Converting AC amp to DC...

[m R g S r]

I bought a mini 2.1 iPod / mp3 playback system from parts express in order to get the order above $100 and get free shipping. That's the ONLY reasoni bought this thing. Anyway, I have no use for it in the house so I figured I'd make it battery powered and use it pool side at my house in FL. (and let my patents use it for the same reason when they want to)
Anyway it's AC powered now. Input to the amp is 8 V AC, 1.6 amps I believe? I forget the exact figure on the transformer when I opened it up. It's the TeiNuro system here....TeiNuro 2.1 Powered Multimedia System MP3/USB/SD Card Input 310-500
Pretty sure it's 12 watts rms total. So not much power is required.

Anyway, knowing that I got this for $30, what's the cheapest / easiest way to make this thing portable / DC / battery powered? Any good source for a cheap rechargeable battery? I'm trying to not spend a lot on this at all.

Thanks!!

[harryz33]

I'm pretty sure a small lead acid battery would work, around 7Ah wouldn't cost very much and would last 7 hours if it was on max volume for the whole time. Just remember to bypass the rectifier part on the circuit board and remove the capacitors, they can explode if the polarity is incorrect.
Good luck, I just made something similar, a 2.1 system for a bike basket!

[RJM1]

Or just leave the rectifiers and capacitors in there to give you reverse polarity protection. Most likely it has a bridge rectifier so it should work either way that you hook up the 12V battery.

[m R g S r]

So wait...I can just hook up the 12V Battery right to the amp board without changing anything, as long as polarity is correct?

[RJM1]

The polarity doesn't matter as the bridge rectifier in the player will take care of that. Yes, just connect your 12V DC battery to the AC input. You don't have to change anything.

[AndrewT]

You can fit a small trs socket and plug in the battery when needed.
This could be downstream of the bridge rectifier saving that wasted voltage.
You still need a smoothing cap across the supply when using battery power. This satisfies the peak current demand of the amplifier.

Why trs for a 2pole connection? Leave the r unconnected in both the socket and the plug. This avoids shorting the battery or the mains supply when inserting or removing the trs plug.

You can even have the mains supply, trickle charge the battery (when plugged in) when the unit is switched to OFF. A voltage regulator preceded by a current regulator achieves a reliable trickle charger with very few components.