* * * MOTOR UNIVERSITY (Lab 101) * * *

[safe]

Power(In)

Power (as understood in electric terms) is the product of voltage times current. The units that are used are "Watts":

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

"That is, if 1 volt of potential difference is applied to a resistive load, and a current of 1 ampere flows, then 1 watt of power is dissipated."

This makes the Power that is "input" to the motor a very easy thing to calculate. All you need to do is multiply the "applied voltage" times the "current" and you get the power that is "input" to the motor. We abbreviate this as "Power(In)".

 

[safe]

Power(Out)

Power that actually is produced by the motor is different than the power that initially is input into the motor. There are various reason why energy is lost. First let's remember what the equation for actual power is going to be:

Power ( Actual ) = Volts ( Actual ) * Amps ( Actual )

So if we take the "applied volts" and subtract whatever losses that the resistance of the motor might cause we get for the above equation:

Volts ( Actual ) = ( Volts Applied ) - ( Resistance * Amps Applied )

...and if we know what the "No Load" is for this specific motor that "miraculously" allows us to figure out the actual current:

Amps ( Actual ) = ( Amps Applied ) - ( No Load Current )

This last part about the "No Load Current" might make you a little uncomfortable and you would have good reason. It's not an intellectual leap that is "obvious", but I'm also not at this point wanting to do the entire "proof" that arrives at this equation because I've seen it done and it's a little scary. Suffice to say that given only the "No Load" current you can "know what you need to know" about the actual current in this equation. I'll leave the formal proof for another time.

So finally we get:

Power(Out) = ( Volts - ( Resistance * Amps ) ) * ( Amps - NoLoad )

 

[safe]

Efficiency

Efficiency is another one of those "easy" things to calculate. All you need to do is take the power that you put in and compare it to the power you get out. The result is a percentage.

In this lesson I've multiplied the percentage by 100 to make it a value that is a whole number, but I could have done it in the chart scaling instead. (done in the later lessons) Oh well, that's a minor improvement that could be added later. :?

So:

Efficiency = Power(Out) / Power(In)

 

[safe]

Heat

Heat is another simple thing to calculate. Heat is produced as current squared times the resistance which means it rises faster than a linear rate. More current is not only bad, but VERY bad for heating. This will be an important thing to remember later on because the fact that there is an exponential rise in heat with current effects how you can manipulate things to avoid heat.

So the formula for heat in watts is:

Heat = ( ( Amps Applied ) ^ 2 ) * ( Motor Resistance )

Some people prefer heat in terms of time and if so you will need to convert to joules which are in units of watts per second. This means you will have to define a framework for time which can be done, but isn't a part of this lesson.

 

[safe]

Open for discussions about Lesson 2

Okay, take your time and look through Lesson 2 and see if there are any questions. I'm going to stop for now and I'll check back tonight to see what people might ask. (otherwise I'll move on to Lesson 3)

 

[Nimbuzz]

S, What does the ^ mean in the equation?
Thanks,
A

 

[TylerDurden]

If someone really wants to learn they deserve the right to access the source material.

The problem is when mis-information is distributed, which has been consistantly the case.

i.e.

"You can NEVER change back EMF".

"More power, Less Heat"

"Fechter and Lowell say I am 100% correct"

"Current Warping"

"Bigger motors are better"

etc. etc. etc.

 

[safe]

S, What does the ^ mean in the equation?

When you use "^" it means raising the value "to the power of" and then whatever follows it. So in this case it means that you are taking current and multiplying it by itself... "squaring" the current.

So for that equation you could write instead:

Heat = ( Amps Applied ) * ( Amps Applied ) * ( Motor Resistance )

 

[silentflight]

TD,

If there are any issues and you know the answer and are talented enough to explain it, then do so.

There aren't many places which present all of this in a clear way meant to instruct those who are completely new. Some of the links in the sticky about motors are already broken, for example.

Even the best professors make statements which are not accurate and universally applicable from time to time. When someone volunteers to teach and is ridiculed by someone offering no better solution, then we all know what's coming out of his mouth, he doesn't need to provide a photo of it.

Nice avatar, as well, really fits you.

Moderators- please remove the offensive photo in TD's prior post it is degrading and insulting to those of us who are here to learn and socialize.

 

[safe]

Thanks for the support silentflight.

Before I start on Lesson 3 can anyone tell me if in the later Lessons they can view the charts? I've heard that the charts sometimes don't convert well and would like to know that people can see them before I discuss them. (or know that they will have to manually recreate the charts from the data)

It's nice to have "live charts" rather than simple images because people can then change the parameters of the motor and watch the effects in real time on the motor powerband. It's the "live charts" that make learning much faster and it's more fun. If the charts don't reproduce themselves in the conversion process the images will have to do...

 

[TylerDurden]

If there are any issues and you know the answer and are talented enough to explain it, then do so.

That is precisely what safe is hoping for.

He will continue to pontificate until corrected by more informed people, then claim he is "bringing a new concept to the public".

As a new member, you might not be familiar with the valuable contributions by:
Fechter
Joe Leeps
Toorbough ULL-Zeveigh
Maxwell
Randy Draper (yes, it's true.)
eP
(others I am forgetting, sorry)

The above are real engineers who have mostly given-up taking safe to task on mis-information.

If you are interested in good, reliable information about ebikes, motors or electronics; ask the folks above.

If you doubt the veracity of my assertions, go read some of safe's other threads, then ask any of the reliable sources above if safe has made any contributions to this board of value.

This is really unfortunate, since new folks get yanked around in the process... sorry for that.


(Just don't forget the 8th rule.)

 

[Lowell]

Please keep it clean guys, and feel free to use the edit button.

 

[Nimbuzz]

So, What's with you Tyler? This is a discussion board not a 'Fight Club!' In a discussion, if you disagree, you simply state your differing viewpoint. Simply stating that something is misinformation with no explanation is like name-calling/fighting.

 

[TylerDurden]

So, What's with you Tyler? This is a discussion board not a 'Fight Club!' In a discussion, if you disagree, you simply state your differing viewpoint. Simply stating that something is misinformation with no explanation is like name-calling/fighting.

Safe started this thread to avoid answering questions in the previous thread:

http://endless-sphere.com/forums/viewtopic.php?t=930&postdays=0&postorder=asc&start=270

...perhaps with the notion that he will get enough corrections (from more informed members) to his formulas to provide a corrected mathmatical proof for his theory about motor heat.

In fact, safe has consistantly avoided providing even one case example in his theory, because it will be proven false.

Most of the engineers on this board won't waste their time with this kind of headcase sh*t. eP will, but he sees through this "university" gag and may or may not give some feedback to the "professor". I will, just because I'm a prick.

Enjoy your class...

 

[maxwell]

Tyler, best calibration is a weight and gravity, lots of rope and a high rise spring to mind!


Safe, I am passionate about people learning as you are to too, just dont give duff gen, explain, or note, the simplifications to prevent limiting potential knowledge and/or confusion.

 

[safe]

My basic premise has been that until everyone can have "access" to common sources of information that people can "get their hands on" and use as a "tool" to express their ideas it becomes a case of simply arguing with nothing behind it. If someone is able to identify an incorrect idea or a simple mistake that I've made then that's fine and it will build towards the process of making "open" what has been a fairly "closed club".

So my goal is to create a sort of "open documentation" that everyone can understand and share and play around with.

Am I allowing "the public" too easy access to electric motor knowledge?

Is that the true motivation one wonders for the hostilities... (that keeping things secretive builds an aura of authority)

So I'm literally "giving the secrets away" and the "biggest secret" is the one that is revealed in Lesson 4 about the way that the "Controller Logic" for a regular battery current limited controller is actually calculated. (the standard type controller most people use)

But I'm going to hold off a little and maybe go into that tomorrow. There is no hurry to get this finished and if there are people that are studying this stuff then it gives them a good nights sleep to think about it. So far all I've done is "set the foundation" upon which the "Controller Logic" will be applied. The controller is really just a device that establishes the "duty cycle" for any given rpm. And it also sort of makes you realize that programmable controllers can pretty much "make things up" any way they want because there's a lot of freedom to decide how the "duty cycle" is applied.

So let me repeat that previous question:

"Are people able to open and view the charts, did they get converted properly or did they get lost in the shuffle?"

 

[fechter]

Copy of my post on the other thread:

Chill out dudes.

OK I think I see what the problem is here.
I'm just not sure how to fix it.

Having a thread explaining the basics of how things work is an excellent idea. The newbies and technically challenged folks need this.

The information, however, must be absolutely correct and presented in a clear and consise manner, or else the newbies are going to get seriously confused or misled. It's no good if it's just 80% correct.

The basic 'how to' guides are not the place to discuss off-the-wall motor theories and what-if kind of mental excercises.

Safe, what you're doing is good, but the way you do it needs help.
Things are in the works for creating a repository of basic information and guides for the general public.

I'd love to create a "motor university" thread of my own, as well as several others, but haven't had time yet. My Crystalyte controller thread was extremely time consuming, and that's just scratching the surface. If there was an easy way to collect content from many sources, edit and combine it, the process might go much faster. I just don't have time to do everything myself.

I appreciate that Safe saw something that needed doing and stepped up to the plate, but just tossing things out there and waiting for others to fix it leaves things in a somewhat disorganized state by the time everything gets addressed.
Quality before quantity.

I'm open to suggestions on creating basic info threads authored by several people.

 

[Nimbuzz]

fetcher, What if safe sent his stuff to you and you would review it and make corrections then send it to him to post? He is doing the lion's share of the writing and you or a team would simply check it before it was posted.

Al's $.02

 

[safe]

...must be absolutely correct and presented in a clear and concise manner

To my knowledge this is all 100% correct and I'm doing my best to create a very easy to understand tutorial. In the end I plan to wrap everything up into a finalized complete "study guide" with all the text included. So there will be a "final copy" that excludes all the chatter that takes place on a messageboard.

 

[safe]

Lesson 3

Let's begin by reviewing what we have so far. We have created a framework of 100 data points within which our formulas will be placed in our spreadsheet. We have placed parameters that approximate the Unite 36 Volt 750 Watt motor. For controller logic we are using a simple wire from the battery to the motor so the "duty cycle" is 100% all the time. The formulas for the motor at any rpm are given by:

Volts = ( Duty Cycle ) * ( Battery Voltage )

Amps = ( ( Volts ) - ( BackEmf ) ) / Resistance

Power(In) = Volts * Amps

Power(Out) = ( Volts - ( Resistance * Amps ) ) * ( Amps - NoLoad )

Efficiency = Power(Out) / Power(In)

Heat = ( ( Amps Applied ) ^ 2 ) * ( Motor Resistance )

From these simple equations we get the behavior of the motor. Eventually when we get to Lesson 4 we will get to manipulating the controller logic and altering the behavior of the motor, but for now we just have the "minimal" equations.

We need to be 100% confident that these equations are indeed correct, so if there are ANY doubts or questions about this foundation we need to examine them before we go on. This is the "core" of an electric motor.

We now begin to look at charts...

 

[safe]

Unlimited Battery Current Chart

Hopefully your charts have been converted in the "study guides", but if they weren't the images will do the same thing. Here's the chart for the motor when the controller is simply a wire from the battery to the motor.

Let's observe some things...

1. Look at the magenta (heat) and gray (Power(In)) curves. When a motor is "stalled" and the rpms are zero the black Power(out) will be zero (since the motor is not moving) the blue efficiency will be zero (since there's nothing to show for all that power input) the green current is at a maximum and the magenta heat is at a maximum. What you have at this point is a "space heater" where 100% of the power running through the motor is translated into heat. This is a "reality check" for us that the formulas are correct because we know intuitively that this is true.

2. Look at the shape of the black (Power(Out)) curve. Notice that it's "bell shaped" and is at a maximum in the middle of the rpm range. What this means is that from a "pure power" perspective the maximum power attainable under ANY conditions is in the middle rpms. If you look at the blue efficiency curve you see that the maximum efficiency is way to the right at about 75% of the rpms. This is important to remember because it's to the higher rpms that better efficiency is attained.

3. In your Lesson 3.xls (.wks) file you will see the scaling of the chart. This is something that you can modify yourself so that you can make the curves suitable for viewing in whatever charting tool you might want to use. Feel free to export the data to another tool if you like and it would be great to see some really nice examples of "top of the line" graphing software displaying this chart raw data.

"Extra Credit" goes to anyone that posts high quality graphs. (and for those of you thinking of high school pranks I'd advise not to... it's just not that funny anymore)

 

[Patrick]

Fechter,

I imagine I'm going to regret this this, but I'm going to give it a stab. I agree that tutorials are are a great idea, and in fact am going to be provding technical content on another project for exactly that reason. This is not a trivial task - it's very difficult to be both correct and abundandtly clear. It's not my intention to piss anybody off, so I freely apologize if I offend anyone. Here are some of the problems I see with this tpoic:

Safes heart is in the right place, but his technical foundation is very weak. He is still learning, which is great, but his experience and thought seems to be limited to brushed DC motors. Things get much more complex when dealing with synchronous and induction machines.

Nobody seems to be using standard engineering notation. There is a reason it's a standard, and a good tutorial should deal with this up front - it's usually in the first chapters of textbooks. And nobody seems to be reading the textbooks! Many of the so-called discoveries posted here are well documented, fully explored engineering design considerations. My own personal favorite is "Motor Control Electronics', McGraw Hill, author Richard Valentine - if you want to really understand controllers, you can't do better than this.

There seems to be a lot of ego involved. Some people want to prove that their approach is the best, some that they understand physics better than the next guy, and others who have years of experince bulding being irritated when told their machines can't possibly perrform the way they do every day. My guess is that these squables are why we no longer have Honk or Happy Hobit - those guys were experts.

The suggestion that you "simply check and correct" other peoples writing is a little naive. Technical editing is a well paid profession for a reason. It won't work to replicate textbooks - and why should we? My thinking is that we need to start from the bottom, explaing the basics, and build on that - rather than trying to do something elaborate at first go. If there is a collaborative effort, it would probably be best if the collaborators did it offline, or, I should say, not in an online thread, and then present results as a cohesive whole.

Anyway, I'm going to be doing this on another project reagrdless. If there is a reasonable mechanism, I'd be happy to help.

 

[safe]

You need to understand that I'm creating a "hands on" electric motor spreadsheet "tool" for a standard brushed motor. This is the "basics" and I really don't want to get into the "advanced theories" or much of the technical jargon that is used within the electrical world. The idea is to provide to the general public a functioning "tool" that will allow people to calculate things that they need for their electric vehicles.

This is "giving the secrets away" without all the work... :wink:

 

[safe]

Lesson 4

Now things get interesting. We have chosen to configure our formulas so that the "variable" part of our spreadsheet is the "Controller Logic" and everything else ALWAYS remains unchanged. This was done on purpose and may vary from standardized ways that people choose to solve motor equations. This is a big advantage as we go forward because now we can simply insert any "Controller Logic" (which can only effect the "duty cycle" in our brushed motor) that we so desire. Programmable controllers are able to customize the duty cycle based on completely "artifical" parameters so we seem to be on the "right track" by isolating this logic at least for our purposes. The "electric motor purist" might wince at this technique, but it does work and does produce correct results.

The "Battery Current Limited" controller requires that we solve a "Quadratic Equation".

Before we begin we need to remember that the laws of "conservation of energy" must apply to the power into the controller and the power out of the controller. The so called "current multiplication" occurs because if on the battery side we have 100 volts and a current limit of 100 amps, then when we reduce the volts to the motor to 50 volts then the amps on the motor side will equal 200 amps even though on the battery side it only measures 100 amps. Crazy? Well, that's apparently how it works and we can discuss that as a separate issue, but for now just accept that "current multiplication" takes place.

Solving the Quadratic Equation

Here's how you solve for the duty cycle. (our spreadsheets "Controller Logic") We begin with these three equations:

MotorVoltage = BatteryVoltage * DutyCycle

MotorCurrent = CurrentLimit / DutyCycle

MotorCurrent = (MotorVoltage - BackEmfVoltage) / Resistance

So let's take the last equation and substitute in the values for MotorCurrent on the left and MotorVoltage on the right:

( CurrentLimit / DutyCycle ) = ( ( BatteryVoltage * DutyCycle ) - BackEmfVoltage) / Resistance

Now we rearrange things:

Resistance * CurrentLimit = ( ( BatteryVoltage * DutyCycle ) - BackEmfVoltage) * DutyCycle

( ( BatteryVoltage * DutyCycle ) - BackEmfVoltage) * DutyCycle = Resistance * CurrentLimit

BatteryVoltage * ( DutyCycle )^2 - BackEmfVoltage ( DutyCycle ) - Resistance * CurrentLimit = 0

Ah ha! A quadratic equation! We can solve for "x" as the DutyCycle so we have:

a = BatteryVoltage
b = - BackEmfVoltage
c = - CurrentLimit * Resistance

Finally we get:

Controller Logic = ( ( BackEmfVoltage ) + ( SQRT ( ( BackEmfVoltage ^ 2 ) + 4 * ( BatteryVoltage ) * ( CurrentLimit * Resistance ) ) ) ) / ( 2 * BatteryVoltage )

Which is the "nastiest equation" you will see in this entire "study guide".

 

[TylerDurden]

You need to understand that I'm creating a "hands on" electric motor spreadsheet "tool" for a standard brushed motor.

Here's a suggestion: Rename your thread "Spreadsheet University" and give it all you got.

That is, after all, your area of expertise.