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 .

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

Edited December 18, 20187 yr by 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

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.

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.

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).

Edited December 19, 20187 yr by Sturmey

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....

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.

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.

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.

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

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...

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.

Edited December 29, 20187 yr by danielrlee

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

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.

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).

You quoted 44.4 volts for your battery:-

 

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.

 

I looked at the document you referenced and could not find a mention of ANY nominal Battery values. See here:-

http://12686946-873973833989121800.preview.editmysite.com/uploads/1/2/6/8/12686946/norme_en_15194.pdf

This is EN 15194 Mai 2009 :-

If you were referring to another version, could you post a link here for us all please?

I found the following on an e-bike web page, it fits in perfectly with my knowledge, but not with yours:-

 

Voltage: most ebike kits are rated for a specific voltage range. A typical 36v ebike needs a battery that delivers power between 42v to 30v. A 36v pack, at 42v is fully 100% charged and holding as much energy as it can and at 30v it should shut down and stop giving power before causing permanent damage..

 

The common " 36v" number is an average operating voltage or sometimes called nominal voltage.

Electric-Find.com says: "Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.May 28, 2009"

Some ebike kits have a wide operating range like 36v or 48v, so be aware and pick accordingly.

Most ebike kits with displays that show battery charge levels with a series of LED lights can only work at that voltage, if in doubt, ask the vendor!

 

But until you are able to do that, I am taking the generally accepted nominal values, which are 48 and 36 volts respectively!

44.4 v is not a nominal value.

But if we stay with the nominal values for example, we are talking about a 12 volt difference.

If we stay with a full charge, the 36 volt will measure 42 volts.

A 48 volt battery fully charged will be around 54 volts , but again a 12 volts difference!!!

Where do you get your 10 volts, or was that simply a "guesstimate"? Its not in the literature quoted as far as I can tell....

 

A 12 volt difference with regard to say a 36 v motor is 33.34 % more voltage!

If we take your 10 volt guesstimate as a value, that is still almost 28% more!

Where are you "coming from" and where are you "going to?"

 

Very little of what you post is true!!!

 

To quote you yourself:-

 

You really do have issues...

 

Awaiting some far more exact and easily verifiable comments from you in the future!!

 

Have a great day!

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).

Indeed, but then what's the point of increasing the voltage if the current isn't increased via software or hardware?

We all can argue the toss about over volting hubs all day long, what may not be theoretical to do and what practically can be done are two different things. For many years hub have been over volted some do fail, usually because to much power(watts) have been put through them. Cwah has a few times stated he has ruined a hub, not by over volting but feeding to many amps/watts through his hubs.

It is not the voltage that is of concern but the actual amps you intend on putting through the hub, if you are sensible the hub will not have any issues. Push the boundaries to far and they fry a bit, end of the day if a hub fries you replace it as they aren't very expensive in most cases.

I have overvolted 4 of my hubs and none have had issues with up to 20a max , max power isn't used continuously as this affects battery range so for the savvy power is used accordingly to manage range and give the extra high torque/power when needed for inclines. An over volted hub continuously run at high amps in the short to mid term will most likely suffer but used carefully the crash and burn that has been alluded to doesn't happen.

I'm happy to do so as are quite a few other members who successfully have had no issue's, it's about control and being sensible with the power. Some of the decent hubs which there are quite a few have a limit as to how much power they can handle and that is about 1000w max before heat and serious issues lead to failure.

:).

Current doesn't need to be increased, simply by overvolting 36v to 48v not only increases hub/bike speed if required but also increases the watts output by 33% at the wheel so gives a nice bonus/increase in torque for inclines esp when used with 5 levels of pas.

You quoted 44.4 volts for your battery:-

 

44.4 v is not a nominal value.

 

Hi. 44.4v (or sometimes called 44v) I presume refers to the 12s battery (12 groups of 3.6 volts in series) and is a standard, and chargers are readily available for same e.g. https://www.amazon.com/50-4V-Charger-Li-ion-Battery-Auto-Stop/dp/B07BFPYYSM

Current doesn't need to be increased, simply by overvolting 36v to 48v not only increases hub/bike speed if required but also increases the watts output by 33% at the wheel so gives a nice bonus/increase in torque for inclines esp when used with 5 levels of pas.

Hi Neal

If the current isn't changed then surely the power into the motor, crudely speaking it's proportional to I^2R, won't change, the controller will limit the voltage it applies in order to keep the current the same.

By the way, increasing the voltage from 36 to 48V without limiting the current would increase the power consumed by 77% not 33%, its roughly proportional to V^2, not V.

The only thing that makes a brushless motor rated for a particular voltage is the fact that its winding pairs nicely with a commonly available battery voltage to give a specific legislatively limited speed, e.g. 25kph in the EU, 20mph in the US, etc. This voltage rating is purely for the purposes of marketing and is not a physical motor limitation.

 

Any motor can be destroyed at any voltage - you just need to introduce a stall condition at any reasonable power level and the windings will melt within 60 seconds due to 0% efficiency at 0RPM.

 

Increasing the voltage fed into a brushless motor (NOT motor controller - this will have a much lower voltage limit determined by the input/output capacitors and MOSFETS) will proportionally increase its no-load speed. Damage will not occur until the breakdown voltage of the motor windings/phase wires are reached (usually in the region of 100’s of volts). As long as the breakdown voltage is not reached, the only physical limitation is that of heat.

 

Heat is generated in a motor from two types of losses, copper and iron. Copper losses are directly related to the amount of current passed through the motor coils to generate torque and iron losses are directly related to motor RPM. Generally speaking, unless you are running silly speeds, iron losses are relatively low to not be of concern in this discussion. That leaves copper losses (I^R).

 

If a motor is used at the same performance specifications (torque & speed) as prior to a voltage increase, no additional heat will be generated by the motor.

 

If the extra speed gained from the voltage increase is utilised, extra heat will be generated by the motor due to the extra power required to overcome increased air resistance at higher speeds. As long as the extra heat is managed and the temperature is kept below an absolute limit (varies by motor type, construction and materials used) the motor will continue to run without issue.

 

Ultimately, anyone involved in EV performance modification in 2018 is "standing on the shoulder of giants". Those before us have tested the limitations of individual components with their own resources and as a result, we all benefit from this knowledge.

Edited December 30, 20187 yr by danielrlee

You quoted 44.4 volts for your battery:-

 

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.

 

I looked at the document you referenced and could not find a mention of ANY nominal Battery values. See here:-

http://12686946-873973833989121800.preview.editmysite.com/uploads/1/2/6/8/12686946/norme_en_15194.pdf

This is EN 15194 Mai 2009 :-

If you were referring to another version, could you post a link here for us all please?

I found the following on an e-bike web page, it fits in perfectly with my knowledge, but not with yours:-

 

Voltage: most ebike kits are rated for a specific voltage range. A typical 36v ebike needs a battery that delivers power between 42v to 30v. A 36v pack, at 42v is fully 100% charged and holding as much energy as it can and at 30v it should shut down and stop giving power before causing permanent damage..

 

The common " 36v" number is an average operating voltage or sometimes called nominal voltage.

 

Electric-Find.com says: "Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.May 28, 2009"

 

Some ebike kits have a wide operating range like 36v or 48v, so be aware and pick accordingly.

Most ebike kits with displays that show battery charge levels with a series of LED lights can only work at that voltage, if in doubt, ask the vendor!

 

But until you are able to do that, I am taking the generally accepted nominal values, which are 48 and 36 volts respectively!

44.4 v is not a nominal value.

But if we stay with the nominal values for example, we are talking about a 12 volt difference.

If we stay with a full charge, the 36 volt will measure 42 volts.

A 48 volt battery fully charged will be around 54 volts , but again a 12 volts difference!!!

Where do you get your 10 volts, or was that simply a "guesstimate"? Its not in the literature quoted as far as I can tell....

 

A 12 volt difference with regard to say a 36 v motor is 33.34 % more voltage!

If we take your 10 volt guesstimate as a value, that is still almost 28% more!

Where are you "coming from" and where are you "going to?"

 

Very little of what you post is true!!!

 

To quote you yourself:-

 

You really do have issues...

 

Awaiting some far more exact and easily verifiable comments from you in the future!!

 

Have a great day!

 

Preface of EN15194:

 

"This document specifies the safety requirements and test methods for evaluating the design and assembly of electrically power assisted bicycles and sub-assemblies dedicated to systems using a battery voltage up to 48 VDC or an integrated battery charger with an input of 230 V. It specifies requirements and test methods for engine power management systems, electrical circuits including the charging system for the assessment of the design and assembly of electrically power assisted cycles and sub-assemblies for systems having a voltage up to and including 48 VDC or integrated a battery charger with a 230 V input."

 

I am using a 12S battery which is 44.4v nominative (3.7v nominative per cell) and which I charge to a maximum of 4.15v per cell for a peak voltage of 49.8v (my LVC is 43.8v).

 

44.4v - 36v = 8.4v however I rarely run the battery down below 46v and hey look:

46v - 36v = 10v isn't that amazing!!!

 

Why would I want to run a 36v mid-drive motor at a higher voltage?

 

- Because I spin quite fast and doing so ups the RPM to between 95 rpm and 105 rpm which suits my riding style better

- It gives me a peak power range between 735 and 690 Watts, about 150 more Watts which come in quite handy where I live now

- Faster acceleration away from the lights, safer riding in trafic

- I no longer sag to below LVC climbing the last hill home

 

Notice there is no mention of illegal speed in my list...

Current doesn't need to be increased, simply by overvolting 36v to 48v not only increases hub/bike speed if required but also increases the watts output by 33% at the wheel so gives a nice bonus/increase in torque for inclines esp when used with 5 levels of pas.

Someone who understands electricity at last!!!

Well put.....

regards

Andy

Yes I totally agree that current doesn't need to be increased, simply by overvolting 36v to 48v not only increases hub/bike speed if required but also increases the watts output by 33% at the wheel so gives a nice bonus/increase in torque for inclines esp when used with 5 levels of pas.