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Electronics Project Help!

Discussion in 'General Electronics Discussion' started by Felix Murray, Jul 14, 2015.

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  1. Felix Murray

    Felix Murray

    2
    0
    Jul 14, 2015
    Hi everyone,
    I don't know what I'm talking about very much, so if I make a mistake in explaining, bear with me :)

    I'm a busker and a student, and want to create a (reasonably) portable power supply that I can take around with me when busking. All I need is to power a small amp (which has a 3-pin mains plug) through which I play backing tracks; I'm a jazz trumpet player so only need a little accompaniment, and a USB phone charger to keep my phone charged so it doesn't run out of battery halfway through playing a track! I have considered just buying a battery powered amp, which would solve this problem, but, 1) I don't have a large budget (under £100) and I can't find a decent battery amp loud enough to busk with for that budget, and 2) I enjoy technology and the idea of building something to solve this problem sounds quite fun! I have a small amp already, don't need another one, and want to use my battery setup for other things too, anyway, like charging a phone while camping, for example.

    From my research so far I have found a few things, correct me if I'm wrong:

    Things called inverters can change the output from a 12V (car?) battery into mains AC current that will power a 3-pin plug - they come in different power outputs, I think I would only need one that does 150W given the amp I'm using is very small. The inverter I'm looking at is here: http://www.halfords.com/motoring-tr...ers-power-packs/12v-150w-inverter-with-2a-usb
    I like that one because it has a USB slot too, meaning I could easily charge my phone at the same time.

    Potentially, I could attach a solar panel that would trickle charge the 12V battery while I'm busking, meaning that I wouldn't have to manually recharge it (hopefully). This would mean I need a solar charge regulator, so I don't overcharge and damage the battery. I like the solar panel idea so want to include if at all possible.

    I can connect the 12V battery terminals (assuming I would need a car battery, but they're very big, will a smaller 12V battery work, like this one? http://www.amazon.com/ExpertPower®-...1415546997&sr=8-2&keywords=12v+sealed+battery) using crocodile clips to the 150W inverter, which would then produce a mains output voltage that would power a small amplifier, and a phone.

    So, here's my circuit idea:

    Solar panel (trickle charge)---solar charge regulator---12V car battery or smaller 12V battery---150W inverter--- small amplifier/USB phone charging cable

    Will that work? I have no idea whether it will. I'll probably make a box/case to carry all this around in as well, hence why I want it to be as compact as possible - the solar panel can just sit on top so that's ok.

    Thanks so much
     
  2. chopnhack

    chopnhack

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    354
    Apr 28, 2014
    I would suggest wheels, carrying this around will not be fun as you will probably need the car battery or two to feed an amp! The solar panel is a great idea, but you will need a fair sized one to recharge your battery. Perhaps you should leave that as phase two of the project and focus first on getting some numbers. Are you able to get a reading on how much power your amp consumes at whatever sound level you will be playing? Do you have a multimeter/ammeter that you can take a reading?
     
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Food for thought. A 3 foot x 3 foot solar panel will provide between 100 - 150 Watts depending on the panel if you are in direct sunlight. If you get a 1 foot by 2 foot panel, your only getting 20-30 watts... So it won't hold up the amplifier unless you get a large panel.
    Additionally... the battery should be sized for the maximum current draw, and the capacity (ie.. how long you want to play)

    The battery you linked is a 7Ah battery... so doing some basic math, a 12V battery witha 7Ah capacity hold about 84Watt hours. This means that pulling 100Watts from that battery will kill it in under an hour. Additionally... pulling 100 watts from that little battery works out to be over 8 Amps, which may be too much of a pull for that battery.

    As a comparison here... that little battery would take well over 4-hours in direct sunlight with the inverter and amplifier turned off to fully charge with that little 1 foot by 2 foot solar panel...

    Something needs to change. You either need a big battery, or a big solar panel. To be honest, I would avoid the solar panel all together. Travelling with it introduces risk of it breaking, and a size small enough to travel with won't do much in terms of providing power for anything other than your cell phone.If you can manage to get a small battery charger, just plug in your device at a coffee shop or any outlet you can manage to find to top up the battery.

    Other than that... a battery powered amp is the next stop. (Heck... you could look at some small 'mono' or stereo car stereo amplifiers. No need for an inverter as they are built for 12V.)

    If you really want to go ahead you need to know the power draw of the amp, and how long you want to be able to play. The solar panel size will define how long in-between sessions you will have to wait to play again.
     
  4. AnalogKid

    AnalogKid

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    722
    Jun 10, 2015
    Adding on - nothing will get you longer battery life than an amplifier designed from the ground up to be battery powered. I don't know if you know the differences between traditional, linear audio amps and newer, switching (Class D) amps, but there are many and this application is why. I know you want to build not buy, but...

    Also, 150 W? Really? You'll need a 2nd set of wheels for the speaker. Are you working a street corner or a gymnasium? I'm not picking on you, just questioning your requirements. Granted the amp won't be making 150 W continuously, but still, the #1 way to extend operating time is to reduce the load.

    ak
     
  5. davenn

    davenn Moderator

    13,901
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    Sep 5, 2009
    gosh
    Felix, talk about trying to make very life difficult for yourself

    you only need 10 - 30 W range for busking use
    an amp with that power output level is an easy thing and a 7.2A/H battery would give a couple of hours of use

    here's one example of many from ebay and a speaker and cabinet and your are in business

    http://www.ebay.com.au/itm/1-X-25-W...92?pt=LH_DefaultDomain_15&hash=item19e789ad4c

    you probably would need a preamp is using a microphone
    a dual channel preamp 1 mic input and 1 line input would be ideal


    Dave
     
  6. Martaine2005

    Martaine2005

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    May 12, 2015
    I think there is a communication error going on here.
    He said he has a small amp!
    The 150w is an inverter, which are small too.8"x4".

    But it all depends on the amp he has.
    So what amp have you got?

    Also, these cheap inverters are being advertised as 'msw'.
    The general public wont have a clue, and that's the idea!!

    The 'msw' Modified Sine Wave, is far from practical for sensitive electronic products.
    I have a 150w msw inverter and it plays havoc with my iphone. It doesn't charge my laptop if the battery is very low and even dislikes charging my cordless tool batteries.
    I have several small guitar amps, I am going to see if the inverter will interfere with the amp.

    Martin
     
    davenn likes this.
  7. Martaine2005

    Martaine2005

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    May 12, 2015
    Also, if your budget is £100, I bet you can find one of these cheaper somewhere.

    Martin
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    I'll put it down to the bronchitis ... am not thinking or reading clearly :(
     
    Martaine2005 likes this.
  9. AnalogKid

    AnalogKid

    2,540
    722
    Jun 10, 2015
    Yeah, about that inverter - using a circuit to turn low voltage DC into true sinewave power so that another circuit can turn it back into low voltage DC to run the amplifier electronics seems just a tad inefficient. OK, make that very inefficient. If the TS wants to build something, open up the amplifier, find the bulk DC filter, remove the rectifiers before the filter, and add connectors and wire to inject external DC directly into the regulator. Even if you have to buck or boost the external DC to be what the amplifier requires, that will be many times more efficient than a sinewave inverter and a linear power supply in series.

    ak
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    yeah severely inefficient
    its going halve the battery life !!
     
  11. Martaine2005

    Martaine2005

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    May 12, 2015
    Cough cough Dave.I didn't realize you were ill.Sorry,
    I take back every thing that may have been construed as non constructive.
    I wish you well Dave and hope you feel better soon.

    Martin
     
  12. davenn

    davenn Moderator

    13,901
    1,971
    Sep 5, 2009
    all cool buddy :)
     
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