Selenium Rectifiers

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EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
Hi, Does anyone have any experience with these items. I am trying to fix an old machine that uses one of these and I have no schematic diagram at all. I have traced the wires and drawn my own. Now having tested it I am suspecting that one of the legs is open circuit which means I will have to replace it with silicon diodes, as Selenium are very expensive. I have included drawings and a pdf file. The pdf file is how the rectifier is connected to the circuit. Basically one of the solenoid coils of the hydraulic valve started to draw a lot of current and I at first suspected the coil but then I needed to know if the rectifier was fine. I feel I am getting too much voltage on the coil. It is going up to 380 V and does not sound correct. On che.cking the rectifier I noticed what appears to be two legs open circuit but I may be wrong. Thanks in advance Ed
 

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EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
Selenium Rectifier

Selenium Rectifier

Hi, Does anyone have any experience with these items. I am trying to fix an old machine that uses one of these and I have no schematic diagram at all. I have traced the wires and drawn my own. Now having tested it I am suspecting that one of the legs is open circuit which means I will have to replace it with silicon diodes, as Selenium are very expensive. I have included drawings and a pdf file. The pdf file is how the rectifier is connected to the circuit. Basically one of the solenoid coils of the hydraulic valve started to draw a lot of current and I at first suspected the coil but then I needed to know if the rectifier was fine. I feel I am getting too much voltage on the coil. It is going up to 380 V and does not sound correct. On che.cking the rectifier I noticed what appears to be two legs open circuit but I may be wrong. Thanks in advance Ed

Yes I can but I need to know what the schematic of this item is so I can get it right. Look at the PDF file and you will see how it is connected. I do not want to make any mistakes as there are clutch coils involved as well. This machine is an old 1930s to 1940s Guillotine, and to get coils for the clutch assembly could be very hard. It is an old Swedish machine.
 

Besoeker

Senior Member
Location
UK
Yes I can but I need to know what the schematic of this item is so I can get it right. Look at the PDF file and you will see how it is connected. I do not want to make any mistakes as there are clutch coils involved as well. This machine is an old 1930s to 1940s Guillotine, and to get coils for the clutch assembly could be very hard. It is an old Swedish machine.
Do you know what voltage the clutch coils are?
 

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
Read this, I had to do something like this a couple of years ago, I found this to be most helpful.

http://w3hwj.com/index_files/RBSelenium2.pdf

Ok, got it thanks but what I want to know is this. Look at the pdf file you will see 5 connections on the Rectifier. why is the first connection connected to the last one, and do you know what the actual inputs etc are. I have an idea but I would like some confirmation on the connections. Ed
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
A selenium rectifier typically consists of a number of disks on a common insulated shaft.
What you are seeing is probably the configuration of a number of separate disk stacks with interconnections to form a two or four diode bridge. There is a connection between the two end wires because the stack ends that must be connected are not adjacent.
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
Ok, got it thanks but what I want to know is this. Look at the pdf file you will see 5 connections on the Rectifier. why is the first connection connected to the last one, and do you know what the actual inputs etc are. I have an idea but I would like some confirmation on the connections. Ed

I've been around a lot of years, mostly military and aerospace electronics, but have never seen the circles with P1, P2 and S1, S2 -- is that a connector, pins and sockets?
Is the relay coil an ac relay? Would suspect so?

If so, 5 is the negative of a full wave bridge, 3 is the positive, and 2 and 4 are the ac inputs to the bridge.
You want to use at least 600 V PIV diode bridge, current rating about 2x what the solenoid valve needs.
You also need to provide a heat sink, size dependent on solenoid valve current draw.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150721-2211 EDT

EdCampbell:

Looks like a bridge rectifier.

I believe terminals 3 and 5 are the DC output. These go to "output to solenoid valve", and "common for solenoid value". My guess is common is negative. But I doubt the solenoid cares what the polarity is unless there is a snubber diode.

I believe terminals 2 and 4 are the AC input terminals to the bridge rectifier. These come from S1 and S2 of the upper circle which appears to be a transformer secondary. Open S1 or S2 and measure the unloaded secondary voltage. This is needed to determine voltage rating of the rectifier.

Apparently 220 V is applied to the transformer primary. I don't know if the third prmary wire is a center tap or what.

The physical size of the selenium plate determines its current rating. They are probably somewhat over 1" on a side. Rating might be 100 mA to 1 A. For convience you could use a 10 A 600 V silicone bridge rectifier. A 1" square plate is probably about 100 mA.

If the transformer secondary voltage is 220 V, then the DC output voltage from the bridge will be about 220 * 0.636 / 0.707 = 198 V. Thus, knowing the secondary AC RMS voltage you can know the DC voltage, and if you measure the solenoid coil resistance, then you can estimate coil current.

The peak inverse voltage rating of the rectifier must be at least a moderate amount greater than the peak of the AC voltage. Many use a 200 V rectifier on a 120 V source, and 400 V on a 240 V source. I feel this is marginal. I use a 400 V PIV on 120 and a 600 or 800 V on a 240 source. If you use diodes in a full-wave center tapped rectifer circuit, then the diode PIV rating has to be double that of a bridge rectifier.

.
 

Tony S

Senior Member
Selenium and germanium bridge rectifiers have the same configuration. The +ve (centre) will have a red dot –ve (the two ends linked) a black dot. AC in is via the two connections at ¼ marked with a green dot.

If your thinking of a straight swap with a modern silicon bridge package, be careful. Plate rectifiers have an inherent resistance which lowers the O/P voltage under load. I fell foul of that on a ladle crane, I burnt the brake coil out. Plate rectifiers are also resilient to reverse voltage. The brake coil de-energising led to high peak reverse voltage, I had to fit a reverse bias diode across the bridge O/P.

If you have a selenium or germanium rectifier burn out there will be a brown smoke. It is highly toxic as is the dust that settles afterwards. One of the reasons they are banned in the UK.
 

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
I've been around a lot of years, mostly military and aerospace electronics, but have never seen the circles with P1, P2 and S1, S2 -- is that a connector, pins and sockets?
Is the relay coil an ac relay? Would suspect so?

If so, 5 is the negative of a full wave bridge, 3 is the positive, and 2 and 4 are the ac inputs to the bridge.
You want to use at least 600 V PIV diode bridge, current rating about 2x what the solenoid valve needs.
You also need to provide a heat sink, size dependent on solenoid valve current draw.


Hi Junkhound, The symbol with the circles is a another way of showing a transformer. It is often used in unipolar drawings and elsewhere. If you google single phase transformer symbol images you will find it. I use it sometimes for clarity on my own drawings. By the way thanks for the info.
 

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
150721-2211 EDT

EdCampbell:

Looks like a bridge rectifier.

I believe terminals 3 and 5 are the DC output. These go to "output to solenoid valve", and "common for solenoid value". My guess is common is negative. But I doubt the solenoid cares what the polarity is unless there is a snubber diode.

I believe terminals 2 and 4 are the AC input terminals to the bridge rectifier. These come from S1 and S2 of the upper circle which appears to be a transformer secondary. Open S1 or S2 and measure the unloaded secondary voltage. This is needed to determine voltage rating of the rectifier.

Apparently 220 V is applied to the transformer primary. I don't know if the third prmary wire is a center tap or what.

The physical size of the selenium plate determines its current rating. They are probably somewhat over 1" on a side. Rating might be 100 mA to 1 A. For convience you could use a 10 A 600 V silicone bridge rectifier. A 1" square plate is probably about 100 mA.

If the transformer secondary voltage is 220 V, then the DC output voltage from the bridge will be about 220 * 0.636 / 0.707 = 198 V. Thus, knowing the secondary AC RMS voltage you can know the DC voltage, and if you measure the solenoid coil resistance, then you can estimate coil current.

The peak inverse voltage rating of the rectifier must be at least a moderate amount greater than the peak of the AC voltage. Many use a 200 V rectifier on a 120 V source, and 400 V on a 240 V source. I feel this is marginal. I use a 400 V PIV on 120 and a 600 or 800 V on a 240 source. If you use diodes in a full-wave center tapped rectifer circuit, then the diode PIV rating has to be double that of a bridge rectifier.

.

Hi Gar, Thanks What you have shared is helpful. I will take all that into consideration. The plates are about 1.5 inches square. I think I have some old heavy Duty diodes I removed from and old DC drive they are the bolt on type which would make it easier to make the heats sink. Ed
 

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
Selenium and germanium bridge rectifiers have the same configuration. The +ve (centre) will have a red dot –ve (the two ends linked) a black dot. AC in is via the two connections at ¼ marked with a green dot.

If your thinking of a straight swap with a modern silicon bridge package, be careful. Plate rectifiers have an inherent resistance which lowers the O/P voltage under load. I fell foul of that on a ladle crane, I burnt the brake coil out. Plate rectifiers are also resilient to reverse voltage. The brake coil de-energising led to high peak reverse voltage, I had to fit a reverse bias diode across the bridge O/P.

If you have a selenium or germanium rectifier burn out there will be a brown smoke. It is highly toxic as is the dust that settles afterwards. One of the reasons they are banned in the UK.

Hi Tony, thanks for the info, By the way I am (Rhodesian) or Zimbabwean however you want to put it. Now living in Mexico. Sadly I never saw the item die I think it died slowly. I will check the voltages and see what I get. if it is too high I will maybe change the transformer. I have a few lying around that may work. I tend to collect old electrical and electronic bits and pieces (it drives my wife up the wall - but you never know when you will need it, and it is always cheaper than having to buy new ones). Ed
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150722-2112 EDT

EdCampbell:

See https://reinventingscience.wordpress.com/tag/selenium-rectifier/ . Current rating about 50 mA/sq-cm, or 50 * (1.5 * 2.54) * (1.5 * 2.54) = 50 * 14.5 = 725 mA for your 1.5" square plate.

If you build your own bridge rectifier you might consider the 1N5059 series of avalanche diodes. The 1N5060 is rated 200 V PIV. No heat sink required other than soldering to PC board. Or mount to terminal blocks, more heat sinking than PC board.

See http://www.vishay.com/docs/86000/1n5059.pdf . This diode was originally created by GE.

.
 

Tony S

Senior Member
Hi Tony, thanks for the info, By the way I am (Rhodesian) or Zimbabwean however you want to put it. Now living in Mexico. Sadly I never saw the item die I think it died slowly. I will check the voltages and see what I get. if it is too high I will maybe change the transformer. I have a few lying around that may work. I tend to collect old electrical and electronic bits and pieces (it drives my wife up the wall - but you never know when you will need it, and it is always cheaper than having to buy new ones). Ed

So I’m not the only one. At work I filled an entire redundant switchroom with “junk”. Junk that got the companies backside out the fire many times.

My wife and I nearly emigrated to Rhodesia, I was at the London embassy when UDI ended and the republic was declared. I was back peddling franticly at that point, I was about to sign on the dotted line.

I’d two offers of jobs, the milk marketing board and electrical supervisor at Wankie coal mines.
 
Last edited:

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
So I’m not the only one. At work I filled an entire redundant switchroom with “junk”. Junk that got the companies backside out the fire many times.

My wife and I nearly emigrated to Rhodesia, I was at the London embassy when UDI ended and the republic was declared. I was back peddling franticly at that point, I was about to sign on the dotted line.

I’d two offers of jobs, the milk marketing board and electrical supervisor at Wankie coal mines.

Hey Tony Small world isn`t it? It seems that Where ever one goes we meet people from Rhodesia or who have been there. Re saving junk that too has helped me many times here at the company as well. Right now the printing industry here in Mexico is flooded and so we do not get as much work as we used to, and trying to keep older machines running is not an easy task. By the way Life in Rhodesia after UDI was really great - the country prospered, then went down after 1980 and look at it now, a crying shame. Any way hopefully today I will have some progress re the rectifier and I think I will have to get some other coils rewound, they are drawing more current than they used to. Thanks again and have a great rest of the week. Ed
 

EdCampbell

Member
Location
Mexico City
Occupation
Maintenance Technician
150722-2112 EDT

EdCampbell:

See https://reinventingscience.wordpress.com/tag/selenium-rectifier/ . Current rating about 50 mA/sq-cm, or 50 * (1.5 * 2.54) * (1.5 * 2.54) = 50 * 14.5 = 725 mA for your 1.5" square plate.

If you build your own bridge rectifier you might consider the 1N5059 series of avalanche diodes. The 1N5060 is rated 200 V PIV. No heat sink required other than soldering to PC board. Or mount to terminal blocks, more heat sinking than PC board.

See http://www.vishay.com/docs/86000/1n5059.pdf . This diode was originally created by GE.

.
Thank you Mr. Gar, I will check that out and I will see if I have anything similar amongst my junk. I tend to collect old electronic equipment for spares. Has saved me lots of money and time. If not I will have to go to the local Electronic shop. Ed
 
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