Go Back   Home > Forums > Live Sound > PA Systems

PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 17th June 2012, 11:33 AM   #1
diyAudio Member
Join Date: Jun 2012
Default Troubleshooting sound issues with battery-powered outdoor PA

We have a small setup consisting of two Mackie SRM-450s, two deep cycle 100Ah 12V batteries in series and a 24V 300W pure sinewave inverter. We tested the Mackies at home at very high volumes going through a watt meter thingy in the wall socket, and found that they never really pulled more than 150W or so. Therefore I picked a 300W inverter.

Last weekend we did our first test run, about a 6-hour session, with an added laptop/controller combo for DJing also powered from the inverter. It worked reasonably well, although as we went a bit louder, especially towards the end, we had frequent drop-outs where the sound would just scrounge up horribly. Quickly lowering the volume and slowly pulling it up again fixed it, but soon it would happen again, especially if pulling in something bass-heavy.

I had the wattmeter plugged in at the output of the inverter all the time and never really noticed it going above 200W. Nevertheless, could the problems be due to the inverter being too lowly rated for handling temporary spikes, or was it just a matter of the batteries running out of juice?

Another strange thing we noticed was that one laptop was not happy about being powered from the inverter at all. It just started flashing and beeping as soon as its charger cable was plugged in. A second laptop worked absolutely fine.
  Reply With Quote
Old 17th June 2012, 04:20 PM   #2
diyAudio Member
Speedskater's Avatar
Join Date: Sep 2002
Location: Lakewood, Ohio
Lots of battery chargers have labels warning to not use them with inverters.

Why not use automotive type power amplifiers that are optimized to operate on a 12V DC supply?
  Reply With Quote
Old 17th June 2012, 04:40 PM   #3
Did it Himself
diyAudio Member
richie00boy's Avatar
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Probably the batteries running low, and the inverter not so good at handling peaks from bass, which your watt meter will be too slow to pick up.

You had 1200 watt-hours of juice available. If you pulled 200W at the meter this would be about 240W from the batteries due to the converter not being totally efficient. 240W for 6 hours is 1440 watt-hours.

Maybe you got lucky by not having it so loud for the first few hours!
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 17th June 2012, 04:51 PM   #4
diyAudio Member
Join Date: Jun 2012
Originally Posted by Speedskater View Post
Why not use automotive type power amplifiers that are optimized to operate on a 12V DC supply?
That would be an option but my friend already had the Mackies from a while back and we wanted a way of powering them outdoors.

In fact, I've already bought one of the HifimeDIY Class T 24V amps but no suitable passive speakers yet.
  Reply With Quote
Old 17th June 2012, 04:58 PM   #5
diyAudio Member
Join Date: Jun 2012
Originally Posted by richie00boy View Post
You had 1200 watt-hours of juice available.
Wouldn't that be 2400 Wh? 2x12V in series gives 100Ah at 24V. 200W/24V = 8.3A. 50Ah (half a discharge) / 8.3A = roughly 6 hours (ignoring inverter losses).
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
mobile PA placed in van battery powered joacableman PA Systems 8 9th May 2012 10:08 PM
Outdoor PA -- What type of Speakers ? poynton PA Systems 19 10th October 2011 03:33 PM
outdoor pool sound smdock Everything Else 3 23rd July 2010 03:06 AM
battery powered pa rig question(s) Rent-A-Rocker Everything Else 12 4th June 2008 07:12 AM
Foam, Cardboard Horn? autosub? Ultra-efficient battery powered PA system required! biggerbyfar Subwoofers 2 15th January 2007 09:07 AM

New To Site? Need Help?

All times are GMT. The time now is 07:55 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2