Modifying a shunt with controlled results

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amberwolf   100 GW

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Re: Modifying a shunt with controlled results

Post by amberwolf » May 19 2019 9:45pm

If all you want is a "soft start" then you can try just adding an "RC filter" to your throttle signal, between the throttle and the controller.

What you want to do is choose a resistor (in series with the signal) and a capacitor (in parallel with the signal, at the controller side of the resistor) that take enough time to charge up the capacitor so it will respond to throttle changes slower than it used to. Use a large value potentiometer instead of resistor (connect only the middle and one leg, leave the other leg open), and you can then adjust it a lot to fine tune it.

The circuit can be made more complex so that it only affects *quick* throttle changes, softening them, while leaving gradual changes alone, or whatever behavior you wish...but the RC filter will probably do what you're after.

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Re: Modifying a shunt with controlled results

Post by jordanjozsef » May 22 2019 2:21pm

Don't think that works, because if I gently pull the throttle, nothing - nothing - nothing, then bam it pushes like crazy. I also noticed when I pull the throttle, the wheel doesn't want to spin, I have to twist more to make it spin, then while it's spinning, if I slowly release the throttle the RPM decreases but I couldn't get that speed at 0 RPM. However I think I found the solution and it is the 3 speed switch. When it's on low speed mode, it decreases the RPM at all throttle range, so if I gently pull the throttle, it won't push me that hard, because the motor wants to reach a lower RPM than before, so the amps aren't that high. And I can ride slower too now. So this is the way to avoid that hard acceleration.
Btw here's the acceleration from standstill even if I slowly and gently pull the throttle it suddenly starts and it actually made my neck hurt.
https://www.youtube.com/watch?v=S71ISZ1SmRA

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Re: Modifying a shunt with controlled results

Post by amberwolf » May 22 2019 7:47pm

When a throttle does not respond at all and then suddenly it does, you should measure it's output voltage across the range. Almost certainly one of two things is happening:

-- the throttle's magnets are positioned such that it takes significant rotation to begin activating the hall sensor and cause any voltage output change. You can make a mechanical stop on the lower range that keeps it from going "below zero" so far. Or change the throttle to a different one that uses the whole mechanical range to output the same voltage range the controller needs.

-- the controller's input range starts at a higher voltage than the throttle's output range, so some of hte throttle's output is "wasted", and it takes more rotation than it should to start activating the controller. The same kind of fixes as the first apply to this.


Sometimes the problem instead is that the controller is a torque (current) throttle control, and the motor is already spinning, so the controller is not going to provide power until the throttle demand exceeds what the system's already doing. With a really high current available, then the throttle range has so much current-per-degree-of-rotation demand available that evne a small movement will create a large surge in motor torque.


But in all those cases, throttle ramping will still help at least a little (and it's easy enough to implement to test it).

If you have a Cycle Analyst you can setup throttle ramping in it's settings (teklektik's UUG is a good guide to setting up everything in the CA). You can also use the CA to take a pot throttle (instead of hall) and convert it's voltage range into that needed for the controller, and give yourself a better mechanical range of movement for the control of the system.

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Re: Modifying a shunt with controlled results

Post by jordanjozsef » May 23 2019 1:19am

I don't have Cycle Analyst, but I had to mention that I was working on how to limit the speed with a potentiometer connected between the throttle and the controller and it worked well, but looks like there's a limit that the controller can't see, so I wasn't able to get lower RPM, it just decreased the throttle "way" - I don't know how to say that, for example I got 40 km/h on full throttle, but below half throttle nothing happened. I also tried Arduino to read the throttle's signal then divide it and then send a PWM signal to the controller, but the controller didn't like it, the RPM wasn't constant, maybe a capacitor could have helped to smooth out the PWM output. That way I could make a cruise function which controls the throttle based on the speed, so if I set 40 km/h, it will keep that speed even on a hilly area.

But my problem is solved, the 3 speed switch worked, when it's on low speed I can go slower and accelerate lighter. I don't know if the 3 speed works the same on all controllers but on mine it solved my problem. I also noticed that on full throttle at speed 1 (slowest) it accelerates better compared to speed 3 (fastest), of course the top speed is much lower. I read that the speed 3 only takes affect on full throttle and I can notice that, when I'm going fast. But looks like it also makes the motor weaker, because when I'm going slow and start to accelerate on full throttle when speed 3 is enabled, it's actually weaker. So that third speed should only be enabled if you want to go fast. I know feeling something and actually test it is different, but I'll test it soon and may I open a new thread to document my 3 speed switch experience with the acceleration and top speed, because I'm worknig on an arduino project which will measure the acceleration from 0 to the given speed, so I could make graphs too.

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Re: Modifying a shunt with controlled results

Post by amberwolf » May 23 2019 1:33am

3 speed switches can work differently depending on controller design and programming.

some are very simple and just limit the speed itself, so you get say 75% of top speed on 1, 100% on 2, and 125% on three, by default (alterable in the programming, if it's programmable).

some hcange the current limit instead.

some change the behavior in more complex ways; one of mine seems to both change the current limit *and* the speed limit.

some change the throttle response, so it scales the throttle input.

some do other things.

Some don't respond to such a switch at all.

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Re: Modifying a shunt with controlled results

Post by jordanjozsef » May 23 2019 2:03am

I guess mine just simply decrease the RPM to the given throttle position. I see that it couldn't work for anyone and I'm lucky it works this way on my controller, so I don't have to do more complicated things. Now the other things I'm interested about is when I do the shunt mod, if it affects the acceleration from standstill or not. The first controller I modded did the same until I reached full throttle, then it started to draw more amps. So on my ammeter the amps were are around 14A (original) then a twisted the throttle a little and then it went to 24A (modded). So the shunt mod only affected the wide open throttle. So in order take effect of the shunt mod, I had to accelerate on full throttle. I guess also this behavior depends on the controller, so maybe this one will work different with the shunt mod. I guess I can mod it to 60A, since it's a 18 FET controller and it's limited to 42A now with only 2 shunts, but on the pcb there's place for a third. The FETs are IRFB4110.

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Re: Modifying a shunt with controlled results

Post by xboxice » Jun 10 2019 7:33am

Hi guys,been reading about from this post,very informative 👌I have a 48V off-road scooter that I made into a 60V with controller upgrade,motor is a 2000W I went ahead and did the shunt mod,but I use soldering,I didn't go nuts,I ran a before and after amp read,my results,
On the 48V 30amp controller not modded -top speed 45kmh max amp 26
On the 60V 30amp controller not modded -top speed 58kmh max amp 28
On the 60V 30 controller shut mod top speed 62kmh max amp 37.5
The scooter has plenty of torque even before the shunt mod and now it feels like it could do with a slightly taller gear 🙄

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Re: Modifying a shunt with controlled results

Post by dannis » Jul 22 2019 12:16pm

what we do in our country is get a china yuyangking 80a controller, 84v 15ah LGHG2 or Sony VTC battery pack, 12inch 1600w HM motor, and we are able to do 110 km/h on GPS. No need shunt, no need mod motor. Want more torque, we just increase battery pack discharge simply by pararrel 2 battery packs.

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Re: Modifying a shunt with controlled results

Post by motomech » Jul 22 2019 8:48pm

No point in telling us what you do in your country if you don't fill out your profile and tell us what country that is.
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

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