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Using Arduino => General Electronics => Topic started by: falexandru on May 24, 2018, 07:23 am

Title: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 07:23 am
I  want to charge one 3.7 LiIon 18650 battery using a photovoltaic panel.

The panel is rated 6V.

The project has two stages:
a) to charge the battery - no matter how
b) to charge in sunlight and light one white LED during dark time

For the a) I think a  0,5W 4,7V DO35 Zener Diode coupled directly to the panel may suffice.

For the b) stage I need an automatic charger/commuter

+++

For the b) stage I found only a couple of schematics on internet - 2, attached.

Both are stated to work on 2V panel - which I cant understand, because I could not find a 2V panel, but only 1V, 6V and above). I know I will not get 6V but only 3-4 V under regular daylight and using not-oriented panel, but still a 2V looks excessively pessimistic.

Question is: although these 2 circuits are  stated to work on 2V solar panel  - is it safe for the 3.7 battery to charge from the 6V panel?

Thank you very much for your kind opinion and for any hint to an alternative simpler schematics!

This is education project (kids).

Title: Re: How to modify the voltage of solar charger?
Post by: septillion on May 24, 2018, 11:10 am
Mm, charging LiPo is not simple. At least not to do it reliable and hazard free. What's wrong with using a LiPo charger IC/breakout?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 12:38 pm
This project is education-centered. Kids to learn how it works and to see what they do.

LiPo are more expensive.

I can think to NiMH (2 x 1.5 V) instead - cheap enough.
Title: Re: How to modify the voltage of solar charger?
Post by: septillion on May 24, 2018, 01:56 pm
NiMH is pretty easy to use indeed. Just supply it a voltage with limited current (resistor) and you're done. Can also sustain trickle charging so no need to disconnect etc.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 02:08 pm
Thank you!

NiMH is a kind of old. But well- cheap .

One NiMH is 1.2 V x 2 = 2.4V. Then it can be charged by the circuits I found - is the provided voltage is still 3 V when I connect it to 6 V panel (panel working voltage will be probably around 4V).

If this 2.4 V(in practice I think it will be some 2 V) would b e sufficient to open an white LED, that is to be checked.

+++

I cant figure out: are those circuits regulated (or limited) to 3 V, or their output will increase with the input voltage? Thank you!
Title: Re: How to modify the voltage of solar charger?
Post by: wvmarle on May 24, 2018, 03:18 pm
White LEDs tend to have a forward voltage of about 3V. So you'd better take a set of three NiMH batteries, then you have a voltage of about 4.5V (fully charged) dropping to about 3.6V when nearly empty. That should be good enough, and your solar panel can still charge them.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 05:24 pm
3 x 1.2V = 3.6V (NiMH) - according to the labels of the units I have in hand (perhaps they is another type of 1.5 V, I will have a look  in the store).

In any case, I can connect the 3 units directly to  the panel - no circuit at all. Even the panel will go as high as 6 V (which I doubt), then the NiMH old sheep will be OK (I hope, communication by smoke is another project :-)).
Title: Re: How to modify the voltage of solar charger?
Post by: wvmarle on May 24, 2018, 05:59 pm
Batteries always have a voltage range: when fully charged usually more than the nominal voltage, dropping to below nominal when almost empty.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 07:01 pm
Oh, I get it now.

I measured my 3.7 LiIon units by multimeter and it was 4.2V when fully charged. I did not  know it is normal

 
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 24, 2018, 07:40 pm
Oh, I get it now.

I measured my 3.7 LiIon units by multimeter and it was 4.2V when fully charged. I did not  know it is normal

 
For this batteries you need a voltage regulator with output 4.2V and current limiting resistor approximately 50 ohm.
4.2V is normal.
For 3 batteries 1,2V you can use also above mentioed voltage regulator
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 07:52 pm
My panel is 6 V 3.5 W 384 mA according to its description (mono-crystal).

I wonder whether I can use a simple Zener regulator like the one in the attachment to charge 3x  1.5 V NiMH batteries.

+++

I am a bit concerned about adapting this charger to a wind turbine (Savonius vertical axis). 
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 24, 2018, 08:34 pm
Link to your batteries 1.5V or picture will help.
Zener 5V =ok
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 08:39 pm
The batteries are supermarket (Auchan) NiMH labelled 1.2 V 800 mAh (blister of 4 units - 3USD). There is no picture available. Something similar is:

http://www.shoptimise.fr/p/2742149361285/piles+rechargeables+ni+mh+aa+x4+auchan+x4
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 08:39 pm
http://www.shoptimise.fr/p/2742149361285/piles+rechargeables+ni+mh+aa+x4+auchan+x4 (http://www.shoptimise.fr/p/2742149361285/piles+rechargeables+ni+mh+aa+x4+auchan+x4)

Except these are AA while mine are AAA.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 24, 2018, 08:49 pm
This are 2500mAh batteries with current charging 384 mA it is take to charge them you need about 7 hour, AAA have less capacity so willb faster.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 08:57 pm
Demo only. So I think time is OK. I guess the real current will be around 200 mA and my unit are 3 x 800 mAh = 2400 mAh. Then charging time (real conditions) might be 12 hrs. Assuming fully discharged of course.

If I use a Zener regulator that will take some current as well (maybe 20 mA? - there is a quite fantastic willy-billy method to label the Zeners so I am reluctant to go for a Data Sheet).

I also assume the variable current will destroy the NiMh within some 200 charging cycles (read 200 days) but this is very good for the kids demo project).
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 24, 2018, 09:08 pm
I also assume the variable current will destroy
What you mean.


When batteries are discharged on beginning of charging current will be max 200 mA - that how much can deliver your charger ? - then will drop to 0 mA when batteries voltage reach 5V.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 24, 2018, 09:27 pm
I am talking about voltage depression and smaller "slices" when the panel only partially charges the NiMH battery.

However, at this cost and for demo only, that is not going to be  problem. I assume the units will last for at least for few months.

I am almost decided to go for NiMH instead of LiIon.

It may be a nightmare to find a Zener on line because of labeling, so I will go to "mortar-and-brick" store.

+++

Next step is to see whether my Savonius turbine can go the same way to charge the NiMH. The turbine's output  will be perhaps a 2V average, which means that I have to push up the voltage and then to regulate it via the same Zener regulator.





Title: Re: How to modify the voltage of solar charger?
Post by: wvmarle on May 25, 2018, 04:43 am
Demo only. So I think time is OK. I guess the real current will be around 200 mA and my unit are 3 x 800 mAh = 2400 mAh. Then charging time (real conditions) might be 12 hrs. Assuming fully discharged of course.
that would be if you place your batteries in parallel, but you'll have them in series so total capacity is still 800 mAh and your charging time at 200 mA about 4 hours.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 25, 2018, 05:48 am
Right, my mistake. But is very counter-intuitive, I must admit. I have to find a simple way to explain this (first to myself :-)).

Question is whether units for a total of 4.5 V (or a 3 x1.2V = 3.6 V) can be charged by a panel which is rated 6 V, but can easily drop to 4V when in shadow. Maybe the prototype will show how (and whether) it works.

Title: Re: How to modify the voltage of solar charger?
Post by: wvmarle on May 25, 2018, 06:01 am
The current runs through all batteries. That's why.

PV cells are current sources rather than voltage sources, making that part more complex. I also still don't fully understand how that works.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 25, 2018, 09:14 pm
Today I want to the field and I measured my PV panels. No load, only multi-meter. It is a cheap multi meter (some 4 USD per unit), so I assume not very accurate.

However, I got 7V in half shadow, out of panels rated 6V. So, no voltage drop as a I (wrongly) expected.

For practical purpose - still OK. But why voltage went up?! OK, maybe low internal resistance of my multi meter has something to do with this, but even so - I am taking about 1-3 V above the mark.

I am thinking to make a voltage divider and feed two LEDs out of this voltage, although it seems bizarre and I never came across such a solution for a PV panel.
Title: Re: How to modify the voltage of solar charger?
Post by: 1steve on May 26, 2018, 04:55 am
As someone else said solar cell are current devices. You gave the panel as rated 3.5 watt and .384 max current. (3.5w/.384a=9.1v ) That is going to give you an open voltage (no load) of  9.1 volts in full sunlight. Cheap solar controller short out the solar panel when the voltage get to high. and when voltage drops it unshorts. So there would be a diode,  the cathode connected to the battery, an the other end connect to the panel and something (circuit ) to short it out when voltage is to high. The battery gets all the current, when voltage is not to high. Now here the fun part, when the battery is pulling more than .384 amp (full sunlight) the voltage will drop to or near the battery voltage. The panel will only supply so much current, so the voltage must go down when more current is wanted than the  cell can supply.
I do not think I have done a very good job explaining this but hope it helps.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 06:16 am
Then what is the meaning of "6V" label on the PV panel?
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 26, 2018, 06:37 am
384mA is probably short circuit current, and 6volt open circuit voltage.
At MPP (maximum power point), voltage and current are both less than the above values.
Thus giving a lower power rating than 0.384*6.
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 06:50 am
It is more fun than I expected.

Attempting to get the picture:

a) in full sunlight, no load = maximum current 384mA(label) only if UxI < 3.5W (label), voltage as high as it can go (9, 10 whatever)

b) shadow, no load - the similar to above, except available power decreases as a result of current decreasing

c) sunlight, load = maximum current PV can provide to a specific load, voltage decreases to match the maximum current in these circumstance, but the available power is still 3.5W (this point I cant understand quite well)

d) shadow, load = similar as above, except maximum current decreases as a result of low light

? (+ emoticon scratching head)
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 26, 2018, 07:21 am
Panel open voltage doesn't change much with light intensity (apart from maybe a low light threshold),
but panel current does (so panel is mainly a current source).

Short circuit current (panel@0volt) is not very useful (no power generated).
Open circuit voltage (no current) isn't useful either.
The trick is to find a voltage under load where "voltage times current" (power) is max.
That's about 0.5volt per cell, or about 2/3 of open circuit voltage.
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 07:37 am
Then 6V label refers to 2/3 of the open circuit voltage the cells are aligned to (open circuit voltage is assumed at 9 V then)?

If I use a Zener to pick 5V to charge my 3 x 1.2 V (NiMH, 800 mAh /unit), that is going to be low efficiency method - much lower current available than the 384mA? 

This is a demo project only, thus optimisation is not an objective. But a clear picture of what happens is a must, for me in the first place :-).
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 26, 2018, 08:35 am
Counting the cells (0.5volt each) might give you a better idea about MPP voltage.

You must use a diode to stop current flowing from the batteries back into the solar panel when it's dark.
That could be a schottky (with a ~0.4volt drop).

You can't use voltage regulation (load dump) on the battery side, but you can on the solar panel side.
That could be a "super zener", made with a zener diode and a TO-220 transistor.
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 08:59 am
I found 1N581 Shotky - which looks as a general purpose one - 1A. Looks that it fits my circuit. I never ever used  a Shotky. From the net it looks like it is about mounting it as it is (no resistor, nothing but  "mount and forget").
Title: Re: How to modify the voltage of solar charger?
Post by: wvmarle on May 26, 2018, 09:35 am
By and large Schottky diodes work the same as a normal diode - key differences are switching speed (very fast), forward voltage drop (low) and reverse current leakage (high - for a diode, that is, in the order of µA normally).
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 09:55 am
Then I can mount a Shotky to prevent back-current to the PV panel and a Zener + resistor to regulate voltage to a value more than 4 V (to charge my 3 x 1.2 V NiMH AAA in series), right?
Title: Re: How to modify the voltage of solar charger?
Post by: 1steve on May 26, 2018, 07:22 pm
I have no idea what the 6 volt name means. My best guess is that the panel has enough over head that it will work with a solar controller to deliver 6 volts. I am more familiar with 12 volt panels and I know the no load voltage will be anywhere from 18 to 24 volts. Also the power rating is at the higher voltage. So a 100 watt 12 volt panel will not give 8.33 amps. (100w/12v=8.33a) It will be more likely (100w/18v=5.55a) 5.5amps.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 08:21 pm
I brought the components:

1) 1 N 5822 Shotky diode -  1 pc
2) Z 4 V 3/0.5 W Zener diode  - 1 pc
3) resistor metal oxid 47/1 W 5%- 1 pc
4) resistor 200 Ohm/ 0.25 W - 1 pc
5) white LED 8mm -1 pc
6) Photovoltaic panel (poli-crystal) 1.1W/6V/200mA (note it is a much smaller one than the initial one)- 1 pc
7) 3.5 mm barrel jack - 1 pc
8) 3.5 mm barrel socket - 1 pc
9) black and red 2 wire (the type used for the speakers) - 2 m
10) perfboard  6 mmx4.5 mm - 1 pc
11)1.2 V 800 mAh AAA NiMH batteries - 1 pc
12) the case for the NiMh batteries (3 in series) - 1 pc
13) commuter 2 ways (2 throws?) - 1 pc

+ various PVC stripes, glue and screws, hooks.

Now, first problem to solve is to pick the right Zener out of the pile of diodes I got. I ordered a range of nominal voltages Zeners and  the seller packed all values together (Zeners are some 2 mm length => [emoticon punches to (my) head].

I will post the schematics asap - I am drawing it by hand.





 
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 09:09 pm
and here it is the shematics

Parts as in the previous list:

R1 = 47 Ohm 1 W
R2 = 200 Ohm 0,25 W

C1= 4.7 uF (not sure I really need it, I know it may protect the active components from voltage spikes, but I cant figure out whether spikes have any chances to occur).

This time I am planning to solder components on the perfboard, in a clear design, components at some distance one to another.

I would be extremely happy if somebody more experienced than myself could spend some time to check the circuit. Thank you very very much!

I am going to first breadboard components and once everything is OK, I will proceed to the case and wiring design.

+++

The PV panel I use to prototype is smaller (200 mA) and less efficient (poly-ristal vs. mono-crystal) than the one I posted in the beginning. Reason ist double:
- it is three times cheaper - nice in this risky phase
- if Ok, then I can make more circuits than in the case I used the expensive one - that is good for demo purpose.


(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=259498)

Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 26, 2018, 10:25 pm
Correction: there are 3 pcs NimH units. Sorry!
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 26, 2018, 11:14 pm
Look ok, you don't need C1 for solar panel.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 26, 2018, 11:18 pm
I brought the components:


Now, first problem to solve is to pick the right Zener out of the pile of diodes I got.

 
Just put any diode and measure voltage on it.
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 26, 2018, 11:18 pm
Why R1. A solar panel is a current source (you can short it).

The whole idea of a schottky backflow diode is that you can leave the panel connected to the battery,
so why a SPDT switch.

Why not use a zener on the solar panel side of the schottky diode (post#28),
so the batteries are not drained by the zener leakage when the sun goes down.
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 12:07 am
Thank you guys, for your kind decision to have a look on my circuit!

Why R1. A solar panel is a current source (you can short it).

The whole idea of a schottky backflow diode is that you can leave the panel connected to the battery,
so why a SPDT switch.

Why not use a zener on the solar panel side of the schottky diode (post#28),
so the batteries are not drained by the zener leakage when the sun goes down.
Leo..
R1 is paired with the Zener downhill

Without the switch, the circuit will light the LED during the day as well.  In a later stage of the project, the same battery will be charged by a Savonius wind turbine, so I am planned to replace the switch by an Arduino board to drive the charging.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 12:10 am
You mean to place the D1 after R1?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 12:21 am
And remove the R1?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 12:25 am
To keep it as simple as possible and easy to explain, I rather refrain to use a transistor.
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 27, 2018, 12:27 am
Try to draw this:

Zener (4.7volt) across solar panel.

Schottky diode from solar panel to battery(+).

Switch between battery(+) and LED circuit (R2).
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 09:56 am
Thank you @Wawa! I followed your advise - see following.

-----------------

Here it is the simplified version of the solar charger from (6V;1.1W;200 mA) Photovoltaic panel to 3 series NiMH battaery units (1.2 V; 800 mAh).

The list of components for this simplified version (see picture attached) is the following:

+++++++++++++++++++++
+ Demonstrative solar charger  +
+++++++++++++++++++++

Components's list

1) Shotky diode: 1 N 5822 -  1 pc
2) Zener diode: Z 4 V 3/0.5 W - 1 pc
3) Resistor: 200 Ohm/ 0.25 W - 1 pc
4) LED: white,  8mm -1 pc
5) Photovoltaic panel: poli-crystal 1.1W/6V/200mA - 1 pc
6) Barrel jack:  3.5 mm  - 1 pc
7) Barrel socket: 3.5 mm  - 1 pc
8) Connection wires:  black and red (the type used for the speakers) - 2 m
9) Perfboard:  6 mmx4.5 mm - 1 pc
10) Batteries: 1.2 V, 800 mAh, AAA, NiMH - 3 pcs
11) Case for the 3 units NiMh batteries: 3 in series - 1 pc
12) Switch: 1 pole - 2 throws - 1 pc

+ various PVC stripes, glue and screws, hooks (drawing pending).

+++++
+END +
+++++




(note that PV is a much smaller one than the initial one)

No more R1, no C1
for this simplified version.

Not sure if I correctly followed:  "Schottky diode from solar panel to battery(+)".

(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=259529)
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on May 27, 2018, 12:34 pm
Circuit is ok.

Can, but don't have to disconnect the battery from the solar circuit.
Just switching the LED circuit on/off should be ok.

Zener voltage must be higher than in your previous circuit,
because of the extra ~0.4volt drop in the schottky diode.
I advised a 4.7volt (1watt) zener.
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 01:03 pm
Thank you!

I found a 1,3 W 4.7V  Zener.

Updated list:

+++++++++++++++++++++
+ Demonstrative solar charger  +
+++++++++++++++++++++

Components's list

1) Shotky diode: 1 N 5822 -  1 pc
2) Zener diode: Z 4 V 7/1.3 W - 1 pc
3) Resistor: 200 Ohm/ 0.25 W - 1 pc
4) LED: white,  8mm -1 pc
5) Photovoltaic panel: poli-crystal 1.1W/6V/200mA - 1 pc
6) Barrel jack:  3.5 mm  - 1 pc
7) Barrel socket: 3.5 mm  - 1 pc
8) Connection wires:  black and red (the type used for the speakers) - 2 m
9) Perfboard:  6 mmx4.5 mm - 1 pc
10) Batteries: 1.2 V, 800 mAh, AAA, NiMH - 3 pcs
11) Case for the 3 units NiMh batteries: 3 in series - 1 pc
12) Switch: 1 pole - 2 throws - 1 pc

+ various PVC stripes, glue and screws, hooks (drawing pending).

+++++
+END +
+++++


+++

"To disconnect the LED" - this just didnt cross my mind :-(.

I have to re-design this switching part anyway because I have to add the wind turbine part to the same battery and LED module.
Title: Re: How to modify the voltage of solar charger?
Post by: Doug101 on May 27, 2018, 02:55 pm
Look on Amazon you can purchase a charger controller that does everything you want, much more and has an LCD display fo $15.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 02:59 pm
This is a demo project (education for kids).

But the idea of a display is worth exploring, I will think to this point.

At the beginning I wanted to show the voltage by small voltmeters,
Title: Re: How to modify the voltage of solar charger?
Post by: Doug101 on May 27, 2018, 04:12 pm
This is a demo project (education for kids).

But the idea of a display is worth exploring, I will think to this point.

At the beginning I wanted to show the voltage by small voltmeters,
I'm doing the same.

I originally purchased a volt meter and an amp meter and was going to show how much electricity was being produced.  Only problem is it's only at that moment in time.  What I really need is a recoding/logging volt/amp meter.  Purchased a Mooshimeter.  I would hightly recomnd you buying one.

The solar panel outpucts different voltages and curents depending on the light intensity.  I managed to fry and in cook or melt two batteries.


This silly $15 chage conrtoller has all circuity and meters you need.

https://www.amazon.com/Bokeley-Controller-Battery-Intelligent-Regulator/dp/B073W1LZKL/ref=sr_1_16?ie=UTF8&qid=1527428542&sr=8-16&keywords=charge+controller

Only thing it doesn't do is logging.

Just realize these things are not as efficient as MPPT.

Couple of things to remind student about solar and batteries.
Solar panels are only about 20% efficinet.

Batteries when changed lose 20% of their energy to heat, exotherminc chemial reactiong occuring when charging.  They lose another 20% when discharging due to the exothermic chemical reaction in the battery.  So for every 100 watts stored in a battery, 40% is lost as heat.


Couple of teaching points....   We recive a lot of energy from the sun.  (You can look up the actual number.)  But if you listen to some environmentalists they say if only we captned all of the suns enegy we would have enough electrity to supply the world with power.  Yes that's true, but then we would be living in the dark, and have no plant life or food as all of the suns energy is being convered to electricty.


With all of the solar and wind electricity generating facilities the US, Germany and Great Brittian has up and running they burned more coal/fossil fuels last year.  Why?  Each country had a period where there were clouds and no wind.  Germany shuttered their nuclear power plants so the only way they could provide electricty was by burning coal/fossil fuels. 

Solar is a stop gap until Next Gen Nuclear.  ITER, NIF, Paul Allen and Bill Gates are all working on Next Gen Nuclear.  It's green, renewable, environementlay friendly, non-polluting and should their ever be a massive nuclear accident, it just 20 years all of the radioactive material will have decayed away. 


If you are intersted our local power company has a slide deck on electrity, power companies, solar, and how custoemrs can save by installing solar.  Let me know if you would like a link to it.  I can also provide links to other material and videos.  Just let me know.










Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 27, 2018, 04:51 pm
Thanks @Doug101!

For me, is one at a time :-). If I will succeed in charging the batteries (and I am sure I will do), that would be a great basis to move forward to displays and more.

I gave up the voltmeters because my demo is a dwarf one, every little counts. :-).

Now I am working on linking a wind turbine to the same batteries (I started another thread in this forum section about this).

+++

Thank you very much for teaching highlight, to!

European Union has an ambitious plan to source no less than 20% of energy out of renewable sources by year 2020. Ans is very close to this target. :-).




 
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 28, 2018, 09:39 pm
For anyone who may be interested - Update after tinkering:

- the barrel connectors is a less-inspired idea - apart from resisting to pulling (not to much however), nothing else make them a preferred solution to something like connection of a pv panel wires (and I am afraid they are not kid-proof :-)) - other connectors to be further explored

- although the measured output voltage of the panel in half sun (:-)) is above 5V (no load), this small panel (200mA, polycristal) can barely rise above 15 mA - lesson learnt: to reverse to the larger one (384 mA, monocristal)

- pvc profiles are easy to clip and mount - the frame I made for the PV panel is unexpectedly sturdy and very versatile - so no need to pay extra for fancy mounting (at least in my demo project) that is something to explore and develop - contrary to the super-glue (instant glue ) I used to the sensor's project, this time I use a 3 hours time glue for plastic - much more handy and I was no longer afraid to glue my cat's tail to the third-hand tool :-)

- I still fight with the Zeners (which is which)- I measured them, but I doubt I did it in a correct way (load?) - maybe I will ask a kid to tell me the written values :-)

- for unknown reasons, although the recommended value of the resistor using an on-line calculator (yes, I am a lazy person!) is 30 Ohm, the LED does a good job (light) mounted in series with a 200 Ohm resistor - directly to the PV panel (rated 6 V, offering 5.6 V in half shadow).

- the Shotky diodes have terminals that do not fit the breadboard's orifices  - that is very annoying- lesson learnt: to either go directly to perfboard or to do it "on air" - that is fun :-)

Now is night here, so I cant finish the circuit and test it. Under a LED light bulb, the Panel cant go above 4V, no matter how (reasonably) close it is.

+++

One word about PV connectors: while the main circuit shall be the same, I needed a solution to replace the panels, just to show differences and experiment. Then I definitely need a connector. The  idea to use barrel connectors came from the fact I saw one panel equipped with this type of connector, I imagine it might be a sort of thing everybody expects from a PV panel. Now I think I was wrong.

Some info about barrel connectors (and Molex and JST):

https://learn.sparkfun.com/tutorials/connector-basics/power-connectors (https://learn.sparkfun.com/tutorials/connector-basics/power-connectors)

I will keep posting.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 28, 2018, 10:36 pm
For anyone who may be interested - Update after tinkering:

 I still fight with the Zeners (which is which)- I measured them, but I doubt I did it in a correct way (load?) - maybe I will ask a kid to tell me the written values :-)

Read post #37 use right side part of circuit, LED and resistor as on post #44 , replace the LED by Zener.
Ignore Schottky diode for now, without it battery may discharge in 100 hour.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 28, 2018, 10:51 pm
@ted - Tank you very much! I will do so.

Amazing process.
Title: Re: How to modify the voltage of solar charger?
Post by: TomGeorge on May 29, 2018, 04:54 am
Hi,
You will have to post some pictures when you get everything setup.

A very interesting project development.

Tom... :)
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 29, 2018, 09:37 pm
I measured the Zeners using the circuit bellow (Thank you @Wawa, WVMarle, @Doug101, @ted and to all guys who are so kind to help me!).

(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=259958)

The multimeter measured 7.06 V for the 2 LiIon 18650 in series that I used in place of the PV Panel.

My 4.7V 1.3W Zener got lost, so I have to use the 4.7 V 0.5W for the time being (hope no smoke communication).

+++

Following the suggestion about a display (thanks doug101!), I am now adding it to the circuit. Since the minivoltmeters have their own consumption- which in this case is relevant- I am planning to  use an (on) off (on) switch to alternatively measure the voltage of the panel and the output voltage of the batteries, only for few seconds (to save battery).
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 29, 2018, 10:17 pm
Those batteries can deliver much more current than zener can handle, for 7V start with R =1k.

I thought that you going to use solar panel for that.

Are you sure that you used 200 ohms, even when zener is shorted the current is 35mA, when is it not, the current will be less - something is wrong here
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 29, 2018, 10:32 pm
@ted

That circuit was only to measure the Zeners which were mixed up by the seller.

+++

The real circuit uses the PV Panel as power source. The one we discuss so far and which is in an advanced stage.

+++

The only reason I used a 200 Ohm was that resistor was at hand, being the one to be mounted in the PV circuit in series to the white LED.

The reason I use 7 V batteries was only to deliver more than the 6V - which is the maximum value in the Zeners range of 5 values I got. Also, it was close to the (roughly) 6V of the panel

+++
Briefly, the above circuit is not going to be used alone.

Do you suspect that circuit is not appropriate to measure the Zeners Voltage or it can destroy them?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 29, 2018, 10:51 pm
@Ted

It was already night when I started to measure the Zeners. That is why I set up an alternative power source. The  deadline I set to myself is tomorrow - for a prototype that works.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 29, 2018, 10:59 pm
Zener Diodes 4.7 Vz 5 Ohm 5 uA 1.5 Vr 319 mA 1.5W - this 1.5W diode can handle 315 mA - I think you have similar
So with current 35mA how is died - it is a mystery.
The circuit is ok.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on May 29, 2018, 11:06 pm
@Ted
The  deadline I set to myself is tomorrow - for a prototype that works.
Can be done in 10 min.
Connect the solar panel through amp meter directly to batteries, if the current is no more than 200mA you ok for 4 hours, then disconnect the pamel.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on May 29, 2018, 11:20 pm
@ted

There is the "mechanical" part as well to be completed.

Status:

- frame of the panel = 90% done,
- concept of the wiring= 50% done (pending: LED support, design of the components to the perfboard, wiring to the switches)
- selection of components = 50% done (switches not yet decided, 4.7 1.3W Zener gone where all the lost components go, limiting resistor to the LED - to be decided by trial and error or to stick on 200 Ohm for no reason).
- overall frame: 0% (maybe two PVC profiles together will do the job, but I shall see)


I will post the pics in the coming days.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 01, 2018, 09:30 pm
Here it is the final stage of the electronic part of the prototype - demo photo-voltaic charger.

(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=260412)(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=260414)(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=260416)

In place of voltmeters, at this stage, I use an ON-OFF switch, to bypass the charging /lightening circuit.

Now, there is something that I cant figure out:
- if the  ON-OFF-ON switch that selects either to charge the batteries or to power the light is on OFF, then operating the ON-OFF switch will let the current from the PV panel to flow to the LED - or not - that is clear and ok
but
- if the ON-OFF-ON switch is on either one of the two ON position, then what is the value of the coltage and current reaching the LED in each case?

In my view, if the ON-OFF-ON switch is closing the left side of the circuit (charging) then the voltage is 4.7V- drop on Shotky.

But if the ON-OFF-ON switch closes the right part of the circuit (namely powering LED from batteries), what is the current and voltage reaching the LED this time?

Thank you very much for enlightenint me! I just cant focus on this second case.  
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 01, 2018, 10:14 pm
The battery will be charged to zener voltage minus drop voltage of schottky diode 4.7 - 0.4 = 4.3V. Typical current of the LED is 20mA, depends to the LED resistor value can be different, put 300 ohm and measure the current shouldbe around 20 mA,
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 01, 2018, 10:20 pm
@Ted

I mean, when I close the ON-OFF while the ON-OFF-ON switch closes the right side of the circuit.

It looks like it does not make any difference in voltage and current to the LED whatever left or right side of the circuit is closed.

Did I get it correctly?

My point is not to blow up the LED while operating the switches.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 01, 2018, 10:23 pm
Zener is 4.7 V/1.3W, R is 220 Ohm/0.25W. LED is 5mm white.

Panel is rated 6V.

Batteries are 3 x 1.2V NiMhd AAA (in series).
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 01, 2018, 10:47 pm
My 5mm LED and 150 ohm resistor @ 4.3 V - current is 9mA and LED is bright.
Use name of the switches SW1 , SW2.
To be save, put  10 ohm resistor with zener
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 01, 2018, 10:59 pm
Case:

SW1 closed.
SW2 closes right side.
PV in sunbright.

My understanding is that in this case the Voltage will still be 4.7V minus Shotky drop, but the current will ad up:

I(R+LED) =  I(PV) + I(Batt).

Now, providing I got it correctly, if I put a 10 Ohm in series with the Zener, the excess current will follow the resistor, thus less being available to the LED. So in a certain reasonable range of current, there would be little chance to reach values that can kill the LED.

Namely, in cases like the above (worst case scenario).

Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 02, 2018, 12:21 am
R LED is limiting the current of the LED, with R= 500 ohm you ok up to 8V, so LED will not die and you will have a light at 3.6V also.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 02, 2018, 06:01 am
Thank you, @Ted!

I will experiment by modifying the value of R LED alone then:

- from 220 Ohm now, Ill check with the R values I can find in my boxes within  range 220 - 600 Ohm.

+++
I still have to solve out:

how to mount one single switch and one single LCD to alternatively show voltage of the PV and voltage of the batteries (some solutions found, but not sure)




Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 02, 2018, 06:47 am
https://www.google.ca/search?q=DIY+Prototype+Board+PCB&tbm=isch&tbs=rimg:CcOHkRasFIuJIjgSnB9NtPQrLAFj_1IJQ7jgG_1tflmlOhAULI7I_14H_1BYfln2rvhMmjNc-IObpK37dFBT-vuQzA1OpyoSCRKcH0209CssEeEitIEpcjmAKhIJAWP8glDuOAYRywGveG3xHB8qEgn-1-WaU6EBQhFtAx2TagIS_1yoSCcjsj_1gf8Fh-EbWVizn5ybxAKhIJWfau-EyaM1wRgb9GPdRbNgUqEgn4g5ukrft0UBEp4HGqA_1EDeioSCVP6-5DMDU6nETwbw4gUaJjK&tbo=u&sa=X&ved=2ahUKEwiH8eWSlrTbAhUk_4MKHfRZCxcQ9C96BAgBEBs&biw=1440&bih=787&dpr=1 (https://www.google.ca/search?q=DIY+Prototype+Board+PCB&tbm=isch&tbs=rimg:CcOHkRasFIuJIjgSnB9NtPQrLAFj_1IJQ7jgG_1tflmlOhAULI7I_14H_1BYfln2rvhMmjNc-IObpK37dFBT-vuQzA1OpyoSCRKcH0209CssEeEitIEpcjmAKhIJAWP8glDuOAYRywGveG3xHB8qEgn-1-WaU6EBQhFtAx2TagIS_1yoSCcjsj_1gf8Fh-EbWVizn5ybxAKhIJWfau-EyaM1wRgb9GPdRbNgUqEgn4g5ukrft0UBEp4HGqA_1EDeioSCVP6-5DMDU6nETwbw4gUaJjK&tbo=u&sa=X&ved=2ahUKEwiH8eWSlrTbAhUk_4MKHfRZCxcQ9C96BAgBEBs&biw=1440&bih=787&dpr=1)
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 02, 2018, 11:07 am
Thank you Ted!

Few days ago I managed to get a stripboard.  Not yet use it. Nevertheless is almost double price than a regular perfboard. And available in one place only :-(.

Old wiring in air looks promising as well.



Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 03, 2018, 07:53 pm
Experiment on small breadboard:

- 4.7 V/1.3 W  Zener
- 1 N 5819 Shotky
- white LED
- various resitors to LED:
  - 220 Ohm
  - 460 Ohm
  - 560 Ohm

Powered, alternatively, by:

3.6 V NiMHd 800 mAh
7.2 V LiIon 18650
PV 6 V 200 mA

Now, the really strange phenomenon is that the 460 Ohm resistor caused the Zener to get hot. While 220 Ohm and 560 Ohm did not. This happens to both batteries sources, but not with the PV.

No explanation so far. I just put the 560 Ohm for the time being.

Two improvements, thanks to guys helping (and encouraging) me on this thread:
- stripboard (veroboard) instead of perfboard - this makes a lot of sense seeing the geometry of the wiring
- solid core wires in place of multi-threads ones to local wiring -easier to solder.

On minor improvement is to use a barrel socked soldered to vero-board in place of the connector mounted on wire.

Circuit OK on the breadboard. I will complete it on the veroboard soon. I will also use a larger panel this time (some 400mA, still 6V). And I will post the pics.


 
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 08:35 pm
You need R1 10 ohms or more as on post  # 34
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 08:45 pm
If you put 7.4V in the same place as 6V = battery can deliver 2A current compared to 200ma by PV, if you going to use strong PV you need 200mA current limiter.

(https://cdn.instructables.com/FFG/HHD3/J3AF9J52/FFGHHD3J3AF9J52.LARGE.jpg)

Circuit with zener has limitations, the proper circuit is;
4.2V voltage regulator output of it to 200mA current limiter, output of  limiter to battery.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 03, 2018, 08:51 pm
OK. I will put R1 Resistor back in circuit. See what I can find in the range 10-50 Ohms.

I used the 7.4 V Lion only to check the circuit (I had it on my desk by chance).

The real circuit will be with NiMHd 3.6 V AAA 800 mAh which will be charged by a 6 V 384 mA PV. The NiMHd uni will power the LED.
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 09:04 pm
The lowest resistance resistor you have is ?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 03, 2018, 09:09 pm
Here it is the new version of the schematics:

(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=260606)

Parts:
1) PV panel 6 V 384 mA  1 pc
2) 4.7 V/1.3 W  Zener 1 pc
3) 1 N 5819 Shotky 1 pc
4) R1 resistor ? (still digging im my boxes) - 1pc
5) 1.2V AAA NiMHd 800 mAh units in series  - 1 pc
6) case for 3 x AAA batteries - 1 pc
7) 560 Ohm R2 Resistor - 1 pc
8) SW1 ON-OFF-ON switch  - 1 pc
9) SW2 ON-OF switch - 1 pc
10) 5mm LED white - 1 pc
11) Case for 5 mm LED - 1 PC
12) morfets 2 connections - 2 pcs
13) barrel connector to board - 1 pc
14) veroboard (stripboard) - 1 pc
15) wires (solid core) - various
 
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 09:18 pm
Circuit is ok, for R1 use a few resistors connected in parallel for example 5x 100 ohm
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 03, 2018, 09:26 pm
I found 10 Ohm/0.25 W  and 56 Ohm /0.25 W for R1.

Perhaps they are other values around - but not lucky so far.

Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 09:38 pm
ok
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 03, 2018, 09:43 pm
Then I shall mount the 10 Ohm one?

I am a bit concerned about resistor having only 0.25 W. For a 200 mA (say) at 5.5. V = 1.1 W - if my calculus is correct
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 03, 2018, 10:01 pm
5.5 - 4.7
Title: Re: How to modify the voltage of solar charger?
Post by: Wawa on Jun 04, 2018, 12:01 am
Are you complaining about the zener getting hot?
It's supposed to get hot.

It 's either the power of the solar panel as charging current into the batteries, or burned off in the zener.
That's why I adviced a long time ago a super-zener made of a zener and a big transistor.

A more complicated regulation is series regulation (voltage regulator IC) instead of simple load-dump (what you asked for).
Leo..
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 04, 2018, 01:06 am
If you are using 6V/200mA PV .
0.2x4.7 = 0.94W = 1.5W zener ok.
If you are using 7.4 V battery which can deliver 3A - 10W zener ......

For new PV you can calculate as above.
And you can't charge AAA battery with more than 200mA
Title: Re: How to modify the voltage of solar charger?
Post by: 1steve on Jun 04, 2018, 01:52 am
I know you are having a lot of fun, but why not just get a solar yard light and see how they do it?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 04, 2018, 06:14 am
@1steve

Theoretically, you are perfectly right.

This particular case however it is a demo project for kids.
 
Therefore, I must find easy the components (no "exotic" or particular or mysterious circuitry), use as few as possible and being able to explain what is there.

To be honest, it is a nice way for me to learn more. :-).

And I have to couple the wind turbine to the same charging circuit (+ additional small  interface to match the particularities of the wind energy).
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 04, 2018, 02:00 pm
@Wawa

I am planning to improve the device later on, so I am moving along a modular approach. :-).  There are two ideas pending so far:
- mini-voltmeters
- more efficient charging

For the second one, I am thinking of a sort of add-on to the already existing circuit.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 15, 2018, 12:43 pm
The device built as above (post 77) works very well.

It passed the transportation test (aka being transported in a plastic bag, circuit in sight). 

It is still in the "screws stage", next phase I will glue it up for ever.

Its "sister component" - aka the wind turbine is in the incipient stage - still to adapt a brushless motor as generator.

I will post pics of the photovoltaic device later on.

Thank you very much for your help that made possible the device!

+++

Questions I face now is how to electronically command the photovoltaic circuit to either charge or supply electricity?

Or, in other words, how to replace the manual switches by electronics?

The problem is I must use only diodes and maximum one bipolar transistor (no Mosfet) and passive components. No solenoid either.

These restrictions are from the fact that the project is a demo for kids, so I will have problems to explain more than that.

The solution I plan is to collect  the small current from a photodiode (or a light sensor), to amplify it to the point it can close one branch of the SW1. And then find a way to close the other branch in a similar manner.

I could not find schematics for such a circuit. Except for something similar that I hope I can adapt- see bellow. I think I can replace the Source ("Voltage")  by a photodiode.

+++

My question is: is it possible to adapt the circuit in the way I plan to? 

Thank you very much for your kind, patient and wonderful help!https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=262360 (https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=262360)(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=262360)
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 15, 2018, 02:17 pm
It is not clear what you want.
Manually you can turn switches any time, in 1 hour or tomorrow.
What factor will decide to do that electronically ?
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 15, 2018, 02:42 pm
To automatically charge during daytime and to automatically light during night time.

Basically, the kind of behavior of an industial photovoltaic lighting system.

My plan is to use the photodiode current to close the charging branch of the circuit (now done manually by SW1).
Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 15, 2018, 03:01 pm
Everything is here, battery is charged all the time = no switch to turn off charging.
The LED is turned on by photoresistor.

(https://i.ebayimg.com/images/g/2yUAAOSw3pVZ15Bf/s-l1600.jpg)

(https://i.stack.imgur.com/lnKWP.png)
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 15, 2018, 04:52 pm
Thank you @ted!

The photoresitor I can find here is  5528, which is recommended to be part of a voltage divider by a 10 K resistor (5V, Arduino).

The 5528 Value in light is 8K to 20K (according to its specifications).


My circuit is 3.6 V (3 NiMH x 1.2V) so I guess the R2 resistor shall be around 68-75 K - if going by the posted schematics.

I also think that the R1  value of 330  shall be reduced to fit the lower voltage - maybe to 100.

Title: Re: How to modify the voltage of solar charger?
Post by: ted on Jun 15, 2018, 05:10 pm
R2 - put potentiometer 100k, R1 don't go to low, the LED are cheap, so you can play with resistor.,
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 15, 2018, 06:22 pm
Ok, Thank you!

Now the fun part is to adapt, design and mount this new module without changing anything in the existing circuitry, so I can revert to the manual command anytime I like to.
Title: Re: How to modify the voltage of solar charger?
Post by: falexandru on Jun 17, 2018, 10:42 am
As promised, the solar charger demo final prototype:


(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=262570)


(https://forum.arduino.cc/index.php?action=dlattach;topic=549219.0;attach=262572)

The solar charger uses the simple 2-diodes design, so it is easy to explain what is in and how it works. Not recommended however for actual devices, which may require more efficiency and reliability.

It is still assembled by screws and make use of barrel connectors - for portability reasons among various sizes and types of PV panels.

Screws are not a good choice for they are easy to un-screw  by themselves by manipulation of the device alone.

However, the modular design makes possible to interact with my sensors and with the vertical axis wind turbine.

+++

Note: I did not cut the components terminals on purpose, because they act as a sort of "guard" to the circuit. :-).