Speed restriction loop ku65

[KirstinS]

Any idea how this works ?

In particular does it still work of the controller is over volted ? Or will the restriction cut out increase in line with voltage increase ? So 15mph cut out at 36v but 20mph at 48v ( just a hypothetical example)

 

[Deleted member 4366]

I haven't tested it, but I'm pretty sure it's constant. The question is how does it know the speed of the bike without a speed sensor? It can't be based on commutation speed because it doesn't know how many magnets the motor has

 

[KirstinS]

Excellent that's what I was hoping. I'll report back and confirm once Ive tested

But if it does work this way - then how is intruiging

 

[Alan Quay]

The controller must know the RPM, because it has to send the 3 phases to complete each rotation. But it doesn't know the circumference of the wheel.

Perhaps they all assume a 26" wheel?

 

[Deleted member 4366]

The number of pulses depends on the number of poles and magnets, so It can't see the RPM. This is puzzling me now. I'll ask on ES.

 

[KirstinS]

The number of pulses depends on the number of poles and magnets, so It can't see the RPM. This is puzzling me now. I'll ask on ES.

I found this D8veh - it talks about the speed restriction on a ku63 being "simple voltage divider"

http://www.avdweb.nl/solar-bike/electronics/ku63-motor-controller.html#h3-disabling-pas-pedal-speed-control

I undertand only a tiny fraction of this page though - maybe you can make sense of it ! I'm aware that the ku65 and ku63 are very similar. To the point they now don't sell them separately but as a Ku63/65 withthe use joining a couple of pins to make the change

 

[Deleted member 4366]

You have to be careful with his diagrams because he's modified his controller a bit. The main circuit diagram shows that, when you join the wires, an extra resistor is bought in to pull down the throttle signal by about 1/3. It doesn't seem to be connected to the PAS in any way, but I thought that when you join the limit wires, the PAS is limited too.

 

[jhruk]

Some years ago I fitted a ku63 to a 328rpm motor in a 20” wheel.. By Referring to that schematic I successfully increased the limited speed from 10mph to 15mph by just adding a 10k resistor across the two speed limiter wires. To decrease the limited speed to below that set you'd presumably have to open it up, locate R87 and reduce it's value, but I haven't tried this.

I'm afraid I don't know if this affects the PAS as I didn't fit it.

 

[Deleted member 4366]

The ratio that the speed limiter splits the throttle according to Adweb's schematic is 20k/30k. If you put a 10k resistor between the wires it changes the ratio to 30k/40k, so my calculation says thats about 8% difference, or from 10mph to 11 mph, so something isn't right somewhere.

 

[trex]

I don't have the KU63 circuit diagram but if the upper resistor of the divider is the 20k and the throttle is 30k, the initial supply voltage to the throttle is 3V. Plug the 10k resistor into the wires changes the value of the upper resistor to 6.6k = 1/(1/10k + 1/20k), the new supply voltage is 5V * 30k/36.7k = 4.09V, that is 36.3% increase over 3V, near enough to the observed change from 10mph to 15mph.

 

[jhruk]

This was some time ago and I'll have to check the actual value. I could see from the diagram that changing the value of R87 should change the limited speed. I wanted to increase the speed, which was easy as R87 could be increased simply by an external series resistor. I arrived at a value by experimentation rather than calculation – I recall I initially used a variable.

As I said I don't know if, or how, this affects the PAS speed. I do have another bike with a ku65 and PAS fitted. If I get some time I'll experiment with that and see what happens, but it won't be today.

 

[Deleted member 4366]

I don't have the KU63 circuit diagram but if the upper resistor of the divider is the 20k and the throttle is 30k, the initial supply voltage to the throttle is 3V. Plug the 10k resistor into the wires changes the value of the upper resistor to 6.6k = 1/(1/10k + 1/20k), the new supply voltage is 5V * 30k/36.7k = 4.09V, that is 36.3% increase over 3V, near enough to the observed change from 10mph to 15mph.

They're not. The throttle resistor is 10k and the the speed restrictor is 20k. He added an extra 10k to make 30k for the speed restrictor. Maybe the controller's response to the throttle is non-linear. The throttle signal is 4.3v max, so the difference between the two situations is 2.867v and 3.225v, i.e.12% difference. I made a mistake before taking 1/12 of the 2.867v instead of the maximum 4.3v as the difference.

 

[KirstinS]

The above are beyond me I'm afraid !

I'll just have to test and see. Won't be this side of Xmas though

 

[Deleted member 4366]

The above are beyond me I'm afraid !

I'll just have to test and see. Won't be this side of Xmas though

No it isn't. It's primary school maths. Try and understand it to enhance your knowledge because voltage dividers are used a lot in ebike electronics..

When you put a voltge, say 36v, through two resistors in a line, it drops from 36v at the top to 0v at the bottom. The voltage in the middle connection depends on the ratio of the value of the resistors.

If you have two 6000 ohm resistors, they're equal. The voltage drops down the same amount for each one, so you get 18v in the middle.

If you had 4000 and 8000 ohm resistors (4k and 8k), the voltage would drop twice as much down the 8k one as the 4k, so that means 24v for the 8k and 12v for the 4k. That means you get either 24v or 12v in the middle depending on which one is at the top.

If R1 is at the top and R2 at the bottom, the formula is that the voltage in the middle will be

Vout = Vtotal x R2/(R1 + R2)

You can put as many resistors in a line as you want and the total voltage will be divided up at any point in the ratio of those resistors below to the resitors above, so if you had 4 resistors and wanted to know the voltage at the middle of them , it would be

Vout = Vtotal x (R3 +R4)/ (R1+R2+R3+R4)

You can use this principle to change the LVC in your controller. Your battery voltage will be divided down to avbout 3v because the processor can only deal with 5v max, so the resistor values will be say 11k and 1k. If you changed to a 48v battery, it would divide that 48v in the same ratio, so you'd have 4v. The processor will therefore judge that your battery is fully charged when it isn't. To get back to the 3v, you'd need say 1k and 15k resistors.

3v = 48 × 1000/(1000 ×15000)

If you're still running with 12s and you want a LVC of 36v instead of 30v, you only have to change the value of one of the resistors. First you have to find the ones you've already got. They're normally little black surface mount resisistors with four digits on at least one of them. They'll be near where the ignition wire is joined to the controller's pcb.

 

[jhruk]

Well, it seems the speed limiter circuit on my ku65 is not the same as that on my ku63. I've just done a quick test on the ku65, by putting a 20k pot across the speed limiter wires, and all I can get is a switch between full speed and the set restricted one, at around 18k, with nothing intermediate.

I also checked the resistor value I used on the ku63 and can confirm it as 10k. Unfortunately, without a diagram for the ku65, it's difficult to proceed any further.

 

[Deleted member 4366]

Can you explain again what was the effect of the 20k resisistor. I don't understand what you wrote.

IIRC, The KU65 PCB is the same as the KU65, in which case adding a 20k resistor between the limit wires would divide the voltage by 4/5, i.e. 3.44v, so there should be a 20% difference in top speed if the speed was linear with throttle signal, however, there's a dead band at the top and bottom. If the dead band were 20% of the voltage say down to 3v, there would be no difference, but I don't think it's as wide as that - I have 3.7v at the back of my mind as the full-throttle voltage.

I forgot about the dead band in the previous examples. I can't remember what it is. You need to measure the voltage at the throttle when the wheel reaches maximum rpm..

 

[jhruk]

I first tried the same as I'd done with the ku63, by putting 10k across the limiter wires. I was expecting a similar effect to the ku63 but instead it ran at the same controller set limited speed, there was no increase as expected. I then added a further 10k pot in series and by adjusting this found it suddenly switched between full speed and set limited speed at a certain point, which I measured to be around 18k, with no intermediate speeds possible.

The voltage measured across the two limiter wires remains constant at 4.8v whatever the throttle position, so it cannot be operating in the same way as in the ku63 diagram.

My conclusion is that the limiter circuits differ and that the limited speed on the ku65 cannot be adjusted by the method I used on the ku63.

I also checked how the limiter affects the PAS. It seems it just puts the same overall limit on as the throttle and does not lower the set PAS speeds in proportion, i.e. lowest speed remains the same with the upper two now limited and identical.

​

And I still haven't answered Kirstin's question about what happens at 48v.

 

[Deleted member 4366]

All these things work off the 5v bus, so are sort of independent of the battery voltage. The PAS and throttle give the same voltage to the controller, so the controller will give the same PWM output, except the PWM voltage will be 48v instead of 36v, so you'll get 33% more torque and power. The speed is complicated and depends on how the throttle signal is translated into speed in the controller's software. I guess you'll get 33% more speed though because I can't see the controller measuring speed in any way. Speed must be regulated by the back emf.

If you measured between the restrictor wires with them disconnected, regardless of any resistors in series, you will always get approximately 5v because no current is flowing. You have to measure between ground and the join point on the pcb with them connected to see the effect.

Thanks for those test results. That's changed my understanding of how it works. It must be different to that KU63 schematic. It looks like it's a simple jumper then with a on/off result to the processor. Without the resistor, connecting them pulls the 5v to ground. If you bring too high a resistor in series with the join, it can't pull ut down far enough to go off. It wouldn't surprise me if the KU63 is the same and the schematic is unrepresentative.

 

[KirstinS]

I have finally managed to test this out at various voltages on the KU65. Results below and this is entirely on a no load basis, using booster batteries, in my kitchen, using a wireless cycle computer that I find is off by about 10% compared to my GPS.

36v (10s) was 38 kph and with the restrict on was 23.8kph

44.4v (12s) not tested as my 2s pack was flat

48v (13s) was 49.9 kph and with restrict on 32.3kph restricted

50.4v (14s) was 51.6kph and with restrict on was 33.6kph

 

[Deleted member 4366]

It's cutting the throttle signal then, which means you should be able to reduce yhe restricted speed by putting an additional resistor on the linkage. You can't make the restricted speed higher at at any given voltage.