250w rated motor and 1000w controller.

Hi everyone it's my first thread here and also my first e-bike build.

First of all, i have already checked this rating stuff and that motors can take even 5 times more than their rated wattage for a short period of time before frying them.

My question is different, i already bought a 1000w controrller and thought to my self if there is a way that i could limit the controller's output to a lower wattage? And another thing is this 3 speed switch, will it lower the wattage eventually?

The motor is mxus xf08, and the controller is some random chinese one with 1000w rated nominal wattage, 48v and amp limit of 41.

I weigh 170lb and where i live is mostly plain, and the bike is a full-suspension haro x3.

I do plan on driving responsibly with this controller (if you would't force me to throw it away and buy some cute 500w controller :lol: ) but would like to get some sort of limitation.

Thank you guys sorry for my english it's not my native language

The catch with small geared hubmotors (assuming that's what youv'e got) is that while they might take more power for a very very limited time, they may not be able to handle the torque the higher current creates. It can break the clutch and/or gears inside.

If you use the higher power repeatedly over a relatively short period of time, the motor can overheat and damage the gears and/or windings and/or hall sensors, etc.



Assuming the controller is not programmable (you would have to already have the software, come with it, and cable; otherwise very unlikely), you could open it up and remove one or more of the shunts inside, if it has more than one.

The shunts look like thick solid bare wires at one end of the board, like this:


If there are two, and you remove one, it cuts the current limit in half.

If there are three, and you remove two, it cuts the current to one third of what it was.

Etc. If there is only one, then you can shave some of the shunt off, to make it smaller diameter in the middle straight part, and it will reduce the current by some amount, but you won't know by how much until you test it, using a wattmeter, with the complete system on your bike under the conditions you will use it under. If it's not low enough you can keep removing more and retesting until it's as low as you'd like, but if you remove too much it's difficult to "fix" (other than by adding solder instead); it's a time-consuming process to get where you want it.

Thanks for the quick reply!

Before i buy a new, lower wattage controller, can you tell me what options do i have in playing with the lcd attached to the controller? tweaking and stuff..

And will keeping my max throttle use to let's say maximum of 50% (and even less on hills) will keep me in the safe zone theortically?

i have already checked this rating stuff and that motors can take even 5 times more than their rated wattage for a short period of time before frying them.

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Make that 1 1/2 to 2 times the motor's rating and you would be a lot closer to reality.

...the controller is some random chinese one with 1000w rated nominal wattage, 48v and amp limit of 41.

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Nothing is random with the Chinese stuff
Actually that would be around a 2000 Watt controller (V X A = W )
Way too big for a smaller geared mini ( I had a MXUS XF07 and I assume the the XF08 is about the same). With that motor, a Hard-hitting Square wave Infineon of 22 Amps on either 48 or 52 Volts would start to hammer the Nylon gears.
Controllers are about the least expensive and easiest to change component in the E-system, so rather than start with a mis-matched system, I suggest you ditch the one you have and get something in the 20 Amp range.
I use these soft-starting square wave controllers w/ a led display which is only $40 shipped to the States. They are rated at 17 Amps, but can be easily shunt modd'ed to 20 to 22 Amps.

https://www.ebay.com/itm/36V-48V-350W-9MOSFET-ebike-Electric-Bicycle-Brushless-Motor-Controller-with-LED/222373438918?ssPageName=STRK%3AMEBIDX%3AIT&var=521242448634&_trksid=p2057872.m2749.l2649

Of course the are many styles and features when it comes to controllers and they should be a focus of interest when building an Ebike.
You may want to study up on them, especially the popular Sine wave models like the KT>

Mati5300 said:

Before i buy a new, lower wattage controller, can you tell me what options do i have in playing with the lcd attached to the controller? tweaking and stuff.

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You'd have to check the manual to know what options it has. There are lots of different controller/display sets, and they are all different. Since your is a "random controller" then there is absolutely nothing to even give a starting point on where you might look for info if you don't already have the manual.

Not all of them even have settings that can be changed.

And will keeping my max throttle use to let's say maximum of 50% (and even less on hills) will keep me in the safe zone theortically?

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No. Various controllers use different throttle methods, some of which directly control the current to the motor (so would let you limit throttle to do what you want) but most don't do that--they just use the throttle to control "speed" (PWM of voltage), so the controller could still put out high current to the motor even at a lower throttle setting under high load conditions.

Since we know nothing at all about your controller (other than it's "random 1000w") then there's no way to know what it will do until you test it with a wattmeter, and hopefully temperature monitoring inside your hubmotors.

Reducing the throttle usage will *help* keep from damaging the motor, but how much it will help is unknown; you have to experiment to determine that.

reducing the throttle demand does reduce the power...but it's variable depending on load and conditions, so you would need a wattmeter on your handlebars so you can watch that while you manually limit throttle to whatever keeps the motor happy.

Having a temperature monitor inside the motor would help you with that, so you know if you are pushing it too hard because it stays hot or gets even hotter, rather than cooling down between bursts of high power usage.


Reducing the current limit of the controller to match the motor's actual capability is how you would stay in the "safe zone".

Either changing the settings (programming) or modifying the shunts are the only two "easy" ways to accomplish that with any certainty with the hardware you already have.


You could also use the Cycle Analyst (v2 is all you need, but v3 would work too) from http://ebikes.ca and have it limit your throttle based on the current or power limit you set in it. But it's a lot more expensive than a lower power controller would be. (or modifying the one you have now)

Thanks you really enriched my knowledge

I think i'll just buy a nice 500w controller and drive carefully

all you should need to do, is use speed 2, on the three speed switch. You can use the full power occasionally, but keep the time you use it relatively short, like less than 20 min, and avoid the temptation to use it on really long, really steep hills.

On the other hand, lower power controllers are really cheap. So your plan is good, just not required if you run on level 2 power.

dogman dan said:

all you should need to do, is use speed 2, on the three speed switch. You can use the full power occasionally, but keep the time you use it relatively short, like less than 20 min, and avoid the temptation to use it on really long, really steep hills.

On the other hand, lower power controllers are really cheap. So your plan is good, just not required if you run on level 2 power.

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Or hardwire for level 2 to remove the temptation of level 3 all together.
(I think this may be the same as removing the switch, since level 2 is the “off” of the on-off-on switch?)

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