Can a small photocell panel be connected to a flashlight type rechargable battery?

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I acquired a dead solar cellphone charger unit. I did minimal testing of
it, and it was totally dead. It has the surface mount components, so I
did not go any further. I salvaged the 2.5" X 4" solar cell panel, and
tossed the rest of it. In a lighted room, (lights turned on) it puts out
just under one volt DC. I imagine it will put out more voltage in
sunlight, but I have not tried it, since we have not seen the sun in
days.

Anyhow, can I connect that panel directly to a common AA rechargable
battery? (or maybe I should charge two batrteries at once, in series)?

If not, is there a simple circuit I can build, or should I just steal a
circuit board from one of them solar yard lights, (which have a much
smaller solar panel).


Re: Can a small photocell panel be connected to a flashlight type rechargable battery?

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Some charge controller chip would be in place.
Do not use AA, use lipos.
What is the short circuit current that panel gives in direct bright sunlight?
And the open voltage?
Your controller needs to be able to handle that.
That also determines if you need a switcher or not
to go the battery voltage level.


Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Thursday, 11 October 2018 06:38:23 UTC+1, snipped-for-privacy@tubes.com  wrote:
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See how much current the panel puts out in bright sun. Also check its voltage unloaded. Then we'll know how runnable this is.


NT

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Thursday, October 11, 2018 at 1:38:23 AM UTC-4, snipped-for-privacy@tubes.com wrote:
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Nope in more sunlight it will put out more current.  The voltage  
is mostly fixed.  You can put panels in series for more voltage.  

George H.  
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
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If it's showing 1 volt "open circuit" in room light, when measured
with a high-impedance voltmeter, then I think it's unlikely to put out
much more voltage under direct sunlight.  More current, yes;  more
voltage, no.
    
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You _can_ connect it directly to one or two batteries in series.

It is unlikely to charge them at all, based on what you've written.

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Ideally, what you would have is a voltage-boost circuit which is
capable of raising the voltage enough to charge the batteries, _and_
to do so in a way which operates the panel at its point of maximum
power delivery.  Professional solar charge-control circuits do this
(although they usually _drop_ a higher panel voltage via a buck
regulator).

You might want to look into the simple "joule thief" circuit.  This is
a simple blocking oscillator voltage booster, which is often used in
small LED flashlights to boost a single AA cell (1.5 volts nominal) to
a high enough voltage to turn on a white LED (roughly 5 volts I
believe).  You might be able to build one which can boost a 1-volt
panel's output up above 1.4 volts (enough to charge a NiCd or NiMH).





Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On 10/11/2018 01:39 PM, Dave Platt wrote:
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You can make a crude maximum power point tracker out of one of those and  
an 8 pin AVR uP. The uP power pin gets hooked up to the boost output and  
its ADC can be used to measure its own supply voltage, which should vary  
with light intensity. The battery can be charged with a PWM output from  
a pin and output current into the charging battery can be sensed  
indirectly via sensing die temperature with the on-chip temperature sensor


Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Thu, 11 Oct 2018 00:32:34 -0500, snipped-for-privacy@tubes.com wrote:

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Most cheap cell phones use 5.0V DC to the charger connector.  My
guess(tm) is that it's either an amorphous silicon or thin film panel
delivering about 6V DC.  Amorphous are nice because they're cheap and
produce usable power in fairly dim lighting, while polycrystalline
cells are more expensive and don't work well in dim lighting.  The
problem with amorphous cells is that the efficiency sucks.  
<https://en.wikipedia.org/wiki/Solar_cell_efficiency
<https://en.wikipedia.org/wiki/Solar_cell_efficiency#/media/File:PVeff (rev180813)a.jpg>
Approximately:
  Amorphous        9%
  Thin film       16%
  Polycrystalline 18%

Lots of guesswork.  Are you sure it's a cell phone charger?  Perhaps
it's solar powered garden light?

Duz the panel look something like this polycrystalline panel?
<https://www.ebay.com/itm/3254-6V-0-6W-Solar-Panel-Poly-Module-DIY-Cell-Charger-For-Light-Battery-Phone/202427427685

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Wrong.  You didn't have enough light to properly determine if the
circuitry was functional.  A minimum light level will be needed before
the electronics will delivery any output. Indoor room testing isn't
bright enough, unless you put the panel under a desk lamp.  Put the
device back together and try again outside in sunlight or with a desk
lamp.

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Well, try it.  You should measure the open circuit voltage and the
short circuit current.  Don't leave the ammeter across the panel for
very long or the panel might overheat.

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I know about NiCd, NiMH, lead acid, LiIon, and other chemistries, but
somehow, I've never seen a "common rechargeable" AA cell.  Is that a
brand name of something?  

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Buy a small 3.6V LiPo cell.  You can buy charge controllers that will
charge it if your solar panel can deliver enough power.  I'm not going
to try and find one until you supply some numbers.



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?

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They don't change colour in response to a load, open-circuit and short
circuit produce almost exactly the same self-heating

--  
  Notsodium is mined on the banks of denial.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Thu, 11 Oct 2018 22:34:37 -0000 (UTC), Jasen Betts

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Change color?  No, I didn't say that.  

I use a short circuit test to check for defective cells in a panel.
Short the panel, full sunlight, and use an IR camera or IR thermometer
to measure the temperature rise of each cell.  A defective cell will
usually be warmer than the other normal cells:
<https://www.novuslight.com/testing-solar-panels-with-thermal-imaging-cameras_N7799.html
<
https://solarprofessional.com/sites/default/files/articles/images/10_NEW_SP7_2_pg24_Mehalic-7.jpg

"Hotspots Detection in Photovoltaic Modules Using Infrared  
Thermography"
<https://www.matec-conferences.org/articles/matecconf/pdf/2016/33/matecconf_icmit2016_10015.pdf
For example, when someone shorts a 300 watt panel, that generated
power has to be dissipated somewhere, which means dissipated in the
solar cells.  With 60 cells, that's 5 watts per cell at the MPP
(maximum power point), which is not a trivial amount.

The instructions for such tests often include some manner of warning
not to leave the panels shorted for too long or they might overheat.
Sometimes, they show a hot cell with an open circuit condition
(usually when the shading protection diode goes open circuit).

The tiny panel the OP is using will probably do nothing dangerous if
the panel is shorted, but I consider it good practice to add the
overheating warning since there's no clear boundary between what size
panel is safe and unsafe to short.  In other words, if he burns his
house down shorting a power source, I would want to at least claim
that I warned him.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
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No, but assuming that conservation of energy is a law of the universe you
implied it.  

A shorted panel produces no power on the terminals. An open circuit panel
receives the same amout of energy from the sun as a shorted one (otherwise
it would change colour), so same temperature.

--  
  Notsodium is mined on the banks of denial.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Friday, October 12, 2018 at 1:31:04 AM UTC-4, Jasen Betts wrote:
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e

Sitting on the side line listening to this the space between what you said  
and what he said became apparent.  You are both right.  You are talking abo
ut the panel and he is talking about individual cells.  Since the panel doe
s not have to be uniform unless it is a single cell, the problem cells can  
be hotter than the fully functioning cells because they are passing the ful
l current when the output is shorted.  Functioning cells are generating ele
ctrical power which leaves the cells so they can be cooler.  So there shoul
d also be a difference in voltage across the cells when some are bad.  The  
bad cells will have a lower voltage (since this is power leaving the cell)  
or even reversed.  

Rick C.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Fri, 12 Oct 2018 05:02:45 -0000 (UTC), Jasen Betts

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Color me confused.

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A polycrystaline solar cell has an internal resistance of about 2 ohms
which is easily measured.  When I short the terminals, the current
produced is dissipated by this internal resistance.  P=I^2*R. However,
with an open circuit, there is no current path through this internal
resistance, therefore no self heating.  Most solar cells and panels
have a Low-E coating on the glass cover designed to reflect IR and
prevent heating of the cells by the sun which reduces the solar cell's
efficiency.


Drivel:  Conservation of energy doesn't work with utility power.  The
more I conserve on my electric power use, the more PG&E charges me for
the power.  See graphs at:
<http://www.learnbydestroying.com/jeffl/crud/PG&E-to-2018-09-19.xls>
Moral:  It doesn't pay to conserve.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Friday, October 12, 2018 at 12:08:10 PM UTC-4, Jeff Liebermann wrote:
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This may be one of your tongue in cheek posts.  

I looked at the data and found a slow rise in cost up to Aug 2016 where there was a rather significant drop from nearly 20 cents per kWHr to about 12 cents per kWHr.  Virtually none of the features in the usage curve show up in the unit cost curve.  

I certainly wouldn't draw the conclusion you did.  

Rick C.  

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Fri, 12 Oct 2018 09:36:11 -0700 (PDT),
snipped-for-privacy@gmail.com wrote:

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Guilty as charged.

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Sorry.  I should have added some annotations to the spreadsheet to
indicate credits, refund, and discounts.  In Aug 2016, I signed up for
the PG&E CARE program, which amazingly declared me to be impoverished
and worthy of being subsidized by a reduction in rate of about
$20/month.
<https://www.pge.com/care/
The large drop in cost in Sept 2018 was due to Santa Cruz joining the
Monterey Community Power Cooperative, which buys bulk power and
resells it to member counties at discounted prices:
<https://www.mbcommunitypower.org
No clue how long that will last.  There was also a "generation credit"
and "conservation incentive credit" which further reduced the monthly
billing.

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I like to draw my conclusions first, and then fabricate the evidence
to prove it.  If I remove that credits, subsidies, programs, politics,
and such from my billing, it would show a fairly constant billing rate
over the 11 year period.  My reduction in electricity usage hasn't
been a straight line decrease (because I'm spending more time at home
these days), but at least up to about 2015, does show that no matter
how much I decrease my usage, the monthly costs are about the same.
Therefore, conservation doesn't pay.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Friday, October 12, 2018 at 1:20:42 PM UTC-4, Jeff Liebermann wrote:
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But, but, but, the graphs *do* show monthly costs varying with the monthly  
usage.  I can see virtually every feature in the usage curve reflected in t
he cost curve.  I'd like to see the correlation coefficient of the two curv
es.  

As you say, you drew a trend line that supports your premise, but did you c
onsider any other lines?  I see a fourth order polynomial produces interest
ing results.  In particular it shows your costs going down the last few yea
rs with no real change in the usage trendline.  Seems to me maintaining the
 status quo in usage gives the best results in costs.  Whatever you did in  
Aug this year gave the absolute best results over the entire graph.  Keep d
oing THAT!  

Rick C.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Friday, October 12, 2018 at 12:08:10 PM UTC-4, Jeff Liebermann wrote:
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u
l
se

Oh yeah, forgot to address this issue.  Your analysis is faulty because it  
doesn't consider all the energy in the cell, only the electrical energy.  
  

In the shorted cell photons create electrical current which is then dissipa
ted in the internal resistance of the cell.  When the cell output is open t
he photons continue to fall on the cell and dislodge electrons, but with no
 place to go those electrons recombine with holes and generate heat directl
y without external current flow.  So the same heat is generated in both cas
es.  

Rick C.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Fri, 12 Oct 2018 09:41:57 -0700 (PDT),
snipped-for-privacy@gmail.com wrote:

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Ok, I'm wrong (again).  The consensus seems to be that the cell
becomes slightly warmer in an open circuit than in short circuit but
with some conditions as to the type of cell and construction:
<https://www.researchgate.net/post/In_which_condition_does_the_maximum_heat_dissipation_in_a_solar_cell_occur_short-circuit_Isc_or_open-circuit_Voc


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
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Same energy in (full sunlight minus that reflected), same electrical  
energy out (nil). Therfore same amount of heating.  With the open circuit  
panel it's conduction through the diode junctions of each cell (hole-electron
recombination at the junction) that produces the same heat energy as the
resistive heating in the shorted panel, If you want to reduce the
self-heating of a panel electrically you connect it to a load (preferably MPPT)

Maybe they do change colour, the hole-electron thing could make
infared light...

Those coatings would also block some visible and near IR light that could
have been used by the solar cells, they would also trap more of the heat
produced by the visible light that isn't converted to electric current
and any heat produced by I^2*R losses.  I can seen them possibly being
useful on thermal solar panels (but ordinary glass is already pretty good at
blocking thermal inrared), but I am not convinced they'd help photoelectric
solar panels.


--  
  Notsodium is mined on the banks of denial.

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Fri, 12 Oct 2018 19:24:30 -0000 (UTC), Jasen Betts

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I was under the impression (apparently false) that a cells internal
resistance was lowest at the MPP and increases on either side, which
reduces the efficiency of the cell at either extreme (open and short
circuit).  Therefore the self heating would be at maximum at the MPP
and less with an open or short circuit.  I guess that's not true,
although right now, I can't see why.

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That would be interesting.  Thermochromic solar panels, where I could
actually see the hot spots and failed cells without having to borrow
an expensive FLIR camera.

IR reflective coatings are getting better.  Here's one that changes
the color of the incoming IR to boost the panels output:
<https://www.fastcompany.com/3049233/this-new-coating-makes-solar-panels-super-powered
<https://www.eurekalert.org/pub_releases/2015-07/uoc--rts072715.php

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About 70% reflectivity at middle and far IR for TiN coatings.  
See Fig 4:
<http://www.learnbydestroying.com/jeffl/crud/Low-E-titanium-nitide-glass.pdf>
You're right about trapping the heat inside, but as the coatings
become better at reflecting far IR, the problem will probably become
insignificant (I hope).  



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
On Friday, October 12, 2018 at 9:26:36 PM UTC-4, Jeff Liebermann wrote:
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t  
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ctron
y MPPT)
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You are thinking of MPPT curve as being controlled by some active circuit.  
 The curve is drawn by varying the load resistance with everything else con
stant.  So in that case the MPP *is* the point of matched impedance.  The a
ctive circuit is needed because the load is the load (usually not resistive
) and the other factors vary.  

Rick C.  

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