AC off car/marine battery -- tips?

March 20, 2005 4:23 PM

I want to take my Mac G5-based sound system on the road, including setting it up outdoors, using my own power source. I understand a deep marine battery is the best source for silent, portable power, and delivers AC via a converter. Anyone have experience with such a setup?

Also, how does one calculate the amount of run time one might get, considering the variables involved?

posted by rleamon to media & arts (4 comments total)

APC has some white papers on runtime of their UPSes based upon current usage. Each UPS is rated for current usage. From this you could either decide on a UPS or go with an equivalently rated marine battery + converter.
posted by AlexReynolds at 6:21 PM on March 20, 2005

If you have the cash, you might want to get a Optima or similar totally sealed battery(~$100). Regular marine batteries may leak acid if tipped and may release acid fumes even if not tipped. Optima makes several different batteries, including deep-cycle (known as the "blue top", but some blue top are made just for starting a gas engine). Another company (Odyssey), makes a dry cell 12 volt car battery.
When I converted an old school bus into a camper, I used 4 golf cart batteries. Golf cart batteries are made to be cycled many times, and some can be rebuilt (or renewed or something). Most are 6 volt, though, so you need to use them in pairs (in series).
A quick look at the specs for the "troll fury" Optima blue top shows a capacity of 110 Amp hours. At 12 volts thats 1.32 kilowatt hours. So, if your setup only draws 100 watts, it would last 10+ hours (not sure what inverter efficiency is like), on the other hand, if it draws 1000 watts, you only got 1 hour or so.
posted by 445supermag at 7:21 PM on March 20, 2005

24 x 75 watt speakers, eh?

That's enough juice that I would reccomend at least 3 or more batteries. If you place all that load on a normal sized battery you're going to find it will create some REALLY nasty hydrogen fumes and die forever supremely fast. Not to mention that 1800 watts will require 150 amps of constant current from a regular battery -- were talking some seriously thick cable here (think, at least, expensive car jumper cable thickness maybe even down to aught [0] AWG).

You could put the batteries in parallel, but doing that safely can be quite tricky. It'd probably be easier ans safer to have a few speakers on each battery seprately, and the cost of the inverters will be lower as well. I can't begin to fathom what a 2000+ watt inverter will run you. I'm guessing a lot more than 10 x 200 watt inverters. :)
posted by shepd at 1:01 AM on March 21, 2005

A 2000 watt inverter is only about $100-200 (costco had a 1500/2000 peak for $69 for a while). You may want to get a true sine wave inverter though, cheap inverters put out a truncated sine or modified sine and may give you speaker buzz. Lots of inverter info on the web from solar/wind power resources and from RV sites. You can occasionally get deals from ebay on used ones from solar/RV take outs.
posted by 445supermag at 8:04 AM on March 21, 2005