LM317T (10V-24V)-1.25V Fan regulator Input Voltage 24V - Page 1
Forum section: electronics / beginners

author: Rafi2022
author_rank: Newbie
timestamp: June 16, 2023, 08:08:44 pm
content: Hi i got a problem. I have potentiometer 1Meg Ohm(thats only i have that i can mount others are smaller), 50k resistor and LM317T.What i can do to create variable power supply 10-24V for example?I need to control fan in my power supply of 3d printer(270Watts) its damn laud.I dont have any thermistor i could use atm.I dont print with heated bed and thats 220Watts. Power supply is 350Watts.So from my calculations its only drawing 50Watts without heat bed.I know how LM317T works and i know the basic circuit.Anyone can draw me a simple thing what i need to add to have 10-24Volts?Thanks in advance.

author: Jwillis
author_rank: Super Contributor
timestamp: June 18, 2023, 12:48:43 am
content: What kind of fan is on the 3D printer. I don't think the fan could be more than 1watt but we can never be sure. Does it say on the fan anywhere how many watts or current consumption?You could just build the LM317 adjustable power supply as you would normally.You mentioned some other potentiometers? You could use those to get the 240 ohm resistor and use the 1 meg as the adjust rheostat . It will be touchy to get an accurate voltage but not impossible. Do you have a couple electrolytic caps around . Used ones with little larger value would work. Most any rectifier or schottky diodes will be OK. You can use any piece of aluminum to create a heat sink.All that needs to be done is to find a voltage source of around 30VDC.Here's the data sheet for the LM317 if you don't already have it.https://www.ti.com/lit/ds/symlink/lm317.pdf

author: srb1954
author_rank: Super Contributor
timestamp: June 18, 2023, 05:04:45 am
content: Quote from: Jwillis on June 18, 2023, 12:48:43 amI don't think using the 1Mpot is viable in a standard LM317 circuit. To obtain the required O/P voltage adjustment range you will be only using the bottom 0.5% of the pot's resistance range. Any adjustment will be EXTREMELY touchy and probably not very stable over time. This application really needs 5Kadjustment pot to be practical.Practical tips:Short the pot wiper to one end of the pot track so that if the wiper goes open the adjustment resistance will be limited to the pot end-to-end resistance and the LM317 O/P voltage won't shoot up to the full I/P supply voltage.Add a reverse polarity protection diode across the LM317 so that it isn't destroyed by back EMF from the motor on power down.Add a reasonable size electrolytic capacitor, say 100uF, across the LM317 O/P to further absorb EMF spikes and other noise from the fan motor.

author: mariush
author_rank: Super Contributor
timestamp: June 18, 2023, 06:00:50 am
content: I would suggest just having a slide switch or some 2-3 position switch to move the fan between a few preset speedsYou could limit the current by inserting a resistor in series with the fan ... if you know the fan voltage and current, you can calculate what resistor to use to limit the current to some specific amount, here's the steps you would do :https://www.blackfiveservices.co.uk/fanspeedcalc.phpAlternatively, with LM317 you would use a 100-240 ohm resistor and another resistor or potentiometer in the feedback so by using different resistor values and switching between them you could adjust the output voltage.You can harvest resistors from faulty hardware, or you could just buy them

author: Jwillis
author_rank: Super Contributor
timestamp: June 18, 2023, 06:44:00 am
content: Quote from: srb1954 on June 18, 2023, 05:04:45 amQuote from: mariush on June 18, 2023, 06:00:50 amThe Op has very few options with limited components.But it's not completely impossible to get the desired range . He could parallel his 50K he has with the wiper and one leg of the 1M and it might help a little bit. But that still puts it at near 50K . He might have to do a little scavenging to get better values.

author: magic
author_rank: Super Contributor
timestamp: June 18, 2023, 02:09:26 pm
content: Quote from: Rafi2022 on June 16, 2023, 08:08:44 pmThe only thing coming to my mind is to connect the pot as a variable resistor between ADJ and ground.LM317 outputs about 50μA from ADJ, so you will have adjustment range from 1.2V (ADJ shorted to ground) up to some 50V (full 1MΩ between ADJ and ground).If the wiper of the pot gets disconnected internally, PSU output will jump to maximum.That 50μA current is not very precise, so for example it may change some ±10% depending on temperature inside the LM317.