I'm converting a desktop sound system into a portable system. I want to know what kind of batteries and anything else I need to ensure that the system has:
15VDC
At least 1200 mA
75 watts maximum power (35 watts program)
and prefrebly the most efficient weight to battery life setup

I've never been sure how to get a certain amount of watts out of batteries, but I know that 75 watts will be hard to achive in a small system.
Thanks

 

The speaker output wattage of the system isn't relevant. The two specs you need to meet are the voltage (15vdc) and the current (1.2 amps). You could test it with a standard car battery to see if it will work with 13 volts. DC devices like this are somewhat forgiving of low voltage. If it works, find a lightweight battery that puts out the amp hours you need.

 

Ahh, So all I have to do is find the right battery, no circuitry neccesarry. Thanks again.

 

You need to find the output side of the power supply if it is built in and there is no auxiliary power jack. You would add a jack for your power in at this point.

 

You're right, ray. I was picturing a typical computer desktop speaker system that's powered off a wall-wart transformer. But if it is an internal supply there's more work to be done.

 

What you are descibing would probably take 10 C cell size nicad batteries in series to run for any length of time. You then need to charge them and would need a charger. Also gel cell batteries like the ones used in UPS power supplies for computer equipment would be a good choice. They come in 12v versions and many currents.

You do not need to match the battery to the current but rather match the battery to the amount of time you want to run the device. You need a battery that is at least several ampere hours in capacity. Meaning you could draw that amount of current for an hour or 1/2 of the current for 2 hours etc. The more the ampere hours rating the longer you can run your device. So a 10 ampere hour battery would run your system for 9 hours assuming it draws 1.2 A Typically due to other factors these time would be less, so you need to go larger on the battery if possible. Size and weight become the issue.

Do a google search on the internet or possibly use a 12 volt portable power tools battery and charger.