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

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Hi All

 

I have a PCB, that is powered using a 2000mAh Li-Poly battery and Charging IC, that is powered with 5V USB cable at 0.5A. That battery last about 2 days before it needs to be charged up.

 

I am trying to get this charging using a solar panel. I am currently using  https://www.amazon.co.uk/gp/product/B0836FKHJT/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

 

I am then using a simple step down DC-DC to achieve 5V,   https://www.amazon.co.uk/Youmile-Module-Supply-module-Charger/dp/B07YDFSR6D/ref=sr_1_17?dchild=1&keywords=dc+dc+step+down+usb&qid=1598093160&s=industrial&sr=1-17

 

This 5V is then inputted into the Li-Poly Charger IC.

 

 

This seems to be working well, when there is clouds are clear and the sun is out, but on a cloudy day there is not much charge.

 

Is there a better panel to use for such weather? 

 

Or 

 

Is it possible that we could make a simple capacitor circuit, that accumulates the low power output from the panel, so its not wasted and can provide some charge into the charging of the battery?

 

Thanks 

 

 

Thanks

Regards

DJ

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There was a recent thread here that discussed the theory and practice of solar charging.

 

Fundamentally, you charge the battery when the sun shines and consume the battery when it doesn't. You need to have sufficient battery capacity to cover the period when it's not charging, and that varies day-by-day and season-to-season. If there's not enough sun, you need a larger panel and a larger capacity battery.

 

And, the charger you have is almost certainly a PWM type, which effectively wastes the difference between the panel voltage (probably 21V) and the 12V output. An MPPT type charger would be able to use more of the panel's capability but will be more expensive.

 

I would discard the charger and the step-down regulator, and just use a 21V to 5V buck converter. It will be much more efficient and enable you to capture more of the solar energy. If that still isn't sufficient, you'll need a larger panel and/or a larger capacity battery.

 

What is the raw voltage from the panel ?

 

 

Last Edited: Sat. Aug 22, 2020 - 11:37 AM
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Thank You for your reply

 

The measured raw voltage is about 27V.

 

The li-poly charger is a simple linear charger ST4054. Its a 5V to 4.2V.

 

We are using this buck converter to make solar output to 5V

https://www.amazon.co.uk/Youmile-Module-Supply-module-Charger/dp/B07YDFSR6D/ref=sr_1_17?dchild=1&keywords=dc+dc+step+down+usb&qid=1598093160&s=industrial&sr=1-17

 

Is it possible to add a capacitor on the output of a solar cell to build up a charge?

 

 

 

 

 

 

 

 

 

Thanks

Regards

DJ

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Is it possible to add a capacitor on the output of a solar cell to build up a charge?

That will not really hold any power, but why don't you just charge a small (or big) 12V battery, (depending or you actually use pattern) let's say of the size of 5 full charges. 

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>> The measured raw voltage is about 27V.

 

That's the first problem. A PWM (assumed) charger will just control the duty cycle to output 12V, discarding (100/(27-12)) or 55% of the solar energy. Or, in other words, you have 45% efficiency, for the few hours when the sun shines.

 

You can buy a LM2596-based module from eBay UK for about three quid which will accept up to 35V and output 5V at up to 3A, at 90% efficiency. Connect that between the panel and the LiPo charger (via a fuse, of course).

 

A problem with LiPo batteries (and chargers) is the charging cycle. If the input is wavering around the minimum voltage level (at sunrise, sunset, or a cloudy day), you'll be continually restarting the cycle. Someone with more knowledge will be able to tell you if this is a bad thing. 12V lead-acid/gel batteries are much more amenable to trickle/float charging, but you may not have the space for this.

 

You can't avoid the fact that, with a few days of bad weather, the battery may not last until the sun shines again. For that, you need a larger capacity battery. You store enough water when times are good, so you can drink when times are bad.

 

Last Edited: Sat. Aug 22, 2020 - 03:38 PM
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Thanks

 

Very sorry, i made typing mistake the raw voltage is 21V and not 27V.

 

I am not using a PWM charger, but a Linear charger with a 5V input and 4.2V output. 

 

I have seen the LM2596 modules, but how is this different to the module i am currently using? 

 

With the module i am using its has input voltage of max 24V and 5V output, but output has USB port.

 

So, it also better to use  a 12V battery, as they are better at charging a low voltages compared to Li Poly. I think this makes sense.

I guess this would a battery like  https://www.amazon.co.uk/NP7-12-Rechargeable-Battery-NP9-12-NP6-12/dp/B00SMRQ7KA/ref=sr_1_13?dchild=1&keywords=12v+battery&qid=1598112019&sr=8-13

 

So my solar panel can connect to this battery, maybe using a special charger(in the link below), even trickle charge at lower light levels.  Then i can use the USB port to power my unit and charge the Li-Poly. Would this be a better option?

 

https://www.amazon.co.uk/Fuhuihe-Controller-Intelligent-Overcurrent-Protection/dp/B07H4K6X7N/ref=sr_1_19?dchild=1&keywords=solar+charger+12v&qid=1598112184&quartzVehicle=29-405&replacementKeywords=solar+12v&sr=8-19

 

 

 

 

Thanks

Regards

DJ

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>> I am not using a PWM charger, but a Linear charger with a 5V input and 4.2V output. 

 

You misunderstand. The charge controller you currently have between the panel and LiPo charger is very likely PWM. You don't need this. It is wasting half of the solar energy.

 

You have: Panel->Fuse->PWM charge controller->LiPo charger->battery. 60% efficiency.

Better would be: Panel->Fuse->LM2596 module->LiPo charger->battery. 90% efficiency.

 

If you have the space, a 12V lead-acid/gel battery will give you greater capacity and be more amenable to fluctuations in charge voltage. But you still ideally need a non-PWM charge controller (ideally MPPT), to get optimum efficiency.

 

There are Arduino-based MPPT designs online if you fancy designing your own. They're basically (a) a buck convertor from 21V to 14.4V, (b) a resistor divider to measure the battery voltage, (c) a PWM circuit to control the battery charge voltage between 12V and 14.4V. Still PWM but it discards less.

 

To continue my analogy; you are collecting water to drink, but the pipe to your storage tank is leaking half the water.

 

My example: the water butt at our allotment has a capacity of 250 litres. During the recent heatwave we had to fill it from the standpipe. Then when it rained heavily last week it was overflowing, and still only contained 250l of water :)

 

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djoshi wrote:
Is it possible that we could make a simple capacitor circuit, that accumulates the low power output from the panel, so its not wasted and can provide some charge into the charging of the battery?

Not simple (impedance of the solar panel varies by an order of magnitude)

ALD Energy Harvesting Module & IC Products

ALD EH301A would be marginal for the load (the PCB); half the load would be a better fit.

 

P.S.

djoshi wrote:
... such weather ...
London UK freezes so a typical lithium secondary cell won't work though can be made to work.

Lead-acid (in earlier comments) is an inexpensive fit; nickel electro-chemistry is a fit though more expensive and reduced weight.

 


EH301A Advanced Linear Devices | Mouser

TLI Rechargable (Tadiran Batteries)

 

"Dare to be naïve." - Buckminster Fuller

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djoshi wrote:
So, it also better to use  a 12V battery, as they are better at charging a low voltages compared to Li Poly.
at low temperatures (SLA/gel/AGM versus common Li-poly) though do adjust for London UK insolation (not mid-latitude, sometimes not temperate)

Simplify Small Solar Systems* with Hysteretic Controller | Analog Devices

by Mitchell Lee

[first paragraph]

...

As a simpler alternative to a switching regulator, linear control is feasible in applications up to about 20W.

...

 

...

As a general rule, choose a maximum or “peak” panel current equal to 10× the load current averaged over a 24-hour period, and a battery ampere-hour capacity equal to 100× this same averaged figure. 

...

These relationships were derived for Milpitas, California to give 4 days’ run time on unassisted battery power, with the panel oriented for maximum winter insolation.

[100mA load]

....

 

"Dare to be naïve." - Buckminster Fuller

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Thanks

 

Might be a silly question, but how do you know that module is PWM controller? As the description does mention a buck module 

 

I will order some of these  https://www.amazon.co.uk/LM2596s-Step-Down-Adjustable-Voltage-Regulator/dp/B08CZ9N1M8/ref=sr_1_4?dchild=1&keywords=LM2596&qid=1598130866&s=diy&sr=1-4

 

What the need for the the fuse? Is it if there is short to prevent damage to the panel?  

 

Ideally, i would prefer to use a MPPT but this for a simple test device. Therefore i will use the LM2596.

 

I need something which quick, but once i get some time i might add a MPPT module on future PCB's.

 

 

 

Thanks

Regards

DJ

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Hi 

 

I found that i have also got some of the following LM2596

 

https://www.amazon.co.uk/gp/product/B07XT8V97Y/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

 

 

Thanks

Regards

DJ

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djoshi wrote:
What the need for the the fuse? Is it if there is short to prevent damage to the panel?  

 

Both the battery and solar panel can generate significant current. You need to ensure the wiring can cope with the worst case current or you need to add some form of protection- ie: fuse.

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Thanks

Thanks

Regards

DJ

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As someone who has built and sold solar controllers, there is a lot of mis-information and marketing hype on the interwebs around the term MPPT.   Usually that means some form of buck converter, but not always.

For simple 12v lead acid charging, PWM work very well and is only about 12-15% less efficient then using a buck converter WHEN the battery is fully discharged, and that advantage decreases as the battery charges.  Note: MPPT makes sense when your trying to maximize the ROI for your whole house, grid tie system, and that is the source of much of the confusion.  

 

In the OP case, he has a 12v solar panel, 21v max open circuit in full Sun, and wants to charge a 4.2v li-poly battery, do I have that right? 

The link showing the panel, also shows a charge controller, the question has come up whether that is a PWM or MPPT controller, but the OP has not said if they are using it. (sounds like they are not).

 

For low voltage charging, the OP needs a series diode between the panel and the battery to prevent the battery from discharging into the panel at night, most 12v panels do not have blocking diodes built in, although it may have a bypass diode, which is not the same as a blocking diode.  This component is critical.  

 

So if I have read the OP correctly, they have the following:   12v Solar panel = 24v/5v buck converter = 5v/4.2v linear charger = 4.2v li-poly battery.

The buck converter needs a minimum voltage/current in order to operate, and the panel alone will not guarantee that due to changing Sun shine and day/night cycles.  Also OP has indicated they only have two days of capacity in the current battery.   So I would recommend a couple of changes, OP needs more capacity, use the solar controller that came with the panel (it will also have the needed blocking diode) to a  12v SLA battery to extend capacity to 7 days or more, the rest of the circuit, buck + linear charger should be ok.   Other configurations are possible, including using a solar li-poly charge controller.

 

Let us know what you decide to do, glad to answer solar questions.

 

Jim

 

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Mon. Aug 24, 2020 - 01:20 PM
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Hi Jim

 

Yes that is right, i want to charge a 4.2 V Li Poly battery. 

 

 

Yes the controller that has come with solar panel is not being used, instead i am using  DC-DC module which outputs 5V. But based on a previous comment it seems my module is PWM module and not DC-DC as a LM2596 ? How can you tell if my DC-DC module is PWM?

 

I have ordered 5000 mAh Li-poly battery.

 

So if i was to use the controller which came with the panel, do i simply connect my DC-DC to the load or battery ?

 

What advantage is there using 12V battery, compared to DC-DC to Li Poly battery? Does 12V work much better in low lighting? 

As my panels are 10W, so should  that not  charge my Li Poly batteries? Is there any recommendations for the 12V battery? And how to store them outside?

 

Thanks

 

 

 

 

Thanks

Regards

DJ

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I would be worried about the Li-Poly charger losing its state if its input voltage goes away (bird fly over the solar panel.) Li-Po battery is not beginner-friendly, and not providing reliable power to the charger is probably a critical mistake. Having the solar panel charge a 12V lead-acid could be a workaround for giving reliable power to the Li-Po charger. Charging a lead-acid does not require knowing its history (it is more or less stateless); the charger can lose input power and then start again without degradation.

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djoshi wrote:
Is there any recommendations for the 12V battery?
What you can source locally or regionally.

Reasons : shipping price and cost, entropy

djoshi wrote:
And how to store them outside?
battery box, usually painted steel though sheet aluminum is nice; stainless steel is possible.

 


Steel Enclosures | Missouri Wind and Solar

 

"Dare to be naïve." - Buckminster Fuller

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ron_sutherland wrote:
... (it is more or less stateless)
float voltage is dependent on kind and temperature; '00 Ford F350 has a soft start for the battery charge that's dependent on air temperature.

Charging Information For Lead Acid Batteries – Battery University

 

"Dare to be naïve." - Buckminster Fuller

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Based in UK

Thanks

Regards

DJ

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What would be a good capacity to use for a 12v battery?

Thanks

Regards

DJ

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djoshi wrote:
What would be a good capacity to use for a 12v battery?

 

What's your ratio of sunny days to non-sunny days?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Worst case scenario would be 2 days sunny and 5 days cloudy

Thanks

Regards

DJ

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djoshi wrote:
Worst case scenario would be 2 days sunny and 5 days cloudy

 

Very roughly it feels to me that...

 

...Your existing battery is 2Ahrs and lasts for 2 days so you are using 1Ahr/day...

 

...In a 7 days period you can only charge for 2 days (worst case)...

 

...so it feels to me that a 7Ahr battery will hold enough charge...

 

...and your solar panels needs to be sized so that it can charge that 7Ahr battery in two days.

 

[A 12V 7Ahr SLA is 84Whrs, your panel is 10W so it should be able to charge the battery in 8 hours]

 

Rather handily 7Ahrs is a standard size for an SLA battery and can be easily had from places like Screwfix... https://www.screwfix.com/p/seale...

 

All these are, of course, BOFP calculations, or is that now BON? (Back-Of-Fag-Packet/Back-Of-Napkin?) and ignore all conversion losses and other inefficiencies.

Hopefully Jim ( ki0bk ) will be along shortly to pull my numbers apart!

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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djoshi wrote:
What advantage is there using 12V battery, compared to DC-DC to Li Poly battery? Does 12V work much better in low lighting? 

The Li types are very popular now, they pack a lot of power into small spaces, but have one disadvantage with solar apps in that they prefer not to be float charged, rather they are charged fully and then discharged in cycles. 

So with solar, the Sun comes up, the battery is fully charged and the charging stops (when using a proper Li charger), so now the load discharges the battery even though the Sun power is available. There are ways around that, but not using your simple power modules.

With float charging, the Sun comes up, charges the battery fully, and continues to float fully charged and run the load while the Sun is shining, only when it gets dark does the load draw from the battery.

 

Float charging a Li battery will shorten its life and may cause it to over charge and spontaneously give off fire works! And Li batteries are very hard to extinguish once they catch fire.  Note: some Li batteries have a built in charge/discharge controller that prevents over charging, over discharging to prevent the above disasters. But to rely on that to prevent over charging is still abusing the battery and not a good practice.

 

So bottom line, what you are doing may work ok for a one off, short term project, but is not best practice for a commercial project or a long term project. 

 

Brian Fairchild wrote:
Hopefully Jim ( ki0bk ) will be along shortly to pull my numbers apart!

No, that was very good!  I would only add that with fixed (i.e. non-tracking) panels, you only get about 4 hrs of good charging a day, a couple of hours either side of local noon time, out of that window of time the power output from the panel drops off quickly.

 

 

 

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Here is an example of a Li-Poly solar charger sold by sparkfun: https://www.sparkfun.com/product...

This may not be the size charge controller you need for you project, but shows what you should be looking for.

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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ki0bk wrote:
Float charging a Li battery will shorten its life ...
Following is a shunt charger though there's a dissipation issue.

LTC4070 Li-Ion/Polymer Shunt Battery Charger System | Analog Devices

...

  • 1% Float Voltage Accuracy Over Full Temperature and Shunt Current Range
  • 50mA Maximum Internal Shunt Current (500mA with External PFET)
  • Pin Selectable Float Voltage Options: 4.0V, 4.1V, 4.2V

...

LTC4071 is 50mA max.

These lack a 0C condition.

 

"Dare to be naïve." - Buckminster Fuller

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Great.

 

I will do the following for now

 

Solar Panel --> PWM charger(included with the panel) --> 12V Battery --> DC-DC--> Li-Poly Chager --> Li-Poly Battery--> System.

 

I will try to order recommended 12v battery, but if i want to use a car battery with a higher capacity would this be an issue or anything i must keep in mind?

 

Is there any enclosure i can places these batteries in for outdoor usage?  

 

 

Thanks

Regards

DJ

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You haven't said whether this is a commercial or hobby project.

 

I got a 70Ah car battery for free from our household recycling centre (aka tip) that has performed perfectly for over a year. It happily runs lights, pumps, USB charging, intruder detection, mifi router, etc. If it fails I'll ask them for another ;)

 

It sits outside the shed sheltered by a plywood cover. It doesn't need any more protection than it would have under a car bonnet/hood.

 

I assume your LiPo battery charger can't accept a c. 12V input. If it can, you don't need the DC-DC converter.

 

If fact, why have the LiPo battery at all ? Just put a buck convertor between the 12V battery and the load, along with any circuit protection you feel is advisable.

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If you could hold off charging the LiPo until the SLA enters float, then charge the LiPo sort of as a diversion load for the SLA that would make a lot of sense. Once the SLA is outside the float range, then stop charging the LiPo.  That way, the SLA is sort of like a middle man that keeps things simple. Don't draw down the SLA. Just keep it fully charged (within 80% of capacity), and the LiPo will start charging soon after the sun is up.

 

Update: as an FYI if you can keep a lead-acid within the upper 80% of its depth of discharge it can last a very long time, many thousands of cycles, but if you take it to 50% discharge it will not do that for many cycles (hundreds), and down below 20% will cause significant degradation with each cycle. 

Last Edited: Tue. Aug 25, 2020 - 10:13 PM
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Most cheap PWM charge controllers have a 'load' output that is switched off if the 12V battery drops below a certain voltage. i.e. you don't draw directly from the 12V battery, but from a controlled 'load' output that protects the battery from deep discharge. So called 'leisure' batteries are more amenable to deep discharge than car batteries.

 

 

 

 

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obdevel wrote:
'leisure' batteries

 

Our labels say deep cycle battery. The cutoff I have seen is around 11V, but that is way too far down if you want a long life.

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I’d suggest a LiFePo4 battery. Smaller and lighter than a lead acid and not as nasty as a LiPo. Can be got in the same form factor as a SLA.

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This is a commercial project.

Thanks

Regards

DJ

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on a cloudy day there is not much charge ...Is there a better panel to use for such weather? 

If you create one, you probably won't be on the freaks anymore--retire to your own island, large yacht, or penhouse suites. 

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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He'll be able to build the penthouse suite on the island, and use the large yacht to get to and from it.

 

Neil

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Hi, I have added a solar panel, with its controller. Do I still need to add a diode even if I have the controller?

Thanks

Regards

DJ

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Most "good" controllers will have a means of preventing drainage of the battery during non-charging periods aka night.

 

Ross McKenzie ValuSoft Melbourne Australia

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You might want to add a second battery... or ditch the Lipo connect the Solar system to a 12V 5Ah battery.

I asume the converter will switch the power to the battery off when it is full and will always ensure maximum loading current when not, So most efficient use of the solar power developed by the PV cell.

After that you can make 5V from 12V using an SMPS or even directly go to the working voltage of your system and skip the LiPo all together.

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At the moment i am using the controller which has come with solar cell, which i can see is not efficient or any good.

 

If i need to connect two solar panels in parallel, so i need to keep anything in mind? I am aware i need to add a series diode on both of them

Thanks

Regards

DJ

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What have you connected to the controller?

The controller will take the power from the PV cell and convert that to 13,8V ( most likely) with as much amp as it can.

If you only have a couple of uF attached to the secondary side the controller will fill them up in no time and be done with it. You drain them very fast with your charging....

Now as those controllers are meant to charge batteries they are not really fast in detecting. So you will probably see an enormous delta voltage on your small buffer capacitors. 

That indeed will be very inefficient. Hence my suggestion to add a small 12V battery that can act as a real buffer and will make the PV controller more happy, give better efficiency and thus faster charging of the LiPo cell.

 

Keep in mind that probably you can only charge the LiPo cell with 2Amp at 4,2V as to prevent it from premature failure or degeneration over time. Check the specification of the cell by the way. We have had manufacturers suggesting cells that could only be charged with 0.5C max peak..... else they might degenerate early.

 

Have you checked real time during a cloudy day the controller?

Measure both voltage and current on both the primary and secondary side at exactly the same time?

So best take 4 meters put them together and take a couple of photographs.

Then use the measured data to see how efficient the controller actually is.

 

 

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My Li Poly is get charged at 0.8 max.

I will do the measurements as mentioned.

If I need to connect two solar panels, do I simple connect them in parallel?

Thanks

Regards

DJ

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I have added high current Schottky diodes in series with the panels I have put in parallel. Take a high current version to minimize the drop. I suggest getting a 3Amp or more that should ensure that they do not drop to much( reducing the efficiency at lower powers)

 

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Will add them next time i am at the location

 

I simple joined both solar panels together in parallel before inputting it into the controller.

 

 

Thanks

Regards

DJ

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If you're using the usual MC4 cables and connectors, there are plenty of inline diodes, fuse holders, junction boxes, etc on eBay UK. Makes maintenance easier in the long run.

 

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djoshi wrote:
I simple joined both solar panels together in parallel before inputting it into the controller.

both panels need series "blocking" diodes to prevent backfeed into the other which can damage the panels.

bypass diode (the ones around the panes, are only needed when you put panels in series (to raise the voltage output of the array), some panels have these built in.

Blocking diodes are needed when two or more panels are paralleled to increase the current of the array.

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Do solar panels light up if they get powered backwards? Serious question...

 

Neil

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barnacle wrote:
Do solar panels light up if they get powered backwards? Serious question...

Not that I know of, but they can get hot!

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Thanks,

 

I guess this issue would arise if the battery is not required to be charged and the energy has no other place for discharge?

Thanks

Regards

DJ

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barnacle wrote:
Do solar panels light up if they get powered backwards? Serious question...

 

A red LED will generate a voltage when sunlight is on it; I have used them as a light sensor. If a solar panel did produce photons (rather than heat), they would be in the IR spectrum like an IR LED, which I think is done with silicon p-n junction(s). But the voltage drop suggests three p-n junctions are involved, so there is probably some magic needed to get photons rather than heat.

 

update: wrong IR led linked, removed

Last Edited: Thu. Sep 10, 2020 - 03:50 AM
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djoshi wrote:

Thanks,

 

I guess this issue would arise if the battery is not required to be charged and the energy has no other place for discharge?

Nope, it will also be an issue if 1 panel is 'lit'  and the other not. The lit panel will backfed the non lit as it has a much higher working voltage.

 

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Great, at the moment ,both are outputting the same voltage. Next time i am there i will add the location i will add the diodes.

Thanks

Regards

DJ

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