I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.

RogerN

RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.


They adjust the phase angle to set the output voltage.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

On Fri, 01 Oct 2010 23:00:08 -0400, "Michael A. Terrell"
wrote:


RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.


They adjust the phase angle to set the output voltage.
Which is just a fancy way of saying adjusting the voltage level it
turns on at.

When a capacitor is used it is phase angle.

They are often used as switches. They can be used to be turned on.
They can't be used to turn it off if DC as a source, but with an A.C.
source the Anode turns off with the frequency.

So with AC it can be a binary gate. On-Off.

The 'unused' wire might have been to switches.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
"Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer
TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Originator & Charter Founder
IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com/

On 10/1/2010 10:07 PM, wrote:
On Fri, 01 Oct 2010 23:00:08 -0400, "Michael A. Terrell"
wrote:


RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.


They adjust the phase angle to set the output voltage.
Which is just a fancy way of saying adjusting the voltage level it
turns on at.

wrote:

On Fri, 01 Oct 2010 23:00:08 -0400, "Michael A. Terrell"
wrote:


RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.


They adjust the phase angle to set the output voltage.
Which is just a fancy way of saying adjusting the voltage level it
turns on at.


Sigh.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

wrote:
On Fri, 01 Oct 2010 23:00:08 -0400, "Michael A. Terrell"
wrote:


RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.


They adjust the phase angle to set the output voltage.
Which is just a fancy way of saying adjusting the voltage level it
turns on at.


Depending on the design they either turn on the scr at the '0' crossing
of the AC input or configure it as a phase angle system. The zero
crossing system works like a hit and miss engine firing for a full half
cycle until the control system indicates the proper voltage and then it
cuts off.
The phase angle firing system usually uses an oscillator that is fed
through a gate that is turned on at the desired phase angle. The gate
is hit with a burst of hi freq pulses which will turn on the scr. Once
the scr is turned on it will remain on until the ac voltage goes
negative. The pulses are much more effective for turning the scr on at
the proper phase angle. A toroid transformer is used to isolate the
gate from the pulse driving ckt.


If you just want to use it as a rectifier diode you can pull a
control voltage from the anode but make sure the cathode to gate voltage
is not exceeded and also you will need a reverse diode across the gate
to keep it from going negative. You will have to figure the limiting
resistor/voltage divider to match the scr that you use.

I would try to use the firing circuits that Karl pulled out of the
machine since they are already set up and matched to the scr's. If I
knew the model of the drive he has I may have a manual for it. That scr
stack sorta looks like part of an old Fuji drive.

John

On Fri, 1 Oct 2010 21:48:50 -0500, "RogerN" wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.

RogerN


Roger, did you get this email?

Karl


Roger, if you are done with all that overtime, could you double check
me?


The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

The way I read the specs., it takes 3 volts on the leads to turn on
and 6 volts shouldn't be a problem. Is this correct? if true, I'll put
four SCRs in series and connect to 24 VDC logic power supply. There
are twelve total SCRs so I would have three sets. The way I read it,
I could go with two sets of six SCRs in series also.

I don't know what I'm doing here, so I'd like another opinion.

Karl

A similar circuit to what I think Karl needs:

http://www.sullivan-county.com/ele/triacs.htm

The third circuit down shows an AC supply with a SCR and a diode and switch
going to the gate of the SCR. To use the SCR as a rectifier just connect
the diode to the like the diagram shows but you don't need the switch.
Connect eacy SCR that way and they will be rectifiers, no other power
supplies or control circuitry needed. But like I mentioned, test at lower
voltages first to make sure everything is working right. Might not be fun
to flip on 230 and find out you have a wiring mistake or a bad SCR!

Also, before I mentioned 1N4004 diodes, I looked them up and they are only
rated for 400V, I would probably look for 1N4007 that can handle 1000V
reverse, since I know you can easily get double your peak voltage in a
rectifier circuit with capacitors charged.

RogerN

He's not likely to be able to find any other power supply to give him a
240VDC source (not much higher and "adjusted" down), than a single rectifier
with a single-phase 240VAC source.

I know about ripple, but LC filtering can minimize ripple.. I dunno if if
filtering will minimize it to a level that fits the application (but likely
will).

The "adjusted" part is more complicated than most imagine, when the desired
current capacity is about 100 amps peak (as mentioned earlier).

The full wave bridge rectifier approach will increase the voltage level to
an excessive level.

The proposed used power supply approaches (SCRs, VFD) to attain a reliable
240VDC power supply will likely result in a lot of wasted time, and isn't
particularly safe for someone who doesn't understand isolation, for example.

He's not likely capable of utilizing parts of this SCR bank, or a VFD to
attain a 240VDC supply.
Others certainly have the knowledge required for such projects.. but the
task isn't an "all-ya gotta do is" project.

One aspect of a lot of speculation is, that many are quick to assume, is
that the aged, used components are all in good working order.

I've worked with large/huge industrial DC supplies (motor drives, plating
rectifiers), and they're typically designed for specific applications.

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


"RogerN" wrote in message
m...
I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should
allow forward voltage to the SCR gate and prevent reverse power if there is
an internal resistor present (Per SCR tutorial provided in the "Power
Supply" posts). This should turn on the SCR a soon a voltage was high
enough on the gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode
of the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart
with AC output, then maybe 120V line cord with fuse, then the 230VAC
mains. Just be careful, 230VAC rectified to DC with capacitors charging
to peak is nothing you want to get zapped by! It's nothing to be
terrified of, I work with 480VAC mains rectified and filtered almost
daily, but I don't take a chance on touching it.

RogerN

"Karl Townsend" wrote in message
...
On Fri, 1 Oct 2010 21:48:50 -0500, "RogerN" wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should
allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on
the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode
of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart
with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains.
Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I
work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.

RogerN


Roger, did you get this email?

Karl


Roger, if you are done with all that overtime, could you double check
me?


The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

The way I read the specs., it takes 3 volts on the leads to turn on
and 6 volts shouldn't be a problem. Is this correct? if true, I'll put
four SCRs in series and connect to 24 VDC logic power supply. There
are twelve total SCRs so I would have three sets. The way I read it,
I could go with two sets of six SCRs in series also.

I don't know what I'm doing here, so I'd like another opinion.

Karl

I got the email and sent a reply. The bad thing about using a 24V supply is
you have to make sure it's isolated an you may need a separate power supply
for each bank of SCR's.

If you use these SCR's as rectifiers and use filter capacitors you should
have a bus voltage around 340VDC. If that is too high you may need to do
something to lower the voltage, maybe control the SCR gates, if voltage too
high, turn off SCR's, if too low, turn on SCR's. Or you could use a step
down transformer to get the voltage where you need it. Look at some of the
sample SCR circuits, they show examples of firing the gate using the voltage
that is supplied to the SCR itself, no extra power supply needed.

I'm done with overtime until Sunday, I got scheduled! :-(

RogerN

On 2010-10-02, Karl Townsend wrote:

[ ... ]


Roger, if you are done with all that overtime, could you double check
me?


The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

The way I read the specs., it takes 3 volts on the leads to turn on
and 6 volts shouldn't be a problem. Is this correct? if true, I'll put
four SCRs in series and connect to 24 VDC logic power supply. There
are twelve total SCRs so I would have three sets. The way I read it,
I could go with two sets of six SCRs in series also.

The problem is that the gates will each be referenced to a
different voltage if you have the SCRs in series (*way* more than 24V
apart), and as normally wired, you have the cathodes of multiple SRCs
tied together, so you *can't* connect them in series. The gate signal
voltage is gate to cathode IIRC. So -- you will want resistors in
series to limit the voltage applied to the gate. Look up the minimum
current needed to turn on the gate, and the maximum allowed current in
the gate, and calculate the resistor for something perhaps half-way
between -- subtracting the gate's forward voltage (probably something
like 0.7V or so) from the 24V from the wall wart.

It would help if we knew what the wiring of the SCRs is like on
the heat sinks. Are they all connected via the studs to the metal of
the heat sinks, or are there insulating washers preventing that? Are
all of the SCRs the same part number? There might be versions with
anode to stud, as well as cathode to stud.

I don't know what I'm doing here, so I'd like another opinion.

That much is clear, I fear.

Get *lots* of information and advice before you fry those nice
SCRs.

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 ---

It would help if we knew what the wiring of the SCRs is like on
the heat sinks. Are they all connected via the studs to the metal of
the heat sinks, or are there insulating washers preventing that? Are
all of the SCRs the same part number? There might be versions with
anode to stud, as well as cathode to stud.

There's pics in the original thread. All SCRs are same part number.
There are four on each phase bolted right to the heat sink for that
node. The heat sink design is so nice, its the reason I'd like to use
this component. Otherwise, a three phase rectifer is only $60 (no heat
sink)

I don't know what I'm doing here, so I'd like another opinion.

That much is clear, I fear.

Get *lots* of information and advice before you fry those nice
SCRs.

Good Luck,
DoN.

The power supply is the only part of this refit that has me
apprehensive. With the help of RCM, I'll get through it.

Yesterday, I cleaned out the original computer cabinet to make room
for the five servo amps, this power supply and a half dozen other
components. I'll lay everything out today and start mounting.

I ended up with a box of more than 50 DPDT 24V relays. Anybody need
them?

Sigh.
What's the sigh about Martin? Where am I wrong? with the "basics".

With leading phase commutation, the basics are you turn the SCR on at
different points ov the rising portion of the sine wave. - Which in
practical terms means when the instantaneous rising emf or voltage
reaches a particular value - or voltage. (or phase angle - all
different terms to explain the same process)
Leading phase commutation is the only scheme that works with SCRs, and
is noisy because of the rapid rate of rise of the Current (di/dt)
(time rat change of current) at turn-on.
Trailing phase commutation can be done with MOSFETS and other devices
which can commutate both on and off and is NOT noisy because the rate
of rise (di/dt) is more or less limited by the sine wave frequency.

Mike said they used a variable resistor "to fire the SCR sooner or
later in the rising + portion of the sin wave."
Roger seemed to dissagree - stating "They adjust the phase angle to
set the output voltage."
To which I replied "Which is just a fancy way of saying adjusting the
voltage level it turns on at."

To which you "sigh"

On Fri, 01 Oct 2010 23:43:51 -0400, "Michael A. Terrell"
wrote:



Sigh.
Sorry Martin - That last question should have been directed to Mike
- not fully awake.

On Fri, 01 Oct 2010 23:24:27 -0500, Karl Townsend
wrote:

On Fri, 1 Oct 2010 21:48:50 -0500, "RogerN" wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.

RogerN


Roger, did you get this email?

Karl


Roger, if you are done with all that overtime, could you double check
me?


The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

The way I read the specs., it takes 3 volts on the leads to turn on
and 6 volts shouldn't be a problem. Is this correct? if true, I'll put
four SCRs in series and connect to 24 VDC logic power supply. There
are twelve total SCRs so I would have three sets. The way I read it,
I could go with two sets of six SCRs in series also.

I don't know what I'm doing here, so I'd like another opinion.

Karl
I'm no expert, but I don't THINK you can but the SCR gates in series
..

Don't think things work that way. The firing voltage is the voltage
difference across the junction.

wrote in message
...



Sigh.
What's the sigh about Martin? Where am I wrong? with the "basics".

With leading phase commutation, the basics are you turn the SCR on at
different points ov the rising portion of the sine wave. - Which in
practical terms means when the instantaneous rising emf or voltage
reaches a particular value - or voltage. (or phase angle - all
different terms to explain the same process)
Leading phase commutation is the only scheme that works with SCRs, and
is noisy because of the rapid rate of rise of the Current (di/dt)
(time rat change of current) at turn-on.
Trailing phase commutation can be done with MOSFETS and other devices
which can commutate both on and off and is NOT noisy because the rate
of rise (di/dt) is more or less limited by the sine wave frequency.

Mike said they used a variable resistor "to fire the SCR sooner or
later in the rising + portion of the sin wave."
Roger seemed to dissagree - stating "They adjust the phase angle to
set the output voltage."
To which I replied "Which is just a fancy way of saying adjusting the
voltage level it turns on at."

To which you "sigh"

That weren't me disagreeing but I didn't take that they were disagreeing
just another way to explain it. With a variable resistor you can adjust the
SCR firing in the rising portion of the sin wave. By phase shifting you can
get the rising portion to extend beyond the peak and fire the SCR later. Or
you can use more electronics to fire the SCR anywhere you want.

RogerN

On Sat, 02 Oct 2010 06:49:18 -0500, Karl Townsend
wrote:

All SCRs are same part number.
What is the part number?

On Sat, 02 Oct 2010 12:07:01 -0500, Don Foreman
wrote:

On Sat, 02 Oct 2010 06:49:18 -0500, Karl Townsend
wrote:

All SCRs are same part number.
What is the part number?

The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

wrote:



Sigh.
What's the sigh about Martin? Where am I wrong? with the "basics".



Who is Martin?


With leading phase commutation, the basics are you turn the SCR on at
different points ov the rising portion of the sine wave. - Which in
practical terms means when the instantaneous rising emf or voltage
reaches a particular value - or voltage. (or phase angle - all
different terms to explain the same process)
Leading phase commutation is the only scheme that works with SCRs, and
is noisy because of the rapid rate of rise of the Current (di/dt)
(time rat change of current) at turn-on.
Trailing phase commutation can be done with MOSFETS and other devices
which can commutate both on and off and is NOT noisy because the rate
of rise (di/dt) is more or less limited by the sine wave frequency.

Mike said they used a variable resistor "to fire the SCR sooner or
later in the rising + portion of the sin wave."
Roger seemed to dissagree - stating "They adjust the phase angle to
set the output voltage."
To which I replied "Which is just a fancy way of saying adjusting the
voltage level it turns on at."

To which you "sigh"


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

On Sat, 02 Oct 2010 12:16:20 -0500, Karl Townsend
wrote:

On Sat, 02 Oct 2010 12:07:01 -0500, Don Foreman
wrote:

On Sat, 02 Oct 2010 06:49:18 -0500, Karl Townsend
wrote:

All SCRs are same part number.
What is the part number?

The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

71RC80 is an old International Rectifier part. 800 volts, 70 to 110
amps.

IR doesn't have it on their website so it must be obsolete, but I have
some old IR databooks in the basement. I'll look later.

On 2010-10-02, Karl Townsend wrote:

It would help if we knew what the wiring of the SCRs is like on
the heat sinks. Are they all connected via the studs to the metal of
the heat sinks, or are there insulating washers preventing that? Are
all of the SCRs the same part number? There might be versions with
anode to stud, as well as cathode to stud.

There's pics in the original thread. All SCRs are same part number.

I saw the photos -- but it was not clear from the photos that
all the SCRs were the same part number -- just the same family of parts.
It could easily be that half of them are grounded cathode and half
grounded anode parts. The part numbers were not visible in the photos. :-)

The test would be whether one wire of each pair feeding a gate
is shorted to the stud in *every* SCR. If not, then some are likely
grounded anode -- and that would actually make sense to make a bridge
rectifier. I would expect the black wire to be the one connected to the
cathode, but I'm not sure.

There are four on each phase bolted right to the heat sink for that
node. The heat sink design is so nice, its the reason I'd like to use
this component. Otherwise, a three phase rectifer is only $60 (no heat
sink)

And -- are the studs electrically connected to the heat sink, or
are they insulated? Such rectifiers have long been sold with mounting
hardware which consists of a pair of large diameter mica washers, a
Teflon ring washer to hold the stud centered out of contact with the
metal of the heat sink, a flat washer and a nut. Also -- they normally
are mounted with a heat sink compound (with or without the insulating
washers) to maximize the conduction of heat to the heat sink. Anyway --
if they are mounted with the insulating washers, there will be ring
terminals connecting to the studs to complete the circuit.

I don't know what I'm doing here, so I'd like another opinion.

That much is clear, I fear.

Get *lots* of information and advice before you fry those nice
SCRs.

Good Luck,
DoN.

The power supply is the only part of this refit that has me
apprehensive. With the help of RCM, I'll get through it.

It really would have helped if you had not stripped it apart.
it would work a *lot* better with the original driver board.

Can you still identify the driver board that all those gate
connections were connected to?

Yesterday, I cleaned out the original computer cabinet to make room
for the five servo amps, this power supply and a half dozen other
components. I'll lay everything out today and start mounting.

I ended up with a box of more than 50 DPDT 24V relays. Anybody need
them?

Don't get rid of them until you are *sure* that you don't need
them. You will probably need quite a few of them for this -- and having
spares helps too.

I just recently got fifty such relays for future projects.

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 ---

On 2010-10-02, Karl Townsend wrote:
On Sat, 02 Oct 2010 12:07:01 -0500, Don Foreman
wrote:

On Sat, 02 Oct 2010 06:49:18 -0500, Karl Townsend
wrote:

All SCRs are same part number.
What is the part number?

The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

Hmm ... thyristors, not SCRs. And it looks as though the one
illustrated has the cathode connected to the heavy-gauge wire, not the
stud. Now -- the remaining question is still "are *all* of them the
same?"

Part number does not seem to match. Just because it looks the
same -- are you sure that it *is* the same?

O.K. According to Wikipedia, "Thryristor" is an alternative
term for SRC -- but it also can refer to a bunch of other devices.

Make sure exactly what you have -- by matching the part number,
not just by finding something which looks similar. Most of the data
sheets for 71RC80 devices appear to be on Chinese sites now, and those
are blocked from here.

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 ---

They both had it - a pot can adjust the phase trigger voltage.
The R-C time constant of the pot/cap combination sets a time delay
which equates to a phase angle and at the trigger voltage there is
a massive rush of current through the main terminals.

It is all how one looks at it. RC is used with AC power - the load is
DC partial wave.

Four terminal Thyristors are used for gate-turn-on and gate-turn-off
operation. Two gating - an anode gate to turn it off and the cathode
gate which is used to turn it on.

There are many version of Thyristors.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
"Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer
TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Originator & Charter Founder
IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com/

On 10/2/2010 8:46 AM, wrote:



Sigh.
What's the sigh about Martin? Where am I wrong? with the "basics".

With leading phase commutation, the basics are you turn the SCR on at
different points ov the rising portion of the sine wave. - Which in
practical terms means when the instantaneous rising emf or voltage
reaches a particular value - or voltage. (or phase angle - all
different terms to explain the same process)
Leading phase commutation is the only scheme that works with SCRs, and
is noisy because of the rapid rate of rise of the Current (di/dt)
(time rat change of current) at turn-on.
Trailing phase commutation can be done with MOSFETS and other devices
which can commutate both on and off and is NOT noisy because the rate
of rise (di/dt) is more or less limited by the sine wave frequency.

Mike said they used a variable resistor "to fire the SCR sooner or
later in the rising + portion of the sin wave."
Roger seemed to dissagree - stating "They adjust the phase angle to
set the output voltage."
To which I replied "Which is just a fancy way of saying adjusting the
voltage level it turns on at."

To which you "sigh"

Don't stack the SCR's!!!!!

The are likely high voltage already.

Stacking means putting anode and cathodes end to end.

If you do that - the gates will be floating up at higher and higher voltages.
The one you showed us was 400V DC. Likely a 220v gated rectifier.

No manual and no cable set that might lead you to believe the use ?

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
"Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer
TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Originator & Charter Founder
IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com/

On 10/1/2010 11:24 PM, Karl Townsend wrote:
On Fri, 1 Oct 2010 21:48:50 -0500, wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers. I'm posting this to confirm or correct me if I'm wrong. Many
diagrams I saw show an AC supply, a load, and the SCR to vary the power to
the load. They used a variable resistor to control power to the gate to
fire the SCR sooner or later in the rising + portion of the sin wave. If
Karl wired his gate to the anode with a diode (1N4004 maybe?)it should allow
forward voltage to the SCR gate and prevent reverse power if there is an
internal resistor present (Per SCR tutorial provided in the "Power Supply"
posts). This should turn on the SCR a soon a voltage was high enough on the
gate, Vf of the 1N4004 + SCR gate turn on voltage (~4V).

So, if I'm thinking about this correctly, if Karl connects the Anode of a
1N4004 diode to the anode of his SCR and connects the gate to the cathode of
the 1N4004 diode, the SCR should work like a rectifier. Correct?

I would recommend wiring it up this way and then powering it from a lower
voltage transformer through a current limiting resistor (or light bulb) to
verify everything is working as hoped. Maybe power it from a wal wart with
AC output, then maybe 120V line cord with fuse, then the 230VAC mains. Just
be careful, 230VAC rectified to DC with capacitors charging to peak is
nothing you want to get zapped by! It's nothing to be terrified of, I work
with 480VAC mains rectified and filtered almost daily, but I don't take a
chance on touching it.

RogerN


Roger, did you get this email?

Karl


Roger, if you are done with all that overtime, could you double check
me?


The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

The way I read the specs., it takes 3 volts on the leads to turn on
and 6 volts shouldn't be a problem. Is this correct? if true, I'll put
four SCRs in series and connect to 24 VDC logic power supply. There
are twelve total SCRs so I would have three sets. The way I read it,
I could go with two sets of six SCRs in series also.

I don't know what I'm doing here, so I'd like another opinion.

Karl

On Fri, 01 Oct 2010 21:48:50 -0500, RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers.

It's trivial. Just connect the gate directly to the anode, and voila!
Diode!

Seems kind of a shame that he didn't keep any of the control electronics,
however.

Cheers!
Rich

On Sun, 03 Oct 2010 22:52:13 -0700, Richard the Dreaded Libertarian
wrote:

On Fri, 01 Oct 2010 21:48:50 -0500, RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers.

It's trivial. Just connect the gate directly to the anode, and voila!
Diode!

That violates reverse gate voltage spec. Circuit behavior may not be
as expected or hoped for.

On Mon, 04 Oct 2010 01:05:09 -0500, Don Foreman wrote:
On Sun, 03 Oct 2010 22:52:13 -0700, Richard the Dreaded Libertarian
On Fri, 01 Oct 2010 21:48:50 -0500, RogerN wrote:

I looked up a bit of SCR info to see how to wire Karls SCR's to act as
rectifiers.

It's trivial. Just connect the gate directly to the anode, and voila!
Diode!

That violates reverse gate voltage spec. Circuit behavior may not be
as expected or hoped for.

Yes, I concur - it should have a diode from gate to cathode to clamp
the reverse gate voltage, and of course, a resistor to limit dissipation.

What I had in mind was the time I made a center-tapped full wave
controlled power supply, and drove the mongo SCRs with 4Nsomething
optos, and just connected them straight from anode to gate, because
when the gate fires the SCR, its forward voltage drops to a diode
drop.

But there was no direct connection for the negative half-cycle, so
based on my experience, I did, in fact, neglect to include the problem
of the negative gate voltage.

Thanks,
Rich

Don Foreman wrote:

On Sat, 02 Oct 2010 12:16:20 -0500, Karl Townsend
wrote:

On Sat, 02 Oct 2010 12:07:01 -0500, Don Foreman
wrote:

On Sat, 02 Oct 2010 06:49:18 -0500, Karl Townsend
wrote:

All SCRs are same part number.
What is the part number?

The numbers on my SCR are 71RC80 S5-5 9L11057 I can't tell who is
the manufacturer

So, I went to digikey and found what looks the same.
http://search.digikey.com/scripts/Dk...T103S04PFL0-ND

71RC80 is an old International Rectifier part. 800 volts, 70 to 110
amps.

IR doesn't have it on their website so it must be obsolete, but I have
some old IR databooks in the basement. I'll look later.


I looked for mine, but it's missing.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.