want to build a power supply

skylinechild · Joined: 12 Sep 2008 Posts: 4 Location: In a Skyline

hey guys i want to build a power supply but not just any power supply i want to build one that can out put 50 Volts and 30 Amps...it has to have variable control for both voltage and amperage as well as 2 different analog meters displayin the voltage output and amperage output.....and give a clean waveform....souns kinda high i know but i really want to do this project....can you guys help out

i already got the basic diagram for a power supply.....transformer....4 diodes....switch....fuse...etc

where can i get such a transformer to step down the 110 volts to 50V and 30amps.....

what type of diode would i need to get...tell me the part number.....so i can go out and ask for it and buy it from the store....also what i was thinking...since it has to rectify 50 volts i was thinking of overrating the diodes a bit..instead of getting a diode to rectify 50 volts get one to rectify 70 volts instead....so it wont be a problem to rectify the 50 volts....so it will be able to handle the task of rectifing such a large voltage...

if rectifying such a large voltage cannot be done can i build two smaller rectification circuits on separate circuit boards and connect them up to each other at the output stage of the rectification...

i already have a switch and fuse...that's taken care of...

also since it's got to have a clean waveform..i was thinking after rectification to make a complete different circuit just for smoothening the wave....just like a lot of capacitors connected up to each other just to do this...since the waveform gots to be smooth i was thinking of building two such circuits just for this.....after all 2 heads are better than one...

since the voltage and amperage got to be adjustable.....i will need two variable resistors.....what values should i use.?

and i know i've got to put an internal load in it....but instead of placing just a 1k ohm resistor as an internal load....i will use the two analog meters and connect them up........one to display output voltage.....one to display output current......and well i also installing a fan in there...

i've already gotten started on building the housing and i can say..it's big..like shoebox big....to mount the circuit boards inside there...i've made like trenches or rails into the sides of the housing....so the circuit board will be able to slide in and to make it stay in i'm gluing the tip of the board onto the trench....

it's kinda like a tongue and trench design.....anyone with woodworking knowledge and skills would know this....the curcuit board is like the tongue and it fits or slides into the trench...

tell me....can u guys help me out..can this build be done...?

vtech · Joined: 08 May 2006 Posts: 1264 Location: USA

Sounds like you have some ideas but, I'd suggest reading a book or research on power supply design to at least get more familiar.
While you may have the basic idea of a design consisting of txformer/diodes/caps used on smaller circuits, building a 50V 30A supply this way is rather undesireable due to cost/size/availability of the txformer alone not to mention the inefficiency involved.
You also mentioned clean waveform; this is normally achieved by means of "switch mode" power supply which allows regulated voltage & higher currents with the use of much smaller txformer w/various control circuitry.

Guest · Posted: Fri Sep 26, 2008 10:36 pm Post subject:

If you have transformer difficulty you could always use 2 identical ones and run the secondary in parallel to double the current, same can be done with a transformer that has two identical secondary windings.

You mentioned variable.... but you didn't say stabilized if this is the case then the power dissipation of the pass transistors will need to be considered, especially when set to a low a low voltage output as the voltage drop across the transistors will be greater this multiplied by the current, say 50 amps will produce heat.

It would be beneficial to say what this is to be used for because there may be a easier way round to doing things, for instance one might get away with a transformer driven from a variac... that is a autotransformer with a variable tapping that feeds the 50V isolation transformer.

Dave

Pentode · Joined: 30 Oct 2007 Posts: 85 Location: Nr. Manchester (UK)

Sorry forgot to log in, I said 50 amps, my bad.... I should have said 30 Amps

Dave

skylinechild · Joined: 12 Sep 2008 Posts: 4 Location: In a Skyline

thanks for the info......so tell me exactly what i need to get and start from the begining...i'm kind of on the intermediate / novice level in electronics

i remember triacs and all them other stuff from school.....lol. but the calculations is what i cant handle....

talk to me...what do i need.?

Justmanuals · Joined: 21 Aug 2004 Posts: 1948

vtech already told you what you need, buy yourself a book.

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skylinechild · Joined: 12 Sep 2008 Posts: 4 Location: In a Skyline

found some good hi quality parts by my local electronics shop....also saw a nice transformer in the display case there....gonna buy it ..

already got housing....input voltage meter power switch and power light and fuse holder....and fuse.....will post back with more info soon....

who ever said it cant be done well.......u wanna bet.?