How fast can my 250W chinese motor go?

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brams87   100 µW

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How fast can my 250W chinese motor go?

Post by brams87 » Nov 23 2019 6:44pm

Hey guys, new here but hope to get some useful advice, thanks in advance!

I recently bought this bike: https://www.aliexpress.com/item/4000121 ... 4c4dS94h5p
I was hoping that I could unlock the speed limit with the LCD, but unfortunately I could not control anything, there were no buttons. The seller told me that there's a combination of pressing brakes to remove the limit, but this doesn't work either.

So that turned me into trying to find other ways.

I just bought this new controller, hoping that I could use this to get more speed: https://www.aliexpress.com/item/3292097 ... 4c4d7M7g5G

However my question is: My motor is 250 Watt. What is the maximum speed I should get from this motor? I want to go as fast as possible :) My battery is 48V 8Ah. The bike with me will be 20 kg + I'm 50 kg. I wanna ride 20 km to my work and back.

Hope anyone can give the answer. Thanks!

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Re: How fast can my 250W chinese motor go?

Post by Compoundbike » Nov 23 2019 7:02pm

about 15mph maybe 16-17mph with backwind and farting.. 8)

That bike is good for vacation or something if you need a foldable bike, i wouldnt get that for commuting.

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Re: How fast can my 250W chinese motor go?

Post by HK12K » Nov 23 2019 7:26pm

Probably about the same speed you can pedal it at now, albeit with a bit less effort. If there are any hills involved then it's pretty much all on you. You also may need to recharge at work with only 8ah on tap.

John in CR   100 GW

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Re: How fast can my 250W chinese motor go?

Post by John in CR » Nov 23 2019 9:02pm

The 25kph max speed listed seems reasonable. 20km on the 8ah battery doesn't seem reasonable though unless conditions are perfect...flat and smooth with dedicated cycling infrastructure, which is the only way I rid a little folder like that. That is perfect conditions and lots of pedal assist for that kind of commute.

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Re: How fast can my 250W chinese motor go?

Post by docw009 » Nov 23 2019 11:38pm

Well, 25 km/hr seems like there's a speed limiter.

Our 20" folding bikes do about 18-19 mph on throttle only, but that's 36V and an unrestricted 20A controller. On 48V, they will do 22-23 mph Folding bikes aren't intended to go much faster than 18 mph anyway. The gearing has you looking like a circus bear if you're using pedal assist, and the small wheels ride hard on uneven pavement.

We ride ours about 14 mph, and a 300 WH pack is good for 30 miles. Your pack is roughly 400 WH.

Unless there is a speed limiter, speed is determined by voltage, motor winding, wheel size. You already got the voltage jump over ours.

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Nov 24 2019 2:52am

Thanks guys. For sure there is a speed limiter because if I turn on the power on the bike and I pedal as hard as I can, I can't get over 25 km/h, it's like the motor holds me back so that it can never go over 25. If I turn off the power of the bike and pedal, I can reach over 25 by pedaling alone.

I've been researching a lot about those Chinese folding ebikes and many of them can reach 40 km/h when the speed limit is unlocked in the controller. Youtube shows a lot of video's about it. For example here: https://www.youtube.com/watch?v=w5_n4eO7LpQ

So I bought a new controller/LCD hoping to ride the bike without speed limit. But could it possibly be that the speed limit is built in the motor itself? Because its so weird that the bike brakes itself when I pedal as fast as I can but can't get over 25 km/h. Or is the speed limit always in the controller?

And I'm wondering if there's no speed limit, how long am I able to ride on maximum speed without overheating the motor.

I have biked with this bike 45 km on a single charge. It has a range of about 50.

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Re: How fast can my 250W chinese motor go?

Post by TheBeastie » Nov 24 2019 6:43am

The speed limit is always set via the controller.
If you change over the controller with an LCD display then you should be good to overclock it.
Most LCD displays show you the power of the bike being used in watts, I would say you will have no problem riding constantly at 350watts unless its a really hot day, but I am not really sure.

The problem might be range with speed, the range drops off considerably when you go faster.
You can use this simulator to work out how fast and range you can go for your size battery and watts you will draw from your battery.
https://www.ebikes.ca/tools/simulator.html
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Re: How fast can my 250W chinese motor go?

Post by Voltron » Nov 24 2019 12:42pm

On flat ground, with an unlocked 72v 250watt controller (not that such a thing exists.. This is just hypothetical) you could go plenty fast.. It would just take forever to accelerate, and the speed would drop off like crazy on even tiny hills. It doesn't take much power for steady load speed until you get up into the 30s where air drag starts to really hit.

But in realish terms, now that you know you want a faster better commuter, maybe sell that one you have to somebody unless you really really love progressive upgrading.
Because once you get it to go faster, then you realise you can't pedal fast enough to keep up, so you get taller gears. Then you're jamming long enough to melt the controller wires. Then you beef those up, then notice you can't stop fast enough, so you upgrade the brakes. Then you go double jamming... and melt the motor.
That's how mine went anyway 😂

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Re: How fast can my 250W chinese motor go?

Post by 999zip999 » Nov 24 2019 2:04pm

I think the limit of the is with emf and that is controlled by how it's round as 4turn or 6turn ect.
22mph should be your top speed.

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Re: How fast can my 250W chinese motor go?

Post by 999zip999 » Nov 24 2019 2:06pm

Fast is a 72v 80amp setup for a bike 3,000 watt motor running at 7,000 watts

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Re: How fast can my 250W chinese motor go?

Post by MadRhino » Nov 25 2019 1:25am

999zip999 wrote:
Nov 24 2019 2:06pm
Fast is a 72v 80amp setup for a bike 3,000 watt motor running at 7,000 watts
Fast is different for everyone. For me, fast is 24s 300A right now. Yet I am conscious that, at astronomical level, I am moving a few 1000 miles per second in the universe, when parked. :twisted:
Make it fool-proof, and I will make a better fool.
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Re: How fast can my 250W chinese motor go?

Post by dogman dan » Nov 25 2019 7:21am

To clarify some on the above posts. First, you should see some improvement with the new controller, if it has higher amps than the old one.

Speed is limited several ways. One is the motor, motors have different turn windings, where a 12 turn motor is slow, and an 8 turn quite fast,,, potentially. So the slow motor will reach a max rpm for a given voltage, no matter how many amps the controller is. This is the back EMF limit, in a way the motor begins be unable to go faster than that max rpm. This is why some spoke of 72v. Higher voltage,, higher rpm limit.

But you should stick to 48v, 45 kph is quite possible with 48v. With your old controller, there may quite well be a 15 kph limiter built in. Your new controller might have same,, or not. Some controllers have a three speed switch, or other limiters that can be set to lower the power of the controller. Some can be changed by the user, some not. Ready made e bikes can easily be 15 or 20 kph limited, to match the law in the market they are sold in.

On to the other limiting factors. Weight can be one, but not in this case.

Wattage is another. In general, regardless of having a fast winding or even high voltage, if wattage is low enough speed is limited. 400w to 600w gets you around 20 mph ( 32 kph) cruising on relatively flat ground. (600 into wind, or up very slight hills) Watts is volts x amps. So with 48v you are capable of decent watts. About 12-15 watts is still a pretty loow power controller, but able to get you the 32 kph. This is plenty for a commute, and your small motor can stand 800 w or so.

I cant see what the wattage of your new controller is, but if its a 15, or 20 amps controller, this should get you going as fast as you should push that tiny motor.

The catch 22 could still be your battery. 8 ah is pretty small, so to pull 800w from it for example, is a pretty hard pull on it. cruising at 400w, say 25 kph, should be fine. But if your battery is weak, which cheaper ones always are, then it will sag in voltage under load. Sag is where you put on throttle, and voltage drops, but springs back when you let off the power. As you ride, the battery voltage gets lower as it discharges too, but this is not sag. So you will always get slower at the end of the ride, even when sag is minimal.

But combining both, your 48v may drop to 42v when you put on the throttle at the start of the ride. So if volts lower, so does watts. 15 amps x 42v is 630 watts, so should still be capable of 30 kph, if the motor is not too slow wound.

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Nov 28 2019 6:53am

Great! This is very very useful information, thanks a lot!
When I receive my new controller from China I will report the results!
Thanks again guys!

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Re: How fast can my 250W chinese motor go?

Post by positiv » Nov 29 2019 7:09am

with my 500w bafang I can get 23 mph. But this is a stock, no tunning or boosting was made. But I've heard that people used to boost it somehow. It requires a more powerful controller and more voltage in the battery. Actually you can boost your motor as well.

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Nov 30 2019 8:00am

I read somewhere on a website that it may be possible to add a front motor wheel to my bike. So I would have 250 watts on the rear and another one in front so I can get double power. Or is this not possible? I have no idea :) Still looking how to safely get more speed..

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Re: How fast can my 250W chinese motor go?

Post by docw009 » Nov 30 2019 11:37am

brams87 wrote:
Nov 30 2019 8:00am
I read somewhere on a website that it may be possible to add a front motor wheel to my bike. So I would have 250 watts on the rear and another one in front so I can get double power. Or is this not possible? I have no idea :) Still looking how to safely get more speed..
Your 8AH pack cannot supply enough current for two motors at top speed. Probably OK for 20km/hr, but then your bicycle's front suspension fork is high risk for breakage with a front motor. In conclusion, a bad idea for that bicycle.

Your new controller, if you bought the 48V 350W model, should allow 30-35 km/hr, and whatever range you get now will likely drop by 1/3 to 1/2 if you ride at that speed.

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Dec 01 2019 5:19am

Ok, thanks, that was actually the answer I was looking for (How fast can my 250W chinese motor go?).
If you are right and it will be 30-35 km/h then that's fine for me.
When I receive the controller I'll report back :)

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Dec 01 2019 5:22am

Oh, one more question: I bought the 48v 250 Watt controller. Not 350. Since I thought I had to buy the 250 because my motor is 250.
Should I have bought the 350 watt controller?

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Re: How fast can my 250W chinese motor go?

Post by docw009 » Dec 01 2019 12:27pm

brams87 wrote:
Dec 01 2019 5:22am
Should I have bought the 350 watt controller?
I would have done so, if looking for more performance, but at least you get rid of the 25kph speed restriction.

By the way, have you examined the wiring on the existing controller. Not all controller designs do it, but many controllers that don't have LCD displays have a speed restriction enabled by a pair of wires ending in a single pin connector.

The controller you just ordered does not have one, as the speed restrictor is in the display.

Here is one on a controller that does have that circuit. Just because it resembles this does not mean it is a speed restrictor. It could also be a self-study circuiy like in the controller you just bought, or it could be for enabling regen braking on more sophisticated controllers. Anyway, on this ebike, it is a speed restrictor. Connecting the pair raises the top speed.
R4240004.jpg
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brams87   100 µW

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Re: How fast can my 250W chinese motor go?

Post by brams87 » Dec 01 2019 7:20pm

Thanks, yeah I read about those wires, I tried disconnecting / connecting all cables that were not connected to anything related to the bike, but nothing removed the speed limit.

I'm still curious to know though, how it's possible that it seems my motor is braking the speed when I'm pedaling as hard as I can with power turned on. When I turn off power I can easily reach 30 km/h by pedaling alone, but when I turn on power, I cannot get above 25, the motor just holds the speed down (which is extremely frustrating, seems like someone is pulling at the back while you're trying to bike).

It's somehow hard for me to believe that's the controller's work, because how can the controller put a "break" on the wheel?
Could it not be that the motor has a hard-wired RPM limit? So that no matter what, it won't turn faster than a given RPM equal to 25 km/h? What is the mechanics behind this "breaking" of the speed, since I CAN reach 30 km/h without power on.

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Re: How fast can my 250W chinese motor go?

Post by docw009 » Dec 01 2019 8:22pm

It sounds almost like you have a direct drive motor with a controller that applies regenerative braking when the motor is not running. Does the bike slow down by itself when you quit pedaling or let up on throttle?

Lift the rear wheel with the power off, and spin it forward and backward. Does it spin the same speed in either direction? A direct drive motor will do that. A geared motor will spin freely in the forward direction because the gears free-wheel. In the reverse direction, it will barely spin at all because the gears are engaged. Because there is a clutch, a geared motor cannot do regenerative braking.

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Re: How fast can my 250W chinese motor go?

Post by E-HP » Dec 01 2019 9:51pm

brams87 wrote:
Dec 01 2019 7:20pm
It's somehow hard for me to believe that's the controller's work, because how can the controller put a "break" on the wheel?
RPM/Speed throttle?
viewtopic.php?t=78882

My controller will brake when the throttle voltage is above 0.8V, but if I let off fully (0V) it will coast without braking.

EDIT: Maybe your clutch is locked up.

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Re: How fast can my 250W chinese motor go?

Post by d8veh » Dec 02 2019 11:52am

I've never read so much disinformation in a single thread. What's going on in this forum? It's been a while since I visited, and things seem to have taken a massive turn downhill. You can' start hating me now if you want. I don't care. I'm only saying it as I see it.

Before you can say anything about that motor, you need to find out it's KV (RPM per volt) or it's max speed with the battery charged, which is dead simple. You need a cycle computer or something similar to measure the actual speed of the wheel. You can buy one for about $4 on Ebay.

Charge up the battery to full, then lift the wheel off the ground and spin it up to maximum, either with the throttle or by turning the pedals in bottom gear. That will give you the motor's maximum assistance speed.

If you think that the controller might be limiting the speed, run down the battery to at least half-way, then repeat the test. If the speed is the same as with a full battery, the controller is limiting the speed. If it's significantly lower in the second test, the motor is limiting the speed.

The speed on the road will be about 75% of the no-load speed because current ramps down to zero at max RPM. Obviously actual speed depends on things like wind, hills weight, etc and how much current the controller allows.

It takes about 250w of output power to reach 15 mph for an average person on an average bike riding along a flat road with no wind. At a system efficiency of around 70% at that speed, it would take around 357W from the battery or 7.5 amps from a 48v battery.

Without knowing the motor's actual maximum no-load speed, it's not possible to say how that applies to your bike..

With an appropriate voltage and enough current, those motors are fairly comfortable up to about 22 mph cruising speed for average working conditions. They can be pushed to around 30 mph for a short race without modification. Bear in mind that some controllers would have trouble commutating at that speed because of the smaller wheel size. Wheel speed would be 523 rpm, and with a typical 5:1 reduction ration, that would be 2613 motor RPM.
Last edited by d8veh on Dec 03 2019 4:35am, edited 1 time in total.

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Re: How fast can my 250W chinese motor go?

Post by d8veh » Dec 02 2019 12:12pm

brams87 wrote:
Dec 01 2019 7:20pm
Thanks, yeah I read about those wires, I tried disconnecting / connecting all cables that were not connected to anything related to the bike, but nothing removed the speed limit.

I'm still curious to know though, how it's possible that it seems my motor is braking the speed when I'm pedaling as hard as I can with power turned on. When I turn off power I can easily reach 30 km/h by pedaling alone, but when I turn on power, I cannot get above 25, the motor just holds the speed down (which is extremely frustrating, seems like someone is pulling at the back while you're trying to bike).

It's somehow hard for me to believe that's the controller's work, because how can the controller put a "break" on the wheel?
Could it not be that the motor has a hard-wired RPM limit? So that no matter what, it won't turn faster than a given RPM equal to 25 km/h? What is the mechanics behind this "breaking" of the speed, since I CAN reach 30 km/h without power on.
That's a good question. You're not the only one who has experienced that problem. I can guess what causes it, but I can't confirm my theory because I've never had a motor that exhibits the problem.

With the controller switched on, the motor will spin whenever you pedal. If you pedal above the motor's maximum speed or freewheel down a hill, the clutch should disengage. I think that it disengages OK when the motor's spinning slowly or not at all, like when you stop pedalling to freewheel to a stop, but when you're pedalling fast, the motor will max out at its max RPM or cut-off speed. I think that there must be some centrifugal force when the clutch is spinning at that speed that prevents the rollers from disengaging or locks them in. You might be able to test that theory by disconnecting the pedal sensor and using the throttle instead. When you let go of the throttle, the motor should slow down and disengage. Try it at different speeds to see if there is a speed above which it remains locked in.

Did you get the version with the cast wheels or the spoked ones? They have different motors. I was thinking of the spoked wheel version when I wrote my previous post.

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Re: How fast can my 250W chinese motor go?

Post by positiv » Jan 23 2020 10:03am

anyone knows what to do when I'm turning off the controller the clutch not able to disengage?

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