Strange Middrive Efficiency

speedyebikenoob · May 11, 2019

So I noticed something kind of weird on my middrive yesterday. I never usually check the wattage consumption readings but this time I did. At 18 mph (I know slow, but the bike trails here allow for 15 only and I don't want too much attention) my bike in third gear uses just under 350 watts. I decided to shift into fourth just to see what happens. I expected my consumption to go up trying to maintain the same 18 mph, but surprisingly it actually dropped to just over 200. This is kind of weird because I thought electric motors were supposed to be more efficient the higher they rev. Of course, as soon as I hit any minor incline I had to downshift or else the consumption would shoot up, but this was on flat ground and I kept it steady at 18. At third gear at this speed, I'm getting 17wh/mile, so in fourth I guess it's possible to get better? Any reason why I'm using less power in fourth gear you think?

liveforphysics · May 11, 2019

Less motor core loss and gearing drag losses.

It's a misconception motors want speed for efficiency. More speed = more losses.

Only if youe copper losses are higher than your core losses do you want more motor speed to increase efficiency. At a steady cruising pace, this almost never happens.

speedyebikenoob · May 11, 2019

liveforphysics said:
Less motor core loss and gearing drag losses.

It's a misconception motors want speed for efficiency. More speed = more losses.

Only if youe copper losses are higher than your core losses do you want more motor speed to increase efficiency. At a steady cruising pace, this almost never happens.

So are you saying I should actually run at lower rpms when just cruising and shift into a higher gear like I would in my car?

fechter · May 12, 2019

Right. Experiment with the gears and find which one gives you the lowest power consumption for a given speed.

speedyebikenoob · May 12, 2019

fechter said:
Right. Experiment with the gears and find which one gives you the lowest power consumption for a given speed.

Right I'll try that. So when would I actually want my rpms to be higher? Other than while climbing hills.

markz · May 12, 2019

Yeah, it is part of the "Pro's" for the mid-drive motor.

I noticed you mentioned you wanted to blend in by going the stated speed limit. The downside is that the mid drive sticks out way more to the commoner then a rear hub. I see the BBSHD's are quite small, I cant compare size between that and C4K, but I'm sure you match the BBSHD with a Sinewave controller it would be much quieter.

There is always a give and take for any type of motor you install whether it be a geared hub, direct drive hub, or geared mid drive. When deciding the consumer should look at the kind of terrain they will be riding the most, steep hills, commuter stop & go, grocery getter/cargo, go-fast. I found when riding my Cyclone 4kw mid drive that people would turn their heads to see what odd sound was coming, everything was stock so must've been a trapezoidal controller. Lots of noise with the brushed 300W geared motor I rode for a few rides before it burnt the brushes to a perfumic scent that any grease monkey would be proud of odoring themselves with. I just threw it out, weaklings like that dont last long in my household.

speedyebikenoob · May 12, 2019

markz said:
Yeah, it is part of the "Pro's" for the mid-drive motor.

I noticed you mentioned you wanted to blend in by going the stated speed limit. The downside is that the mid drive sticks out way more to the commoner then a rear hub. I see the BBSHD's are quite small, I cant compare size between that and C4K, but I'm sure you match the BBSHD with a Sinewave controller it would be much quieter.

There is always a give and take for any type of motor you install whether it be a geared hub, direct drive hub, or geared mid drive. When deciding the consumer should look at the kind of terrain they will be riding the most, steep hills, commuter stop & go, grocery getter/cargo, go-fast. I found when riding my Cyclone 4kw mid drive that people would turn their heads to see what odd sound was coming, everything was stock so must've been a trapezoidal controller. Lots of noise with the brushed 300W geared motor I rode for a few rides before it burnt the brushes to a perfumic scent that any grease monkey would be proud of odoring themselves with. I just threw it out, weaklings like that dont last long in my household.

Lol, I feel the same way about the 500w e scooter I also have, very weak atleast for me but I still keep it because it's reliable and for incase one of my friends wants to tag along. I have a mini-cyclone on my bike and it's very noisy, it does seem to irritate other people but I found that if I stick to "bicycle" speeds they don't get annoyed as much, plus it's not very smart to go 30+ mph on multiuse trails. The added efficiency is also a bonus, of course if there's no one around though I speed it up quite a bit

markz · May 14, 2019

I noticed when I went out for a cruise last night at 2am, there were a couple of dogs that barked. The lights were all off, and the dogs were not outside. I was riding on the road, across the street when the 1st dog barked. I was going to take the cut-thru path between the houses. Though I am riding the mxus 3kw direct drive + Greentime Trapazoidal with no sense wires and I was just going slow cruising speed. Once the big dog in the one house barked, the other dog in the other house barked too.

Same thing happened 2 months, at 3am but that was more like I dropped a 2L bottle and I was in the alley and a dog barked, then the lights turned on :lol:

LeftieBiker · May 14, 2019

Dogs will bark at pedestrians walking by silently, so don't assume it was the motor whine.

Strange Middrive Efficiency

speedyebikenoob

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liveforphysics

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speedyebikenoob

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fechter

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speedyebikenoob

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markz

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speedyebikenoob

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markz

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LeftieBiker

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