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Need help with mid-drive electrical connection (controller/display)

richj8990

100 W
Joined
Jan 21, 2020
Messages
277
48V450W mid drive motor kit with LCD&PAS for ebike 3speed brushless gear motor | eBay

$470 USD including shipping, and I'm about to throw it in the trash. 30 day returns on E-Bay but no way I'm attempting to ship back 17 lbs of junk to mainland China. I told myself that this may not work; it's so close, yet so far away. Just a good controller away from working...but I need to 'guess' on the correct controller!

Controller that came with the kit (if you can even call it a kit) is Brainpower XLD 48V 450W 23A limiting. Problem is that the connection to the battery is horrible. Display that came with it does not work at all, and zero identifying marks on it. Throttle light lit up very weakly (lights for low / medium / high battery level indicator on throttle), throttle itself did not work; now even the light doesn't turn on.

Tried a few other controllers, nothing. I've read the 46.3-48.0V coming from my battery with a voltmeter, and the battery is also used regularly on a different hub drive e-bike, so I know for sure this is an electrical issue. The battery is fine. It's finding the correct display and throttle for matching up to ANY 48V controller that actually has a good electrical connection to the battery.



There is only one controller/display that turns on: KT 36V/48V controller 12 mosfet

E-bike Controller KT Controller 6/9/12/18 Mosfet for 36/48V 250-1500W Hub Motor | eBay

The display is the familiar LCD-3. However, this one is a lame duck and is on it's last breath from the other ebike. As in it will not read any battery power and the throttle doesn't work, etc. And even if I buy a new controller/display that is the same as above, there is no guarantee anything will work with the motor, including the throttle. That's the real issue: how much more money should I throw at this before giving up.
 
I'm waiting on a new KT controller and display (along with KT PAS and throttle). Will update later. These kits, either side mounted in place of the left rotor, right cassette/freewheel (left = removing rear brake or right = making the bike a singlespeed) and this mid-drive one are all over E-Bay and Amazon by the way. It may look like a joke but people are buying them and one way or another making them work. The side mounted ones are stupid IMO because you can just buy a hub drive instead, but this mid-drive, if I can only get power to it...here is a detailed technical report from an Amazon customer below. My notes in italics.



1. The mounting bracket for the motor will not fit your bike. You need to create your own, or modify the one provided. (this was for the side mounted one)

2. The controller provided is very basic and should not be used with a battery that exceeds 20amps peak (Pick one that has a 15amp nominal discharge rate) :)::FIRE RISK:::)

3. Expect to do some soldering. The connectors between the motor and controller melted on my system and should be changed for safety (Use XT90, or direct solder)

4. Take care installing the sprocket and drive chain. The sprocket must mount to the rear wheel near perfectly with minimal wobble. The chain must have the correct tension, (little to no sag) failure to do so will result in derails which have the potential to bend or break your spokes, or break the chain.

5. Check your brakes and tires frequently. The motor can have some serious pull when set up correctly. (it can work)

This was installed to the rear of a full suspension mountain bike. The battery i used is a 36v, 20Ah, 35 peak amp. My build took a month and a half to get working reliably. This kit can get my setup to beyond 40KM/H on motor alone, or 60KM/H with some pedaling.


My experience with it:

My first problem was the fact that the seller didn't ship the kit with a chain. I had to buy my own because the seller refused to send one and directed me to buy the chain they should have shipped. (minus one star for that little stunt)

My second problem was the bracket. I bought the kit knowing it wouldn't fit, as the bike this was put on had rear suspension I solved this using a couple of simpsons ties (roofing joist brackets), and by bending the existing bracket with a clamp, hammer, and blowtorch. (the mid-drive brackets fit similar to a CYC motor; they were off around 5mm and I simply bought longer 110mm side screws and put a couple washers on one side in each screw outlet between the motor and bracket). That got the chainline to within 1-2mm at least by eyeing it.)

The third problem i had was maintaining correct chain tension. As with my awkward mount, my motor sits in such a way that i cannot add or remove a link from my chain, or move the motor/mount. Solving this entailed building a tensioner using a skateboard bearing, a right angle simpsons tie, and a jockey wheel from an old rear shifter. (I don't think the chainline/tension will be quite as critical up front near the seat tube to the crankset.)

Fourth. The electrical issues. After several rides, The connection between the controller and motor began to melt and nearly shorted. This was rectified by replacing the controller (similar model, a mistake) and adding fuses between both the battery and controller, and the motor and controller. a couple blows later and the controller was fitted with a heat sink and a 40 amp fuse between motor and controller. (I have a real deal KT controller & display coming with 1200W / 35A capacity, if that doesn't work it must be a bad motor; funny thing is you can buy the motors as cheap as $80 online. I think the main issue with some of these kits are that they are labelled 24V when the motor is rated up to 750-1000W and 139 Nm torque. As this reviewer said, don't cheap out on the controller, get something that can handle more than 10-15 amps. As mentioned previously, a KT controller/display CAN work but it's just a question of if and how the motor responds to that setup.)

Overall, It's both a basic and difficult kit. My use case and specs are beyond what is recommended, however i can understand a lot of people being frustrated with it. Advertising this as "plug and play" is a big mistake on part of the manufacturer and seller. However if you can make it work. The motor is overspeced and can possibly accept a higher voltage battery. The controller however is atrocious, dangerous, and the connections are a fire risk. The rest is acceptable enough.

As of two months since completion, My new ebike works well with few issues, I use it daily to get to work and commute. It hits speeds around 35-40KM/h reliably. And has been a huge boon to the weekly grocery runs.

This review will be updated.

UPDATE: 4 months of use.

After four months, my build still holds up well. However two issues have cropped up, and through use, some more has been learned.

The first is that the replacement controller I purchased for this kit shorted on two of it's four mosfets. (both controllers used within my set up are nearly identical.) Now i am slated for my third controller for the build. Don't make the mistake of cheaping out on this part. I will be buying one that is overspecced, has better heat sinking, and will be placing breakers and fuses between other critical components.

The second issue is the motor. While it still runs and has burned in nicely with no performance loss, the carbon brushes seem to have underwent a burn in period where they produced a burning rubber/plastic smell when run in high torque/low speed situations (hills) This problem was not present for low torque high speed situations, and has mostly been rectified by modifying my usage patterns and assistance levels to the motor. (Not the first time I've heard of a mid-drive doing this when climbing something steep).

Long story short, listen to your motor; the louder and higher pitched it sounds, the better, as it seems to like high RPMs and low amperage. The controller as well, is likely to favor the same electrical profile to a increased degree. The supplied sprocket and freewheel are not appropriate for hilly terrain.

If you plan on using your motor for assisting you up hills, you may want to purchase a smaller freewheel or larger wheel sprocket. (The stock side-mounted sprocket looks like 36T; mid-drive one is 44T, with 104BCD you can get up to 52T so that should not be an issue on the mid-drive kit. I think the freewheel on the motor is 16t, so the reduction on the mid-drive is 2.75/1; with 52T it would be 3.25/1. Hopefully 52T later can get the torque around 60-70 Nm at 500W uphill).
 
The motor has brushes but you’re running a controller for a brushless motor… you have strange smells and talk of “burning in the motor”.

So is the motor brushed or brushless? Might help with the burning out controller thing.
 
The motor has brushes but you’re running a controller for a brushless motor… you have strange smells and talk of “burning in the motor”.

So is the motor brushed or brushless? Might help with the burning out controller thing.

I copied and pasted a review of a different customer's experience. I believe it's brushless.
Just got the KT LCD-5 in the mail, will try again tonight if I have time. Supposedly these motors 'do' work; it may just be that I got a bad one.

It's only $80 to try again if this particular motor is bad. After I already have the motor mounts and crankset. Can't use a standard 68/73 crank axle regardless of the type because you need a special extended one on the drive side to clear the motor chain & freewheel. So it's not quite as cheap as it could be.

You know what would be really cool? Someone makes a 1000-2000W direct drive, they compact it so the total width is not more than 100mm, and they put transverse mounting holes on it. And good, standard battery cable and hall/phase sensor wires. That's all I would need to then DIY the mounting to a normal 2x or 3x crankset w/o freewheel anywhere. But all of the generic direct drives I've seen that are more than 200W or so are greater than 100mm wide, so they cannot fit in front of a standard crankset. It should not be that hard for a company to simply make one, really just modify one they already have.
 
New controller / display worked (throttle). I'll try to finish everything up and test ride by Monday.

Seems like the unchained direct drive sprocket sticking out of the motor is rpm limited, guessing it's around 300-400 RPM at full throttle, maybe 500. Think I saw somewhere that it's 470 RPM w/o the chain reduction. We'll see how it rides later. The stock controller that came with the kit was terrible lol. Threw it right in the trash.

Honestly a Bafang BSS02 is pretty much the same price, considering that I had to buy the display / controller / throttle / PAS separately, and that would have been the safer choice if I wanted to put a mid-drive on a thin-tubed aluminum frame. I just don't see many thinner-tubed mountain bike frames now; all of the 27.5 and 29 frames I see are super thick at the down tube, so much so that it's hard to even tell on the trail if someone is riding a normal (acoustic) or e-bike just by the frame. So the Bafangs seem better suited for older frames like 26 inch. If this motor sucks, I'll probably try a CYC Stealth V3 later. If it's good enough, I'll do a little write-up.
 
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