where do i find a high amp potentiometer

Discussion in 'General Electronics Chat' started by daveyjones97, Dec 8, 2011.

  1. daveyjones97

    Thread Starter Active Member

    Oct 21, 2011
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    hi, my kids have a 6v ride on quad and the power is either on or off, the way it was designed id guess less than 10 amps 50w. im wondering where i'd find a high amp potentiometer to make a simple voltage divider to control the "power" better. advice on a suitable rating would be very helpful too.
    im also wondering about the feasibility of using exactly the same setup to make myself a cheap crude ebike, im thinking 40v 20amp? do pots even exist at that amp rating? and does voltage even matter to a pot (within reason)
    any comment is a good comment. im a circuit ameteur and have no idea where/who would have pots that size.
     
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  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    They are normally called Rheostats, but in your case , due to the heat that would be generated on "slow", the best solution would be high power PWM. Pulse Width Modulation turns the motor on and off thousands of times per second with varying duty cycle to control the RPM. PWM is pretty much the standard for controlling the speed of DC motors today.

    How familiar are you with electronics, soldering, reading schematics, etc.?
     
  3. daveyjones97

    Thread Starter Active Member

    Oct 21, 2011
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    oh man, if you only knew... the q was born out of fustration, i realise its an ugly way of doing it.
    i have no formal electronic background outside of some auto 12v and failed science at school. about 2 years ago i became interested in ebikes and since have read all i can find on motor and controller designs and workings. a lot of controller info still goes over my head, see the thread i posted a few weeks ago trying to trouble shoot a razor e300 pwm brushed motor controller. i have a thing for efficiency and the original goal was to try and make my own motor and controller using quality parts. thats is still way beyond me. i have read the pwm and amplifier bits here, but as someone once said "the more i read, the less i understand" i really need a motor controllers for dummies type book. how bad would a rheostat be for wot running, do they have a no resistance position?
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    They are pretty bad (think fan cooling). They do have a "wide open" position, but I think even finding one these days will be difficult.

    Look for PWM speed controllers at 6V and 15 amps (add 20% for overhead to be safe).

    I'm pretty sure you aren't the first with this problem, so a product might be out there, especially for those who converted to 12V if they have what I'm thinking of. Otherwise, you could change the gearing, but that could get... messy.


    --ETA: The e-bike would normally use a brushless motor, you may want to make sure the other one you are working on isn't brushless as well (brushless have 6 wires out), for an H-bridge speed controller, your motor should have only 2 wires out.

    Found this, but it needs the Radio control servo (150mS center PWM) to control.

    http://www.robotshop.com/content/PDF/datasheet-SXXL.pdf

    Here is a potentiometer controlled 5.5-40V, 28A max speed controller for $70, little pricey, but pretty straightforward
     
    Last edited: Dec 8, 2011
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  5. daveyjones97

    Thread Starter Active Member

    Oct 21, 2011
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    thanks, if i did take the lazy way i would use a brushed motor with a freewheel geared for rated voltage and wot to be 20mph approx, just use the the rheostat for starting and brief as posssible half throttle situations. how simalar are motor controllers to class d amplifiers? my brain cell noticed simalarities. i was wondering about upgrading speed controllers with amplifier parts, il read up on it unless someone tells me im wrong.
     
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Frankly, if you find this subject hard to understand, this project might be better left alone. It has the potential to do real harm, for instance giving your children burns, or making the vehicle go out of control if something fails, so that they may be injured. I do not think this is a good beginners' project for someone who is struggling with the subject.

    Perhaps the safest answer to this, if you can afford it, is to buy your children a better ride from a reliable supplier.
     
  7. daveyjones97

    Thread Starter Active Member

    Oct 21, 2011
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    valid points adjuster, until i did the ohms law i didnt realise the kids quad would be 10amps, im right in thinking 6v 10a will still produce a lot of heat on light throttle? how fast would a temp switch cut it out if they only used half throttle? hmmm maybe dump that idea for kids quad.
    anyone able to reccomend books on motor controllers?
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The second motor controller I posted is a PWM controller, similar to a Class D amplifier, but without the output filters for audio use.

    It takes a potentiometer 0-5V input, or you can use up/down buttons to increase or decrease speed. You'd want to mount it where airflow over heatsink is good, but not where the kids could touch it, or weather could mess with it.
     
  9. daveyjones97

    Thread Starter Active Member

    Oct 21, 2011
    46
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    thanks guys, i would be confident making and testing a voltage divider circuit, i have learnt electrical safety, but have no successful circuitboard experience
     
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