Solar Panel for Li-Poly Charging for Cloudy Sky(UK Weather)

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Yes, I knew about LEDs working backwards - I've used them as cheap'n'cheerful light sensors for timing pulses. That was why I wondered about PV panels. I'd expect the reverse bias to produce photons of the same frequency as those absorbed - at least with a semiconductor bandgap doing the work - but I have an idea that it may not be the same mechanism for PV generation.

 

Neil

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"Dare to be naïve." - Buckminster Fuller

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The following has a cold start that's an order of magnitude less power :

AEM10941 Solar Energy Harvesting IC - e-peas | Mouser

 

20mA at 1.8V to MCU; AVR DA, DB, and DD have extended SOA (1.8V, 24MHz) and approx 7mA typ for AVR DB.

What are the AVR28DA128 AVR32DA128 AVR48DA128 AVR64DA128 ?? | AVR Freaks

 


Photovoltaic Energy Harvesting | e-peas

 

edit :

EVK10941M Mini Evaluation Board - e-peas | Mouser

ETA tomorrow :

DEMPV-BLE Batteryless Photovoltaic IoT Demo Kit - e-peas | Mouser

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Sep 24, 2020 - 01:25 AM
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If i was to have solar panel what was 6V 1.8A = 10-11W compared to 19.5V 0.5A 10-11W, would that better for efficiency when charging Li-Poly Battery using standard Li-Poly battery charging IC?

Thanks

Regards

DJ

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would that better for efficiency

Maybe, maybe not...depends on your converter, probably a switcher.   Remember higher current===> higher loss, due to I2R.  Double the current, and even the loss in the wires & connectors goes up by 4x 

Your example, such losses go up by around 10X to 13X !!!  

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Hi

 

I am hoping to plug the output of the solar pannel via diode directly into Li-Poly charger(ST4054). As voltage will be about 5V, i guess a switcher might not be needed.

 

 

Thanks

Regards

DJ

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I am hoping to plug the output of the solar pannel via diode directly into Li-Poly charger

Note that is not MPPT, but at a few watts, probably nobody cares.  If you are dealing with getting 100W or 1000W , then you care about % delivery from the cell

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sun. Nov 15, 2020 - 09:35 PM
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It will be 10-20W panels.

Thanks

Regards

DJ

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better check what the maximum allowed voltage at you charger IC is. Note that the 19V is probably the working voltage and not the non load voltage. That might be a lot higher, your charger IC needs to be able to handle that when it does not have to charge the battery

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My charger IC is 6V max.

 

Currently i am using  LM2596 , to generate 5V from a much higher voltage before it goes into the charger.

Thanks

Regards

DJ

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Correct me if my understanding about MPPT charging is wrong.

 

From what i have understood, a battery charger with MPPT regulated the charge current so that battery charger does not cause the Input Voltage to drop, if the available current was less?

 

My ST4054 charger, is set to 0.8A. In theory if 0.8A was not avilable, voltage would drop and the battery would not get any charge?

 

I experimented by limiting the output power from my desktop power supply to 5V 30mA. This is to simulation of when the sun might be low.

 

When i connect that to my battery charger, i am seeing the VIN dropping to 3.7V(my current battery level) from 5V and a charge current at 30mA. 

 

To me it seems like i am getting the max charge current available, therefore what would be the advantage of using MPPT as the battery is getting charged with max current available?

 

 

 

 

Thanks

Regards

DJ

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djoshi wrote:
therefore what would be the advantage of using MPPT as the battery is getting charged with max current available?

MPPT only makes sense when you want to maximize the return on investment by getting the max power from your house array when feeding power into the grid!  Other wise it's just a bunch of marketing hype!

What you need is a solar charger designed to charge the type of battery you have, or use the type of battery your CC is designed for, so Solar Panel => charge controller => battery => load!  Whether it is mppt or not makes little difference.  JMHO.

Jim

Edit: little difference when used to charge batteries!

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Tue. Nov 17, 2020 - 05:23 PM
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MPPT is based along the lines of an optimally matched load.

 

Imagine that a cell voltage varies as the load increases or decrease, maybe in a nonlinear way.

 

Imagine an extremely heavy current drawn  (short) and thus a near zero voltage from the cell    V=0, W=0

Imagine a rather heavy current drawn and thus a rather low voltage from the cell   W=V*I

Imagine a rather light current drawn and thus a rather high voltage from the cell    W=V*I

Imagine an extremely light current drawn (open) and thus the highest voltage from the cell      I=0, W=0

 

In each case the power drawn//delivered is volts*amps

As you can see from the above, at both extremes the delivered power is zero.  

The other conditions, of course, have higher power.

These slopes must connect by a curve of some sort.  Somewhere along this curve, at least one maximum power delivery point will occur. 

MPPT tres to dynamically find this point at all times.   

By adjusting the duty cycle, the conversion ratio is changed such that the input resides at this optimal setting to deliver the required load voltage.

Normally a fixed input supply requires an exact duty cycle to give a desired output.   Here, the input varies so the duty cycle will be "mushy" ... more than one duty cycle will give the desired output & at least one of those be the highest cell efficiency.

However, if you aren't trying to draw the max output possible from the cell, it really wouldn't matter how efficient the cell is acting (perhaps other than cell heating considerations).

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Tue. Nov 17, 2020 - 06:36 PM
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I am doing a little test to see what preforms better. As the goal is to charge a Li Poly batter, I am thinking

Option 1
19-23V solar panel --5Vdcdc--Li ion charger.

Option 2
5V solar panel -Li ion charger.

I had a discussion with solar panel company, who advised that if my goal is to charge a Li ion battery, then for better performance then what I am using , best to use a 5V panel.

Has anyone tried the 5V panels used for mobile phones before? The type you see on Amazon

Thanks

Regards

DJ

Last Edited: Sat. Dec 19, 2020 - 11:22 PM
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I am doing a little test to see what preforms better. As the goal is to charge a Li Poly batter, I am thinking

Are you making fish and chips? 

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I guess best to use a pc, and not a smart phone to make a post

Sorry for the typo

Thanks

Regards

DJ

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djoshi wrote:
I am doing a little test to see what preforms better. As the goal is to charge a Li Poly batter, I am thinking Option 1 19-23V solar panel --5Vdcdc--Li ion charger. Option 2 5V solar panel -Li ion charger. I had a discussion with solar panel company, who advised that if my goal is to charge a Li ion battery, then for better performance then what I am using , best to use a 5V panel. Has anyone tried the 5V panels used for mobile phones before? The type you see on Amazon

yes, they are crap. with the low surface area they cannot give much current so will not charge much. I started off playing with these small panels.

You should not be looking at the voltage alone, but also at the wattage a panel can deliver, that is far more important. What ever the voltage you should be able to get a converter to make the right voltage from it, but if you do not have the wattage no voltage is going to really help you as as soon as the wattage is reached independent of the voltage at the output it is game over.

 

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Well, I agree some of them look crap, but I am thinking about doing something more customised.  At this stage, my application circuitry can not be changed as they have already been manufactured and have a standard Li-ion charger(ST4054), but in the future revisions, we could add an MPPT charger IC.

 

 I have a few hundred small 5V 350mA solar panels, I am thinking about joining multiple of them in parallel. Maybe about 8. Giving me about 5V 2.8A = 14W.

 

The reason for mentioning the 5V voltage is to avoid using a DC-DC stepdown and losing some power due to efficiency, as these cells will output only a max 5V. I am thinking that output can connect directly to my charger.

 

 

Thanks

Regards

DJ

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If you connect them all in parallel, don't you need blocking diodes?

 

Hook 'em all in series for lots of volts, and a step down regulator can be pretty efficient... amps, volts, what you're collecting is electrons. Joules, if you insist.

 

Neil

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Hi Neil

 

Thanks

 

Yes in principle you should, but as they are all low current, i thought i could get away with my simple test.

 

 

Thanks

Regards

DJ

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Solar panels have an Optimum Operating Voltage for example 17V or 18V.

 

Does this mean, at 16V, there is not much charge current?

 

I am thinking about trying the following charger  LTC4162-L Datasheet and Product Info | Analog Devices OR  LT3652 Datasheet and Product Info | Analog Devices.

 

It seems that the MPPT voltage can be manually configured, so I am thinking if it was set to 5V instead of 17V, would that give me a little extra charge current?

 

 

 

 

 

 

 

 

 

 

Thanks

Regards

DJ

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inverse (short circuit current is the maximum current)

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

inverse (short circuit current is the maximum current)

 

 

Yes, but that would mean voltage would be close to 0V mark.

 

So would that mean, that if I can get the panel to drop down to maximum to 5V using Mppt, that would give me a bit more current compared to setting the mppt level to 17V for example?

 

 

Thanks

Regards

DJ

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open circuit (zero current) is maximum voltage

short circuit (zero voltage) is maximum current

voltage at MPPT is maximum power

 

LTC4162 will regulate both input (MPPT) and output (CV/CC)

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

open circuit (zero current) is maximum voltage

short circuit (zero voltage) is maximum current

voltage at MPPT is maximum power

 

LTC4162 will regulate both input (MPPT) and output (CV/CC)

 

Yes, there seems to be two option

a) the automatic algorithm( f mppt_en is set )

b) or you can manually set the voltage to the optimum to your panel, therefore I was thinking I could set it to 5V.

 

I guess I need to download there simulation software an experiment.

 

 

 

 

Thanks

Regards

DJ

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djoshi wrote:
you can manually set the voltage to the optimum to your panel, therefore I was thinking I could set it to 5V.

There are two voltages here, the input voltage from the panel, and the output voltage to charge the battery.  For a buck converter, the input voltage must be higher then the output voltage.

For most so called 12v solar panel, the optimum power point under full sun will be in the 16 - 18 volt range, note this changes with the level of sun light hitting the panel, so only a auto setting will be optimum.

Unless you want to stand there and adjust for every cloud passing! 

 

However for battery charging, mppt is not required, as the charging level varies with the state of charge on the battery.  mppt is fine, but simple pwm works too, for 12v panels the diff is far less then 20% under most conditions, mppt works far better for 24v and higher solar panels where the diff between input and output voltage is greater.

 

JMHO, and experience!

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Wed. Jan 6, 2021 - 07:17 PM
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djoshi wrote:
So would that mean, that if I can get the panel to drop down to maximum to 5V using Mppt, that would give me a bit more current compared to setting the mppt level to 17V for example?

 

The solar panel acts as a voltage source (somewhat) until the load pulls the current caused by photons generating carriers (in the depletion region of a P-N junction). If the load wants more current, the voltage will drop, but not much more current is provided; it is then acting more like a current source.

 

I have tinkered with the LT3652, did a fair number of board spins before I could figure out what my problems were. I had the MPPT input voltage set at about 16V at room temp; it would drop to a lower voltage as the solar panel heated up (datasheet is a good read). It charged a 6V lead-acid and was in absorption mode most of the time (e.g., not MPPT).

 

It was a good educator, but in the end, I went with a 12V battery and solar panel. The solar panel was sized, so the short circuit current was a fair match for the charging current.

 

After all the games, I ended up with a solar panel directly charging a battery (sized to match each other). Also, a PMOS is used to disable charging when the battery is full. An MP2467 based converter steps down the battery voltage to regulated 5V. It minimized the number of converters I needed, and matching the battery and solar also maximized the storage efficiency. I need to do this with Li-ion at some point; I probably need to start learning that stuff soon since it's growth is past the exponential nee.

 

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ron_sutherland wrote:

djoshi wrote:
So would that mean, that if I can get the panel to drop down to maximum to 5V using Mppt, that would give me a bit more current compared to setting the mppt level to 17V for example?

 

The solar panel acts as a voltage source (somewhat) until the load pulls the current caused by photons generating carriers (in the depletion region of a P-N junction). If the load wants more current, the voltage will drop, but not much more current is provided; it is then acting more like a current source.

 

I have tinkered with the LT3652, did a fair number of board spins before I could figure out what my problems were. I had the MPPT input voltage set at about 16V at room temp; it would drop to a lower voltage as the solar panel heated up (datasheet is a good read). It charged a 6V lead-acid and was in absorption mode most of the time (e.g., not MPPT).

 

It was a good educator, but in the end, I went with a 12V battery and solar panel. The solar panel was sized, so the short circuit current was a fair match for the charging current.

 

After all the games, I ended up with a solar panel directly charging a battery (sized to match each other). Also, a PMOS is used to disable charging when the battery is full. An MP2467 based converter steps down the battery voltage to regulated 5V. It minimized the number of converters I needed, and matching the battery and solar also maximized the storage efficiency. I need to do this with Li-ion at some point; I probably need to start learning that stuff soon since it's growth is past the exponential nee.

 

 

Ok, when you say you matched a battery directly, did you have a controller between or was the PMOS the only circuit you used? 

 

So with the LT3652 and setting 16V as your MPPT as that manual setup? I guess that is way a using the automatic detection might be better as shown on LTC4162 datasheet.

 

I have seen some setups where a panel is connected directly to a 12V battery used for cars.

 

Is there any power below 17-16V that can be harvested? Or is this very minimum 

 

 

Thanks

Regards

DJ

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ki0bk wrote:

djoshi wrote:
you can manually set the voltage to the optimum to your panel, therefore I was thinking I could set it to 5V.

There are two voltages here, the input voltage from the panel, and the output voltage to charge the battery.  For a buck converter, the input voltage must be higher then the output voltage.

For most so called 12v solar panel, the optimum power point under full sun will be in the 16 - 18 volt range, note this changes with the level of sun light hitting the panel, so only a auto setting will be optimum.

Unless you want to stand there and adjust for every cloud passing! 

 

However for battery charging, mppt is not required, as the charging level varies with the state of charge on the battery.  mppt is fine, but simple pwm works too, for 12v panels the diff is far less then 20% under most conditions, mppt works far better for 24v and higher solar panels where the diff between input and output voltage is greater.

 

JMHO, and experience!

 

Jim

 

 

Yes, my battery voltage will be 4.2V, therefore need a minimum 5V to power the charge IC. So with the full sun will be in the 16 - 18 volt range, what would happen if we were to let the panel drop to 5V using MPPT?

 

How can I work out, how much current there would be from 16V to 5V? As I am trying to get a good charge during cloud times as well.  Can it be possible the auto setting could still get some charging current at lower voltage.

 

OR is it possible that after 16V, the current output will be 0A?

 

  

 

 

Thanks

Regards

DJ

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djoshi wrote:
as that manual setup?

 

Lets look at the LT3652 datasheet (to get some rust off those neurons).

 

https://www.analog.com/media/en/technical-documentation/data-sheets/3652fe.pdf

 

 

My setup had temperature compensation so that the input voltage would drop as the solar panel heats up. But yes, that is a "manual" setpoint... which looking at the datasheet, has made me recall it was 17.6V (not 16V) at room temperature. When I put the panel outside, it gets hot (65C), about 43C delta from room temperature. That caused the MP setpoint to shift 3 volts down, to bellow 15V.

 

djoshi wrote:
Is there any power below 17-16V that can be harvested? Or is this very minimum

 

The LT3652 will not let the input Vin_reg go below its reference voltage (2.7V); in other words, it turns off when the input voltage is less. You have to divide down [and optionally compensate] the voltage to Vin_reg from the panel.

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interesting use of the solar panel as a very poor "light source" for their inspection

 

The DTU group’s new technique involves electroluminescence — the glow produced by photovoltaics in response to an applied voltage. This phenomenon can enable detection of cracks, broken interconnects, shunts, and other problems.
“Electroluminescence makes it possible to find a defect before it’s severe,” said Peter Poulsen, senior scientific officer at DTU and a co-author of the paper.

https://www.photonics.com/Articl...

 

you can even buy a tester from China

https://www.made-in-china.com/sh...

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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djoshi wrote:
Ok, when you say you matched a battery directly, did you have a controller between or was the PMOS the only circuit you used?

 

After giving up on the LT3652, I now have a 12V panel connected to a PMOS (p-channel MOSFET) that I can turn off, and that is then connected to the battery. The battery needs to be sized so the panel does not harm it. The latest version looks like this.

 

 

Alternat power should say charger power or something like that, I guess. The solar panel connects there, and I can measure its voltage at the ALT_V node and it's current with the ALT_I node. I can turn off the input with ALT_EN. Some of the confusing stuff helps with reverse connection protection, but explaining that is not the task.

 

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Looks like some testing will need to be done.

Are there any pcb modules available with mppt that are available as my initial test?

You get alot on Amazon, but can't manage to find one with mppt from linear tech.

Thanks

Regards

DJ

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ron_sutherland wrote:
Also, a PMOS is used to disable charging when the battery is full.
NMOS for lead-acid :

Simplify Small Solar Systems* with Hysteretic Controller | Analog Devices

 

"Dare to be naïve." - Buckminster Fuller

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I salvaged what I could from my projects with an LT3652, then put what remained in the trash.

 

This has a LT3652.

 

https://www.sparkfun.com/products/12885

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