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

[Phil Allison]

"Ray"

I have a bunch of old 80 amp scr's (GE C46h) out of an old lighting
dimmer

I would like to use 4 of them to make an ordinary bridge rectifier for a
heavy duty 12-15 vdc power supply...

What do i do with the gate, and the other wire sticking out of the scr ?

** 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.

When these are connected, do I gave an 80 amp bridge, or a 160 amp bridge
?

** Neither.

I have read arguments about this, havent heard a definite conclusion...(Is
each diode only in use half the time ?

** 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.

http://www.datasheetarchive.com/preview/959231.html

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

 

[John Popelish]

Ray wrote:

I have a bunch of old 80 amp scr's (GE C46h) out of an old lighting dimmer

I would like to use 4 of them to make an ordinary bridge rectifier for a
heavy duty 12-15 vdc power supply...

What do i do with the gate, and the other wire sticking out of the scr ?

When these are connected, do I gave an 80 amp bridge, or a 160 amp bridge ?

I have read arguments about this, havent heard a definite conclusion...(Is
each diode only in use half the time ?

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]

I am looking to make an 80 amp or greater power supply, and havent found any
bridges in that category, and 100 amp diodes seem expensive and hard to
find,

Ray
"John Popelish" <jpopelish@rica.net> wrote in message
news:bbqdnfzuub_z4yranZ2dnUVZ_t2inZ2d@comcast.com...

Ray wrote:
I have a bunch of old 80 amp scr's (GE C46h) out of an old lighting
dimmer

I would like to use 4 of them to make an ordinary bridge rectifier for
a heavy duty 12-15 vdc power supply...

What do i do with the gate, and the other wire sticking out of the scr ?

When these are connected, do I gave an 80 amp bridge, or a 160 amp bridge
?

I have read arguments about this, havent heard a definite
conclusion...(Is each diode only in use half the time ?

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

 

[Phil Allison]

"Ray"

I am looking to make an 80 amp or greater power supply, and havent found
any bridges in that category,

** 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

 

[John Popelish]

Ray wrote:

I am looking to make an 80 amp or greater power supply, and havent found any
bridges in that category, and 100 amp diodes seem expensive and hard to
find,

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.

http://www.vishay.com/docs/93521/9352170h.pdf

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:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250

--
Regards,

John Popelish

 

[BobG]

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.

 

[BobG]

On Feb 16, 10:11�pm, John Popelish <jpopel...@rica.net> wrote:

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:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250
======================================John... I saw a dozen of those at Skycraft Saturday

(skycraftsurplus.com)

 

[Ray]

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.

http://www.vishay.com/docs/93521/9352170h.pdf

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:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250

--
Regards,

John Popelish

 

[John Popelish]

BobG wrote:

On Feb 16, 10:11�pm, John Popelish <jpopel...@rica.net> wrote:
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:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250
======================================> John... I saw a dozen of those at Skycraft Saturday
(skycraftsurplus.com)

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

--
Regards,

John Popelish

 

[Ray]

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" <argyle1nospams@hotmail.com> wrote in message
news:m3Ptj.47104$Ly.26584@pd7urf1no...

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.

http://www.vishay.com/docs/93521/9352170h.pdf

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:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250

--
Regards,

John Popelish

 

[Phil Allison]

"Ray"

The synchronous mosfet seems like a good idea, I'l l be reading up on
that,

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



........ Phil

 

[Jamie]

Phil Allison wrote:

"Ray"

I am looking to make an 80 amp or greater power supply, and havent found
any bridges in that category,



** 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

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"

 

[Jamie]

Ray wrote:

I have a bunch of old 80 amp scr's (GE C46h) out of an old lighting dimmer

I would like to use 4 of them to make an ordinary bridge rectifier for a
heavy duty 12-15 vdc power supply...

What do i do with the gate, and the other wire sticking out of the scr ?
Learn a lot more electronics before even thinking about this?

When these are connected, do I gave an 80 amp bridge, or a 160 amp bridge ?

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)

I have read arguments about this, havent heard a definite conclusion...(Is
each diode only in use half the time ?
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"

 

[Michael A. Terrell]

John Popelish wrote:

BobG wrote:
On Feb 16, 10:11�pm, John Popelish <jpopel...@rica.net> wrote:
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:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160208680250
=======================================
John... I saw a dozen of those at Skycraft Saturday
(skycraftsurplus.com)

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

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

 

[default]

On Sun, 17 Feb 2008 04:51:30 GMT, "Ray" <argyle1nospams@hotmail.com>
wrote:

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

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.
--

 

[BobG]

On Feb 16, 11:52�pm, John Popelish <jpopel...@rica.net> wrote:

I can't find any through their web page.
Maybe you had to be there.
===================================They do a lot of mail order and ebay sales.... but I bet if you called

and described the gizmo and tell them its sitting on the top shelf
right by the bridge rectifiers they'd put it in a bag and mail it to
you. I think they were marked about $2. I was looking in the box next
to them for IGBTs... they get those once in awhile. Hamfest was last
weekend. Place was shoulder to shoulder with folks from all over the
southeast.

 

[Ray]

I have a bunch of old 80 amp scr's (GE C46h) out of an old lighting dimmer

I would like to use 4 of them to make an ordinary bridge rectifier for a
heavy duty 12-15 vdc power supply...

What do i do with the gate, and the other wire sticking out of the scr ?

When these are connected, do I gave an 80 amp bridge, or a 160 amp bridge ?

I have read arguments about this, havent heard a definite conclusion...(Is
each diode only in use half the time ?

m