Controllers, Torque and heat

Hello Guys

Could someone explain to me if it is possible to alter the torque characteristics of a motor through the controller to produce greater torque with less heat.

I want to go real slow up hills with a lot of torque (I know I can use gearing to achieve this as well) and it would be nice to know how much torque I have in reserve (I understand that it will be proportional to the % of max amps I'm drawing) but how does one quantify it for a particular set-up?

Please point me to a reference site/thread if available (I haven't been able find anything I understand).

Thanks

The controller can’t alter motor physical properties.

If you want to produce more torque, you have to feed the motor more watts. A motor has a limit of watts that it can transform into torque, that is saturation point. The windings of a motor has a resistance (impedance) that defines the loss, energy that is turned into heat rather than producing torque. The loss curve is exponential, meaning the closer the watts are to the motor saturation point, the higher the percentage of them watts are lost into heat.

The only ways to produce more torque, yet less heat are:

1- Physical modification of motor properties (winding pattern, copper mass, size, weight, material...). A slower winding will let you ride slowly, with lesser watts and loss.

2- Gearing down (wheel size for a hub motor, gear ratio for chain drive...). A smaller wheel will let you have more torque with less watts.

Then, controller spec and settings can alter system efficiency, that makes some theorical improvement in torque/power ratio. Yet it can’t feed less watts and produce more torque at once.

That may not be very scientific explanations, but it is the easiest way I found to make it clear.

Some ES members who are into science more than I, will be able to give a better detailed explanation.

I am unsure why everyone is wanting more torque. It is a rather pointless property. What you want is power which is a function of torque.

Let's say power can be calculated:
p = M x r x C
p is power
M is torque
r is rotation
C is a constant containing something like pi

So why is torque interesting? It is the only thing in this equation you can influence. the constant "C" us - well - constant. The rotation r ist basically your speed.

So increasing torque will increase your power at a given speed. More power will let you travel at a higher speed at steeper hills.

So when will we return to our eBike? What can we alter about our motor?
Voltage: "U" and Current: "I"

Increasing the voltage will mostly increase your top speed.
Increasing your current will actually do what you are after: More power at lower speeds.

So it's easy: More current. Just feed it 40A and fly up the hill.

No. If you double the power at lower speeds the heat dissipation (or entropy) will increase exponentially. mathematically speaking.

More power at lower speeds and less heat dissipation?
You need a new motor. You want a slower motor and feed it your standard current which will decrease your top speed.

You will solve your problem by taking a slower motor with average current but increased Voltage.

BUT:

increasing your current will actually increase your power (p = U x I) which will help you travel at higher speeds and therefore leave the speed of lower efficiency faster and lower heat dissipation.

So. well. Its complex. You will certainly not be able to alter the physical properties of a given motor.

tentman said:

Could someone explain to me if it is possible to alter the torque characteristics of a motor through the controller to produce greater torque with less heat.

I want to go real slow up hills with a lot of torque (I know I can use gearing to achieve this as well) and it would be nice to know how much torque I have in reserve (I understand that it will be proportional to the % of max amps I'm drawing) but how does one quantify it for a particular set-up?

Click to expand...

No; if you run the motor slower, it produces less rotational power for the same input power, so you get more waste heat power instead.

The only way you can get more power out of the same motor while decreasing waste heat is to spin it faster (up to a point dependent on motor design), so to go slower while doing that you'd have to gear it down.

Alternately, you can use a bigger motor that's designed to run at the slower speeds and still provide the power you need, and designed to deal with what waste heat it does make. Then it can still usually work at the higher speeds as well.

Depending on your needs and limitations, sometimes it's cheaper and lighter to go with a bigger motor, and sometimes it's cheaper and lighter to go with a multispeed transmission.

Ford Prefect said:

I am unsure why everyone is wanting more torque. It is a rather pointless property.
What you want is power...

More power at lower speeds and less heat dissipation?
You need a new motor. You want a slower motor and feed it your standard current which will decrease your top speed.
...

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You totally lost me with your logic and you are not explaining it more than halfway correctly. OP question is about low speed - torque is everything since it's what gets you up.

Answer to the question is simple: only thing that can be done based on the question is optimise the driving of the motor. Set the hall sensors optimised for slow speed with an oscilloscope. The possible gain will be small.

OP also asks for the torque reserve so i guess he means how much more current until heat issues occur. A good reference is to go to the ebikes.ca simulator (https://www.ebikes.ca/tools/simulator.html) and run the motor/controller setup in some different scenarios.

You don't need a slower motor, only the correct amount of current for the winding you have combined with the same capability of battery and controller. It's a common misunderstanding. Here the OP seems to have an existing system and wants to alter the torque through the settings in the controller without added heat so the winding is not optional.

Answer to basic question (already stated in earlier posts )
More torque and less heat can only be had through better efficiency. What OP's asking for can't be done.

Let us know what your total weight is, and the grade of the hill, and its length. With that info, we can start to make practical suggestions based on our real world experience.


If the speed will be limited by the power, then what you need is a mid drive you can gear down, or a very small wheel on a low rpm motor. You can also gear down a hub motor by lacing it into the smallest possible rim. But it only gears down a little bit.

NO the low rpm dd motor does not make more torque, and in fact it will not develop the same power as seen on a watt meter that a fast rpm motor does. It will stop pulling harder sooner, at lower rpm. All motors pull less as they get up to rpm.

BUT, it will waste less power at a low speed than the faster rpm wind motor. The low rpm motor is the choice for max efficiency at low speed, NOT for more torque. But you will see them sold as the "torque version kit" .

My best, most efficient trailer hauling bike for the rocky mountains was this bike, that burned in the garage fire.

The small wheel gave me a slower speed without going to such low rpm it made heat. Then the low rpm 500w motor, made it run even more efficient at slow speeds, like 10 mph. It was still inefficient at 5 mph, but it could grind up a mountain towing a trailer at 10 mph, without overheating. It could handle easily, 400 pounds total weight, while the same motor in 26" wheel could handle only about 300.


But it only had the torque that 1000w fed into it, and the size of the magnets inside, could produce. It never had crazy torque. Going up hills, it would do about 12 mph, pulling about 700w max. But it did it efficient, partly because it stayed cool, partly because I could help more pedaling when going slow. Again, in this case my goal was efficiency at low speeds, which led to not overheating on the rocky mountain passes, while overloaded.


But crazy torque is easy,, just double, or quadruple the power. Two 1000w motors on the same bike would have flown up those hills at the slower motors top speed. Or faster, with faster motors. Same with a motor twice the size, running twice the watts. Its just simply physics, a given weight will require a given wattage to climb a hill at a given speed. for more speed, and torque, adding watts is the real answer, up to the motors limits. Then increase the motor size for more.


So more torque is simple, bigger motor, more watts controller, and usually a bump in voltage. Just putting that smaller wheel on 60v, and 2000w total power would have made it giddy up. (2000w is that type motors practical limit)

Best possible torque on a DD motor will be a fast wind, large motor, on a very small wheel, and run on 72v, with 3-4000w . See John in CR's scooter motor bike.

You may want to consider some cooling improvements to the motor if you are set on sticking with your current motor. That would allow for more time before overheating at increased power levels. Something like Statorade and/or hub-sink may be of interest (that is a road I will be going down). Also, there are some great venting/active fan mods as well.

EDIT: Ultimately though, like the last post; a bigger motor will get you the best torque increase.

MadRhino said:

The controller can’t alter motor physical properties.

If you want to produce more torque, you have to feed the motor more watts.

Click to expand...

Well, to be 100% accurate, more current gets you more torque. More voltage gets you more speed. Current is mainly what causes heating, which sucks if you want tons of torque at low speed - because 1) at very low speeds maximum current might occur at 200 watts, which means you can't produce much power and 2) at low speeds there's not much airflow over a hub or mid-drive.

Which is why matching motor constant to application is important. A good match means that lower current gives you more torque (more turns=more flux at a given current) and doesn't limit your top speed _too_ much.

1- Physical modification of motor properties (winding pattern, copper mass, size, weight, material...). A slower winding will let you ride slowly, with lesser watts and loss.

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Yes - at the cost of speed, since the back EMF will also be higher.

Ford Prefect said:

I am unsure why everyone is wanting more torque. It is a rather pointless property. . .So why is torque interesting?

Click to expand...

Because it determines acceleration, top speed and how steep a hill you can climb.

So increasing torque will increase your power at a given speed. More power will let you travel at a higher speed at steeper hills.

Click to expand...

Well, no. A direct drive motor capable of 5000 watts will not get you up a steep hill if the motor constant is wrong (i.e. at current limit, it can't provide enough torque.) That's why small, powerful motors are geared for ebike applications.

Increasing the voltage will mostly increase your top speed.
Increasing your current will actually do what you are after: More power at lower speeds.

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Agreed there.

Well, if a motor is rated for 5000w, it is going to be capable of serious hauling ass up hills, overloaded.

I betcha though, hes running a 500w DD hubmotor, which has about a 2000w practical limit. I used to run that type motor all winter on 3000w, 72v 40 amps, and had great torque, because of both the current and voltage increase over the typical 1000w setup. Off road riding, I'd fly up hills with the limit of grade at about 20 degrees. Degrees baby, not percent.

But then warm weather would arrive, and sure as shit by may I'd melt the halls in the motor. Id fix that, and then run 72v 20 amps all summer, 1500w.

My first suggestion for him for a quick fix, assuming his battery is super strong, is a 48v 40 amps controller, for 2000w. But not in summer. :lol:


That controller would serve well for later, when he buys the bigger motor he really needs.