Shunt mod worth while?

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chas_stevenson
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Re: Shunt mod worth while?

I can swap between an XB500 controller, and the Motofino controller, (same motor, different controller) and the max speed on the dynamometer will remain virtually the same.

So from this I can deduce that the controller is NOT the limiting factor for the motor's RPM at a given load. So as I said if you want to go faster you must increase the voltage.

Grandpa Chas S.

richardb
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Re: Shunt mod worth while?

Yes, apparently, at least for my case, the limiting factor is the motor, not the controller. My controller, and my battery pack match a scooter with a max speed of 30mph, and my mx500 motor is supposed to max out at 20 mph. I'm going to guess that if I had bought both a Motofino controller, AND a Motofino motor, I would now have a bike that would go 30 mph on a 48 volt pack. I think I'm going to solve my whole problem by getting an XM3000. Here in Michigan, I'll have to get a motorcycle license, but I think it's worthwhile. My commute to work takes me over some roads with a 55mph speed limit, and I feel too vulnerable when I'm going only 24mph with the 60v mod. I'll keep my XB500 for trips around town, but I'm thoroughly convinced that small electric bikes are the green answer for short commutes to and from work. It's a 10 fold savings in cost per mile, and the carbon footprint is on the order of 30 to 1 less. Also, I admire AztecFemBone for taking her child to school on an E-Bike. It really burns me to watch parents line up in SUVs at the school a block from my house... their massive engines idling away enough energy to run a household for a week as they wait..... Is it really necessary to use a 6000 pound vehicle to pick up a 60 pound child from school? Thanks everyone for your input about the technical aspects of getting more speed. Oh, and back to the original subject of this thread.... yes, the shunt mod is definitely worthwhile.

Dickey_b
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richardb
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Re: Shunt mod worth while?

I don't believe that the voltage is clamped to a level, or we wouldn't see a speed increase with added voltage, going from 48 to 60 v. My guess, and it is only that, is the limiting factor is the frequency of the pulses from the controller. The motor running in Synchronous mode is in step with the pulses that are timed by the Hall sensors. Increase the frequency of the pulses and the motor has no choice but to run faster.

This is an interesting thought...
My understanding is that these are actually DC motors, not synchronous motors. The big difference between these and your everyday DC motors with brushes is that they substitute the hall sensors for the brushes. The hall sensors serve only to tell the controller when, not how fast, to apply voltage to each winding of the motor. The controller uses the throttle position to determine how long to leave the voltage applied. If you are asking for less than maximum output, then the controller will turn off a particular winding before the hall sensor turns off, otherwise, it will leave the voltage applied to the winding until it's corresponding hall sensor reverses signal, thus signaling the controller that it should shut off that winding, and turn on another winding.
I'm not sure that clarifies much, but at least it explains the purpose of the hall sensors, and how the controller uses their signals.
The clock frequency of the controller may be used to time the frequency of the hall sensor signals to determine the speed of the motor, and changing that could have an effect on the max speed, but that's just conjecture at this point. I wish I had the program for the controller. Fat chance on getting hold of that!

Dickey_b
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JamesS
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Re: Shunt mod worth while?

A brushless DC motor (BLDC) is a synchronous electric motor which is powered by direct-current electricity (DC) and which has an electronically controlled commutation system, instead of a mechanical commutation system based on brushes. In such motors, current and torque, voltage and rpm are linearly related.

Brushless motors are given a Kv rating, which is RPM per volt, that lets you determine how fast that motor will rotate with a given voltage supplied to it. A 950Kv motor powered by an 12.0V battery would spin at 950 x 12.0 = 11400 RPM with no load.

By Lenz's law, a running motor will create a back-EMF proportional to the RPM; the motor will accelerate until this back-EMF equals the supply voltage, at which point it is in equilibrium. Note that kV is the voltage constant.

So, with these three points in mind our scooters have about a 11.25 kV rating if my math is correct and our only way to increase speed is with voltage ( as Gramps pointed out).

Our shunt mod took care of the current/torque linerarity increase, now increasing voltage/rpm, which is limited by the controller's rated components, would seem our only hope to go faster with the hub motors we have.

Not really what I wanted to hear, but seems to be the facts of the matter.

Happy scooting,
JamesS

richardb
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Re: Shunt mod worth while?

A brushless DC motor (BLDC) is a synchronous electric motor which is powered by direct-current electricity (DC) and which has an electronically controlled commutation system, instead of a mechanical commutation system based on brushes. In such motors, current and torque, voltage and rpm are linearly related.

I have always been under the impression that a synchronous motor is an AC motor whose rotor spinns with coils passing magnets at the same rate as the alternating current and resulting magnetic field which drives it. (electrical engineering 101)... In other words, running synchronous to the frequency of the AC signal driving the motor.

Dickey_b
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ttunes
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Re: Shunt mod worth while?

Some really interesting thought processes here. Let me add one more.
In the picture below you will see the motor voltage at full speed applied by the throttle. What I found interesting was that the duty cycle is approximately 50%. Pulse width modulated motor speed is controlled by duty cycle. At lease from what I read.
What I wanted to do was change the reference voltage that the ADC would be set for. When the Vref is reached no more digitization occurs -- no matter what the Vin is. I think Richards experiment with the battery in series with the throttle proves this or at least substantiates this thought.
The Chinese were kind enough to put stickers on the chips inside the controller -- when lifting the sticker there is not enough marking to correctly identify which ADC is being used.
I spent a couple of hours playing Googel games to find a data sheet. All I could find that were possible contenders was written in Chinese. I don't read this language so was stumped.
After looking at datashets for other manufacturers I found the only common element was the packaging. Dang. Even from say TI the pinouts would change.
So until I can get more information I am at a stand still. I won't be causing controller failure without additional information.....
This has been interesting though -- great discussions.
Here comes the motor picture at full throttle.

Best Regards.
Thom

motorVfullSpeed.jpg

richardb
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Re: Shunt mod worth while?

This is great! We finally got someone who has a scope into the discussion.
First of all, I do have a part number and a spec sheet for the microprocessor chip that is used in the XB500 controller. When I get time on Monday or Tuesday, I will place that information on my website for all to access.
Now, for a couple of questions.......
1. Is this signal referenced to ground? (I guess it must be unless you have a differential input on your scope) Also... Is this a three-pole motor, or two pole? It confuses me how there could be a 50% duty cycle when there are three windings. It would make more sense if it were either 66%high/33%low, or 33%high/66%low.
2. Would you mind taking a scope picture at a very low throttle position for comparison? (I'm thinking somewhere between 5 and 10 mph, or 1/4 throttle) I want to know if there is just one narrow positive pulse and one wide negative pulse for each winding, or if each positive portion is composed of a number of higher frequency spikes which are narrow at low throttle and wide at higher throttle positions. (I hope that makes sense).
3. If you have three channels, would it be possible to connect one channel to each motor winding, and look at the phase relationship between the three windings?

Dickey_b
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ttunes
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Re: Shunt mod worth while?

the trace you are seeing is referenced to the big black wire coming into the controller. So this is the negative side of the battery with positive lead from scope connected directly to one of the motor phase wires. From what I am understanding the motor is actually in conduction on the negative side of the sweep. But we can check.

All three phases are the same -- there is a phase shift but I thought this might be "good enough" to get started.
Low throttle position is with more "wide" on the postitve side as I remember. I took the scope back but I'm sure I can borrow it again.
to capture all 3 phases I'll have to capture the A-B phases then the B-C -- only have dual trace. It's a tek2232 so maybe I can capture and record then do a math add to bring phase relationship out. I'll have to play with that.

Any other things to look at? Hall effects compared to each phase?
I was wanting to watch the throttle input compared to Vref of the ADC but got lost looking for data sheets.
I was also wanting to see throttle input compared to Vout -- got lazy as I could watch the motor ramp up. Fairly simple theory to observe.

Get me a xmas scope output list and I'll borrow the scope again -- it might take a few days as the guy travels frequently.

Later.
Thom

JamesS
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Re: Shunt mod worth while?

Here is a link where you can find out more about your BLDC Synchronous motors and motor control.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1523

Happy scooting,
JamesS

richardb
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Re: Shunt mod worth while?

I am understanding the motor is actually in conduction on the negative side of the sweep. But we can check.

I was wanting to watch the throttle input compared to Vref of the ADC but got lost looking for data sheets.

Gee, I was hoping you owned the scope. Do you reckon you could borrow it and let me use it for a while? (just kidding)

There is some tricky stuff going on regarding how the voltages are applied to the three legs of the motor. for each cycle of a given leg in the positive direction, one of the other legs must be energized in the negative direction. (because the other ends of each leg are all connected together) Actually, each leg of the motor is configured into a half-bridge circuit, so that it can be either floating, connected to Negative return, or connected to +48 volts (B+), so there are 6 Power Fets connected to the three legs of the motor windings. (on the XB600 controller, there are twice as many Power Fets, but there are two in parallel in the place of each One Power Fet in the XB500 controller.

I was able to read the Chip Identification off of the top of the microprocessor in one of my XB500 controllers. It's a PIC16F716 chip, and I found data sheets and app notes for it. I put them up on my website at:
A. Data sheet - http://bergerweb.net/xb500/PIC16F716DataSheet.pdf
B. DC Motor Control Tips - http://bergerweb.net/xb500/PIC16F716DCMotorControlTips.pdf
C. Timer1 Data Errata - http://bergerweb.net/xb500/PIC16F716Timer1DataSheetErrata.pdf
D. Microprocessor family - http://bergerweb.net/xb500/PIC16F716solutions.pdf

The Motor Control Tips offers a lot of insight into how our controllers work, and you will readily see why at least two legs of the three leg motor must be energized at any given time. I hope these documents are helpful.

Dickey_b
Waste Not, Want Not

ttunes
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Re: Shunt mod worth while?

Interesting reading. Yes there is something tricky going on.
The chip I have in my controller is a 28pin. So it seems we have differences in control.

Ideas?
Thom

RANDEL24
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Re: Shunt mod worth while?

Has anybody figured out how to get some more power out of this thing yet?{700 li) Also, does anybody know what the blue keyfob looking thing with the valve core cap is for? you can't remove a valve core with it as the end retracts.

Cerious Krysis
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Re: Shunt mod worth while?

I would just like to thank all of you who came up with this mod. I bought my daughter a xb-600 and after riding it around (I weigh 220 )it was a serious disappointment. It was very sluggish and would slow way down climbing even the little hills. My daughter (120 pounds ) lives in San Francisco and needs this to tool around to school and work. After the mod it only drops 2 mph climbing moderate hills so I think my daughter will have a nice vehicle to get her around the city for next to nothing. I only changed one thing . I used to be a radar tech on a really old airplane so I knew all I had to do was install one more shunt so I just used a very fine soldering iron and popped it right between the existing shunts without drilling the pcb. works like a charm.

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