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Dumb newbie 12v to 9v question

Discussion in 'General Electronics Discussion' started by spoonman, Oct 21, 2011.

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  1. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    Hello,

    I am pretty much a dumbass when it comes to electronics, so excuse my ( current ) stupidity :) I have a couple of questions that I hope someone can help me with whilst I try to relearn what i should have learned in physics, instead of drawing pics of my teacher and looking out the window!

    I am running a 60w lamp, and a Roland TD-6 electronic drum kit, off a 12v leisure battery, via an inverter. I only plug in one of these at a time. The drum kit has an ac transformer plugged into the inverter, at 9v 1200ma.

    I want to get rid of the inverter, keep the battery topped up with a decent sized solar panel, and connect a small led lighting circuit to the battery ( I think I can manage that), and it is clearly ridiculous to go from DC 12v to AC 240, and then back down to DC 9V for the drum kit, so I want to power that device straight from the battery.

    Firstly, I have ‘blown’ three AC transformers with this setup, and would like to understand why this is. On a full charge the drum kit works beautifully. When the battery voltage drops to around 12.3v ( I keep an eye on it and endeavour to recharge it around this time ), and I plug in the drum machine, the display flickers. It will either flicker faster and faster until it starts, or it will just continue flickering until I give up and turn it off and back on. At this point I discover that the ac adapter no longer works. However, if I plug in the 60w bulb it will continue to give clear, consistent light. Huh? What the hell? How do I break an ac adapter with not enough power?

    My second question is related to bypassing the need for an ac adapter. Can I take a + and – off the battery and power the drum kit that way? I’m guessing I’d need an inline fuse and some kind of voltage regulator to drop from 12v to 9v. But, I don’t want to shaft my drumkit. This might sound like a dumb question but I’m asking for advice because I am basically a monkey that can memorise how to connect things together – but has no idea how they work.

    Thanks in advance…I realize that you might get a lot of dumb questions on here, but I am going to sit down and learn the rudiments of electronics properly in the next couple of weeks, honest!

    Cheers

    Spoonman
     
  2. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    12 to 9 volts

    Hi spoonman.
    I take it your not near any mains power outlet, as your using a battery and an inverter.
    You could drop the 12 volts to 9 volts with a regulator circuit, but as the battery is 12 volts the difference between input to the regulator and output is right on the lower limit for normal function, 3 volts you need to drop to get the 9 volts is ok, until the battery starts dropping again, then the regulator cant maintain the steady 9 volts and will start dropping as the battery does.

    Solar charging is fairly slow, if you have power hungry music gear.
    You could use a second battery in parallel to increase current and running time, in series the voltage to drop to 9 volts is to high, the regulator might, or probably struggle to cope, its the difference in voltage to the input, and what you want out, typically most regulators are fine if kept with an input 3 to say 5 volts above what voltage you want out, i would say yes to a voltage regulator circuit, but double the battery's current capability. Other members might come up with a better idea.
    Oh and it would be handy to know how much current your gear is using at 9 volts, there should be a label on there somewhere. First start to your new found electronics study, the link below, this will give you some idea on battery configurations.
    Talk more on a regulator when you can find out the total current your drawing from your music gear.
    Dave. :)


    http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations
     
  3. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    Thanks for your reply Dave,

    You are right - the battery is in my shed, and its 30 meters from the house through all sorts of obstacles making it too far to safely route power.

    I just bought a hefty 15w solar panel and I think it will keep the battery topped up. I only use the drumkit for about an hour a week. I'm definitely considering a second battery though....seems a good idea, thanks.

    As for current, I am just using the drum kit for direct recording into a precharged laptop, so nothing too demanding on the battery - no ampification is taking place. The original AC adapter says it requires 9v 1200ma.

    Cheers in advance,

    Spoonman
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You mean the original adapter says it can supply up to 1200mA, but that on the back of the Roland TD-6 it says it needs 9V 1000mA - center negative.
    It would be best to use a heatsinked 9V regulator between the 12V battery and the Roland. Google 7809 regulator. The circuit is extremely simple.

    The reason electronic power supplies may fail when operated from inverters is that most cheap inverters doesn't produce a sine wave, but a square wave.
    It may be called a "modified sine wave" but it's nevertheless quite square. See attached pic for the difference. All are 120V effective but notice peak voltages etc.
    The peak voltage from a modified sine wave inverter will vary with battery voltage. It's often the peak voltage that is rectified and used by power supplies.
    As the voltage drops the inverter will compensate with a wider pulse to maintain 120V effective. There are harmonics in the square waveform that may stress PSU filters.
     

    Attached Files:

  5. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    Thanks Resqueline

    Yes, you're right sorry, the TD-6 requires 1 amp - I checked the manual.

    THANKS SO MUCH for explaining the adapter failure for me - it makes sense now that the inverter ( which is indeed a cheap mod sine wave and therefore probably square ) was the culprit.

    The 7809 regulator does exactly what I need and is cheap as chips! Do I still need an inline fuse though?

    I'll have a go at it this week. Thanks for the help and encouragement.

    :)

    Spoonman.
     
  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It's always wise to have a fuse (2-5A) near such batteries, before the wires can have any chance at all of making a short. Heatsink the regulator for 4-5W of dissipation.
     
  7. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    Ok, I got a 7809, some wire, 1.6amp fuses - but couldn't get a heatsink. The guy didn't have anything in stock, and didn't know which one was best anyway.

    I googled around when I got home. Do I need one of these twisted vane things?

    http://www.maplin.co.uk/twisted-vane-heatsink-forto126-2592

    Also, I was planning to solder the wires straight onto the 7809 prongs, and then stick it to a heatsink with thermal compound, and then screw the whole thing to a piece of wood. Does any of that sound unwise? ( Did I mention that I don't really know what I'm doing? )

    :)
     
  8. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi again spoonman.
    If you have a flat piece of aluminum or copper sheet about 2 - 3 mm thick, say 6 "x 4" or a little bigger would suffice, thicker is better, and a part of it dead flat so the regulator will bolt up to it.

    You should use a little heat sink compound, a white thermal paste, a thin layer on the back on the regulators case, where it bolts up to the heat sink, bolted up dry might cause access heating problems.

    The case metal is a negative conductor IE volts - .
    If your running above 1000 milliamps, 1 amp, i would opt for a 2 amp regulator, or a variable voltage regulator, the voltage is fixed with a horizontal or vertical preset potentiometer, or fixed value resistors, the 2 amp regulator will be the easiest route.
    The regulator off 2 amps is the L78S09CV, Link below, the other regulator is an LM317, or LM338T, or LM338K, there are others, but for simplicity these should pose no problems.

    The L78S09CV is the same as the 7809 but a 2 amp version, i suggested it as 1 amp, 1000 milliamps is at the 7809's limit, no room for extra current.
    Any way the L78S09CV is available at all the electronic stockists, For the circuit google the regulator for the data sheet, the simple power supply will be on it.
    And as stated yes you must fuse the supply.
    Dave. :)

    www.maplin.co.uk/2a-positive-fixed-voltage-regulators-7939

    PS, the heat sink in your maplin link is way to small, thats ok for a few hundred milliamps, but not 1000 milliamps. As i said a piece of aluminum or copper plate will be fine.
     
    Last edited: Oct 24, 2011
  9. spoonman

    spoonman

    7
    0
    Oct 19, 2011
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Hehe, I guess you're spot on, it being ten times larger than you need. It's a waste of aluminum allright but nevertheless they can't be too big, it'll just run ten times cooler.
    The heatsink in the maplin link is just a little too small (21 deg. C / W), I guess you'd be ok with one having a thermal resistance of 16 deg. C / W (would run hot) or less.
     
  11. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    The 7809 regulator didn't work,and the drum kit display just glowed around the edges like it wasn't getting enough power. I guess 1 amp output wasn't enough. After an hour of messing about, I gave up, joined the wires together, crossed my fingers and hoped the Roland had some kind of internal regulator to handle the 12v.

    It did, so thankfully, I am now powering my drum kit off a car battery. :)

    Thanks for your help. I'll try a 2 amp 7809 another time.
     
  12. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi again, your drum kit might be expensive to replace, drop the battery voltage with a few 3 amp silicone diodes, each diode will drop the voltage by 0.7 volts, try 4 diodes in series on the + volts from the battery, you will drop 2.8 volts, so down to 9.2 volts, if thats to low remove one diode, all diodes forward biased, simple to do, dont even need a board to mount them on if you dont want, copper strip is tidy but not essential.

    Its really a super easy solution to not wreck your gear.
    Dave. :)
    PS, Its really easy, and costs penny's or cents dimes or what ever currency you have.
     
  13. spoonman

    spoonman

    7
    0
    Oct 19, 2011
    Sounds like a plan! I'll get some this week and give it a go. So we're looking at 0.7w of heat on each diode on a 1 amp circuit...should be ok I guess. Cheers Dave!
     
  14. davenn

    davenn Moderator

    13,877
    1,964
    Sep 5, 2009
    just make sure you use diodes that can handle 1A of current. meaning 1N4001 to 1N4007 series wont do as you would be running them at their max
    preferably a 2 amp diode.

    Dave
     
  15. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    No not watts, each diode drops the voltage by 0.7 volts the diodes you could use are 1N5401, 1N5402, 1N5403, 1N5404, 1N5405, 1N5406, 1N5407, 1N5408, are all 3 amp silicone rectifier diodes, available at nearly all component stockists.

    A car battery fully charged voltage is a nominal 14.4 volts DC, ok for 9 volts gear, some gear maybe, but a gamble, add a extra diode if its still to high, or get a 2 amp voltage regulator like the LM78S09CV, or a 2 amp or higher current equivalent.
    Dave. :)
    PS. ( 4x diodes in series forward biased )
    volts + ------->|------>|------>|------>|------- to + volts drum machine.

    12v 0.7 0.7 0.7 0.7 = 9.2 volts
     
    Last edited: Oct 31, 2011
  16. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    As the Dave's said it's possible to use diodes to reduce the battery voltage. Although it's not ideal it's possible the drum machine is happy with it, who knows.
    But the assumption that the venerable "1A" 7809 is incapable of supplying 1A (or even 1.2A) is wrong. From 11.5V to 24V input it's actually able to deliver 2A.
    So my assumption is that you have connected the 7809 up wrong. Check out the attached diagram to verify the correct way of using it.
     

    Attached Files:

    • 7809.GIF
      7809.GIF
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  17. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Yep thats the schematic diagram, try wiring it up again as said, the 2 amp 78S09 will also fit in the same, the regulators legs out are same as the 1 amp 7809.
    Dont forget a heat sink, aluminum or copper plate would do say 6" x 4" about 1/8 inch or so thick.
    Dave. :)

    PS, if you go with the regulator i really would use some heat sink compound on the back of the regulator, thin layer is fine, thats sold in small tubes as well. General purpose compound is fine.
     
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