Calculating energy usage...

alexthecheese

alexthecheese

alexthecheese

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Joined
10 Mar 2006
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Looking at constructing a 'portable' stereo out of a car stereo and a car/leisure battery.

Not sure if this is the right forum (or if anybody would actually know!), but I'm just wondering how long the battery would last on a car stereo that puts out 4 x 45 watts? I understand that the maximum consistent output is about half of that.

Looking at using something like a 90amp/hour battery - 110 amp/hour tops.
 
Measure how much power in amps the amp consumes at a reasonable volume. Then divide 110 by this number. That will give you hours of musical joy before it conks out.

4x45 watts is musical power, you need the amp draw of the amp.
 
Pinter75 said:
Measure how much power in amps the amp consumes at a reasonable volume. Then divide 110 by this number. That will give you hours of musical joy before it conks out.

4x45 watts is musical power, you need the amp draw of the amp.
Click to expand...

Is there any way of working out what it draws without electrically testing it? The car stereo is on it's way through the post and we're looking into buying a battery for it, so wondering how much to spend.

A website I've just found states that Amps = Watts/Volts.

So, if I have a car stereo drawing on average 22 watts at 12 volts, that's 1.83 amps.

Does that mean that a 100amp/hour leisure battery would run for about 50ish hours?
 
the headunit will draw from 11volts to 14 volts.

and i would use a higher than 22watts average. just to be safe.

but you are still looking at 20 hours. which is pretty good. assuming the battery if fully charged.

edit. that would only be the pull of the amp inside the head unit. dont forget the pretty lights, cd mechanism etc.

still. even if you add a chunk on for that probably 15 hours playback.
 
It's a pretty basic stereo that we bought purely because it had an aux input as we're going to be running ipods through it. Fingers crossed it wont suck up much power more than quoted, but like you say even with 25 hours that is plenty!

The weight of these things might be a bit prohibitive when it comes to buying online, but can anybody recommend a good dealer of these kinda things?
 
When I went to Reading a few years back, there were some guys near us that had a CD headunit, 2 speakers and a battery or two in a little wooden box on wheels :) It was on for pretty much most of the time we were in the camp over the weekend (Fri-Mon) :)

I thought it was a darn good idea, good on you for deciding to do it! :)
 
Haha, yes mate - this is exactly what it is for! :D

We're going to Glastonbury (all going well!), V and Reading this year so need something to provide us with ample tunes for the nights and monging around by the tents. I had the idea to do it last year, but not wanting to spend over £100 setting it up by myself meant that it didn't go ahead, but this year I've got mates in on it and we're splitting the cost.

I just really hope it doesn't get nicked when it comes to using it. :p
 
Many moons ago I used to run CB radio's off car batteries as a lot of units were designed as in car units. You got quite a few days off fully charged car battery iirc. Just make sure you have something that can resist corrosion to sit the battery in, i used to use an old plastic vegetable crate. You really don't want battery acid leaking onto your carpet in the house.
 
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