[LAU] [OT] Building a battery powered PA

[andy baxter]

On 28/05/10 21:31, Folderol wrote:
> On Fri, 28 May 2010 11:13:46 +0200
> Jörn Nettingsmeier<nettings at folkwang-hochschule.de>  wrote:
>
>    
>> 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.
>
>    
This is something I'm not sure about - how much power you need for 
busking to a small audience? I'm thinking of using a cheap chinese amp 
off ebay that does 180W per channel, but I'm not sure if this is more or 
less than he'll need. He also wants to be able to use the amp for 
gigging in a small room (which takes about 50 people), so I want it to 
be able to run off mains power as well.