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Cantdosleepy

Battery-powering?

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Hey guys!

I'm hiring a garage to keep a set-up acoustic drum kit. The garage has no power supply. The dream would be to be able to stick a bass amp in there as well and use it as a two-person practice space.

I've seen buskers playing through amps, so I know such tech must exist somewhere.

What's the best way to go about this? Some potential thoughts I had:

1) Petrol generator? - expensive, noisy, smelly. Can't imagine this working, but if any of you guys've got success stories, I'd love to hear them.
2) 'Chargeable' amp? - plug into the mains at home for [i]n[/i] hours, play for 3 hours, take home and re-charge. Do such things exist? How much are we talking?
3) Rechargable battery with 3 pin plug socket(s) in it? - is there a battery I can charge, bring to the garage and just plug my current bass amp into it? Maybe also even a Line6 POD too? This would be the dream. Do such things exist? How much do they cost? Can you get a good couple of hours of rock out of them?

Any knowledge in this area would be greatly appreciated.

Edited by Cantdosleepy

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A car battery, a trickle charger and a power inverter. You can probably sort that out for about £100 and then use your existing bass amp.

Alex

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Hey Alex,

Thanks for the swift response! I've had a quick Google, and there's a bewildering array of all three things you mention above.

Would I have to use a (minimum) 500w continuous inverter to power a 350w head? Any idea of how long a battery would last churning that out? Any idea how long it would take to charge?

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Small petrol generators are pretty cheap and very quite these days.
Having said that you still wouldn't want it in the garage with you, kicking out all that CO!

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So, some quick maths. Assuming I want to play through the bass amp for 3 hours:

Amp: Little mark II - stated output power of this is 300 W RMS @ 8ohm (my cab is 8ohm)

As you shouldn't discharge battery beyond 50% (to keep battery in good nick):

I need 600 W RMS (per hour).

The inefficiency of the inverter needs to be taken into account. I haven't fully explored this yet but going with his worked through calculations assuming 90% efficiency then the inefficiency factor is 1.1.

Therefore 600 * 1.1 = 660

So we need a battery that can deliver a 660 watts per hour for 4 hours.

Battery capacity (Ah) = Current in Amps (I) * Time (H)

Need to know current drawn by our system which is done with the following: I = P/V

660W/12V = 55 Amp

Therefore our battery capacity needs to be:

3 * 55 = 165 Ah

So I'd need a 12v 165Ah battery to get a reasonable session at a reasonable volume?

Is this terrible maths?

Edited by Cantdosleepy

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[quote name='Cantdosleepy' post='522657' date='Jun 24 2009, 03:13 PM']Amp: Little mark II - stated output power of this is 300 W RMS @ 8ohm (my cab is 8ohm)[/quote]

Surely it's the power [b]consumption[/b] rather than the output that is relevant here? Normally written somewhere on the amp? (small plate thing near the power input perhaps???)

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You'll want to use marine or other deep-cycle batteries, as they can be discharged almost fully without damage.

Also, there is no way a 165 Ah battery is going to source 55 amps for three hours -- that's not exactly how the Ah rating is performed. It would be like assuming a tiny little 2700mAh AA battery could actually produce 2.7 amps for an hour -- not going to happen! A load of them in parallel might work however.

What does work in your favor, is that your amp is no way going to draw maximum wattage continuously when it's on.

Just one more point -- it would make sense I think, for this application, if you were to use a 24V series/parallel system instead -- the lower current demand on the batteries will actually mean they last longer per discharge.

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