modding an AC/DC radio to a battery only radio.

[laser83]

I need a small sized radio that can carry in my jacket pocket. Rather then spend extra money, I bought this cheap one which works only when plugged in. I want to make it battery operated and I'm hoping the electrics experts here can give me some tips on how to do it.

Here is the radio the power supply specs are

Input: AC/DC adapter 120VC~60Hz 4W
Output: 8V AC 100ma

I don't quite understand it but to me it means it needs 120V to function. My goal is to make this a battery operated radio and change the antenna to something that picks up stations.



Thumbnail so click on it for a larger image



Same click it on and you see the the circuit board in full view.

I'm unsure how to go about this, I know how I put in an antenna but making this battery operated only is what I don't how to do. It will not work unless it is pulled in.

An easy project or too difficult and not worth the trouble?

 

[MarioMaster]

Well since the AC adapter ouputs AC that means the rectification is taking place inside the radio.

The section you have labeled as power supply contains the four rectifier diodes in a bridge arrangement to convert the AC into pulsed DC. The big capacitor next to it then smooths the pulsed DC to constant.

You'd want to solder wires to that capacitor and feed in your power there. Anywhere from about 8-10v or so should be fine to run it as voltage tends to increase when being rectified.

 

[MarioMaster]

Also, I don't see a crystal on the circuit board - which implies that the timebase for the clock comes from the 50/60 Hz AC waveform. So running it off DC will prevent the clock from functioning.

 

[rog8811]

The first picture seems to show a connector for a 9v battery.... have yoiu tried using it? The wires from it seem to go to the circuit board near the rectifier bridge....they may of course just support the clock if it has one....

Regards rog8811

 

[chipdouglas]

also your title reads ac/dc radio. the you say the converter is ac/ac. i don't have a lot of experience but i've never seen something used on such a low ac voltage.

 

[laser83]

I broke my right hand yesterday so I won't be trying this for a while...

Also, I don't see a crystal on the circuit board - which implies that the timebase for the clock comes from the 50/60 Hz AC waveform. So running it off DC will prevent the clock from functioning.

Meaning running this cheap $5 radio on a battery won't be so easy?

The first picture seems to show a connector for a 9v battery.... have yoiu tried using it? The wires from it seem to go to the circuit board near the rectifier bridge....they may of course just support the clock if it has one....
Regards rog8811

On the bottom there is a connection for 9 volt battery. However, the battery only serves to backup the time and it will not start with that alone.

also your title reads ac/dc radio. the you say the converter is ac/ac. i don't have a lot of experience but i've never seen something used on such a low ac voltage.

The adapter does say AC/AC. This was going be a fun little project but with my hand out for a while that's done.

 

[MarioMaster]

The radio will probably still function on DC current, although the time will not change as it won't be receiving the clock signal from the AC line current.

 

[lasersbee]

Like MarioMaster said... the best place to input the DC power is at the big ripple
smoothing capacitor next to the 4 diodes...
8 VAC through a full wave bridge and smoothing cap can net you 10-12VDC..
so you can start to test it with an alcaline or rechargeable 9Volt battery...
(it probably won't last too long but it will let you know you're on the right track)

Jerry

 

[dr-ebert]

The only clocks using the 50/60Hz from the input AC voltage are the very old ones with synchronous motors driving little wheels with numbers on them, displaying the time - the very first "digital" clocks. You don't need a crystal for a clock, any old oscillator will do. A quartz just supplies precision; this radio/alarm clock doesn't look like that was a primary design directive. If the time really would require an AC input, the backup battery would be pointless as well.

 

[jamilm9]

and this

 

[lasersbee]

Yeah... I think dr-ebert hit the nail on the head...

How could a 9VDC battery keep the clock time accurate without the 60Hz
waveform during a power a power failure...

There must be an on board oscillator for the clock...

Jerry

 

[laser83]

When my right hand heals in month I'll fully take it apart. That was a preliminary look... then my right hand was slammed in a car door a day later. Once my hand recovers, I'll fully take it apart. Meant to be a cheap radio and project, I don't need the time visible.