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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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