whit3rd wrote:

> Well, the 500V side will average 4 nA or so, so a switchmode solution
> has to have leakage well under that.

Even the primary side capacitor would need to have leakage well under 
that, which makes this entire approach a brain fart in practice. But it 
can have some value as a food for speculation. Certainly doable, this
unit has been working since 1840:

https://en.wikipedia.org/wiki/Oxford_Electric_Bell

> That presumes  you can get by with PWM and the transformation ratio of the
> photonic conversions, but no feedback.

A ball on a thread turns out to be sufficient to get a 2Hz fixed duty 
cycle switched capacitor converter. :-)

> but a lithium cell can give your 2 uA for a decade, and that's how I'd usually go.

If a decade is long enough, then no question about it. But how about a 
century? Betavoltaics?

On a similar note: why there are no small NiFe batteries with catalytic 
hydrogen burners on the market, say 1Ah? They would be eternal, have a 
look at that:

https://www.nickel-iron-battery.com/Edison%20Cell%20Rejuvenation%2085%20yr-old%2013.%20DeMar.pdf

A guy revived a number of 85yo Edison cells and brought them close to 
their peak capacity.

	Best regards, Piotr  	

piglet wrote:

> I think that means you have not seen a wet tantalum? They are hermetic, 
> glass-metal sealed. Plenty to be seen at Mouser and Digikey - admire the 
> prices.

You are perfectly right, I have no experience with them. This one looks 
decent:

https://pl.mouser.com/datasheet/2/427/he3-240943.pdf

But the specification of this kilobuck part says: "Life Test: capacitors 
are capable of withstanding a 2000 h life test at a temperature of +85 
°C at the applicable rated DC working voltage."

Pardon me, how many hours? Three months of uninterrupted operation?
A hamster lives for 2 years despite not being exactly hermetic...

This unreliable electrochemical technology should have long been forgotten.

	Best regards, Piotr

On 08/01/2020 21:45, piglet wrote:
> On 08/01/2020 19:02, Piotr Wyderski wrote:
>> piglet wrote:
>>
>>> I think 500V to 2V at 2uA is a very tough challenge, John Larkin said 
>>> to use a regular inductive converter in burst mode, but I am 
>>> unconvinced.
>>
>> 2uA I_out, I should have added. Nanoamps at the HV side. Indeed, very 
>> though, but there it is. The Oxford bell electromechanical converter 
>> might not turn out to be that silly an idea, methinks.
>>
>>> Wet tantalum used within ratings has no known wearout mechanism but 
>>> the prices will amaze.
>>
>> The price of a service visit can be even more amazing, so sometimes it 
>> pays off overall. But why is there no wearout? A rubber seal is just a 
>> rubber seal, i.e. leaky.
>>
>>      Best regards, Piotr
> 
> I think that means you have not seen a wet tantalum? They are hermetic, 
> glass-metal sealed. Plenty to be seen at Mouser and Digikey - admire the 
> prices.
> 
> piglet
> 

Correction: cheaper ones can be elastomer sealed, the really high spec 
units are hermetic. I don't know the details but there must be tricks to 
keep hot pressurized sulfuric acid inside!

piglet

On 08/01/2020 19:02, Piotr Wyderski wrote:
> piglet wrote:
> 
>> I think 500V to 2V at 2uA is a very tough challenge, John Larkin said 
>> to use a regular inductive converter in burst mode, but I am unconvinced.
> 
> 2uA I_out, I should have added. Nanoamps at the HV side. Indeed, very 
> though, but there it is. The Oxford bell electromechanical converter 
> might not turn out to be that silly an idea, methinks.
> 
>> Wet tantalum used within ratings has no known wearout mechanism but 
>> the prices will amaze.
> 
> The price of a service visit can be even more amazing, so sometimes it 
> pays off overall. But why is there no wearout? A rubber seal is just a 
> rubber seal, i.e. leaky.
> 
>      Best regards, Piotr

I think that means you have not seen a wet tantalum? They are hermetic, 
glass-metal sealed. Plenty to be seen at Mouser and Digikey - admire the 
prices.

piglet

On Tuesday, January 7, 2020 at 2:12:51 PM UTC-8, Piotr Wyderski wrote:

> > The advantage is at low power. I built a 6 stage capacitive divider 48V 
> > to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp inductor 
> > based buck converters do not appear to be easy.
> 
> If I wanted 500V->2V step-down at 2uA and reasonable efficiency (say, 
> 50+%), how would you approach that requirements? The Oxford bell? :-)

Well, the 500V side will average 4 nA or so, so a switchmode solution
has to have leakage well under that.   Maybe you want an acoustic delay line,
triggering (and excited by) a UV flash tube, feeding a long-delay phosphor
and snazzy photocells.   The phosphor is your filter, the UV tube can
be made self-starting with small amounts of radiioactives, and the
acoustic delay will look like a slinky.   To quench the arc,  though, you might
want to have some more recognizable electronic components clustered around
the slinky coupling transformer.

That presumes  you can get by with PWM and the transformation ratio of the
photonic conversions, but no feedback.   Its tricky to get feedback when
the permissible leakages are down under the level of mass-production testing.

Perhaps an electroluminescent panel and silicon cell is a more sane alternative, 
but a lithium cell can give your 2 uA for a decade, and that's how I'd usually go.

piglet wrote:

> I think 500V to 2V at 2uA is a very tough challenge, John Larkin said to 
> use a regular inductive converter in burst mode, but I am unconvinced.

2uA I_out, I should have added. Nanoamps at the HV side. Indeed, very 
though, but there it is. The Oxford bell electromechanical converter 
might not turn out to be that silly an idea, methinks.

> Wet tantalum used 
> within ratings has no known wearout mechanism but the prices will amaze.

The price of a service visit can be even more amazing, so sometimes it 
pays off overall. But why is there no wearout? A rubber seal is just a 
rubber seal, i.e. leaky.

	Best regards, Piotr

On 08/01/2020 09:12, piglet wrote:
> On 07/01/2020 22:12, Piotr Wyderski wrote:
>> Piglet wro
>>
>>> The advantage is at low power. I built a 6 stage capacitive divider 
>>> 48V to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp 
>>> inductor based buck converters do not appear to be easy.
>>
>> If I wanted 500V->2V step-down at 2uA and reasonable efficiency (say, 
>> 50+%), how would you approach that requirements? The Oxford bell? :-)
>>
>> I am thinking about a ~5uW supercap replacement for backup purposes,
>> which can't dry out -- a 10uF polypropylene cap at 1kV is equivalent 
>> to 10F@1V in 1/2*C*V^2 terms. According to the specs, supercaps are 
>> expected to last some mediocre thousands of hours, e.g. 4kHr is just 
>> 166 days at the max ratings.
>>
>> Why there are no glass-embedded supercaps, or 'lytics in general, 
>> looking like vacuum tubes? What did they use in Voyager?
>>
>>      Best regards, Piotr
> 
> I think 500V to 2V at 2uA is a very tough challenge, John Larkin said to 
> use a regular inductive converter in burst mode, but I am unconvinced.
> 
> Voyager used off-the-shelf capacitors e.g. ceramic, mica, film-foil at 
> smaller values and wet tantalum at higher values. Wet tantalum used 
> within ratings has no known wearout mechanism but the prices will amaze.
> 
> piglet
> 
> 

By "off-the-shelf" I did not mean commercial grade. Clearly 
aerospace/military spec parts were subject to extra screening and 
qualification processes. Voyager used capacitors of similar technology 
that we can still access.

piglet

On 08/01/2020 05:54, George Herold wrote:
> On Tuesday, December 31, 2019 at 5:32:59 AM UTC-5, piglet wrote:
>> On 30/12/2019 16:52, Klaus Kragelund wrote:
>>> AFAIR the step down cap supplies is not that bad
>>>
>>> 7 stages or more sounds like a nightmare, but since individual voltage is low, the process can be low voltage and thus cheap
>>>
>>> That said, I am yet to see one that can compete with inductor step down
>>>
>>> Cheers
>>>
>>> Klaus
>>>
>>
>> The advantage is at low power. I built a 6 stage capacitive divider 48V
>> to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp inductor
>> based buck converters do not appear to be easy.
>>
>> piglet
> 
> Huh? If it's not to late to ask, (being next year and all*)
> What was the 48 V 10 uA source?
> George H.
> 
> 
> *Happy New Year :^)
> 

Happy New Year George.

Power source was plain old telephone system, in the on-hook idle state 
telcos had limits on loop current that could be drawn in some cases 50 
or 100uA and multiple units of my item could have been present hence the 
low allowance.

piglet

On 07/01/2020 22:12, Piotr Wyderski wrote:
> Piglet wro
> 
>> The advantage is at low power. I built a 6 stage capacitive divider 
>> 48V to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp 
>> inductor based buck converters do not appear to be easy.
> 
> If I wanted 500V->2V step-down at 2uA and reasonable efficiency (say, 
> 50+%), how would you approach that requirements? The Oxford bell? :-)
> 
> I am thinking about a ~5uW supercap replacement for backup purposes,
> which can't dry out -- a 10uF polypropylene cap at 1kV is equivalent to 
> 10F@1V in 1/2*C*V^2 terms. According to the specs, supercaps are 
> expected to last some mediocre thousands of hours, e.g. 4kHr is just 166 
> days at the max ratings.
> 
> Why there are no glass-embedded supercaps, or 'lytics in general, 
> looking like vacuum tubes? What did they use in Voyager?
> 
>      Best regards, Piotr

I think 500V to 2V at 2uA is a very tough challenge, John Larkin said to 
use a regular inductive converter in burst mode, but I am unconvinced.

Voyager used off-the-shelf capacitors e.g. ceramic, mica, film-foil at 
smaller values and wet tantalum at higher values. Wet tantalum used 
within ratings has no known wearout mechanism but the prices will amaze.

piglet

On Tuesday, December 31, 2019 at 5:32:59 AM UTC-5, piglet wrote:
> On 30/12/2019 16:52, Klaus Kragelund wrote:
> > AFAIR the step down cap supplies is not that bad
> >
> > 7 stages or more sounds like a nightmare, but since individual voltage is low, the process can be low voltage and thus cheap
> >
> > That said, I am yet to see one that can compete with inductor step down
> >
> > Cheers
> >
> > Klaus
> >
> 
> The advantage is at low power. I built a 6 stage capacitive divider 48V 
> to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp inductor 
> based buck converters do not appear to be easy.
> 
> piglet

Huh? If it's not to late to ask, (being next year and all*)
What was the 48 V 10 uA source? 
George H.  


*Happy New Year :^)