Battery decision

[Andy-Mat]

View attachment 28180

Same motor, same controller, different battery.

Oh dear the motor with the 48v battery goes faster ... Something must be wrong with the years and years of hands on experience of the people at ebikes.ca not to mention all those crazy hot-rodders over at endless-sphere.com.

Because we both know I am halucinating and don't know SFA about electric motors and pedelec controllers don't we? Hey did you know I haven't managed to fry a controller or a motor yet? Only 7,000 km under my belt so I probably still have time.

I think you need to read up on how a common KT controller actually works.

View attachment 28180

Same motor, same controller, different battery.

Oh dear the motor with the 48v battery goes faster ... Something must be wrong with the years and years of hands on experience of the people at ebikes.ca not to mention all those crazy hot-rodders over at endless-sphere.com.

Because we both know I am halucinating and don't know SFA about electric motors and pedelec controllers don't we? Hey did you know I haven't managed to fry a controller or a motor yet? Only 7,000 km under my belt so I probably still have time.

I think you need to read up on how a common KT controller actually works.

This is only valid for identical motors that were most likely built to "cover" more than one voltage.
Or possibly both were 48 volt motors, one disguised.
The easy way to check that out, is to simply put each motor on a accurate weighing machine, a true lower voltage motor of otherwise identical manufacture, the lower voltage motor will be significantly lighter! e.g. Different parts! Especially the heavy copper field coils.
This was not detailed on the sheet you posted.
But manufacturers will do anything to reduce having to make extra and different parts, and relabeling a motor to a lower spec is the cheapest trick of all!
And also a very safe one for all concerned.
Which seemingly takes some people in as well!!
Furthermore, I see no information as to the internal temperature of the motors while under test!
A parameter that a good and valid test would have shown!!
Maybe intentionally not shown comes to mind as well.....
Therefore the test data you supplied, is not simply a "license" for anyone to believe its the same for all 36 volt bike motors available, as you appear to think!
Maybe "someone" wanted to mislead people for some reason, it's usually money!
Now if you produced the same data for all 36 volt bike motors in current usage, we could make a better/safer decision either way.
But as you have not managed to do that (neither could I!), then you should curb your statements for "informing" other people here with blanket, untested, information! Its simply not safe.
Its the only decent and correct way to treat our other members here.....
No unknown guesses that might mislead some!
I notice that still no one has offered to guarantee that! I wonder why!!!
If you are SO CERTAIN that its good info, why are you not stepping up?
Also, you apparently did not take the time to read up any of the links that I posted!
Your choice, as you have simply not had time to study either fully since I posted!
Also, I am sure the infos would have prompted many valid questions!
And as I have now informed the rest of our members here, with our conversation of what is safe to do and what is not, while trying to improve your knowledge...
I now see no more problems!
Now all here can make an educated decision if needed, with fully correct and safe information available!!
Also, if anyone wants to follow your route, at least he is fully forewarned!!
Do remember, that if I see you, promulgating unsafe, possibly dangerous information again, we will have the same/similar conversation again, OK?
I am retired and have plenty of time and interest in such things!!
regards and have a great day

Andy

 

[danielrlee]

Has d8veh come back as a forum troll?

 

[anotherkiwi]

I do understand what you are saying - you don't understand how the Chinese make and market geared hub motors apparently. These motors are not very sophisticated and the Chinese will cut costs where they can... There are different speed windings - the codes are engraved on the motor. And sometime you even get the speed winding that is engraved on the motor! Voltage wise there are two basic motor sizes the big ones are marketed as 500 W and 48 v. The small ones can be 250 or 350 W and the 350 W version is often available as 36 or 48 v. Other than the windings they are more or less identical.

I am running an overvolted mid-drive because I spin the pedals too fast for it at 36 v and was having huge problems with back EMF. Now that it is at 44.4 v it is near to perfect RPM wise, it even makes less noise!

Oh, and some people have even measure RPM with a tach and guess what? Yep unloaded speed increases by the percentage you increase the voltage. So I guess the controllers aren't as sophisticated as they could be either...

 

[Nealh]

I'm not an 'expert' or an electrician and have yet also to fry a controller or hub motor by over volting.
My 36v hub runs at about 23mph err@36v but show it 48v and it bumbles along at 28mph, it would go faster if my legs could spin faster or I change the gearing.

Even Daniel disagrees with you and he is quite well qualified I believe.

As I mentioned we don't generally do scare mongering without cause, over the years we have not had any accounts of over volted ebikes crashing and burning if current supply is kept to a sensible level and many have tried and done it without nay issues.
Member Cwah has burnt out hubs but then again he likes to pump 30 + amps into them.

 

[Nealh]

Has d8veh come back as a forum troll?

Blimey Daniel, you mean he's come back to haunt us using reverse psychology.
I think many miss his input on the forum as he helped many of us to understand the possibilities that hubs are capable of.

 

[Nealh]

I'm sure if the new troll goes on ES to spread his gospel they will soon shoot him down or crash and burn him .

 

[Sturmey]

Hi Andy. I think the one important thing thats missing in your explanation is the effect of the 'back EMF' on the controller output. When the motor spins up, it generates a voltage that opposes the voltage from the controller. This limits the RPM to a certain value, depending on the output voltage of the controller. Increasing the controller output AC voltage (from 36v to 48v peak to peak) allows the motor to go faster before its back EMF exceeds the controller output voltage.
Therefore manufacturers such as Bafang often quote different RPM values for their motors at different voltages.e.g.
https://www.bafang-e.com/en/components/component/motor/rm-g130500dc.html

 

[Deleted member 128]

Hi Andy. I think the one important thing thats missing in your explanation is the effect of the 'back EMF' on the controller output. When the motor spins up, it generates a voltage that opposes the voltage from the controller. This limits the RPM to a certain value, depending on the output voltage of the controller. Increasing the controller output AC voltage (from 36v to 48v peak to peak) allows the motor to go faster before its back EMF exceeds the controller output voltage.
Therefore manufacturers such as Bafang often quote different RPM values for their motors at different voltages.e.g.
https://www.bafang-e.com/en/components/component/motor/rm-g130500dc.html

Interesting spec with that link, thanks. The way I read it is that the motor can operate off 36, 43 or 48V with increasing power and rpm. Only one torque figure specified though, I wonder why.
But this isn't to say that ALL motors designed to run off 36V can safely run off 48V.
I'm an electronics engineer and derate component specs in designs, not enhance them eg with 10V on a 10R resistor the power dissipation is 10W and I'd use a 10R resistor rated at at least 12.5W and would NEVER use a component rated at less than 10W. That would be asking for reliability problems.
Going back to motors, It's like increasing the power of a car engine by 33% and expecting the gearbox and brakes to cope without any issues. That's not how quality engineering is done.

 

[Nealh]

Not forgetting we are using DC not AC voltage, so only a tingle is felt if at all and not a heavy jolt/shock.
The smaller spec motors seem to run off 48v like Keyda etc, but at a much lower current rating due to their smaller size and capability. The Q100s don't last long at 20a it's horses for courses so you need to pick the hub carefully.
We generally know which hubs are capable of extra power.

In the Op's case it is a mid drive which isn't suitable for over volting they have in built controllers and the controller capacitors won't be 48v rated so he would have to stick with 36v , but a hub is amenable to some over volting as long as you don't go mad 17/20a max for 250/350w.

 

[Sturmey]

Interesting spec with that link, thanks. The way I read it is that the motor can operate off 36, 43 or 48V with increasing power and rpm. Only one torque figure specified though, I wonder why.
But this isn't to say that ALL motors designed to run off 36V can safely run off 48V.
I'm an electronics engineer and derate component specs in designs, not enhance them eg with 10V on a 10R resistor the power dissipation is 10W and I'd use a 10R resistor rated at at least 12.5W and would NEVER use a component rated at less than 10W. That would be asking for reliability problems.
Going back to motors, It's like increasing the power of a car engine by 33% and expecting the gearbox and brakes to cope without any issues. That's not how quality engineering is done.

Power is a product of both speed (RPM ) and Torque. You can increase the power of the motor by either increasing the torque (e.g. by increasing the current) or by increasing the speed or RPM (by increasing the voltage.) Now in many cases, the two enemies of the electric motor is excessive heat (caused by excessive current(I²R)) whic can'cook' the motor and excessive turning forces (torque) which can damage the nylon gears and clutch.. Hence, its relatively safer to increase the power of motor by increasing the speed.(voltage) (provided the motor is well balanced etc) and this explains why there is only one torque figure.

When it comes to 'quality engineering', I suppose you are talking about safety margins (in terms of making things much stronger just to be on the safe side and to allow for deterioration or misuse etc). Now if we were designing motors for elevators or boats or airplanes or bikes for public use etc, then we would expect a large margin of safety. However, with cheap and robust hub motors and diy, this is not as important for some and we are really only dealing with relatively low power anyway in many cases. I think there is a tradition even with ordinary cycling in general with tweaking/customization and getting the most out of component. (e.g with road bikes, using light narrow tyres, using less spokes on wheels, lightweigh frames etc).

 

[Deleted member 128]

Power is a product of both speed (RPM ) and Torque. You can increase the power of the motor by either increasing the torque (e.g. by increasing the current) or by increasing the speed or RPM (by increasing the voltage.) Now in many cases, the two enemies of the electric motor is excessive heat (caused by excessive current(I²R)) whic can'cook' the motor and excessive turning forces (torque) which can damage the nylon gears and clutch.. Hence, its relatively safer to increase the power of motor by increasing the speed.(voltage) (provided the motor is well balanced etc) and this explains why there is only one torque figure.

When it comes to 'quality engineering', I suppose you are talking about safety margins (in terms of making things much stronger just to be on the safe side and to allow for deterioration or misuse etc). Now if we were designing motors for elevators or boats or airplanes or bikes for public use etc, then we would expect a large margin of safety. However, with cheap and robust hub motors and diy, this is not as important for some and we are really only dealing with relatively low power anyway in many cases. I think there is a tradition even with ordinary cycling in general with tweaking/customization and getting the most out of component. (e.g with road bikes, using light narrow tyres, using less spokes on wheels, lightweigh frames etc).

If you increase the voltage applied to a motor you will increase the current drawn and the heat dissipated (V^2/R, I^2R).
Which raises an interesting point, is the power rating the power in or power out?
By "quality engineering" I'm referring to the difference between things that seldom break down and things that often break down. Each to their own I suppose....

 

[Sturmey]

If you increase the voltage applied to a motor you will increase the current drawn and the heat dissipated (V^2/R, I^2R).
Which raises an interesting point, is the power rating the power in or power out?
By "quality engineering" I'm referring to the difference between things that seldom break down and things that often break down. Each to their own I suppose....

Motors are not simple passive components like resistors but rather more dynamic and how they respond depends on their speed, loads etc. You can, for example, have a situation, where a reduction of voltage causes a motor to stall and then to burn out. (e.g fridge compressors during brown out). Hence you really need to graph out motor characteristics torque/rpm against its load line for a given set of conditions e.g. https://www.ebikes.ca/tools/simulator.html

The 250 watt power rating is a nominal figure and it comes closer to the average mechanical output imo. My standard (and legal) halfords 250w bafang is quoted as 500w peak. Bear in mind also that mechanical power = electric power x efficiency.
https://www.ebikes.ca/learn/power-ratings.html
http://www.ebikeschool.com/myth-ebike-wattage/

But back to engineering quality. I worked as a phone technician and everything was well built e.g. Fuses were typically 3 times the load, all essential equipment was duplicated etc. , ring circuits, standby generators in case of power failures etc. Thats because in a complicated network situation, the network is only as strong as its weakest link and failures can be catastrophic to the network, with a loss of revenue. However, with ebikes, we are just talking about a consumer good and although the quality of engineering is good, it need not be as good as above.

 

[anotherkiwi]

When you read of 250 W geared hub motor failure in general they have been hot rodded by using a controller supplying over 30 Amps and using a battery of over 52 v. That is to say they usually fail at over 1.5 kW (over 6 times rated power) and the first thing to go are the nylon gears. On ES you can find photos of burnt out motors which have usually recieved insane amounts of current.

However depending on the mass and the windings small motors will fail at lower current, some at 20 Amps. Even then it is usually the nylon gears which are the first to go because they can't stand temperatures above 120°C.

No geared hub motor I have seen on the market includes an internal temperature sensor, that is always a hot rodder add on. That tends to indicate that the manufacturer has built in enough safety margin for it to be ignored as a standard feature.

 

[Deleted member 128]

When you read of 250 W geared hub motor failure in general they have been hot rodded by using a controller supplying over 30 Amps and using a battery of over 52 v. That is to say they usually fail at over 1.5 kW (over 6 times rated power) and the first thing to go are the nylon gears. On ES you can find photos of burnt out motors which have usually recieved insane amounts of current.

However depending on the mass and the windings small motors will fail at lower current, some at 20 Amps. Even then it is usually the nylon gears which are the first to go because they can't stand temperatures above 120°C.

No geared hub motor I have seen on the market includes an internal temperature sensor, that is always a hot rodder add on. That tends to indicate that the manufacturer has built in enough safety margin for it to be ignored as a standard feature.

Indeed, heat is the killer and nylon gears are usually the weakest link. Increasing battery voltage from 36V to 48V potentially nearly doubles the heat dissipation in the motor unless current is carefully restricted in which case what's the point in increasing the voltage in the first place...
As you say, manufacturers should have built in enough safety margin for temperature sensing not be be required at the RATED voltage but they're unlikely to build in enough safety margin to allow motors to operate at 130% of rated voltage in the case of a 36V motor running off 48V.

 

[Andy-Mat]

Interesting spec with that link, thanks. The way I read it is that the motor can operate off 36, 43 or 48V with increasing power and rpm. Only one torque figure specified though, I wonder why.
But this isn't to say that ALL motors designed to run off 36V can safely run off 48V.
I'm an electronics engineer and derate component specs in designs, not enhance them eg with 10V on a 10R resistor the power dissipation is 10W and I'd use a 10R resistor rated at at least 12.5W and would NEVER use a component rated at less than 10W. That would be asking for reliability problems.
Going back to motors, It's like increasing the power of a car engine by 33% and expecting the gearbox and brakes to cope without any issues. That's not how quality engineering is done.

I agree fully, that is exactly what I was trying to get across.
Its one thing for some here to take risks with their own equipment, but it shows poor quality when advising others, with possible less technical knowledge to do the same.....and as you say, not all 36 volt motors can handle 48 volts!!!
So the "blanket" comments from some here, should be considered as being wrong!!!
Some here have got away with it, good for them, but why did they not buy the correct bike battery and voltage wise in the first place?
As getting caught in any EU country(for example) with an unlicensed Electric bike at over 25 KMH, will soon take the smile off the rider's face as the bike will be confiscated and probably crushed, plus a fine!!!
regards and thanks for you bringing some common sense here.
Andy

 

[anotherkiwi]

My cut off speed is set to 25 km/h
My battery is 44.4v nominative (EN15194 specifies 48v)
So I am well within the limits of the law.

When you consider a 36v motor is designed to work with a voltage of 42v, battery hot off the charger, and that the great majority of motors are built with tollerances over and above that then there is little to no risk adding 10v into the mix.

No one has suggested that asking for advice before overvolting any given motor was not a good idea.

You really do have issues...

 

[danielrlee]

Andy. Is it possible that you are confusing 'brushed' and 'brushless' motor theory? Some of what you state is true in the context of brushed motors, but not when applied to brushless motors.

 

[Andy-Mat]

My cut off speed is set to 25 km/h
My battery is 44.4v nominative (EN15194 specifies 48v)
So I am well within the limits of the law.

When you consider a 36v motor is designed to work with a voltage of 42v, battery hot off the charger, and that the great majority of motors are built with tollerances over and above that then there is little to no risk adding 10v into the mix.

No one has suggested that asking for advice before overvolting any given motor was not a good idea.

You really do have issues...

.......and of course if you ever get any "ISSUES" with your 36 volt motor on 48 volts (you do have one I would imagine!), of course you will come online here, apologise for your unfriendliness to me and tell us what went wrong with your motor!!!
NEVER in 100 years!!! You will simply keep quiet!!!
All your comments are simply "throwaway" comments, no thought or regard for anyone else or their property!!!
IMHO, just feeding your ego is more important!!
I believe that anyone who recommends anything, even with the minimum possibility of causing damage, to in this case an e-bike motor, should be man enough to accept the consequences on behalf of the person he mislead!!!
Just as I have mentioned before and you still completely ignore doing it!!!
What I also fail to understand, is why you even do it in the first place!!! But no need to answer, as I am sure I would still not understand why!
Do you "get off" or similar when giving poor quality advice to others? Is that the "issue" you have?
But very sadly, something is still driving you on, but very difficult to understand from a normal person's standpoint!
I ask again, what does such questionable quality "advice" gain you, or the person you are advising to take such risks, no matter how small, assuming you are in anyway correct for a moment!
Ones that will possibly invalidate a long term manufacturer guarantee anyway?
There are far better and safer ways to increase bike speed/acceleration, but without taking any risks of ruining a motor that you recommend, except that of the extra speed (if used) being illegal in many countries around the world, if the bike is not then licensed as it should be, once it goes above that legal speed limit!!
Very important in the EU, and getting a license is fraught with regulations for the private person!
According to that badly written test you posted, they achieved 33 KMH if I remember correctly! And at that time, that was your aim apparently, now its suddenly not anymore!! Very strange!
But as you make me and others here simply laugh at your antics.......and we all need something to amuse us from time to time, so a great many thanks for that at least!!!
I am pretty sure, from reading other friendlier posts here, that the general consensus is that what you feel is a good idea, is simply not worth doing for many, as buying the correct/needed bike/battery/motor in the first place is always the best way to go.....as the extra cost, when carefully carried out, can be considered to be negligible!
Have a great day anyway, I am!!
Andy

 

[anotherkiwi]

You haven't been reading or understanding my posts... I am not the kind of person to recommend something that would damage another persons motor.

I am pretty sure, from reading other friendlier posts here, that the general consensus is that what you feel is a good idea, is simply not worth doing for many, as buying the correct/needed bike/battery/motor in the first place is always the best way to go...

Some of us don't have the finances to buy so we make our own. As more money comes along we upgrade.

.......and of course if you ever get any "ISSUES" with your 36 volt motor on 48 volts (you do have one I would imagine!), of course you will come online here, apologise for your unfriendliness to me and tell us what went wrong with your motor!!!
NEVER in 100 years!!! You will simply keep quiet!!!

Read my build threads - all the issues I have ever had are published for all to see there. I am not being unfriendly, I am simply saying you are wrong. Maybe that counts as unfriendliness in your world, in that case stay away from the internet would be some friendly advice.

 

[Laser Man]

If you increase the voltage applied to a motor you will increase the current drawn and the heat dissipated (V^2/R, I^2R).

Not necessarily true.
In the case of these electronically commutated motors, the current is limited in the controller.
Increasing the voltage ***allows*** more current to be fed to the motor, but the current is only increased if you change the current limit settings (software) or tamper with the shunt (hardware).