500w vs 750w motor differences?

[LightningP38]

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.

 

[LightningP38]

Good info, fellow MI survivor. I had both my heart attacks while I was on bike rides 12 and 14 years ago. I got a hub motor kit 4 years ago for assistance going up hills when I moved to Scranton. At the time the hub motor seemed the easiest to install, so that is what I went with. Living in Scranton, which has 800 foot hills, as well as lesser hills. I could make it up any of the hills on PAS 1 or 2 and in granny gear at 5 mph, with me doing half the work and the motor doing half the work…a deal we both liked. And that conserved the battery power as well. I also could go up hills in PAS 4 or 5 at 20 or 25 mph…which felt like riding a rocket booster, and I would pedal in a middle gear at a comfortable pace, but would suck a lot of power out of the battery, so I avoid that. I was happy with its hill climbing assistance. I ride a 28 lb recumbent bike.

Then I moved to flat area in New England, so my setup is more suitable to this terrain.

If I had it to do over, I would definitely get a mid drive kit, not just for the gearing efficiency. But to change a flat rear tire is much easier with the original road wheel/tire, as the hub wheel needs a torque lever (1 or 2) to help hold the motor axle in the dropouts. I have 2 because I had the motor pull out once, which means extra bolts to undo, and it takes extra time to fit the slotted axle into the dropouts. 3 bolts on each torque arm x 2 torque arms, is 6 extra bolts to R+R.
And finally, the wheel and spokes are heavy duty which adds stiffness to the ride, which makes the ride harsher over bumps, as I can’t unweight my body from the seat when crossing bumps.

So that is about 4 reasons why I would go with a mid-drive setup.

 

[P5k]

Strictly speaking, there's no such thing as a 500w controller. If you read the label that is typically found on one, it well tell you something like '36/48v' or maybe just '48v'. Then it will have two separate amperage ratings. One for maximum and another for continuous. Typically the 'continuous' will be exactly half that of the maximum.

So, if the controller says its 48v compatible, then Part 1 of the answer is Yes. Part 2 of the answer can be ascertained once you know the peak and continuous values of your battery's BMS. The BMS also has peak and continuous values, but this time you can't count on the continuous being half that of peak. What you want to do is match your battery's continuous amp output to your controller's peak value, and then throw in 5a or 10a of fudge for good measure.

Why do Part 2? If your controller has lets say a 35a peak, but your battery's BMS has a 35a peak, you might be thinking that you have a match. But you don't, because it is very possible the controller could want 35a of peak power for a couple of seconds longer than the battery wants to deliver at peak... and as a result the BMS pops for safety, and will not re-enable itself until you plug into a charger to reset it (which means you are riding home unpowered). So to get around this, you instead match the controller's peak to the battery's continuous value. And you throw in that extra fudge just in case. Why the fudge? If your battery manufacturer and your controller manufacturer calibrated their products exactly the same, exactly true to what the label claims, life would be beautiful and no fudge necessary. But you can't count on that.

I learned that the hard way once when I had a 5w fudge factor. I decided to stress test the system by hammering the awd bike's dual throttles up a long but gentle hill just steep enough to make my bike work some. The BMS popped, the bike shut down and I had to grunt it out to get home. From then on, I build in 10a of fudge and I have never had this happen again.

Thanks a lot. Really opened my eyes.

 

[P5k]

@m@Robertson

Hi, sorry to bother you again.

I looked at the made in China controllers online and they only had one rating for Current. Can I assume they mean peak current?

Also for a 48v 17A controller , what is the top speed like on a flat terrain ?

 

[m@Robertson]

I looked at the made in China controllers online and they only had one rating for Current. Can I assume they mean peak current?

Don't lump all controllers together as just 'Made in China' There's all manner of crap you should ignore, and then there are KT controllers which are actually very high quality. And priced higher to go with that quality increase.

You should see two ratings an a respectable controller. Here lookit this picture. This is an old-ish KT 25a controller (top) and a new-model 30a controller. Click on the pic to zoom in.

Top right of each label it reads "Maximum current". thats your peak. Lower right it says "rated current". Thats the continuous value. Typically the continuous rating is half that of the peak on all controllers. If your controller just says "rated current" then its telling you the continuous value, and staying silent on the peak which is a controller I would not be fond of spending money on..

Also for a 48v 17A controller , what is the top speed like on a flat terrain ?

Speed is not dictated by amps. Its dictated by volts. As an easy comparison, if you are familiar with automobile power ratings, more torque means faster acceleration. More horsepower means more top speed. As the old saying goes: "Horsepower sells cars but torque wins races". Knowing that background, you can equate controller amps to torque and battery voltage to horsepower. So your 48v controller peaks at 54.6v, and you can expect ANY 48v system with a 26" fat wheel to peak at around 24-25 mph (assuming no weird crap like sticky brakes and whatnot). If its a skinny 26" tire you will get less top speed, and if its a 20" wheel you will get less still. These are general rules. You won't know for sure what your bike delivers until you run the thing. Also, a 52v pack will deliver 1-2 mph more top speed on that fat 26" wheel (speed is not why you go to 52v) and a 36v pack will lose you about 2-3 vs. a 48v system.

Your body weight introduces another big variable into the system, with Bluto riding the bike, speed suffers. If its Olive Oyl she goes faster.

 

[P5k]

Don't lump all controllers together as just 'Made in China' There's all manner of crap you should ignore, and then there are KT controllers which are actually very high quality. And priced higher to go with that quality increase.

You should see two ratings an a respectable controller. Here lookit this picture. This is an old-ish KT 25a controller (top) and a new-model 30a controller. Click on the pic to zoom in.

View attachment 18236

Top right of each label it reads "Maximum current". thats your peak. Lower right it says "rated current". Thats the continuous value. Typically the continuous rating is half that of the peak on all controllers. If your controller just says "rated current" then its telling you the continuous value, and staying silent on the peak which is a controller I would not be fond of spending money on..


Speed is not dictated by amps. Its dictated by volts. As an easy comparison, if you are familiar with automobile power ratings, more torque means faster acceleration. More horsepower means more top speed. As the old saying goes: Horsepower sells cars but torque wins races". Knowing that background, you can equate controller amps to torque and battery voltage to horsepower. So your 48v controller peaks at 54.6v, and you can expect ANY 48v system with a 26" fat wheel to peak at around 24-25 mph (assuming no weird crap like sticky brakes and whatnot). If its a skinny 26" tire you will get less top speed, and if its a 20" wheel you will get less still. These are general rules. You won't know for sure what your bike delivers until you run the thing. Also, a 52v pack will deliver 1-2 mph more top speed on that fat 26" wheel (speed is not why you go to 52v) and a 36v pack will lose you about 2-3 vs. a 48v system.

Your body weight introduces another big variable into the system, with Bluto riding the bike, speed suffers. If its Olive Oyl she goes faster.

Hi, thanks for taking the time to reply. Your comments are full of gold and I always learn alot from them. Its great that I stumbled upon this forum.

Just a little back story, i do delivery in Singapore, the bike i'm using now has a 48V 250W motor, 2.125 inch wide 20 inch wheels, and a 15AH battery, a kids bike compared to what you have in your country. Our laws dictate that the bike must have a speed limit of 25km/h. Its almost impossible for users like me here to buy a quality controller, and the ones that I found all come with chinese labels and one reading. Suppose I want to 'tinker' with my bike i would have to visit bike shops that offer such services 'under the table'. Majority of those mechanics only learn through trial and error, and either because of our tiny market or deliberate obfuscation by bike shops, theres a huge information vacuum here, In fact, not even the sales guy I talked to know whats the peak and continuous current of his controller and it seems like he never heard of it. so needless to say the shops are making good money on this.

So back to my current bike, whenever i do my runs i would look at my display. On flat terrain it peaks at around 370W , i believe thats the speed limiter coming into play. On steep terrain it maxes out at 600W while going at less than 10km/h.

so from what i gather from your comments, am i right to say that it is the continuous current that is being adjusted by the controller when i step up the speed so meaning that its using around 8A max on flat terrain and 13A on steep climbs? Is it safe to assume that my 15AH battery is also capable of 15A continuous current?

I'm thinking of 'upgrading' my controller to 15A so as to go up above the 25km/h speed limit while leaving the hub motor unchanged for the time being. Do you think thats a good idea?

Thanks in advance.

 

[m@Robertson]

On flat terrain it peaks at around 370W , i believe thats the speed limiter coming into play. On steep terrain it maxes out at 600W while going at less than 10km/h.

Given your restricted speed situation, thats a maybe. You can expect a controller on a hub motor to pump out MUCH less power when it is at speed. Its just the nature of how hub motors work. My own hubs have nothing like this restriction and they can put out less power than that while traveling faster (although I am pedaling and helping forward progress).

If your 48v battery is at a 58% charge (which is exactly 48.0v) then your controller is outputting around 7.6a. So you could either have a low-continuous (rated) output controller, or you may be right its the speed limiter that is holding output back. There's no easy way to tell unless you find a way to lift the speed limiter and watch to see if output climbs. Anyway my point is there are two potential causes to what it is you are seeing.

so from what i gather from your comments, am i right to say that it is the continuous current that is being adjusted by the controller when i step up the speed so meaning that its using around 8A max on flat terrain and 13A on steep climbs?

Maybe. See above. You'll know which one it is if you find a way to lift the speed limiter and your display starts showing higher power and higher speed. And also, top speed is generally governed by the display, NOT the controller. So if you can get into your display settings, and it has a speed limit setting, you can raise it on the display and the controller will obey the new limit.

Thinking on it some more, there is also another 'typical' cause of speed limitation: Motor rpm limits. I use a 20" wheel with a Bafang G020 with 10T winding. It turns out that motor, built into that smaller, slower wheel, has a top speed around 21-22 mph with no limiter in place. I can find this out by increasing my speed and watching the motor output taper off to just about nothing as speed increases. I'm using a 30a controller and a 52v battery so there is no lack of power on offer. But the motor is at its limit of output and internally tells itself to back off and stop asking for power. It'll output a minimum value of between 15 and 35w but that just keeps it spinning freely.

Is it safe to assume that my 15AH battery is also capable of 15A continuous current?

If its a 48v battery, 30a continuous is the commonly seen 'low' limit. But who knows what yours is? Nobody unless its written on the casing. For all I know there's a local law that limits output at the BMS level, although I doubt it. Still, manufacturers will cut every corner they can get away with so maybe thats one that is cut in your local area.

I'm thinking of 'upgrading' my controller to 15A so as to go up above the 25km/h speed limit while leaving the hub motor unchanged for the time being. Do you think thats a good idea?

I think this will increase your acceleration and do nothing for your top speed, since top speed is governed by the display. You are going to have to change the display too, and its very possible you will have to also change other bits on the bike so the connections and the parts themselves will work with the new controller. Throttle, PAS sensor, brake cutoffs.