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Author Topic: Very surprised how much sound I could run off a 400w power inverter  (Read 4217 times)

Brian Jojade

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #10 on: October 13, 2016, 02:11:34 pm »

What you're learning is that the average power draw of an amplifier is nowhere near the sometimes hugely over-rated peak number power rating of the amps

With normal recorded music, your average power draw is usually 1/8 power.  So a 1000 watt amp is only delivering about 125 watts AVERAGE when you see the clip light the first time. Efficiency of the amplifier design would determine the current draw from the wall.  An amp with 80% efficiency would be drawing just over 150 watts, average.

While the current draw isn't consistent, capacitors in the amp help average the actual draw.  The larger the capacitors, the more even the draw from the wall would be.  An amp with no reserve capacitors would have to have all the power needed always available. ie, if you need 1000 watts output for a split second, it would have to pull 1000 watts from the wall.  If the wall can't provide, the amp can't amplify.
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Brian Jojade

Scott Holtzman

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #11 on: October 13, 2016, 02:42:29 pm »

What you're learning is that the average power draw of an amplifier is nowhere near the sometimes hugely over-rated peak number power rating of the amps

With normal recorded music, your average power draw is usually 1/8 power.  So a 1000 watt amp is only delivering about 125 watts AVERAGE when you see the clip light the first time. Efficiency of the amplifier design would determine the current draw from the wall.  An amp with 80% efficiency would be drawing just over 150 watts, average.

While the current draw isn't consistent, capacitors in the amp help average the actual draw.  The larger the capacitors, the more even the draw from the wall would be.  An amp with no reserve capacitors would have to have all the power needed always available. ie, if you need 1000 watts output for a split second, it would have to pull 1000 watts from the wall.  If the wall can't provide, the amp can't amplify.

I have an old Samson SX series amp on the bench that I use to test speakers.  I think it is 300 watts at 8 ohms.  I have had STX828 off of a just one side and was surprised at what it would still do it's less than 9db down from the max power, we never really put that into the sub so it really is less than 6db down from as hard as we ever push them.

I know I shouldn't be surprised but to see a practical demonstration of the science is impressive.

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Scott AKA "Skyking" Holtzman

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Kevin Conlon

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #12 on: October 13, 2016, 03:26:51 pm »

Last week I had a speaker demo at an outdoor athletic complex that was under construction. I hadn't been to the site yet, so I had no idea what stage of construction they were at. Silly me assumed they had power... :o

I have a generator but didn't bring it with me. I had a 100' 12/3 extension cord with me, but the nearest power source was easily 1000' away. The owner had a 400w inverter built into the bed of his Toyota Tacoma. I had a Crown XTI4002 amp, and I knew that being a switchmode amp the inrush current would be minimal compared to a toroidal amp. So I was confident that it would turn on, but I told the customer I didn't think we would be able to get anywhere near full output from the system. But we had nothing to lose (except maybe the amp) and I was 30 minutes from the office and the generator.

I was running a single SM80 on channel 1 and a single TH118 on channel 2. To my surprise, I was able to run the amp to clipping (and then I backed off a bit) on BOTH channels, and didn't notice any audible distortion, and it sounded just as loud as I would have expected it to with shore power. I was shocked. I thought surely it would have tripped whatever fuse or breaker Toyota put in there, or the amp would have just shut down when the line voltage sagged. I know the 100' cord will act as somewhat of a damper, but still, I was very impressed.

Now, I'm not suggesting to run a gig off of a power inverter, but if you're ever in a bind it just might work. Given how well it worked, I'm going to pick up a 1500w inverter just for tailgates and other 'recreational' portable use.

Here's a video at 750' (well beyond the 'usable' distance of the speaker, but surprisingly you could still hear it):

https://www.youtube.com/watch?v=0__upKnY58Y

And another video at about 300-400':

https://www.youtube.com/watch?v=Fl0GtAmKFMI
We have run delay speakers on a 24volt input inverter more than once. We had 4 of the agm red top batteries, two in use and two on a solar charger for back ups. Volt meter in the system that someone would run out and check every hour. Ran a pair of mackies (don't remember which model) for four hours on the first set of batteries. They were not cranked too high. Also sent the audio wireless. Really cool not having any cable runs through the crowd. I can look at the inverter when i get home if anyone wants the name and model.
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Steve Loewenthal

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #13 on: October 13, 2016, 09:03:07 pm »

I have a 700W inverter that I always keep in my vehicle. I hooked up some connectors to the battery and inverter that allow quick connect / disconnect. I have used this to run speakers in parades, etc. I have also used it to run my electric chainsaw with 400 feet of 12/3 power cord. It is amazing how many uses for portable power I have found since I've had this. I haven't ever tried to run a full band, but I suspect might even be enough to run at very small venues with no backline and no subs.
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Steve Loewenthal

"I'm, just the guy in a band that owns the PA and I'm trying to figure out how it works. (Been trying to learn somethin' about it for about 20 years and I hope somethin' learns me soon)"

Stephen Swaffer

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #14 on: October 14, 2016, 06:39:06 pm »

A quick search shows a common rating for deep cycle batteries in the 24/27 size group to be 180 amp/hrs at the 8 hour rate.  So around 21 amps or 250 watts average for 8 hours-2 batteries should double that-and if you only need to run 4 hours you could get more (not likely double though).  Thes calcs do not allow for ineffeciency, of course.

Seems like that would be a plenty for a lot of smaller SOS gigs-portable power without the noise of genny sounds like a cool idea.  There is no reason that an inverter off a battery should be any different than an inverter off a genny-they generally convert to DC then invert the power anyway the only difference would be the step up in voltage. (or the quality of the inverter!)
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Steve Swaffer

Scott Holtzman

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #15 on: October 15, 2016, 03:42:03 am »

A quick search shows a common rating for deep cycle batteries in the 24/27 size group to be 180 amp/hrs at the 8 hour rate.  So around 21 amps or 250 watts average for 8 hours-2 batteries should double that-and if you only need to run 4 hours you could get more (not likely double though).  Thes calcs do not allow for ineffeciency, of course.

Seems like that would be a plenty for a lot of smaller SOS gigs-portable power without the noise of genny sounds like a cool idea.  There is no reason that an inverter off a battery should be any different than an inverter off a genny-they generally convert to DC then invert the power anyway the only difference would be the step up in voltage. (or the quality of the inverter!)

At $250/300 each the UPS batteries get expensive quick.  Much higher total cost of ownership than a gas engine.

When you start adding a few lights, backline and such I think 250w would be a tough power budget.

Maybe I am missing the application. 

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Scott AKA "Skyking" Holtzman

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Scott Carneval

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Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #16 on: October 15, 2016, 04:36:47 pm »

At $250/300 each the UPS batteries get expensive quick.  Much higher total cost of ownership than a gas engine.

When you start adding a few lights, backline and such I think 250w would be a tough power budget.

Maybe I am missing the application.

I agree. When you start talking about carrying multiple heavy batteries around a small Honda eu1000 becomes much more attractive.
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ProSoundWeb Community

Re: Very surprised how much sound I could run off a 400w power inverter
« Reply #16 on: October 15, 2016, 04:36:47 pm »


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