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car battery + practice amp vs battery powered amp?

Discussion in 'Amps and Cabs [BG]' started by Mindabout, Apr 28, 2010.


  1. Mindabout

    Mindabout

    Apr 11, 2004
    Australia
    A guitarist and I are working on a project to get a set list together and go busking before expanding to a full band and looking for actual gigs.

    Before we have our set list together I need to think about what I'm going to be playing on as we won't have power. I'm leaning towards using a car battery and inverter to power my practice amp as I think this would be most cost effective. I have a car battery charger so recharging would be no problem.

    I'm just wondering if there's any cons to the car battery/inverter set up that might make buying a battery powered amp a better option. Has anyone tried both set ups?
     
  2. Work out the Wattage factors and see if you like the Amps/Hours output. Convert everything to Watts and get a good idea.

    Remember that inverting the battery and adding the sine wave to it cost a lot of extra energy that you'll never get to use as it's radiated out as wasted heat too.

    What size battery and load are you talking about here? It makes a BIG difference!

    If it pencils out OK - you might consider a gell-cell battery that won't leak and can tip over with impunity and leave no holes in your clothes, carpet and wiring.
     
  3. Mindabout

    Mindabout

    Apr 11, 2004
    Australia
    Thanks SurferJoe. I must admit I don't know too much about the technicalities behind using a car battery. My practice amp is 30W. I'd have to buy a battery especially for this so battery size isn't fixed. I was thinking of one of those no-maintenance batteries that don't have the screw caps on them - I guess this might be the same gel-cell battery you are talking about?
     
  4. Exploiter8

    Exploiter8 Demons run when a good man goes to war

    Jan 18, 2010
    Midwest
    Commercial FREE!
    Hi There!
    All-though not exactly what your asking, I toyed with running my Peavey MINX 110 (50watts since I replaced the 8ohm speaker with a 4ohm) off of a SEARS DieHard Portable Power 1150. It's one of those all-purpose car battery jumper, inflater, inverter, etc. It has a built in battery that would power my MINX, but at 50watts electrical draw, it drained the battery in no time. It has the option to hook up to a car battery, which I did, but the buzz/hum, was too annoying to even consider using. I hope others have better results and recommendations! Good-luck!

    X8
     
  5. Maintenance Free and Gell-Cell are totally different animals.

    Only one is OK for aircraft use - and they are priced accordingly! Figure on $250 for a decent sized one.

    If you don't run a Power-Pack type system with a built-in charger, it might not 60 cycle buzz at you - but then again, they are not designed to be RF, hum or REMF free either.

    They are basically for starting engines and running lights that don't give a fig about waves that are off-kilter. Anything that basically stays on one side or the other of the Nullpoint (or ZERO volts) is OK by them!

    Remember that it's only your amp OUTPUT @ 30 Watts, that's not the electrical PULL it take to light it up! No way!

    Take a simple algebraic value and multiply it out:

    Amps (times) Volts = Watts. ​

    So - a 13.2 Volt battery can deliver (say) 200 Amps over the time of an hour. That's approx 2,640 Watts (right?)

    HINT: It won't do that well at all!

    This factor is in a perfect world however - beware! Be VERY aware! Real-time and real-world values are not gonna be that good.

    A battery would obviously never make it to it's real values - at lest on a slow-draw like this - it drops off fast and reliably!

    Then you will have to invert the battery voltage to 120 or so, not forgetting loses in heat, voltage de-ramping, losses and pasting the sine wave (the 60 cycle stuff) to it and you might lose about 15-20% of the total Watts.

    That's about 2,120 Watts left if the battery can hold decent voltage (it won't) and not make the inverter pull more (it will) to compensate for dropping voltage (it's gonna!) from it.

    There's a lot of fudge factors here too! ​

    I figure about 50% one way or - no, there is no OTHER way!

    Your practice amp runs at 120 Volts +/- a smidge, and it might pull about 3-4 (maybe) Amps - OK so far?

    Now convert that to Watts (VxA=W) and it's pulling about 400+/- Watts.

    Then divide that into the Watts you can reliably get from the inverter/battery combo and you MIGHT get about 5.5+ hours.

    And --------- I don't think so, Al!

    But that's assuming that the battery doesn't down-ramp and the draw from the inverter pulls more Watts than I've assumed - and it's a slippery slope at best.

    But so am I.

    Hopefully my math is OK and I don't have a case of "Part-Timer's" brain fade. That's like Alzheimer's, but a lot less predictable.
     
  6. DRafalske

    DRafalske

    Nov 6, 2008
    Hebron, KY
    It'll work fine. Our marching band at school had this exact setup. The battery and inverter were mounted in a little cart that one guy would push behind the bass player while in a march.
    Just make sure it's a deep cycle / marine battery to handle constant charge/discharge cycles.
    D
     
  7. Oh - I didn't say it wouldn't work - just that there's a lot of variables and unknowns here.

    Time-of-running is the issue, well that and the inverter noise problem.

    But it is workable - er, somewhat if you don't push the envelope too hard.
     
  8. Mindabout

    Mindabout

    Apr 11, 2004
    Australia
    Thanks SurferJoe - that's interesting. I guess I can see your concerns based on the unknowns of consistency and thus reliability. I am curious what you would do in the same situation - would you prefer a battery powered amp (that is specifically made to run on batteries)?

    Thanks for chipping in Exploiter8 - I had momentarily wondered about those car battery jumper things but didn't think they'd hold enough charge for any sustained power drain.

    DRafalske - thanks for the tip on the deep cycle / marine battery.
     
  9. You're in Upsidedown Land #2 ? I call NZ #1.

    Are you running 220 volts there? I know NZ does on a single leg-to-earth system to save copper and 'redundant' parts like return legs and such lol.

    .
     
  10. Agreed..... I had the same set up in high school...Peavey Mark IV, Peavey Cab, Peavey T-40........yup 1984.....
     
  11. experimental bassist

    experimental bassist

    Mar 15, 2009
    The particulars seemed to have been covered, the total watts that the amp pulls needs to be taken into account, not just the output rms rating.

    Most amps will have this value in watts on the back near the A/C plug.

    Long story short, sure a battery and inverter (properly sized) will work. The problem is, if you are just using an inexpensive car battery you won't be playing very long.

    And if you step up to a good size marine/deep cycle battery, then you're looking at enough $$$ that perhaps you'd rather have spent on a used Crate Taxi or Pignose "Hog 30" or similar.

    I have a 30 watt Crate Taxi myself, bought it used at a pawnshop and it will run for at least 4-6 hours when it's fully charged.
     
  12. Mindabout

    Mindabout

    Apr 11, 2004
    Australia
    SurferJoe I believe we have 240V as standard here. I'm not sure exactly what you're referencing with "single leg-to-earth system". Our power plugs have three prongs in upside down triangle formation - the bottom one is the earth. I haven't travelled but have never seen plugs with more than one earth prong... :confused:

    DogBone - I have just looked up the cost of a good brand marine deep cycle battery and think you might be on the money. I haven't checked out prices on the battery powered amps but can see it could come in close or better if I can go second hand. I will now go have a hunt around to see what prices I can find locally - I wouldn't hold my breath hoping to find such specific 2nd hand bass gear around these parts though...
     

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