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Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
I have this bridge rectifier, and across its + and - terminals, there is this finned um.. thing... placed on the terminals, ive metered it, and it appears to be a diode, question is, what kind?
I think it will be useless as a regular diode, maybe some high wattage old zener? a TVS? judjing by the fins on it, it is probably of decent ratings, and far older then me.
I have no ratings of the bridge (nothing writen on it other then ~ ~ - +)
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Looks like an old metal rectifier to me.
These are essentially a stack of washers and fins, with a bolt through the middle. The washers are the rectifying elements, the semiconductor being either a Copper oxide or Selenium coating, and the fins cool the device.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
I believe bit it is a Thyrite supressor-the old name for a MOV.
They are used to prevent inductive loads from flashing the bridge in the event of a very fast loss of AC at the peak (fuse blows). Certain machines (passenger elevators, cranes) once used selenium rectifiers because surges would heal over and not short out and when they went to semiconductors that issue had to addressed.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Nope It's a selenium rectifier. They were used in place of vacuum diodes in 1950's radios. They have a very low reverse breakdown voltage, typically 1.2volts per "fin". As they age their internal resistance raises, and they become useless after a while. The higher the resistance the hotter it gets, and eventually the selenium will evaporate, and it'll die.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
Selenium rectifiers are very low current, especially this little cute thing ^^ dont expect more than 1 oder 2 amps from it. i once had selenium washers that could be stacked the way you wanted to get the amperage and voltage you needed. each washer was a selenium disc rated 35V 0,2A ^^
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
These are still in use on old rolling stock in the rail industry - where I work we service and repair force commutated 110VDC thyristor panels that use them as suppressors like radiotech mentioned. We've had one or two blow up as well The panels we service are designed to provide a field current of about 10A to an alternator, and the suppressor is about twice the size of the one pictured. No idea what the original rating is though!
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
wierd, this thing is dead, I took a scope shot, and the output is still sinusiodal, same as the input, then I placed a modern diode, and there we go, half wave output.
so yeah, this thing is fried if anything, yet it still displays as a diode on the multimeter (I checked with ohmeter)
in the test ive fed it from a limited AC source, 5VAC at 100mA
oh well, at least ive got a cute little thing to look at now when im bored...
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Strange diode?
The panels we service are designed to provide a field current of about 10A to an alternator, and the suppressor is about twice the size of the one pictured. No idea what the original rating is though!