M2faux

I'm trying to understand the difference between the three different size motors? Is there a difference?

kickstart

It's basically a way to quantify an electric motors rated potential power output.

350W = .46 HP,
500W = .67 HP
750W = 1 HP

M2faux

Volts x Amps = watts.
(( Less power loss ))
That's why I see 15amp controllers on Ebikes with a 52v battery.
52v x 15amps = 780watts (less powerloss thru the solder joints)
That's a lot of power. Watching the video that KingCat just posted was impressive.
My friend rides a Bromptom with a 250w motor. But he just installed a 52v battery and I know he has a 15amp controller. PAS only. He put well over 15,000 miles on his 250w motor. I'm sure he'll get another 15,000 miles easy .

2old

Theoretically, the watt rating of a motor is the amount of power that it can withstand and run indefinitely. Of course, many motors can take much more power for short periods of time and many are grossly underrated. I have a 48V, 1000w system with a 30 amp controller and 52V battery (58.8V hot off the charger). I've never noticed it even getting warm.

M2faux

Nice. Over engineered is the way to go. I'm also hearing different stories now from my friends that ride local. The higher watt rated motors with lower "kV" wind go up hills with less pedaling required but are not as fast on flat terrain.

Robert C

I have a 350W geared front hub motor on my commuter and a 750W Mid drive on another bike. I keep the the 350W set to 5/5 on the controller and th e750W set to 1/5 on its controller. As such, they are generally pulling about the same amount of power, in the range of 100-20W.

Based on this I see that the mid drive, even when set to the lower power level, feels more powerful, as an effect of using the "gears" (it is going through a Nu-Vinci, so there really aren't gears, just a crank, sprocket, and transmission).

Clearly, I could have used a 350W mid drive, for my purposes. As was pointed out, the difference, all other things being equal, ceteris paribus, the 750W motor will have more power available. If you are planing to use it on a utility bike, for things like groceries, passengers, and frequent trailer pulling, then you may want a larger motor. For commuting, a smaller motor may be more appropriate.

M2faux

Thanks for your input Robert C . Can you post a pic of your 750w Ebike?

Robert C

Here it is, loaded for touring:

chas58

oh, so much to say.

If you are regular biker, you can probably put out 200+ watts. I do 200-300 in a steady state, so a 350 watt motor basically doubles my power. Its a lot like riding a tandem with my brother. Its fun, but not OMG!
a 500 watt bike accelerates like I do when I'm sprinting at full power.

for moderate current:
350 watt = 36 volts
500 watt = 48 volts.
750 watt = 48 volts and more current (or less likely, 36 volts and lots of current).

roughly speaking
voltage = speed
current = torque (pulling power).

750 is the legal limit in the US, because that is 1hp - and anything above that is classified as a moped.

FYI - it seems that the steady state draw from a controller is about 2/3 of its rated max current. Thus the 15 amp controller your buddy uses likely draws something like 10 amps at the cruising speed and 15 amps under acceleration (with a proper design, the motor will hit top speed significantly after the controller has hit max current, and is on the downward slope of power output).

chas58

yeah, and any motor will overheat if bogged down - like putting full power through it going up hill at slow speed. So the motor should be rated somewhere where that is less likely to happen. Many motors can be bumped up by 30% power if you don't bog them down - much more than that and something is going to overheat sooner or later...

If you want to know the exact point, you can always go to Motor Simulator - Tools

2old

Good point about bogging down C58; the rule of thumb that I use is don't go slower than 50% of your maximum speed, but I'm conservative.

chas58

good rule of thumb for hub motors!

chas58

I can't remember when I last heard someone use that phrase. Well done!

BBassett

Remember that you can't compare hub motors and center drive motors easily. They simply can't do the same things. Yes, they are both electric motors and comply with Watts Law, but the way the power and torque are applied are vastly different. Hub motors (in my opinion) are for racing around the streets on day rides. Center drive motors will take you anywhere including Up. Most importantly, you can't suspend a hub motor.

Dunbar

Nominal motor rating also doesn't tell you peak system power. What you want to look for is the peak power output of the bike or, as mentioned, the maximum continuous current output of the controller. My Cross Current has a 350W motor but can do 700W continuous with a fully charged battery.

speculant

Does that have a solar panel or is that just a sun cover?

Robert C

Solar panels, I have never plugged it in after putting them on.

M2faux

I like this video.

Namida12

Watts comparison might be a numbers game.

https://ebikes.ca/learn/power-ratings.html