Re: PS AC current leakage

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "oldpayphones" <larry@...> wrote:

>
> Is there any backyard way to measure AC leakage from a DC rectifier
> other than using a o-scope. If measured with a multi-meter what would
> be an acceptable amount? I assume there will be some leakage. Can I add
> more Caps to smooth the wave?
>
> Thanks,
> Larry Olson

Define leakage current? That would have to be current that goes
through a diode when it is reversed biased. Reverse leakage can be
measured with an ohmmeter on a high ohms scale. It will be a very
small amount. That is not what is causing your ripple. Ripple is
porportional to load. If you have more than 5% ripple (meaning the ac
component on top of the DC volts (measured with a scope)under full
load then you need more capacitance. The bridge conducts each half of
the AC sine wave and without a cap it is a series of AC "humps" each
peak 8ms apart. Also known as pulsating DC. It no longer swings
negative but all of the humps are postitive. The cap charges each
"hump" up to the peak of the wave. It discharges as the hump goes to
zero and starts back up again. The cap has to store energy during the
center part of the hump and then feed the load during the other parts.
It will sag in voltage based in the value and the amount of load.
The trick is to place the cap value at a level high enough to feed
current and not sag too much. A charged cap can supply a lot of
current into a heavy load/short for a short amount of time.