24-30v dc power supply schematic

--- View using a fixed-pitch font:

+-[BFD>]----------+-->OUT+ MAINS>-----+ +-+ | BFT | | +-[OUT- \ P||S | | R||E +-[BFC+]-+ I||C | | | | +-[-----+ +-+ | +-[BFD>]----------+

BFT:

BFC:

BFD:

-- JF

For high current designs a full wave using a center tap transformer is more efficient, it makes better use of the iron in the transformer and you only have one diode drop.

Let me get this correct here, you'd be happy with a 24V AC or

20v DC supply?

Jamie

I'm at a loss on how to view this.

--- Please bottom-post.

Fixed-pitch fonts are ones that have equal spacing between characters, like Courier.

Variable-pitch fonts are ones that don't have equal spacing between characters, like Times Roman.

If you view ASCII art with a variable-pitch font, the result will generally be an unintelligible mess.

Also, it's a good idea to start each line of an ASCIImatic with a character other than a space in order to keep some newsreaders from deleting a space if the first character in the line is a space.

I forgot to and my drawing got messed up; here's how it's supposed to look:

. +-[BFD>]----------+-->OUT+ .MAINS>-----+ +-+ | . BFT | | +-[OUT- . \ P||S | | . R||E +-[BFC+]-+ . I||C | | . | | +-[-----+ +-+ | . +-[BFD>]----------+

-- JF

--
I disagree. 

With a bridge you're using all of the secondary all of the time, while 
with FWCT you're using half of the secondary half of the time and the 
other half of the secondary the other half of the time. 

Also, FWCT takes twice the number of turns on the secondary and the 
rectifiers have to stand off twice the reverse voltage.

you're going to make an induction furnace, but need help with the brute force power supply?

a plain bridge rectifier and some giant caps is probably fine for what you need. something around 20VAC from the transformer will be about right.

Since you only need about 300 watts you might be able to use the 12 VDC from a couple of old computer power supplies, in series. A 400W supply usually has 12V at 15 amps or more. You may even be able to hack it to get what you need with one unit, and if you can use the frequency of the supply for the induction furnace, you may be able to tap off before the output rectifier and use it directly on your induction coil.

fo/17094+PS/ (12V 14A, $10) fo/17980+PS/ (12V 22A, $16)

You can also get single output switching power supplies for 15 amps or more:

($15)

Paul

actually, I was thinking he could gets his hands on a 24 volt charger from an auto parts store.

I have a large garage charger I gutted out and made a heavy duty 13.8 volt supply to test run 12 volt auto equipment.. I got large caps in there filling the hole and a soft start. N channel power mosfets sinking the (-) side output through an inductor to switch mode regulate it.

Works a treat, the caps are in 2 stages, one set before the switch and another set after.

I figure even if it fets shorted, the full output isn't that much higher, some equipment should handle it. ;)

Jamie

Bad idea. The negative is tied to the case, and the power line neutral.

That's what I'd always heard. You need center tap only if you need output balanced about zero. It's also easier to filter the output from the bridge with a solid ground reference.

--
Les Cargill

that only wrks if you plug one of them into an isolating transformer.

--
?? 100% natural

An easy option is two car batteries in series, with a couple of chargers attached. If the induction furnace only operates for a few minutes at a time, you can switch the batteries from series to parallel and charge 'em offline.

Anything DC has to be filtered, if not regulated, and 15A of ripple current is going to require some thought. Car batteries might be overkill, but as long as the problem gets dead...

If you decide to get a regulated supply, there's surplus options. Consider:

"Rick"

** That is 100% WRONG !!!!!! ** The link is full of damn silly errors, shame on Hammond.

A full wave bridge plus filter cap is the most efficient by far.

And to a close approximation, peak DC and average DC are the SAME !!

... Phil

neutral.

The negative MAY be connected to the case, but certainly not to the power line neutral. So you may be able to remove the case ground connection, or just float the second supply case 12VDC above the other. Here is a schematic of a 300W ATX supply showing the separate grounds:

Paul

power

or

Here is an article about using two server PSUs for 24 VDC:

And here is a good article about using components from a PSU to build your own, with high efficiency synchronous rectifiers:

Paul

Every PC power supply I have, has the negative connected to the ground pin.

What about the leakage current from the PFC, and EMI caused by an ungrounded supply? You can do lots of things that aren't good ideas.

that depends on the voltage you want from the power supply. If you want a low voltage high current supply, a bridge rectifier can be a poor choice.

that's if there's no ripple. They never defined it, so yeah you could question the pdf.