Siemens B30C600 selenium bridge rectifier - diyAudio
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Old 26th March 2013, 03:23 AM   #1
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Default Siemens B30C600 selenium bridge rectifier

I've attached the Vf vs If curve as measured from a working part off a Fisher 500C for the benefit of those interested in replacing the original with a silicon diode.

To the mods, if this is not the right place please move it to the appropriate location. I reckon it should be in the tubes area since no modern design incorporates selenium rectifiers
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File Type: gif Siemens_B30C600_characteristic_curve.GIF (21.1 KB, 203 views)
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Old 26th March 2013, 11:49 AM   #2
DF96 is offline DF96  England
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The peculiar axes (bilinear current, and opposite way round to the normal convention) hide the fact that this appears to be not much different from a pair of silicon diodes in series.

Useful data, though.
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Old 26th March 2013, 01:14 PM   #3
GoatGuy is offline GoatGuy  United States
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Actually I just tickled the X and Y values out of the graph to figure slope & intercept. (and therefore, forward cutoff voltage and equivalent series resistor value). Magic of EXCEL, and taking the two visually different segments

Vf = 0.51, Req = 7.3 ohm ... and then the second part in parallel:
Vf = 1.14, Req = 9.3 ohm ... in parallel with the first one.

HOWEVER, that being said ... there are a couple oddities in play: one is the forward voltage of 2.5 ... has a current-flow of 0.42 amps. My recollection of selenium-stack rectifiers was that each section (plate) is only good for like 20 volts reverse or something like that. Since they're technically a kind of Schottky, forward voltage drop can be low. How many plates though does this unit have?

As I found, there really isn't an exact silicon replacement. Pretty close is a standard silicon rectifier in series with a 7 ohm resistor, and from the diode-resistor point, another silicon rectifier with a 9 ohm resistor "across" the first resistor. Simple, and will have similar I:V characteristics. Just a bit higher shift in the forward conduction voltage, is all.

GoatGuy

[I researched CREE high-voltage Schottky SiC rectifiers... but they have a 1.5V drop or higher. Not much of a Schottky! And the silicon high-PIV diodes/rectifiers also seem to have the higher 1.4-1.8V forward voltage drop ... i guess 'cuz they put two lower-voltage rectifiers in series... (? anyone know ?) ... and there are no high-voltage germanium parts, and low-volt-drop conventional Schottky's also have depressingly low reverse breakdown voltage. So... I think the 'just use silicon' answer remains the best]

Last edited by GoatGuy; 26th March 2013 at 01:19 PM. Reason: Wanted to include information about alternatives
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Old 26th March 2013, 10:31 PM   #4
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Hitachi-nut: Selenium rectifiers deteriorate with age;
your curves bend in the "wrong" direction, and there is that "knee" in the middle - both indicating your specimen is no longer in its original condition;
these flat Siemens had spring loaded plates or pills inside, and if they became loose over time, it may look like yours ...
max voltage for Se was 18Vrms per plate, so B30C600 had 2 pills per branch, total of 8.
voltage drop for Se was usually 1V at indicated max current (actually lower than Si).
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Old 27th March 2013, 09:20 AM   #5
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from textbook
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Old 27th March 2013, 12:02 PM   #6
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index
http://www.w3hwj.com/index_files/RBSelenium2.pdf
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Old 27th March 2013, 01:42 PM   #7
GoatGuy is offline GoatGuy  United States
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Default Diodes for Selenium

Quote:
Originally Posted by payloadde View Post
from textbook
that's from one OLD textbook! Out of curiosity... I moused over to Fairchild's site, to see what the good ol' 1N4146 forward voltage drop was ... what a well behaved chunk of silicon sand! 0.7V at 5 ma. I think now that the recommendation I made above stands. Either use the small-value resistors in series with the replacement silicon rectifier to simulate a softer switching curve, or if there's sufficient filtering in C(L/R)C stages ... then dispense with it. Having a small value resistor though does substantially damp the peak amperage that will flow, thus much extending the life of the replacement diodes.

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Old 27th March 2013, 09:22 PM   #8
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I deliberately picked one from the time when these Se rectifiers were produced - I think that was the topic.
yes your Si diode is .7v@5mA and 1v@rated max dc current (100,200mA) and that is what my curves show, the vertical axis is standardised to max dcrating =1.
And Si max is rated @175 oC whereas Se max was rated @just 40 oC - hence the large cooling fins - or the flat Siemens which had to be bolted to the chassis when operated any near the rated current
and if we consider, that B30C600 is 30vrms and C600 means cap loaded 600mAdc, we have to take into account that peak current is maybe 10x or more for c-load, we talk of 1n4001 rather than 1n4146 and peak current 10A maybe ... where a 1n4001 has 1,5v forward drop, so ...
anyway, series R helps control inrush current and switching noise which is much higher w/Si than w/Se. Se behaved very soft in that it had no sharp threshold - no need for snubbers.
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Old 27th March 2013, 09:29 PM   #9
GoatGuy is offline GoatGuy  United States
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So... then... do it, it sounds like.

A 1 amp 1N400X (x=1..7) any of which would be OK. The insertion of a 4 ohm progressive V(forward) response resistor (snubber) is also a good measure, and simulates the overall "brand new selenium" rectifier response. Even if the average is 1 amp IČR is only 4 watts. EI on the 1N4001 rectifier runs about 1 watt, which a bit above its max rating, isn't it? Maybe not.

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Old 28th March 2013, 05:37 AM   #10
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OK. I have attached an updated plot, this time with the axis swapped and used a different free CSV to graph program, not M$ Excel. I have also the characteristic curve of one of the bridge legs using my Tek 577. The axes units and scaling are very close making comparison easier.

I forgot to add on the original post that the plot was the average values of the 4 legs, hence the kink on the curve.


Quote:
Originally Posted by DF96 View Post
The peculiar axes (bilinear current, and opposite way round to the normal convention) hide the fact that this appears to be not much different from a pair of silicon diodes in series.

Useful data, though.
Attached Images
File Type: gif Siemens_B30C600_v2.GIF (13.4 KB, 77 views)
File Type: jpg Siemens_B30C600_curve_tracer.JPG (76.8 KB, 75 views)
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