I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

On Sep 17, 9:20*am, Karl Townsend
wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:http://www.digikey.com/scripts/DkSea...l&name=641-138...

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll

The anode/cathode studs let you use only two heatsinks.

jsw

On Sep 17, 9:51*am, Jim Wilkins wrote:
...
Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll
The anode/cathode studs let you use only two heatsinks.
jsw

That copied URL didn't lead to the part, so search for DSA75-16B and
DSAI75-16B.

jsw

I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
The largest I found is 50 amp [...]
Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

I've always heard that diodes don't parallel very well, I think
because they won't always trigger at the exact same time, so whichever
triggers first will take the brunt of the current. Even if a fuse
blows, the remaining diodes are now taking more than what they are
rated for. And as the old saw goes "the diode will blow to protect
the fuse."

I'd be tempted to take a page from the guys throwing together bridges
for getting DC out of AC-only welders, and use 4 individual stud
diodes...? Apparently if you get two pairs, one pair with the stud on
the anode, and another pair with the stud on the cathode, it's easier
to assemble. Then at least in theory, every component would be
capable of sustaining the full current it is exposed to.

Maybe you would you be able to find a suitable bridge as a welder
replacement part? Though finding one rated for 240V RMS (350V or so
peak) might then be an issue...

Just my $0.02,
--Glenn Lyford

On 09/17/2010 06:51 AM, Jim Wilkins wrote:
On Sep 17, 9:20 am, Karl
wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:http://www.digikey.com/scripts/DkSea...l&name=641-138...

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll

The anode/cathode studs let you use only two heatsinks.

If Digikey doesn't bring you joy, try Newark -- they seem to list more
'heavy industry' sort of electronics than Digikey.

You may also want to check Surplus Sales of Nebraska:
http://www.surplussales.com. They have a lot of heavy metal electronics
surplus, and I've never gone wrong buying from them.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Sep 17, 10:11*am, Glenn Lyford wrote:
...
I've always heard that diodes don't parallel very well, I think
because they won't always trigger at the exact same time, so whichever
triggers first will take the brunt of the current. *Even if a fuse
blows, the remaining diodes are now taking more than what they are
rated for. *And as the old saw goes "the diode will blow to protect
the fuse."...
* --Glenn Lyford

Diodes have a negative temperature coefficient, meaning that the
forward voltage drop decreases as they warm up, so the diode passing
the most current becomes the easiest path for more current. Internal
or external series resistance can help overcome this.
http://www.vias.org/encyclopedia/sem...de_basics.html

jsw

In article ,
Karl Townsend wrote:

I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

As others have pointed out diodes don't parallel very well. Depending on
the frequency of the surge you may be able to use a much lower rated
diodes. If you look at a detailed data sheet you will find the surge
rating. If you doubt this look inside an ordinary battery charger that
you can use to start your car with. The diodes in there are no way 100
amp or even 50 amp. If you don't want to chance this you can use 4 50
amp diodes in a bridge which will give you a 100 amp output. I can hear
the skeptics now. When you say 50 amp diode what does that mean? It is
defined as the average rectified current. As it only conducts over a
half cycle, the other diode in the bridge conducts on the other half
cycle thus the total current over a cycle is 100 amps.

Chuck P.

On Sep 17, 7:20*am, Karl Townsend
wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:http://www.digikey.com/scripts/DkSea...l&name=641-138...

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

Rectifier size isn't your only problem here, you're going to have to
have a wonking big cap or two and a suitable inductor, too, for
filtering. Diodes CAN be paralleled, the usual thing was to add
resistance in line with each, for 100 amps, that's going to be a
pretty good sized resistor(physically). Better to use discrete stud
or press-mount parts of the proper ampacity. If you could come up
with a center-tapped transformer, you'd only need two to get full-wave
rectification. That would also get you proper isolation from the
line.

Better still, cast around on the surplus market for a power supply
already built. Herbach and Rademan and Surplus Center might have
such, there are other places. With the economic down-turn, there's
got to be a bunch of that stuff out there.

Stan

On Fri, 17 Sep 2010 07:06:25 -0700 (PDT), Jim Wilkins
wrote:

On Sep 17, 9:51*am, Jim Wilkins wrote:
...
Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll
The anode/cathode studs let you use only two heatsinks.
jsw

That copied URL didn't lead to the part, so search for DSA75-16B and
DSAI75-16B.

jsw

Thanks, these parts are diodes. One is an anode stud, the other a
cathode stud. Do I need two of each? Draw me a picture of how to make
these parts into a bridge rectifier, please. (I'm thinking each AC
line gets one of each with both cathodes on one block and both anodes
on the other.) Does a cathode or an anode stud go to ground?

Do I tap these into an AL block for heat shink ? For my "hot" bock
could I also tap cap connections and four spots to send power to the
four servo amps? I would plan to fuse each servo here.

Karl



Karl

You may also want to check Surplus Sales of Nebraska:
http://www.surplussales.com. They have a lot of heavy metal electronics
surplus, and I've never gone wrong buying from them.

Thanks for the idea. Nothing big enough??

http://www.surplussales.com/Semicond.../Diodes-3.html

On Sep 17, 12:21*pm, Karl Townsend
wrote:
On Fri, 17 Sep 2010 07:06:25 -0700 (PDT), Jim Wilkins

wrote:
On Sep 17, 9:51*am, Jim Wilkins wrote:
...
Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll
The anode/cathode studs let you use only two heatsinks.
jsw

That copied URL didn't lead to the part, so search for DSA75-16B and
DSAI75-16B.

jsw

Thanks, these parts are diodes. One is an anode stud, the other a
cathode stud. Do I need two of each? Draw me a picture of how to make
these parts into a bridge rectifier, please. (I'm thinking each AC
line gets one of each with both cathodes on one block and both anodes
on the other.) Does a cathode or an anode stud go to ground?

Do I tap these into an AL block for heat shink ? For my "hot" bock
could I also tap cap connections and four spots to send power to the
four servo amps? I would plan to fuse each servo here.

Karl

Karl

http://en.wikipedia.org/wiki/Diode_bridge

http://en.wikipedia.org/wiki/Rectifier

Dave

Better still, cast around on the surplus market for a power supply
already built. Herbach and Rademan and Surplus Center might have
such, there are other places. With the economic down-turn, there's
got to be a bunch of that stuff out there.

Stan

I've spent time looking for large power suppliers with no joy. The
problem is a "snow storm" of offers with nothing the right voltage and
amps. I'm mostly looking eBay here, no way I've found to filter. I
would rather just buy this and let somebody else do the proper
engineering design.

Karl

On Fri, 17 Sep 2010 08:20:27 -0500, Karl Townsend
wrote:

I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

http://www.galco.com/scripts/cgiip.e...0100SB600-CRDM

On Fri, 17 Sep 2010 11:21:35 -0500, Karl Townsend
wrote:

On Fri, 17 Sep 2010 07:06:25 -0700 (PDT), Jim Wilkins
wrote:

On Sep 17, 9:51*am, Jim Wilkins wrote:
...
Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll
The anode/cathode studs let you use only two heatsinks.
jsw

That copied URL didn't lead to the part, so search for DSA75-16B and
DSAI75-16B.

jsw

Thanks, these parts are diodes. One is an anode stud, the other a
cathode stud. Do I need two of each? Draw me a picture of how to make
these parts into a bridge rectifier, please. (I'm thinking each AC
line gets one of each with both cathodes on one block and both anodes
on the other.) Does a cathode or an anode stud go to ground?

Do I tap these into an AL block for heat shink ? For my "hot" bock
could I also tap cap connections and four spots to send power to the
four servo amps? I would plan to fuse each servo here.

Karl



Karl

Be aware that both heatsinks will have to be electrically isolated
from ground, as will both - and + DC. If you want - DC grounded then
you'll need an isolation transformer before the bridge.

The Crydom module
http://www.galco.com/scripts/cgiip.e...0100SB600-CRDM
may be attached to a grounded heatsink, but - and + will still need to
be isolated from ground unless an isolation xfmr is present on the AC
side.

On 09/17/2010 09:24 AM, Karl Townsend wrote:

You may also want to check Surplus Sales of Nebraska:
http://www.surplussales.com. They have a lot of heavy metal electronics
surplus, and I've never gone wrong buying from them.

Thanks for the idea. Nothing big enough??

http://www.surplussales.com/Semicond.../Diodes-3.html

Looks like it.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 09/17/2010 09:21 AM, Karl Townsend wrote:
On Fri, 17 Sep 2010 07:06:25 -0700 (PDT), Jim Wilkins
wrote:

On Sep 17, 9:51 am, Jim wrote:
...
Digikey lists rectifiers up to 400A
http://search.digikey.com/scripts/DkSearch/dksus.dll
The anode/cathode studs let you use only two heatsinks.
jsw

That copied URL didn't lead to the part, so search for DSA75-16B and
DSAI75-16B.

jsw

Thanks, these parts are diodes. One is an anode stud, the other a
cathode stud. Do I need two of each? Draw me a picture of how to make
these parts into a bridge rectifier, please. (I'm thinking each AC
line gets one of each with both cathodes on one block and both anodes
on the other.) Does a cathode or an anode stud go to ground?

Do I tap these into an AL block for heat shink ? For my "hot" bock
could I also tap cap connections and four spots to send power to the
four servo amps? I would plan to fuse each servo here.


.--|-----.
| |
| |
-. ,----o--)--|-----o--o-----o VDC+
AC in )|( | | |
)|( | | |
-' '----)--o--|---. ---
| | ---
| | |
'-----|---o----o-----o VDC-
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The "VDC-" here is probably what you want to use for ground. You can
see how two anode-stud and two cathode-stud rectifiers would simplify
the heat sinking.

Usually you see these bolted to a heat sink -- the heat sink has a
through hole, with a bolt on the back. You could tap the heat sink, but
then you'd have to be sure to put the rectifier in before soldering, and
unsolder it before removing if you ever have to replace it. I'd prefer
working on a piece of equipment that's design such that I can take the
diode loose easily without unsoldering -- so, easy access to both sides
with wrenches, and a bolt-on diode.

Your idea of using the heat sink as a terminal block has merit, as long
as you pay attention to aluminum's deficiencies as an electrical contact
material. Check the data sheets -- if you need to use copper heat
spreaders anyway you can use those for your electrical termination. Or
just use some thin copper for a conductor, and only use the aluminum for
heat conduction.

Use all due caution in protecting innocent bystanders from the high
voltage, of course.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 09/17/2010 09:42 AM, Karl Townsend wrote:

Better still, cast around on the surplus market for a power supply
already built. Herbach and Rademan and Surplus Center might have
such, there are other places. With the economic down-turn, there's
got to be a bunch of that stuff out there.

Stan

I've spent time looking for large power suppliers with no joy. The
problem is a "snow storm" of offers with nothing the right voltage and
amps. I'm mostly looking eBay here, no way I've found to filter. I
would rather just buy this and let somebody else do the proper
engineering design.

Karl

Yup. Unless you're dealing with fairly standard voltages like 5V, 12V,
and 48V, it can be hard to get just what you want.

Power supplies are too easy to design to make it economical to force
users into a "one size fits all" design.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Sep 17, 12:21*pm, Karl Townsend
wrote:
...
Thanks, these parts are diodes. One is an anode stud, the other a
cathode stud. Do I need two of each? Draw me a picture of how to make
these parts into a bridge rectifier, please. (I'm thinking each AC
line gets one of each with both cathodes on one block and both anodes
on the other.) Does a cathode or an anode stud go to ground?

Do I tap these into an AL block for heat shink ? For my "hot" bock
could I also tap cap connections and four spots to send power to the
four servo amps? I would plan to fuse each servo here.

Karl

If you don't already know, I'm not going to help you blow yourself up.
There are too many subtle ways to get this wrong, like a burr on the
mounting hole that lets a diode overheat. I've taken long field
service trips to repair such mistakes.

No matter how carefully I write operating instructions, the first
person to test them makes a mistake I didn't anticipate. "When I nod
my head you hit it" Now when I say "Press any key to continue" I test
for Alt, Shift and Ctrl, and fake a BSOD with the bell ringing if the
joker hits one of them.

The Wiki:
http://en.wikipedia.org/wiki/Diode_bridge

You put two of the same gender on the (+) and the (-) heatsinks, or
two opposite ones on the AC if that somehow is more convenient. If you
used four identical packages you'd need more insulated heatsinks. The
problem is making good strong heat-resistant insulators from common
materials. Reinforced phenolic sheet is good, most plastics aren't. I
wouldn't trust perfboard to carry much weight.

Personally I use a large Variac to bring up high power circuits
gradually, watching the line current for unexpected increases. At
first the line fuse is the smallest fast-acting one that should
survive.

jsw

Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Reading the data sheet for that product, it will handle a 100A surge for a
little less than one second; the 50A rating refers to the maximum average
current.

If your 100A surge is limited in duration, that product might work just
fine.

Jon

On Sep 17, 1:58*pm, "Jon Danniken"
wrote:
...

If your 100A surge is limited in duration, that product might work just
fine.

Jon

If this circuit really does rectify the AC power line the
instantaneous fault current is somewhere over 5000A. This is no place
to push the component specs.

jsw

On 9/17/2010 9:20 AM, Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

http://theelectrostore.com/shopsite_...95d08-new.html

Close enough?

Kevin Gallimore

Jim Wilkins wrote:
On Sep 17, 1:58 pm, "Jon Danniken"
wrote:
...

If your 100A surge is limited in duration, that product might work
just fine.

Jon

If this circuit really does rectify the AC power line the
instantaneous fault current is somewhere over 5000A. This is no place
to push the component specs.

OP stated he needed a component to satisfy the demands of a 100A surge.
According to the specifications, as I specified in a reply which was longer
than the short section which you quoted above, the part he suggested might
work, depending upon the duration of the 100A surge.

As to a 5000A surge, that was not mentioned by the OP as a design criteria.

Jon

On Sep 17, 6:07*pm, "Jon Danniken"
wrote:
....

As to a 5000A surge, that was not mentioned by the OP as a design criteria.

Jon

It's not part of the intended use, it's what you get if a diode fails
short, before the breaker responds.

jsw

On Fri, 17 Sep 2010 12:07:44 -0500, Don Foreman
wrote:

On Fri, 17 Sep 2010 08:20:27 -0500, Karl Townsend
wrote:

I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

http://www.galco.com/scripts/cgiip.e...0100SB600-CRDM

BINGO!!

I like this better than four diodes. I wasn't going to ground DC- and
my plan was to connect direct to 240 through a contactor and fuse. I
see I should look at resistors in front of my caps. I'll look into
this and probably ask for confirmation.

Karl

On Fri, 17 Sep 2010 17:41:48 -0400, axolotl
wrote:

On 9/17/2010 9:20 AM, Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

http://theelectrostore.com/shopsite_...95d08-new.html

Close enough?

Kevin Gallimore

I LIKE that price. thanks

Karl

On Sep 17, 7:05*pm, Karl Townsend
wrote:
...

Please remember that the DC+ and DC- lines are still connected to AC
HOT and anything that they attach to must be isolated from all other
circuits.

jsw

Jim Wilkins wrote:
On Sep 17, 6:07 pm, "Jon Danniken"
wrote:
....

As to a 5000A surge, that was not mentioned by the OP as a design
criteria.

Jon

It's not part of the intended use, it's what you get if a diode fails
short, before the breaker responds.

Sure, if he's going to hot chassis the thing, but hopefully he would know
better than that.

Jon

On Sep 17, 7:43*pm, "Jon Danniken"
wrote:
Jim Wilkins wrote:
On Sep 17, 6:07 pm, "Jon Danniken"
wrote:
....

As to a 5000A surge, that was not mentioned by the OP as a design
criteria.

Jon

It's not part of the intended use, it's what you get if a diode fails
short, before the breaker responds.

Sure, if he's going to hot chassis the thing, but hopefully he would know
better than that.

Jon

The fault current path is through the shorted diode and the forward
biased one connected to the other AC line, IOW right across the pole
transformer.

jsw

There are numerous devices to rectify AC to DC at the capacity stated. The
appropriate rectifier arrangement might be full wave bridge rectifier ( 4
rectifiers), or just a full wave rectifier (2 rectifiers).

Packages are available with dual rectifiers ( 3 terminals) arranged in
common cathode or common anode configurations, with heat conducting mounting
surfaces.

Stud rectifiers don't usually get threaded into the material they're mounted
to, I dunno where that fairly common thought came from.. Uhm, looks like a
bolt, it must screw into a threaded hole, then.
Instead, they're generally mounted with proper insulators (to provide
isolation) to a heatsink material with hardware (often included parts such
as mica disc and plastic insulating shoulder washers, crimp or solder tab
ring terminal and a hex nut).
The required hole sizes and precautions are stated in the installation
instructions, sometimes included in the device datasheet.

The mica disc washer allows thermal conduction from the rectifier base to
the heatsink.
The plastic shoulder washer provides additional electrical insulation
between the stud and heatsink.

With the proper insulating parts in place, the heatsink isn't tied to the
anode or cathode of the rectifiers. The heatsink should then be tied to
earth ground.

When installed without insulating parts, the heatsink becomes a conductor in
the circuit, and must be electrically isolated from chassis and/or earth
ground.

For fabricating a FW bridge rectifier with 4 stud rectifiers, it's often
desirable to utilize 2 pairs of opposite polarity terminals.

An equivalent FW bridge rectifier can be fabricated with 2 dual rectifier
packages.

A replacement guide such as NTE/ECG components will have selection charts
and required information regarding the use of industrial rectifiers with
various electrical and physical characteristics.
Basic application specifications are also included.

BTW, proper protection for the 240VAC side would provide 2-pole
interruption, unlike just one hot line connection for 120VAC.

--
WB
..........


"Karl Townsend" wrote in message
...
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

Wild_Bill wrote:
There are numerous devices to rectify AC to DC at the capacity stated.
The appropriate rectifier arrangement might be ...
or just a full wave rectifier (2 rectifiers).
^^^^^^^^^^^^

IF he had a center tapped transformer, but he's using 240v "mains" as a
source.

Bob

On Sep 17, 7:11*am, Glenn Lyford wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
The largest I found is 50 amp [...]
Do I need to come up with some way to put three in parallel?


I've always heard that diodes don't parallel very well, I think
because they won't always trigger at the exact same time,

The recommended way to rectify very high currents is with
paralleled rectifiers, each having a small series inductor.
The inductors don't waste energy, and keep the multiple
units at similar currents.

A 50A rectifier will carry 50A average, there's presumably repetitive
peaks
of (half-wave duty cycle) 140A involved in doing that. So, '100A
surge'
is just fine with the 50A rated rectifier. Maybe.

The other way to ensure current sharing is to separately
fuse all the rectifiers; the small resistance of the fuse is enough
to balance them, if you do it right.

I like this better than four diodes. I wasn't going to ground DC- and
my plan was to connect direct to 240 through a contactor and fuse. I
see I should look at resistors in front of my caps. I'll look into
this and probably ask for confirmation.

Karl

My formula for cap size:

Smoothing capacitor for 10% ripple, C = (5 × Io) /( Vs × f)
C = smoothing capacitance in farads (F)
Io = output current from the supply in amps (A)
Vs = supply voltage in volts (V), this is the peak value of the
unsmoothed DC
f = frequency of the AC supply in hertz (Hz), 50Hz in the UK



C= (5*50)/(400*60)
C=.01 farad or 10,000 MFD


I haven't found anything for a resistor to keep a huge amp surge right
at startup under control. Should i just get something like a 2 ohm
ceramic tube resistor?

Karl

On 2010-09-17, Karl Townsend wrote:
On Fri, 17 Sep 2010 17:41:48 -0400, axolotl
wrote:

On 9/17/2010 9:20 AM, Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

http://theelectrostore.com/shopsite_...95d08-new.html

[ ... ]

I LIKE that price. thanks

Note that is a three-phase rectifier, not single phase. I
suspect that you would need to derate the current rating if you were
using only two thirds of it. At least the 800 V rating is sufficient
for the PRV you would encounter.

Enjoy,
DoN.

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Make sure to use proper heatsink.

i

On 2010-09-17, Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

On Fri, 17 Sep 2010 15:07:40 -0700, "Jon Danniken"
wrote:

Jim Wilkins wrote:
On Sep 17, 1:58 pm, "Jon Danniken"
wrote:
...

If your 100A surge is limited in duration, that product might work
just fine.

Jon

If this circuit really does rectify the AC power line the
instantaneous fault current is somewhere over 5000A. This is no place
to push the component specs.

OP stated he needed a component to satisfy the demands of a 100A surge.
According to the specifications, as I specified in a reply which was longer
than the short section which you quoted above, the part he suggested might
work, depending upon the duration of the 100A surge.

As to a 5000A surge, that was not mentioned by the OP as a design criteria.

Jon

Put a big inductor on the load. It will limit the power surge without
wasting any DC power. Make sure the rectifier is rated for at least 3
times the operating RMS voltage if using an inductor or inductive
load.

On Fri, 17 Sep 2010 21:18:54 -0400, "Wild_Bill"
wrote:

There are numerous devices to rectify AC to DC at the capacity stated. The
appropriate rectifier arrangement might be full wave bridge rectifier ( 4
rectifiers), or just a full wave rectifier (2 rectifiers).

Packages are available with dual rectifiers ( 3 terminals) arranged in
common cathode or common anode configurations, with heat conducting mounting
surfaces.

Stud rectifiers don't usually get threaded into the material they're mounted
to, I dunno where that fairly common thought came from.. Uhm, looks like a
bolt, it must screw into a threaded hole, then.
Instead, they're generally mounted with proper insulators (to provide
isolation) to a heatsink material with hardware (often included parts such
as mica disc and plastic insulating shoulder washers, crimp or solder tab
ring terminal and a hex nut).
The required hole sizes and precautions are stated in the installation
instructions, sometimes included in the device datasheet.

You'd be very surprised at how many applications use the stud mount as
teh terminal as well as the heat transfer point - bolting directly to
the heat sink. Why ele would they be produced as both positive case
and negative case devices??


The mica disc washer allows thermal conduction from the rectifier base to
the heatsink.
The plastic shoulder washer provides additional electrical insulation
between the stud and heatsink.

With the proper insulating parts in place, the heatsink isn't tied to the
anode or cathode of the rectifiers. The heatsink should then be tied to
earth ground.

When installed without insulating parts, the heatsink becomes a conductor in
the circuit, and must be electrically isolated from chassis and/or earth
ground.

For fabricating a FW bridge rectifier with 4 stud rectifiers, it's often
desirable to utilize 2 pairs of opposite polarity terminals.

An equivalent FW bridge rectifier can be fabricated with 2 dual rectifier
packages.

A replacement guide such as NTE/ECG components will have selection charts
and required information regarding the use of industrial rectifiers with
various electrical and physical characteristics.
Basic application specifications are also included.

BTW, proper protection for the 240VAC side would provide 2-pole
interruption, unlike just one hot line connection for 120VAC.

PROPER protection would be a 2 pole contactor with a crowbar at that
current and voltage level.

On Fri, 17 Sep 2010 21:33:05 -0400, Bob Engelhardt
wrote:

Wild_Bill wrote:
There are numerous devices to rectify AC to DC at the capacity stated.
The appropriate rectifier arrangement might be ...
or just a full wave rectifier (2 rectifiers).
^^^^^^^^^^^^

IF he had a center tapped transformer, but he's using 240v "mains" as a
source.

Bob
If he was in America the 240V "mains" WOULD be center tapped - in
Britain or Europe he needs a FW Bridge.

wrote:
On Fri, 17 Sep 2010 21:33:05 -0400, Bob Engelhardt
wrote:

Wild_Bill wrote:
There are numerous devices to rectify AC to DC at the capacity stated.
The appropriate rectifier arrangement might be ...
or just a full wave rectifier (2 rectifiers).
^^^^^^^^^^^^

IF he had a center tapped transformer, but he's using 240v "mains" as a
source.

Bob
If he was in America the 240V "mains" WOULD be center tapped - in
Britain or Europe he needs a FW Bridge.

He is in America, but his center tapped (pole) transformer is 120-0-120,
where he would need a 240-0-240 for a 2 diode full wave rectifier.

Bob

"Karl Townsend" wrote in message
...
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG

The largest I found is 50 amp:
http://www.digikey.com/scripts/DkSea...me=641-1381-ND

Do I need to come up with some way to put three in parallel? If I do
this do I need to fuse each rectifier?

If a 100 amp unit is out there, my life would be simpler.

Karl

Mains to DC bus is built into most ACVS inverter drives. If you could find
a large, bad, obsolete drive in the trash you would probably have what you
need to get the DC bus voltage. Note this is going to be over 300V DC, be
careful. I've seen a lot of old model drives in the scrap bin at work,
usually from an upgrade to a newer drive.

Also I think you can use an SCR as a rectifier if you connect the control
lead to the correct end. I'm not sure if you need to use a resistor or not,
thought someone here would know more about this.

So, on your ebay search, rectifiers, diodes, SCR's, and drives (obsolete or
bad to be cheap) could do what you need. Sometimes companies stock power
SCR's for their old drives, as drives are obsoleted, their replacement SCR's
can end up on eBay. The newer drives I've worked with usually have IGBT's.

RogerN

On Sep 17, 11:00*pm, "DoN. Nichols" wrote:

On 9/17/2010 9:20 AM, Karl Townsend wrote:
I'm looking to rectify 240 VAC into DC with 100 amp surge capacity.
This will power the servo amps on my Matsuura bedmill. I probably
won't ask as many questions as Iggy about my winter projectVBG


Karl


* * * * Note that is a three-phase rectifier, not single phase. *I
suspect that you would need to derate the current rating if you were
using only two thirds of it. *At least the 800 V rating is sufficient
for the PRV you would encounter.

* * * * Enjoy,
* * * * * * * * DoN.


If you have three phase power , use it. The ripple will be much
lower.

Dan