1. You can use a 48 v battery with a 36 v motor, it will spin 33% faster
2. You can't use a 48 v battery with a 36 v controller (unless you are very clever/have experience)
3. When you upgrade a 36 v motor to 48 v it is recommended to keep the controller limited to 17-18 Amps (about the same number of Amps you would use at 36 v)
There, I think all points have been covered?
A 250 W nominative motor will run all day at 500 W without even getting warm. They are designed to do that - read EN15194 to understand why.
Doing the math on the modifications listed above, the controller Watts (not the Watts at the wheel) will peak at 936 W with the battery hot off the charger. Let's say you are being silly and use your motor badly - you might have a hill steep enough that you take in the wrong gear and so 50% of that power is lost as waste heat into the motor.
468 W of heat* is not enough to warm any of the brand name geared hub motors most people have to above 80°C. That is the lowest internal temperature that can cause (temporary) damage. Permanent damage to a motor starts at about 120°C, the nylon gears on the clutch wil strip their teeth. At 180°C the insulation on the wires will melt.
*I have an induction hob - 600 W level takes forever to bring a pot of water to a simmer, about 80°C.
If there are any other electrical engineers reading this post of yours, I am sure that they are all having a good laugh at your misunderstanding(s) about electricity.
By the way, I "did the math" probably many years before you were born!!!
I started my studies almost 60 years ago!!!
I really am very surprised that anyone would open up their lack of fairly basic electrical knowledge to possible ridicule!!
For your information:-
Some e-bike motors are simply built for a higher voltage/wattage, just to save money in having different models available, IMPORTANT please note that the speed is not "affected" by the voltage!! But the power is partly, so speed control is therefore achieved.
The good e-bike motors on most bikes nowadays are basically a miniature 3 phase motor, often with hall effect sensors built in, to give feedback to the electronics of "where" the motor rotor "is" in its revolution.
The speed itself is therefore governed by the controller, by it setting a "frequency of switching" on and off, of large MOSFET transistors, allowing variable speed control. The quicker they switch, the faster you go!
The voltage therefore has therefore no net effect on speed.
Once the current set is achieved, the field(s) is switched off early, if need be.
As no overheating can be allowed.
The time between pulses to each field coil (there are at least three or sets of threes, depending upon design!) sets the speed of the motor therefore the e-bike.
Plus other settings with wheel size of course.
A cheap speed upgrade that many do not understand for some reason, is to set a smaller wheel size than the bike actually has, as the controller has no way of measuring wheel size! Though I have never heard of anyone actually doing that!!! But its very simple to do if the controller can be used on smaller diameter wheels!
VFD motors work in a very similar manner. Look here for further infos:-https://en.wikipedia.org/wiki/Variable-frequency_drive
There are still some e-bike motors with "brushes" around on the bike market, these are partly affected by voltage. BUT the controller then uses PWM to reduce the POWER to control the speed of rotation!!
A short tutorial for PWM can be found here:-
https://www.electronics-tutorials.ws/blog/pulse-width-modulation.html
Then there is the problem of brush wear and the mess the carbon makes inside the motor for such motors!
If simply by changing the voltage, the motor speed was also changed as you apparently believe, I can see some huge possibilities for even more danger to the rider than he already has.....
Remember, we are not talking about simple DC motors as <ou seem to imagine.....
A place to start reading, which covers the theory even better might be here:-
https://en.wikipedia.org/wiki/Pedelec#Motor_control
Where you can read the following with regard to e-bikes:-
When the motors are regularly used heavily, especially when going uphill they may heat up significantly, some have a temperature sensor in the motor winding, where if a certain temperature is reached the electronics may reduce power to the motor.
Just for your information only, I spent a great many years learning my job and studying as well, to know how electrics (and electronics by the way!) REALLY work.
But for example, in all my years, I have never ever in my life ever found an electrician that really knew his job, in all the countries I have worked in, mainly the USA, the UK and Germany!
But I have identified and repaired their "handiwork" in those countries plus all the Scandinavian, EU,Middle East and African ones, for over 50 years now.....
They apparently knew,only little bits of knowledge, cobbled together into what they thought was electrical knowledge......it wasn't! It cause expensive damage to expensive machines!
Why did you mention this:- "*I have an induction hob - 600 W level takes forever to bring a pot of water to a simmer, about 80°C."
Let me address that for you too so you may understand better just how an Induction Hob REALLY works:-
The hob runs at a set frequency, (but variable amplitude for power/heat control), which has been selected to work best with
most cookware.
Therefore the basic functionality, when comparing between an e-bike and an induction hob is quite different, but still power control!!
Different frequencies are needed for different cookware metals.....which is why only certain ones will work! Aluminium, copper and some stainless steels will not work!!
Often, in my experience, cast iron cookware works best, though I have only tested using such cookware that I have possessed of course!!
Aluminium or most types of stainless steel, will either not work, or will only work badly.
A simple test is a magnet.
When it sticks to the base, that usually implies that the pot will work on induction hobs. Using the same magnet on the sides will often not stick there if aluminium or certain types of stainless.
This is why a good stainless steel or aluminium pot, one that works on an induction hob, has a steel disk moulded into the base.
It is only that disk which actually gets hot!!! Many do not know this!!
Not the rest of the pan, except by conduction, not induction!!
A cast iron pot is basically similar to that disk of course, but "all over"! Which is why it works so well generally!
So you either have a pot(s) not designed fully for induction, or of the wrong material, but remember 800 Watt is very low for Hob cooking anyway.
I would suggest a minimum of 1800 Watt per hob, or better.
Also, its possible that the hob has the wrong frequency as well of course due to a failure in design or manufacture.....so try it with cast iron to see if that helps in any way....If not, it is simply too weak to be useful for some reason.....
Comparing the two as you wish to do is a really bad idea, comparing apples and pears.....as they regulate power in different ways to each other.....that only an engineer would fully understand.....
Finally, there is no way to inform you accurately, without you possibly getting upset, about what you do not understand, but that is your problem not mine.....
Furthermore, I have no interest in trying to train you (or anyone else for that matter) to being fully electrically literate on an online bike forum, as that sounds like rather hard going for us both.
Maybe the Open University runs such courses nowadays in the UK on electricity and motor control.
So today, I have only raised a few points to hopefully spike your interest in learning properly what you think you already know, but don't!!
As the more you write here, the more obvious you make it as to just how little you really know/understand.....Sadly! As I am sorry to be the bearer of such news.....
Have a great day anyway.
Andy
