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 10Likes
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 Originally Posted by mattb
Yes and of a very old 'solid state' type. Stacked plates - at one time (1920's) copper/copper oxide 'junctions' physically clamped.
This one probably selenium, which were not uncommon up through the '60s. While they proved fairly durable, I've no idea how 'good' this one might still be nor could be expected to remain over the years yet to come.
Modern silicon replacements are cheap and cheerful, best to go a bit overboard on voltage and current rating, and also provide for getting heat away. Tab-bolt to the metal case with a bit of thermal goop is usually fine.
If you choose to retain this one, refrain from putting any side strain on the through-bolt or torque on the stack 'fins' and keep solvents or corrosives well clear of it.
NB - can't tell for sure from the angle, but the BLACK item with silvery portion looks to be one of the more modern packaged silicon bridge rectifiers - half-wave, perhap even full-wave.
A good VOM with the diode symbol at one test-range is your friend.
Bill
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Originally Posted by mattb
I don't think I have the taps for the higher voltage. With the help here I think I have the rest figured out. Here are some pictures of the transformer and rectifier. Is the blue thing a rectifier?
Attachment 54911Attachment 54912
I'm not sure that I understand the diagram on the upper right of the red plate. It seems to indicate that there are 8 wires on the primary side and 8 on the secondary side, for a total of 16 wires. How many wires are coming out of the transformer? What are they labeled?
If Bill's right and that's a selenium rectifier, I would get it out of there. They can and do fail catastrophically and emit nasty smelling, toxic fumes. A modern, super heavy-duty full bridge rectifier costs less than $10.
Cal
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Originally Posted by Cal Haines
If Bill's right and that's a selenium rectifier, I would get it out of there. They can and do fail catastrophically and emit nasty smelling, toxic fumes. A modern, super heavy-duty full bridge rectifier costs less than $10.
The modern silicon ones can ALSO 'detonate', though only with obscene stress. The fumes from the small amount of silicon are less hazardous, and the highly toxic dopants present in only extremely small concentration. That said, the stench from the vaporized encapsulant is no picnic.
Good idea to provide for at least double the voltage and current expected. 1000V and 50A packaged FW bridge are both cheap and compact enough that I keep a few around as 'universal' replacements.
Bill
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Originally Posted by mattb
Your transformer is rated at 500VA. 500VA / 120V = 4.2A rated output and it's fused at 4A. The exciter it replaced was probably rated at 2.4A at 115VDC. A 15A rectifier would be sufficient, but a larger one is fine.
Here's rectifier that I've used in the past:
GBPC3510 - FAIRCHILD SEMICONDUCTOR - BRIDGE RECTIFIER, 1PH, 35A, 1KV | Newark
Personally, the few dollars saved going with an unknown module, shipped from mainland China, would not be worth it to me.
Newark, Mouser, Digikey, Allied are all possible sources.
What are the 8 wires coming out of the transformer labeled and how are they connected? (The wire numbers are printed on the woven casings of the wires; I can see on labeled "H3" visible in one of your photos.)
Cal
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I ordered the rectifier from Digikey.
The wires are labeled
x2,x4 -go to the fuse then to the black rectifier
x1,x3- go to the black rectifier
h2,h3- connected together
h4- black wire labeled 460 ac input
h1- red wire labeled 460 ac input.
The 2 wires labeled 120 volt dc output comes from the black rectifier.
The older blue rectifier is connected to the black rectifier by 2 wires.
Thanks
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Originally Posted by mattb
I ordered the rectifier from Digikey.
The wires are labeled
x2,x4 -go to the fuse then to the black rectifier
x1,x3- go to the black rectifier
h2,h3- connected together
h4- black wire labeled 460 ac input
h1- red wire labeled 460 ac input.
The 2 wires labeled 120 volt dc output comes from the black rectifier.
The older blue rectifier is connected to the black rectifier by 2 wires.
Thanks
Some of this is supposition, a VOM can confirm it;
Looks like a step-up/down transformer with two (identical) primary windings H1, H3 and H2 H4. As-connected they are in series for 460 VAC. Opening at H2. H3 and re-connecting with H1, H3 at one side of a 230 VAC line and H2,H2 at the other side should prep it for 230V input with no other changes..
Because .. . X1,X3 and X2,X4 are already in parallel, so if they were in fact delivering 120 V, the transformer was wound with a 2:1 ratio.
As to the diodes ... need to confirm how many terminals are on each, and specifics of HOW wired to fuse et al. Looks as if they may be wired as two half-wave elements of a full-wave bridge.
Not a good mix, as their charactertics are quite different.
OTOH, with the wires fully traced-out, the selenium rectifiier could be in series, post silicon recifier, pre load, thereby serving-up its multiple diode-drops as a crude voltage reduction device. Using the junction characteristics this way can be quite stable under varyng load, as - unlike a resistor, voltage drop is relatively insensitive to current or load changes.
It should be better to replace BOTH with a single-package modern FW bridge rectifier, see if the voltage NEEDs dropped, apply a larger number of high-current/voltage simple silicon diodes in series (.6V drop per junction, typically, and a given package may have 'stacked' junctions, not just one).
But the nuances want confirming.
Bill
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Originally Posted by mattb
I ordered the rectifier from Digikey.
The wires are labeled
x2,x4 -go to the fuse then to the black rectifier
x1,x3- go to the black rectifier
h2,h3- connected together
h4- black wire labeled 460 ac input
h1- red wire labeled 460 ac input.
The 2 wires labeled 120 volt dc output comes from the black rectifier.
The older blue rectifier is connected to the black rectifier by 2 wires.
Thanks
Everything you need to know to wire up the transformer is shown in the diagram on the right side of the red tag, above. The diagram has 5 parts. Across the center is a schematic diagram that shows how the transformer’s 4 windings are labeled. The 4 leads that connect to the primary are labeled H1 through H4; the secondary windings are labeled X1 to X4. The use of ‘H’ and ‘X’ to suffix primary and secondary winding leads, respectively, is common.
Above the winding diagram are two small diagrams that show how to connect the primary for either 240 or 480 VAC input. The one on the left shows that H1 and H3 are connected together for one side of the 240 VAC input and H2 and H4 are connected together for the other; this places the two primary windings in parallel. The transformer is currently wired according to the 480 diagram, which places the windings in series. Note that in either configuration, 240 VAC appears across each winding.
Similarly, two small diagrams appear below the winding diagram, showing how to configure the secondary for either 240 or 120 VAC output. The diagram on the right shows that for 120 VAC output, X1 and X3 are connected together for one side; X2 and X4 are connected together for the other. Again, this places the secondary windings in parallel (which is how the transformer is currently configured). As before and regardless of the configuration, each secondary winding will have 120 VAC across it. Placing the windings in series would produce a 240 VAC output.
The input to the transformer appears to be unprotected. I would place two, 2A slow-blo fuses in between the incoming power from the AC contactor and the transformer, one fuse for each side of the primary. If using a rotary phase converter (RPC), you will also want to make sure that the transformer is connected to the real legs of the RPC. (See my 480 to 240 conversion checklist for additional information on RPCs.) You should also run a green safety ground wire from the machine’s incoming green safety ground wire and one of the mounting bolts for the transformer. Make sure that you have good metal to metal contact.
You can now check that the transformer is correctly configured: With the input fuses and safety ground wire in place and power applied to the primary you should read about 120 VAC between the secondary lead pairs (X1+X3 and X2+X4). Obviously, power must be turned off again before any further wiring is done.
Connecting the output of the transformer to your new full-wave bridge rectifier is relatively simple. The AC inputs to the rectifier will be labeled; the symbol ‘~’ is frequently used. One pair of secondary leads (X1+X3) go to one ‘~’ terminal, the other pair (X2+X4) go to the other ‘~’ terminal; it doesn’t matter which pair goes to a particular ‘~’ terminal. You should now read close to 120 VDC between the positive and negative terminals of the rectifier (the voltage will be less than 120 due to the forward drop across the diodes). Don’t forget to turn off power when you are done checking!
To finish the job, connect the positive terminal of the rectifier to the fuse and the red wire that runs to the MG terminal box. The black wire connects to the rectifier's negative terminal. Assuming that the electrician that put the rectifier in originally had things correctly polarized you should be ready to go, at least as far as this portion of the conversion goes.
The above is presented simply to let you know what needs to be done.
You should hire a licensed electrician to do the work.
The voltages involved here can kill you!
Cal
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It's Alive! Still need to check the voltage coming from the transformer. Tried it with the old rectifiers and it started right up. DC motor worked forward/ reverse. MG direction was correct. Going to change the rectifiers and check the voltage next. Or should I leave whats working alone? I also need to rewire the coolant pump to 220. There are no fuses in the main disconnect so I probably need to do something there also. 30A? Would a 3 phase breaker be better? Anything else electrical I'm missing? Big thanks to all of you for taking the time to walk me through this.
Last edited by mattb; 07-14-2012 at 04:25 PM.
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Originally Posted by mattb
It's Alive! Still need to check the voltage coming from the transformer. Tried it with the old rectifiers and it started right up. DC motor worked forward/ reverse. MG direction was correct. Going to change the rectifiers and check the voltage next. Or should I leave whats working alone? I also need to rewire the coolant pump to 220. There are no fuses in the main disconnect so I probably need to do something there also. 30A? Would a 3 phase breaker be better? Anything else electrical I'm missing? Big thanks to all of you for taking the time to walk me through this.
I would definitely replace the rectifier. I would also install fuses for the coolant pump.
30A time-delay fuses ahead of the AC contactor and after the main disconnect switch would be OK.
Does your main disconnect have just a 3-phase knife switch, or what?
Cal
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Originally Posted by Cal Haines
I would definitely replace the rectifier. I would also install fuses for the coolant pump.
30A time-delay fuses ahead of the AC contactor and after the main disconnect switch would be OK.
Does your main disconnect have just a 3-phase knife switch, or what?
Cal
The main disconnect only has the knife switch. No fuses.
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If you can find space in the disconnect box or in the contactor enclosure, you can mount a 3-pole Midget fuse block. I'm using 3 FLM-30 Midget fuses on my machine.
Fuse blocks: McMaster-Carr
Fuses: McMaster-Carr
Midget fuses would be a good choice for your coolant pump and the input to the transformer for your exciter replacement as well.
Cal
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Interesting history. The lathe was sold to McQuay Norris in 1943. Not many companies can tell you where there product was shipped 70 years ago.
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Better pictures of what we discussed earlier about replacing with a new rectifier. I am not 100% sure how to wire this. Maybe I should say 20%. The older black rectifier has + and - marks. The new one has the marks you see. Mainly I am looking for info to help my more qualified help when they are able to get back over. Thanks again.
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"The old black module appears to be a full wave bridge rectifier. I have no clue what the blue device does."
The blue device looks like a snubber to keep the HV transients from frying the bridge rectifier. Many DC relays have a large spike when they close, that can't be snubbed with shunt diode since the spike is in the same polarity as the energizing voltage. (the spike that occurs when the field is dropping can be snubbed with a diode in reverse) I use varistors for the purpose (Digikey P7264-ND or similar ) connected the same as the blue device, across the + and - terminals of the bridge rectifier.
Bill
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Originally Posted by hitandmiss
"The old black module appears to be a full wave bridge rectifier. I have no clue what the blue device does."
The blue device looks like a snubber to keep the HV transients from frying the bridge rectifier. Many DC relays have a large spike when they close, that can't be snubbed with shunt diode since the spike is in the same polarity as the energizing voltage. (the spike that occurs when the field is dropping can be snubbed with a diode in reverse) I use varistors for the purpose (Digikey P7264-ND or similar ) connected the same as the blue device, across the + and - terminals of the bridge rectifier.
Bill
Should I replace the blue thing or keep it?
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Originally Posted by Cal Haines
The old black module appears to be a full wave bridge rectifier. I have no clue what the blue device does.
It LOOKS like a selenium rectifier. It is WIRED where an MOV or sputnik would be. Unless the FW bridge had developed an open diode-leg.
Here's the data sheet for your rectifier: All is says is " Polarity: as marked on body", which is a pretty odd way to do things.
in the day and age of machine-inserted components, yes, odd. For the several decades when they were manually assembled, they generally did not have a keyed-corner.
Normally the corner with the chamfer and the tab that is oriented differently from the other three tells you which tab is positive.
On this one, only the positive terminal turned 90 degrees is present.
It appears that the positive terminal is the one nearest to the '+' symbol on the case. The negative terminal will be the one diagonally opposite the positive terminal.
And it should be so marked.
Don't fool around with this stuff if you don't know what you're doing. You can easily kill yourself or set the shop on fire if you mess up.
Seconded. And not to put too fine a point on it .... all indications are that you do NOT know.
Nothing wrong with that. You didn't claim otherwise.
But best to get 'local hands' who DO know electricity and electronics involved.
Bill
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Originally Posted by mattb
Should I replace the blue thing or keep it?
That one should come out, if only because no one is certain what it IS or was intended to DO.. we are having to guess.
An MOV (Metal Oxide Varistor) could go in. Plenty of information about those on the web.
Bill
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