On Thursday, 1 December 2016 22:06:10 UTC, John Fields  wrote:
> On Fri, 11 Nov 2016 14:55:30 -0800 (PST), tabbypurr wrote:
> >On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:
> >> On Sun, 30 Oct 2016 11:16:52 -0000 (UTC), Cursitor Doom
> >> <curd@notformail.com> wrote:
> >> >On Sun, 30 Oct 2016 02:41:24 -0500, John Fields wrote:
> >> >
> >> >> Let's say you need a >10 microfarad bipolar cap rated to stand off 10
> >> >> volts, right away, and and all you have in your junk box is a 50
> >> >> microfarad monopolar aluminum electrolytic rated to stand off 50 volts.
> >> >> 
> >> >> If you connect the cap, backwards, to a DC supply and limit the current
> >> >> into the cap to something which won't blow it up, the current into the
> >> >> cap  will eventually fall close to zero as the plates reform.
> >> >
> >> >Late night then, John?
> >
> >> Not at all.
> >> 
> >> If you delve into the literature and take a look at how aluminum
> >> electrolytics work, you'll find that they look like diodes with a huge
> >> junction area when they're reverse biased and, basically, like
> >> resistors when they're forward biased.
> >> 
> >> From my experiments I've found that oxide can be grown on the normally
> >> metallic plate with a thickness which will decrease the capacitance of
> >> the unit, but stand off higher voltages.
> >> 
> >> JF
> >
> >I've not studied the lit on lytics, but I've not encountered one that looks like a resistor.

> What do you think one looks like if you hook it up backwards? 

I did it accidentally years ago. It worked ok. Presumably the circuit limited current, whereupon the cap formed a new oxide layer and stopped leaking.


NT

On Sun, 13 Nov 2016 13:07:00 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>On Fri, 11 Nov 2016 14:55:30 -0800, tabbypurr wrote:
>
>> On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:
>
>>> If you delve into the literature and take a look at how aluminum
>>> electrolytics work, you'll find that they look like diodes with a huge
>>> junction area when they're reverse biased and, basically, like
>>> resistors when they're forward biased.
>
>So not ideally suited for use in the microwave spectrum, then. ;-)

---
Indeed. :)
---

>>> From my experiments I've found that oxide can be grown on the normally
>>> metallic plate with a thickness which will decrease the capacitance of
>>> the unit, but stand off higher voltages.
>
>> I've not studied the lit on lytics, but I've not encountered one that
>> looks like a resistor.
>
>I'm guessing he's referring to the ESR which these caps are known for.

---
I'm not.

If you connect a formed electrolytic capacitor across a DC power
supply, backwards, and limit the current through the capacitor to a
level which won't damage the cap, the current will eventually drop to
the leakage current allowed by the new oxide grown. 

If the process is allowed to continue until there's twice the voltage
across the cap, its capacitance will have been reduced by a factor of
two, and it'll be bipolar.

JF
 

On Fri, 11 Nov 2016 14:55:30 -0800 (PST), tabbypurr@gmail.com wrote:

>On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:
>> On Sun, 30 Oct 2016 11:16:52 -0000 (UTC), Cursitor Doom
>> <curd@notformail.com> wrote:
>> >On Sun, 30 Oct 2016 02:41:24 -0500, John Fields wrote:
>> >
>> >> Let's say you need a >10 microfarad bipolar cap rated to stand off 10
>> >> volts, right away, and and all you have in your junk box is a 50
>> >> microfarad monopolar aluminum electrolytic rated to stand off 50 volts.
>> >> 
>> >> If you connect the cap, backwards, to a DC supply and limit the current
>> >> into the cap to something which won't blow it up, the current into the
>> >> cap  will eventually fall close to zero as the plates reform.
>> >
>> >Late night then, John?
>
>> Not at all.
>> 
>> If you delve into the literature and take a look at how aluminum
>> electrolytics work, you'll find that they look like diodes with a huge
>> junction area when they're reverse biased and, basically, like
>> resistors when they're forward biased.
>> 
>> From my experiments I've found that oxide can be grown on the normally
>> metallic plate with a thickness which will decrease the capacitance of
>> the unit, but stand off higher voltages.
>> 
>> JF
>
>I've not studied the lit on lytics, but I've not encountered one that looks like a resistor.

---
What do you think one looks like if you hook it up backwards? 

JF

On Sunday, 13 November 2016 13:07:35 UTC, Cursitor Doom  wrote:
> On Fri, 11 Nov 2016 14:55:30 -0800, tabbypurr wrote
> > On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:
> 
> >> If you delve into the literature and take a look at how aluminum
> >> electrolytics work, you'll find that they look like diodes with a huge
> >> junction area when they're reverse biased and, basically, like
> >> resistors when they're forward biased.
> 
> So not ideally suited for use in the microwave spectrum, then. ;-)
> 
> >> From my experiments I've found that oxide can be grown on the normally
> >> metallic plate with a thickness which will decrease the capacitance of
> >> the unit, but stand off higher voltages.
> 
> > I've not studied the lit on lytics, but I've not encountered one that
> > looks like a resistor.
> 
> I'm guessing he's referring to the ESR which these caps are known for.

They have ESL too, not just R. More or less all caps do, hence the vee shaped impedance graph.


NT

On Fri, 11 Nov 2016 14:55:30 -0800, tabbypurr wrote:

> On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:

>> If you delve into the literature and take a look at how aluminum
>> electrolytics work, you'll find that they look like diodes with a huge
>> junction area when they're reverse biased and, basically, like
>> resistors when they're forward biased.

So not ideally suited for use in the microwave spectrum, then. ;-)

>> From my experiments I've found that oxide can be grown on the normally
>> metallic plate with a thickness which will decrease the capacitance of
>> the unit, but stand off higher voltages.

> I've not studied the lit on lytics, but I've not encountered one that
> looks like a resistor.

I'm guessing he's referring to the ESR which these caps are known for.

On Friday, 11 November 2016 19:06:35 UTC, John Fields  wrote:
> On Sun, 30 Oct 2016 11:16:52 -0000 (UTC), Cursitor Doom
> <curd@notformail.com> wrote:
> >On Sun, 30 Oct 2016 02:41:24 -0500, John Fields wrote:
> >
> >> Let's say you need a >10 microfarad bipolar cap rated to stand off 10
> >> volts, right away, and and all you have in your junk box is a 50
> >> microfarad monopolar aluminum electrolytic rated to stand off 50 volts.
> >> 
> >> If you connect the cap, backwards, to a DC supply and limit the current
> >> into the cap to something which won't blow it up, the current into the
> >> cap  will eventually fall close to zero as the plates reform.
> >
> >Late night then, John?

> Not at all.
> 
> If you delve into the literature and take a look at how aluminum
> electrolytics work, you'll find that they look like diodes with a huge
> junction area when they're reverse biased and, basically, like
> resistors when they're forward biased.
> 
> From my experiments I've found that oxide can be grown on the normally
> metallic plate with a thickness which will decrease the capacitance of
> the unit, but stand off higher voltages.
> 
> JF

I've not studied the lit on lytics, but I've not encountered one that looks like a resistor.


NT

On Sun, 30 Oct 2016 11:16:52 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>On Sun, 30 Oct 2016 02:41:24 -0500, John Fields wrote:
>
>> Let's say you need a >10 microfarad bipolar cap rated to stand off 10
>> volts, right away, and and all you have in your junk box is a 50
>> microfarad monopolar aluminum electrolytic rated to stand off 50 volts.
>> 
>> If you connect the cap, backwards, to a DC supply and limit the current
>> into the cap to something which won't blow it up, the current into the
>> cap  will eventually fall close to zero as the plates reform.
>
>Late night then, John?

---
Not at all.

If you delve into the literature and take a look at how aluminum
electrolytics work, you'll find that they look like diodes with a huge
junction area when they're reverse biased and, basically, like
resistors when they're forward biased.

From my experiments I've found that oxide can be grown on the normally
metallic plate with a thickness which will decrease the capacitance of
the unit, but stand off higher voltages.

JF

jurb6006@gmail.com wrote:
> Well, I hate to sat this but if you need a bipolar cap in the higher values that is an engineering failure.
>
> But to do it you simply take four of those 50 uF in series in opposite polarity and you get 12.5 uF.
>
> It is rare you would really need a bipolar electrolytic except in like a speaker crossover. Possibly some in instrumentation. However taking them in series like that the ESR adds up. However your idea is not any better.
>
> It is possible that like a 250 volt cap could stand like 5 volts reverse without harm, but that is not good engineering practice. Electrolytics are damn unreliable enough as it is and you are going to do this ? No way. I wouldn't.
   Has nobody suggested the Sprague TE series capacitors?

   They seem to work very well RP at half voltage rating and as bipolars 
at half voltage rating.

   That was about 40 years ago; maybe they still make that series or 
equivalent.

On 30/10/2016 23:56, tabbypurr@gmail.com wrote:
> ... IIRC there's nothing polar about a lytic expect the forming step, so a reverse formed cap should be just as reliable.
>

A polar electrolytic is wound from two differently etched and oxidized 
foils; cathode and anode. A non-polar cap is wound from two identical 
foils, I think two anode foils but could be the other way round.

So a polar cap does have a polarity from birth but can as you say be 
"bent" to some extent.

piglet

On Sun, 30 Oct 2016 15:06:33 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Sunday, October 30, 2016 at 12:41:33 AM UTC-7, John Fields wrote:
>> Let's say you need a >10 microfarad bipolar cap rated to stand off 10
>> volts, right away, and and all you have in your junk box is a 50
>> microfarad monopolar aluminum electrolytic rated to stand off 50
>> volts.
>> 
>> If you connect the cap, backwards, to a DC supply and limit the
>> current ...
>
>Rummage until you find two 50uF caps, connect the (-) terminals
>together and diode-clamp each one.   Now from one (+) terminal
>to the other, is a 25  uF capacitor.   On really big transient
>swings, it's a 50 uF capacitor and the impedance of a forward-biased
>diode (or 50 uF) in series, whichever is less.

Yup. Back-to-back aluminums get complex. I assume a single "bipolar"
aluminum electrolytic cap is similarly complex.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics