Power supply

Turns out I have a power supply for my Matsurra bedmill. After stripping everything not needed away I ended up with this:
http://www.metalworking.com/dropbox/supply1.jpg
http://www.metalworking.com/dropbox/supply2.jpg
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 grounded?
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"
Karl
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On 09/29/2010 09:55 AM, Karl Townsend wrote:

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.
--

Tim Wescott
Wescott Design Services
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Tim Wescott wrote:

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.
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Pete C. wrote: > Absolutely those are SCRs or Triacs, you can see the control terminal in

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

It looks more like a 3-phase line reactor. For example: http://www.transcoil.com/Products/InputSide/KLR.htm
--
Ned Simmons

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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.
--
jiw

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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 lines.
But, as others have said, without the control electronics, you have a pile of probably not very valuable spare parts.
Sorry! Rich
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Tim suggested checking for continuity. Theres 0 ohms accross leads, so its not an isolation transformer. Any use for a chocke, or just toss it?

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.
Karl
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    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 setup.
    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 anode instead.
    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 supply?
    Good Luck,         DoN.
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wrote:

DoN, 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.
RogerN
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SCR tutorial: http://www.allaboutcircuits.com/vol_3/chpt_7/5.html
The gate may have a maximum current rating and should be protected with a series resistor.
jsw
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Jim Wilkins wrote:

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.
http://cgi.ebay.com/Powerex-Dual-SCR-POW-R-BLOK-25A-800V-CM4308A2-/250527946625?pt=LH_DefaultDomain_0&hash=item3a54a11781
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.
John
John
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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 tomorrow.
RogerN
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wrote:

I'd really appreciate the help Roger. This unit was built for this machine, it has to be designed and sized for it.
Karl
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Karl Townsend wrote:

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 output voltage.
John
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    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 the rectifiers.

    What is certain is that it is a high current three-phase transformer..
    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 current reading.
    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.
    Good Luck,         DoN.
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What's that Lassie? You say that Karl Townsend fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Wed, 29 Sep 2010 11:55:59 -0500:

It's a three phase choke. Keeps line transients from triggering the SCRs.
--

Dan H.
northshore MA.
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#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
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On 9/29/2010 11:55 AM, Karl Townsend wrote:

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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.
John

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