I think I am being a little slow here, and I have taken on board what you all have kindly said. When you say safe level what then comes to mind is motor capability i.e. what it could handle until reaching its unsafe level, and yes I can appreciate the many factors that are also involved.
HUB MOTOR CAPABILITY
- Thread starter mountainsport
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D
Deleted member 4366
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Yes, It's a bit counter-intuitive. It's not the current that destroys your motor, it's the heat. Heat depends on speed. The slower you go under full power, the more heat you produce. It's your actual speed compared with the winding speed of the motor that counts in that respect. If the motor has a low-speed winding, it will have less problem with heat.
As I said above, its not simple because there's lots of parameters all working together. Basically, the thing that kills most motors is having a motor that's too fast for its power and then running it at full power too slow.
As I said above, its not simple because there's lots of parameters all working together. Basically, the thing that kills most motors is having a motor that's too fast for its power and then running it at full power too slow.
Let us start a fresh and do things back to front. If I was to buy for instance a 3000Watt motor before anything else, how would I then size the controller and battery according to the motor capability?
The manufacturer of the motor will recommend the size of the controller to you.
Which then narrows down your choice of battery.
Give us an example of the motor you are thinking of, we'll help you to understand what to do and why.
Which then narrows down your choice of battery.
Give us an example of the motor you are thinking of, we'll help you to understand what to do and why.
Thank you Woosh, I was just using the 3000 watt motor even so a 500 watt as an example for calculation sake and if also someone on here wanted to build an ebike system from scratch, sorry to you ALL i am not looking for a motor. I just wanted to add technical information to my note book.
MS, motors aren't built with the same features in mind.
in order to work out the parameters, we need the motor's characteristics which are normally found on the manufacturers' website.
There is a very useful tool at ebikes.ca called the motor simulator. It has a database of about 60 of the most popular motors.
it's much easier to use a particular model as example.
However, to give you a quick idea: a 500W motor is usually fitted with 36V 25A controller and a 36V 15AH battery. A 1000W motor with 48V 30A controller and a 48V 15AH battery, A 1500W with 48V 35A controller and 48V 20AH battery. 2000W and above, you'll have specialist 52V, 63V, 72V system. They all need type approval.
in order to work out the parameters, we need the motor's characteristics which are normally found on the manufacturers' website.
There is a very useful tool at ebikes.ca called the motor simulator. It has a database of about 60 of the most popular motors.
it's much easier to use a particular model as example.
However, to give you a quick idea: a 500W motor is usually fitted with 36V 25A controller and a 36V 15AH battery. A 1000W motor with 48V 30A controller and a 48V 15AH battery, A 1500W with 48V 35A controller and 48V 20AH battery. 2000W and above, you'll have specialist 52V, 63V, 72V system. They all need type approval.
D
Deleted member 4366
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You missed the point. Everything is meaningless unless you state the winding speed (kV) of the motor.
Design sequence.Thank you Woosh, I was just using the 3000 watt motor even so a 500 watt as an example for calculation sake and if also someone on here wanted to build an ebike system from scratch, sorry to you ALL i am not looking for a motor. I just wanted to add technical information to my note book.
1. Expected speed ... S. In M sec. Pi x D x R
2. Intended wheel diameter D in metres
3. Revs of wheel R per second
4. Power required ... Needs estimates of weight and cross sectional area of vehicle.. no simple formula here. Let's say you decide on 3000w. P
5. Select voltage for motor , 12, 24 , 36, 48, 60 72 volts etc. V
6. Current demand I = P/V both battery pack and controller must be capable of at least supplying that and at the voltage as previously stated
7. Size of battery ... Duration a 3000wh battery will in theory supply 1 hours travel.
8. Technology of battery determines weight.
9.. Weight of battery .... Feeds back into #4 above..
Wow! Danidl, you are now dealing here with mega efficiency, thanks for that brake down list. I am sure that some of us on here have learnt from this.
You said in part 5. select voltage for the motor, so can you run a 3000w motor using a 12volt battery?
Sorry d8veh, you are totally correct. Ok then lets work with both types of windings. I do not want to be inconsiderate by choosing one type because we all need to gather as much relevant information for future reference.
... In theory yes . The starting motor in a domestic car might be drawing 3000w for the duration . Such a motor will be drawing 300amps!, So will deplete the battery quickly. It would also burn out if kept on for any length of time. Look at the thickness of the cables going from the battery to the starting motor...
In practice motors are designed to operate at specific voltages, so a 3000w motor might be intended to operate at 60v and draw 50amp or 120v and 25amp.. The heating in a wire, increases as the square of the current, , so a fixed length of a cable will lose 4 times the energy into heat if the current in it doubles.... It becomes unrealistic to try and power a heavy load with a low voltage
I don't want to start any arguments, but we're going into territory that is often misunderstood, even by those with high levels of technical knowledge.
There is nothing about a specific winding of motor ('fast' or 'slow' winding) that makes them inherently better at delivering torque or speed. Different windings exist purely to move the efficiency curve of a motor to allow the usage of a wide choice of operating voltages and currents. At any given performance point, two correctly wound motors (same copper fill) of different winding speeds will generate exactly the same levels of heat.
It is often commented that a fast winding running on higher current is disadvantageous due to the larger conductor required to deliver power from the battery to the motor, but since this is offset against the advantage of a lower operating voltage and simplified BMS, it's not so clear cut.
Here is a link to a thread discussing this very topic on Endless Sphere:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907
It jumps straight into the subject at an alarming pace, since I think it was a continuation of a discussion on a separate thread. Even though the argument continues throughout the thread, it contains lots of educational value. In fact, I think I have learnt more about motors from this thread than any other.
There is nothing about a specific winding of motor ('fast' or 'slow' winding) that makes them inherently better at delivering torque or speed. Different windings exist purely to move the efficiency curve of a motor to allow the usage of a wide choice of operating voltages and currents. At any given performance point, two correctly wound motors (same copper fill) of different winding speeds will generate exactly the same levels of heat.
It is often commented that a fast winding running on higher current is disadvantageous due to the larger conductor required to deliver power from the battery to the motor, but since this is offset against the advantage of a lower operating voltage and simplified BMS, it's not so clear cut.
Here is a link to a thread discussing this very topic on Endless Sphere:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907
It jumps straight into the subject at an alarming pace, since I think it was a continuation of a discussion on a separate thread. Even though the argument continues throughout the thread, it contains lots of educational value. In fact, I think I have learnt more about motors from this thread than any other.
This issue (the efficiency curve) is often overlooked by a lot of members, resulting in buying the wrong kit for the job.
Perhaps you should start a new thread.
Thanks for the link. I would be agreeing with the person called KS ,
Very simply if you need a fast rotation motor you need to use multiple parallel coils of low number of turns in order to minimise self induction and consequent back EMF. , The cost of this is very high copper losses as the heating is proportional to square of current in all the windings.
If you can live with lower rotational speed you can up the voltage, lower the current , reduce the copper losses. And maybe use a gearbox. ..
I'm not able to add anything to the discussion that hasn't already been posted in the Science, Physics, Math, & Myth thread previously linked to. I will reiterate however that copper losses in this instance would be equal since the decrease in resistance of the shorter, wider 'faster' winding perfectly balances the I^2*R difference.
EDIT: Also, adding any kind of gearbox to a correctly designed system can only decrease the overall system efficiency. You'd be much better off using the additional 'gearbox mass' to increase the copper fill of the motor and do away with the gearbox altogether.
... That argument of true, within the motor itself,.. but ignores the effect on the system, all external wiring etc. , Where the wiring mass has to square to compensate for the additional losses
That's correct, but no big deal - £1 of heavier gauge cable will combat that and the lower system voltage has additional benefits.
I hope to bring the mxus out of temporary retirement this year and am going to feed it with 44.4 V 12S lipo through a 17 Amp controller which d8veh has said is about the maximum it will handle before thinking about oil cooling. This will bring me close to the mythical horse power or 750 W if you prefer.
D
Deleted member 4366
Guest
Most of what was written in that thread is correct, but the content is often misunderstood and mis-quoted. The main conclusion is that if you have two different motor windings, say 36v 201 rpm and 36v 260 rpm and run the 201 rpm one at 36v and 20 amps and the other at 48v and 15 amps, they'll behave exactly the same - torque, power, speed and efficiency (all those numbers are approximate, so don't calculate to the nearest watt and say it's wrong);
however, if you run both motors at 36v and 20 amps, the 201 rpm one will give more power and less heat at low rpm than the higher speed one and the high speed one will give more power at high rpm than the low speed one. The higher speed one will always make more heat and waste more battery than the 201 rpm one when they run at the same rpm. This paragraph is the important difference between the two motors that people seem to struggle to understand, and this is why it's important to choose a motor with the right winding speed and voltage combination.
In this chart you can see that the higher speed motor always has lower efficiency, lower torque and lower power than the lower-speed one in the range that the lower speed one can run. The battery, controller, throttle, incline etc. are the same for both.
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