Trying to identify internal solder pads in a JP 20A controller

[Fallingwater]

I got a Laotie L6 Pro electric scooter. It comes with two JP 20A 48V controllers, a master driving the rear motor and a slave driving the front one. The wiring is the usual Chinese ratnest, but with the help of a multimeter, a few videos (tip: the Yume X11 scooter seems to be wired identically) and the good old technique of unplugging something at random and checking what isn't working, I've managed to trace most of it.

Problem is, there doesn't seem to be a limiter wire loop that'll keep the scooter from exceeding 25kmh if it's connected, like I've always seen on every other box controller from China. I received the scooter with no limiter enabled, such that it'll reach 40kmh before I even notice and will happily go on to 50kmh. The whole reason I took it apart is to find the limiter and find some way of enabling it as needed (wanna be legal in the city centre, don't care in deserted fields...), but it doesn't seem to exist. Which is weird, because in the reviews on Banggood there are at least a couple users complaining that their scooters are stuck at 25kmh...

I took the master controller out of its shell expecting lots of disconnected pads, hoping to identify where a limiter wire might be connected in other iterations of this controller, and this is what it looks like. There are indeed plenty of pads there (along with ugly resin residue everywhere), but I've no idea what the various identification letters and numbers mean.

Does anyone know if any of those pads is the speed limiter?

I'm also a curious soul in general so I'd love to know what the other pads are, so I can identify them and see if there's anything useful. For instance, what the heck is that "SD" pin on the left there, and why is it soldered grounded? What happens if I disconnect it? (I'm not brave enough to test this without knowing what I'm doing.)

Thanks.

 

[fechter]

I don't see anything that looks like a limiter or speed select pad.

Plan B would be to install some kind of resistor divider in line with the throttle signal to limit the speed.

 

[Fallingwater]

I don't see anything that looks like a limiter or speed select pad.

It does have speed select - a button on the handlebars that selects between "turbo" and "eco". Unfortunately eco mode isn't limited enough, as it reaches 33kmh. I don't suppose there's any way to reprogram this, as it seems coded in firmware. Man alive, how I hate proprietary boxes... I might just stick a dual VESC into this thing at some point (read: if I find one that isn't expensive).

Anyway, I've found the eco button's cable and could disable it so it's always in eco whenever I'm not using it for leisure. Then I'm thinking I could twiddle the P setting for the magnet groups until the displayed speed at 33kmh is 25, ride at displayed 19 (ought to be around 25kmh actual), and hope if the cops stop me they're happy lifting the wheel and checking displayed speed. Never seen a rolling road setup used by cops in a lifetime of riding...

Plan B would be to install some kind of resistor divider in line with the throttle signal to limit the speed.

Unfortunately the throttle is one with the display unit, and the signal goes directly from the hall sensor to the board. I suppose I could add such a circuit by tapping the hall sensor's output directly - it'd be internally messy but it shouldn't be evident from the outside.

How would I go about building this resistor divider? I'm familiar with basic electronics and have soldering gear, but I don't have, like, a big drawer full of different kinds of resistors or anything like that.

 

[amberwolf]

The easy way is to use a potentiometer, which can even just be a volume knob off some old radio, amp, etc. Most of these are between 5kohm and 20kohm, which is a good range to use for this.

Cut the throttle signal wire somewhere between throttle and controller--wherever you want to fit this potentiometer. If there is room inside the controller case, it will give you a secure place to glue it down or otherwise mount it that is out of the way...but hard to adjust unless you mount the pot's shaft or knob or dial so that you can access it from outside the controller.

Most pots have three wires, two on the "outside" and one between them.
--One of the outer ones goes to throttle ground.
--the other outer one goes to throttle signal from throttle.
--the middle one goes to the controller's throttle signal input.

Set the pot to the center position.
Setup the scooter with the powered wheel(s) offground.
Turn it on, and begin moving the throttle upward to full. It will only go to around half speed; hold it there and adjust the pot until it reaches the speed limit you want.


If you want to be able to turn this limit on and off at will, simply wire a latching or toggle switch of whatever type you wish so it's common contact is connected to the throttle signal wire on the controller, and the other contact is connected to the throttle's signal output wire. Turning the switch on shorts across the potentiometer and bypasses it, feeding the full signal to the controller.

A "better" bypass would cut the pot out of the circuit first, but isn't really needed and is just extra complexity.

 

[amberwolf]

For instance, what the heck is that "SD" pin on the left there, and why is it soldered grounded? What happens if I disconnect it? (I'm not brave enough to test this without knowing what I'm doing.)

On some controllers I've opened, SD is the throttle signal input wire. I've never tried grounding it on any controller, but it is possible that if this controller is the slave controller, and the throttle only goes to the master, and there is serial communications between the two, that when the SD is grounded it forces the controller to *be* the slave, by the MCU's programming reading the 0V (instead of 0.8v common throttle minimum) as a command to enter slave mode.

But that's complete speculation.



Here's one of my controller threads on the archived ES version

C-SMD1.2 Controller pad functions, Regen, etc. XC8M06 based - ES 1.0 Graveyard

unfortunately the images are gone, but the text descriptions are still there.

 

[Fallingwater]

On some controllers I've opened, SD is the throttle signal input wire. I've never tried grounding it on any controller, but it is possible that if this controller is the slave controller, and the throttle only goes to the master, and there is serial communications between the two, that when the SD is grounded it forces the controller to *be* the slave, by the MCU's programming reading the 0V (instead of 0.8v common throttle minimum) as a command to enter slave mode.

That would make sense, as it's completely controlled by the display unit - the trigger throttle is part of it, and the MCU inside the display converts it to digital signals that command the controller via serial communication. I guess that requires the hardware throttle to be soldered to ground. I suppose opening that would enable use of a separate throttle, which might actually be useful for a thumb-throttle conversion, if I can find a potentiometer throttle in the future. Good to know, thanks.

 

[Fallingwater]

The easy way is to use a potentiometer, which can even just be a volume knob off some old radio, amp, etc. Most of these are between 5kohm and 20kohm, which is a good range to use for this.

Good to know, I have a ton of pots around from a part salvaging spree I had a few years ago.

Cut the throttle signal wire somewhere between throttle and controller--wherever you want to fit this potentiometer. If there is room inside the controller case, it will give you a secure place to glue it down or otherwise mount it that is out of the way...but hard to adjust unless you mount the pot's shaft or knob or dial so that you can access it from outside the controller.

Problem: my scooter's throttle is not potentiometer-based, but rather hall-sensor-based. Does this fix work with this type of throttle as well?

The throttle trigger is part of the display unit. From what I've read around the controller has very little smarts in it, with the display unit doing most of the actual controlling - all the box in the deck does is receive serial communication from the display unit and run the motor and lights accordingly. By which I mean, there isn't a throttle wire going from the handlebars to the controller down in the deck.

As for the display unit itself, there is a hall sensor inside the unit, and the rotating trigger assembly has a magnet that acts on it from outside the display unit's casing, for rain resistance. I could cut the hall sensor's output leg and solder the pot in-between, but I'd like confirmation that this actually works before I start opening things and cutting legs.

 

[fechter]

That style of throttle will be hard to modify. Sometimes the throttle signal will go to the controller and you could place a resistor at that end. I've also seen some that use the throttle signal to generate serial data at the throttle and only data goes to the controller. This would be hard to modify.

I have a stand-up scooter with this kind of trigger throttle/display unit. It also has a 3-speed switch that limits the speed.

A less sophisticated approach would be to install some kind of throttle stop that limits the throttle travel.

 

[Fallingwater]

That style of throttle will be hard to modify. Sometimes the throttle signal will go to the controller and you could place a resistor at that end.

It wouldn't be hard to cut the output leg of the hall sensor and interpose a resistor/potentiometer, I just wanna know if that'll work before I start disassembling the thing, cutting and soldering. Lots of work for nothing if it turns out hall sensor throttles can't be resistored and I have to undo the mods.

A less sophisticated approach would be to install some kind of throttle stop that limits the throttle travel.

I thought about that, but I don't see a way of doing it at will. If I made it so it's removable I could be fined, but if I set it in place tightly enough that it isn't removable and won't get me fined I won't be able to remove it myself when I want to ride for fun in deserted places.

An electric solution would be a lot neater.

 

[amberwolf]

Problem: my scooter's throttle is not potentiometer-based, but rather hall-sensor-based. Does this fix work with this type of throttle as well?

Yes, it works with any voltage-based throttle signal. The actual results you get from a specific setup will depend on what the device reading the throttle signal expects.

So yes, you would place the pot (and bypass switch) between the hall sensor's signal output pin and the device that reads this, either by cutting the actual hall sensor leg or the trace from teh pad that it's soldered to to the device that reads the signal.

(Not relevant to your system, but there are a very few old brushed controllers I have seen that used a current thru a potentiometer-based throttle to generate the voltage of the signal, so it would technically work on those, however those

 

[fechter]

Depending on the circuit the hall sensor is connected to, you may be able to use a single resistor in series with the throttle signal. Then you can use a pair of wires and a switch to bypass the resistor. If the circuit has a very high input impedance, you may need two resistors to form a voltage divider. With the resistor in series, the throttle will likely have a big dead band at the beginning before the motor starts. This can be annoying, but works. To avoid the dead band, it takes a more complex circuit.

 

[wjg707]

I think that the throttles are all the same in their voltage output range, regardless of their placement or method of obtaining that voltage. The hall-type thumb throttle that I have has an output voltage of 0.5-4.3v which seems to be the same as you'd get from a standard pot with a wiper. The hall-type is used because of it's immunity to damage from water. Standard pots are unusable when wet, and often damaged beyond repair.
Although the trigger-type may be physically integrated into the head unit's case, it is a separate unit electrically. The head unit only displays information sent from the controller, such as speed of travel, etc. , but since the throttle input is not displayed, it has no use for it. The head unit does not intrepret or understand anything- it just passes control signals to the controller, and displays what it is told to display by the controller.

 

[wjg707]

The speed limiter on my Arwibon Q6 Pro is working (except they call it 'economy mode') It's similar to your L6 Pro; it has a nearly identical name and description.
On mine there's an interconnecting wire set between controller A & B, on which one wire is white/blue (which controls the limiter) and a one is black (ground). A switch across the two will cap the speed at 14mph when closed. Internally, the white/blue wire connects the solder pad marked 'SL' (Speed Limit?) on both controllers' PCBs.
The switch doesn't break the connection; they're always connected and it grounds them both.
When enabled the limiter sets the top speed at 14mph. There isn't a P-setting to adjust it, but i'm trying to figure out whether I can change a resistor on the PCB to adjust it.

 

[wjg707]

The throttle could also be limited by a zener diode, if you knew the voltage corresponding to your desired top speed. You probably wouldn't have to disconnect anything else to add it. If you put the diode between ground and the throttle wire it would shunt the excess voltage to ground, effectively making the throttle limit equal to the zener 's trip voltage.

 

[Fallingwater]

The speed limiter on my Arwibon Q6 Pro is working (except they call it 'economy mode') It's similar to your L6 Pro; it has a nearly identical name and description.
On mine there's an interconnecting wire set between controller A & B, on which one wire is white/blue (which controls the limiter) and a one is black (ground). A switch across the two will cap the speed at 14mph when closed. Internally, the white/blue wire connects the solder pad marked 'SL' (Speed Limit?) on both controllers' PCBs.
The switch doesn't break the connection; they're always connected and it grounds them both.
When enabled the limiter sets the top speed at 14mph. There isn't a P-setting to adjust it, but i'm trying to figure out whether I can change a resistor on the PCB to adjust it.

My "eco" limiter is set in the same way, but unfortunately in my case it limits it to 33kmh (21mph or thereabouts). If I were to get stopped and the scooter speed-checked, it wouldn't make a difference if it goes up to 33 or up to 50 - both are equally illegal.

Did you ever find out how to adjust it? If I could set a resistor to 25kmh I'd have solved all my problems.

 

[Fallingwater]

I have an interesting update on this thread.

I've embarked on a full rewire of my scooter to reduce the unmanageable amount of ratnest wiring in the deck.

While tinkering with the wiring I have discovered something useful: if I put a potentiometer across the "eco" line instead of just bridging it, I can vary the amount of speed restriction that the controllers apply.

Unfortunately this is of limited use at the moment, because all I can do with the pot is make the limiting *faster* - the less resistance the slower it goes, but I can't decrease it further than a dead short and it does 33kmh then, so I still have no way of using Eco to get the scooter to 25kmh.

However, this does suggest that there must be a resistor somewhere on the board that determines the extent of the limitation, as hypothesised by wjg707 above. If the board has been built with anything like practicality in mind, this resistor should be directly inline with the limiter trace, so it shouldn't be too difficult to find.

I suspect eliminating the resistor and bridging the trace will cause the entirety of the limitation to happen according to whatever resistance is placed across the Eco line, from zero speed on a dead short to no limitation on open-circuit.

I'll start tracing soon and report on my findings.

 

[Fallingwater]

I've most likely found the resistor - it's right by the solder pad where the Eco line gets soldered. You can see it here: "XS" is the solder point, and that 20kOhm 203 resistor is the one.

Unfortunately, this turns out to be much less useful than I thought. I've tested the throttle pin's resistance as well, and it turns out enabling Eco mode just modifies that. It seemingly does absolutely nothing else.

To reiterate, there is no software regulation at all in eco mode - all it does is reduce the amount of throttle the controller sees, and is absolutely no different than simply adding a potentiometer to the throttle line exactly like I was doing.

I've elected not to test Eco mode and its resistor any further; from practical purposes, this research line is a dead end.

This is unfortunate, because I was hoping for Eco to trigger a software control of some sort on the speed. Being effectively the same method, both the throttle pot and Eco mode cause on-road speed to be different than what's visible on the dashboard when the scooter is lifted and the wheels are spun up in the air by about 5kmh. Essentially this means if I get stopped by cops without a rolling road and they test speed by lifting the wheels, it'll register as 5kmh overspeed. I'm not sure if they have the sort of flexibility to accept the argument that the scooter goes slower when actually being ridden.

I've decided to change the magnet pole number in the P menu so the dashboard shows 25kmh when the wheels are spinning at 30kmh, so a lift test will show legal speed. The fact it'll now show 20kmh on a rolling-road test (and while riding...) shouldn't be much of a problem. If I ever need precise speed measurement I can just run a GPS app on the phone.

I think this concludes this thread's purpose. Sorry it didn't have a happier ending.