Using a KT LCD Controller With Throttle Only


100 W
Jan 21, 2020
A lot of people have complained that much of the Bafang stuff has basically an on/off throttle. As in you push the throttle and it shoots up to max watts. This can be a real problem offroad climbing on dirt with both a hub or mid-drive, because the driven tire will spin out and you could even crash. I don't know about the BBSxx-specific displays like the C850, but for the KT LCD 3/5, I think I finally figured it out.

1. Reduce starting current. This is parameter C5. I used to simply put C5 at 10 and forget about it. But for throttle-only, you can't do that. You set the max current to translate over to watts for what you need as a 'safe' maximum power level, as in the motor doesn't overheat, then estimate the other PAS levels below for power. I have 48V and a 22A max controller, so 1056 max watts on paper. C5 at 5 brings that down by 1/1.33 or down to around 800W max (see below). C6 is 1/1.25 or around 850W max. C6 has noticeably more power and that's the number I stuck with for the C5 parameter.

2. C14 at 3 (strong). Remember you are limiting the current so you want everything else to be full strength relatively speaking, after the watts are maxed out significantly lower than what the controller can take on paper.

3. P3 is set to 0 (PAS-based). Imitation torque is not a good idea if the power surge from the throttle is so high that it spins out the driven wheel.

4. C4 is set to 4 (PAS-based). Remember to be consistent about P3 and C4 because they are linked; one must help the other.

5. P5 set at 0 (real-time voltage and not some smart supposed battery saver voltage). Again everything else needs to be robust because you are limiting your max current = limiting max watts.

The LCD5 doesn't read watts but I'm guessing with 48V and current limited to 22 amps / 1.25 = 17.6 amps (x48V) = 845 max watts, then:
PAS 1 100-150W
PAS 2 200-250W
PAS 3 300-350W
PAS 4 400-450W
PAS 5 800-845W

This means that for throttle only and no PAS, it's very similar to pedaling with PAS but you are simply 'maxing' out the throttle at whatever thumb or twist travel that may be and getting the watts above. PAS 4 is good for climbing offroad. No more power wheelies up singletrack, because the limited current is limiting the watts. The modulation is much more controllable. Remember at a tiny bit of throttle, the numbers above will be much less; the above numbers are for max throttle position or wherever it maxes out the watts in its travel by thumb or twist.

You can also fine-tune the watts on your PAS 1-4 output (both for real PAS and PAS number-based throttle output) by playing around with C5:
1 n/a
2 n/a
3 max current /2.00
4 max current /1.50
5 max current /1.33
6 max current /1.25
7 max current /1.20
8 max current /1.15
9 max current /1.10
10 max current / 1.00

Parameter C5 is the key to this whole thing. A parameter I previously ignored 100% for years. Go figure.
Yup. C5 is maximum current, not starting current, but setting a lower maximum current reduces proportionally the output relative to throttle position. In other words, it's easier when the throttle controls 0W to 500W then if it's controlling 0W-5000W. For offroad, you could also just unplug the PAS sensor and set P3=0, and use the assist level buttons to adjust maximum current for the throttle, unless you find 100W-150W is something you would use in practice.
Setting P5 to 0 was not the right move. The battery died on the way back to the trailhead. It read 1/4 left for only a few miles and then blank, then full, then pretty much dead. I'll set it to 15 after charging. Luckily most of the climbs back were done by the time it died. When P5 is set to at least 6 with a 48V battery, the 1/4 left display means it has at least 5-10 miles left. But not when P5 = 0.

I'm going to try P3 = 1 imitation torque one more time; P3 = 0 is pretty annoying when PAS 2 and 3 can't go more than about 6 mph anywhere. PAS 4 can go maybe 8-9 mph, so P3 = 0 means you have to ride in PAS 5 most of the time.

Other than those two issues, the bike did pretty good. I climbed a super steep 25-30% fire road and was 1/2 way up the first 200 feet, lost traction in both DH tires. If it was more hardpacked I would have made it!

The Kenda Hellkat is a pretty good tire, rolls well, good grip but my next in the back will be the Vittoria Mota. That thing looks like it will really grip up hills --- looks excellent for a rear e-bike tire.

I'm going to buy 6 different throttles, all returnable from Amazon. Like someone else said on a different site, they have had a lot of different ones in the past, some worked better than others. When they are $20 it's a crapshoot. I've had exactly one work well but I'm not sure if it was the throttle itself or the (discontinued) controller. Will buy a 2nd of that throttle: L-Faster 48V Wuxing E-Bike Throttle