Linear(ish) ramp-up circuit for dc motor

Discussion in 'The Projects Forum' started by summersab, Mar 1, 2016.

  1. summersab

    Thread Starter Active Member

    Apr 8, 2010
    132
    0
    I've seen a number of products, schematics, and discussions about this, and I'm rather unclear where to start. I've seen this thread but I have no idea what a PWM is even after looking it up:
    http://forum.allaboutcircuits.com/threads/simple-dc-motor-ramp-up-circuit.112540/

    I just bought one of these. It's not here, yet, but another source claims it's 12V, 0.25A:
    http://www.ebay.com/itm/281485837958?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

    What I'd like to do is ramp the voltage when switched on from 0-12V in about a minute (precision isn't key, here). If it's possible to make it variable and take several minutes (<5) to ramp up, that would be great. I've seen some pre-built circuits and controller boards that look like they'd do what I want (yay, cause I suck at building circuits!) The problem I have is that they all use pretty bulky parts or are really complex. I don't mean to be crude, but certain, uh, "adult" products definitely have settings that pulse, ramp up and down, etc, and they're certainly not stuffed with capacitors. Is there any off-the-shelf board or a combination of a few simple parts that would do this? How come those other... "products" manage to work without tons of circuitry?
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    You have your motor connected to a 12 V power supply thru a pushbutton switch. Each push is one second,
    You start pushing once per min.- motor just growles a bit, two/ min, motor starts turning. As spacing gets closer together the motor speeds up until pulses run together , now full speed; that is the effect of PWM. Instead of one minute we might use a period of 2 msec. & vary the pulse width from 0 to 2 msec. Sgt W PWM 00000.png For a motor might set VR1 to give a clock of 500 HZ. Instead of the pot for input use a R-C generated ramp. Need more inf. on what the motor is supposed to do after reaching full speed.
     
    Last edited: Mar 1, 2016
  3. summersab

    Thread Starter Active Member

    Apr 8, 2010
    132
    0
    That makes perfect sense. I may come back with more questions about the circuit (again, I really suck at it - analogous to a handyman with 10 thumbs). Does that pulsing stress the motor?
     
  4. summersab

    Thread Starter Active Member

    Apr 8, 2010
    132
    0
    I'm going to bump my own thread. I ended up using a circuit by AnalogKid from the following thread:
    http://forum.allaboutcircuits.com/threads/simple-dc-motor-ramp-up-circuit.112540/
    http://forum.allaboutcircuits.com/attachments/rampdriver-gif.87260/ (actual circuit)

    I picked it because it's dead simple and it uses parts I can get at Radio Shack. However, I'm having some trouble. My needs changed a bit, and the motor I'm driving is more like 6V @ 3A. What I'm trying to accomplish is build a ramp-up circuit that will ramp up the motor over the course of about a minute, uses pretty common parts that I could get at Radio Shack, and is simple to build/doesn't use many parts (to me, op amps are just like bolts - they all work the same, and I have no idea what rail-to-rail or slew rate means).

    Here are some of the issues I've had with the circuit by AnalogKid:
    1. I tried using a LM741 since I had one, but I didn't have all the correct resistors, so I made some substitutions. It worked just fine at first, but then it stopped working. I think the 741 burned out. That's either because my "substitutions" were bad or because the 741 can't handle the load. If I ordered more, should it work for this circuit?
    2. After burning out the 741, I grabbed a LM324 (Radio Shack stopped carrying the 741). It works, but it does this weird thing where the motor ramps up, then drops back down, ramps up again, drops back down, and continues to do so. What's going on?
    3. I noticed that Radio Shack started carrying the TL082 (presumably because they stopped carrying the 741). I figured I'd save some space with 8 pins instead of 16. However, it doesn't do anything. Do I need to ground the second op amp or something? Why won't it work?
    4. When the circuit DOES work, Q1 and R1 as labeled on the circuit get REALLY hot. I used a 2N6107 and some higher-watt resistors, but I'm worried that this circuit isn't designed for what I'm trying to do.
    Should AnalogKid's circuit meet my needs with a different op amp, or is there another simpler circuit that would work better?

    Thanks!
     
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