You really need someone who knows their stuff with electronics, and to buy decent kit and wire it up properly. Especially with the batteries as if those go pear shaped you could end up setting a big fire! If you don’t want to get involved with the techie stuff (though from other posts on here you come across as intelligent enough to do do) there should be at least one person in your crew who can.

To get the loudest sound from the least power, you need the most sensitive speakers. Speakers are rated in decibels per watt, this number should be as big as possible.

what is the reason for doing this? I ask this because if the idea is that it will be easier to buck licensing requirements with a smaller system that won’t work – however I can see how if done correctly (particulary if you use renewable energy to power the batteries) it would make it easier for you to get permission to use land/buildings – if you do it right your image will change from the stereotype of a rave crew as “a bunch of young unemployed kids with thousands worth of sound equipment bought from drug dealing” to “some smart and eco-aware youngsters learning and using valuable skills”. And this isn’t exactly a bad thing!

(this link might help you)

Lead Acid Batteries

What he has done is used one channel for the woofer and another for the tweeter, having used a crossover after the mixer.

It may be worth getting the amps first and then borrowing a couple of speakers to try them out and see how loud you get…

Remember that you don’t have to use car batteries – they are heavy bulky things. taking a 12V feed from yours or your mates car / van isn’t a good idea either as if someone “helpfully” starts the engine to charge it, it will send dirty power to the amps and blow the chips in them (not very eco-friendly either!)

The sealed lead acid kind of battery found in golf buggies, cheaper e-bikes and other such items are also a possibility (but you need the right charger). Also give some thought as to how you will power the mixer and decks / CDJ’s / MP3 player (unless you are instead using a laptop).

You can also charge the laptops battery from the 12V one with the right convertor, but it does use a fair bit of current.

Don’t forget to put fuses in all the right places and use good thick cable for the amp power feeds…

That battery is mislabelled.

its 7AH rather than 70AH, this is a big difference. The amp uses about 2A when running at full power, the 7AH battery would only last 2 hours. You do not want to run these things down too much over half the AH capacity as the batteries will get knackered quickly if you do.

if you have a actual 70AH battery and use 36AH (I deliberately use the extra AH for this figure to make the maths easier) then you should get 18 hours. But a 70AH SLA is expensive and heavy. I’d go for about 20AH if you can afford it, maybe even two in parallell (this doubles the AH)

If you have friends who work in IT you might be lucky and be able to pick up old UPS batteries as companies replace them after 3-5 years – or if they work on burglar or fire alarms (which also contain them).

As for the speakon connectors, all you have to do is buy a roll of speaker cable, the connectors and then wire them up, you then connect the bare ends to the green connector.

These two places will sell you all the other bits you need like connectors, don’t buy them in Halfords or places like Maplins as you will get ripped off big time..

Rapid | Distributors of electronic components, electrical products and educational supplies
CPC | CPC – Over 100, 000 products from one of the worlds leading distributors of electronic and related products.

it depends how much of the battery’s capacity you use. Using the full 6/7AH will knacker it quickly. Others on there are suggesting 70-80% of the capacity (to be fair I was thinking of e-bikes when I said 50% and these use way more current). but even that means you are getting only 5AH from the battery.

They also claim on speakerplans the amp uses much less current but that may be a different design without the other circuitry like protection relays, or just measuring the power draw of a chip on a breadboard circuit. 0.350A seems like way too little for 40W output!

The comments on the fleabay page claim that one chap used a power supply and got good volume at 1.5A power draw – the Chinese sell a 5A power supply to go with it (for running it from mains)

I’d be sceptical until I’d actually got the amp on a test bench with an ammeter on the power supply checking the exact current draw whilst playing your favourite tunes …

I’ll freely admit because of what I do for a living when it comes to batteries and power supplies (I’ve installed a fair few UPS units) I am very fussy about getting reliable power and thus tend to take a “worst case” approach to estimating how much power equipment draws specify a larger battery if at all possible – lives and safety depend on some of the stuff I work on, so if we spend £20 or £30 more on a bigger battery in the UPS its not a big deal. (its all installed out in the sticks where the mains can be flaky anyway!)

I do appreciate that for a group of younger folk wanting to listen to music cost may be more of an issue, but if you can afford a larger battery it won’t hurt (unless you get a short circuit, which you must be careful against!)

Some chap from up near March had a business selling batteries, UPSs and the older style e-bike (not the ones like mountain bikes but the ones the OAP’s ride) but his website is down so I’m not sure if he’s still in business. I’ll try and check next week at he had some decent ones for OK prices..

depending on the amps construction it probably won’t do the chip any good. you are better off using two small speakers.

BTW for the power what you need is a 2.5mm DC connector, decent quality cable good for about 2-5 amps current, a 5 amp inline fuse and spade connectors for the battery end.