Re: [LAU] [OT] Building a battery powered PA

From: Ken Restivo <ken@email-addr-hidden>
Date: Sat May 29 2010 - 02:12:30 EEST

On Fri, May 28, 2010 at 09:31:03PM +0100, Folderol wrote:
> On Fri, 28 May 2010 11:13:46 +0200
> Jörn Nettingsmeier <nettings@email-addr-hidden-hochschule.de> wrote:
v>
> > On 05/27/2010 06:36 PM, Bob van der Poel wrote:
> > >> A friend of mine was talking about how he would like to be able to busk with
> > >> his keyboard, and I said I would look into the possibility of building him a
> > >> battery powered PA for it. Does anyone have any suggestions for good ways of
> > >> going about this? We would like to keep the cost as low as possible.
> > >>
> > >
> > > How about an off-the-shelf UPS? Don't know how big you'd need, would
> > > depend on the gig time, etc. There is probably a way to calculate that
> > > :)
> > >
> > > The consumer UPS units I've see all have lead-acid (sealed) batteries
> > > and are quite reliable.
> >
> > not really recommendable for a permanent setup. with an ups and standard
> > mains equipment, you will waste battery (and carry dead weight) twice:
> > in the inverter that generates grid voltage from the battery, and in the
> > PSUs of your gear that will re-transform the precious grid voltage back
> > into low-voltage DC. throw out the middle man.
> >
> > the nice thing about car equipment (as a previous poster has suggested)
> > is that all the gear is standardized to work at 12 volts dc. many car
> > radios have line ins these days (for file players etc.). it's easy to
> > hook up a small mixer here - you should be able to find a cheap one by
> > the Brand That Shalt Not Be Named or one of the other manufacturers they
> > steal their designs from - i've seen a few that take 12v dc.
>
> How much sound output power do you actually need? In bridge mode an
> amplifier running off 12V can deliver a maximum of 18W RMS into 4ohms.
>
> Here in the UK Maplins supply a suitable power module (they call it 40W
> - that's peak power) very cheaply - 15.99ukp
> http://www.maplin.co.uk/Module.aspx?ModuleNo=37737
>
> It's actually a Kemco product. I don't know how available that would be
> in other countries.
>
> At 500mV sensitivity it will probably be a pretty good match for
> direct connection to most keyboards. If not, a small buffer amp could
> easily be patched in.
>
> I don't recommend using a car battery. They are not designed for steady
> discharge, but for short bursts and long recharge times. Although
> initially more expensive you would do a lot better getting a sealed gel
> type lead-acid battery with suitable charger.
>

An Optima or other AGM car/boat battery would work well, but they are pricey and HEAVY.

There are large Li/Ion batteries available that might work, designed for electric bicycle applications, but they tend to run at 24v or 48v or some odd voltage.

Or, you could just buy a Crate busking amp. Those things are A/B amps (I think) can run forever on a few D batteries.

-ken
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Received on Sat May 29 04:15:03 2010

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