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Old 27th August 2008, 09:24 AM   #1
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Default very newbie stuff

hi all, new to diyaudio, sry if this is in the wrong section of the forums,
basically im jus wondering if there would be any problems if i tried to hook an car amplifier such as this one http://www.partsexpress.com/pe/showd...number=265-089
to a 12v hobby battery like this one
http://www.radioshack.com/product/in...entPage=search

this is the desired driver
http://www.partsexpress.com/pe/showd...number=297-462
if its relevant, but that is secondary, i can use another driver if neccesary
basically id like to know if anything would explode/fail or any problems id run into
helpful commentary very much appreciated.
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Old 27th August 2008, 10:14 AM   #2
lineup is offline lineup  Sweden
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Location: the north
The short answer is YES.

But as your 12 Volt battery is only 7.2 Ah
you will have to recharge rather often
As the battery will get empty soon.
A bit depending on how hard you play of course.
(higher sound takes more power = more current from Battery)

Normal car battery in my country has got ~ 60 Ah capacity.
This will last much longer than small 7.2 Ah battery.

60 / 7.2 = 8.3 times longer

Ah = Ampere x hours
Ampere = current level
hour = time
The more Ampere (current) you use, the shorter time before is empty.

Example:
One device (amplifier) running on battery takes 0.5 Ampere at average
Battery is 7.2 Ah
now normally battery is considered EMPTY and need re-charge at 50% = 3.6 Ah
Estimated time: 3.6 / 0.5 Ampere = 7.2 hours of play

Example two:
Current drawn: 0.5 A
Battery 60 Ah ( 50% is 30 Ah )
Estimated time will run: 30 Ah / 0.5 A = 60 h
Will run like 60 hours, before battery needs to be re-charged.


12 Volt car batteries have capacity (and price) by SIZE and WEIGHT.
Bigger size = Bigger Ah value = longer time
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Old 27th August 2008, 10:44 AM   #3
AndrewT is online now AndrewT  Scotland
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Location: Scottish Borders
most batteries are designed to have adequate life when used in conjunction with a trickle charger.
The charge/use/recharge/use duty requires a deep discharge battery which generally costs much more to get an adequate life from it.
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Old 27th August 2008, 11:43 AM   #4
acid_k2 is offline acid_k2  Italy
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battery and speaker are too small for such amplifier (2x125W rms) for normal or heavy use.

With large input signal, you can burn the speaker (rated 40W rms) or battery can overheat, and amp can go into under-voltage protection.
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Old 27th August 2008, 04:33 PM   #5
jol50 is offline jol50  United States
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That amp will drag that battery down in no time if you play it loud. I would buy a car jumper for the same price and get the battery and free charger/carry case/flashlight/12v outlet/power meter/switch and you could jump a car if you needed to

What would work better is an efficient class d but they are more expensive, and full range used are not common but there are a few around. There are some smaller kit type amps, I'm sure someone here can tell you more about those. Otherwise I would get an old 2x30/40 rms at 12v amp like say an old black alpine (3522s) they are reasonable, maybe a ppi or rf. They put out well and can be had cheap as everyone wants 50+rms larger ones. Some of the RF have bass/treble even. Anyway a good old school amp for maybe <$30 shipped (if you wait for one) would run those speakers hard but still have limited play time on that little battery if run hard. Now if you want to use this large amp in a car later then it would work if you took it easy. I think it would take a little more power on average but the amps I have tested have all different idle currents to hard to say....but smaller tends to be smaller current. I can't really measure efficiency but can tell you a class D sure goes louder at same amp draw as a class AB.

I did have a pyramid pb444 amp about half the size of the one you list. http://www.teptronics.com/pb444x.html It might work ok if you want a cheap and new amp for this, those speakers are not going to take the one you list at full output.

If you are thinking of making a portable music deal, I would really look into some kind of full range class d/t/etc amp they take less power and are very ideal for that...if you have budget or shopping time to find one.

Do those speakers come with passive crossovers?
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