Bridge Rectifying Help

[CitizenDC]

Hi Guys,

I'm working on a project and I'd appreciate some help with a problem I'm having rectifying AC to DC.
The AC voltage is 22v. When I setup a diode bridge and rectify it I measure 10.5/11volts DC volts with an analog and digital mulimeter...
When I measure the voltage using the meters AC setting I get 21/22 volts.
Thinking that maybe one of the diode in the bridge is faulty I wired up a second bridge with the same results.

Any ideas? Have any of you come across this sort of behavior?

[Jetijs]

Put a capacitor on the DC side and measure the voltage then. If your input is 22VAC, then you should get about 30VDC on the cap.

[broli]

That's indeed strange behavior. Even if one diode was fault it would still function as a half wave rectifier. Filter it with a cap like Jetijs suggested and see what happens.

[CitizenDC]

Thanks for the suggestion guys.

I tested three electrolytic capacitors (50v-1uf, 63v 47uf, 200v 560uf) as filters for the diode bridge.
All three displayed similar results when measuring DC, showing 14-15 volts.

I then tested the AC voltage across the caps with both my digital and analog meters and I see it now reads 30v AC.
The caps appear to be making an improvement to both AC & DC readings and again the DC output is about half the AC.

While I was taking measurements, I got to thinking about the switching happening in this circuit. The switching is very fast... I wonder if a general diode is enough to handle the frequency of the output AC voltage and that maybe because the frequency is so high that its bypassing all the diodes (if thats possible...).
Any ideas? Is there maybe a faster diode I can use?

[broli]

That might just might be the issue here. I'm no expert but you can probably find the ratings of the bridge using its model number. There are a lot of guys here that can give you more specific advise.

[Joit]

Broli found the Hint with the Ratings.
Probatly your Rectifierbridge is overrated, and better use a lower one.
Even when you have low Amps and a Thick Diode, the Diode can eat a lot from the current.
Big Diodes need even more Current, that the current can break through.
And each Diode takes something from the Current away.
And for your low Voltage, you can maybe make your own Rectifier.
Here is a Link for some basic rectifier.
Gleichrichter-Grundschaltungen
But its all in German, so maybe you can find a Page in your Language.

Or you even only put a Diode at one wire, and a Cap between the output from the Diode, and the other End of the Coil
like Jetijs mentioned, then you can see, how much left.
And maybe you use a 1N4xxx Diode.

In doubt, you an look here for the Values of the Parts.
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view

Usual the Retifiers are allways fast enough, to change Ac to Dc, you see that, how much AC is left behind the Rectifier.
But for this, you put a Capacitor thereto, that it smooth the DC out.

[CitizenDC]

I've got two leads to go with right now, faster switching diodes or alternately efficient lower voltage rectifiers. I'll try both and see which does the trick.

Again, thanks for your help and advice!