Power Invertors and Batteries for Mobile Sound

[paradigm]

Is an Optima 75Amp-hour Spiracell Battery along with a Cobra 3600W DC to AC power invertor sufficient enough to power a basic mobile DJ Sound System at 350W/channel @ 4ohms or must I use a power generator.

[Pete Schumacher ®]

> Is an Optima 75Amp-hour Spiracell Battery
> along with a Cobra 3600W DC to AC power
> invertor sufficient enough to power a basic
> mobile DJ Sound System at 350W/channel @
> 4ohms or must I use a power generator.

A 75AH battery means, 75 amp supplied at rated voltage for one hour. 75A x 12V = 900W.

You are going to need a few more batteries.

[Deward Hastings]

> A 75AH battery means, 75 amp supplied at
> rated voltage for one hour. 75A x 12V =
> 900W.

Actually it's worse than that. OPTIMA, like most lead batteries, is rated for capacity at C/20 (steady discharge over 20 hours). They typically can deliver around half the rated capacity (in this case about 37 Watts) at a 1 hour discharge rate.

On the plus side, an amplifier does not draw its max rated power in normal use . . .

[wg_ski]

> Actually it's worse than that. OPTIMA, like
> most lead batteries, is rated for capacity
> at C/20 (steady discharge over 20 hours).
> They typically can deliver around half the
> rated capacity (in this case about 37 Watts)
> at a 1 hour discharge rate.

> On the plus side, an amplifier does not draw
> its max rated power in normal use . . .

Yeah, but he's a DJ. It will be played loud. And amps are not that efficient backed off at less than full power. To put out say, 100 watts average power to the speakers (not unreasonable for the application) you need at least 300 watts off the AC line. That will kill the battery in under two hours.

[envisionelec]

> Is an Optima 75Amp-hour Spiracell Battery
> along with a Cobra 3600W DC to AC power
> invertor sufficient enough to power a basic
> mobile DJ Sound System at 350W/channel @
> 4ohms or must I use a power generator.

All those parts? Why not a big car amp and start the engine?

[dwk]

> Is an Optima 75Amp-hour Spiracell Battery
> along with a Cobra 3600W DC to AC power
> invertor sufficient enough to power a basic
> mobile DJ Sound System at 350W/channel @
> 4ohms or must I use a power generator.

As the others have said, a single 75aH battery is peanuts in terms of actual energy storage. No way can you run a conventional PA rig for any length of time.

I've been looking at battery/off-grid solutions since we recently got a remote off-grid property. The only viable way to get high power off grid is to use Class D output stages and run them straight off the battery voltage. Running the DC through an inverter to get AC which is then converted back to DC is far to wasteful to be practical.

Get one of the quiet inverter based generators like the Honda EU series (pricey but they work and are quiet), or similar units. Don't get one of the cheapie open-frame deals, or nobody will be able to hear the music over the racket of the generator.

[Deward Hastings]

dropped a "0" there . . . meant 370 Watts (for 1 hour, allowing for inverter losses and not destroying the battery by running it completely flat).

That same battery might be able to provide 3000 Watts from the inverter (300 Amps at the battery) for four or five minutes, but the number of such discharges before destruction would be . . . low . . .

[paradigm]

> Yeah, but he's a DJ. It will be played loud.
> And amps are not that efficient backed off
> at less than full power. To put out say, 100
> watts average power to the speakers (not
> unreasonable for the application) you need
> at least 300 watts off the AC line. That
> will kill the battery in under two hours.

Hmmmm!...My intial plan was to connect an DC-AC power invertor to the 12 volts 75Ah battery and power all my DJ gear from the invertor. A basic 300W per channel power amp @ 4ohms, simple DJ mixer, cd player and a pair of 4ohm 3-way speakers.

What if I use the 12 volts 75Ah battery to power a 12Vdc car stereo power amp rated at 300Wrms @4ohms which would feed the speaker system and then use a less powerful battery to just feed the DC-AC invertor to power the mixer and CD Player.

How much hours of music can I play continous with this setup?

[wg_ski]

> As the others have said, a single 75aH
> battery is peanuts in terms of actual energy
> storage. No way can you run a conventional
> PA rig for any length of time.

> I've been looking at battery/off-grid
> solutions since we recently got a remote
> off-grid property. The only viable way to
> get high power off grid is to use Class D
> output stages and run them straight off the
> battery voltage. Running the DC through an
> inverter to get AC which is then converted
> back to DC is far to wasteful to be
> practical.

> Get one of the quiet inverter based
> generators like the Honda EU series (pricey
> but they work and are quiet), or similar
> units. Don't get one of the cheapie
> open-frame deals, or nobody will be able to
> hear the music over the racket of the
> generator.

A 5kW "cheapie" loafing along driving an 800W PA doesn't make an unreasonable amount of noise. When you load them fully, they do make racket but at less than half load they quiet down quite a bit. And you can run 100' of extension cord to the rig and move the generator out of the way.

[wg_ski]

> Hmmmm!...My intial plan was to connect an
> DC-AC power invertor to the 12 volts 75Ah
> battery and power all my DJ gear from the
> invertor. A basic 300W per channel power amp
> @ 4ohms, simple DJ mixer, cd player and a
> pair of 4ohm 3-way speakers.

> What if I use the 12 volts 75Ah battery to
> power a 12Vdc car stereo power amp rated at
> 300Wrms @4ohms which would feed the speaker
> system and then use a less powerful battery
> to just feed the DC-AC invertor to power the
> mixer and CD Player.

> How much hours of music can I play continous
> with this setup?

300 watts is 300 watts. The 'car' amp will draw a little less power if it's an honest 300 watts becasue you don't have to deal with an inverter, but still you won't get a lot of run time. And deep cycling batteries wears them out. If the 'car' amp is "300 car stereo watts", and really only does 30 to maybe 50 watts you get more run time but less dB.

One possible solution to the run time issue is to use horn loaded speakers. You can get 50 watts pretty damn loud with large boxes. I used to use 10-15 cubic foot 18" 3-ways back in school to get every last possible dB out of low powered amps. If I knew how to build horns back then I'd have done that. You can build something efficient down to 70 or 80 Hz that's loud as hell.