Triple Rewind of Unite 500W Motor

If the motor has a low enough inductance then whatever is the "Time Constant" of the motor it will find itself a shorter time period (for the field to collapse) than before.

If you go from a Single to a Double you typically drop the Inductance by a factor of four.

So if 20 kHz is "adequate" before the rewind then 80 kHz is "adequate" afterwards.

Maybe the secret of the Rewind is the controller-to-inductance relationship?

The motor I'm using starts off with this sort of high pitched sound... almost like a whistle and then deepens to a raspy sound and then rises to a whine before it crackles and breaks up.

Maybe I'm spending more time in the discontinuous area? (not my central theme, but it's probably another factor)



http://en.wikipedia.org/wiki/Buck_converter

Output Voltage Ripple

"Output voltage ripple is the name given to the phenomenon where the output voltage rises during the On-state and falls during the Off-state. Several factors contribute to this including, but not limited to, switching frequency, output capacitance, inductor, load and any current limiting features of the control circuitry. At the most basic level the output voltage will rise and fall as a result of the output capacitor charging and discharging."

...

"Qualitatively, as the output capacitor or switching frequency increase, the magnitude of the ripple decreases. Output voltage ripple is typically a design specification for the power supply and is selected based on several factors. Capacitor selection is normally determined based on cost, physical size and non-idealities of various capacitor types. Switching frequency selection is typically determined based on efficiency requirements, which tends to decrease at higher operating frequencies, as described below in Effects of non-ideality on the efficiency. Higher switching frequency can also reduce efficiency and possibly raise EMI concerns.

Output voltage ripple is one of the disadvantages of a switching power supply, and can also be a measure of its quality."

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Don't forget that I'm using cheap Chinese controllers.

If I wanted to smooth out the signal I guess I could upgrade to larger capacitors.

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Wikipedia has these images that compare the low duty cycle verses the higher:

Low Duty Cycle:


High Duty Cycle:


...also, just forget about the ACL analogy. My point about that was that ACL behaves "like" a controller that had a huge capacitor hanging off of it. If you significantly increased the capacitors on these controllers you MIGHT be able to make it behave like an ACL circuit. That's an interesting thought in itself.

(but let's not get distracted too much)

500W Rewind Analysis

As best as I can tell this is an accurate representation of how the 500W Rewind turned out. The no load speed ended up a little low because the commutators seem to lose the ability to conduct at about 6000 rpm. This does not seem to effect Power or Heating as they seem to be falling into their predictable slots.



...not all that bad.

1400 watts (all day long if you want to)

New Top Speed Set (Downhill) 60 mph

I knew this motor could do it... it was on a long gradual downhill a few miles from my house.

(different than in the video)

While it is true that the inductance decreases four to one,that does not necessarily prove that the motor current is not maintained over the entire cycle,it depends on how adequate the inductance was to begin with.(before the rewind) and the on/off ratio.Looking at my numbers, my educated gut feel is that it is likely to be the still the case after the conversion.But that can only be verified by actual measurement I suppose.In any case it would only affect the system at low duty factors (low speeds),where you don't want to run at all if you can help it.
These quasi linear systems,consisting of motors which are reasonably linear and nonlinear component such as switches,are quite tricky to analyse.Real-life semiconductor switches don't necessarily behave like ideal bilateral switches,diodes are also difficult to handle and going back to the differential eq. is something of a nightmare.It is clear that if the current cannot maintained high instantanuous currents could result if the average current needs to be high also,due to high torque reqd.The current limiting should help out if fast enough.
As far as the commutation is concerned that may well be the limiting factor in terms of running at high rpm.As far as the armature is concerned we are dealing with ac currents,the absence of commutation poles does no help either, I'm sure.

What's needed is a way to log the actual signal that the motor sees.

A computer could be used so that a shunt current is sent to the computer input and then software could log the data. I'm sure there's stuff to do that already (and I think that I saw a chart that was produced that way) but it's also going to cost $$$.

There seems to be various separate regions upon which the motor behaves differently. At the lowest rpms and low duty cycle the motor creates a "whistle" sound. Higher up there's a throaty hollow sound. Up top the commutator seems to break up. It all seems to make sense and match the expected performance.

I managed to pass 6400 miles on the bike today which means that this new Rewind has at least 250 miles on it. (more like 350 miles) It's still a little early to be taking about the long term life of this 500 watt Rewind, but so far it's looking really good.

1400 Watts... no guilt... no heat... high efficiency...

That would be instructive but expensive.Have you looked at the commutator.This motor is completely enclosed I assume, so you can't check for arcing.Do you have STRONG wheels&adequate protection?

I wear full road racing leathers, racing boots, a full faced helmet and gloves. The spokes on the wheels have broken on occasion, but after 6400 miles it's been a rare event... normally when the spoke tension has gotten too loose. My future bike will have double wide rims. (2x as strong) The 24x3" tires provide adequate cushion so that the rims are okay.

Have you seen my video?

http://www.youtube.com/watch?v=YdrWpLQc-Kc

...or this is the same thing:

http://www.youtube.com/user/EBRRUSA

(EBRR stands for "Electric Bicycle Road Racing")

AussieJester actually uploaded it as I've managed to forget my Google account username and password. (if I make more videos I'll deal with fixing that later)

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The commutator is the largest size that Unite makes. It's the same as their 1200 watt motor. But they designed everything to handle about 3000 rpm at peak, so by the time you get to 6000 rpm the brushes are probably too weak to maintain constant connection.

Long term wear will be interesting to watch... just like with a racing motor in the combustion world the long term life might not be all that great. Only time will tell. But the best thing is that heat is not a problem. I rode 10 miles today at an average speed of over 30 mph and when I got home the motor was just barely warm. On previous motors they would be smoking hot after such a ride.

Commutator life is hard to predict,I once spent a summer near London in a shop where they rebuilt traction motors for the Underground. Found out there were marked correlations between the year they were built and the type of failure.One year it might be predominantly commutators another year embrittlement &hairline cracks of conductors where they connected to the comm.,other years insulation problems.These motors lead rough life,but were quite durable.I think a lot had to do with material problems. Some dated back 30-40 years !.
Saw the video.you were moving along !!.That motor looks ridiculously small compared to the battery pack.Do you have any specs. type &weight ,that sort of stuff

"That motor looks ridiculously small compared to the battery pack. Do you have any specs."

Um, hello... that's the 500 Watt Rewind. :alucard:

The video was produced using the Rewind motor we have been discussing.

I've gone 60 mph (downhill) and 50 mph (on the flat) using the Rewind. Even uphill I'm pulling 25 mph up hills that I used to have trouble just getting up.

The video provides the proof that the Rewind isn't just imaginary... I'm really getting 1400 watts of power out of it without any overheating.

I agree S,the combination of low rpm/V, adequate gearing and getting as much copper in the armature does pay off,no question about that.What about stats, I'm a data fiend,you know.Looked at WM el-cheapo bike,(only $300 mailorder),bike itself not too bad,has some kind of auto-assist,your cadence is being monitored no info at all on it.Motor looked pretty dinky for 450 W to me (an innocent),smaller than yours I think,but it does have exterior chain reduction&freewheel drive to rear axle. In principle you could use larger sprocket and go to 36V to get more efficiency&power.Motor must have extra inside reduction (planetary?).Currie wants &130 for extra 24V 10Ah battery, which seems pretty steep to me.I'm thinking Nicads or NmH, scared of LI, do you know good source?