Solar Charging Night Light not working

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Hi all,

I am trying to implement a very simple solar charged night garden light.
Schematics is here: https://www.jameco.com/Jameco/workshop/JamecoFavorites/solarled.html
Basically a solar panel charges a battery. When the solar panel output is low (at night), a joule thief circuit lights a led.

The joule thief part works just fine, the problem is that the dark detector (2n3906 + 4.7K resistor) never triggers the joule thief and I cannot understand why.

Here are the pictures of the breadboard:
https://ibb.co/khNBjft
https://ibb.co/SKsSMxJ

If I bypass the dark detector connecting the positive wire from the battery to the center of the transformer (moving the yellow wire from row 16 to raw 14) the led lights up.  

Thanks a lot for your time.

Re: Solar Charging Night Light not working
On 26/05/2020 4:50 am, Alberto wrote:
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It would seem to me that the 5K resistor is not going low enough when  
the solar panel is covered. Try covering or disconnecting the panel and  
putting the 5k resistor to battery neg ( the end that was connected to  
the diode). That should enrgise the led, if not test the transistor.

Re: Solar Charging Night Light not working
Hi, thanks for your reply.
I tried without the panel connected and covering it with black tape, nothing happened.  
I did not try connecting the 5k resistor to the battery negative as I cannot do it now, but I will give it a try in the next week and I will update you.

Thank you very much!

Re: Solar Charging Night Light not working
On Tue, 26 May 2020 00:56:56 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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When you say the blocking oscillator works are you saying the light
works as long as the battery is charged, and the cell has full
sunlight on it?  So the light stays on all the time and doesn't turn
off when there is light on the cell?

It would be better to think of it as a light detector that stops the
oscillator while the cell has light on it.

(the "famous" joule thief, is ancient technology from the days of
vacuum toobes)
https://en.wikipedia.org/wiki/Blocking_oscillator

Re: Solar Charging Night Light not working
On Tuesday, May 26, 2020 at 2:36:40 PM UTC+2, default wrote:
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Hi!

When I say "The joule thief part works just fine" I mean that, with a charg
ed 1.2 AA battery, and bypassing the light detector, a 5mm blue led lights  
up very bright. So, the oscillator works, otherwise the led would not switc
h on at all.
"Bypassing the light detector" means that I connect the battery positive to
 the center of the transformer directly, without going through the first tr
ansistor so that the transformer is always powered by the battery as far as
 it is charged. This works with or without the solar panel, with or without
 light on it.

I am interested in making the light detector work, to switch on the light o
nly when meaningful and to maintain the battery charged.

Eventually, I would also try to replace the battery with a capacitor but I  
am not 100% sure this is a good idea. And I would like to know the frequenc
y of oscillation, I don't know if there is a practical way to calculate it,
 I do not an oscilloscope.  

Thanks link too!


Re: Solar Charging Night Light not working
On Tue, 26 May 2020 07:28:37 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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OK now I think I get it.  

It appears as if the solar panel is part of the bias circuit for the
PNP transistor.

Solar panels normally supply power when the sun shines, but when the
sun is absent they turn into resistors and allow power to flow
backwards.  Which biases the PNP transistor "on" allowing power to go
to the oscillator circuit etc..  The light presumably turns ON and all
is happy with the world....

got it?

If you were to use a panel that doesn't "leak" or has a built-in diode
to prevent reverse flow, that circuit would not work.

So what are you using for a solar cell?

I'm assuming you are using the specified panel and your battery is two
cells just like the schematic shows, the 1N914 diode has the right
polarity, etc..  Right?

Try connecting a 5-10K resistor between the base of the PNP to ground,
that should get it conducting and turn the light on, and that will
provide a clue to why it isn't working.  (solar cell dark during the
experiment)  It must have a resistor to protect the base from drawing
too much current and killing the PNP transistor.  

The idea is to provide a leakage path that may be lacking in your
solar cell.

Re: Solar Charging Night Light not working
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Switching the main current to the Joule Theif is probably the wrong
approach, switch the current to the base instead, that is only switch
the current that flows through the transformer branch that goes to the
base. this is a much smaller current, and so it takes less energy to
run the switch. (you can use a smaller base current to the switch)

A second problem is that the joule thief may not start automatically
when power is gradually applied.  Some sort of positive feedback to  
ensure that the power snaps on should help there.

--  
  Jasen.

Re: Solar Charging Night Light not working
On Thu, 28 May 2020 10:13:52 -0000 (UTC), Jasen Betts

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How do you plan to switch only the base of the oscillator transistor?

https://www.jameco.com/Jameco/workshop/JamecoFavorites/solarled.html

Re: Solar Charging Night Light not working
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the transformer has two windings, connect the other one to the supply.



--  
  Jasen.

Re: Solar Charging Night Light not working
On Thu, 28 May 2020 19:29:11 -0000 (UTC), Jasen Betts

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The windiings have the turn on  bias a well as the inductive feedback
and turn-off riding on them.  The center-tap is integral to the
operation..

There should be a way to do it: pass the AC feedback while isolating
the DC bias, but it is a little more complicated than separating the
center tap and it would take a few more components.

Re: Solar Charging Night Light not working
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it's just a node.

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current into the base is close enough to monodirectional that it
doesn't matter.

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a capacitor across the added transistor could maybe help with charge
scavenging a little but that 1K resistor is going to slow that down
anyway.

--  
  Jasen.

Re: Solar Charging Night Light not working
On Fri, 29 May 2020 06:02:32 -0000 (UTC), Jasen Betts

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So you have... nothing.  Post a schematic.

Re: Solar Charging Night Light not working
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No, asshole, I have built it and it works. I am not wasting any
further time responding to your clueless taunts with useful
information.


--  
  Jasen.

Re: Solar Charging Night Light not working
On Sat, 30 May 2020 05:32:30 -0000 (UTC), Jasen Betts

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ROFLMAO

sure you built it  

Re: Solar Charging Night Light not working
On 30/05/2020 5:11 pm, default wrote:
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Nice to see you guys getting along :-)

Re: Solar Charging Night Light not working
Oh guys, come on.
Unfortunately I still cannot try your suggestions as I am not at home, but please, let's try to be pragmatic.
If any of you have ideas, schematics or whatever, post it. I have limited components at home and some are just scavengered but I would give a try to any good idea that would allow me to keep 4 bright led on all night long.

BTW, is replacing the battery with a capacitor an idea worth trying/meaningful?

Thank you all

Re: Solar Charging Night Light not working
On Sat, 30 May 2020 03:53:45 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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That would depend on how many hours of light you expect to get out of
one charge.  Some guy had posted a series of fountain lights he was
running from a cap.  Farad size caps aren't cheap as a rule.

I think Jasen has the glimmering of an idea, bias the oscillator
itself to stop during daylight rather than have the voltage drop of
the PNP transistor, to contend with when it's on.  I suspect it may be
trickier than he suggests though.  The circuit works because when the
oscillator transistor switches off abruptly, it causes a high voltage
spike in the inductor.  Diddling the bias may have other consequences
in addition to shutting it down during daylight.  But, I have my own
projects to play with.

BTW there are Chinese IC's that do exactly what you want, using a
single inductor.  see:  https://tinyurl.com/yag3y9g9

The YX8182 IC does the same thing without an inductor.

I built several circuits of that type to illuminate a buoy, so I could
kayak before the sun came up.  A flashing light attracts attention
faster and uses less power.

Re: Solar Charging Night Light not working
On Saturday, May 30, 2020 at 3:48:49 PM UTC+2, default wrote:
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Ok, how would be the schematic?

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Any specific schematic to suggest?

I would like a steady light effect (high frequency on/off is also fine as far as it seems constant at human eye).

Thanks

Re: Solar Charging Night Light not working
On Sat, 30 May 2020 09:12:54 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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When it come to the Chinee, circuits are given for the chip type in
the datasheet.  (often written in Chinese, but the numbers and symbols
can sometimes be gleaned and the schematic is readable)

BTW I did put together a stack of super-caps in a box to start my
truck.  500 F 2.7v each.  It is currently doing duty as a wifi router
backup battery.

Some months ago one of the surplus outlets had some 50F 2.7 volt
beauties on sale for $0.59 each.  I see them priced at ~$3 each from
US sources and as low as $0.50 each from China.  I got several of the
50 F (~5/8" diameter ~1-1/2" long) and subbed two/series in place of a
battery on my buoy flasher (runs 6 months on 3-AA cells) and in one
day it could slurp up enough energy to run for 4 days.

Re: Solar Charging Night Light not working
On Sat, 30 May 2020 09:12:54 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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How long would a 150 Farad Capacitor light up an LED?
https://tinyurl.com/y6w4k4ka

There is at least one well-thought out answer to the question in the
replies.

Another interesting application for those solar cell to USB charger
modules I see on the web.   https://tinyurl.com/ybwxfxt9

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