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KT36SVPR-LCD Controller

Posted: Jan 24 2020 11:34am
by Magnus

I'am new here on Endless Sphere.
It seems to be a lot of people who tinker a lot.

I have a problem that i hope someone can help me with.

A Bafang 250 W hubmotor with a KT36SVPR-LCD controller. The problem i have is that sometimes the motor wont work.
When i pedal, the motor helps me for a while, and suddenly it dont. After a couple of seconds it begins to work again.

When i got it, it worked fine. It was this summer.

And it can work for a couple of 100 meters. And then the same.

It seems to work ok in the beginning of the ride. And even when testing indoors it seems to work ok.

I have tried with a different controller of same type, but the problem remains.
Earlier i had lead acid batteries, but today i changed to Lithium, but as always, the problem remains.

I am beginning to think if it is the controller that doesn't like cold. But it's not even freezing here.

And if it is the PAS that is the problem, it should work bad all the time i think.

Does anyone have an idea what the problem could be?

Re: KT36SVPR-LCD Controller

Posted: Jan 28 2020 11:25am
by Swell6
I have the same issue - I've just bought a similar setup with the same KT36SVPR-LCD controller - 250W 36V. I'm not sure of the motor manufacturer. I'm also using lead acid batteries, but have ordered a Li ion battery from Aliexpress which is a fraction of the weight.
It works fine when lifting the wheel off the ground when static, but as soon as I'm out on the road with some torque on the motor it cuts in and out. Pedal assist actually works best, but it is intermittent. The thumb throttle only works at all if I very slowly increase the power, and then cuts out as soon as it reaches any sort of speed.
Is this a controller issue, battery issue or motor issue? Any help would be very much appreciated!

Re: KT36SVPR-LCD Controller

Posted: Feb 14 2020 4:11pm
by egul
Magnus - I had a similar problem with the KT pedal sensor. This sensor has a centre disk which is enclosed within a case which has the hall sensor in it and the wire coming out of this outer case.

It turned out that the bottom bracket of the bicycle wasn't perfectly centred. This meant that as the crank turned around completely the inner part of the sensor would jam and stop turning. As it thought that pedalling had stopped the motor would turn for a couple of seconds, it would jam so stop, then it would restart etc. Filing the outer case to enlarge it helped.

Do you have a throttle? Does it work with the throttle? If it works OK with the throttle this might suggest the pedal sensor.

If you don't have the throttle but have an LCD display you can activate the pedal assist mode by holding the down button for a couple of seconds. If the motor turns OK with this it might also suggest the pedal sensor.

Swell6 - I don't suppose the speed cutoff is set low on yours is it? If it is OK can you measure the battery voltage with a voltmeter connected across the terminals? If the battery voltage drops when it is under load it might indicate either a problem with the battery, or that the battery physical size/capacity is too small to provide the required amount of current.

I don't know if this is the correct answer to either of you, but as nobody else has replied I thought I would in case it helps!

Re: KT36SVPR-LCD Controller

Posted: Feb 29 2020 7:00am
by hemo
The 6 fet KT's suffer from thermal cut outs, warm weather riding especially when cooling is limited. Slow riding up inclines in high power mode is one cause asking for to much current. One needs to find ways of adding cooling for the mosfets extra heat sink or better still the addition of mini computer fans to aid cooling via a separate 5v or 12v sources. Once the controller cuts out it will cool and then will operate again until heat again causes cut out, the fets in time will suffer and eventually short out permanently so either better grade fets need fitting or opt for a 9 or 12 fet controller upgrade.