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

[safe]

Thanks for proving what most people knew already. As usual eP folds again. Shall we deal the next hand?

eP is obviously new to the game and he doesn't even have his first bike together yet. He's starting where I was last August. He's learning a lot really fast. I was thinking of creating a "teaching thread" for motor basics, but I think he's up to speed now. His questions were good and showed that he understood what was going on. Be easy on the guy he's new.

The "next step" is to actually create "Motor Current Limiting" in a real circuit and the last time Fechter was here we discussed using a combination of a Hall Effects Sensor with rigidly specified outputs and if it might be possible to directly link that to a Solid State Relay which also has very rigidly defined inputs and outputs. It might save a whole lot of pots that were going to be needed since the voltages were not easily defined using a comparator circuit. Plus my "simple brain" understands a Solid State Relay very easily... too much current equals "open the relay and reduce the current"... whereas the other was was like practically creating your own radio it had so much variability.

 

[Mathurin]

Well, I still am under the impression you'll be riding something kinda like my bro's motorcycle:

It's a 50cc water cooled 2 stroke, but the previous owner tuned it so it blows by LSM territory and goes at least in the 90's, probably more but I was riding a 50 zone when I tried it. Once it gets past 20-30 or so the motor stays pegged at 9K RPM just before the red line, and accelerates rather nicely. But from a stop acceleration is eventual, so things like merging in traffic are tricky. While starting on a fair hill it strains and creeps onwards, if you had no compassion and kept it up it would probably pickup speed and go, but it's shurely a lot slower then it could be.

Last I met him, bro had the intent to change the gearing so it tops off around 70 so as to get better low end acceleration, it would also make his bike a proper LSM.

 

[Lowell]

Well, I still am under the impression you'll be riding something kinda like my bro's motorcycle:

It's a 50cc water cooled 2 stroke, but the previous owner tuned it so it blows by LSM territory and goes at least in the 90's, probably more but I was riding a 50 zone when I tried it. Once it gets past 20-30 or so the motor stays pegged at 9K RPM just before the red line, and accelerates rather nicely. But from a stop acceleration is eventual, so things like merging in traffic are tricky. While starting on a fair hill it strains and creeps onwards, if you had no compassion and kept it up it would probably pickup speed and go, but it's shurely a lot slower then it could be.

Last I met him, bro had the intent to change the gearing so it tops off around 70 so as to get better low end acceleration, it would also make his bike a proper LSM.

Now imagine if you had multi speeds on that bike, you wouldn't have to mess with variator weights and compromise the gearing. Depending on what make, there's usually a 70 or 80cc big bore kit available that will drop in, and with some fab work 100cc + motors can be fitted.

I can't remember where it was, but I recall seeing pictures of an Italjet Dragster 50cc with a 172cc motor installed

http://www.loonracing.co.uk/eastkirkbyreport0406.html

 

[safe]

Once it gets past 20-30 or so the motor stays pegged at 9K RPM just before the red line, and accelerates rather nicely. But from a stop acceleration is eventual, so things like merging in traffic are tricky. While starting on a fair hill it strains and creeps onwards, if you had no compassion and kept it up it would probably pickup speed and go, but it's surely a lot slower then it could be.

That's what I'm expecting. First gear... until you are up to about 5-10 mph... the accelleration will be about half of what it could be if you were using a standard controller. But after about 10 mph the extra amps gives the "Motor Current Limited" bike more power and like that "peaky" bike you're talking about it's pretty powerful up top.

Think of it this way...

You subtract from the low end and you add to the top end while at the same time keeping the same average heat. As long as you get up to speed (10 mph should be enough) and stay in the right gear (which is easier because the "feel" is more clearly defined) you will have about a 20% power boost depending on how many amps you decide to "boost".

20% is 20%... if you want to go even bigger and jump up to 60 Amps and maybe blow air through the engine to cool it then all of a sudden your little 750 Watt motor is pumping out something like 2.5 hp.

That's "crazy" horsepower for a little motor... (with a standard controller you would be more likely to burn it up and even with this idea it's still going to be placing a lot of strain on it)

And don't forget that you could have "Boost Control" that was variable. So maybe you want to run "lean and cool" some of the time or "rich and hot" for others. It makes the motor more flexible.

Just by looking at the chart it's pretty obvious that if you crank the "boost" enough that you have all the torque you need...

 

[Lowell]

Sign me up for the best of the red curve plus 60 amp curve along with a kick ass cooling system for the motor.

What you're saying makes perfect sense though, and with a lower 1st gear 5mph will go by so fast it won't even be noticed.

 

[safe]

Sign me up for the best of the red curve plus 60 amp curve along with a kick ass cooling system for the motor.

What you're saying makes perfect sense though, and with a lower 1st gear 5mph will go by so fast it won't even be noticed.

That's one way to do it... simply focus on the cooling side and let all the heat get generated, but cool it quickly so it doesn't burn anything up. The biggest downside of that is the fact that your efficiency goes down... you are after all heating something for no good reason. (wasting energy)

My core point is that if you are going to use gears then it only makes sense to get rid of "current multiplication" otherwise you really aren't USING your gears for what they are there for. The whole point of gears is to narrow the powerband much like a race bike and increase the efficiency and power.

Hub Motors are best when they "overwhelm" the problem with so many volts and so much power that they make problems disappear. Hub Motors get into trouble when they are UNDERPOWERED and are asked to do things that they can't do.

I still believe that there is a "magic ratio" where gears make no sense. Something like a factor of 2-3 times more power in a fixed gear will equal what you can get from a geared bike. But if you are going to go down the geared route you should be faithful to it's natural tendencies.

 

[Lowell]

Agreed, Safe. Are you going to implement this on your 80lb bike?

 

[eP]

That's what I'm expecting. First gear... until you are up to about 5-10 mph... the accelleration will be about half of what it could be if you were using a standard controller. But after about 10 mph the extra amps gives the "Motor Current Limited" bike more power and like that "peaky" bike you're talking about it's pretty powerful up top.

Are you sure "the accelleration will be about half ..." ?

At what slope ?

At 20% slope the acceleration at motor current limited will be less than 20% if the 25% is the max. slope. At 10% slope it be close to 40%.

The other questions is the nominal power the motor you need.
If your motor has only 8.8V sag at 50A, so its nominal power out should be greater than 3 kW i suppose.
So the next question is how much is stator loss for that huge monster.
Is the 439W of heat loses - the windings resistance loss alone or combined with the stator loss ?

 

[Lowell]

How about the best of both, where 1st gear allows battery current limiting at the push of a button and once you're moving 5-8mph or so it switches to motor current limiting? The 1 second it takes to get to that speed won't make any significant extra heat and you only push the button when you want the extra torque.

 

[safe]

Agreed, Safe. Are you going to implement this on your 80lb bike?

I'd like to...

Fechter says he's going to "think about" the idea of using an "off the shelf" Hall Effect Sensor and Solid State Relay. If it can be done without much effort using standardized components then you have less "fiddling around" to get it right. Of course, if you make an error there's less of a chance you can correct the error. (so you would need to do your homework on the specifications in advance)

As for "hybrid solutions"... it's just not worth it... constant torque is still torque, just because you have a little less torque for a second compared to a standard controller you can still get going. "eP" seems to be unable to accept that this works and is trying to find "extreme cases" where it might not. (like hills that you never encounter in real life) When you think in terms of "averages" like "average power" and "average heat" the "Motor Current Limited" idea is clearly a better way to go if you use gears. Hub Motors are normally tied to their "fixed gear" so you need the "help" of "current multiplication" just to survive a hill. Racing motorcycles and cars use the same kind of theory for their motors and it seems to work fine for them. At a tractor pull... well, you would want a torque focused motor for that! (or a hill climbing bike)

"Motor Current Limiting" and "Gears" are a perfect match in a performance oriented "Road Race" environment...

Now let's get back to the core issue which is "how" to build that circuit!

 

[safe]

http://www.crydom.com/products/productFamily.aspx?id=19

Solid State Relay:

DO061B
Control - 1.7-9 Volts DC
Load Current - 0.02-1 Amps DC
Switching Type - DC
Load Voltage - 3-60 Volts DC

Hall Effect Sensors that are custom built for electric vehicles:

http://www.raztec.co.nz/Solar%20Fern%20Project.aspx

How about this for "easy to interpret" voltage output without worry about temperature:

And the throttle is 1 - 4 Volts:

 

[safe]

The circuit for "Motor Current Limiting" might be very simple:

 

[Lowell]

The DrainBrain V2 has adjustable current limiting built into the throttle circuit. All you would have to do is have the DB sense motor current instead of battery current, although that would throw off most of the other useful power features.

 

[eP]

Agreed, Safe. Are you going to implement this on your 80lb bike?

I'd like to...
...
As for "hybrid solutions"... it's just not worth it... constant torque is still torque, just because you have a little less torque for a second compared to a standard controller you can still get going. "eP" seems to be unable to accept that this works and is trying to find "extreme cases" where it might not. (like hills that you never encounter in real life) When you think in terms of "averages" like "average power" and "average heat" the "Motor Current Limited" idea is clearly a better way to go if you use gears. Hub Motors are normally tied to their "fixed gear" so you need the "help" of "current multiplication" just to survive a hill. Racing motorcycles and cars use the same kind of theory for their motors and it seems to work fine for them. At a tractor pull... well, you would want a torque focused motor for that! (or a hill climbing bike)

"Motor Current Limiting" and "Gears" are a perfect match in a performance oriented "Road Race" environment...

Now let's get back to the core issue which is "how" to build that circuit!

You give us an example which shuold be able to go at 25% slope. So i ask you for stator loss 'coz i see the winding sag (winding loss) is still relatively low at that case. And as a consequence that motor nominal power out must be very high.
Such types motor are usually have relatively high stator loses (especially at high rpms until they are coreless), so i ask you: did you assume stator loss value or you skip off that ? The same question is for transmission loss (more transmission ratio - more loss).

I dont looking for extreme cases or hill climbing specialized vehicle.
What i'm looking for is efficient bike at wide load range (from 0.2 HP to 1.2 HP for example).
A don't care about extreme powers and extreme speeds, but i want still be able smothly accelerate at moderate hills.
So i suppose 500% gears ratio is still not enough for me - maybe 750% will be enough ( 4 mph-30 mph ).

I still see you have to sacrifice more torque(acceleration) than you can imagine even at moderate slopes (close to %10), until you use huge motors with huge nominal Power_out.
But for that last you will experience big inefficiencies at low load range i'm afraid.
If you are going to build the bike for racing it is no problem for you of course.

So tell us again what is the purpose your motor current limited controller: inefficient racing style riding or more efficient riding at wide load range ?

 

[safe]

...inefficient racing style riding

That's a funny one "inefficient racing style riding" when was the last time a race machine was ever inefficient?

No.

The "Motor Current Limited" controller has been shown through the course of this thread to be more efficient, have more peak power and produce less heat that it's ordinary "utility" based standard controller and is the preferred way to operate a geared bike.

eP... what are you doing here?

If you were sincere you would realize that I presented valid information and the other "smart guys" that post here agree that this controller idea is simply a "fact of life" of the way things work. (there are controllers that exist that already do this type of current limiting)

You're back at that level of appearing like a "troll" again.

What's blocking your ability to accept this as true?

I want to "move on" to the actual circuit for this and get past educating you on motor theory. Could you from now on restrict your questions/ideas to things associated with the CIRCUIT. (we're up to page 10 of this "education process")

Thanks.

 

[safe]

The DrainBrain V2 has adjustable current limiting built into the throttle circuit. All you would have to do is have the DB sense motor current instead of battery current, although that would throw off most of the other useful power features.

All that would mean is that you connected the DrainBrain to the motor side wires rather than the battery side wires.

Could it be THAT easy?

Since you own one could you try switching the wires and see what happens? It's possible that all that is being limited is the peak voltage in which case it's really not current limiting. Such a circuit would be identical to placing a pot between the throttle and the controller.

 

[eP]

...inefficient racing style riding

That's a funny one "inefficient racing style riding" when was the last time a race machine was ever inefficient?

No.

The "Motor Current Limited" controller has been shown through the course of this thread to be more efficient, have more peak power and produce less heat that it's ordinary "utility" based standard controller and is the preferred way to operate a geared bike.

If you want to use 1.5 kW at flat your bike will be extremly fast but inefficient for me. (Many Wh/km)

I want to be able to use only 0.15 kW at high efficiency, so i need the right motor (low stator loss-low idlle current at high rpms).

eP... what are you doing here?

I'm asking gently and waiting for the answer.

If you were sincere you would realize that I presented valid information and the other "smart guys" that post here agree that this controller idea is simply a "fact of life" of the way things work.

You're back at that level of appearing like a "troll" again.

Not enough valid for me. I'm sorry.
If you want to use 4 kW P_out high rpms motor you will get HIGH stator loss and very low efficiency at low load i suppose.

If i'm wrong so tell us the real motor parameters as an example.

Maybe for racing your idea is good. But for efficient riding at wide speed range is not good i'm afraid.

What's blocking your ability to accept this as true?

I want to "move on" to the actual circuit for this and get past educating you on motor theory. Could you from now on restrict your questions/ideas to things associated with the CIRCUIT. (we're up to page 10 of this "education process")
Thanks.

If you want move on to circuit so move on. A few simple answers for me is not a big obstacle for you if you are sure your idea is good and you have made enough calculations.

So i'm still wating for answers.
Thanks in advance.

 

[safe]

I'm going to allow you to drop off the thread.

At this point I want to "move on" to the design of the circuit itself.

Thanks for your understanding...

 

[eP]

I'm going to allow you to drop off the thread.

At this point I want to "move on" to the design of the circuit itself.

Thanks for your understanding...

Ok. :wink:

If you are sure what you are doing.
But i'm sure you still don't know where you are will go.
This circuit will be useless for 1 kW motors or less and 305% wide gears will be to narrow at that case.

But you will do what you want.

Please dont tell us it is for efficiency at general riding.

 

[TylerDurden]

Let's consider:

No one has validated safe's concept in the theoretical realm or the physical realm, and the spreadsheets have been fatally flawed on numerous occasions. I'll wager not one person other than safe will spend real $ on a similar implementation until they see it working on the street.

Everyone is welcome to ingnore EP's questions... it is easy to ignore the issues that can make the system fail in a cloud of smoke, like the last cheap motor did.

This is an open forum. Any user is welcome to discuss the ideas shared, within the boundries of relevance and respect for the group.

 

[safe]

"Motor Current Limited" controllers have been built and do exist already, so it's not like I'm actually inventing a new idea. The main charactoristic of a "Motor Current Limited" controller is that the motor produces less heat. This has been done as a safety precaution on some electric bikes.

My observation is simply that "Gears" and the "Motor Current Limited" controller are a perfect match.

So there's really no debate that this "works"... it really should be more about how well it will work and how one might use it. (how far up in the amps does one dare go in the top end?)

And the bigger and more central question is:

"What is the easiest way to convert existing geared bikes to 'Motor Current Limited' control?"

Think of it this way... if Fechter (our local electrical guru) accepts the idea as valid then it has to have at least some merit.

 

[safe]

Back to the circuit issue...

Here's another example of a Solid State Relay that might be used. The "trigger" is from 1.5 volts to 3.8 volts. So one might start with a 0-10 volt signal from a Hall Effects Sensor and then trim it with a pot to match the current limit you want.

"Boost Control" might be achieved with as little as:

1. Hall Effects Sensor

2. Trimmable Potentiometer

3. Solid State Relay

 

[eP]

And the bigger and more central question is:

"What is the easiest way to convert existing geared bikes to "Motor Current Limited" control?"

Think of it this way... if Fechter (our local electrical guru) accepts the idea as valid then it has to have at least some merit.

Before you start the think which way is easiest, the better is start to calculate what we can gain after conversion and what we will lost.

As an example lets take 600W geared motor which is 60% efficient at nominal P_out, so it take 1 kW from the battery pack.

First of all we need calculate the gear range we need. At the lowest gear we can afford max. 4 mph if we want accelerate at 10% slope after conversion.
At the top gear we can get 30 mph, so we need 750% range or we must sacrifice the top speed to 20 mph at that case and to buy expensive (500% range) hub.

I'm sure the gain in efficiency will not be enough for such pain sacrifice.

But maybe i'm still wrong ?

 

[safe]

Before you start the think which way is easiest, the better is start to calculate what we can gain after conversion and what we will lost.

We're moving on to the circuit design now.

Suffice to say that you now know that you have an "option". If you decide on using gears on your bike then you have the option of trying this controller design to optimize the benefits of gears.

If you go with that dual hub motor concept you would NEVER need this, so why do you even bother? If you aren't using gears then this idea does not apply to you.

So let's get back to the circuit design... no more time spent reviewing this as an "option" let's explore how one makes the "option" actually happen...

 

[TylerDurden]

"Motor Current Limited" controllers have been built and do exist already, so it's not like I'm actually inventing a new idea. The main charactoristic of a "Motor Current Limited" controller is that the motor produces less heat. This has been done as a safety precaution on some electric bikes.

snip

So there's really no debate that this "works"... it really should be more about how well it will work and how one might use it.

That is what we are discussing. As much as anyone may want to avoid the tough questions, they will always be there.

That application of motor-side current limiting is simply another way of reducing power to the motor. Lower power at the motor may reduce the potential for overheating, but the resulting loss of torque may significantly limit the usefulness of the method:

Torque will generate heat. A specific amount of torque is needed to accellerate. The resulting heat will need to be dissipated.

How much torque will be generated?
What amount of heat will be generated?
Can it be dissipated?
How many gears will it require?
How long will it take?

Fechter can make the circuit, there is little doubt about that.