500w vs 750w motor differences?

[leehop71]

Greetings Fellow Riders,

I have a Denago City 1 e-bike. It has done me well but I am thinking the commuter might be better with the added 8th gear as I often run to the stores and in the higher PAS I would probably do less ghost pedaling.

However, I’m wondering, since I’m considering selling my Denago and moving up I’m wondering if going to a 750w motor might be wise?

Is there a significant difference between the 750 and the 500?

TIA

 

[addertooth]

I can't speak for mid-drive systems, but geared hub 500 Watt motors tend to be about 20ish MPH bikes. 750 Watt motors tend to make the bikes run around 28ish MPH.

 

[Hoggdoc]

Greetings Fellow Riders,

I have a Denago City 1 e-bike. It has done me well but I am thinking the commuter might be better with the added 8th gear as I often run to the stores and in the higher PAS I would probably do less ghost pedaling.

However, I’m wondering, since I’m considering selling my Denago and moving up I’m wondering if going to a 750w motor might be wise?

Is there a significant difference between the 750 and the 500?

TIA

First you have to clarify for the you're looking at 750 W peak power or nominal power. If it's 750 W nominal power, those motors will typically peak over 1000 W. The biggest advantage of the bigger more powerful motor is hill climbing power. You have to change the voltage of your system to really get higher top speeds.

 

[m@Robertson]

The difference between a 500w motor and a 750w motor is truly only the motor's ability to take sustained current (i.e. punishment). The wattage rating is used in consumer marketing but functionally, its pretty well meaningless on its own.

You have to realize for starters that Volts x Amps = Watts. So if you have a 48v system (48v packs are actually 54.6v when fully charged) and a very common mediocre 20 amp controller, your motor 'wattage will be a peak of 54.6v x 20a = 1092w. No matter what your motor is rated for, it is almost certainly outputting well over what it is rated for on the casing.

This is oversimplifying, but in more commonly understood terms, battery voltage is horsepower, and controller amperage is torque. So if you want to go faster, you want to use a higher voltage system. If on the other hand your eventual top speed is not what you are after, and instead you want more oomph off the line, then more controller amps will increase motor torque, and thus acceleration up, for example, a hill.

Just changing the motor and leaving the battery and controller alone likely will do absolutely nothing to your performance. Leaving the motor alone and changing the controller will increase motor acceleration, assuming a more powerful controller is sub'd in. Going to a higher voltage battery will increase your top speed, assuming that increased voltage doesn't fry your controller (48v and 52v systems tend to be interchangeable).

There's more to this than just comparing motor wattages. Sorry no easy answers unless you get lucky.

 

[Chuy]

If you want higher gearing, get a different size cassette/freewheel. How many teeth on your current smallest cog? Freewheel or cassette? You can also get a larger chainwheel but those can be more difficult to replace and will cost more.

 

[Numnuts]

The difference between a 500w motor and a 750w motor is truly only the motor's ability to take sustained current (i.e. punishment). The wattage rating is used in consumer marketing but functionally, its pretty well meaningless on its own.

You have to realize for starters that Volts x Amps = Watts. So if you have a 48v system (48v packs are actually 54.6v when fully charged) and a very common mediocre 20 amp controller, your motor 'wattage will be a peak of 54.6v x 20a = 1092w. No matter what your motor is rated for, it is almost certainly outputting well over what it is rated for on the casing.

This is oversimplifying, but in more commonly understood terms, battery voltage is horsepower, and controller amperage is torque. So if you want to go faster, you want to use a higher voltage system. If on the other hand your eventual top speed is not what you are after, and instead you want more oomph off the line, then more controller amps will increase motor torque, and thus acceleration up, for example, a hill.

Just changing the motor and leaving the battery and controller alone likely will do absolutely nothing to your performance. Leaving the motor alone and changing the controller will increase motor acceleration, assuming a more powerful controller is sub'd in. Going to a higher voltage battery will increase your top speed, assuming that increased voltage doesn't fry your controller (48v and 52v systems tend to be interchangeable).

There's more to this than just comparing motor wattages. Sorry no easy answers unless you get lucky.

On my new Electric Bike Company model "R" bike, it is a 48v with a 26 amp controller and a 500w motor. To say it is weak as hell going up any kind of grade is an under statement, In gear 1, PAS 4 or 5, I'm pedaling as hard as I can and at my age of 76 its unbearable. Both my previous Ebike's had absolutely no problem going up the same grade just using the thumb throttle. It's ok on level ground but I really expected more performance than this POS. Money is not an issue for me, I just want to go home without having a heart attack. Please advise.

 

[m@Robertson]

On my new Electric Bike Company model "R" bike, it is a 48v with a 26 amp controller and a 500w motor. To say it is weak as hell going up any kind of grade is an under statement, In gear 1, PAS 4 or 5, I'm pedaling as hard as I can and at my age of 76 its unbearable. Both my previous Ebike's had absolutely no problem going up the same grade just using the thumb throttle. It's ok on level ground but I really expected more performance than this POS. Money is not an issue for me, I just want to go home without having a heart attack. Please advise.

What you are describing is common with hub motor ebikes. Worth noting: almost daily I see people in Rad Rovers, Rad Wagons, Rad Runners and Lectric Xpeditions (3 guesses what the common bikes are in this town, especially for the bike rental places we have all over the place) walking their bikes up some of the steeper hills here because of what I am about to describe.

The reason for the problem you are having is straightforward: A hub motor powers the wheel thru its axle. So by definition, it cannot use the gears to help you get up a hill. A hub motor is thus single-speed. Try riding up a hill on a normal bike using the same gear you ride comfortably in on flat land and you will immediately see the problem the hub motor faces. Its life sucks trying to struggle up a hill, just like yours does if you don't use the bike's gears. And so hub-motor-ebike owners think its normal to have to bust their ass and hump the bike up a steep hill along with a motor that can't do the job on its own.

By the way, this is the time when someone with a hub motor bike starts typing furiously that their bike can do hills. Its testimony to the fact that the meaning of 'steep' is subjective, different people weigh different amounts, there are differing ideas about what constitutes acceptable performance etc. etc.

You can overcome this inherent hole in a hub motor's capability with high power and a super hub motor. We're talking the 3kw range here, and lots of volts in the system. At least 60v and a 35a controller. The sort of power you don't usually find on storebought ebikes. Worth noting: A 48v system with a 26a controller is, at peak, pumping out 54.6v x 26a = 1420w. So on paper at least you can figure even with your battery run down you are pumping out around 1000w (going up the hill should keep that controller at its peak amperage of 26) and it still sucks mightily.

The alternative that is pretty much guaranteed to always work vs. any hill is a mid drive-powered ebike. It works like you do and powers the bike thru the chain. So you can shift down like you would on any normal bike with no motor and the bike scoots up the hill like its not there. It just goes slower because, of course, you downshifted to a lower gear. Just yesterday I tested out staying in one gear to go all the way up from sea level (literally. I live on the coast) to my house at the top of a hill and on this higher-than-normal gear that I tried, I got up - pedaling - at 15-16 mph. On flat land I would have gone 18-22 and used less power. But I was testing to see if I could stay in a not-too-low gear and just more or less roar up the hill. BTW I am a heart attack survivor myself and I have to have a bike that either lets me work hard up a hill (dial down pedal assist) or shoulders the burden almost entirely by itself like this test I ran yesterday.

 

[m@Robertson]

On my new Electric Bike Company model "R" bike,

Dang I just looked that bike up and even its chain is single speed. On a hub bike, the chain is only used by the rider. So you are doubly screwed trying to go up a hill because you can't downshift to try and lend your gear-assisted muscles to help the motor. If you have hills, a bike like this is worst-case.

 

[Numnuts]

The model R that I have has the optional 7 speed Shimano. But no torque. While in Shimano speed 1 or 2, PAS 3,4 or even 5, no power to go up even the smallest grade. Terrible. But you don't know this until after they build your bike for you and it's delivered. Although I will say it's pretty to look at. And my thanks to you for your info and opinions. N/N

 

[m@Robertson]

The model R that I have has the optional 7 speed Shimano. But no torque.

Unfortunately, only you can deliver torque thru the chain on any hub motor bike. So that 7s only helps you and your muscles to supplement the motor. But still its crucial to have or you are completely SOL.

While in Shimano speed 1 or 2, PAS 3,4 or even 5, no power to go up even the smallest grade. Terrible.

Regardless of the fact the Shimano does nothing for the motor, that lack of ability sounds a little extreme, considering you were told you have a 26a controller on a 48v system. As noted above, doing the math on that comes out to more than 1400w of output on a full battery, which even on the 26" wheel option should give you more power than you are describing.

I would talk to the manufacturer and ask them if there is a setting that can be changed.

KT brand controllers atre used as oem equipment on many bikes. They have the ability to correlate wheel rotation (speed) and cadence to let them ramp power up as you hit grades, and then ramp it back down again as you crest your summit and the slope decreases. They are very common but there is no indication of what it is that bike has. If you have a KT display on your bike, that would mean you have access to the settings inside and can make some significant changes to the power output of the motor.

I can't tell from the pics on that bike's web site what the display is. Regardless, you should first contact the manufacturer.

 

[Rifeg2]

Greetings Fellow Riders,

I have a Denago City 1 e-bike. It has done me well but I am thinking the commuter might be better with the added 8th gear as I often run to the stores and in the higher PAS I would probably do less ghost pedaling.

However, I’m wondering, since I’m considering selling my Denago and moving up I’m wondering if going to a 750w motor might be wise?

Is there a significant difference between the 750 and the 500?

TIA

If I’m reading this correctly, moving up to a bike with a 750w nominal motor and proper controller will most definitely give you more speed and torque.. I have a bandit x trail pro with a 750w front hub and 1000w rear hub. A single 500w assists to about 20mph at full charge, single 750w around 28mph assist, 1000w about 32mph.. dual motor bikes doesn’t necessarily mean faster it just means you can get to speed much faster and hold top speed on minor inclines without having to pedal (using throttle). But draw backs of dual motor usually means dual batteries and a much heavier bike. My bike weighs 107lbs, I weigh 260lbs and carry a 20lb bag.. my top speed at full charge on flat ground is 37.5mph and can go about 15miles until im down to 80% on both batteries.. then my top speed pulls down to 35.7. In short, yes a 750w hub will increase your top speed by about 8mph.

 

[m@Robertson]

In short, yes a 750w hub will increase your top speed by about 8mph.

Unfortunately, generally speaking that is not true.

The wattage rating of the motor is about how much sustained current input can take. Has nothing to do with output. Sure you can gain a little in efficiency (maybe) by stepping up to a higher rated version of the same motor, but thats not going to yield much. What makes a motor go 'round faster is higher voltage from the battery system. As in, going from 36v to 48v to 52v and so on. More volts translates to more motor rpms. More amps on the controller translates to more power to get that motor up from a start to those rpms.

A very, very general comparison in automotive terms that are much more broadly understood is voltage = horsepower, and amps = torque.

Using a 26" Sondors fat bike with a Bafang 350w-rated G060 motor as an example, with 36v it will go about 20 mph. Step it up to 48v and that otherwise identical bike is up to about 25 mph. 52v puts that same bike/motor at about 28 but at that point you're also using an upgraded controller. Upgrade the controller from 20a to 25a on 48v and thats a bridge too far... the 350 will cook itself on long hills. We saw lots of these on the Sondors user group forum I am a moderator at, back in its heyday, when the brand used off-the-shelf KT controllers. It was common to swap controllers and plug in a 52v pack in place of the 36v it came with. My own G060.350 ran perfectly on flat land with a 20a controller and a 52v pack.

You don't have to have two batteries on 2wd btw, but its part of a custom build. If you build a pack with a badass BMS capable of high output, you can split the power leads to both motors. This one has a single 30ah 30Q-cell pack in the triangle that is nowhere near as heavy as a dual-battery solution.

BMS is capable of 90a continuous output. Between that and the fact that Samsung 30Q cells can be flogged hard, you get a pack much smaller that can take a beating from two motors. Dual 35a controllers so 58.8v x 35a =2058w x 2 = 4116w. I would pedal it on full PAS on both wheels at around a 34 mph cruise. If I don't set the power to slow-roll on, I'll have front wheel burnouts and stress the crap out of the frame regardless of the torque arms in play.

 

[Smaug]

@leehop71 What are you thinking now, 5 weeks later?

In case you're still on the fence, I'll give you my thoughts.

On a city-type bike with at least 26" wheels running on smooth tread, going from a 500 W to 750 W motor is going to mostly show a difference in torque. As m@ points out, nominal motor voltage is just a starting point, as that is the power that can be sustained by the motor. These days, you'll see more manufacturers referring to peak watts, since legislation refers only to "watts". They can rate and mark the motor as 750 W motor, which is the max allowed by law, but sneakily advertise and specify something like: "2,000 peak watts"

If you spend a lot of time going above 20 mph and find your current 500 W struggling or do a lot of climbing, the 750 W motor might be a good thing.

Going from 7 to 8 speed and 500 W to 750 W in a city bike is not worth buying a new bike on its own. If you also add something else, like belt drive Pinion or internal hub gears, it might be.

My Aventon Level.2 is a similar style to your bike, also with a 500 W motor. I find it will go 25 mph pretty easily, but works harder to get to 28. I also find that it really chews through the battery quickly when going over 20 mph, so I don't do it that often. If you do find yourself wanting to go over 25 mph pretty often, the 750 W would help.

 

[Smaug]

What you are describing is common with hub motor ebikes. Worth noting: almost daily I see people in Rad Rovers, Rad Wagons, Rad Runners and Lectric Xpeditions (3 guesses what the common bikes are in this town, especially for the bike rental places we have all over the place) walking their bikes up some of the steeper hills here because of what I am about to describe. <snip>

You assume that they are pushing because the hub motor isn't torquey enough. It could be that the battery is dead or dying. Or they left it in top gear, so they are essentially not helping at all. Flippin' muggles.

Unfortunately, generally speaking that is not true.

The wattage rating of the motor is about how much sustained current input can take. Has nothing to do with output.

Wattage (or power) is only partly about current, since it's defined as Volts x Amps. I'm not sure why you feel that it refers to input power instead of output power. Lacking any documentation, I would assume the opposite, as it's motor OUTPUT that people are interested in. It may need 1,000 W in to produce 750 W out, depending on the motor's efficiency.

What makes a motor go 'round faster is higher voltage from the battery system. As in, going from 36v to 48v to 52v and so on. More volts translates to more motor rpms.

False, at least for brushless motors. The controller and its electronic commutation is what determines RPM. You can have a 24 V brushless motor that spins faster than a 52 V brushless motor if the motor controller is set up that way.

More amps on the controller translates to more power to get that motor up from a start to those rpms.

That's true, assuming the same voltage, since power = volts x amps. (Watt's Law)

A very, very general comparison in automotive terms that are much more broadly understood is voltage = horsepower, and amps = torque.

This is a horrible analogy; you can't really equate these units. You should equate electrical power, in Watts to mechanical power, in Watts, Horsepower or Joules.

What matters is that power denotes how much actual work can be done. If you have a controller that provides 10 V @ 1 A, its theoretical max output is 10 W. If you have a controller that provides 1 V @ 10 A, its max output is also 10 W, due to Watt's Law. Either situation, if the motor and controller are set up properly will yield the same mechanical power available to the motor. That said, higher current requires bigger conductors, and copper is expensive and heavy, so higher voltage is the preferred way. (though higher voltage requires better electrical insulation and/or bigger spacings)

Looking back at your analogy, if we see an eBike rated 52 V, we are initially impressed. The educated among us will next look at the ampacity of the controller, since 52 V means nothing if it's choked back by a controller's lower current limit. Then, we look and try to deduce whether the battery pack can supply that amount of current.

Put another way: We can have a 52 V system with a 19.2 A current rating on the controller, and that is 1,000 W available to the motor.
Or, we can have a 48 V system with a 20.8 A current rating on the controller. Here too, 1,000 W is available to the motor. One rating means nothing without the others. In either of those cases, if the battery pack can only supply 15 A, then the 52 V system will be more powerful, since 52 V x 15 A = 780 W and 48 V x 15 A = 720 W.

You're not doing any one any favors by over-simplifying. That's what politicians and executive managers do that really messes things up.

We do appreciate what you're trying to do though.

 

[m@Robertson]

You assume that they are pushing because the hub motor isn't torquey enough. It could be that the battery is dead or dying. Or they left it in top gear, so they are essentially not helping at all. Flippin' muggles.

Well, I live in a small town, and I ride a bike that is something of an attention magnet. So I have a lot of conversations with riders at waypoints along the beach trail, intersections and so on. A common refrain is that the bike is gutless. Not so long ago I was going up a residential street hill that had zero traffic. There was a rider who tried to stay on the bike by tacking up the hill. Zigzagging so he didn't take it straight up. He was standing on the pedals and giving it everything he had, while I more or less gently pedaled up. Since I was only going about 5 mph, we had a moment to exchange pleasantries. Me encouraging continued effort and him saying what a POS his bike was.

Its an old story.

Wattage (or power) is only partly about current, since it's defined as Volts x Amps.

You are referring to the measurement of watts, not their actual effect/the net result in the world, which is what I am talking about.

I'm not sure why you feel that it refers to input power instead of output power. Lacking any documentation, I would assume the opposite, as it's motor OUTPUT that people are interested in. It may need 1,000 W in to produce 750 W out, depending on the motor's efficiency.

Again I am limiting my comments to what they mean to someone riding a bike. To the real-world results. A 750w motor versus a 500 - functionally - is doing exactly as I said: Its capable of absorbing more punishment (amps of current) thanks to its beefier construction (more copper blah blah blah). I gave a real world example with the Bafang G060 series of motors, where a 350w motor can go just as fast as a 750w unit. Just not for as long, for the reasons stated. 350w, 500w, 750w... they all reach the same top[ speed if given the same battery/controller input (actually that includes the 250w as well but adding it is kind of cheating because the 250 and the 350 are genuinely identical on the inside).

False, at least for brushless motors. The controller and its electronic commutation is what determines RPM. You can have a 24 V brushless motor that spins faster than a 52 V brushless motor if the motor controller is set up that way.

Ask around DIY circles where people actually build the bikes, and know what makes them go, or go faster (in particular the guys doing big direct drive hub motors). You're only going to get one answer insofar as how to make an ebike motor go faster. More volts. @Hoggdoc made the same comment on volts = speed in this thread. On paper / in the lab, I'm sure there's merit to all manner of details large and small. But in actual practice building bikes that go fast, or making them go faster, there's only one way this cat gets skinned.

This is a horrible analogy; you can't really equate these units. You should equate electrical power, in Watts to mechanical power, in Watts, Horsepower or Joules.

Disagree completely. First of all, note my 'very very general' caveat. Adding this to the sentence comes from long experience with the electrical engineers out there who barf all over their bibs when they see that, and start quoting sacred texts.

More horsepower makes the wheels turn faster on a car. You get more top speed when you have more horsepower. Ergo Horsepower = volts. Torque on an ICE is also known as 'grunt' and it governs rate of acceleration. More engine torque = faster acceleration. Hence: amps = torque. Its not meant. You don't say this to an acolyte who is studying the principles of electricity. You do it to give someone a quick understanding that is sufficient for them to get a quick general understanding of the issue at hand, so they can make a decision ... and then forget about it and move on.

(However I am guilty of being a petrol-head and assuming the reader knows what horsepower and torque do on a car).

If someone wants to know how it all really works, they can go study the subject, at which point they won't need a simple analogy.

You're not doing any one any favors by over-simplifying. That's what politicians and executive managers do that really messes things up.

I disagree both in your conclusion and I don't think your follow-on is relevant to a discussion of ebikes. We aren't trying to balance the budget or cure cancer here. The subject is "how do I make my bike go faster?" With that perspective established, simpler is better.

We do appreciate what you're trying to do though.

Same

 

[HoppyUK]

For a proper understanding of what’s going on with torque and watts and amps and stuff, I’m not sure how helpful many of the common generalisations are.

Torque, per se, doesn’t mean that much by itself because it’s only one component of ‘power’ and power is the stuff that actually pushes you forward. Horse-power, bhp, PS, watts, kW, etc - they’re all common measures of usable power. Acceleration and top speed are both dictated by the power available at any given time and that is always true.

Many moons ago, I learned a very simple formula: POWER = TORQUE x TIME. ‘Time’ is basically how fast the motor is spinning, expressed as revs or rpm (revolutions per minute). This also explains how gearing works, because gearing changes rpm for a given road speed and so multiplies the amount of power available.

Here’s an example of how misleading torque figures alone can be very misleading. The Honda Fireblade is an exceedingly fast motorbike, capable of ripping your arms off on its way to almost 200mph. Yet the motor only produces 112Nm of torque and that’s less than many e-bikes. The difference is that e-bike hub motors only spin slowly, typically topping out at 200-300rpm. On the other hand, the Fireblade revs to 14,500rpm where it delivers 214hp (about 160,000w).

 

[Rifeg2]

Unfortunately, generally speaking that is not true.

The wattage rating of the motor is about how much sustained current input can take. Has nothing to do with output. Sure you can gain a little in efficiency (maybe) by stepping up to a higher rated version of the same motor, but thats not going to yield much. What makes a motor go 'round faster is higher voltage from the battery system. As in, going from 36v to 48v to 52v and so on. More volts translates to more motor rpms. More amps on the controller translates to more power to get that motor up from a start to those rpms.

A very, very general comparison in automotive terms that are much more broadly understood is voltage = horsepower, and amps = torque.

Using a 26" Sondors fat bike with a Bafang 350w-rated G060 motor as an example, with 36v it will go about 20 mph. Step it up to 48v and that otherwise identical bike is up to about 25 mph. 52v puts that same bike/motor at about 28 but at that point you're also using an upgraded controller. Upgrade the controller from 20a to 25a on 48v and thats a bridge too far... the 350 will cook itself on long hills. We saw lots of these on the Sondors user group forum I am a moderator at, back in its heyday, when the brand used off-the-shelf KT controllers. It was common to swap controllers and plug in a 52v pack in place of the 36v it came with. My own G060.350 ran perfectly on flat land with a 20a controller and a 52v pack.

You don't have to have two batteries on 2wd btw, but its part of a custom build. If you build a pack with a badass BMS capable of high output, you can split the power leads to both motors. This one has a single 30ah 30Q-cell pack in the triangle that is nowhere near as heavy as a dual-battery solution.

View attachment 16622

BMS is capable of 90a continuous output. Between that and the fact that Samsung 30Q cells can be flogged hard, you get a pack much smaller that can take a beating from two motors. Dual 35a controllers so 58.8v x 35a =2058w x 2 = 4116w. I would pedal it on full PAS on both wheels at around a 34 mph cruise. If I don't set the power to slow-roll on, I'll have front wheel burnouts and stress the crap out of the frame regardless of the torque arms in play.

You’re right.. I guess I spoke way to generally.. I was assuming the OP would be buying a quality 750 with matching controller capable of maximum performance as well as tailoring for optimal battery life as well as appropriate battery capacity. Basically buying either a whole new bike or buying a complete upgrade kit.)

 

[m@Robertson]

You’re right.. I guess I spoke way to generally.. I was assuming the OP would be buying a quality 750 with matching controller capable of maximum performance as well as tailoring for optimal battery life as well as appropriate battery capacity. Basically buying either a whole new bike or buying a complete upgrade kit.)

Yeah on that orange bike I pictured, it uses the Bafang 750w motor with the (no longer produced) bigfoot core. The 750's use the big version of the motor plug, which is meant for higher voltage and current - The smaller plug on the 250, 350 and 500w motors is supposedly only for lighter duty.

So the 750 has to use a controller with the big plug. And the big-plug controllers all offer higher amps. The ones I use are 35a, which are maybe the lowest output available from KT, so just to get the 750 to work you step up to more torque by default. Most of the small-plug versions peak out at 22a.

Also the smaller motors can fry when you step up to 52v. The Sondors user group found this out the hard way with 500w G060 motors that had stepped up to 25a controllers. On long hills, the motors could burn out on 52v systems, but not on 48v with the same controller.