While I did make note of this ...John in CR said:Your Determining Peak Motor Output - Simple Cheap Method does not taking into account current limiting, so ambitious effort but no cigar since it won't work on any bike I own.
In my example, the motor shows capable of taking advantage of >90A at low rpm.DrkAngel said:(The exception is if the controller is of inadequate amps to allow maximum peak watt output.)
DrkAngel said:1. Determine no-load maximum motor speed - digital speedometer on motor wheel, blocked up (EG - 36mph)DrkAngel said:Observing the ebike.ca\simulator, I notice a consistent ~50% relation of input watts to watts output occurring at ~40% of no load motor speed.
Using this, it is possible to determine peak motor output.
2. Multiply no-load speed by 40% (EG - 36mph x .40 = 14.4mph)
3. Cruise near 14.4mph, Apply full throttle and note watt usage as speed hits-passes 14.4mph (1498w x .50 = 749w motor output)
(Precise 50% of input occurs at 38.6% of no-load speed- 13.9mph (this EG) ... but 40% is a fairly close, easy to figure number )
40% of no-load speed intersects 50% efficiency near the center of peak watt output nicely!
Surprisingly, this seems fairly consistent among all the simulations I have tried and looks to be a reasonably reliable measure.
"Reasonably" accurate!
Not precise but accurate within a few percentage.
(The exception is if the controller is of inadequate amps to allow maximum peak watt output.)
Update - I just sampled various-more motor types and found a variance of ~ 40% to almost 50% of no load speed as the peak watt output and 50% efficient point.
The 50% efficiency point remains firmly within the peak watt output region!
This graph is misleading and has been misinterpreted in this thread. It should be interpreted as a guide to how a throttle should be used at low speed and an argument in favour of phase current sensing in motor controllers.DrkAngel said:DrkAngel said:Thought I'd graph a direct comparison of the electrical watts supplied into a motor and the actual motor output (watts) power.
Based on a 750w motor at full throttle ...
At 1mph energy efficiency is ~3% ... 97% wasted heat.
John in CR said:Sorry Ken, but if your motor is getting bogged down on a hill then reducing throttle won't save the motor either. Assuming phase current control isn't an option, which it isn't with bargain controllers, then reducing pack voltage can help, because it that reduces phase current multiplication for the same power resulting in better efficiency at lower speeds. The real answer is a more powerful motor and/or a gearing reduction.
I live in a mountainous country and hills are a part of almost any ride. My rule of thumb is that if the bike can't maintain about 50% of top speed on the flats, then then hill is too steep regardless of throttle position, so it better be a short climb, because motor temps can get out of hand in tens of seconds.
Yes, a motor that is run too slow can not produce much power but that isn't the misinterpretation I was claiming. I was claiming motors can run efficiently at low speed. Even a little extra power can help reduce the pedaling load. ThenJohn in CR said:The real answer is a more powerful motor and/or a gearing reduction.
Yes, that is entirely consistent with what I said. However, it will lower the output power at higher speeds so would not produce the same higher speed portion of the "Watts out" curve in the graph.John in CR said:reducing pack voltage can help, because it that reduces phase current multiplication for the same power resulting in better efficiency at lower speeds.
That's where I'm confused as it is inconsistent with the other statement. Reducing the throttle has the same effect as reducing pack voltage with most controllers. Reducing the throttle sufficiently will definitely save the motor from overheating.John in CR said:Sorry Ken, but if your motor is getting bogged down on a hill then reducing throttle won't save the motor either.
That's got me more confused. Regardless of the wind there must be somewhere it hits peak efficiency before unload speed.cal3thousand said:Ever try running a motor that is wound too fast for the wheel size? Doesn't matter how soft you baby the throttle, it will be inefficient all the way up to unloaded speed.
Ken Taylor said:It's nice to get a response but I'm a little confused by those from John in CR and cal3thousand. First.
Yes, a motor that is run too slow can not produce much power but that isn't the misinterpretation I was claiming. I was claiming motors can run efficiently at low speed. Even a little extra power can help reduce the pedaling load. ThenJohn in CR said:The real answer is a more powerful motor and/or a gearing reduction.
Yes, that is entirely consistent with what I said. However, it will lower the output power at higher speeds so would not produce the same higher speed portion of the "Watts out" curve in the graph.John in CR said:reducing pack voltage can help, because it that reduces phase current multiplication for the same power resulting in better efficiency at lower speeds.
That's where I'm confused as it is inconsistent with the other statement. Reducing the throttle has the same effect as reducing pack voltage with most controllers. Reducing the throttle sufficiently will definitely save the motor from overheating.John in CR said:Sorry Ken, but if your motor is getting bogged down on a hill then reducing throttle won't save the motor either.
That's got me more confused. Regardless of the wind there must be somewhere it hits peak efficiency before unload speed.cal3thousand said:Ever try running a motor that is wound too fast for the wheel size? Doesn't matter how soft you baby the throttle, it will be inefficient all the way up to unloaded speed.
The suggestion being that with his new trip analysis software people would discover:-justin_le said:For instance I know a lot of people who don't use their throttle until after pedaling up to speed because supposedly they've been told that throttling off the line wastes a huge amount of power.
I'm then thinking; as useful as good analytics can be, this wasn't a good example as people don't think "throttling off the line wastes a huge amount of power". I then come across this thread and blow me down; it says:-justin_le said:... when you look at all the net watt-hours used on the average ebike trip, your initial starting acceleration after each stop will only account for a tiny fraction of that, and that throwing away this most useful aspect of the ebike away (getting quickly up to speed) doesn't buy much in return.
with a graph to prove it. In my view it is misleading because that graph assumes wide open throttle.DrkAngel said:At 1mph energy efficiency is ~3% ... 97% wasted heat...
Here I would only disagree with "Of course this will limit acceleration" because with the optimum throttle setting, the blue Watts Out line in the graph is unchanged, only the red Watts in line is reduced. Therefore reducing throttle to the optimum level does not limit output power and therefore does not "limit acceleration".DrkAngel said:The good news?DrkAngel said:Yes efficiency at low speeds is horrific!!!
Inefficiency can be regulated through the use of throttle restraint!
At most any speed maximum efficiency is attainable.
Of course this will limit acceleration ...
But, since the worst region is from a standstill till mid-speed, the application of pedal assist combined with moderated throttle can deliver satisfactory acceleration...
cal3thousand said:Yes, that is entirely consistent with what I said. However, it will lower the output power at higher speeds so would not produce the same higher speed portion of the "Watts out" curve in the graph.John in CR said:reducing pack voltage can help, because it that reduces phase current multiplication for the same power resulting in better efficiency at lower speeds.
That's where I'm confused as it is inconsistent with the other statement. Reducing the throttle has the same effect as reducing pack voltage with most controllers. Reducing the throttle sufficiently will definitely save the motor from overheating.John in CR said:Sorry Ken, but if your motor is getting bogged down on a hill then reducing throttle won't save the motor either.
Yes and I hope nothing I've written has appeared to contradict this. However when it is said:-DrkAngel said:I've always recommended restrained throttle combined with pedal assist, from a dead stop ...
I disagree. They are often referred to as speed based controllers but they aren't. They control the voltage seen by the motor. I realise there are limitations in that model but to quote the guy wholiveforphysics said:With the typical speed control based ebike controller, all you change with the throttle is the target speed.
:-liveforphysics said:nailed it
and that is also my understanding. When liveforphysics says:-John in CR said:Lower throttle position doesn't exactly equal lower voltage. It approximates it pretty well under low load conditions
I'd say it doesn't. That would require a feedback loop which varied motor voltage with speed. It is an open loop controller and the speed at any throttle position depends on the motor characteristics and load. On a low power motor you will get a significant reduction in speed on an appropriate hill that can be recovered by increasing the throttle. This is what cruise control does, using a feedback loop. On high power motors and low weight bikes the motor characteristics are such that speed as a function of throttle position is a good approximation which is whatliveforphysics said:The controller dumps everything it has up to its current limits into achieving that speed.
So where I think I'm most exposed is in defining what representsliveforphysics said:makes extremely high power low weight bikes unrideable. When I ran a 1200A controller to a Perm132 setup on 25S lipo on my bicycle, we had a single attempt of speed-based throttle and immediately realized only torque control throttle.
I think it is everywhere on the "watts in (electrical) at optimal throttle" curve on this graph:-John in CR said:low load conditions
only in the region of "excessive waste heat due to too much throttle" on the graph, which I recommend trying to avoid.John in CR said:...that breaks down ... due to spiking phase currents.
Sounds like an expensive programmable controller programmed ... badly!liveforphysics said:... With the typical speed control based ebike controller, all you change with the throttle is the target speed. The controller dumps everything it has up to its current limits into achieving that speed. ....
Take care that at low RPM, you can reach motor saturation. In a good system, input electrical power is more limited at low speed than at higher speed to avoid saturation.Although a full Amp motor system will supply full possible watt output from e.g. 20A, At 0 rpm the motor is capable of much higher input (60-80A ,,, possibly more)
I think it depends on the system, with a high power battery (low internal resistance) and if you don't reach motor saturation, increasing amps should increase maximum motor output power.Increasing amps will neither increase top speed or maximum motor output!
You also need to consider steep slopes where increasing amps allows to keep appropriate speed and improve efficiency.It can, improve acceleration to mid speed, ... at the sacrifice of energy efficiency and increased heat production ...
Take a better look at the eBike Simulator!Alan B said:It is unfortunate that Justin's wonderful simulator is not graphing at equilibrium.
It presents useful info but in a confusing way. At full throttle, and without controller current limiting, and assuming the motor doesn't saturate. So many things are carefully calibrated about Justin's data, and yet a few things are not modelled completely in this wonderful tool.