10 simple hobbyist questions, help please!!

Discussion in 'General Electronics Chat' started by Konduction2, Feb 13, 2014.

  1. Konduction2

    Thread Starter Member

    Feb 12, 2014
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    Here are questions that Google couldn't help me answer. Please help me answer just as many as you can, thank you!! :)

    1) I have a 6VDC brushed motor. Can I run it with 12VDC? I hear both that it would shorten its lifespan, and also that it should be perfectly fine. What's the truth, in my case?

    2) I hear that supplying insufficient voltage to a DC motor will cause it to draw too much current and thus get too hot. Is that because an insufficient voltage drives the motor with insufficient speed&back-EMF, which is actually the direct reason of it drawing too much current? If yes, then would I be right in guessing that supplying an appropriate voltage to a motor but also holding the shaft still would also cause it to draw too much current? If no, then why do insufficient voltages cause motors to draw too much current?

    3) I bought a 5mW laser pointer that works with 2 AAA batteries, which I know is ~3VDC. However, when I take out the batteries and connect it to my PC's PSU in different ways to supply it 3, 3.3, 4, 4.5, 4.8, 4.95, and 5 volts, how come it only works when I supply 5 volts? And I measured it with my multimeter while it's all connected and the "on" button is pressed, so I don't think it's because I messed something up regarding laser diodes being non-ohmic devices. Do batteries have some unique characteristic that accounts for this?

    4) Is there a device that takes in a voltage input and outputs a corresponding position, like a speaker driver, but with a higher displacement range? And I'm not talking about a servo, because data, not voltages, correspond to positions (or so i've heard) for those. I'm looking for either rotary or linear displacement.

    5) Is there a transistor or op-amp I can buy that has similar characteristics to the TIP31C, but maintains a constant voltage and amplifies only the current?

    6) What is the common voltage range for music signal coming out of a desktop headphone jack? Sometimes my multimeter reads between 0 and negative 1.3V, sometimes between 0 and positive 1.3V, and sometimes simply doesn't ever go over 100mV even when I'm playing songs with lots of bass at max volume. And google-imaging music oscilloscopes reveal a wide range of voltages, so I'm confused.

    8) Is there a device that takes a voltage input and outputs a PWM, with higher frequency output corresponding to higher voltage input?

    9) Laser diodes often have duty cycle specs, for example, 45 minutes on and 15 minutes off. If I cool it sufficiently, could I keep the laser diode on indeterminably without reducing its lifespan?

    10) I have an electromagnetic relay that has the label
    "COIL: 24VDC
    CONT: 40A/30A 12VDC". What does that mean?
     
  2. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    1: You can run a 6 volt motor from 12V in many cases without incident.
    You should definitely be safe running it with a chopper pwm control to average the voltage at 6Volts.

    2: At least partially correct. Different motors will have different tolerances.
    There are several issues that are specific to different motors. Some motors have brush issues. Some motors are brushless but have internal circuitry that is voltage dependent. The field interactions depend on the current which will be too resistive at the lower voltage, so the force and torque available are reduced. Lower voltage can cause stalling and stalling causes more heat. Heat burns brushes and coils.

    3. Two batteries will have ≈ 3.3 to 3.7 Volts. Also I would worry that you actually used the -5V from the PSU to get the pointer to turn on. It might have been a polarity issue.

    4. A solenoid? What kind of precision do you want?

    5. What you describe can be done with the TIP31C in a variation of a common collector configuration. It is a basic Voltage Regulator circuit that is built by every electronics tech in their learning labs during training.

    6. The polarity is important. Measuring DC or AC? You should be measuring AC but the multimeter is likely to be confused by AC above 400Hz. Use a test tone if you want a consistent scope reading.

    7. 42.

    8. Look at VCO (Voltage Controlled Oscillators) and PFM or Pulse Frequency Modulation.

    9. Duty Cycle Specs for diodes are more likely to read as 45 Milliseconds on and 15 Milliseconds off. Cooling can be useful but the actual area of the die that is at risk from overheating might not care that the outer casing is bathed in a circulating flow of mineral oil.

    10. The coil of the relay is rated for 24 volts DC. The contacts that are switched by activating the coil, will handle 40A/30A at 12V DC. Seems strange to have less voltage on the contacts than the coil requires. There are likely to be at least two sets of contacts making this a double pole or double throw relay. That is how I would interpret two different current ratings. Double throw would make sense with a relay specific to certain vehicle systems where there is a 24Volt stack that switches between the two 12V batteries in the stack to control where circuits draw their power.
     
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  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Welcome to the forums!

    It depends. If you don't mind burning out the motor go for it. If it stops working then it is not capable of working at 12V. Lots of heat will alert you before failure if you wish to save the motor.

    AFAIK the only thing to worry about is when the motor stalls, or stops turning but still draws current. Then it starts looking like a small value resistor, draws lots of current, heats up, and may burn out. Back when driving model trains (12V DC motors) I got them to creap along at an inch per minute by using narrow 12V pulses. Wider pulses made them run faster

    Unknown, depends on what ths supply really is, I suspect it cannot give enough current. Batteries can give HUGE ammounts of current if but for a short time; they can be dangerous to use: I've seen entire breadboards get eaten by the smoke monster because of a simple short and a battery supply.

    You mean like an old school analog panel meter?

    Huh? The TIP31C is still in production. An emitter follower circuit "maintains a constant voltage and amplifies only the current" albeit for a base-emitter voltage drop (about .7V).

    Did you say "positive 1.3V?" If you are using a DC meter you may not see anything as the signals are fast AC signals with very little (preferably zero) DC. There are meters that can handle music but they are customized to this purpose. However, the signal will only hit a few volts at it's (very brief) peak.

    I dunno nuthin offhand, but there's probably something out there.

    I would expect you could but have no expierence with them.

    "COIL" means it needs 24VDC to turn it on. "CONT" means how much it can switch, looks like the AC voltage rating is removed but it can handle 40A of it, but just 30A at 12V DC. DC ratings are lower then AC because DC causes more arcing on the contacts.
     
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  4. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
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    There is such a thing called a "speaker coil motor" I have no experience with it. It's displacement is small, but can be mechincally 'amplified'
     
  5. Konduction2

    Thread Starter Member

    Feb 12, 2014
    52
    0
    2) Ah okay. So, for a brushed DC motor, low speed is not a problem, but low voltage is (when not stalling)? Does this mean low voltage is not a problem if the motor is not stalling?

    4) A moderate precision is fine. I'm looking to use such a device to tilt a mirror (and bounce a laser) in synch with an amplified music signal. Is a solenoid what I'm looking for? Would I be better off making such a device instead of buying one?

    5) Oh. Could you guys either describe how to make such a circuit or tell me what to google? Should I google "TIP31C voltage regulator circuit" or something like that?

    6) Oh, thanks! DC works sometimes too, for some reason, but the AC Vmeter works consistently. However, when I used the AC meter, my music wavered between 0 and 800 mV. I'm still curious what the normal range is supposed to be.

    7) LOL I did not realize I skipped this number. But thanks, 42 is a good answer hahaha.

    1,3,8,9,10) Awesome! Thanks guys!!!

    I did not expect to get so many responses so quick. Thanks! This forum is awesome!!
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    It will vary with the motor. Generally if the motor is turning and not heating up there will be little risk, but brushes can still be sticking.
    Yes, This would be easier to make than to buy.

    Look at the common collector or emitter follower amplifier.

    800mV sounds like plenty for a head phone jack.

    Jackie Robinson would agree.

    You're welcome.

    The internet will save the world. Helping you build a disco laser is just a bonus.
     
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  7. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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    I thought 42 was a "Hitchhiker's Guide to the Galaxy" reference. :p
     
    Last edited: Feb 13, 2014
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  8. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    It was. But maybe the computer that answered 42 was referring to Jackie Robinson.

    The answer is that everyone gets a chance or else we will all fail. Live and let live. Intelligence and will, can overcome anything except itself.

    Or not.
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,436
    3,360
    We don't mind answering questions. In fact, we love answering questions.
    But ten unrelated questions all in one post is a bit too much.
    Let's have one at a time next time.
     
  10. Konduction2

    Thread Starter Member

    Feb 12, 2014
    52
    0
    I see. Oh okay. Thank you so much!!!!!!!!
     
  11. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
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    I got a sense that these questions were related. Outlining the whole project would help you get things sorted out for yourself and would have made it clear how these questions fit together. Not too late for that by the way.

    I would be more worried about flooding the forum with 10 post threads related to the same project. That would be annoying. One post thread with 10 questions is ambitious but not awful.
     
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  12. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
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    I would recognize that as a better answer than mine.
    I just don't work with relays that much.
     
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  13. MrChips

    Moderator

    Oct 2, 2009
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    I agree with you Pudding. I didn't spend the time to see how the questions are related. If they were then the OP could stick to the same thread, give us the big picture and feed us one question at a time so that we can see where he's heading.
     
  14. Konduction2

    Thread Starter Member

    Feb 12, 2014
    52
    0
    Ah okay. Well thank you all!! Haha I'm making music synchronized lasers. I've already made one that spins a dot pattern lens, but now I'm trying to make one that uses spinning mirrors. Basically, I want to use a laser-mirror setup to draw a circle repeatedly&quickly on the wall, and the circle will grow in diameter with the music.
    I'm working on the solenoid now, which will be used to tilt a spinning mirror - if I run into any trouble, should I seek help in this thread or a new one?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
    2,369
    DC/BLDC drives do exactly that, see the A-M-C site for other applications apart from motors.


    1) if you use a PWM to regulate the maximum current, then it will take double voltage easily, it is over current that burns it out.

    2) If that were the case, almost every DC motor in motion control operation would be in trouble.
    Any thing that increases the difference between applied voltage and generated voltage cause over heating/current, IOW LOAD.
    Max.
     
    Last edited: Feb 15, 2014
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  16. Konduction2

    Thread Starter Member

    Feb 12, 2014
    52
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    Ah okay, thanks!

    What is "DC/BLDC"?
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
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    For DC brushed and Brushless DC servo motors, principally. Most BLDC drives will also work in the DC mode.
    They also can be used for other actuators apart from motors.
    Max.
     
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  18. Konduction2

    Thread Starter Member

    Feb 12, 2014
    52
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    Oops I never actually clicked to post my reply.

    Anyway, thanks! I went to the AMC site and looked at it - seems it would work! I'll use that if I can't do the job cheaper with an NE555 timer chip
     
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