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Voltage regulator.. or Help the noob!

Discussion in 'General Electronics Discussion' started by eheadj, May 19, 2014.

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  1. eheadj

    eheadj

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    May 19, 2014
    Hi guys this is my first one, so be gentle.

    I have just finished a construction identical with the one you can see in this link:
    http://www.garyseronik.com/?q=node/52

    If you go to the BOTTOM of the link's page you'll see a simple LM317T voltage regulator circuit. It is exactly what I've made.

    So to the question:
    This thing has to be portable, so the power source has to be a battery.

    My first thought was to power it of a classic 9V alkaline battery, on second thought I presume that the working time such a battery will give me will be minimal.

    So now I am stuck between buying a 12V lead acid "UPS type" battery OR powering it directly from my car battery (with a direct connection to the poles of the car battery).

    I would prefer the CAR battery solution since it's free (I have it already).
    If I buy a UPS 12V battery, I will also have to buy a charger for it which sums up to approximately 50 - 60 Euros which is double the cost of all the other stuff for this project.

    So, if I use the car..
    a) Am I going to fry my circuit and/or motor?
    b) Am I going to electrocute myself?
    c) Am I going to damage my car's battery?


    Secondly, since I have read that linear regulator circuits waste a lot of energy, will the excess voltage (my motor runs on approximately 3 - 3.8V) which is going to be turned into heat be too much?

    I can't understand the amperage stuff so I'm worried that although the motor "draws" only a tiny amount of current, the LM317T circuit might draw a large current and cause problems to my or my car's or my circuits health.. : )

    Help the noob guys!
    Thanx.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    motorcontrol.gif

    Yes, you won't get much running time from a little PP3-type 9V battery.

    As you mentioned, a linear regulator like that one wastes a lot of energy, especially when you're dropping so much voltage (3V out, 6V drop - the regulator wastes twice the output power, i.e. the circuit consumes three times the amount of power the motor needs).

    One solution (which I recommend) is to use a switching regulator instead of a linear regulator. These are available cheaply on eBay: http://www.ebay.com/sch/i.html?_nkw=adjustable buck regulator

    These have a wide input voltage range, adjustable output voltage, and efficiencies over 80%.

    Even that will probably not be enough to give you a usable running time from a PP3 battry. To work that out, we need to know the power consumption of the motor.

    This may be specified in watts, or it may be specified as a current (in mA, milliamps, or A, amps). You can convert between them if you know the voltage, using the Power Law:

    P = V I
    (or I = P / V)

    where P is power in watts;
    V is voltage in volts;
    I is current in amps (or current in mA divided by 1000).

    The power consumption of the motor will vary depending on its speed (which roughly relates to the applied voltage) and the amount of loading (torque).

    Once you have a figure for power consumption, divide that by the efficiency of the regulator (e.g. for an 80% efficient switching regulator and a 2W motor load, calculate 2 / 0.8) to get the regulator input power, i.e. the battery load power.

    Then calculate the battery load current by dividing that power by 9V (or whatever voltage you decide to use). In the example, 2.5W / 9V = 280 mA.

    Then you can look up the data sheet for the battery and estimate how long it will last at that load current.

    For a PP3 at 280 mA I expect you'd get less than an hour. But repeat the calculations when you know how much power your motor will be consuming.

    It is quite important to know how much power your motor will use. If there's not enough data available, you can measure it with a multimeter on DC current range connected in series with the motor, running from a suitable supply voltage. Remember to load the motor.

    If you already have a car battery, yes that would make an ideal source. Use your cigarette lighter socket. You should add some clamping components to protect the regulator against noise, surges, and "load dump" that is normal in an automotive environment. I can draw you up a circuit for this if you ask.

    With a load of only a few watts on a car battery, you don't need to worry about charging it more than once a week or even less often.

    Using a car battery, you won't fry your circuit if you add a few protection components. You won't electrocute yourself, but I strongly advise against connecting directly to the battery; any mistake and you could burn yourself quite badly because of the extremely high currents available, which can turn a piece of wire (even a thick automotive one) into a nice little bar heater.

    So you won't damage your battery, but your battery could damage you. Have you ever seen guys with half of their fourth finger on their left hand missing? It's probably because they forgot to remove their wedding ring when working on an automotive electrical system. I'll leave you to imagine what happened.

    Yes, heat dissipation in a linear regulator could be a problem. That's another big reason why I recommended a switching regulator. More efficient = less energy lost = less heat.
     
    Last edited: May 19, 2014
  3. eheadj

    eheadj

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    May 19, 2014
    Firstly, thank you for taking the time to answer me so thoroughly.

    I regognize that you are pointing me towards the correct/efficient way to do this, but I will insist a bit on what I have done so far (because I have already done it).
    I mean, if I clear this out, I can go out and shoot tonight!

    Also the swithching regulator you point out is (I presume) a rather abrupt one (since the pot is not precision grade), compared to the one I made which has a 500Ohm, 10 round precision pot that
    can manipulate the voltage with a rock steady accuracy of 0.01V.
    This accuracy is necesarry for small tweaks that will be needed in order for the mechanism to work properly (1rpm steady speed required).

    So, I will measure the current my motor draws and do the calculations but initially from the specs I see that with load, the current it draws is about 0.250 to 0.300A.

    I have done tests at home by powering the circuit (with load) from a transformer (220VAC to 12VDC) and it seems ok, LM317T heats up allright but doesn't overheat to the point of melting everything down.
    If I add a heatsink to it I think it will be ok.

    So the 'new' question is this:
    Is there any reason for the heating to change (increase) if I connect to the car's battery (through the car lighter socket) instead of a transformer???

    I mean: (If I understand this stuff a bit)
    a) I will power with 12V and use 3.5V and NOT use 8.5V
    b) I will use 0.300A*3.5V = roughly 1Watt??
    c) I will have to dissipate 0.300A*8.5V = 2.55Watt?? Not too much I think, right?

    Are the above calculations correct??
    I don't care about heat and efficiency as long as it does not affect the motor and circuit since the car battery can handle it and takes care of itself while I drive.

    Lastly, you say: "Using a car battery, you won't fry your circuit if you add a few protection components."

    Which are these? Can you please explain?

    Thanks a lot,
    eheadj
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    No; I think those switching regulators have ten-turn trimpots and can be adjusted pretty accurately.
    Right. I meant to mention this before. A standard DC motor will not give a stable rotation speed. You would be much better off using a stepper motor, or a brushless motor, whose speed can be controlled by a quartz crystal. A high gearing ratio can be used to minimise the jumpiness of the telescope due to the discrete rotation angles of the steps of a stepper motor. You can try with a brushed DC motor initially but I think you'll find the rotation speed is not stable enough.
    OK, good.
    OK, good.
    Yes. The car battery voltage will normally be somewhat higher than 12V but that's close. Heat dissipation running from a car battery will be lower than running from a 12V AC transformer with bridge rectifier and smoothing, because 12V AC corresponds to around 15V DC. So you'll be fine.
    OK.
    Here's a suggested circuit with protection components. I may be going overboard with the protection but better safe than sorry.

    268688.001.GIF
     
  5. eheadj

    eheadj

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    May 19, 2014
    Wow, thanks for the circuit. I will implement.

    If at sometime I overdo it with questions, please say so.

    You said:
    "Right. I meant to mention this before. A standard DC motor will not give a stable rotation speed. You would be much better off
    using a stepper motor, or a brushless motor, whose speed can be controlled by a quartz crystal.
    A high gearing ratio can be used to minimise the jumpiness of the telescope due to the discrete rotation angles of the steps of a stepper motor.
    You can try with a brushed DC motor initially but I think you'll find the rotation speed is not stable enough."

    Well, this will be "plan B" if plan A (which we are talking about now) doesn't work.
    In general though, it does seem to work accurately enough requiring only minor tweaks every 5-7 minutes or so. Which I consider acceptable.

    I will probably try "Plan B" anyway just for the learning experience.
    I have a bipolar stepper motor of unfortunately unknown specs (from an old printer), an Easydriver v4.4 stepper motor driver and a raspberry pi.
    So far I have done tests with Rpi, ULN2803 and another small unipolar stepper + python and have managed to drive the stepper as I need through a headless RPi
    by buttons connected to GPIOs. I don't know enough about resonating crystals you mentioned yet so we'll see..
    But I have a BIG new set of problems and questions for that one also, so when the time comes.. but it's not the time yet for that one.

    Questions about the circuit you drew:
    1) C1 is a polarized electrolytic capacitor?
    2) The R1 D2 part and the R2 D3 part seem to be repeating, although I noticed the different zener diodes. What is the purpose of having 2 of them?
    3) I noticed you changed the pot and resistor values (I have a 500Ohm pot), is that necesarry?
    Having to wait another month or more for ebayChina is going to kill me I think.. :)

    4) Quoting Wikipedia: "In packages with a heat-dissipating mounting tab, such as TO-220, the tab is connected internally to the output pin,
    which may make it necessary to electrically isolate the tab or the heat sink from other parts of the application circuit." Do you think I have to do this?
    5) Yesterday I measured the current. I got some strange results. I will try to post a pic later today so that you can see.

    The multimeter was on this setting - - - (A) [Scale:200mA] and the measurement showed 0.07 (Amps??). I hope I haven't messed up with the scale..

    5) Which software do you use for circuit drawing?

    I can go on with questions, but I will stop now..

    Thank you for your time, I will feedback with results.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi Eheadj

    I'm going to jump in here'
    Kris may not have realised, but this particular astro camera drive system has come up a number of times over the years on this forum, and have seen it on other forums as well.

    There isn't anything wrong with the circuit as shown in your link and works quite adequately when the build instructions are followed

    I hope you understand you cannot use just any old 3V motor. Did you actually get the motor type listed in the article ?
    Note its VERY SLOW rotation speed 4 RPM. ( it already has some gearing built into it) and note the gearing to further slow that down to 1 RPM

    The circuit will run quite happily off your 12V car battery or for more portability you could use a 12V 7.2A/Hr sealed lead acid or gel battery

    1) Yes C1 is a polarised capacitor ... an electrolytic
    2) Kris's R1/D2 and R2/D3 are just his over cautious circuit protection :) The LM317 can handle up to ~30 or so volts on the input so excessive protection isn't really needed ... but at least R2/D3 would be good inclusion ... see that D3 is a 15V zener diode
    3) Kris's 1k pot will give a wider variation in voltage adjustment
    4) depends on how you are going to mount it all metal box ? plastic box ?
    5) Kris can answer that :) .... I use MSpaint preferably the Win XP version ... the Win7 version sux haha

    cheers
    Dave
     
  7. eheadj

    eheadj

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    May 19, 2014
    Thanx Kris, Dave,

    All clarified now..

    You said:
    "There isn't anything wrong with the circuit as shown in your link and works quite adequately when the build instructions are followed
    I hope you understand you cannot use just any old 3V motor. Did you actually get the motor type listed in the article ?
    Note its VERY SLOW rotation speed 4 RPM. ( it already has some gearing built into it) and note the gearing to further slow that down to 1 RPM"

    Yes, I know. The motor I use is an [ebay china] 3V, 1/64 geared motor that works at 2.4RPM and I further reduce with [2 old printer] gears 1/2.5 so RPM is ok.
    The circuit [as the link has it] is done and works nicely. The mechanical construction is done and works very well [hand tested]. All is assembled and ready to go catch some stars!!
    All that I need is a (cheap and safe) power source --> Car battery = [cheap], protection from Kris's circuit = [safe]. A, o.k.!

    eheadj
     
  8. davenn

    davenn Moderator

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    ok from the other side of the story .... mainly cuz I'm an astronomer and astro photographer...

    what camera are you planning to use on your platform ?
    have you done any star photography at all so far ?

    just trying to get an idea where you are at

    Cheers
    Dave
     
  9. eheadj

    eheadj

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    May 19, 2014
    Small world.. or better small Universe.. :)

    Well I guess not really, I am starting as we speak in astrophotography and electronics simultaneously. [maybe in film developing too, Ill see how it goes, one step at a time)
    I have done some night photography which I like a lot and since I was always fascinated by the Universe it kinda came on its own as the next step.
    I have tried some multistacks with my Lumix point n shoot and saw that i had to upgrade due to noise problems.
    But since there's no money for real equipment [e.g. Canon EOS 60Da] (I live in Greece and yes we don't need to start the financial crisis conversation)

    I decided to go for film. [Yes, I think I'm brave too].
    So I bought an old reliable Yashica FX3 Super, 3 cheap lenses (50mm Yashica ML 1.9, Tamron 28 - 85mm and a 135mm Makinon [last one is a bad choice I know]).
    I built my barn door tracker, and I'm ready to go..

    I have no idea what kind of results I will have with this equipment.
    I have seen online guys that have astonishing results on film but I guess I'll have to shoot at least a few dozens of rolls before having something worth of mentioning, I am a patient guy.

    Many difficulties here since: Film is dying, Labs process only C41 films, the diversity of available films is small... etc, etc.

    I don't know how it will endup, for me the trip is important too, not only the destination. (I have learned a ton of stuff by all trying this out)
    I'll post as soon as I have a worthy one. [if the mods don't kick me out] :)

    eheadj
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Thanks Dave for answering those questions.

    Yes my input protection is over-cautious, but automotive "12V" can be a lot higher than 35V during short spikes (due to heavy current flow and inductance) and under a condition called load dump (https://en.wikipedia.org/wiki/Load_dump). It is the reason that voltage regulators intended for automotive use are specified with maximum input voltages between 70V and 100V.

    For schematics, I use an old MS-DOS program called OrCAD/SDT III from 1988. I like the clean, simple look, and the absence of distractions like "fruit salad" colouring, and I've never found a bug in the program. It is (was) commercial software, so it's not available for download.
     
  11. davenn

    davenn Moderator

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    Its probably not too much of a worry, as the car isn't likely to be running at the time, and its definitely not going to be travelling along the road ;)
    The headlights wont be on as that will destroy nite vision/dark adaption and also destroy any photos

    You still have a puter running MSDOS ? far out!! :)
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I would rather avoid the requirement for him to unplug the regulator from the cigarette lighter before using the car. That's the kind of thing that can be easily forgotten.
    Well, I do have a desktop machine that dual-boots with MS-DOS, but on my main computer, I use DOSbox 0.74 to runOrCAD/SDT III under Windows 7.
     
  13. davenn

    davenn Moderator

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    I would prefer that it doesn't even go into the cig. lighter outlet
    it is much better off being able to be clipped directly across the car battery or whatever battery he wants to use :)

    I think you are still not totally realising what this thing is for .... its for doing astronomy photography ;)
    You have to be able to take it to the dark site away from streetlights etc.
    The BEST place for the regulator board/and its housing will be on the base of the camera mount
    that way it (it = the mount, tripod, camera) can be taken well away from the car and run off a SLA etc .... in his back yard out on a dark track where the car cannot reach etc. That ensures total freedom and portability and that is the really important point

    I find essential to be able to do that with my computer controlled telescope system and he is likely to find the same.
    The car battery is not always going to be able to be used. I only use the car and its battery if its totally necessary.
    The rest of the time ... including my own back yard, where the car cannot get to, I use a SLA

    cheers
    Dave
     
  14. eheadj

    eheadj

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    May 19, 2014
    The more you guys write, the more I lean towards just going out and buying a small SLA and get it over with.
    Is the kind of protection that Kris suggests needed even for a 2 or 3Ah Sealed Lead Acid battery?

    I will try to upload a pic of the whole thing hoping I don't violate any forum rules.
     

    Attached Files:

  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    That's a good idea. No, you don't need any protection with a separate SLA battery.
     
  16. BobK

    BobK

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    Nor for a car that is not running.

    bob
     
  17. eheadj

    eheadj

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    May 19, 2014
    Finally I tried with the car battery [with a non running car] and all worked very well.
    For the time beeing I think this will do.

    Thanks to all.
     
  18. davenn

    davenn Moderator

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    lookin' good mate :)

    I'm looking forward to seeing some of your photo results .... feel free to post a couple of your best pics either in this thread or create a thread in the off-topic section of the forums :)

    cheers
    Dave
     
  19. eheadj

    eheadj

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    May 19, 2014
    @KrisBlueNZ,

    You said: "You would be much better off using a stepper motor, or a brushless motor, whose speed can be controlled by a quartz crystal."

    Since plan A seems to work well, I thought of giving the stepper a try. I googled and read quite a lot and as usual, as a noob, I got more confused than I was...

    The theory:
    I would like to control my stepper through the Easy Driver v4.4 I already have. ( http://www.schmalzhaus.com/EasyDriver/ )

    But I would like to pulse (5V pulses) the easy driver from a [precision] pulse wave generator (crystal? or are there other choices as well?).

    From what I've understood so far, and by SUPPOSING (don't know for sure) that I have a 200 steps/rev stepper,
    I would have to make a circuit with an e.g. 1MHz crystal and use a "divide-by-n counter" IC to divide the frequency to the one I want to use.

    Do I have any errors in my thought? Is all this implementable by common mortals as myself, or goes beyond the "simple circuit" stuff?

    By googling I found this: http://www.ebay.ie/itm/Hi-Precision...201?pt=LH_DefaultDomain_0&hash=item3382b1a4a9

    What do you think? I will keep on reading about all that.. just want a correct direction.


    @davenn, will post a couple when I have something. The tracker works very well (at 10min exposure stars are perfectly round), but I had light pollution in my first test attempt. Will have to find darker skies..

    Maybe I should have opened a new thread about this..?

    eheadj
     
  20. davenn

    davenn Moderator

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    Sep 5, 2009
    the same subject ... the same thread its all cool :)


    D
     
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