Kind friends

I have encountered an unanticipated (albeit intriguing) difficulty in the course of attempted characterization of several unmarked rectifier diodes salvaged from working Allegretti units...

Granting appropriate current limiting, I expected {even} non-avalanche Si rectifier diodes to 'survive' reverse breakdown and, indeed, operate much as 'Zeners' over a portion of their curves --- Thus it seems theory and reality are, once again, 'at odds' inasmuch as said diodes are frequently damaged (altered) by maximum reverse currents of as little as 20 uA and, often, instantly destroyed above 200 uA

At this point I am more interested in understanding the described phenomenon than identification of the rectifiers! -- Any insight, thoughts and/or wild guesses will be greatly appreciated!

FWIW - based upon appearance and identity of application - I believe said devices to be CEHCO 301R100
Epr=1kV
If = 300A
Ef @ 10A = 300mV

Very best regards
HP

Specimen of unknown diode

 

Source: http://electronics.stackexchange.com/questions/5670/damage-to-diodes-by-exceeding-vrrm

"When reverse-biased you are essentially damaging the thin junction and it is for this reason that it's not the same as simply forward-biasing the diode. Avalanche and Zener diodes are designed to operate reverse-biased and have differently-formed junctions which are designed to withstand this mode of operation. Zener diodes especially have a much more heavily doped junction than normal diodes."

Source: http://www.highvoltageconnection.com/articles/avalanche-diodes.htm

They are not designed to limit reverse current.

Not really satisfying answers. Didn't find anything about specifically what was done in the design. Maybe thicker P layer or a layer that is designed to distribute the heat/current better, since the edges break down first?

John

 

Source: http://electronics.stackexchange.com/questions/5670/damage-to-diodes-by-exceeding-vrrm

"When reverse-biased you are essentially damaging the thin junction and it is for this reason that it's not the same as simply forward-biasing the diode. Avalanche and Zener diodes are designed to operate reverse-biased and have differently-formed junctions which are designed to withstand this mode of operation. Zener diodes especially have a much more heavily doped junction than normal diodes."

Source: http://www.highvoltageconnection.com/articles/avalanche-diodes.htm

They are not designed to limit reverse current.

Not really satisfying answers. Didn't find anything about specifically what was done in the design. Maybe thicker P layer or a layer that is designed to distribute the heat/current better, since the edges break down first?

John

Thanks for your reply and research on my behalf!
Thus --inasmuch as I am (externally) limiting maximum current to a few uA-- it seems it's a matter of dielectric alteration (e.g. 'puncture', electrostrictive deformation/fracture, etc)... Counterintuitively, the most 'sensitive' devices in this regard appear to be those exhibiting relatively high forward current ratings (>100 Amps) -- Then too it may be a matter of the devices' "packaging" being insulated only to rated Epr - as opposed to actual Ebr - (CIP 1kV and ~1.4kV respectively) -- In any event I'm pleased to learn I'm not 'cursed'

Again, many sincere thanks!

Best regards
HP

 

Suggestions for a 'non-iatrogenic' method of Ebr determination applied to Si rectifier diodes?

HP sry but thread title is lame! I say you must have been newspaper journalist writing captions in past life!
So I'm saying how about _Help with non destructive diode testing_? Cuz if title looks verbose and stuffy ppl will just move on!

Anyhow I say is possible diodes aren't burning out after all? Cuz from what you're saying you're putting test voltage of 1400v through 70M resistor to get upper limit of 20uA. HP you know even slight contamination on insulator surface will leak that much! So I say check it out!

 

Anyhow I say is possible diodes aren't burning out after all? Cuz from what you're saying you're putting test voltage of 1400v through 70M resistor to get upper limit of 20uA. HP you know even slight contamination on insulator surface will leak that much! So I say check it out!

Interesting thought! -- Even the 200uA 'leakage' could, conceivably, owe to superficial 'electrolytic' conduction over the ceramic... As you suggest, I'll 'check it out' then post my findings here!

Sincere thanks!
HP

 

Interesting thought! -- Even the 200uA 'leakage' could, conceivably, owe to superficial 'electrolytic' conduction over the ceramic... As you suggest, I'll 'check it out' then post my findings here!

Sincere thanks!
HP

To test Aleph()'s theory, I would clean the outside of the device with DI water wipes followed by 70% isopropanol wipes.

Then, to remove internal moisture (and minimize conduction of moist salts), dry them in a 225F (ouch, using non-SI units hurts) for 3 hours, let them cool in a desiccator (or sealed mason jar that was also heated in the oven (while opened)). Keeping them in a low humidity environment is key, otherwise moist air will be drawn into the ceramic as the air volume collapses during cooling. Once cool, make your test in reasonable short order.

 

@HP, I'd love to be a "fly on the wall" to hear your "pillow talk" with your significant other.

 

@HP, I'd love to be a "fly on the wall" to hear your "pillow talk" with your significant other.

HP's significant other? Now, there's something to ponder.

 

To test Aleph()'s theory, I would clean the outside of the device with DI water wipes followed by 70% isopropanol wipes.

Then, to remove internal moisture (and minimize conduction of moist salts), dry them in a 225F (ouch, using non-SI units hurts) for 3 hours, let them cool in a desiccator (or sealed mason jar that was also heated in the oven (while opened)). Keeping them in a low humidity environment is key, otherwise moist air will be drawn into the ceramic as the air volume collapses during cooling. Once cool, make your test in reasonable short order.

Inasmuch as the ceramic is sealed (glazed), I had thought to clean the surface with diethyl ether followed by desiccation via anhydrous ethanol? -- Further to the latter, I could place the devices in a VC then pump-down to 5 μmHg (Abs) - though I am dubious of the effects of low ambient pressure on the seals (such as they are)?

@GopherT -- Should any of the above look like my 'riding for a fall' please tell me about it!

Very best regards
HP

 

@HP, I'd love to be a "fly on the wall" to hear your "pillow talk" with your significant other.

That only happens when I forget to cover that spooky old mirror at the foot of my bed

TTFN
HP

 

HP's significant other? Now, there's something to ponder.

What part of confirmed hermit do you find incomprehensible/worthy of contemplation?

TTFN
HP

 

What part of confirmed hermit do you find incomprehensible/worthy of contemplation?

TTFN
HP

Worth pondering what type of Significant Other is possible for Pillow Talk when you have thrown out comments like, "confirmed hermit", high-voltage research, shallow-water recovery of antique vacuum tubes, unwillingness to specify gender and willingness to live in Duluth, MN (and all of the fashion that goes with that location - recently advertised nationally by Duluth Trading Co).

I would think one of those iron rangers with a penchant for ice fishing could meet the bill. Quiet enough to let you feel like you are still a hermit and culturally (genetically?) tuned to not ask about your hobbies. I'm thinking a nice down vest over a flannel shirt. Public displays of affection are usually a single nod (up or down) and a "hey, how ya doing".

My point, it may be possible to feel like a hermit in Northeast MN while still having a significant other.

 

Inasmuch as the ceramic is sealed (glazed), I had thought to clean the surface with diethyl ether followed by desiccation via anhydrous ethanol? -- Further to the latter, I could place the devices in a VC then pump-down to 5 μmHg (Abs) - though I am dubious of the effects of low ambient pressure on the seals (such they are)?

@GopherT -- Should any of the above look like my 'riding for a fall' please tell me about it!

Very best regards
HP

Your assumption of glaze is likely false. Glaze is a secondary treatment to ceramics. Few base ceramics fire to a "full density". Alumina (99%+) is common as an insulator and, depending on the grade used, interconnected porosity is possible and makes drying difficult (vacuum is not enough, some heat is required for complete drying (steady weight) if hoping to get it done in a reasonable time.

On 96% alumina! the silica that is intentionally added become glassy and fills in the gaps to achieve full density. A look with a 5x or more magnifying glass (or microscope) is normally indicative. Look for smooth/glossy/reflective) for this grade of alumina (usually pure white). Matte surface looking like 1000 grit sandpaper with a slight yellow/beige hue is 99% alumina (more porous).

 

Worth pondering what type of Significant Other is possible for Pillow Talk when you have thrown out comments like,

confirmed hermit"

Meaning, among other blessings, that I'm quite content in my domestic solitude liberty!

high-voltage research

shallow-water recovery of antique vacuum tubes

Are you suggesting that I'm 'looking for' a gymnotiform-obsessed Jacques Cousteau?

willingness to live in Duluth, MN

...But it's home!

...and all of the fashion that goes with that location - recently advertised nationally by Duluth Trading Co).

--Emphasis Added--

A bit 'gritty' perhaps, but by way of compensation for -- and highly preferable to -- the "Mr. Roger's Neighborhood" paradigm 'Donny' tried to impose upon our venerable community!

unwillingness to specify gender

At the time of my registration it was a matter of privacy -- now it's a matter of principle (said principles being 'need to know', relevancy, etc...) -- As a practical matter, my gender is hardly a secret!

I would think one of those iron rangers with a penchant for ice fishing could meet the bill.

Are we talking a 'significant other' or a soporific?

My point, it may be possible to feel like a hermit in Northeast MN while still having a significant other

Be that as it may I prefer the 'direct route' to wit eschewel of a 'significant other' and all the encumbrance attendant thereto!

Best regards
HP

 

Your assumption of glaze is likely false.

On 96% alumina! the silica that is intentionally added become glassy and fills in the gaps to achieve full density. A look with a 5x or more magnifying glass (or microscope) is normally indicative. Look for smooth/glossy/reflective) for this grade of alumina (usually pure white)

Indeed - the surface (at least) affects a glass-like appearance (as viewed both by the 'naked eye' and via a 15X compound loupe) albeit of a 'lilac-esk' hue (please see the image attached to post #1) -- Should I find that I indeed have a 'sacrificial lamb' (a.k.a. 'dud') I plan to investigate the ceramic's alleged homogeneity

Many thanks for your informed response!
HP

 

Indeed - the surface (at least) affects a glass-like appearance (as viewed both by the 'naked eye' and via a 15X compound loupe) albeit of a 'lilac-esk' hue (please see the image attached to post #1) -- Should I find that I indeed have a 'sacrificial lamb' (a.k.a. 'dud') I plan to investigate the ceramic's alleged homogeneity

Many thanks for your informed response!
HP

Seems like 96% alumina. The purple is likely the remnants of an organic "penetrant dye". Used to check for cracks/defects. On high high volume parts, it is done on a statistical basis - parts of yester-year (and some high voltage modern parts) see 100% testing. A dark line indicates a crack and an uneven haze shows incomplete firing.

 

As the electrons are swept across the broken down junction by 1400 V they can pick up enough energy to damage the lattice since the junction was not designed to operate that way (and, in all likelihood, it's ability to behave well under those conditions was sacrificed in order to get better performance under the conditions that it WAS designed to operate under. I would not be surprised that the sacrifices made to achieve the tradeoff are more severe for diodes that are designed to carry higher and higher forward currents.

 

That only happens when I forget to cover that spooky old mirror at the foot of my bed

HP admit it! You'd be lonely without your ghosts!

 

Not related but since it was HP's thread I could not help it

@HP, I'd love to be a "fly on the wall" to hear your "pillow talk" with your significant other.

Took the words right out of my mouth.

 

Seems like 96% alumina. The purple is likely the remnants of an organic "penetrant dye". Used to check for cracks/defects. On high high volume parts, it is done on a statistical basis - parts of yester-year (and some high voltage modern parts) see 100% testing. A dark line indicates a crack and an uneven haze shows incomplete firing.

Based upon it's 'glassy' appearance - I take it that said dye is applied prior to (final) firing?

Best regards
HP