1000watt (24v 40A) powersupply help / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

1000watt (24v 40A) powersupply help

1 2 3 next

Move Thread

LAN_403

El_Roberto

Wed Nov 26 2008, 10:40PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

As the title says I am building a new desktop powersupply (My current one is my dads and it is only designed for radio work at 3amp max). I found two old industrial transformers in the shed, one is rated at 20v and just higher than 40Amps

and the other is 20v and around 35Amp. For now I will probably just use the smaller one (the bigger one weighs about 20kg) but I want to be able to use the bigger one if I ever need more current. But I dont know how I should go about this, I want to build it like my dad's which has variable voltage from (0-20v) and variable current limiting (0-3A). Im thinking a variable voltage regulator (I have lots of 1Amp ones) and some high power transistors. But I dont know how I should connect this (Can I use the transistors in parralell? I have some rated at 10amp 400v). Ill post a pic of the transformers soon (They need a good dusting first). Thanks in advance for any help.

ConKbot of Doom

Wed Nov 26 2008, 11:31PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

first off, do you really want to dissipate 760 W when you need 1V @ 40 A for some purpose? Usually linear power supplies are low current because they make so much heat at high currnts and low voltages.

What sort of noise is allowable on the output? and would you consider a switchmode pre-regulator?

El_Roberto

Wed Nov 26 2008, 11:47PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

Hmm I didnt think of that, Also I am going to use the big Transformer because it is in better condition after opening it I found it is 1KVA (24v at 41.6A). Can you please discribe how a switchmode preregulator works? Ive never heard of one (Im only just starting to get back into electronics after a few years of not doing much). I dont think the noise will matter much on the output will it? Because I can just use a large filter capacitor. Also it is unlikely ill ever use 40amps at 1v... maybe at 12v (But that still leaves 500watts of heat)

ConKbot of Doom

Thu Nov 27 2008, 02:19AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

A switchmode preregulator is basically just switchmode power suply that feeds a linear power supply, with enough voltage to to keep it regulated, but not so much that the linear portion has to dissipate a ton of heat.

The pre-regulator doesnt need to be too fancy. At 24V you could make do with a simple buck regulator that runs at a fixed frequency, filter it well, and then have a linear regulator output stage.

As far as noise, 200mV of noise would be a noisy power supply, and my nice agilent power supply at work tops out at around 1-2mv of noise.

A large cap will help some, but wont eliminate all high frequency noise from a switchmode only power supply, given that it would only be a first order filter (3 db per octave from the corner frequency)

What do you want to power with this? Depending on how noise tolerant it is, you could make a switchmode only power supply, or do a linear with a switchmode pre-reg if you need the power cleaner.

Any 40A regulated power supply is a significant undertaking, and luckily there are quite a few knowledgable people here with a ton more experience then me.

El_Roberto

Thu Nov 27 2008, 02:57AM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

Thanks for your help, I probably dont want too much noise as im going to be powering microchips and things with it as well as all the other more powerful things such as boost converters and such. I would use a less powerful transformer if I could but I cant afford to buy one (about NZ$90 for one) as well as all the other components. And it will be an interesting project.

Sulaiman

Thu Nov 27 2008, 06:35AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

A simple approach is;
- Line filter
- Variac
- Mini circuit breaker
- Transformer
- Bridge rectifier
- Capacitor(s)

Although not perfect it's very simple, easy to diagnose any problems and rugged.
A major benefit is very low noise - useful for audio/radio frequency use.

If regulation/ripple is important then ADD a linear regulator, adjust the variac for low regulator power dissipation.

El_Roberto

Thu Nov 27 2008, 07:50AM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

While that is a simple approach it is also rather expensive ($250 for a 500VA variac). I want to try and keep it as cheap as possible that is why im trying to use parts I might allready have. After looking in the shed again I found about ten good filter capacitors I can use (from about 3200uf to 9000uf and 35v to 200v)

EEYORE

Thu Nov 27 2008, 04:42PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Not expensive at all. Variacs are cheap on ebay.
matt

El_Roberto

Thu Nov 27 2008, 08:38PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

I cant buy stuff offf ebay, I live in new zealand and shipping is allways in the hundreds of dollars. I recently looked at getting some capacitors from ebay and the shipping would have been $400, for some $100 capacitors!

Proud Mary

Fri Nov 28 2008, 10:35AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Why not go for a happy and inexpensive compromise, Robert?

Use the 25V 35A rectified, smoothed and unregulated, but connect across it a three terminal regulator like LM338 to supply ~1.2 - 30V at more than 5A to create a second very useful output.

And you could add a variable current regulator, like the famous L200, across it to create a third output with both variable voltage ~3 - 30V and adjustable current limiting up to 2A?

So you would have a very versatile three outptut PSU using only very light weight (postage!) and inexpensive parts.

1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob