Motor quieter at 120% throttle - Why?

I have noticed a strange phenomenon when riding my recumbent commuter in 120% throttle mode. It seems much more quiet than when at 100% or less.
For background, my commuter is detailed in this thread: http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=57751#p899059

The setup, as per my sig is a 6Fet Infineon @ 25A, with 15AH 16S LiFePo4. The motor/wheel is a '1000w' golden motor in a 20" rim, radially laced. I have my 3 speed switch set to 67-100-120% throttle. At 120% throttle I can hit about 55-60kph.

Now before people say, how can you tell it's quieter whem your moving through the air faster and there is more wind noise etc, I will say this...I have been riding this bike almost every day for the last 6 weeks since building it. I would not be claiming it is quieter unless I was sure. I was recently riding with a very strong tail wind and the air around me was practically still while I was doing ~55-60kph. It was at this point I was sure I wasn't just imagining it...the bike is virtually silent at 120%! This compares to your typical electric wine when riding at 100% throttle.

I'm just curious as to why this might be happening? I know that the main reason sine-wave controllers are silent is due to the lower push-pull effect on the motor magnet ring, but why would a square wave controller over-driving be almost as quiet if not just as quiet as a sine-wave? :?

Cheers

Could you make a video pulling the throttle to 120% with the bike in a stand? just to hear the motor motion noise

Nobuo said:

Could you make a video pulling the throttle to 120% with the bike in a stand? just to hear the motor motion noise

Click to expand...

I will try to find the time...not sure when though. When I was building it I did run it WOT upside-down at 100% and 120%. The noise changes, but does not seem any quieter at 120% when running unloaded.
I think under load might make a difference to the sound. Either it's just as loud free-spinning at 120% as it is under load and the noise it does make is to little to perceive over other noises, or some how it is actually quieter under load than free-spinning.

Cheers

Well, without actually hearing your motor, let me remind you of something. As the motor runs faster, the frequencies it generates get higher. What was in the normal midrange the ear hears best move so high on the spectrum we stop hearing them as pitch but a tone might remain. Then that goes away. So one possibility is that the sound pressure reaches a range you don't hear anymore. But the dogs still hear it, right?

How does this controller go beyond 100% throttle? Does it boost the voltage? If so, do you know how efficiently?

SpeedEBikes said:

How does this controller go beyond 100% throttle? Does it boost the voltage? If so, do you know how efficiently?

Click to expand...

I think it that even at 100 per cent throttle there is still some pulse width modulation. The 120 per cent mode on Infineons removes the modulation - feeding the motor more continuous power from the controller.

Going to 120 per cent can create issues though. You could probably go as far as 110 per cent without much trouble. However, I have no experience and I'm just parroting back stuff that I've read here previously.

I think someone here may have done oscilloscope tests to see what happens the waveform at different percentages and posted a video.

Edit: Nevermind what I said - completely misremembered.

Here is the post from Zombiess.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=49504#p731223

Very interesting...doesn't explain the noise being less though. Similar to that video my bike sounds much the same when free-wheeling. It just seems like under load it is quieter by comparison to 100% or less.

I don't know how it can create issues. I've used 120% on Crystalyte HS 35xx and HS 40xx as well as my Golden motor without any issues at all.
It is less efficient though, that is certain, but I don't care too much when my battery has more than enough capacity to make the distance.

Cheers

I don't remember for sure, but you might want to look up "block commutation" which is likley what the cotnroller is doing at 120% when actually at full throttle voltage input. This doesnt' use any PWM but simply puts the full pack voltage across two phases at a time as it commutates around which phases are powered, to spin the motor.

Without PWM, it's probably a lot quieter becasue it is only switching current when the magnet poles move past a tooth and it needs to switch to the next phase combination that keeps pulling/pushing that magnet past the next tooth, adn the next.


I'm not certain that block commutation is what's happening, but it probably is.