# Pot instaed of hall effect throttle



## nirbaer (May 25, 2010)

I found that the part of the controller that handles the high current works o.k. and I want to use it rather than throw this controller away, also because it has reverse.

Now I need to build or to source a PWM simple circuit and connect them together.

Any advise is welcomed.

BTW, TNC are not willing to change the controller.


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## nirbaer (May 25, 2010)

Hi,

I need feedback about the suggested schematic.
In blue is the existing circuit, in red all he additions I am planning.

My questions
1. main switch (SW1) & relay (J3) - is this a common setup? the idea is to connect it to the ignition key which have 3 positions: off, on and reverse.

2. Regenerated braking - in case the kart is going downhill and the motor is acting like a generator, the diode D will allow the generating current (mostly in forward but should also work in reverse). Is that o.k.? which diode should I use?

3. Brake - suggested a relay (J4) that will disconnect the motor from the circuit and will short it so it will act as a brake. Will this damage the motor?

The circuit is 24V, motor is MY1016 24V/350W.
The kart should be very small, total weight about 50-60 Kgs.


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## Duncan (Dec 8, 2008)

Hi Nirbaer

You may find this useful
http://ecomodder.com/wiki/index.php/ReVolt


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## Tesseract (Sep 27, 2008)

nirbaer said:


> 1. main switch (SW1) & relay (J3) - is this a common setup? the idea is to connect it to the ignition key which have 3 positions: off, on and reverse.


I suppose at 24V it's ok. Not the reverse part - that's not going to work (see below).



nirbaer said:


> 2. Regenerated braking - in case the kart is going downhill and the motor is acting like a generator, the diode D will allow the generating current (mostly in forward but should also work in reverse). Is that o.k.? which diode should I use?


No, diode "D" is already present in the MOSFETs themselves and has nothing to do with braking, whether regenerative or dynamic. Regenerative braking requires changing the converter from the buck to boost configuration which requires a lot more work than what you've drawn. You are pretty close to having dynamic braking, though - just add a resistor for a load (ie - don't short the motor out)



nirbaer said:


> 3. Brake - suggested a relay (J4) that will disconnect the motor from the circuit and will short it so it will act as a brake. Will this damage the motor?


You need to insert a load resistance otherwise, yes, you will damage the motor (and probably the relay, too). Keep in mind the resistor will need to be capable of handling the peak current and power expected. Since this is a small motor you could probably get away with a bank of cement-filled resistors (5W to 10W) that comes out to around 0.5 to 1 ohm and at least 50W (the peak power handling capacity for a few seconds will be at least 4x that amount).


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## nirbaer (May 25, 2010)

Tesseract said:


> I suppose at 24V it's ok. Not the reverse part - that's not going to work (see below).


Do you mean the reversing circuit will not work? that part already exists and reversing the motor well.



Tesseract said:


> No, diode "D" is already present in the MOSFETs themselves and has nothing to do with braking, whether regenerative or dynamic. Regenerative braking requires changing the converter from the buck to boost configuration which requires a lot more work than what you've drawn. You are pretty close to having dynamic braking, though - just add a resistor for a load (ie - don't short the motor out)


O.k, I will remove the diode.



Tesseract said:


> You need to insert a load resistance otherwise, yes, you will damage the motor (and probably the relay, too). Keep in mind the resistor will need to be capable of handling the peak current and power expected. Since this is a small motor you could probably get away with a bank of cement-filled resistors (5W to 10W) that comes out to around 0.5 to 1 ohm and at least 50W (the peak power handling capacity for a few seconds will be at least 4x that amount).


O.k.


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## Tesseract (Sep 27, 2008)

nirbaer said:


> Do you mean the reversing circuit will not work? that part already exists and reversing the motor well.


Sorry - I was thinking of regeneration when I wrote that.


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## nirbaer (May 25, 2010)

Ok, I built a PWM circuit using schmitt trigger from here (only used cmos 4093 instead of ttl 7414) and the circuit seems to work fine - I don't have oscilloscope so I checked it with a larger capacitor so I could see the on/off duty cycle visually with led going from 0 to 100% and then I replaced back to normal frequency (about 3KHz).

It seems to work - when I change the potentiometer (throttle) the motor speed changes but the speed is not stable i.e. without touching the potentiometer the motor speed also goes up and down (mostly up).
I suspect the fault is with the PWM circuit - too simple perhaps. Any advise about PWM circuit which is more dedicated to DC motor?

Here is a pic of the circuit.


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