how many amps per hour do my powered spekers use

[gaz9012]

Hi people, newbie here,
so glad i found this place. I can only seem to post here, so am happy if my thread gets moved to the right place.

I'm a Market trader for festivals and trying to work out the cheapest lightest way to have sound in my stall. I was thinking of a deep cycle battery with an inverter powering an mp3 player with my old pc 240v speakers. i have tried to work out how many amps per hour my speakers use but just cant get my head round it.

i'd rather not get a portable stereo and pay out for loads of D cell battery's, which i know would be my lightest option.

on the back of the powered speakers it say 16 x 4.5 x 2w RMS The speakers are 2.1 with the sub being the amp which then runs the two small speakers.

any help would be great, thanks in advance.

 

[tazz]

Just not enough information to help.....we need to know wattage or current of unit...not its rms music output.

 

[Marvo]

You can't work backwards using the RMS output of speakers to work out the power consumption of the system. There's many stages involved between the the actual speaker and the power supply and each stage has large losses involved which you can't really put a figure to. Every stage you add will add even more losses to the overall system so if you use a battery to power an inverter you've just added another stage which has just added to the losses involved. There's also another problem where sound equipment manufacturers are bare faced liars when it comes to stating the output figures of their products because the know that customers base their purchasing decisions on how many watts of sound the equipment supposedly gives out.

Best thing to do is set the equipment up as you intend to use it and test the power consumption using a clamp meter or in-line ammeter.

 

[trev]

There's also another problem where sound equipment manufacturers are bare faced liars when it comes to stating the output figures of their products

Andy, I think I need to talk to you about that 3 Gigawatt guitar amplifier you sold me

 

[gaz9012]

Thanks for your reply's.
I was hoping not to have to go and buy any bits and bobs to be able to test the set up, but if its the only way i can, then i'll just have to wait to gets some spare cash.

I cant set it up until i have the leisure battery, which i dont want to buy untill i know how many Aph i need. There is some other numbers on the back which might be what you guys need
230-240v-50Hz-0.17A

sorry for being a numbty!

i know what you mean about people buying speakers on the watts they give out, i use to work in a hifi shop believe it or not.

I'm not looking to have a rave going on in my stall, just some nice back ground atmospheric music for 8-10 hours a day for three days

cheers for reading

 

[R G]

Just pull up your yellow reliant robin next to the stall and plug in an inverter into cig lighter socket ,,,,

 

[davesparks]

You will never get to an amps per hour figure as no such thing exists. I think you are probably getting confused with the a Amphour rating of the battery (AH)
The amp hour rating tells you how long the battery can supply a certain current (Amps)

For example my landrover has 2 1000Amp Hour batteries in it.
One of those batteries could theoretically supply a current of 1Amp for 1000hours or a current of 1000Amps for 1hour.

In practice it will only achieve the 1000AH at the current at which the manufacturers tested it.

As far as the power consumption is sound systems goes it is really a bit of a black art working it out!

I also work festivals but on the power distribution side of things, if a small festival has a main stage with a 20KW sound system and they are playing lighter/pop music then you'll likely not need more than 5KW for the whole lot. But if it is bass heavy dance music etc you could be looking at something more like a 10KW a supply.

I once had a sound system where the sound man insisted he had to have a 63A supply, he had a strop about the 16A he got and proceeded to push the system as hard as possible (18KW if you believe the ratings) recorded a grand total of 15Amps (~3.5KW) at its loudest!

 

[gaz9012]

sorry am mistaken,
i ment the AH

Ahhh the dream of owning my own yellow robin one day!!!
this time next year i will be a million air

 

[Knobhead]

Just when you thought things couldn't get any worse...............

 

[nadger]

Buy a Bose portable sound dock, mine lasts roughly 8hrs playing at a reasonable volume

 

[moospark]

Can you not get a wind up / solar radio with an ipod dock? no humping car batteries about.

 

[trev]

Buy a Bose portable sound dock, mine lasts roughly 8hrs playing at a reasonable volume

Reasonable volume? WTH is that? If it's too loud you're too old

 

[Lucien Nunes]

It doesn't matter very much what the speaker power rating is, more important is how efficient they are (loudness per watt consumed) and how loud you play your music. The power rating itself can be taken with a pinch of salt.

Filling my lounge with reasonably loud music takes about 20W RMS audio output. My speakers are fairly efficient, your PC speakers won't be, lets make that 30W to achieve the same volume. Class-B amplifier stages run around 70% efficiency (for a sine but it's a good starting point) plus we have to allow for transformer losses, call it 60%. A typical small 12V inverter might reach 85% efficiency at moderate load. Therefore current taken from 12V battery = 30/12/0.6/0.85=4.9A

smoke-packet estimate - 5A continuous load at 12V DC to make a noise that would be OK in a large room. Push it a bit harder with a lot of bass, twice that. Useful running time from 100Ah leisure battery maybe 10 hours (you don't want to keep running it totally flat).

PS as mentioned above, 'amps per hour' is nonsense. The amp is the unit of current, and the amp-hour (i.e. amps times hours) the measure of battery charge capacity. You can also talk of 'amp-hours per hour' i.e. amps averaged over a period of one hour. If you use 2 amps for half an hour and nothing for the other half, you will have used one amp-hour at the end of the hour, or an average of one amp.

 

[Geordie Spark]

Just when you thought things couldn't get any worse...............

Electricians Forums - the forum created for insomniacs and masochists.

 

[Geordie Spark]

Reasonable volume? WTH is that? If it's too loud you're too old

Pardon???

 

[Marvo]

I didn't think this was a stupid question THB. Yeah, trying to work out energy consumption from the speaker wattage was an misconceived idea but I thought the question had some merit.

 

[Knobhead]

My four amps are each capable of an output of 70A short circuited. OK if you want to do a bit of light welding.

Just thought I’d add another useless fact.

 

[Adam W]

How loud do you need it?
I use one of these on site:
BLUETOOTH WIRELESS MINI PORTABLE SPEAKER SPEAKERS FOR IPHONE IPAD MP3 Rechargble | eBay
I think I paid more like £12 for mine and it's loud enough for what I want it for.
The battery (rechargeable via USB) lasts about an hour on full volume, although I have an external battery like this:
50000mAh Backup Battery USB Charger Portable Power Bank for iPhone iPad Samsung | eBay
Which will keep it going for a couple of days. Again, you can charge it from USB, eg car cigarette lighter, mini solar panel etc.

Alternatively maybe a site radio with external input - some of those can go quite loud.

 

[shanky887614]

How loud do you need it?
I use one of these on site:
BLUETOOTH WIRELESS MINI PORTABLE SPEAKER SPEAKERS FOR IPHONE IPAD MP3 Rechargble | eBay
I think I paid more like £12 for mine and it's loud enough for what I want it for.
The battery (rechargeable via USB) lasts about an hour on full volume, although I have an external battery like this:
50000mAh Backup Battery USB Charger Portable Power Bank for iPhone iPad Samsung | eBay
Which will keep it going for a couple of days. Again, you can charge it from USB, eg car cigarette lighter, mini solar panel etc.

Alternatively maybe a site radio with external input - some of those can go quite loud.

Makita site radios are really good if you like drum and bass

 

[gaz9012]

once again thanks for the help.
So what your saying is, my idea cant be done, well not unless i have a 300ah battery. well looks like i'll give up on that idea then!! years ago i use to run pc speakers with a mp3 player all night round camp fires. never checked to see how much jiuce was left in the 85ah battery, so am guessing i was almost running it passed the %50 mark if not more.
looks like i am better of buying some portable speakers that sound like two tin cans and charging them up on a leisure battery between usage with a cig light socket and a usb cable.
thanks anyway people
happy posting
Gaz