Motor Current Limiting: More Power and Less Heat!!!

[safe]

Fri May 25, 2007 9:39 pm

Whiskey Tango Foxtrot.

Motor current limiting is not a difficult concept, and combined with gears it will work very nicely to maximise the performance envelope. It may not be for everyone, but the theory is sound.

 

[safe]

Sun May 27, 2007 7:38 am

I see now.
Heating is a function of current, so is torque. In the motor current limited case, the current is lower in the lower part of the power band.

If you are using your gears properly, you won't spend much time in that part of the power band.


I still don't get the issue with climbing a 10% grade. If the motor current is limited, you would just have to gear down and travel slower to make a hill. You won't be able to do 50mph on any kind of hill (except downhill) with 1400 watts.

 

[safe]

Fri May 25, 2007 10:37 pm

This thread is about 'more power and less heat' which motor current limiting does both of. Any more questions?

 

[safe]

Mon May 21, 2007 3:40 am

Safe, I hate to admit it, but I think you're on the right track.

In fact, I've already done your idea of using a 7 speed gear hub with the exact motor you pictured. It plows up hills, and when I get my shifter attached, I anticipate that it should go about 35mph on flat. (lots of wind resistance in design) I already love the thing.

I'm going to put pictures and video up soon.

As soon as I'm done, I'm going to be trying to do exactly what you're describing.

My next project, will be modifying a CVT transmission to maximize the effeicency of the motor. I plan to remove the weights that make it "change gears" and control the gearing with a microchip.

I read your discussion, and I think you only need sensors to get two numbers:

1) The speed the bike is traveling
2) The gear ratio it's using

You can work backwards to get the motor rpm from these numbers.

The mph can be found using a hall effect sensor like speedometers use. The microchip will be controlling the position of the cvt using a stepper motor, and it will constantly be moving it and keeping track of the movement.

I agree with you that using gears that span a 300% range should suffice for all situations. So, by that thinking, you don't need to concern yourself with managing the electric current. For example, if you're going up a steep hill, the microchip will start downshifting until the motor is running in its peak effiiency, and it will chug up the hill. As long as it has the proper gear to work with, it should adjust automatically to avoid the overcurrent situation (or you could just limit it).

I think the easiest way to do this is to use a 2hp motor, and a controller that will max-out at 1 1/2hp. Then just don't worry about it.


The program would work in two stages: When you first accelerate, it will be in the lowest gear, and the entire acceleration will be from the motor. This would last until about 15mph. Then the motor would stay at a constant rpm, and the bike would spped up by adjusting the gears (CVT).

I was going to suggest that this is a "gear based throttle."

This process could be entirely managed by the microchip. In fact, I plan to just a on/off throttle. You push the button to go faster, and release it to coast. The microchip would manage the acceleration, it wouldn't just "floor it." It would incrementally increase voltage when the bike is ready to go to the next speed. There could easily be a cruise control button too.

My dream scenerio would be to use this motor:

<a href="http://www.thunderstruck-ev.com/sailboatkit.htm">Mars Motor</a>

which should be about 90% effient to start with. Use a 60 amp controller, so it would never break a sweat. That scooter would go forever.

Now all I have to do is build it! (I haven't even posted my first project yet!)

 

[safe]

Thu May 17, 2007 8:51 am

safe, just press onward.

The summations tie up a lot of the points rather well.

 

[eP]

Sun May 27, 2007 7:38 am

I see now.
Heating is a function of current, so is torque. In the motor current limited case, the current is lower in the lower part of the power band.

If you are using your gears properly, you won't spend much time in that part of the power band.


I still don't get the issue with climbing a 10% grade. If the motor current is limited, you would just have to gear down and travel slower to make a hill. You won't be able to do 50mph on any kind of hill (except downhill) with 1400 watts.

At 10% slope the acceleration at 1400 watts will be strongly limited or ultra span gearbox is needed if you want be able ride 50 mph at flat.

The same gearbox must be use at hills and at flat.

 

[safe]

eP

I would like very much if you would follow the "study guides" that I've developed over in the "Motor University" thread. When we can all agree on the "basics" and have a shared and open framework on which we can discuss issues it will go a long way towards resolving questions about what can and can't be done with a motor.

All discussions need to begin with the "basics" first. Once the "basics" are agreed upon then we can argue better about the "advanced topics".

The way it has been is that we are trying to debate things without the proper foundation and so it just ends up getting nowhere.

So please... review, ask questions, find possible errors, play around with the spreadsheets, examine the charts, and look at the formulas. In the end we can share one document that is "open" to both people.

 

[eP]

eP

I would like very much if you would follow the "study guides" that I've developed over in the "Motor University" thread. When we can all agree on the "basics" and have a shared and open framework on which we can discuss issues it will go a long way towards resolving questions about what can and can't be done with a motor.

All discussions need to begin with the "basics" first. Once the "basics" are agreed upon then we can argue better about the "advanced topics".

The way it has been is that we are trying to debate things without the proper foundation and so it just ends up getting nowhere.

So start to work to get the proper foundation Mr Teacher.
For the begin try to understand what is the difference between force and power.

I'm patient - i can wait. If you get the proper foundation so let me know Mr Teacher. 8)


So please... review, ask questions, find possible errors, play around with the spreadsheets, examine the charts, and look at the formulas. In the end we can share one document that is "open" to both people.

 

[safe]

So start to work to get the proper foundation...

That's in the "Motor University" thread.

You need to go there now...

http://endless-sphere.com/forums/viewtopic.php?t=1062&sid=ca28b1a2f254f2a32bc98a6a6cada562

 

[eP]

So start to work to get the proper foundation...

That's in the "Motor University" thread.

You need to go there now...

http://endless-sphere.com/forums/viewtopic.php?t=1062&sid=ca28b1a2f254f2a32bc98a6a6cada562

I know what i need Mr Teacher 8)

But i see you dont know what you need. So i've give you a hint: get a proper foundation before you produce more bullsh*ts.
So try to understand what is the Power and what is the Force as a first step to your foundation.
When you will be ready to the next step let me know.
Then i will give you the next hint 8)

 

[safe]

If you "eP" are sincere about actually learning and communicating the "truth" about electric motor theory then you would be eager to want to share documents. Any professional person makes it a habit of having standard tools with which they exchange information. The "spreadsheet" is probably the most generic and universal document that exists in the world and though it comes in a variety of formats that reflect it's long history it still stands as the "common dataset" for a lot of business and scientific communication.

However, if you are in reality a "troll" then I'm seriously beginning to consider lobbying to get you blocked for bad behavior.

So I leave it up to you and your own conscience to decide what kind of person you want to present to the world. We don't need "bad behavior" here... really... we don't and you CAN be blocked. So far I don't think anyone has been blocked yet (because most of the people have behaved appropriately) but it's starting to look like a situation where maybe an email from one of the moderators would help.

TylerDurden has been around a long time and I'm simply at a loss for what's going wrong with his behavior. It seems as though his "meltdown" has effected you in a negative way as a "bad influence". You should not be following his example.

Anyway, I hope the behavior improves from both of you guys...

 

[fechter]

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, 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.

 

[safe]

Changing the Subject

Moving forward...

Fechter, you use a BMC motor that is brushless. Other than the controller circuitry and the higher efficiency the general rules for the brushless motor are similiar to the brush one. Efficiency is still best at a more narrow set of rpms and so the creation of a powerband that exaggerates the good areas and suppresses the bad areas ON A GEARED BIKE (got to throw that in) is still a good idea.

So how does one make the transition from Batttery Current Limiting on a Brushless motor to a Motor Current Limited setup?

Since you (Fechter) are very knowledgeable about the BMC I'd also like to examine your best recommendation of the places to buy all the components that might be needed.

 

[fechter]

The motor on my Vego I got for free as a burned up internally controlled version. I modified it for external control. PowerPack motors sells them already wired for external control.

To do a motor current limit, you could use one of the Allegro current sensors in one of the phase wires with the appropriate filtering to average the current, since it's alternating. Getting the filter setup right shouldn't be too hard.

It might be possible to use a simple torroidal AC current pickup, but I haven't tried anything like that.

 

[safe]

To do a motor current limit, you could use one of the Allegro current sensors in one of the phase wires with the appropriate filtering to average the current, since it's alternating. Getting the filter setup right shouldn't be too hard.

It might be possible to use a simple torroidal AC current pickup, but I haven't tried anything like that.

I figured this would happen.... :?

You took me into the "deep water" already and left me to drown. :lol: I have a feeling I'll be learning a lot of new stuff in order to master the brushless motor.

Brushed Motor - Done

Brushless Motor - A whole new frontier... (which means this is going to involve some more study)

 

[Patrick]

Safe -

In science, the goal is to explain, so that everyone can understand, what has never been known. You do the exact opposite.

You have not been dropped into deep water; you are still in the wading pool, but definitely drowning. Before you pontificate about brushless drive systems (not just motors, not just controllers, but they way they interact as part of a cohesive whole) to everyone here, try to get a deep, intuitive understanding of at least:

closed loop control
PID algorithims
3 phase AC
DQ vectors
PWM modulation techniques

And while you're at it, start using using standard terminology. It's not Motor Voltage, it's Ea (armature voltage - DC motors can have windings, and you have to differentiate). It's not the Motor Constant, it's Kv or Kt. I can barely read your posts because you call things "Amps" - which amps are you refering to, and how are you measuring them? It drives me batty.

Drop the ego. Your describing Fechter as "an advanced student" is the most insulting thing I've ever seen on this forum. I suspect he has forgotten more than you will ever know. If you could invent a bike that ran on ego, you would set the land speed record. Try instead to to put things out there for peer review, and accept your peers with graciousness, instead of telling them "you don't get it yet - read my post again".

Refering to brushless controllers - all the good ones already HAVE what you call motor current limiting. Do yourself a favor, and read a manual for a brushless controller. I've included one as an attachment; it's only 80 pages.

You seem like a smart guy, but a little over-excited (NPI). Like you just discovered sex, and want to tell everyone how great it is, and everything about it. It's the old adage - the people that do it don't talk about it, and the people that talk about it don't do it. Remember the old Monty Python skit - nudge, nudge, wink, wink? I know you're old enough.

So just relax - try to learn instead of teaching everything, of dominating every thread - it gets tiresome.

Hope you get this,

Patrick

P.S. Do ME a favor, and think about this - maybe 48 hours. Don't just shoot off a reply like you always do. I will not be impressed, and I will not give you any help.

The same for some others. I know there is a strong sense of community here, and I would like to see that sense of community improve. A few spitballs (to use Xysters term) in good fun is one thing, but constant backbiting is another. How the Admins put up with it I don't know - they have more patience than I do. We've already lost some very good members, and I'd like to get them back. Let's give them a neighborhood they want to join.

 

[safe]

Brushed Motors - Done

Brushless Motors - A whole new frontier...

I've made it clear already that now that I've gotten the core elements of the brushed motor "down" and even made spreadsheets that completely automate the process of calculation that it's time to start looking at the "next level"... the brushless motor.

My attitude is that in the online electric vehicle world there existed a "vacuum" of really usable tools and understanding about the basics of brushed motors. To supply something so simple as a spreadsheet that anyone can understand fills the void that existed. If another "humble student" (with a cocky attitude :? :lol: ) like myself were to show up in the future they could now take an accelerated course (* * * Motor University (Lab 101) * * *) and learn in hours what otherwise takes days and weeks to piece together.

So the "bottom line" is that I HAVE filled the vacuum... Someone should have done it before and maybe now someone will do it again even better than I have done and make a new and better course to study... Patrick... ever thought of creating your own study guide on some basic concept like the brushed motor? Maybe you could take what I've done and correct everything that I've stated incorrectly? Re-release it in a more polished form?

From now on the motor powerband profiles of a brushed motor will no longer be a mystery in any way. Everything that it takes to go from square one to the final chart is in the spreadsheets. Problem solved. Information made public. Mysteries and debates resolved. No more need to build everything from scratch. The caveman enters the world of the spreadsheet. Civilization has taken root.

So I don't want to allow you to completely dissipate the change by pointing out that there are other areas to study beyond what I've done so far...

As for the pdf... I thought this was interesting:

Torque Control
In Torque Control mode, the voltage applied across the motor armature is proportional to the
accelerator demand. When climbing an incline, the operator will need to increase the accelerator
demand to maintain the speed. When descending an incline, there will be no maximum speed
limit applied.

Closed Loop Speed Control
In Closed Loop Speed Control mode, the speed of the vehicle is controlled to the speed demand
from the operator. The controller will increase or decrease power to the motor or will initiate
braking to maintain the target speed.

So apparently you have the ability to either use the throttle as an rpm based speed control or like Fechter's "Current Based Throttle". That's really nice... all that built right in... makes it worth the money... (which is something like $1000 right?)

I haven't really gotten into the "deep study" yet, but eventually I'll want to dig into it more... the road ahead is long...

 

[safe]

Starting with this motor:

I'm planning to overvolt and overamp it and add MCL (motor current limiting) and forced air cooling. Take a look at how the theory stacks up on how this same motor "could" be configured and the efficiency that you get as a result. MCL seems to offer efficiency benefits as well as peak power advantages.

 

[cadstarsucks]

Practical Route to Conversion

The most practical route to convert an existing controller that is using "Battery Current Limiting" to one that uses "Motor Current Limiting" is to do something like "Boost Control". If you add a Hall Effects Sensor to the motor side wire and compare that to the throttle voltage you can create a circuit that knows when to turn down the throttle to keep the motor side current under control. It's a simple circuit to make.

You could in theory have a switch where you could turn the circuit off when you wanted and you could toggle between "Battery Current Limiting" and "Motor Current Limiting" at will.

You can also set the level of "Boost" that you desire.... so the ability to really lean out the bike for long range is also possible.

So that's the "practical" side to all of this...

The solution is to run more poles and/or smaller wheels to maintain low end torque on a small brushless motor. Do NOT overamp.

A cheap 300RPM 500W 70% efficiency at full load motor then becomes 1200RPM 2000W 90% with the original 500W 70% at nameplate load/RPM.

Dan

 

[The7]

A cheap 300RPM 500W 70% efficiency at full load motor then becomes 1200RPM 2000W 90% with the original 500W 70% at nameplate load/RPM.

Yes. This is based on the assumptions:

1) The motor could run at 1200 rpm (4 times its rated 300 rpm)
(The centrifugal force on motor part is 16 times)

2) The motor loss is mainly copper loss. (Iron loss could be the order of 16 times) .

3) The motor would stand 4 times its rated voltage.

There is no free lunch!!

 

[cadstarsucks]

A cheap 300RPM 500W 70% efficiency at full load motor then becomes 1200RPM 2000W 90% with the original 500W 70% at nameplate load/RPM.

Yes. This is based on the assumptions:

1) The motor could run at 1200 rpm (4 times its rated 300 rpm)
(The centrifugal force on motor part is 16 times)

2) The motor loss is mainly copper loss. (Iron loss could be the order of 16 times) .

3) The motor would stand 4 times its rated voltage.

There is no free lunch!!

Most BLDC motors can run safely and reliably at 10-50K RPM - the only limitation is the bearings.

Looking at the curves it is mostly copper losses, iron losses don't start going up until you hit high frequencies or high flux densities. Neither of which will happen at 1200PRM at rated current. (looking at a golden 36V 500W BLDC for reference)

Basic enamel insulation is good for 500V or more.

Dan

 

[Miles]

Most BLDC motors can run safely and reliably at 10-50K RPM - the only limitation is the bearings.

 

[The7]

A cheap 300RPM 500W 70% efficiency at full load motor then becomes 1200RPM 2000W 90% with the original 500W 70% at nameplate load/RPM.

Yes. This is based on the assumptions:

1) The motor could run at 1200 rpm (4 times its rated 300 rpm)
(The centrifugal force on motor part is 16 times)

2) The motor loss is mainly copper loss. (Iron loss could be the order of 16 times) .

3) The motor would stand 4 times its rated voltage.

There is no free lunch!!

Most BLDC motors can run safely and reliably at 10-50K RPM - the only limitation is the bearings.

Looking at the curves it is mostly copper losses, iron losses don't start going up until you hit high frequencies or high flux densities. Neither of which will happen at 1200PRM at rated current. (looking at a golden 36V 500W BLDC for reference)

Basic enamel insulation is good for 500V or more.

Dan

Your understanding is different from mine!!

 

[cadstarsucks]

Your understanding is different from mine!!

Well there is also the possibility of severe under rating by manufacturers, but generally speaking a motor's wear out mechanisms are the brushes, the bearings, and the insulation.

In an AC machine (You can actually drive a BLDC with a sine), there are no brushes, you can drive with more of a sine to prevent ultrasonic bearing pitting, and diode clamp the phases to the rails to prevent arc over.

That leaves normal bearing load and speed as the wear mechanisms.

Dan

 

[xyster]

Most BLDC motors can run safely and reliably at 10-50K RPM - the only limitation is the bearings.

...

Basic enamel insulation is good for 500V or more.

As reported by Knoxie and others here, the popular brushless kollmorgen motors fly apart at around 60 volts. The magnets separate from the rotor. Don't know the RPMs, but doubt it's near 10k.
Outside of tiny RC motors, I've not heard of ebike-sized BLDC motors surviving those kind of RPMs and voltages. Can you site some examples? Do you think my 5304, spinning 700 rpm at 80 volts, can handle 500 volts with just better bearings?

I could go 250mph....