Pete C. wrote:
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. ...

Actually, those are 4 terminal devices - there are 2 control lines
(black & white) for each. What does that make them? Bob

Bob Engelhardt wrote:

Pete C. wrote:
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. ...

Actually, those are 4 terminal devices - there are 2 control lines
(black & white) for each. What does that make them? Bob

Nope, most likely three terminal. The two small wires are the control
terminal and the reference connection to the main lead. The reference
connection is at the device, so that it is not affected by the high
currents / voltage drop in the main lead. They are/were probably driven
by an opto isolator on the missing control board.

On 2010-09-29, Bob Engelhardt wrote:
Pete C. wrote:
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. ...

Actually, those are 4 terminal devices - there are 2 control lines
(black & white) for each. What does that make them? Bob

For really high current SCRs (as these appear to be), it is
common to bring out both the gate (the control terminal) and a second
wire which duplicates the terminal to which the control is referenced,
usually the cathode on an SCR. This keeps you from having to run an
extra lead to the appropriate terminal for each (usually rather
isolated) control circuit.

Check out:

http://www.surplussales.com/semiconductors/SemiC-SCR.html

and scroll down to the SRC -TO-94 example, and you will see the twisted
pair of small gauge wires ending in ring terminals in addition to the
high current lead to a *big* ring terminal.

Enjoy,
DoN.

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They might have 4 terminals MT1, MT2, GT1, GT2. Might be Triacs or SCRs as
well. On the triacs and SCR's - one circuit wire is likely an Anode connection
to be used on an outside design. Without part numbers these Thyristors are
our speculation.

The current transformer looks like it runs to a contactor that controls
the AC input. e.g. if there is a DC short or high current - open the AC.
Save the supply and transformer. Simple safety device.

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 9/29/2010 2:20 PM, Bob Engelhardt wrote:
Pete C. wrote:
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. ...

Actually, those are 4 terminal devices - there are 2 control lines (black &
white) for each. What does that make them? Bob