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 27th August 2008, 10:24 AM #1 deltastryke   diyAudio Member   Join Date: Aug 2008 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.
 27th August 2008, 11:14 AM #2 lineup   diyAudio Member     Join Date: Dec 2005 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 __________________ lineup
 27th August 2008, 11:44 AM #3 AndrewT   diyAudio Member   Join Date: Jul 2004 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. __________________ regards Andrew T.
 27th August 2008, 12:43 PM #4 acid_k2   diyAudio Member   Join Date: Oct 2006 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.
 27th August 2008, 05:33 PM #5 jol50   diyAudio Member   Join Date: Nov 2007 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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