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Triple Rewind of Unite 500W Motor
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safe
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Safe's Ebiking Polka Video Collection
Oh, just download them and try them... mpg format.
http://www.ebikehub.com/forum/download/file.php?id=428
http://www.ebikehub.com/forum/download/file.php?id=429
http://www.ebikehub.com/forum/download/file.php?id=430
Oh, just download them and try them... mpg format.
http://www.ebikehub.com/forum/download/file.php?id=428
http://www.ebikehub.com/forum/download/file.php?id=429
http://www.ebikehub.com/forum/download/file.php?id=430
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D
duivendyk
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What do these graphs purport to show,is the ordinate the motor current when applying a rectangular pulse at 20Khz to it?.You assumed? some series inductance in it.Most buck convertors I've come across had a series inductor to smooth out the current, which depending on the inductor size serves to keep the current going for the entire cycle.
safe
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The graphs are just guesses about how the pusles might be working. Nothing specific... just rough ball park estimates.
You get the idea though right... the thinner and shorter wire conducts current faster at first, but then stops because of it's resistance. The thicker and longer wire is slower to get it's current going, but it continues to build longer.
It's interesting enough to want to play around with.
To my knowledge there are no series inductors to smooth out the controller current... it's because there AREN'T any smoothing techniques that the "Current Multiplication" takes place.
If you smoothed the current, then you would have effectively created an ACL controller.
BCL means "No Smoothing"... other than the motors natural tendency to even things out. (the motor acts as an inductor)
You get the idea though right... the thinner and shorter wire conducts current faster at first, but then stops because of it's resistance. The thicker and longer wire is slower to get it's current going, but it continues to build longer.
It's interesting enough to want to play around with.
To my knowledge there are no series inductors to smooth out the controller current... it's because there AREN'T any smoothing techniques that the "Current Multiplication" takes place.
If you smoothed the current, then you would have effectively created an ACL controller.
BCL means "No Smoothing"... other than the motors natural tendency to even things out. (the motor acts as an inductor)
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safe
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Longer Video (but temporary)
http://media-convert.com/convert/?xid=15-cgirtckq
...and AussieJester, if you could download this and load it into YouTube it would save me the hassle of figuring out what is wrong with my Google account.
This link will go bad in 24 hours.
http://media-convert.com/convert/?xid=15-cgirtckq
...and AussieJester, if you could download this and load it into YouTube it would save me the hassle of figuring out what is wrong with my Google account.
This link will go bad in 24 hours.
D
duivendyk
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No, you are mistaken,wether or not there is an series inductor has nothing to do wether it is an ACL or BCL system per se.I'm afraid you again have a basic misunderstanding as to what is actually involved.The other point is what inductance value did you assume?and why,just some arbitrary number? I suppose and what's the rationale for the particular wire size scaling you employed,you can assume anything you want and get all sorts of results.I am of the opinion that the wire size is sort of a red herring.It's too late for more detailed explanation.more to morrow.
safe
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Remember how I always operate...
I start with reality and work backwards.
The charts resemble the actual data output I've seen from some guys that are doing electric motorcycle road racing and trying to diagnose their motor and battery performance. The charts might not be exact... but I can assure you that it works this way based in the real world.
Eventually I'll have to find you a real data output chart... it has pulses that are clearly defined. The numbers need to be made more accurate (obviously) but let's not be "perfectionists" yet, right now it's about broad theory. (it's still the brainstorming stage)
Our electric bike motors NEVER see a completely smooth signal.
I start with reality and work backwards.
The charts resemble the actual data output I've seen from some guys that are doing electric motorcycle road racing and trying to diagnose their motor and battery performance. The charts might not be exact... but I can assure you that it works this way based in the real world.
Eventually I'll have to find you a real data output chart... it has pulses that are clearly defined. The numbers need to be made more accurate (obviously) but let's not be "perfectionists" yet, right now it's about broad theory. (it's still the brainstorming stage)
Our electric bike motors NEVER see a completely smooth signal.
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safe
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safe
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http://www.4qdtec.com/pwm-01.html
PWM and motor Heating
"A popular 'old wife's tale' is that PWM causes the motor to heat more than pure d.c. Like most old wives' tales, this springs from a partial truth nurtured by misunderstanding. The 'myth' comes about because, if the frequency is too low, the current is discontinuous (or at least variable over the pwm waveform) because the motor's inductance cannot maintain the current properly during the off period of the waveform. So the motor current will be pulsed - not continuous. The average current will determine the torque but heating will be an integral of the current squared (heating is proportional to I²R)- the 'form factor' of the current will be greater than unity. The lower the frequency, the higher the ripple current and the greater the heating.
So consider an oversimplified case where the current is either on or off. If the current flows for, say, 1/3 of the time and you require a torque from the motor equivalent to that given by 1 amp continuous, them you clearly need an average current of 1 amp. To do this with a 33% duty cycle you must have 3 amps (the current flows for for 1/3 of the time).
Now a current of 3 amps will give 9 times (I squared) the heating effect of 1 amp continuous.
But if 3 amps is flowing for only 1/3 the total time - so the heating in the motor is 9 times for 1/3 the time - or a factor of 3 greater than the steady 1 amp! This waveform is said to have a 'form-factor' of 3 (or is it 33% - no doubt someone will put me right!)
However - if the pulse repetition frequency is high enough, the motor's inductance will cause a flywheel effect and the current will become stable. For instance the Lynch motor has an inductance of only 39 microhenrys (being one of the lowest inductance motors I know of) and a resistance of 0.016 Ohms. The 'Time constant' for an L-R circuit is L/R which (for the Lynch motor) gives 2.4 mSec. For an SEM DPM40P4 (1kW) the inductance is 200 microhenries and the resistance 40 milliohms - giving a time constant of 5mSec.
As a rule of thumb and to avoid too much maths, the pulse repetition period must be significantly shorter than the motor's time constant.
Other factors that affects PRF are:
If is it is in the audio band the motor can emit a whine (caused by a phenomenon known as 'magnetostriction', so keep above the audio band.
A MOSFET circuit dissipates most while switching from one state to the other so the frequency should not be too high - MOSFETs can be used upto 100kHz with care, but this is getting a bit high.
RF emissions: these increase with increasing frequency, so keep the frequency as low as possible!
It is clearly difficult to chose a 'best' compromise between these but an optimum frequency would seem to be around 20kHz."
PWM and motor Heating
"A popular 'old wife's tale' is that PWM causes the motor to heat more than pure d.c. Like most old wives' tales, this springs from a partial truth nurtured by misunderstanding. The 'myth' comes about because, if the frequency is too low, the current is discontinuous (or at least variable over the pwm waveform) because the motor's inductance cannot maintain the current properly during the off period of the waveform. So the motor current will be pulsed - not continuous. The average current will determine the torque but heating will be an integral of the current squared (heating is proportional to I²R)- the 'form factor' of the current will be greater than unity. The lower the frequency, the higher the ripple current and the greater the heating.
So consider an oversimplified case where the current is either on or off. If the current flows for, say, 1/3 of the time and you require a torque from the motor equivalent to that given by 1 amp continuous, them you clearly need an average current of 1 amp. To do this with a 33% duty cycle you must have 3 amps (the current flows for for 1/3 of the time).
Now a current of 3 amps will give 9 times (I squared) the heating effect of 1 amp continuous.
But if 3 amps is flowing for only 1/3 the total time - so the heating in the motor is 9 times for 1/3 the time - or a factor of 3 greater than the steady 1 amp! This waveform is said to have a 'form-factor' of 3 (or is it 33% - no doubt someone will put me right!)
However - if the pulse repetition frequency is high enough, the motor's inductance will cause a flywheel effect and the current will become stable. For instance the Lynch motor has an inductance of only 39 microhenrys (being one of the lowest inductance motors I know of) and a resistance of 0.016 Ohms. The 'Time constant' for an L-R circuit is L/R which (for the Lynch motor) gives 2.4 mSec. For an SEM DPM40P4 (1kW) the inductance is 200 microhenries and the resistance 40 milliohms - giving a time constant of 5mSec.
As a rule of thumb and to avoid too much maths, the pulse repetition period must be significantly shorter than the motor's time constant.
Other factors that affects PRF are:
If is it is in the audio band the motor can emit a whine (caused by a phenomenon known as 'magnetostriction', so keep above the audio band.
A MOSFET circuit dissipates most while switching from one state to the other so the frequency should not be too high - MOSFETs can be used upto 100kHz with care, but this is getting a bit high.
RF emissions: these increase with increasing frequency, so keep the frequency as low as possible!
It is clearly difficult to chose a 'best' compromise between these but an optimum frequency would seem to be around 20kHz."
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D
duivendyk
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I don't know what these pulses are supposed to represent,the current from the battery to the controller,the motor current,or the motor input voltage,just what is being represented?.What circuit configuration it is related to?.Usually in these buck convertors there is a series switch,followed by a shunt diode to ground (the freewheeling diode)or a FET switch which is turned on as the series switch is turned off, to provide a continuity path for the armature current and possibly an energy storage inductor.The inductance reqd to maintain the motorcurrent during the off period at say 20khz switch rate is quite small, in the order of 50-100 uH (micro!) and the motor inductance should be more than adequate.A higher value does not adversely affect the circuit's operation
As far as I understand the terminology,ACL refers to armature current control,which to me at least, means that the control input to the controller controls the motor current.
This requires a feedback control loop in which, by measuring the motorcurrent and comparing it to the control input, the duty factor is controlled to bring about the desired
current.It has nothing to do with the presence of an extra series inductor in the circuit even if one were to be put in.The question to my mind is: What you want to do with your "reality',such as a particular wave form,do you have any clear welldefined objective?
As far as I understand the terminology,ACL refers to armature current control,which to me at least, means that the control input to the controller controls the motor current.
This requires a feedback control loop in which, by measuring the motorcurrent and comparing it to the control input, the duty factor is controlled to bring about the desired
current.It has nothing to do with the presence of an extra series inductor in the circuit even if one were to be put in.The question to my mind is: What you want to do with your "reality',such as a particular wave form,do you have any clear welldefined objective?
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