Turns out I have a power supply for my Matsurra bedmill. After
stripping everything not needed away I ended up with this:
A few questions. Each of the twelve diodes has a pair of wires, 24
connections on the terminal strip. I don't know the function here and
if anything needs to be connected.
Is the part labeled 1 an isolation transformer? If so, should DC- be
Can the part labeled 2 be used to read current? There are four leads,
how would they be connected. The part says "Nana Electronics NNC-05AF"
Diodes with great big main leads and itty bitty 'extra' leads make me
think that you're looking at an SCR or triac or transistor or some other
not-really-just-a-diode thing. I'd peel the insulation back a bit from
one and see if there's separate leads coming out of the case -- if there
are, then you've just ripped a bunch of control electronics away from
the SCRs (or triacs) that they control.
Most likely it's a three-phase step up or down transformer. It looks a
bit small compared to the diode array, but what do I know? If the leads
on the left don't show any conductance to the leads on the right it
isolates as well as any step-up or -down.
It certainly has the look of a current transformer about it.
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. Without the electronics that were
connected to those terminal strips, you have a pile of scrap parts, not
a power supply.
It may be a 1:1 isolation transformer which may help explain it's
relatively small size. If it were a step-up or step-down I expect there
would be a few voltage taps.
Almost certainly a CT. Almost certainly of no use without the rest of
the control electronics that formerly made this pile of parts into a
high current DC power supply.
On Wed, 29 Sep 2010 13:41:14 -0500, Pete C. wrote:
Item 1 seems to have 2 contacts per winding so probably is a
choke (inductor) rather than a transformer. Each left wire is
attached to the inside of a coil and each right wire to the outside,
and each winding probably is a wide, thin, copper strip.
On Wed, 29 Sep 2010 11:55:59 -0500, Karl Townsend wrote:
The purple stud mount things are definitely not diodes; they're either
SCRs or triacs. Label 1 is a three-phase trsnsformer; "DC-" should only
be grounded if it is grounded in the original design.
Item Label 2 is a current transformer; the wires you've cut were used
in the control circuitry.
In pic 2, it looks like label 1 _could_ be a 3-phase common mode choke,
to keep the switching transients of the SCRs/triacs out of the power
But, as others have said, without the control electronics, you have
a pile of probably not very valuable spare parts.
Tim suggested checking for continuity. Theres 0 ohms accross leads, so
its not an isolation transformer. Any use for a chocke, or just toss
Looks like i spent the morning making a large hunk 'o junk into a pile
'o junk parts. But at least I learned a little bit. Thanks everybody.
I've got a very old VFD I'll tear down next. I know it has
electrolytic caps and I'll look for diodes.
0 Ohms from side to side along one coil, or 0 Ohms between
terminals on the same side of the transformer?
If the former, then yes, it is a choke.
If the latter -- and high resistance between sides, it could
still be a transformer.
Keep it. You'll reduce the hash which you put into the power
line (especially if you brew your own circuitry to turn on the SCRs),
and it will help keep the circuit from blowing away in a hurricane. :-)
[ ... ]
If you have the manuals -- maybe you can restore the control
board to the SCRs and wind up with a nicely regulated power supply to
drive the servo amps.
If not -- you could perhaps hook up some wall warts to power the
gates of the SCRs to turn them on full time and at least use them as
rectifiers. The wall warts will probably be cheaper than that many high
current rectifiers would be. The main trick is determining how many of
those you can wire to a single wall wart (through current limiting
resistors to each gate). I suspect that you can get away with three
wall warts -- one per bank of SCRs.
Are you going to be running this from true three phase? If not,
you can probably get away with fewer wall warts.
Hmm ... I wonder about those banks of SCRs. If all are the same
part number, then you have three rows of common cathode ones and three
wall warts for three phase. However, this does not sound right for a
proper three phase bridge -- so you either have half of them with a
different part number (anode to case instead of cathode to case) in
which case the number of needed wall warts increases, or some strange
A lot better if you can get the original control board working,
and each set of terminals connected to the right SCR's terminals.
(Proably coupled pulses through small transformers on the logic board,
so you get proper isolation between SCRs.
Does the VFD still work? What kind of horsepower is is supposed
to drive? If it still works, I would be tempted to keep it intact. And
if it doesn't, it is likely that the rectifiers were what failed -- or
the failure of the output MOSFETs took out the rectifiers too.
The diodes in that are likely to be combined in fewer packages,
one package being three rectifiers in a single package with common
cathode, and the other three rectifiers in a single package with common
The real question is whether they will handle enough current for
your needs. Based on the looks of that original supply, it was to drive
some hefty motors. (Hmm ... could it be that big supply was purely to
drive the spindle servo motor and the axis motors were some other
I don't remember SCR's all that great but I remember once the gate voltage
goes high the SCR turns on and latches on until current goes below some
threshold. A person gave me some small hockey puck SCR's to use to make a
rectifier for my welder. I didn't get the details but I thought he said you
could connect the gate to the (?anode or cathode) and the SCR would turn ON
and operate as a rectifier. I'll have to experiment before I recommend to
Karl but as soon as the SCR turns on it prevents the gate voltage from going
any higher than the (I think Anode ?) voltage. I could try hooking up one
using a resistor to connect the gate to the anode (?) and seeing if there
are any voltage or current spikes showing up at the resistor.
What I do remember of SCR's is that you can turn them on in the rising part
of the sin wave with a simple voltage divider, and you can use a resistor
and capacitor to get a phase shift to be able to turn the SCR on almost
anywhere during the sin wave.
On most all of the high power SCR's there is an internal low value
resistor across the gate to cathode terminals. The resistance can run as
low as 15 ohms and sometimes will go as high as 150 ohms depending on
the particular SCR. The scr gate is usually fired through a toroid
transformer, isolating it from the transistor firing circuit. The firing
pulses are usually at a On older scr circuits when they burn out or
short it is usually cheaper to replace them with the modular units that
contain two scr's with the heatsink plate on the bottom fully insulated
from the active voltages.
Most all of the spindle drive motors were DC units until about the
middle 80's when you started to see AC motors and drives. Those other
small diodes and scr is part of a separate half wave supply for the
field of the dc motor. The field supply was usually current regulated
and was designed for field weakening above the bass motor speed. Once
the base speed of the motor was reached the field was reduced which
would increase the motor speed as the field was decreased to a minimum
value. If the current went below this minimum set value the drive would
alarm and shut down the drive. Above the base speed if the field
current goes to 0 theoretically the rpm will go to infinity or the rotor
will explode which usually happens first, not a pretty sight.
Don't give up yet, it doesn't take much to use an SCR as a diode. Probably
just connecting the 2 control lead wires together or maybe connected through
a resistor. A SCR is a silicon controlled RECTIFIER, it is a rectifier that
can be turned ON and OFF. To use as a diode rectifier you just have to wire
it to be turned ON all the time. I haven't messed with SCR's much and don't
know how you connect it without looking it up but find out, make a simple
connection, and use what you have if possible, they are already mounted on a
heat sink and everything. I worked 13 hours today so I'm not going to be of
much help today but I'll try to look up a little info on SCR's maybe
That part is half of a DC drive unit for a DC spindle motor. The parts
that look like diodes are actually SCR's since there are 12 of them it
is a full wave unit vs. a half wave unit using a center tapped Y type
transformer with the center tap being the motor return attach point.
The vfd you are going to dismantle is probably the other half of this
unit. The "transformer" attached to the unit is the reactor to keep
harmonics from getting back into the power line.
The unit could be used to build a nice regulated dc power supply if you
can find the rest of the stuff to go with it. Follow the leads that
went to the 12 thin wires on the terminal strip. Instead of having the
tach feedback from a motor you could use a voltage divider feedback into
the tach input ( you may have to isolate the input) to regulate the
I *think* those are SCRs (Silicon Controlled Rectifiers), and
one of each pair is the gate, while the other is likely the cathode
(which the gate signal is applied relative to. Try a resistance
measurement between the black and the white to the high-current lead
from the top of the rectifier -- and to the end bolted to the heat sink.
Whichever one reads zero should be a low-current duplicate connection to
the cathode, and the other needs to go positive relative to the other
lead to turn on the SCR. It may be that you should have kept the board
which was connected to those leads to regulate the output voltage by
turning those on at the right time.
To double check -- look for part numbers stamped on the sides of
What is certain is that it is a high current three-phase
It is likely to be an isolation transformer. Check with an
ohmmeter between the terminals on the heast sink side and the terminals
connecting to the contactor. If it isolation, you should get an
"infinity" reading for resistance -- except with certain rare meters
which can measure very tiny leakages.
And yes -- DC- should be grounded.
It *looks* like a current transformer -- though why there are
four leads remains to be seen. Normally, you hook a known (fairly low)
resistance across the *two* terminals, and measure the voltage
developed. This, with the turns ratio of the current transformer
(you've got two turns on the primary -- and the number or a ratio should
be somewhere on the label of the CT.) will let you turn the voltage to a
Or -- you use a current meter on the secondary, which provides
its own low resistance.
Look for something like 250:1 (or some other ratio) on the
label. I wonder whether it includes some kind of alarm sensor to
account for the extra terminals.
#2 is a current transformer. The wires cut off at the top were the
output sensing connectors. Maybe two sets - to a meter and to a controller.
It appears that power comes in from the right - through fuses ?
goes through a contactor and fires up the three phase transformer.
The secondary of the three phase transformer is sent to the bridge
of Thyristors - Likely SCR's the small wire are the control gate and
a reference wire. That is a great mount of power being rectified there.
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
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On 9/29/2010 11:55 AM, Karl Townsend wrote:
the DC should not be grounded unless there is a three phase isolation
transformer feeding the input to the contactor.
Since the output from the scr pack is DC it cannot be a current
transformer. It is most likely a variable reactor with a ac input and
the other pair of wires is the output. The more current flowing through
the heavy wires the more saturated the core of the transformer and the
amount of ac passed from one winding to the other is diminished.
Newer units use Hall effect detectors.
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