Help! Motor cutting out and speed on screen incorrect

pajtaz

Pedelecer
Nov 8, 2019
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Netherlands
Hello,

I just finished installing my ebike kit. I took the bike out for a test ride today for the first time. Overall everything is ok but I have two problems.

To start, my kit is Q128C 48V 328 rpm rear hub motor, KT36/48SVPR-20A controller, KT LCD3, and 48V 12.8Ah bottle battery with maximum discharge current of 30A. I have only PAS, 12 magnet, right hand side. LCD3 settings are:
Max speed = 45 km/h; Wheel size = 700c;
P1 = 227; P2 = 0; P3 = 1; P4 = 1; P5 = 15;
C1 = 7; C2 = 0; C3 = 0; C4 = 0; C5 = 8; C6 = 3; C7 = 0; C8 = 1; C9 = 0; C10 = n; C11 = 0; C12 = 4; C13 = 0; C14 = 2.

First problem is that speed on LCD3 is a little bit more than half of what is actually is. For example, if I am going 30 km/h, speed on LCD3 is about 17 km/h. I first had P2 = 6 but speed didn't make sense, it was barely going above 3 km/h. Then I changed P2 = 1 with similar results. Then I changed to P2 = 0 and speed is what it is now. It is more realistic but nowhere near accurate.

Second problem is that motor randomly cuts out for a second or less than a second. This happens at any assist level, at any wattage, seemingly at random. I changed battery voltage monitoring to P5 = 0 but I saw no voltage drop that would cause the cut outs. It is quite cold out right now, around 4 deg C so I don't think it is the controller getting warm. Either way it is happening at 150 W or at 250 W or at 450 W at various assist levels. It happened at PAS level 2, 3, 4, and 5. It only happens for a second or less, and could happen several times within 1 minute or it could happen once per minute. I am riding on completely flat ground with occasional bump.

I checked PAS, it seems to be properly registering all magnets when I test it, although maybe PAS cuts out randomly during riding. Currently I do not suspect the PAS.

Maybe the two problems are connected. I was thinking it could be related to speed sensor from motor or hall sensors? If the connection is not good, could this be the reason for random cut outs? Any help is appreciated.
 

pajtaz

Pedelecer
Nov 8, 2019
84
7
Netherlands
I fixed the problem with speed on LCD3 and I think I know what the problem is with motor cutting out.

For speed problem, it was the P1 and P2 settings. One of the posts by Nealh suggested various P1 settings for Q128C. I tried all of them in a random order (why do things sequentially when you can guess) and P1 = 192 combined with P2 = 1 worked for me. It took 10-15 seconds for speed to get displayed but once it did, it was accurate.

As for motor cutting out, I am now convinced it is PAS. I noticed that although cutting out was random, it did happen often when I changed gears to higher gear. Also it did seem to be somewhat linked to an occasional bump on the road. So I moved the sensor closer to the magnet and tightened it. It was already close, about 1 mm but at a slight angle and was not too tightly screwed at the bottom of the frame. I will test it tomorrow. If it is indeed the PAS, it must be solvable. It could also be the magnet since only thing keeping it in place are magnets. If I continue to have problems with cutting out, I will secure it better to the chainring.
 

Nealh

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Aug 7, 2014
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For PAS C1 try the values 5 & 6 as well. The 12 count disc sometimes don't work to well and you are better using an8 or 10 count disc.
C3 try 5 or 8.
For P1 to be near spot on you need to ride with GPS for setting up. Set the lcd to 25km/h and then adjust the P1 value up or down until the speed readout matches as near as a damn the GPS reading. Once you have the P1 set for accuracy at 25km/h you can then ride with what ever speed you set in the lcd knowing it is right.
 

pajtaz

Pedelecer
Nov 8, 2019
84
7
Netherlands
P1 is now perfect. I used your suggestion for 192 which kind of makes sense if there are 16 magnets in Q128C and gear reduction ratio is 12 (16 x 12 = 192). I was on Aikema's site and there Q128 is listed as having 14.2 ratio but in other posts I read that the motor sold by BMS Battery (where I got mine) could have "old" ratios such as 8 or 12. So P1 = 192 makes sense.

As for C1, I tried 5 for a few km and didn't like it, it felt it was cutting out more often. Then I used C1 = 6 for rest of the ride, about 16 km, and although it did cut out, it was less often. I had almost no cut outs as long as I pedaled consistently. I was getting to the point where I could "feel" what was good pedaling and what will not cause cut outs.

C3 is only for which PAS assist level is brought up start up. I set this to 0 to make sure I don't get any sudden movements of the motor. This would have nothing to do with the cut out problem.
 

pajtaz

Pedelecer
Nov 8, 2019
84
7
Netherlands
I reverted back to C1 = 7. I had a few cut outs but it is negligible compared to entire trip.

So for future reference, my P and C LCD3 settings are now:
P1 = 192; P2 = 1; P3 = 1; P4 = 1; P5 = 15;
C1 = 7; C2 = 0; C3 = 0; C4 = 0; C5 = 8; C6 = 3; C7 = 0; C8 = 1; C9 = 0; C10 = n; C11 = 0; C12 = 4; C13 = 0; C14 = 2.

Do you know what C14 does in terms of current? It is now at 2 which is “General” assist. I want to increase motor assist just a little bit more in level 4 (but of course all levels must be increased together). As it is now, using assist percentages for LCD3 you listed in another post, PAS 1 gives about 13% of current (108 W), PAS 2 about 20% (166 W), PAS 3 about 33% (275 W), PAS 4 about 50% (417 W) and PAS 5 about 100% (834 W). This is calculated with my C5 = 8 which limits max current to 20A / 1.15 = 17.4A. I never use level 5 in this setting but I just want a bit extra in level 4.

So will changing C14 to 3 increase the above percentages? If so, do you know how much? Otherwise I will have to adjust C5 to 3 and then use level 5 to get a bit more (it would then be 480 W at level 5).
 

Nealh

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C14 doesn't give any current change, afaict all C14 does is increase PAS signal strength.
 

pajtaz

Pedelecer
Nov 8, 2019
84
7
Netherlands
I tried C14 = 3 today and it increased power consumption of motor in each assist level, which means higher current at each level comparing to other two settings. At each level I was getting more assist because of more current (looking at motor power on display). Those percentages listed above were slightly higher at C14 = 3. Either way, I lowered it to 2 again because more power meant more battery consumption and maybe too much speed at level 4.

What is the sweet spot for this motor again? Do I want to be at the part of curve where I am getting consistent assist or at the part where the power starts tapering off? Is there an efficiency benefit or lifetime benefit? Because at C14 = 3 with my best pedaling I was still getting full power at level 4 and I was just at the point where power would be decreased. At C14 = 2 depending on wind or my fitness the motor was frequently lowering its power output. Any suggestions?

With respect to the motor cut outs, I am now thinking it is the brake sensors. I believe they are very sensitive and are signaling without me touching the brakes. Could be due to wind or vibration. I will test it tonight by disconnecting them. Is there any way to lower their sensitivity?
 

Nealh

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I have never seen this with C14 on my bikes.
The economical sweet spot is above the cut off, if you can maintain it or in lower PAS.
I very rarely use more then PAS 2 unless the terrain is steeper.

The motor is at it's most efficient at about 60-70% of it's ultimate speed
 

pajtaz

Pedelecer
Nov 8, 2019
84
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Netherlands
I've been reading on forums about making sure motor or controller don't overheat. I don't understand how this can happen with my 20A controller with Q128C 48V 328 RPM 500W motor in 700c wheels if at level 4 PAS the maximum current being supplied is around 8.7A (with C5 = 8 max current output is limited to 20/1.15 and PAS 4 is 50% of max current). Motor power is around 415 W until I can pedal hard enough for power to start dropping off slowly to 360-380W. At this power I am going anywhere between 38 and 48 kmh depending on the wind. So am I risking burning anything like this?

As for efficiency, if I was to use level 3 and then pedal such that motor power starts going from max at that level (around 275W) towards let's say 50W, that would be efficient and greatly improve battery life but my top speed would suffer, especially against wind. However, would riding like this not risk overheating my motor or controller, as I read on other posts?

You've been very helpful, thank you very much. I am just trying to hit the right balance between efficiency, battery life, lifetime of motor, controller, and battery, and speed. I did this conversion to shorten my commute time (so I need speed) but I am willing to sacrifice a bit of speed to improve lifetime of parts (battery life less so than motor and controller).
 
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Nealh

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The 328rpm motor is likely to have more issues then a 201 or 260rpm esp in 700c form, for efficiency it needs to run at above 16 mph. It will get warm/hot on hills if it labours at lower speeds.
At 38 -48 km/h little damage will be done as the motor can handle that assist speed.
It has a 500w rating so can continuously run at that without damage so it will also be quite efficient, running it at a lower wattage will be less efficient and may lead to warmer running if speed drops too low.
The worry of controller damage isn't to important as they are cheaper to replace then the battery or hub, you are probably over worrying to much.
 
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pajtaz

Pedelecer
Nov 8, 2019
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Some update on the issue of motor cutting out for anyone who might have similar problem. I disconnected the brake sensors and tested it. Motor was still cutting out in the same frequency as before so it was not the brake sensors. I also rewired many of the connections (put XT60 on battery connections, put MT60 for motor power connections, shortened some cables) so disconnected and reconnected everything. I am still having motor cut outs.

Now I think it might have to do with P1 setting. Next thing I am doing is trying different P1 settings. I was at P1 = 192 but then I switched to 202. I also tested at 204 but still getting cut outs. Since I do not know the actual gear reduction ratio and P1 setting is linked to it, this could be the cause of these occasional cut outs. I will next try 211 and 212 (would equal to gear reduction ratio of 13.2). And if that doesn't work, I'll go again to 227 (equal to ratio of 14.2, as it is on Aikema website for this motor).
 

Nealh

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I had motor issues due to incorrect P1 figure, not complete motor cut out but more of a delayed slow motor pick up. d8veh AKA vfr400 I think also posted along the same line in the thread that was running. I solved the motor pick up by setting the odometer reading to read correctly which gave me a more precise P1 to work with.
You need a GPS to verify the cut off speed is correct on the LCD3, you need to set the actual speed cut off to 25km/h and then go for a ride using said GPS to match the speed readings. If the LCD reading is lower then the GPS one you need to raise the P1, if the LCD is higher then the GPS reading you need to lower the P1.

For a laugh you should try P1 87 which is approx. 5:1 for Bafang and other hubs, 9mph is the cut off speed. When you change a hub over and forget to change the P1 and go for a ride, you have a WTF moment until you realise your mistake of not changing P1.
 
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pajtaz

Pedelecer
Nov 8, 2019
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I think my setting at 212 is almost perfect. I used GPS app yesterday and compared speeds. I tried 211, 212, and 227 and 212 seemed the most in line. Also I had the least amount of the motor "cut offs".

So I was wondering, does Q128C have 3 different "gears" like a car transmission? Meaning, does it change gears from 1 to 2 to 3 depending on the speed? If so, that would explain why the motor disengages occasionally, it is actually switching gears as I speed up or slow down.
 

Nealh

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The internal gearing is simple, the metal hub body has the large outer gear machined to the body and the main motor /clutch mechanism has the nylon planet gear's that sit centrally. The planet gears are a two stage stepped gear unlike Bafangs/others which have a one stage gear, there is no gear changing inside. No shifting or complicated stuff occurring inside.
I'm not an engineer so maybe some else can explain better.

Only the Xiongda hub motor has two stage speed gearing inside that will /can automatically change the internal speed.
 

Nealh

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If your pick up still suffers from intermittency in use then look at your PAS fitting and C1 settings.
I changed my 12 pole PAS disc to a 10 pole one and found PAS worked so much better, the KT appears not to always like 12 pole counts.
 

pajtaz

Pedelecer
Nov 8, 2019
84
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Netherlands
So today was terrible, the worst day so far with respect to motor cutting out. On the way to work (17.5 km one way), it was fairly good but occasional cut out of the motor. There was wind in my back. However on the way back the wind was against me, it was very strong, probably the worst wind in the last 6 months, supposedly gusts of 44 km/h. So the motor was cutting out all the time, on all PAS levels, mostly on 2, 3, and 4. There is clearly a connection between strong gusts and motor cutting out.

When I am talking about cut out, I mean that motor stops delivering power for less than a second, maybe maximum of two seconds, no error codes, no power loss on LCD, just motor not delivering power. It even feels like it is braking at that moment (maybe that is air resistance but it feels worse than when I just stop pedaling). Motor power on LCD starts going down and depending on the length of the cut out, it will either drop 50-100 W or all the way to 0.

I tried playing with C1 setting, anything besides 7 makes it worse. It cannot be PAS since if the wind is in the back the problem occurs much less frequently. Either way, even against wind it will happen if I am consistently pedaling. Keep in mind that motor reacts perfectly when I am going from full stop and stops quickly when I stop pedaling. PAS response is perfect.

It is not brake sensors because I already tested with those disconnected. It is not battery since it was fully charged today and this happens on various charge levels and there is no sudden voltage drops while cycling. Unless the P5 setting has anything to do with voltage drops, the battery is not the problem.

I am losing my mind now, there has to be a way to fix this, it cannot be anything else besides motor or controller. It seems to behave as if motor is being starved of power. Maybe the motor wants more current when it cuts out and controller can't deliver it or is somehow limited in delivering it. Maybe this is due to settings in LCD3 or due to build of controller. Thing is, it is a 20A max current controller with nominal current of 10A, designed for 36V and 48V (pswpower KT controller). Besides, the cut outs occur at motor power of way less than 500W. They happen at PAS level 2 (150W), level 3 (270W), and level 4 (380W). It occurred at least 15 times today at level 3 and motor power is limited to around 270W in that level. I cannot see how it can be the motor (unless its faulty) and the controller.

By the way, motor otherwise runs so smoothly. It is quiet, no hickups, no grinding, quick start, quick stop, just runs beautifully besides these cut outs. It just doesn't make sense.

I have not played with C2 setting, currently it is set to 0, this might affect how the motor behaves but the explanation in the LCD3 manual makes no sense. It does not explain what it does at all.

Oh and the maximum speed limit on LCD3 does nothing, I am not sure if this is connected. I tested it today by setting it to various levels and the motor never cuts out on PAS levels 1 through 4, it does not even begin to lower. I didn't use PAS level 5. For example, I set it to 25 km/h (and I have already verified speed is correct by using GPS speedometer), and in all levels 1 through 4 I exceed it without motor cutting out. I was riding at 39 km/h in level 3, no change in power of the motor.

So, can anyone help me before I go insane? Has anyone played with C2 setting? Has anyone had a similar/same problem and fixed it? Do I have to get a new controller, new motor, or is this fixable? I am open to suggestions. Thank you ahead of time.
 

Nealh

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C2 is phase sequence any other then 0 results in the phase timing being out and you here very harsh electric grumbles from the controller some of them won't work at all.
It's not the hub as the hub relies on the controller, a few have had niggling problems with the Yose KT. I never used mine but sold it on, instead I opted to use my old connector style KT 6 fet model before ditching it for a 9 fet 25amp max controller.
 

Nealh

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I would be inclined to fit a different PAS on the RHS and use 8 or 10 pole version, if that doesn't work better use a KT from another source.
Ofkeet or C&N on Aliexpress sell 9 fet ones 22 or 25a max or buy from PSWPower or Topbikekit.
 

pajtaz

Pedelecer
Nov 8, 2019
84
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Netherlands
First, I figured out the max speed limit. Since I disconnected the "speed limit" wires on the KT controller that "decrease speed by 30%", seems like whatever speed limit I set in LCD3 is actually increased by the controller. So if I set 25 km/h, the speed limit was increased to around 36 km/h with motor completely cutting out around 41 km/h. When I set it to 30 km/h, it started reducing power around 43 km/h with no power at around 48 km/h. So at least I know it works.