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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