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'[EE] Long-term reliability of cds photo-resistive '
2007\03\31@180345 by Peter Todd

picon face
I have a few projects that I'm using cds-type photocell resistors in
them. Specifically they are all digikey #PDV-P9001-ND in a simple
voltage divider circuit. I'm running them to spec, 1ma max-current etc.
They've all gotta last at least 10 years. My definition of failure would
be their specs drifting by more than about 30% In the applications they
are at worst completely uncovered and *may* be subject to UV light, but
would generally be used in a standard office environment.

I mentioned this to someone who said that photocells are unreliable and
won't last more than a year or two. He said they all fail due to light
exposure within a few years.

Seems pretty dubious to me, photocells are used in streetlamps after
all, and the datasheets don't mention anything worrying, but... What do
you guys think?

--
http://www.petertodd.ca

2007\03\31@182635 by Jinx

face picon face
> I mentioned this to someone who said that photocells are unreliable
> and won't last more than a year or two. He said they all fail due to
> light exposure within a few years

Sound pretty pessimistic. If you're really worried about UV then just
about any plastic will block it. Cut up a sunglass lens, everyone's got
a busted pair of sunnies in the drawer



'[EE] Long-term reliability of cds photo-resistive '
2007\04\02@025126 by Peter Todd
picon face
On Sun, Apr 01, 2007 at 10:26:20AM +1200, Jinx wrote:
> > I mentioned this to someone who said that photocells are unreliable
> > and won't last more than a year or two. He said they all fail due to
> > light exposure within a few years
>
> Sound pretty pessimistic. If you're really worried about UV then just
> about any plastic will block it. Cut up a sunglass lens, everyone's got
> a busted pair of sunnies in the drawer

Thanks, that's good to hear. As for the guy I heard it from... Well,
suffice to say I've had my suspicions that he can't stand being anything
but the smartest guy in the room, even when the subject is electrial
engineering and he's a Java programmer... But, wanted to see what you
lot thought first.

--
http://www.petertodd.ca

2007\04\02@052832 by Jinx

face picon face

> Thanks, that's good to hear

Hey, don't mistake me for an expert !! ;-)

"8 Year Standard Warranty"

http://www.imexcom.com/p2-electrical-photo.html

Silicon vs CdS

http://www.precisionmulticontrols.com/PDFdownload/Sulfidevssilicon.pdf

http://www.selcoproducts.com/CFM/photocell_toc.cfm

www.selcoproducts.com/CFM/photocells/photocell_PDF/Selco_PhotoCells_C
onstruct.pdf

OPERATING LIFE

Figure 13 illustrates the change in illuminated resistance (at
10 lux) of CdS cells with operating time, showing slightly
increasing curves. If used within the maximum ratings specified
in this catalog, the CdS cell recovers from this time change and
maintains stable values for quite a long period. Exceeding the
maximum ratings can cause deterioration or damage. If this is
kept in mind, the life of CdS cells can be expected to be quite
long

www.selcoproducts.com/CFM/photocells/photocell_PDF/Selco_PhotoCells_p
recautions.pdf

Use at high temperature and humidity shortens the cell life and
should be avoided

Avoid usage that exposes the CdS cell to strong ultraviolet light

2007\04\02@071330 by Gerhard Fiedler

picon face
Jinx wrote:

>> Thanks, that's good to hear
>
> Hey, don't mistake me for an expert !! ;-)
>
> "8 Year Standard Warranty"

Peter,

Possibly helpful could be a response from the manufacturer of your cell.

Gerhard

2007\04\02@130234 by M. Adam Davis

face picon face
Silicon type photocells (tiny little solar cells, essentially) have
some of the same problems that power solar cells have - degraded
output current over time.

CDS (Cadmium Sulfide) should be much more stable over long periods of time.

As far as longevity, consult your manufacturer - some cheap ones last
forever, some expensive ones dies quickly, and vice-versa.  Horses for
courses...

-Adam

On 3/31/07, Peter Todd <spam_OUTpeteTakeThisOuTspampetertodd.ca> wrote:
{Quote hidden}

> -

2007\04\02@141935 by Dwayne Reid

flavicon
face
At 04:03 PM 3/31/2007, Peter Todd wrote:
>I have a few projects that I'm using cds-type photocell resistors in
>them. Specifically they are all digikey #PDV-P9001-ND
>
>I mentioned this to someone who said that photocells are unreliable and
>won't last more than a year or two. He said they all fail due to light
>exposure within a few years.

He may in fact be thinking of early failure in street-lamp usage.

Early street-lamp photo-cell units were notorious for failing after
only a few years.  My limited experience with these failures is that
the failures were caused by excessive power dissipation within the
photo-cell while driving the relay coil in low to moderate light
levels.  Seemed to be much more of a problem in northern areas
because of the slow change from bright to dim and vice-versa.

As far as I know, those problems don't exist on modern street-lamp
photo-cell controllers.

I do think that you may be running your photo-cells a little hot if
you are operating them at their maximum rated current.  Depends upon
the voltage across the cell.

Hope that helps!

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam@spam@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2007\04\02@143644 by David VanHorn

picon face
>
> Early street-lamp photo-cell units were notorious for failing after
> only a few years.  My limited experience with these failures is that
> the failures were caused by excessive power dissipation within the
> photo-cell while driving the relay coil in low to moderate light
> levels.  Seemed to be much more of a problem in northern areas
> because of the slow change from bright to dim and vice-versa.


I took one apart, and was rather surprised to see about a 1" diameter CDS
cell, and a relay, in series.
No electronics at all.. I was wondering about dissipation, but I assumed
they had such things under control.

It certainly couldn't get any simpler :)

2007\04\10@091506 by Alan B. Pearce

face picon face
>> > I mentioned this to someone who said that photocells are unreliable
>> > and won't last more than a year or two. He said they all fail due to
>> > light exposure within a few years
>>
>> Sound pretty pessimistic. If you're really worried about UV then just
>> about any plastic will block it. Cut up a sunglass lens, everyone's got
>> a busted pair of sunnies in the drawer
>
>Thanks, that's good to hear. As for the guy I heard it from... Well,
>suffice to say I've had my suspicions that he can't stand being anything
>but the smartest guy in the room, even when the subject is electrial
>engineering and he's a Java programmer... But, wanted to see what you
>lot thought first.

Cds cells used to be used in camera light meters. They suffered form 2
problems -

1. they have a long time constant going from bright to dark, to get the last
bit of sensitivity out of them at the dark end required a quite respectable
time out of bright light (several tens of seconds typically).

2. they suffered from failure to reach a high enough resistance at the dark
end after a time. This was a specific failure mode for some, and the only
solution was to replace the cell. The reason for failure was not known by us
(my father used to repair cameras) but could have been some form of
contamination during manufacture, or just plain bad manufacturing process. I
just remember my father did replace a fair number of them over time. More
recently photodiodes have proven more popular due to better linearity with
light levels, smaller devices for fitting into ever more cramped camera
bodies and better overall sensitivity.

I don't know that there is any inherent failure mode in them, but from
experience as given in point 2, there may be some form of chemical migration
or similar problem if exposed to high enough light levels.

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