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    Lm317 Variable power supply potmeter question

    Hey!
    I've made a variable power supply (see the circuit below) but only need to solder the potmeter on. Is it possible to have two potmeters, one from 0-40 v, another one from 0-100%. For example: I have a 12v fan so i turn one of those potmeters to 12v and with the other one i can control from 0-100%, from 0-12v so I can't burn out my fan. I now also that with one potmeter i would need one from 4k ohm, does that mean that i need two potmeters from 2k ohm?
    Regard Cecemel!Click image for larger version. 

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    Re: Lm317 Variable power supply potmeter question

    hi,
    If you had two 2K pots in Series, setting the Top pot to 0 ohms would enable the Lower pot to control from +1.25v thru ~12V.
    For higher than 12V operation set the Lower pot to maximum ohms and adjust the Top pot.

    Take care not to exceed the LM317 heat dissipation.

    E



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    Re: Lm317 Variable power supply potmeter question

    Hey!
    I've made a variable power supply (see the circuit below) but only need to solder the potmeter on. Is it possible to have two potmeters, one from 0-40 v, another one from 0-100%. For example: I have a 12v fan so i turn one of those potmeters to 12v and with the other one i can control from 0-100%, from 0-12v so I can't burn out my fan. I now also that with one potmeter i would need one from 4k ohm, does that mean that i need two potmeters from 2k ohm?
    Regard Cecemel!image.jpg
    Hi Cecemel
    I highly offer you to refer into the datasheet which has been presented for LM317 . it will lead you through how to use it and will clarify you any kind of doubt !

    Best Wishes
    Goldsmith
    When you sensed that i can help you , feel free to ask me .
    ************************
    Experience is a good professor of mine !
    ************************
    The only thing that i couldn't understand yet , is why humans should fight together ? why not helping each other to have a better world ?



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    Re: Lm317 Variable power supply potmeter question

    The speed of a dC motor is best controlled with Pulse-Width-Modulation so that each pulse provides full power but the width of the pulses provides speed control.
    Reducing the voltage applied to a DC motor reduces its torque. Then it might not begin running slowly and a load might stop it.



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    Re: Lm317 Variable power supply potmeter question

    For speed control best is Pulse-Width-Modulation, there you can get good torque at low current.I agree with Audioguru.



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    Re: Lm317 Variable power supply potmeter question

    Quote Originally Posted by Audioguru View Post
    The speed of a dC motor is best controlled with Pulse-Width-Modulation so that each pulse provides full power but the width of the pulses provides speed control.
    Reducing the voltage applied to a DC motor reduces its torque. Then it might not begin running slowly and a load might stop it.
    Thanks but that fan is just an example.



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    Re: Lm317 Variable power supply potmeter question

    A wheelchair is another example:
    1) The wheelchair is stopped. A small DC voltage is fed to the motor and it does nothing. A higher DC voltage is fed to the motor and it still does nothing. The voltage is slowly turned up and suddenly the wheelchair jumps and goes very fast.
    2) The wheelchair motor is fed a DC voltage and has a constant speed. A hill must be climbed but the wheelchair slows down then stops.
    3) The wheelchair is stopped. A PWM waveform with narrow pulses is fed to the motor and it begins to run slowly. Wider PWM pulses are fed to the motor and it runs faster. The width of the pulses are slowly increased and the speed of the motor slowly increases.
    4) The wheelchair motor is fed PWM and moves at a constant speed. A hill must be climbed and the wheelchair continues at almost the same speed.



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