Selenium Bridge Voltage Drop ??

[W6TOM]

  I have an old military power supply that has a selenium bridge rectifier for a 12 volt supply, what would the typical voltage drop across one of those old devices be?? Thanks!!

[Mike/W8BAC]

to many unknowns. Unless you can find a data sheet it is a shot in the dark.

Mike

[K4RT]

Tom - If you have an ARRL handbook from the 1950s, it should include a chart with the specs for several selenium rectifier types, which might help.  The E&E handbook might include a chart as well.  I don't have either at hand at the moment to check.  Rectifier manufacturer catalogs from that era might also include specs and I have found several on the web.  If memory serves I think there is an AMfone thread on this subject or similar from the past year or two and some charts posted so you might search the database here.  Of course military nomenclature may vary from that used in commercial gear.

The forward voltage drop & reverse leakage current increases to some degree as selenium  ages, perhaps up to 7-10 percent if I recall correctly, but it probably varies.

[w4bfs]

several volts comes to mind .... if so replace with adequate silicon diodes and a variable low value resistor.... adjust until you get proper current/voltage

[Opcom]

A procedure would be to

1.) not energize that supply,
2.) disconnect the transformer from the input of the selenium rectifier,
3.) and short the output of the selenium rectifier,
4.) then feed DC through both input legs (if it has two), limiting the current to the rated current,
5.) and hastily read voltage drop across the stack.
6.) turn off the other supply and put things back the right way.
7.) count the cells,
8.) divide volt drop by number of cells,
 - and there you have the answer.

It sounds like a lot of fuss but it's very logical. Co-workers often think I resort to divination or dark arts.

I still have a battery charger I made from an old Sorensen 28V 50A Nobatron. An inductancre in series limits the current to give a 10A charge to a 12v battery, and to go to "cranking" mode an oil capacitor is put across the inductor to resonate and it pushes 150A or better. The selenium stack's about done for, and when abused for too long in 'cranking' mode, one of the diodes will sometimes 'pop' with a foul stench following the report. This thing can not be used with any modern car as it will blow the electronics to pieces. I miss the good ol days.

The shortest answer is: Generally each cell has a reverse voltage rating of around 20-25V. The forward drop is about 1V. They decay over time with heat etc. and so the characteristics can vary. Selenium is toxic so wash hands.

wikipedia has a decent article. One point is: "Selenium rectifiers had a shorter lifespan than desired. During catastrophic failure they produced significant quantities of malodorous and highly toxic fumes that let the repair technician know what the problem was. By far the most common failure mode was a progressive increase in forward resistance, increasing forward voltage drop and reducing the rectifier's efficiency. During the 1960s they began to be superseded by silicon rectifiers which exhibited lower forward voltage drop, lower cost, and higher reliability.[4] They are still manufactured for exact replacement purposes but are not designed into new equipment."

[W6TOM]

  Appreciate the answers, didn't think this would be as involved but was just curious as I have a number of old radios that have selenium rectifiers.

  I just got a TCS PP-380 power supply, it has a poorly done replacement for a selenium bridge, I just ordered a Chinese 12 volt regulator board I will replace it with, for $19.81 not worth my making something. If the voltage drop is excessive I'll calculate a series dropping resistor.

[KE5YTV]

Can you give me info on the 12 volt regulator board. I also have a PP-380/U power supply that I'm about to start on.

Mike

[W6TOM]

 Mike,
            Email to your QRZ address.

     
                                           Tom, W6TOM

[K4RT]

Let us know how it turns out.

I wouldn' t hesitate to replace selenium units with selenium, although it may be more practical to use silicon.  I have done both.  I have yet to see any data that supports the notion that a burned up selenium diode is "highly toxic".  That's an idea that seems to have originated with a web posting or two some years ago and was perpetuated by an otherwise good article about selenium units that appeared about 10 years ago in the AWA journal.  Nevertheless, if you smoke one it's probably a good idea to avoid the fumes and open a window!  

[K9PNP]

According to my HAZMAT database (WISER):

When heated to decomposition it emits toxic fumes of selenium.

The Immediately Dangerous To Life and Health (IDLH) level is 1 mg/cubic meter.

Selenium DUST is an eye and respiratory tract irritant, and can cause coughing, sneezing, breathing difficulty, and headache. The FUME is also irritating to the eye, nose and throat, and can cause pulmonary edema, delayed in onset by 1 to 4 hours. INHALATION of selenium fumes caused bronchospasm, chills, fever, headache, and chemical pneumonitis; similar to symptoms associated with metal fume fever. Skin burns can also result from exposure to fumes.

WITH POISONING/EXPOSURE you can get low blood pressure, and cardiac arrythmias which could lead to cardiac arrest.  Low blood pressure and rapid pulse are early signs of acute toxicity.

For acute exposure, Dizziness, decreased reflexes, central nervous system depression, and coma have been reported.

That  being said, realize that you would not normally get the required concentration from a hot/burning rectifier unless you were in a really small unvented space with it.  The nice thing is the smell makes you want to get away from it anyway.

[W3RSW]

We being amateurs were mostly exposed to everything now considered toxic.

So I'm now over 70, used to chew solder for hours while building stuff, probably was exposed to PCB's, was Exposed to hard gamma radiation right square in the face at the Nevada NTS, used to wash myself with naptha after staining caskets part time, have experienced chlorine gas leaks when cleaning diatomaceous earth filters, back washing and regulating Cl gas injection in an acient pool at a C Club in summer, still siphon gasoline when emptying snow blower after winter, have been sunburned numerous times as a kid and even in later years, swam in the West Fork of the Mon back when raw sewage floated ugliest surprises right by your nose, ate the fish with the rest of the kids out of same, ...I don't know where to stop.  But most of it by far was intermittant.

Puffing a stogie as I write this, but always in moderation, and don't inhale.  

Most of early years in leaded gas, soft sulfur coal heating smoke, trashy, dump picked  environment in the hills of W.Va.

Today's little hot house tomato kids are "protected" from everything under the sun with SPF 50 and are coming to realize they're vit. D deficient.

I'm tired of catering to the sterile safety gods, or pretending to.

Now if I worked all my days in a coal mine, or in friable asbestos manufacturing or one of those old steam or open frame belt driven motor lash ups, I'd probably being paying a real price.  In the gas and oil patch a missing finger or two is considered a rite of passage from chain lash when running casing down hole on a rig.

Oh wait, crankiness is probably the chief symptom of long term exposure.  

The problem with getting older is you know too much.

Geese are honking as they light on the lake right now, fine ending of a sunny warm summer day. And yes they're landing on a lot cleaner water, breathing better air and not shot out of the sky willy nilly thanks to sensible regulation.  Trouble is the harpies don't know when to stop and want to control every aspect of your life.

[W6TOM]

 I'm 2 1/2 years ways from 70, I have severe hearing loss, too many power tools and fire arms, now I wear hearing protection, might as well keep what I have. When I was young no one gave that much thought.

 Both my parents smoked, they both would have lived longer and better lives if they hadn't, I quit 20 years ago.

 I remember blowing out bell housings and brakes when I worked in a gas station and brakes and clutches were made of asbestos. A guy I worked with took early retirement, he worked a few years in his 20's at an asbestos plant, would come home covered with white dust. He retired because he had asbestosis, not good.

 A year ago I retired from the local power company, they had a VERY GOOD safety program, I'm grateful for that too. It made me more aware and also informed me of hazards I didn't know about.

 I remember working in a radiator shop in Massachusetts in 1972, in the Winter all the doors were shut and you couldn't see the other end of the shop for the smoke. The one year I worked there two guys died suddenly, they were just about at retirement age and smoked and had worked in that trade all their working lives. I decided that was not what I wanted to do. A few years later I visited the shop, OSHA has just come into effect. The owner had installed a ventilation system, what a difference!!

 I'm glad we have OSHA and also that there is an element of liability for companies that operate unsafely, better than in the old days when employees were just another expense. I agree that there is a loss of "common sense" in some of the regulations which are written by those who haven't done the work. There needs to be a better balance. I remember when the higher ups told use we needed to wear RUBBER GLOVES when running cross connects for telephones, WTF? Ever tried that?? Obviously who ever came up with that idea hadn't!!

 I also remember when the selenium rectifier in the shortwave receiver my parents gave one Christmas failed, you remember that smell. YUCK!!!!

[K4RT]

According to my HAZMAT database (WISER):

When heated to decomposition it emits toxic fumes of selenium.

The Immediately Dangerous To Life and Health (IDLH) level is 1 mg/cubic meter.

We don't know that a smoked selenium diode in a 1950s ham rig equates to the hazard noted in the HAZMAT data.  It's possible I suppose, but I have my doubts. 

Anyway, GL with the PS project, Tom.

[KD6VXI]

Besides being exposed to HF in a lab accident,  I remember thinking green caps in those junk radios where lookin just like chiclet gum.

Tried a few,  didn't taste like it.

Might explain a lot.

--Shane
KD6VXI

[WD5JKO]

Selenium is an essential mineral needed in our bodies....

http://www.drweil.com/vitamins-supplements-herbs/supplements-remedies/selenium/

Maybe that is why some hams live well into their 90's.....

Jim
Wd5JKO

[W3RSW]

You maybe close to a shred of truth.  That's how we developed our immune system and never heard of much asthma or peanut allergies? Not sure that was even recognized 60 yrs. Ago.

Well I could go on and on, swishing mercury in my mouth to coat real copper pennies in chem lab, burning sulphur under the hood to get that fresh-lit match aroma in spades, all in an era way before carting back real stuff from 'Nam; or riding down the road when little standing up in the front bench seat being held by my dad.  Gasolene b-0m!b (see? Can't be too careful now) tossing around the back forty,  filling big plastic laundry bags by covering them over the gas stove so we could balloon them away.  Shooting arrows straight up overhead pretending they were rockets, got one back in upper knee for that trick. --all the stuff we all did. Charging up caps to shock the unwashed at school, cherry b...ing ponds for fun and fish. I'm sure I've only scratched the surface , all this tried at home

Back to half handed driving artistry, Dad probably had lots of practice when younger, you know, coffee or beer in one hand, cig in sort of another, another on the shift lever, and another on the wheel at times,.. Oh, and the last one on his honey. ... Who could sit in the middle of a loooong bench seat, um better stop there.

So enough of that from boiled frog land.

Say I think it was Heathkit, but do you remember how bright orange and kuhl-colorful those Sarks Tarzan seleniums were?  I can remember being disappointed when dull gray ones were included in a kit.  The VTVM had a low current, black square one with some sort of red encapsulation peaking out the non-threaded end.  How bright and shiney all those parts were.

[K4RT]

Rick - They're still around.  At ths Berryville, Va hamfest a few weeks ago I saw a bright orange selenium stack on a table with other vintage parts.

[Opcom]

 Shooting arrows straight up overhead pretending they were rockets, got one back in upper knee for that trick.

we were spoiled. we had Lawn Darts

[W3RSW]

Well at least your darts didn't go out of sight. I knew enough to not look up on arrow return, but the impulse to was oh so strong. Took up golf and imagined a phalanx of golfer war-men launching exploding golf balls at the charging enemy. Couldn't quite figure how to eliminate predetonation what with the compression from the club impact.  We didn't have those great slo-mo movies to watch that action, at least available to a kid.

ARRL handbook, 1963, mentions that all silicon, germanium, and silicon diodes have a low (about 5 v) voltage drop compared to a 5Y3, but don't say a whole lot more except not to exceed current rating, hence in typical circuits seem to recommend a 22 ohm resistor in series, understood I guess by smarter readers to be in typical receiver or small transmitter application.