that to be the case when riding the very fastest winding of a gear motor. So I don't consider the 6t Mac a good motor for city riding. It's just so fast that the gears benefits are not as big. But the 8t would do ok for efficiency, if the 10T is just too dang slow for you.

Any of the mid speed motors, such as a 9 continent 9x7, are not that bad in stop and go riding. But my wattmeter says time and time again, that the 6x10 winding of the same motor goes farther in urban riding. So if 20 mph is fast enough, the very slow 6x10 works good in the city. Many really like a 6x10 on 72v, and then you do get 30 mph if you want it.

 

[Paul_G]

I live in NYC and basically riding and ebike would means of stop and starts, which would kill battery life.

Then i saw this pedal assists, item and it states under the description:
"Extends battery life – Avoid power wasted by inconsistent acceleration (example: accelerating with a throttle, only to waste power by braking soon afterwards"

Is that true? or just BS marketing? If it's true then how come?
cause even with pedal assists don't the motor stop when you stop and still have to turn on again? can anyone explain how the motor and controller works with pedal assists and without pedal assists?

Also are pedal assists just more trouble then they're worth? should i even bother?

A big YES is saves far more without a throttle on a proper censored bike, look for a bike with a torque sensor and not a RPM sensor. Being that your in NYC test ride a Stromer ST1 Platinum at NYCeWheels on the east side.

I have a Bomber and now a Stromer ST1 Platinum and the Stromer has a 522 WH battery and will run 40+ miles at 27-30 MPH....amazing low draw and good power.

If you get one order with the suspension forks and add a ThudBuster seat post and it rides nice.

Paul G

 

[dogman dan]

To clarify, with throttle or pas, if you select a lower rate of burn, the battery obviously lasts longer. That's how bionx got so much range from such small batteries. On level 1, they'd go forever.

Run a throttle with a low power level selected, and you also get lots of range.

But by far and away, the best way to avoid losing your range to stop signs is to pedal away from them rather than use lots of power in the motor.

It's difficult to sort out all the effects of this or that while riding e bikes. It took me 2000 miles, without a wattmeter to help me, just to learn to ride more efficiently. It takes many miles of riding to run proper experiments with only one variable changed. Soon as you switch from one bike to another, I bet you just changed three variables, not just pas and no pas. It's hard as hell to just run experiments where the weather is identical on each run. On the same day wind and temp start changing.

40 miles at 27 mph with 522 wh. That makes me wonder what the weather was like.

 

[miro13car]

to much generalization.
It all depends what PAS and what throttle.
Throttle acting like ON-OFF type of throttle can waste WHours of el. energy for sure.
It is not only the throttle itself but how it is electrically implemented /however mechanical construction of throttle is also important= $$$/.
Edrives which digitize signal from throttle before processing in controller achive seemlesly smooth acting throttles, very linear - every 1cm of lever or twist gives result = speed increase.
on ONOFF acting throttles user often overshoot and back up throttle = clear wastage of Wattshours.
EPLUS AND STROMER are examples of wonderfully liner throttles.

 

[electr0n]

When I need to go far I set a really low amp limit in my cycle analyst and that makes a huge difference. I don't even need to be too light on the throttle that way. You can also move to a smaller diameter wheel for a significant increase in stop and start efficiency. I went from a 26" setup to a 20" back to a 26" and the amount of time I spent drawing big watts accelerating is huge with the bigger wheel. The motor also gets very noticeably warmer in the larger diameter.

I've never used a pedal assist, interested to hear from others. The way the throttle is used has a big impact on efficiency. I could see the potential for a good algorithm could simulate this.

 

[aroundqube]

My experience with pedal assist mirrors what mlt34 describes. Plus- my bike has multiple gears,using a derailleur for shifting. So when approaching a stop situation I stop pedaling and then after a delay, the assist cuts out. Then I have to pedal while stopping to downshift so that I will restart from a stop in low gear. The pedal sensor restarts the controller at full throttle while fighting it to stop the bike with the brakes,and go without the brakes so that I can shift .No savings there. Also had a bad experience one time when I briefly got off the bike during a ride and rolled the bike forward.The pedals turned and activated the controller causing the bike to leap forward while I held on.This setup did have functioning e-brake (kill switch) levers.

 

[tomtom123]

to much generalization.
It all depends what PAS and what throttle.
Throttle acting like ON-OFF type of throttle can waste WHours of el. energy for sure.
It is not only the throttle itself but how it is electrically implemented /however mechanical construction of throttle is also important= $$$/.
Edrives which digitize signal from throttle before processing in controller achive seemlesly smooth acting throttles, very linear - every 1cm of lever or twist gives result = speed increase.
on ONOFF acting throttles user often overshoot and back up throttle = clear wastage of Wattshours.
EPLUS AND STROMER are examples of wonderfully liner throttles.

Are bafang BPM motor thottle linear like the stromer and eplus? or are they just On or OFF?

 

[mlt34]

Are bafang BPM motor thottle linear like the stromer and eplus? or are they just On or OFF?

Nearly every modern ebike with a twist or thumb throttle is a linear style throttle. On/Off style throttles are rare, and usually on smaller electric kick scooters. Cheap PAS systems usually work like an on/off throttle, or else have a few 'levels' of RPM counting (not the settings on the display) which would equate to something like "off", "20% throttle", "50% throttle" and "100% throttle". Anything that doesn't let you manually fine tune the amount of throttle you are giving is going to limit your efficiency maximizing potential.

Even better than a linear throttle is a logarithmic one, which would allow you to fine tune the lower end of the throttle range better.

 

[dogman dan]

Yes, ask a vague question, get generalized answers. But the trend is pretty clear, efficiency in stop and go riding depends more on other things that pas or throttle.

It's what motor you have in what size rim, and how you ride it. PAS on the lowest setting available would of course be one way to keep the big amp spike down on the starts.

Personally though, I'd rather be riding a slow motor on 72v in NYC traffic, than a fast motor with no power. Use a motor that doesn't struggle is such a no brainer to me. It could be a slow motor, or just a small wheel. Either way, in heavy city traffic, the last thing you really want is a slow take off.

 

[miro13car]

mlt34,
you misinterpreted my post
Maybe I was not clear ...
I wrote
"throttles acting like on-off type of throttle..." - meaning cheap linear throttle /and electronics to which it connnects/ which is not really linear because it acts more like a on-off switch, that is what I ment.