power rectifier circuit

[zeed]

I am having some trouble with "simple" power rectifier.
Have one 24V transformer but when I mesure voltage after rectifier and capacitors i get as much as 38V.
i have 2x1000uF capacitors connected.
How do I get rid of the extra voltage??

Dont know if you can understand my problem because my english is not so god...

[Bubba]

Zeed,
The 24 V AC is measured at rms voltage which is .707 of the peak voltage and the DC voltage is the peak voltage of the system. In order to get "rid" of the excess voltage, you need to reduce the "ac" voltage. DC voltage of this "simple" unregulated voltage is 1.4 times the ac voltage.

Hope this helps.

[Zig]

What are Your requirements?

X VDC at Y Amp?

[Al_The_Man]

One efficient way to reduce the voltage if possible is to reduce the secondary winding, i.e take turns off, typical is 2~3 turns/volt.
The secondary is usually wound last so it could be as simple as this.
Al.

[martinw]

Dear Zeed,

It would help us if you could let us know what DC voltage you would like, and also the DC current that the circuit will need. Could you send us details of your transformer? Are you using a bridge rectifier circuit for the power supply?

If you can tell us that, there are plenty of people who can help here. There really are, and they will do so gladly. All we need is a bit more information.

Best wishes,

Martin

[zeed]

Thank you all for answering.
This is salvaged transformer with multiple outputs so I just took 18V instead 24V...It has 12,18,24 and 32V outputs.
Now I got 20,4V dc after the rectifier.

"DC voltage of this "simple" unregulated voltage is 1.4 times the ac voltage. "
I learned something new today

My driver board can only take 24V so this will be OK.
I tried to connect it to 25V and one of the capacitors on the board went to heaven....

Thank you again.

[Al_The_Man]

18v ac should give you nearer to 24+ than 20.4DC, unless you had no cap connected?
If so the result will be pulsed DC. 120Hz ripple, or 100hz on 50Hz supply.
Al.