Can I use 4 scr's as a ordinary rectifier bridge ?

"Ray"

** The C46H SCR has two terminals on top of the case - the gate is the smaller and the larger is the cathode. Connect a 1 amp diode from the case ( ie anode) to the gate to convert the SCR to simple diode operation. ** Neither.

** For a bridge feeding a capacitor input filter - each diode conducts only about 10 % of the time.

Down load the pdf on this page - it has all the gory details.

Your idea will maybe create a 30 amp ( average DC current) bridge.

It will need a massive heatsink too.

Buy an ordinary 40 amp bridge.

...... Phil

You have to figure out a way to trigger the gates each time the SCR is forward biased, but not over voltage the gate in reverse, when the SCR is reverse biased. And you will have to put up with about twice the forward voltage drop compared to normal rectifier diodes, since each SCR has two junctions in series when they are conducting.

Are actual rectifier diodes so expensive?

If I were building a 12 to 15 volt supply, I would use Schottky diodes and cut the forward drop about in half, compared to silicon junction diodes, and cut the waste heat.

--
Regards,

John Popelish

"Ray"

** You CAN use more than one 40 amp bridge - you know.

Either wired in parallel and mounted on a common heatsink - OR and much more technically elegant, have the AC transformer wound with 2 or three

*identical* secondaries.

Then you only parallel the + and - terminals.

...... Phil

Do you want a two diode (half bridge) to use with a center tapped winding, or a 4 diode (full bridge) to use with a single winding?

70 amp stud diodes from Digikey run $8 each, and can be had in reverse polarity, so two of the cathode to stud polarity can be mounted on one isolated heat sink for the positive output and two of the anode to stud polarity can be mounted on another isolated heat sink for the negative output.

Those 4 in a bridge can deliver more than 80 amps out.

The ones to watch for on eBay are two diodes in series (the common terminal connects to the anode of one and the cathode of the other) in an isolated module. A pair of them make an easy to cool bridge. Here is an example:

--
Regards,

John Popelish

Get a couple of 80 amp mosfets and make a synchronous rectifier. If the diodes are wasting .7V * 80A (56W!) the mosfets should be able to do better than that.

John... I saw a dozen of those at Skycraft Saturday (skycraftsurplus.com)

I want a full bridge, as I have a couple of 80 pound transformers with a single output winding,

I guess I'l just buy the appropriate diodes.... I was just trying to utilize some of the stuff I've been collecting, and the scr's seemed like a good idea. I want to build a heavy duty general purpose power supply for battery charging large batteries at my cabin, driving a winch, maybe light welding. I have built a pwm controller for the output so I can use it with both small and large generators, I see some 250 amp diodes on Ebay i'll probably bid on

I learned something, I didnt know they made dides in a series configuration... Thanks for the input

Ray

" tive output.

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I can't find any through their web page. Maybe you had to be there.

--=20 Regards,

John Popelish

The synchronous mosfet seems like a good idea, I'l l be reading up on that, as the 75 amp controller was the only thing I've ever done with mosfets. probably could be able to integrate it all into one circuit.

"Ray"

** Be aware that mosfets are diodes when non conducting.

....... Phil

example:

Their web page has always been useless, and about as informative as the people who work there. The last time I looked at it, it was nothing but pictures of them at the Orlando Hamfest.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Don't count them out entirely. If you want welding, battery charging etc. you can use them in a partial bridge - two regular diodes and two SCR's for a pretty good adjustable power supply. Much more efficient than a linear supply of the same amperage.

You just need a phase control for them - the basic unijunction and phase shifting network to trigger them. I did something like that awhile ago and was happy with the results. I used a pair of SCR's and a center tapped transformer, but if I were to do it again I'd use a pair of diodes and scr's.

The only downside was I needed a source to trigger the SCR's that was more positive than the cathodes (positive output). If you used pulse transformers that would be unnecessary. In my case I had a toroidal transformer so just wound a 10 volt winding on top of the windings already there. It just supplies a low current so doesn't need a massive second transformer.

The upside is it is relatively bullet proof. Mine had no feedback so didn't "regulate" just controlled the output. Mosfets in a welding environment wouldn't be my first choice. SCR's TRIAC's or IGBT's would.

Learn a lot more electronics before even thinking about this?

No, you get only what the max of a single item can deliver and that is with proper heat sinking and voltage ranges. (80 amps)

only 2 diodes out of a bridge are active at once. the pairs alternate in a time sequence.

that's about as simple as I can make it.

Unless you're planning on making a phase controller for these SCR's I would suggest you stick to diodes rated for the load and voltage.

--
http://webpages.charter.net/jamie_5"

Come one Philip, you know better than paralleling bridges with out load balance compensations. And I really don't think you can achieve that with bridges since there is no guarantee all diodes used in the bridge are matched. In the end, one bridge is going to be doing more work than the other. Using resistors is just going to deteriorate the output.

--
http://webpages.charter.net/jamie_5"