ssj_kakarot
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Registered: 29th Apr 03
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the power consumption of a 12v cd player,
just built a stereo system, 12v 14a/h lead acid battery powering a lg head-unit and running 2 150w speakers, just using the mp3 input connection to play songs from my phone.
how would i measure the amps per hour usage of it so i know how long it would last before needing to be recharged?
or can any one give me a general idea of how long it would last, cant find any information saying roughly how many amps an hour a mp3 connection of a head unit would use.
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Dan
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what is the wattage of the cd player
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ssj_kakarot
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40w x4 but only using 2 speakers if that makes a difference
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Dan
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thats the power output, what is the power consumption of the actual head unit :/
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ssj_kakarot
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well if it said that i wouldn't be asking would i :/
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Dan
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Well if you dont know how much Wattage the head unit is, u wont be able to find out the a/h
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Dan
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Also, what is the amp rating on the battery.
[Edited on 23-07-2010 by Dan]
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ssj_kakarot
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yeah i kind of figured that out, i was more asking what type of testing device measures a/h
yeah sorry i meant 14A not 14a/h
[Edited on 23-07-2010 by ssj_kakarot]
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Dan
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I can work it out if you give me the total wattage of the system.
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ssj_kakarot
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all it says is
"dc 12v --- negative ground 3.5a"
that the one?
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Dan
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No, but lets say your system is putting out 200w constant.
200w is 16amps roughly (16 amps / hour used)
You now just need to know the capacity of the battery 
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Dan
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Now i think about it, your probably only using 2 x 40w, meaning 80w.
which is only 6.6a, thats much more likely
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ssj_kakarot
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well the battery is 14Ah, if that was the case wouldnt that meen the battery would last less than an hour lol ?
you sure your working it out correctly, most of the stuff i have read seems to say a cd player will use rounf about 1a at normal use?
[Edited on 23-07-2010 by ssj_kakarot]
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Dan
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No, amp hours is how much ampage the battery can produce. The battery will have a capacity on it im sure. What does it say on the label
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ssj_kakarot
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NP14-12 Ultramax 12v 14Ah Lead Acid Battery NP12-12
i thought Ah was the total ammount of amps per hour before the battery needs to be charged again
hence why lesisure batteries are sold as 85Ah, and using 1amp an hour would last 85 hours?
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ssj_kakarot
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in theory, if you have a 100 amp hour battery, it will provide 1 amp of electricity for 100 hours. So, work out how many watts of power your appliances are using and divide the number by 12 (voltage of battery). This will give you how many amps you are using. Then divide the number of amp hours of the battery, by the number amps being used and this is the number of hours that the battery will, in theory, last.
E.g If you are powering a 60 watt light bulb by a fully charged 100 amp hour 12 volt battery, firstly divide 60 by 12 = 5 (amps) then divide 100 by 5 = 20 hours.
Hope this helps
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Dan
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Im unsure, ive even confused myself :/
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ssj_kakarot
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haha me too cheers any way, think ill just leave it on full blast and sit with a stop watch lol
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Dan
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Yea...
so at 80w, which is what your rated to if your using 2 speakers at max volume.
you will use 6amps roughly. So you will last just over 2 hours
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ssj_kakarot
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yeah that makes sense but....
if thats the output power of the speakers, would that mean the total watts of the unit being used is 80w or would the amp in the unit use less watts to power the speakers ?
also how would the cd factor into it, i meen obviously if the laser is being ran to read the disks the total wattage that the system is using would go up?
ive read a few things that say cd players should draw between 1 - 2 amps an hour which would meen it would last between 6 - 12 ish on this battery.
obviously if it uses 6amps an hour yeah it will last only 2
[Edited on 23-07-2010 by ssj_kakarot]
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ssj_kakarot
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Registered: 29th Apr 03
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ok think i may have sussed it
you can calculate wattage using this
Amps (A) * voltage (V) = Watts
the amps are 3.5A the voltage is 12V
so 3.5 x 12 = 42Watts
then to convert watts to amps is 42 / 12 =
3.6 amps which would give me around 4 hours on a fully charged battery
however, i presume that would be with the cd spinning and the volume whacked fully up on 4 speakers, so i guess the reading i was doing which said normal usuage would be around 1 - 2 amps was correct.
hopefully just using the aux inputs would lower this to 1.5amps or lower, but at the least i guess im getting 4 hours of usuage.
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ssj_kakarot
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ok turns out i had a multimeter which can read amps.
at half volume using the mp3 connection is was using 0.4A ill crank it up full volume tommorow but im guessing its going to be less than 1A so should be good for at least 12 hours good stuff :-)
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John
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Registered: 30th Jun 03
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Do you need it to be a headunit?
Would some powered speakers not last forever on a car battery?
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ssj_kakarot
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quote:
Originally posted by John
Do you need it to be a headunit?
Would some powered speakers not last forever on a car battery?
i did toy with that idea, i even got a £15 mp3 amp off ebay which runs on 12v but it means its no where near as loud and the sound quality took quite a large dive for the worst especially at high volume levels.
with the car having a pretty decent built in amp it sounds much better and goes very loud, which is good for the likes of festivals ect.
i never got a car battery mind its about half the capacity of a standard car battery but is actually really small, about the side of a bag of sugar.
overall im quite happy with it the battery only cost £14 the head unit was spare the wires ect came to about £5 and the speakers where £15, it seems a much better solution than a battery powered boom box type affair.
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John
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We had an ipod and a set of sony powered speakers at T, had to turn it down most of the time as we couldn't hear each other, sound quality was shit though.
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