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  1. #1
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    Default Senior Moment. Can't rem eber what this device is called.

    Having a senior moment. Can't remember what this red device is called. In control panel of a lathe. Please help this old fart.
    .
    dscf1067.jpg

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    looks like a diode bridge rectifier

    p.s. that particular style is quite old, would be a good idea to replace it with a modern one, since you're cutting wires there already

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    Selenium rectifier

    Tom

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    Maybe I'm not quite as senile as I thought. I kept thin king its a rectifier but couldn't find anything that looked like it.

    That wire was cut when the machine was acquired last December. Bought for a particular job. It runs and gets the job done. Been told it has a spindle brake, but haven't been able find it yet. Schematics don't completely match machine; as in this device and a modern bridge rectifier are not in the schematic, nor is there any mention of a spindle brake.

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    Quote Originally Posted by TDegenhart View Post
    Selenium rectifier

    Tom
    Yup. Haven't seen one of those for about 65 years! My HO train power supply had one. I once connected it backwards. Bad idea. The smoke I let out really stunk horribly!

    (PS: Why do I never see typos until after I click Reply?)
    Last edited by Yan Wo; 04-16-2021 at 07:06 PM.

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    The smoke is toxic.

    W&S has them in the automatics, supplies the motor brake.

    IIRC there isn't a silicon based drop in replacement.

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    afair the difference between these and silicone ones is the efficiency, less voltage drop on the silicone ones, so I don't really see reason why an appropriately rated silicone one wouldn't work for something like dc injection braking (if that is the brake type he has there), less heat to dissipate on the diodes and more braking energy...

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    Quote Originally Posted by TDegenhart View Post
    Selenium rectifier

    Tom
    "Most probably". But it is not the only semi-conductor metal put up in that physical arrangement.

    Annnnd the several types are still made, brand-new, and in the marketplace.

    Largest single user of seleniums, the electroplating industry.

    They have different characteristics from Silicon-based rectifiers. Some applications, that "difference" fills a crucial need.

    How they react to draw of current and excessive current, linearity or not, if they limit or foldback instead of overheating, whether they can "self heal" by reforming, the native (or "doped") junction fwd voltage drop, inverse Voltage handling...etc.

    Ladies pantyhose sizes and dust covers for parked dirigbles are much the same.

    One size does NOT "fit all".


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    ok, so lets now put your argument in this particular context - how many of those characteristics useful in 1000A plating rectifier are relevant for a simple dc electromagnet? (I'm still assuming this is a dc injection motor brake application)

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    Quote Originally Posted by jz79 View Post
    ok, so lets now put your argument in this particular context - how many of those characteristics useful in 1000A plating rectifier are relevant for a simple dc electromagnet? (I'm still assuming this is a dc injection motor brake application)
    What "argument?"

    Why would I be the one to give a s**t? I wasn't defending the selection.

    Now that you are aware that most technology retains a niche of some kind even once no longer dominent, it is not hard to research it you are he who DOES care.

    As has been said "Right here, on PM"

    Bronze Age didn't end because we ran out of Bronze.
    Stone Age didn't end because we ran out of Stone.

    I'd add "nor run out of advantageous USES for Bronze or stone, either!"

    Nor rectifiers other than Silicon.

    And IS it motor braking, anyway? Not my lathe. Not concerned with what it was or is used for.



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    "one size does not fit all", and "not" even in caps, as to suggest the importance of what is being said

    and now I see that it was said completely out of context, so I'll ask - does every topic here really needs to be about everything or can we stay on point?

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    Quick answer: yes and no.

    That rectifier may be for a DC injection brake, or may be just a rectifier for control voltage that's been bypassed or may be the machine's been converted to single phase. There are other possibilities, but these come to mind. Not quite enough info to reach conclusions.

    FWIW, Wade screw machines have this style rectifier for control voltage and to power electromagnetic brakes/clutches. The spindle brake needs voltage to activate, which could be the reason your spindle brake doesn't work, if it exists.

    Tell us more about this machine.

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    Quote Originally Posted by neilho View Post
    Tell us more about this machine.

    40" x 240" engine lathe. Italian. imported and marketed by S&S Machinery(defunct 2013?) as Lansing G40. 480 volt 20 hp. Power rapids.
    dscf1024.jpg

    Notice that there is a wire running from the 28volt output of the step-down transformer to the rectifier. Wire #1 is a neutral/ground. Haven't traced the #47 or the blue wire at the top of the device.

    There is a pair of wires that go into the headstock and attach to something on the very bottom of the case. Haven't been able to get a mirror down there to see what is there. If it is a brake(as I suspect) and is broken, it will stay that way because everything in the case would have to be removed to get to it.


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    Wire is cut but there is a purple wire attached that looks like a add on.

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    Almost certainly selenium, the number of junctions suggests that. Selenium has much higher reverse voltage withstand capability than copper oxide, the other popular choice. It appears to be a full-wave rectifier, easily replaced with a solid state (silicon) type at low cost.

    Characteristics? Well, they ended up being higher resistance than silicon or germanium, but that was not always an advantage. If the resistance was used in the circuit, an added resistor will generally do the trick when using a silicon replacement.

    Mostly they were used because they were functional, low cost, and easily available up into the 1960s, when solid state (so called) became dominant and cheaper.

    You do not HAVE TO replace it, they work fine when not defective, and used within their ratings, same as any other component.

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    Quote Originally Posted by JST View Post
    Almost certainly selenium, the number of junctions suggests that. Selenium has much higher reverse voltage withstand capability than copper oxide, the other popular choice. It appears to be a full-wave rectifier, easily replaced with a solid state (silicon) type at low cost.

    Characteristics? Well, they ended up being higher resistance than silicon or germanium, but that was not always an advantage. If the resistance was used in the circuit, an added resistor will generally do the trick when using a silicon replacement.

    Mostly they were used because they were functional, low cost, and easily available up into the 1960s, when solid state (so called) became dominant and cheaper.

    You do not HAVE TO replace it, they work fine when not defective, and used within their ratings, same as any other component.
    They are no less available in the 2020's. Just not as often WANTED!
    Silicon is usually MUCH cheaper as well as physically more compact.

    Also more widely stocked. Cheap enough I stash "many" packaged Silicon FWB myself, wouldn't have to leave the house. Well... maybe to go over to the Court House and get SEARCH Warrant? You'd have to know electronics packrats 70 years in the collecting?



    SELENIUM RECTIFIER - CEHCO

    Many of them are made in India these days:

    Selenium Rectifier Manufacturer, Supplier & Distributor - Rectifier India

    Regardless.. I'd class that lathe worth the bother of doing the detective work to see if the functionality of "whatever" might not be so hard to restore after all.

    The wire may be routed through an area you don't want to mess with. But the device on the other END of it might be more easily accessed?

    Italian designers did things their own way, but that is not necessarily the "hard way" when it came to goods as might need serviced.

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    Lot bigger lathe than I thought!

    A 250VA transformer seems small to be powering a spindle brake, in addition to all the other contactor coils. But there may be other transformers in the machine - 120V is coming into this one and maybe 220 ( lowest terminal, partly obscured) from a 440V main.

    Or, if you're just interested in making the spindle brake work, tracing the wires back from the brake to its control and checking for voltage/amperage would be a start.

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    Quote Originally Posted by neilho View Post
    Lot bigger lathe than I thought!

    A 250VA transformer seems small to be powering a spindle brake, in addition to all the other contactor coils. But there may be other transformers in the machine - 120V is coming into this one and maybe 220 ( lowest terminal, partly obscured) from a 440V main.

    Or, if you're just interested in making the spindle brake work, tracing the wires back from the brake to its control and checking for voltage/amperage would be a start.
    Italian lathe doesn't INSURE "Baruffaldi":

    Company - Baruffaldi

    .. but that TOO is "a start", because if you can FIND a brake or clutch, any info on it to ID it, and what it takes to OPERATE it, even if you do that from a cold start won't be much of a mystery.

    Useful creatures. But not exactly rocket science, given they grew off the back of motorcycle brakes!


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    Traced wires to possible brake. They come directly back to #47 and #F-- (actually blue wire on top of stack) on the rectifier. Seems to be no resistance between wires that go to (brake?) device in bottom of gearbox when disconnected from terminal strip.

    #1 on rectifier goes to operator panel on/off switch then to clutch on/off switch then to #0 neutral/ground.

    Apply power to system. Panel switch off position= 30 volts at #F-- and #47. Panel switch on position= 13.6 volts at #F-- and #47. ??????



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    Schematic/circuit of selenium rectifier.

    Voltage between 47 and F-- at rectifier is .1DC volt. I have to believe this is not designed output. Or am I full of shit? Any ideas on a replacement?

    The clutch switch is a microswitch that breaks the circuit when the spindle is supposed to turn. The Brake On switch gives you option to run without braking. Makes for some difficulty in stopping spindle without overworking the clutches.

    dscf1068.jpg


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