diy PSU design

Thread Starter

adamclark

Joined Oct 4, 2013
472
im not trying to argue or question you guys.. im only trying to understand how things work.. you could give me a schematic and I could build it but if I don't understand why it works and how it works then I have failed with this project.. I have a decent psu right now that's adj. to 30vdc but its only 750ma which wont even power up a car dvd player.. but its great for small projects. I also have an astron that will give me 100a at 13.5vdc all day.. I don't need this psu.. I only decided to build a badass psu because I think most of the basics are covered in the design of one..
 

bance

Joined Aug 11, 2012
315
That is not a data-sheet! The data-sheet is here !

The design I refer to was that in post #11.

can somebody please explain to me in newbie terms how the second picture in post 14 works also please?
Did you not read the circuit description? (on page three, as you carefully pointed out?)
 

bance

Joined Aug 11, 2012
315
im not trying to argue or question you guys.. im only trying to understand how things work.. you could give me a schematic and I could build it but if I don't understand why it works and how it works then I have failed with this project.. I have a decent psu right now that's adj. to 30vdc but its only 750ma which wont even power up a car dvd player.. but its great for small projects. I also have an astron that will give me 100a at 13.5vdc all day.. I don't need this psu.. I only decided to build a badass psu because I think most of the basics are covered in the design of one..
Then start with a simple circuit and figure it out as you go!
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
That is not a data-sheet! The data-sheet is here !

The design I refer to was that in post #11.

Did you not read the circuit description? (on page three, as you carefully pointed out?)
so the schematic with the 2 3055's and single 317 will work? really 15a capable and adjustable? if this is the case I will build it tonite..lol
 

bance

Joined Aug 11, 2012
315
Invariably the first Technical section of a data-sheet is the "ABSOLUTE MAXIMUM RATINGS",
this will tell you what can or cannot be tolerated by the device in question.

If anything is outside of that scope, it will not be guaranteed to work.
 

#12

Joined Nov 30, 2010
18,224
Figure 24 from the datasheet in post #27 explains what is wrong with the second drawing in post #1.

I did not read most of this thread, so if I am repeating somebody, please forgive and ignore.
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
ok so I started with the project, I used the center tapped coil and my mb34 rectifier, I hooked up each wire from the transformer to the ac legs on the rectifier and I put an orange wire on the + leg on the mb34 and a red wire on the other.. now I have dc voltage on the red and orange wire 20.9vdc each? the math said my dc voltage would be higher. but the center tap is the - the red should be the +vdc and the orange should be the -vdc .. now how do I invert the voltage from the orange wire? and after voltage drop from the rest of the circuit, Am I still going to get at least 16vdc from it?
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
nevermind,, the orange wire is -20.9vdc and the red is +20.9vdc.. so ,,,, so far so good..right??? whats next, do I start the 317 regulator or do I do the filter caps? Im really green to this, I tried to get as much info as I could before starting, but it came down to start building then work it out... which usually works best for me,, but I don't want to burn up to many parts getting through this.. But I have made progress,, awesome... Thanks for helping out.. ive banked a plethora of info so far.. and I want to understand why its doing what its doing,, that's why I ask so many questions.. plus the whole point of the build really
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
here is a drawing of where im at.. do I need the filter caps at this point? whats next? im into it now.. now I need to figure values of the filters and the pots that im going to adjust it with.. im pretty exited at this point
 

Attachments

bance

Joined Aug 11, 2012
315
Ok, you're making progress, good!

A couple of things I noticed, first :-

In post #1 you stated that the voltage across each tap was
Ive chose a transformer its an old Marantz with a sec hv coil that is center tapped and from the center to each side it is 44.5 vac. I have that figured to make 62.47 VDC.
Not sure how you arrived at these figures.....? But anyhow let's assume that the figures in post #32 are correct, since they are measured?

Second, did you read the data-sheet for the mb34 rectifier? What is it's current rating?

Do you have an oscilloscope? If you do, it might be interesting for you to have a probe around the secondary side of the circuit to see whats going on.
DO NOT PROBE THE PRIMARY SIDE.:eek:

The filter caps come next.....
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
the rating for the rectifier is 100v 50a, I must have measured it wrong in the beginning,,because my notes say 44.5vac also,but I think that may have been across the secondary not from center out.. 44.5 split in half is what I ended up with.. minus voltage drop across the rectifier of course..
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
yes I definetly put the wrong numbers up,, theres a small note in my notes that show from the center tap to each leg of the hv sec. being 22.6vac.. so whats next? filter caps or regulator circuit? or something totally different? 22.6vac works out to 31.7vdc.. so ive lost 10v from the rectifier?
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
I was able to get 19a out of it before the transformer and rectifier started getting warm.. so I think 10a shouldn't be a problem,, and I put it on the oscope and the wave looked smooth and just like the unfiltered rectified wave on your link..Im not sure what other tests to do before moving on.. still trying to calculate the filter caps. I understand the math equation but Im not sure what parameters I need to use to calculate them. I don't always understand the technical terms. thanks again, still stoked to have got this far and when I seen the wave was so smooth on the oscope it put a smile on my face.. im so ready to move forward on my psu project
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
Here's a link to a page that shows how to calculate the filter caps.
A few questions on your link sir,, In the example they are using a set value of 9v 500ma so all the examples relate to that. so to choose on a variable supply( that I think im going to limit to +/-16vdc max) do I use the max voltage in the equation or what? And I think im going to use the 8.1vac tap to power my meters and such and Im thinking im just going to use diodes as the rectifier instead of a rectifier. any problems with that? And am I reading it wrong or does it say towards the end the filter caps may increase the actual voltage I measure before the filter? It also says I need to find the dropout voltage, so is that for the lm317 or the 2n3055 I plas on using as a pass transistor?
 
Last edited:

Thread Starter

adamclark

Joined Oct 4, 2013
472
interesting observation.. im hooked to my oscope/volt meter and my ammeter. I have a dc motor that pulls 5-7 amps and my psu so far is 20vdc.. when I turn the motor on the ammeter shows the draw but the voltage on the oscope goes up to 23.4vdc.. Why is that? how can voltage rise under a 5a load?
 
Top