PowerSupply Voltage problem

[grabben67]

Hi, i´m about to connect my xylotax to PowerSupply, but got some voltage problem.


I have built PowerSupply as attached jpg, Without capacitor of 10000mF i´ve got 28V as expected, BUT when i also attache the capacitor i got 40Volt!!

I´m not a rocket scientist and cant understand this, can anyone please help me to sort this out....

I guess i should have 28 V and capacitor...

Best regards

Rikard

[motomitch1]

that would be right 28v X 1.4 = 39.2 V

[motomitch1]

You would need a 24v p/s if you need 28 volts

[Al_The_Man]

You would need a 24v p/s if you need 28 volts

Wouldn't that be 19.7 (20v)?
28 x .707.
Al

[unterhaus]

You say that there is an attached jpg, but I don't see it.
If the transformer is rated for 28v AC you will get 1.414x28=39.6vdc when you rectify and filter it, as someone said above
If you have some other setup, we would need to see it in order to figure out the problem.

Al, didn't you show us how to add an inductor after the rectifier feeding the cap in order to cut down the peak voltage somewhat?

[Al_The_Man]

Al, didn't you show us how to add an inductor after the rectifier feeding the cap in order to cut down the peak voltage somewhat?

No that was'nt me but this is the link, although I would not use it to drop the 10v he needs.
Transformer voltage seems too high for Gecko
Al

[ESjaavik]

I have built PowerSupply as attached jpg, Without capacitor of 10000mF i´ve got 28V as expected, BUT when i also attache the capacitor i got 40Volt!!
Rikard

Hei Rikard,

Without the capacitor your output voltage will vary between 0V and 28V*SQRT(2). Looking at it with a scope it will look like a sinewave where you cut out everything below 0V and turn it around to become positive. The RMS value of your waveform will be 28V.

When you connect the capacitor, it will supply the voltage inbetween the peaks and get a recharge on each peak if there is a current draining it. So with no load you will have a constant DC equal to the peak voltage. If there is a load, it will look more like a dull saw form ramping up to peak, then falling slowly down to the next recharge 100 times / second.

I hope your capacitor is rated for 50V, or I might hear it all the way over here.

[Al_The_Man]

Rikard, If you go to the Plitron Transformer site and look at the tech notes, it will explain all. http://www.plitron.com/
Al

[grabben67]

Thanks all! Then i guess 24 Volt is nearly to blw my card...24 x 1.414 = 33.93 Xylutex burns at 35 volt including backVoltage. I Guess the best thing i can do is go down to 18V and then get 25,452 V.

Anyone of you using Xylotex? What Powervoltage does you use?

Thank´s

Rikard

[grabben67]

What difference does the voltage of the capasitor make? if i use 25 Volt DC and a capacitor og 63V, will it be ok? or is 38V okey, or should it be 50 Volt??

Best regards

Rikard

[unterhaus]

The voltage of the capacitor makes no difference other than if you use a lower voltage capacitor it is more likely to fail. Sort of like using a wire that is too thin