HELP NEEDED WITH DC POWER NOISE

[S1runner]

Hey all! I'm very new to building my own circuits and need some specific help.

I have a video camera that only has ac power adapter of 12v and 500mah.  I put together a small circuit of 8AA batteries to get the voltage needed and making that camera portable.  but now the audio is just a high pitched whine that drowns out all other audio.  The circuit runs all the batteries in series, then to a power switch, then into the camera.  Any help and suggestions would be greatly appreciated!

[Hero999]

I don't know.

It sounds like the voltage is too low or the batteries have too higher impedance.

Have you measured the battery voltage?

Try connecting a 100

[Kevin Weddle]

Replacing an AC adaptor with just a series of small batteries is probably not good enough. A larger capacitor battery is what you could try.

[S1runner]

I don't know.

It sounds like the voltage is too low or the batteries have too higher impedance.

Have you measured the battery voltage?

Try connecting a 100

[Kevin Weddle]

I tried using a 12v battery with an AC/DC converter and the Audio whining noise was even worse (plus added video distortion).

Just connect a 12V battery to the input power connector. To be sure, use an oscilloscope to verify that the adaptor connected to the camera produces 12V regulated. If it's 12V regulated, then try a higher capacity battery.

[Hero999]

Thanks for the response, i'll give that a shot.  How did you determine the farads of the capacitors?  

There's no magic formula, it's just something one should try when they encounter a problem like this.

Also, with DC power, when the caps are full, won't they stop the camera from working?

Why would it?

It sounds like you don't understand what the capacitors do.

The amount of energy stored by the capacitors is negligible compared to the batteries. The capacitors should be connected in parallel with the batteries, not in series.

When the capacitors are connected across the batteries, they will charge to the battery voltage and stay at that voltage until they they are flat and won't prolong or shorten their life much.

The capacitors just reduce the impedance (AC resistance) of the batteries at higher frequencies. When the device draws a short but large pulse of current, the battery voltage can drop a bit before returning to its original voltage which can some some appliances malfunction. When a capacitor is added it supplies the current when the device wants to draw more than the battery can provide and recharges when the current drops. A good analogy is a water tower which is used to keep the mains pressure constant and smooth out peak and troughs in demand. Note that a capacitor does not create energy: if the device continuously draws more power than the batteries can supply, it won't help, just as a water tower doesn't stop reservoirs becomming empty during hot and dry weather.

I tried using a 12v battery with an AC/DC converter and the Audio whining noise was even worse (plus added video distortion).

What sort of 12V battery did you try?

Did you measure the voltage whilst the camera was connected to it?

If it's a large battery, such as a car battery and it's in good condition then the capacitor idea probably won't work as the battery should have such a low resistance, it won't make any difference. If so then there is some other problem, but we'll cross that bridge when we come to it.