I've been asked to get some recorded music onto a trailer / float for a local gala.

I have a 12v car inverter rated at 150w. I have a few speaker options, but am electronically challenged as to the equations needed to calculate what this supply can power. does anyone know if it would suffice for;

- An AER Alpha
- A single mackie srm350

Alternatively can someone advise how to work this out for other speakers?

Thanks

I had a bit of this thinking to do for a camp at Afrika Burn this year (www.afrikaburn.com)


You would be surprised at how little gear you can run on 150W !

The power consumption of an amp is a lot higher than its nominal output. For example, my SWR 220W head uses about 450W. You will find this out from the manual or the back of the unit .... if you are lucky. Or an email to the manufacturers.

You will likely need to hire a gennie or a big solar panel. Generators are rated as KVA. KVA converts to Watts as follows:

KVA=W/(1000*PF) Where PF is 'Power Factor.' Power Factor varies case by case, but try values for PF of 0.6 to 0.85, and choose large to be on the safe side.

When the capacity of your gennie is insufficient, stuff just stops working in an embarrassing and fairly random way.

The good news: gennies don't use much fuel. 10 litres will get you a few hours (test UNDER LOAD to find out how long your will run for).

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Instant gratification is actually pretty good. It's fast as well.

Not nearly enough. For LOUD. But try it out first, no harm done. Or, Hire a generator ... 1kva minimum ... and a quiet one!

Or, get some of those PA systems used at fetes and agricultural shows, the ones with great big metal horns. Efficient, loud and good projection, but not hifi!
But who cares about hifi these days?

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PA stuff on FB


Edited by Guy Johnson (15/06/12 10:08 AM)

thanks SS. The 40w (output) Alpha is rated as follows; 220-240 V / 50-60Hz / 55 VA (110V / 50-60Hz.

I'm not sure how these figures sit in your equation... at the risk of sounding like I'm asking you to hold my hand / do the sum for me.... can you hold my hand and do the sum for me?!:)

Edit; posted before I saw Guy's reply - I know a club with those horny (!) things. Might try them right enough

Edited by saltybrian (15/06/12 10:09 AM)

Well, you can run up to 150W from it which is not a lot! Larger inverters are available for not a lot of money.

The spec for the Mackie says 120W musical program and limit LED blinking. But they recommend 1.25A, which is twice what your inverter can push out.
I can't find any useful spec for the AER, but it will not use a lot.

I would invest in a meter like this and do some real life measurements.

Another thing to be aware of is that many inverters monitor battery charge so it's not just about what the inverter can deliver in terms of current.

I have a 600 watt inverter which is fine for small set-ups. BUT once the voltage drops below a certain level as perceived by the inverter it just shuts down. I usually get about an hour before shut-down. And that's with a 110AH Leisure Battery.

So these portable set-up are about battery capacity as well as what the inverter can deliver. I much prefer a generator if at all possible. But be aware that certainly around here if it's council land they only permit diesel generators.

Thanks for input folks - I'm a bit reticent about buying anything as this is a one off event and it's the first time in 25 years of music making that I've had this come up. However, I've contacted a club with the lo-fi horn announcement style PA (what are those called?)and it looks as if they're happy to loan it for the night. It's to play conga music on, and since there's no PA known to man that can make that sound good I'm happy with that compromise.

Gennies can be hired easily enough, and the nice man in the hire shop will be able to do the maths for you. Perhaps !

I think we paid about 50 quid for four days for a nice Honda gennie that would deliver 2500 watts. But this is Africa, so UK prices may differ. We went through about 15 litres of fuel in total for a sound check, six gigs and some DJ-ing. I have to say the gennie wasn't terribly quiet: we put it on the end of a 25m cable. Quiet ones might cost more.

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Instant gratification is actually pretty good. It's fast as well.

The 2500W gennie ran a computer, small mixing desk, two powered PA speakers (about 150W output each IIRC) and a keyboard for Jazz sets. We had a separate little 650W one for the bass amp.

A rock band used the same rig but with a guitar amp instead of the keyboard.

Interesting thought: a 650W gennie will run a comfortably loud bass amp, but won't boil a kettle. So now you know.

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Instant gratification is actually pretty good. It's fast as well.

Saltybrian:

It looks like your AER amp consumes between 33 and 47 watts depending on the power factor, which I don't know. It looks like the srm 350 consumes about 312 watts at maximum; 120W 'for a musical programme'.

So no, your 150w inverter won't cope reliably with them both, and would struggle with the srm350 on its own.

BUT

1. I am not an electrician, and
2. You don't know where I live

So do seek a second opinion !

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Instant gratification is actually pretty good. It's fast as well.

If you go down the generator route, get one from a company that understands live music events and not from a building site supplier. They're very different beasts. There's a recent thread over on the Blue Room if you're interested in the details.

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There's nothing we can't face... Except for bunnies