To shunt or not to shunt?

Well…. I modified my replacement controller. When I took it apart I found that it had 2 shunt wires & pre-drilled holes for another. So I added the extra cable & got ready to install it, but when it came to fitting the controller I found that two of the connectors were different to my original controllers.
Also, I noticed that my original controller has a label that says: ‘Break : High Level’ & ‘Current Limit: 35A 1400W’.
But my replacement controller has a label that says: ‘Break : Low Level’ & ‘Current Limit: 34A 1400W’.
And the new controller is a bit bigger.
I thought I’d remove the back-plate from my original controller & find out where the wires all go. When I removed the back, the first thing I saw were the shunt wires. 3 of them!
MMM I thought. It seems that the controllers were actually designed to have 3 shunts in place as standard. What a waste of time that was…….
So I had a quick think & decided to remove the extra shunt I had previously installed.
I tried the the scoota with the ‘2 shunt’ controller & it worked fine, but I noticed that it was a bit slower on acceleration, but the top speed was about 3MPH higher.
I put my orginal back in & the acceleration increased again & the top speed was back to normal.

My conclusion from this is that if you need a scoota to handle hills, you should keep with the ‘3 shunt’ controller. If you would prefer top speed, you can remove a shunt to gain speed but lose power.

I am going to try out the contoller again & remove another shunt (so it only has 1) & see what the top speed is & how slow the acceleration is. I’ll let you know in due course….

If you want to remove a shunt, it can be done by simply removing the back plate from the controller & snipping the nearest wire. You don’t even need to remove the circuit board from the box.


6 Responses to “To shunt or not to shunt?”

  1. hohisilver Says:

    Hi Nick

    That’s interesting. I suppose from my (relatively limited) knowledge of electronics, it makes sense. The batteries can only deliver a maximum wattage, so if you increase the current delivered to the motor, the voltage will drop, and vice-versa.

    What I’d like to find is a “variable” controller where you can switch these things in and out while you’re riding, thus getting the best of all worlds. For example, start with high current to get acceleration from a standstill and once you’re up to say, 25 mph, to be able to decrease the current and increase the voltage to improve the top speed.

    I’ve yet to hit the 20-mile mark, so come back in a few years and I’ll tell you how it’s doing at 1000 miles! 😀


  2. Mike Says:

    Hi Nick and hihosilver,

    I am working on being able to make the current limit variable at the moment and looking at the full charge startup problemas well.

    Nick, does the charge meter still display ok with 60V? With 48V the controller should shut off the power when the voltage gets down to about 40V to protect the batteries. With 60V it will never get there. The controller may be clever enough to sort it itself but I don’t know. Did you have to do anything to compensate for that?



    • nigsego Says:

      Hi Mike.
      No, the charge meter shows the batteries to be at full charge the whole time 60 volts are connected. I found this out to my dismay. I had travelld about 50 miles (on the clock) without a re-charge & it suddenly dropped the charge lights down to amber & then red. This caused the scoota to act like a bucking bronco! It was quite funny though 🙂 I managed to get another mile or so out of it like this & the battery lights were going from red up to full green & then back down again etc.
      When I got to work I put the 4 batteries on charge & gave them a full 8 hours, but the battery charger still never said they were fully charged (it got me home though).
      Hope this helps.

  3. Mike Says:

    Looks like something else that will need sorting then.
    Got some important technical info coming from the suppliers tomorrow that may just confirm my thoughts on the full charge fix.


  4. nigsego Says:

    Cool. I look forward to hearing all about it.
    A strange thing happened today. I had to make up a new cable harness (because I stupidly arced mine out!). I discharged the cap’s (just to make sure) & pugged all 5 fully charged batteries in & to my amazement the motor worked straight away. I did not need to slightly discharge them. I never normally discharge before ‘plug in’ but next time I do a full charge, I will do the same & see what results I get. Fingers crossed.
    All I did was to flick off the circuit breaker & keep the throttle open until the red battery light faded. This seemed to do it.

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