My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

On 01/14/2011 01:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

Does the data sheet say anything about junction temperature, thermal
conductivity to ambient, or thermal conductivity to the case?
Generally, power semiconductor device power ratings are made assuming
pretty darn good heat sinking.

What current is the motor going to be pulling?

At 12A the rectifier will be dissipating something like 24 watts; that
feels like something that would need a 4" square finned heat sink rather
than a flat plate, but I do that sort of work so seldom that I always
need to go do the math.

--

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 Fri, 14 Jan 2011 15:35:21 -0600, Terry
wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

In typical RCM fashion I'm ignoring your question and answering one
you didn't ask. g Speed regulation will be poor with a simple power
supply. You'd be much better off with a DC motor drive similar to
this:
http://www.galco.com/scripts/cgiip.e...um=KBIC-120-KB

--
Ned Simmons

Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

I don't know how much current you're dealing with, but figure about 1-2
volts drop across such a module X how many amps you're pulling = how many
watts it will dissipate.

since it's rated 12 amps, you're probably going to need larger than 4x4 of
heatsink to keep it happy.

quite honestly though, it's going to be easier to just mount the thing and
do the touch test than to try to calculate all sorts of stuff with
guestimated values.

If it gets too hot, use a larger heat sink. big deal.

The voltage drop is approximately 1.5-2 volts, so at 20 amps it will
be 30-40 watts. You need an aluminum plate or a heatsink for sure. I
would also get a much larger rectifier, to account for starting
current, at least 50 amps. Those bridge rectifiers are dirt cheap
these days, I see no sense in getting something that just barely is
adequate.

i

On Fri, 14 Jan 2011 15:35:21 -0600, Terry
wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

Have a look at this datasheet:

http://www.vishay.com/docs/88612/gbpc12.pdf

Figures 1 and 2, especially (they show some example heat sink
dimensions). You can derive this by looking at figure 3, and at the
degrees C/watt for various commercial heat sinks.

You'd probably be safe up to 5A continuous, for much more I would go
to a much bigger heat sink and a 35A bridge rectifier (only a few
dollars).

On Jan 14, 4:35*pm, Terry wrote:


The question is: *should a bridge rectifier be heat-sunk (sinked?) in
such an application? *If so, how big (roughly) should the heat sink
be? *Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? *Thanks for your input.
--
Best -- Terry

The rectifier should have a heat sink.

Where are you? The local recycling place ( Actually scrap yard ) has
aluminum finned heat sinks. Not especially cheap at a dollar a lb.
They range from small to big.

Dan

On 01/14/2011 03:35 PM, Terry wrote:


The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
Yes, it needs to have a heat sink. if the enclosure is 1/8" aluminum,
this may well be enough. If thin steel, then maybe not, but it will be
better than just hanging in the air. You can figure that any time the
bridge is conducting current, there will be two diodes in conduction,
dropping about a volt each. So, at 12 A, you would have about 24 Watts
to get rid of. If the cabinet is too light for removing the heat, a
chunk of 1/8" aluminum would help. Also, you should put heat sink
grease on the back of the bridge to conduct the heat better to the plate.

Jon

On 01/14/2011 03:43 PM, wrote:
On Jan 14, 4:35 pm, wrote:


The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

The rectifier should have a heat sink.

Where are you? The local recycling place ( Actually scrap yard ) has
aluminum finned heat sinks. Not especially cheap at a dollar a lb.
They range from small to big.

OTOH, if you've got some sheet aluminum, some heat sink goo, and no
cash, you can bend up a bunch of ever-narrower 'U' shapes and stack
them. I wouldn't do this unless I was _seriously_ short on cash,
because if your scrapyard doesn't have heat sinks (mine doesn't) you can
still find them cheap at electronics surplus places.

--

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

Don't forget the silicon thermal compound between the rectifier and the
mounting surface.

Pete Stanaitis
--------------------

Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

On Fri, 14 Jan 2011 15:35:21 -0600, Terry
wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
Yes, you should heat sink it - I'd try for 100 sq inches of surface,
more or less, in free air. Thats about half a sqare foot if both sides
are exposed to the air.

On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

But, as others pointed out, you would be much better served with a
SCR/Triac controller with feedback - the ones I like are made by
Minarik. They are frequently available on ebay but peruse the minarik
catalog first

--
www.wbnoble.com

For most full-wave bridge rectifiers with holes in them, the device should
be mounted to a metal panel (minimally) or a heatsink with a proper heatsink
compound to transfer heat.

Many datasheets will indicate a notation that recommends heatsinking of a
device, when used in excess of a nominal power (watts) rating.

As Ned commented, speed regulation will be fairly poor with a variac. That
means the motor will slow down considerably from a set speed (no load),
during the actual metal cutting operation.
A variac will provide variable speed, which is a lot "better than" (it get's
a gold star) single speed.

Variacs (autotransformers) do not provide line voltage isolation, so the
output voltage is hazardous. Proper insulating practices need to be followed
to protect the equipment users from potential electrical shock hazards.

Most commercially-built 180VDC motor controllers are typically 240VAC input
modules, and the DC motor controllers for 90VDC motors are typically 120VAC
input modules.
So, the existing 180VDC motor will be slightly under-powered from a DC
supply derived from 120VAC.. the results may be similar to the performance
from the previous attempt with a treadmill controller.
Finding a commercially-built 180VDC motor controller would likely provide
the best results.. variable speed with excellent speed regulation, plus
other features.

Looking up the manufacturer's specs for the existing motor would be
worthwhile, before buying a controller that may not be suitable for your
application.

Another consideration could be the need to cool the variac to prevent
overheating, which could be accomplished with a small fan.

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


"Terry" wrote in message
...
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

Bill Noble wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.

On 2011-01-14, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V.

[ ... ]

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

Good!

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

Hmm ... your transformer is capable of putting out 20A, and the
bridge is only rated for 12A. How much will the motor draw worst case?

I would certainly use a heat sink -- and a local fuse between
the output of the variable autotransformer and the bridge. One with
*lots* of fins to increase the surface area for better transfer -- and
perhaps a fan to assist cooling if you are runing close to the 12A
rating of the bridge rectifier.

And you want a heat sink compound between the bridge and the
heat sink.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

How much current will your motor draw worst case? (For a lot of
PM motors, you should find a maximum current rating on the motor's data
plate -- because more than that current will partially demagnetize the
permanent magnets.) If you find such a rating, go for a smaller
quick-blow fuse, because it does not take any significant time for the
excess current to degauss the (im)permanent magnets.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Bill Noble wrote:
... But, it is AC, so you won't pull the
12 amps continually.
...

AC current is "dimensioned" in RMS amps. So the fact that it's not
pulling them "continually" [sic], has already been taken into account.
12 is the correct number to use for figuring power.

Bob

Terry wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

You probably don't even need to "filter" it - the inductance of the
motor windings should provide all the filtering you need.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

If you're planning on running 20 amps through the motor, this rectifier
will die. If the motor current is guaranteed to not go over 12A, then no
problem.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application?

Yes, absolutely. And use some kind of thermal goo - NOT a "sil-pad" -
they're crap.

If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure?

It's hard to answer this sight unseen - you need to look up the thermal
resistance of the diode in the data sheet, and the enclosure, enough to keep
the rectifier chip itself below the rated max. temp. It's pretty simple
arithmetic if you have those figures. Personally, I like as much surface
area as I can manage; forced-air cooling (like a fan) helps a LOT, but
unless it's a great big huge heatsink, you should mount some kind of guard
so that nobody gets their hand burned. You can look up thermal resistance
of various extrusions and stuff on websites like Aavid and such. Google
"heat sink."

It also could do no harm to ask this same question at
sci.electronics.design.

Thanks for your input.

My Pleasure!
Rich

On Jan 15, 9:02*am, Bob Engelhardt wrote:

AC current is "dimensioned" in RMS amps. *So the fact that it's not
pulling them "continually" [sic], has already been taken into account.
12 is the correct number to use for figuring power.

Bob

You are right about using the RMS value of Amps. But I would look the
motor nameplate. I doubt if 12 is the right number. WW Grainger
lists 5 amps as the current for a 1 hp 180 volt motor.

Dan

On Jan 15, 10:01*am, Rich Grise wrote:



Personally, I like as much surface
area as I can manage; forced-air cooling (like a fan) helps a LOT, but
unless it's a great big huge heatsink, you should mount some kind of guard
so that nobody gets their hand burned.

Rich

The heat sink ought to be big enough that no guard is needed. If the
heat sink is hot enough to burn someone, the silicon junction is
probably shot.

Dan

On 2011-01-15, wrote:
On Jan 15, 10:01?am, Rich Grise wrote:
Personally, I like as much surface
area as I can manage; forced-air cooling (like a fan) helps a LOT, but
unless it's a great big huge heatsink, you should mount some kind of guard
so that nobody gets their hand burned.
The heat sink ought to be big enough that no guard is needed. If the
heat sink is hot enough to burn someone, the silicon junction is
probably shot.

While I kind of agree with all that, the lathe would be unlikely to be
pulling 12 amps at 190 volts continuously. Anyway, aluminum plates are
inexpensive (www.speedymetals.com), and a 1/4" thick 8x12" plate can
be had for $8.86. That is far more than necessary.

i

On Jan 15, 12:15*am, Bill Noble wrote:
...
it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. *Fullwave rectifiers have two in the
forward path conducting on each half wave. *1.4V drop. *If you pull 12
amps, power is therefore 16 watts. *But, it is AC, so you won't pull the
12 amps continually.

Yes, from YOU.

The forward voltage isn't one value, it varies as the log of the
current, which you should know if you ever curve-traced
semiconductors. The Measured drop across a power rectifier near its
rated load is 1 - 2V as others have posted. Some of that is Vf, some
is IR drop, some possibly corrosion on the hardware, but the heatsink
has to remove it anyway.

I'd plan for a fan to use if needed, like for a larger motor.

jsw

On Sat, 15 Jan 2011 10:08:28 -0600, the renowned Ignoramus25553
wrote:

On 2011-01-15, wrote:
On Jan 15, 10:01?am, Rich Grise wrote:
Personally, I like as much surface
area as I can manage; forced-air cooling (like a fan) helps a LOT, but
unless it's a great big huge heatsink, you should mount some kind of guard
so that nobody gets their hand burned.
The heat sink ought to be big enough that no guard is needed. If the
heat sink is hot enough to burn someone, the silicon junction is
probably shot.

While I kind of agree with all that, the lathe would be unlikely to be
pulling 12 amps at 190 volts continuously. Anyway, aluminum plates are
inexpensive (www.speedymetals.com), and a 1/4" thick 8x12" plate can
be had for $8.86. That is far more than necessary.

i

Yup, and in the spirit of reasonable excess for cheap, I'd suggest
picking up one or two of these babies for $2.35 each quantity 1.

http://www.mouser.com/ProductDetail/...Qyol7c n1I%3d



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Fri, 14 Jan 2011 15:35:21 -0600, Terry
wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

Thanks to everyone for their input. I have a bigass finned aluminum
heat sink, about 10" square, that will go on the rectifier. And will
bolt the heat sink to the enclosure for good measure.

And I also appreciate the education on calculating heat dissipation.
My knowledge of electronics is none too good. I understood the
five-tube radio I built in high school, but these confounded
solid-state thingies just mess up my head. ;-)
--
Best -- Terry

Good input but one designs for the worst case not the easy one.

Surge currents - stall currents - start-up currents - Host of higher
than Ave or running or typical currents.

What you should do is double the possible wattage and then double that.

Keep the bridge cool as they will overheat and start dissapating more
wattage.

I used to work with IC's that when turned on would burn a 2" square hole
in thick FR4. We used liquid cooling and high volume coolant. It was
a GaAs Gate Array that had more gates / transistors than a Pentium.
Intel design told me that. I had to run faster that the hottest (speed)
device.

Be sure to use quality heat sink grease between the device and the sink.

Martin

On 1/15/2011 9:47 AM, wrote:
On Jan 15, 9:02 am, Bob wrote:

AC current is "dimensioned" in RMS amps. So the fact that it's not
pulling them "continually" [sic], has already been taken into account.
12 is the correct number to use for figuring power.

Bob

You are right about using the RMS value of Amps. But I would look the
motor nameplate. I doubt if 12 is the right number. WW Grainger
lists 5 amps as the current for a 1 hp 180 volt motor.

Dan

On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.

--
www.wbnoble.com

On 2011-01-16, Bill Noble wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.


Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i

Bill Noble wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.
--
Best -- Terry

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.

there you have it folks- the man cited electronics-tutorials.ws

he's right, anybody else is wrong.

case closed.

On 2011-01-16, Ignoramus25553 wrote:

[ ... ]

Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

For a single junction -- no. Pretty much the same range as a
function of the current through the device.

However -- high voltage rectifiers can be multi-junction devices
-- junctions in series -- to get sufficient PRV from a device which can
handle the current needed.

These multi-junction devices will drop a nominal FV for each
junction in series. Yes, it is about 0.700 V at some nominal current
and temperature, but yes, the Forward voltage drop will increase as the
current increases, and as the temperature increases. (And the nominal
0.700 V is for silicon junctions. Germanium ones are down around 0.150
V, but you are not likely to find germanium diodes in use these days.
Various other semiconductor materials (e.g. GaAs) will each have their
own nominal forward voltage drop

Now -- when you stack a bunch of diodes in series -- you can't
just grab any old handful from a bin and stick them in series. They
need to be individually tested and matched for junction capacitance and
for leakage at various reverse voltages so when there is a high voltage
(steady state or a spike) the voltage is evenly spread across the
diodes. Back in the old days, such things often had a set of resistors
and capacitors in parallel with each diode, to swamp the individual
leakage resistance and junction capacitance variations. Sometimes,
these assemblies were potted to make them look like (and fit in the
sockets for) high voltage rectifier tubes. Four pins on one end (only
one of which matters here, since there is no filament to heat up) and a
cylindrical cap on the other end for the high voltage connection.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Ignoramus25553 wrote:

(...)

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

Yup. Forward voltage is largely independent of
Peak Reverse Voltage.
Here is a part available in PIVs from
50 V to 1 KV:
http://www.fairchildsemi.com/ds/1N/1N4007.pdf

Notice that Vf at 1A is the same for all flavors
at 1.1 V in 'non-pulse' service,
largely due to the material spec of each
side of the junction.

Like all good rules, this one has an exception, for
'rectifiers' made up of series diode elements to
withstand very high peak inverse voltages will have
one diode drop for each diode in the string.
This device for example:
http://www.hvpsi.com/pdf/D4468A01r03.pdf

...has 22 diodes in series to provide rectification
at 220 KV.
We can expect forward voltage to be upwards of
17-24 V at maximum current for this device because
we have to saturate all 22 junctions before the
device turns on.

--Winston

On Jan 16, 12:58*am, Ignoramus25553 ignoramus25...@NOSPAM.
25553.invalid wrote:
On 2011-01-16, Bill Noble wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill *wrote:
On 1/14/2011 1:35 PM, Terry wrote:

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. *It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: *should a bridge rectifier be heat-sunk (sinked?) in
such an application? *If so, how big (roughly) should the heat sink
be? *Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? *Thanks for your input.

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. *Fullwave rectifiers have two in the
forward path conducting on each half wave. *1.4V drop. *If you pull 12
amps, power is therefore 16 watts. *But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

ok, have it your way - here is a reference showing that what I said is
right *http://www.electronics-tutorials.ws/diode/diode_6.html, ...

Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i-

http://www.allaboutcircuits.com/vol_3/chpt_3/1.html
Scroll down to the bottom to see the large jump in complexity when you
consider a diode's actual properties instead of simply calling the
drop 0.7V.
It doesn't mention that the positive and negative scales on the diode
curve graph are very different to compress the image. +Y could be Amps
while -Y is microAmps.

Look at Figure 3:
http://www.datasheetcatalog.org/data...d/GBPC1210.pdf
The drop is about 0.7V between 0.5A and 1A, but between 1 and 2V at
normal operating currents. I used to build the type of equipment that
made those measurements on the production line. The note in the bottom
of Fig.3 shows how they were done without heating the diode.

jsw

On Sat, 15 Jan 2011 23:58:39 -0600, Ignoramus25553
wrote:

On 2011-01-16, Bill Noble wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.


Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i
No it is not. Which is why it is not "smart" to massively over-spec
the voltage of a diode.

On Sun, 16 Jan 2011 15:57:47 -0500, wrote:

On Sat, 15 Jan 2011 23:58:39 -0600, Ignoramus25553
wrote:

On 2011-01-16, Bill Noble wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.


Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i
No it is not. Which is why it is not "smart" to massively over-spec
the voltage of a diode.
I should have said "No, it is not, necessarilly"

There is a lot of miss understanding on diodes.

The very high voltage diodes are lower quality in many respects
than lower ones. The Peak Inverse volage of 1000 means a 1000v
reverse voltage can be applied without a lot of current flowing.

The leakage in both directions is higher than say a 100v model.
The 100v one would vaporize on high voltage so each have their job.


If you are running motors in 240 or 375v range, the 1000v would be ok.
Magnetic loads can create double voltage spikes.

Martin

On 1/15/2011 11:58 PM, Ignoramus25553 wrote:
On 2011-01-16, Bill wrote:
On 1/14/2011 10:24 PM, Cydrome Leader wrote:
Bill wrote:
On 1/14/2011 1:35 PM, Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

maybe you should check a datasheet for a bridge rectifier some day, or
takes some actual measurements.

Vishay is even kind enough to tell you the dissipation in watts for such
items.


ok, have it your way - here is a reference showing that what I said is
right http://www.electronics-tutorials.ws/diode/diode_6.html, there are
at least 10,000 other references - perhaps you have found some new kind
of silicon, with new semiconductor properties. Go ahead and give more
bad information to the OP, this is not my problem. In fact, maybe YOU
should take some measurements and check your facts.

and no, I will not respond, I have no need to get into a screaming
contest for no money with people who have no information. I will let the
OP do his own research and determine what he wishes to do. I've offered
my recommendation, YOU choose to tell me I am wrong.


Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i

On Sat, 15 Jan 2011 23:58:39 -0600, Ignoramus25553
wrote:

Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i

The forward voltage of a diode depends on quite a few variables
including geometry, doping levels, current and temperature. If Vf is
important to a design, it's always best to consult the data sheet to
see what Vf will be with a particular part at the anticipated current
level and temperature.

Those packaged 25 to 35 amp bridges tend to have Vf of about 1.1 volt
per diode at rated current, and this is essentially independent of the
peak inverse voltage rating. Vf of 0.7 volts is seen at lower
current, perhaps a couple of amps. Vf varies about logarithmically
with If.

Martin Eastburn wrote:

There is a lot of miss understanding on diodes.

"Misunderstanding" is one word.

And the convention on USENET is bottom-posting.

Rich Grise, Self-Appointed Chief,
Internet Grammar Police
;-) - Winky-smiley for the humor-impaired.

Don Foreman wrote:
On Sat, 15 Jan 2011 23:58:39 -0600, Ignoramus25553

Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

The forward voltage of a diode depends on quite a few variables
including geometry, doping levels, current and temperature. If Vf is
important to a design, it's always best to consult the data sheet to
see what Vf will be with a particular part at the anticipated current
level and temperature.

Those packaged 25 to 35 amp bridges tend to have Vf of about 1.1 volt
per diode at rated current, and this is essentially independent of the
peak inverse voltage rating. Vf of 0.7 volts is seen at lower
current, perhaps a couple of amps. Vf varies about logarithmically
with If.

FWIW, I concur with Don here, but I've only been an electronics tech
(and sometime de facto "engineer") for about forty years now. ;-)

Cheers!
Rich

In terms of checking junctions while troubleshooting, a typical DMM diode
test function (go/no go check only), the indicated voltage drop will
basically be the same for most common rectifiers.
Different brands or models of DMMs will likely have different readings.

Rectifiers of all types have various working parameters, one of which is
leakage (not the kind you see visually) which is internal current leakage.
Most rectifiers fail by shorting, some will open, and some exhibit leakage.
Acceptable leakage limits are generally stated in uA micro-amps.
Measuring leakage is usually performed with a leakage tester or a test
circuit which will apply the rated voltage determined by the manufacturer's
specs (or the working voltage of the intended circuit).

Checking high voltage rectifiers with a DMM will very likely result in open
junction test readings because the voltage available at the DMM test leads
is too low (many meters will only have about 2 volts at the test leads).

Checking zener diodes with a DMM may result in slightly different junction
voltage drop readings than ordinary rectifiers.
Many of the DMMs I've used over the years have had this characteristic, and
a slightly different reading (of about 0.1V) is generally nothing to be
concerned about.

Other types of diodes will will exhibit somewhat odd-looking DMM readings,
so knowing what specific type of diode is necessary to knowing how to
interpret the DMM readings (or lack of).

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


"Ignoramus25553" wrote in message
...

Guys, can I ask an ignorant question. I thought that voltage drop
depends on the maximum reverse voltage that the diode would withstand?
Is that true or not?

In other words, is the voltage drop on a 1,000V rated diode, the same
as on a 30v rated diode?

i