12v constant charger

Hi, I am trying to run a car sub in my house (how ghetto cliche, right?). This is more of a learning experience as as well as a matter of convenience. I am interested in running a car battery (to a car amp) at home and supplying a constant charge to it (can this be done with a trickle?). I would like to build the charging circuit myself. Can anyone provide me with a schematic for this? Do you need more info to answer this? Is the12volt the right place for me to be asking this question? Thank you! Justin((x1^2+x2^2+x3^2+x4^2+x5^2)/5)^(1/2)

The problem is enough Amps for the amp. As a rough rule, the Amps needed is the Watts output (RMS) divided by 10. IE - 600W RMS out = 600/10 = 60 Amps. That's a big charger! If you only use that (say) 60A 1 hour per day, you could get away with a charger of ~60A/20 = 3A (where 20 is the approximation for 24 hours - ie, 60A x 1hr = 60AH drain = 3A x 20H = 60AH recharge, but a bit extra is needed for battery inefficiency (typically ~30% when comparing "charge in" to "charge out"). Hence a 4A charger may do. That also assumes the battery has enough reserve to last one hour. As a general rule, a cranking battery should not be discharged more than 20% and a deep-cycle not more than 50%. Also note that when the charger (alternator) does not supply enough current, the voltage drops from a typical 14.2V to under 12.6V. The cheapest high-current PSU is a PC supply, but the 12V rail (which typically have ~10A - 20A capability) needs to be adjusted for ~14.0V to a max of 14.4V. The 5V rail (with its typical 20A - 60A capability) might be an alternative provided it too can be adjusted for 14-14.4V AND its output capacitors disconnected (since they are only rated for ~5V and will blow at the required 12-15V) as well as any other <15V rated components (though there shouldn't be any with such a low voltage rating). But you'll need to figure out your average current draw and add ~30% for recharging. Overall, the cheapest AC/wall-plug amp or sub is an AC system, not high-current 12V systems.

Probably far cheaper to buy a domestic amp and a filter.

Well thanks for all the info. To make sure I understand: The problem is that a car alternator sends much more power (amperage) to the battery than any conventional charger I can (or should) build. This causes the battery to drain below its designed capacity, making it unusable. Is that the main idea? It seems that I could still use the sub woofer I have and just put a resistor inline. Would that still work? Also, I'm having trouble finding an AC amp. Any suggestions? ((x1^2+x2^2+x3^2+x4^2+x5^2)/5)^(1/2)

Yes. Best Buy. The type of power supply as used by car audio shops for their amps will set you back about $500.

I apologize for dragging this on. Are saying I should get a $500 DC amp from Best Buy and ignore the suggestion of buying an AC amp. Sorry I just didn't quite follow you there. ((x1^2+x2^2+x3^2+x4^2+x5^2)/5)^(1/2)

Not at all, sorry for the confusion, I was a little too fast and furious with the reply. Your first line about the alternator was correct, thus yes. A domestic (home audio) amp with possibly a line in filter available from Metra, Scosche etc. Available from Best Buy etc. The stabilised power supply as made for car audio shops etc. 60 amp version would cost about $500 in the UK, probably cheaper in the US, most of ours as supplied by Kenwood, Pioneer etc. are made in the US. Frankly you'd be better off financially by buying a cheap home cinema system!

Sounds as if you are on another path now... Just wanted to Add, if using a Wet/Lead Acid Battery, make sure it is vented. Otherwise, Carry-On...!M.E.C.P & First-Class

Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

By the way another point, a car sub will sound completely different in your house.

If you ran a car battery a stabilised (regulated) power supply with about 10 amps output at 14.4 volts will do the trick. Problems... Battery needs venting as Tommy says. You will need to keep the power supply constantly running, you will probably cook the battery in abut 2 weeks, the whole thing isn't cost effective.