Choose the right controller

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Choose the right controller

Postby alfak » 31 Jan 2021, 00:16

Hi everyone! :wave:

Just a "simple" question for all of you...

If I got a motor with this "specs"
Image

And inside the batteries are 2 fuses for 40A:
Image

Can I only go with 24V 500W? like this one: https://www.ebay.co.uk/itm/24V-500W-Mot ... SwHsRYEjm~
because: 500W/24V = 20A

Thanks for your tips! :thumbup:
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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 04:25

Your 500 watt motor will have a stall current of anything between 150 and 400Amps Depending on motor. The stock controller is current limited by software.

So its possible to send maybe 100Amps or greater, at 24V to the motor depending on the stock controller. Thats 2400 watts or possibly way more. So the 500 watts thing tells you very little. Its basically a best max continuous rating where the motor has good efficiency and doesent overheat and cook itself. It can take way more intermittently. At stall or as you set off from a standstill that motor maybe needs 50A or greater and sometimes a lot greater on a hill.

And unless you have some programming software to reset the motor load compensation with that controller the only really important criteria is that it has the same brake voltage and the same motor impedance/resistance. Or close. But it may not have any programming capability? And 20A isnt goint to make much effect as you set off... And if that controller isnt current limiting it will go bang. I just read, its limited to 28A. It might work, but it will not be very powerful. And it has no programming capability as far as I can tell. So you get whatever you get. You canot control acceleration rates, deceleration rates etc. And it wont have any motor load compensation. So I wouldnt bother. You need a proper mobiity scooter controller. Theres a reason they are 10x that price new. But used ones are cheap.
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Re: Choose the right controller

Postby woodygb » 31 Jan 2021, 10:04

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Re: Choose the right controller

Postby LROBBINS » 31 Jan 2021, 11:02

Generally motor "watts" is mechanical watt (= torque x RPM) output at peak efficiency NOT current consumption. As Burgerman says, current draw can be many fold higher than this under load, even before the motor is stalled. At stall, mechanical watts output is 0 and electrical watts used is maxed out (and may destroy the motor if held in that state too long).
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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 11:33

I am not so sure thats correct on DC motors. Its true that it is on AC motors because of the way they work.

Its also the point where the motor is designed to be used. If you go much past that for a long period, like up a steep hill, then it draws more amps (and so more watts) will cook the motor. That doesent happen on the AC induction motors that are rated in watts/HP output.

Because as load goes up, rpm falls below that most efficiend region and then current rises. Along with watts. In and out. And because its less efficient at lower rpms under heavier load the motor heats up. Mobility controllers have 2 systems built in to protect motors. One is a thermal rollback of current. As the controller gets loaded it warms up and to protect motors and itself it reduces current output. The other way is that a controller starts at sat 120A for a few seconds to be sure the motor starts and crosses a threshold its. Then it drops a few seconds later to 90A. Then to 60. to prevent motor heat damage (smoke!).

If you live in a place where theres a lot of hills, or you are heavy, you can feed the motor more power (watts) without damage if you fit a fan or cooling fins as we do with hobby motors. But in your case with that eBay controller non of this stuff, and no programabiity of drive parameters, or motor load compensation id possible. So it may work in a fashion. But not properly and nowhere near enough power.
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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 12:08

From my experience when talking about permanant magnet DC motors the watts rating is a subjective figure that the motor runs continually without overheating. And runs in an efficient area of its output.

It isnt just my opinion, its what EMD told me. Its also what many pages on the web such as this ebike technical page/site says.
https://www.electricitybikes.com/blog/nerdystuff Motor manufacturers are not refering to power output as that varies wildly with PMDC motors depending on load, voltage etc. They are refering to max safe continual average electrical input in watts.


Nominal Watts vs Peak Watts So the same limitation on peak vs continuous power for humans apply to electric motors - motors are rated "nominally" for how much power they can safely output without overheating.

However, this can be subjectively determined, mostly to conform to EU regulations that require an eBIke with more than 250 nominal eWatts to be regulated like a motorcycle, which requires registration at the DMV, a drivers license, and a license plate. Typically the peak eWatt usage of the modern mid drive motor is between 400-600 watts, even if they are stamped with a 250 eWatt "nominal" rating.


With AC induction motors, for eg then horsepower is usually used as a power measurement. My pressure washer is 3 HP (I didnt look lately but its something like that). And watts generally refers to electrical input power. My pressure washer is 3300w 240V for e.g. This does not increase to high levels like a dc permanant magnet when loaded or stalled. The max allowed in a UK socket. A light bulb may be 30W 240V.
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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 12:17

And... http://rcboats.kiwi/index.php/ct-menu-i ... nu-item-43

Your brushless motor should have a watt rating on its spec sheet, something like “180W”. This means that that is the amount of “horse power” that it should produce safely. Running anything over this rating could damage your motor, especially over a long period of time.

The Motor will also have an efficiency rating, for brushless this will be around 80 – 90%. So if your battery is supplying the ESC with 180 watts then your motor will only be producing around 85% of that or (180 x .85) = 153 watts.


From another tech site. Hobby motors Brushless but still PMDC motors.
My 700 watt tiny motors is a continuous rating. I run them at double that for a few mins. Because the 180mph airflow cools them well! So they are not damaged.
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Re: Choose the right controller

Postby alfak » 31 Jan 2021, 15:49

Thank you guys! I'm amazed by your feedback :o

I've got mine (sterling pearl, 2012) from a 2nd hand market and I only want to speed up the motor a little because the stock controller cuts off at 4mph.
It puts more current to go up a hill and brakes when pass that speed, but in a flat terrain is a little bit slow.

I've asked a few technicials from orthopedic workshops and they said "the manufacturer said no, and we say no. There's no way to do what you want"

So you don't think this controller can make the work? I was not able to find a 24V with more Watts.
I know I'm gonna lose some things (reverse, if I not put a 6pin switch) but only need to make that.

Really appreciated. :thumbup:
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Re: Choose the right controller

Postby woodygb » 31 Jan 2021, 15:59

the stock controller cuts off at 4mph
...Why do you think that?

The voltage being supplied to the motor dictates the speed.

IF your motor is getting the full battery voltage of 24v and this gives you a speed of 4 mph then ....THAT IS YOUR MAXIMUM SPEED.
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Re: Choose the right controller

Postby alfak » 31 Jan 2021, 16:54

woodygb wrote:
the stock controller cuts off at 4mph
...Why do you think that?

The voltage being supplied to the motor dictates the speed.

IF your motor is getting the full battery voltage of 24v and this gives you a speed of 4 mph then ....THAT IS YOUR MAXIMUM SPEED.


Maybe I'm totally wrong, but when the scooter goes down in a ramp it not speeds up even if I keep holding the throttle.
And as I said, when going upwards it tries to maintain the speed.

Could it be possible, as you said, that the motor always operate at 24V and regulate the speed/torque? czy

I keep learning with all this stuff.

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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 17:10

A DC motor is SELF REGULATING. It is a generator and a motor. If you go down a ramp then the motor tries to charge the battery, and the back EMF slows you or rather prevents it going faster. Aided by negative Motor Compensation.

As you approach a ramp at full speed, or any speed, the ramp presents a load. That slows the motor slightly which increases current. Which increases torque. The motor compansation add even more voltage to maintain speed. Its a positive current feedback loop. It cant add more than 24V whatever it does however. It also works in reverse to maintain a steady speed on a downhill ramp,
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Re: Choose the right controller

Postby woodygb » 31 Jan 2021, 17:48

Could it be possible, as you said, that the motor always operate at 24V
It uses pulsed 24v.... many pulses per second.... called P.W.M

https://www.4qd.co.uk/docs/what-is-pwm/
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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 18:01

But its easier to think of it as a voltage because once you add up all the pulse lengths and off periods and average it thats what you see on a volt meter. 50% pulsewidth? 12V... 25% pulsewidth? 6 volt. Etc.
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Re: Choose the right controller

Postby alfak » 31 Jan 2021, 18:46

Ok then ... to summarize.

If my motor is getting all the 24V from the batteries and the speed is 4mph, I can't do anything to gain more speed.
Even if I switch to a more powerfull controller (e.g. 24V 1000W) when the motor receive the 24V will keep the same speed because is its "nominal" speed.
That more power only affects to the torque and not to the max speed. It's correct?

In the other hand, if I make the motor run without load (wheels raised), measure the voltage and there is less than 24V it would be possible that the controller was limiting the voltage.
It's the only case that maybe putting other main controller would be worth.

Because add more batteries to reach 36V and overvoltage the motor with a 36V controller it's not a good idea, isn't it? :lol:

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Re: Choose the right controller

Postby Burgerman » 31 Jan 2021, 19:53

Ok then ... to summarize.

If my motor is getting all the 24V from the batteries and the speed is 4mph, I can't do anything to gain more speed.

Correct. Only taller gearing. That increases load and so also Amps at all speeds. That needs a bigger motor (lower impedance, greater torque, which needs bigger controller that is higher amp capable. And that all needs bigger cables and larger lower impedance batteries. Ever wondered by there are "bigger" scooters?

Even if I switch to a more powerfull controller (e.g. 24V 1000W)

Unless buying junk on ebay, a scooter or powerchair or EV controller is rated in working volts. And in maximum amp capability. Not watts.
And yes its still just sending the same 24v to the motor. To get more power you need less resistance, a lower impedance motor. That may or may not be higher watts. Watts isnt any help here.

when the motor receive the 24V will keep the same speed because is its "nominal" speed.

All DC permanant magnet motors used in practically everything battery powered have an RPM PER VOLT rating. So my hobby motors may be 900RPM/Volt. So at 2 volts it turns at 900x2=1800rpm. At 6 volts it turns at 900rpm x 6...

That more power only affects to the torque and not to the max speed. It's correct?

What do you mean by power? Power is VOLTS X AMPS = WATTS. Watts is power. You get more power to any DC motor just by loading it more. Or by increasing the voltage at the same RPM/LOAD. You must be specific. If you mean fitting a greater Amp controller like say a 150A mobility controller? No it wont make a blind bit of difference to speed. Only to stall torque and that extra torque tails off as rpm increases. Unless the motor is much lower impedance.

In the other hand, if I make the motor run without load (wheels raised), measure the voltage and there is less than 24V it would be possible that the controller was limiting the voltage.

Max pulsewidth is usually a fraction less than 100% so it will always read a little bit less than battery volts. But not by enough to make any real diference.
It's the only case that maybe putting other main controller would be worth.

Unless its been programmed to less than max speed. Which isnt very often, then you will not gain anything. Other than a lack of proper programming, motor compensation and control. And far less torque.

Because add more batteries to reach 36V and overvoltage the motor with a 36V controller it's not a good idea, isn't it? :lol:

Yes it is. Provided you use a PROPER controller that can be configured not to exceed your motors wattage rating for long periods as you hill climb or accelerate. Thats why I did exactly this with my own powerchar. Trust me it isnt simple! Theres no plug and play way to do this.
E.G. In this case I doubled the speed to 16mph, and increased range fron around 15 to 45 miles at the same time. And used 8mph 24V motors.
http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm




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