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Author Topic: Battery power for small PA  (Read 1637 times)

Mike Sokol

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Re: Battery power for small PA
« Reply #10 on: June 08, 2017, 02:53:27 pm »

So here's the high-priced solution. http://aervoe.com/paints_coatings/Solar-Link-1000.html along with a pair of their 120-watt solar panels which are designed to link into it: http://aervoe.com/paints_coatings/120-Watt-Solar-Collector.html

So, just how much backline and PA do you think this box would run from its 1,000 watt pure-sine inverter? Of course it's way too much money unless their marketing department would supply one for promotion, but for a green-fest concert in a field with some "unplugged" bands, this could be a pretty good source of clean-green electricity, not that dirty petro-chemical or nuclear stuff I typically use. 

Stephen Kirby

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Re: Battery power for small PA
« Reply #11 on: June 09, 2017, 01:38:03 am »

Personally, if I did much of this I'd dig out my old Sx80s and hook them to a 12V car stereo amp of moderate output and some sort of basic 12V preamp.  AGM RV battery.  Put the whole thing in a box with a hand truck like handle and wheels or even some modified rolling luggage.
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Brook Hovland

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Re: Battery power for small PA
« Reply #12 on: June 10, 2017, 11:30:35 am »

Thank you for all the info guys!
I am going with a Dewalt DCB1800M3T1 charger loaded with 3 20 volt and 1 60 volt batteries.
There are less expensive options but I figure this can power my Dewalt tools when its not being used for sound or light power.

I tested it with 2) RCF NXL24a speakers, a Yamaha 12 ch mixer with constant blues/rock recorded music at a medium level and got 5 hours off a single charge.
I figure even with walk up, the longest i would trust this setup for anything critical would be a few hours.

I also plan on going with 4) 60 volt batteries instead of 3) 20volt and 1) 60 that it comes with for a little more reserve.
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Frank DeWitt

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Re: Battery power for small PA
« Reply #13 on: June 10, 2017, 04:39:49 pm »

Thank you for all the info guys!
I am going with a Dewalt DCB1800M3T1 charger

This makes a lot of sense  The availability of high voltage DC batteries got me thinking.  For a semi permanent rig, would it make sense to modify a nice efficient class D amp by tapping directly into the rails and supplying DC to them from the batteries.  Seems more efficient then going from DC to AC and back to DC

BTW Here is a 80 volt 5 AH  off the shelf battery  http://www.cpogreenworks.com/greenworks-2902502-80v-5-0-ah-lithium-ion-battery/gwkn2902502,default,pd.html
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Mike Sokol

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Re: Battery power for small PA
« Reply #14 on: June 10, 2017, 04:45:48 pm »

This makes a lot of sense  The availability of high voltage DC batteries got me thinking.  For a semi permanent rig, would it make sense to modify a nice efficient class D amp by tapping directly into the rails and supplying DC to them from the batteries. 

They do this for car SPL wars all the time. Not sure just how much "real" power is aviable on some of these, but there's lots of multi-KW car amplifiers that run off of 12-volts DC.

Stephen Swaffer

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Re: Battery power for small PA
« Reply #15 on: June 10, 2017, 10:33:10 pm »

This makes a lot of sense  The availability of high voltage DC batteries got me thinking.  For a semi permanent rig, would it make sense to modify a nice efficient class D amp by tapping directly into the rails and supplying DC to them from the batteries.  Seems more efficient then going from DC to AC and back to DC

BTW Here is a 80 volt 5 AH  off the shelf battery  http://www.cpogreenworks.com/greenworks-2902502-80v-5-0-ah-lithium-ion-battery/gwkn2902502,default,pd.html

Perhaps the biggest obstacle is a lack of a standard voltage.  12 volts is common and often used- but requires high current and lots of copper, 24 v is a common industrial control voltage with lots of stuff available and has the advantage that a -24/0/+24V stays under the 50 V safety threshold, 36 V is used for forklifts and gets more power with less current.

Any conversion is less than 100% efficient-and we really only need AC because we design to run off mains.  Running off straight DC would eliminate noise issues from the power supply.  In portable situations, staying under 50 volts would be a huge plus for safety.  Now with LED lighting, a whole gig could be run off batteries.

I haven't done the math, but if we can routinely run a forklift 8-12 hrs almost non stop, surely we could power a lot of lights and sound.  All that is missing is gear designed to run on DC and a distro infrastructure.  Yes, forklift batteries are heavy- but so are gennies. 

I knowvthis is outside the scope of the OP- just seems like its something the manufacturers should take a hard look at and find a way to standardize.  Amps/mixers etc with dual AC/DC power options should be easy to design.
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Steve Swaffer

Frank DeWitt

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Re: Battery power for small PA
« Reply #16 on: June 10, 2017, 10:49:17 pm »

They do this for car SPL wars all the time. Not sure just how much "real" power is aviable on some of these, but there's lots of multi-KW car amplifiers that run off of 12-volts DC.

OK, that takes care of the high current needs, Now a smaller Class D amp with a nice clean 60 HZ input could provide pure sine wave 120 VAC for your mixer or other devices that need AC.
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Mike Sokol

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Re: Battery power for small PA
« Reply #17 on: June 11, 2017, 01:02:05 am »

OK, that takes care of the high current needs, Now a smaller Class D amp with a nice clean 60 HZ input could provide pure sine wave 120 VAC for your mixer or other devices that need AC.

Well, that's exactly what a pure sine inverter does: http://www.theinverterstore.com/600-watt-pure-sine-wave-inverter.html

Stephen Kirby

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Re: Battery power for small PA
« Reply #18 on: June 11, 2017, 08:44:08 am »

Those car stereo amps still have switchers in them to run the 12V up to some rail voltage that will get them the power output they want.  80+ or whatever.  My suggestion of using one was just to save the loss of converting 12V into 120 first.
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Mike Sokol

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Re: Battery power for small PA
« Reply #19 on: June 11, 2017, 09:48:13 am »

Those car stereo amps still have switchers in them to run the 12V up to some rail voltage that will get them the power output they want.  80+ or whatever.  My suggestion of using one was just to save the loss of converting 12V into 120 first.

Yes, exactly. In the olden days before Class D amplifiers and switch-mode power supplies, the most voltage swing output you could get from a car stereo amp was 0 to 12 or 14 volts volts. So that works out to 7 volts peak divided by the square root of two (1.414) which is around 5 volts RMS. To get the watts delivered to the speakers just square the volts RMS and divide by the speaker load. That's 25 volts divided by 4 ohms which is 6 watts max. Now many of the higher powered car stereos of the day used bridge mode amplifiers for more power. So that's 5 volts RMS times 2 = 10 volts RMS. Then 10 squared = 100. And 100 divided by a 4 ohm speaker load = 25 watts. So with a 14 volt car electrical system (the alternator normally puts out 14.4 volts to charge the ~12 volt car battery) you got maybe 6 watts from a cheap 8-track player, or 25 watts from an expensive aftermarket amplifier. Of course with switch-mode supplies and Class D amplifiers it's possible to get thousands of audio watts from a car battery. But of course TNSTAAFL (There's No Such Thing As A Free Lunch), so the amperage draw on the vehicle goes up proportionally. 

P.S. I believe that each of us has a private hell designed just for them, and mine would be installing car stereos. So please don't make me do this anymore... :-\
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