Hello everyone, this is my first time on something like this, so be gentle.
I am building a portable bluetooth speaker system and have been scratching my head a bit on how to get the battery charging and power supply sorted out.
I will be using a 12v Lithium battery, a three position switch for ON, OFF and CHARGE. I want to use a standard power supply and put the battery charging circuit inside the unit. I would like system to recognize weather or not the power supply is plugged in. So that when it is plugged in you have the choice of A." Running directly from power supply,bypassing the charging circuit, with switch position ON, or B. Charging the battery and bypassing the supply to the Amp, with the switch position in CHARGE.
Obviously,when the unit is not plugged into the power supply the unit runs from the internal battery with the switch in the ON position.
I have made a design using a Relay that energizes when the power supply is plugged in and switches 2 switches, one NC and one NO.
Is there any chance this will work? cheers Dean.

 

You should examine How to Charge Lithium Batteries.

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

 

How about a nice SLA battery? No switches.

 

I second #12 suggestion of using a sealed lead acid battery. Lead acid batteries work so much better (simpler) in this application. Ni-cad or Ni-MH also work very well in this configuration. No need for switches or relays.

 

Awesome size and performance of lithium ion battery comes at a cost:

Awesome complex and difficult charging circuitry!

 

How about a nice SLA battery? No switches.

Hi, yes, I was originally going to use SLA battery because of the simplicity of things. But then I found a simple automatic style charging circuit from a guy on youtube "electronicsNmore" for charging Lithium batteries which I intend to use inside the box of the speaker. Also I want to keep the weight down. And I have already bought a 12.6V 3000mAh Lithium battery that cost me around 10 pounds.