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First ebike build, cheap Chinese front wheel!

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First ebike build, cheap Chinese front wheel!

Old 04-25-19, 06:44 AM
  #1  
murgenslardar
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First ebike build, cheap Chinese front wheel!

Hello esteemed e-bike experts and enthusiasts!

I have just more or less finished putting together my first ebike. My wife takes the train to and from work every day, and there is a steep and long hill when her train arrives going to her workplace and also one when she returns. I sought to make this trip a bit easier for her with an ebike so she can pedal as usual when going downhill (although with the degree of decline pedaling is mostly an added hazard), but get a little help on the way when trying to climb these inclines.

I used a bike that i got for free from helping a friend with some work, and purchased a 48v 1000w front wheel kit from either wish or aliexpress, at this time i can't really remember which. I then purchased a frame mounted battery and put all of it together. It wont let me link pictures until i have a few posts, so those will have to wait for a little while!

Since the bike had probably not been in use for some time, and as i have not used a bike for quite a few years myself i did have some trouble with adjusting the brakes, gears and such. But with some help from youtube i eventually managed to get everything the way it's supposed to be (i think ).

Now to the issues!

First of all, i'm having problems with the battery turning off as soon as i use the throttle ever so slightly as soon as there is a load and me having to use the button on the battery to restart it. If i lift the tyre from the ground and throttles it spins just fine, but if i sit down on it, even when pedaling up to a fair speed, even slowly turning the throttle just a litte bit shuts of the battery. I have read about other people having this problem, but have not really found a conclusive reason to why it happens. I have tried measuring the amperage when it happens, but with the delay on a clamp-meter it just gets to about ~8A before shutting down.

My battery is rated at
48V Li-Ion
10,4 Ah
50A Peak current
30A Continuous current
Cells: 2500mAh, 18650


How do i accurately measure the amperages with a faster reaction time? Ampere-meter somewhere on the vcc line? I'm assuming it's the BMS shutting down for some reason, but i have a hard time believing that with just a slight twist of the throttle while already up to speed from pedaling the motor could draw 2400w peak, or even above 1440w for any sort of extended time.

The second thing i can't figure out is how to replace the throttle with a pedal sensor instead. Since my wife is using it, and it is illegal in Sweden to use a throttle on an e-bike i would like to replace it with pedal assist instead, but i'm having trouble figuring out how i would connect one. The controller i'm using is the one that came with the kit, and it only has the vcc/gnd, motor phases, brake shutoff line, hall sensor and throttle connections.

I did open up the controller and found that it has a bunch of additional unused solder points, so i'm wondering if there is a possibility to connect a pedal sensor, just that the cables has not been added to the controller from factory. Since i cant post pictures it's a bit hard to show, but there is a sticker on the controller that says LY48V1000W.


If you have any suggestions to help solve my problems that would be perfect, and if you have other tips for me to improve my bike it would be dearly appreciated!
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Old 04-25-19, 09:00 PM
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pierce
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those generic chinese controllers, all bets are off trying to mod them. if the motor kit didn't come with a crank sensor, and the controller doesn't have the 3 pin connector for one, then its not supported. odds are, its not only missing the wires, but any circuit board components it requires.

thsoe inexpensive hub motor kits with a crank sensor, its NOT a torque sensor, its just a 'you are pedaling' sensor, and typically has about a half crank delay, eg, turn the crnak about 1/2 a turn, and then the power comes on. the power just comes on, its not proportional, but you usually have a pushbutton control on the handlebars that lets you set one of 4 power assist (PAS) levels.

when I've had trouble with my wheel motor kit, its almost always been the three heavy gauge wires from the controller to the motor... they used very cheap bullet connectors, and these kept coming loose, and they also get really hot. I am waiting for some blue, yellow, green Andersen PowerPole PP30 connectors to arrive tomorrow, when they get here, I'm rewiring the power wiring (I've already replaced the battery connectors with black and red PP30)
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Old 04-25-19, 09:35 PM
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Sounds, to me, as though your battery may have a problem. Until you have elucidated the cause, I would keep my eye on the battery when you're charging it and do it in a place where you wouldn't mind having a fire (fireplace, outside away from combustibles...).
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Old 04-26-19, 06:23 PM
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The battery should be good for 25a but the BMS is cutting it on safety. How many amps is the controller? Is the computer a single speed or does it have power settings (usually 3 or 5 speeds plus walk speed)? A computer can lower the output, and that should stop it cutting out.

As Pierce says, there should be a 3-pin plug for a PAS sensor - the one for the throttle won't work. If no such provision, then no option.

PAS sensors vary in responsiveness, depending how many magnets they have. Eight are better than five, naturally. Plus the computer may have settings for this - the Risunmotor KT-3 screen i use has loads of settings to tailor everything to how you like it. This includes being able to switch the throttle for use only when the pedals are turning, to comply with the law. And even vary the response on pedal start-up, so you have a soft start or fast start when the pedals start turning...

I suspect your issue is it's going full power, and your controller amps are too much for your battery management - a throttle-only controller is one most likely to be too strong for a 10ah battery. It should have a specification sticker on it, stating it's max amps.

I'd find another controller, with a low amp rating (peak 25a max for a 30a battery) and a PAS output.

Alternatively, use a second battery and wire them inline so you have double the amps at the same voltage. I've done this, with a pair of 15ah batteries supplying over 2,000w via a 45a controller.

Last edited by MikeyMK; 04-26-19 at 06:39 PM.
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Old 04-26-19, 06:41 PM
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the controller that came with my 1000W kit, you press up and down the same time, then cycle through the parameters to P014 by pressing the "M" button, then use up or down to set the current limit. mine came set for 26A but I've reduced it to 16A and am thinking of further reducing it to 12A.
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Old 04-26-19, 11:34 PM
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I wouldn't expect a 10.4 AH pack to be pushing 50A. Excuse me, but sounds like vendor BS. A conservative rating would be 20-25A

Your problem sound like battery unable to supply the peak currents.It's probably sagging in voltage under 40V and a low voltage alarm trips, Pick up onr of them $12 RC wattmeters. They will display max current and min voltage. It's self powered from your bike battery but will lose the data id the battery shuts off, If you power it off an aux 9 volt battery, it will keep these readings and tell you what happened.
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Old 04-30-19, 07:51 AM
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Sorry for being so slow to respond, i have been caught up in a few of my other projects the last week.

Thanks for all the tips, i've gotten a few ideas where to start! First of all i will replace the cables since i suspected it myself and you have told me that it's usually to weak for the currents involved, also i want to replave the connectors with ones i trust. As i am an electrician, that has been the easiest problem to solve!

Now to the controller, i have been looking to replace it with a KT 500w controller instead with a KT-LCD5 display and a pedal sensor that i have checked with the store is compatible with the controller.

Could that work or would the controller not be able to power the motor properly? Or perhaps if there is another way of lowering the power input/output on the motor?
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Old 05-01-19, 08:47 PM
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If you use the KT-3 LCD 5-speed computer with a 35a 48v controller, your motor will be kicking out around 270w in speed one, with a maximum speed of under 20mph.

Your battery should cope with this just fine. Speed 2 will take you to about 350w and 25mph. This will be about the limit for a 10h battery. Speeds 3,4 and 5 will cut the battery safety. But the screen is worth having for all it's features.
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