Sunflower: solar power manager 9v/12v/18v

Hello All, I purchased this product to power a logger that I have as well as various sensors.
I was hoping to use the 3.3V output for my logger but the logger consumes 10uA - Remedy is to use the USB out and get a Pololu stepdown to to provide the constant power.
I have 5V 100mA supply on my logger, which I use to power sensors - but when I exceed 100mA I was thinking of using the 5V out on the sunflower - with a seperate relay - but is it possible that this would be asleep?
Next - I was going to use the 12V out to be available to 1. drive sensors when i log as well as continuously drive a pump and sensor that cant be shut down,
The question is if my constant load for pump and sensor will the Sunflower think nothing is connected? and will it be available for the other sensor when I switch it in

Hi Henk

Ten millionths of 1A or 0.00001A ??? How much lower would you like it to be. Compare this to 100mA which is 0.1A.
Cheers Bob

This device arrived today, have been going through a number of tests for another post on the forum.

The Sunflower is designed to charge a LiPo battery from a Solar Panel or via a USB connection. It then uses the battery to provides 5V, 3V3, 9/12V outputs at 1.5A, 1.0A, 0.5A respectively. The Core Electronica title is a misnomer, the 9V/12V/18V refer to the type of Solar Panel connected.

As long as the battery is connected and charged, power will be available from the Sunflower, it will not go to sleep. The green LEDs consume a couple of 100uA anyway, so there is load on the battery even when nothing is connected.

The 3V3 output can provide up to 1A, in my testing it exceeded this easily. Only tested briefly, unsure if more than 1A would cause damage over time. Anyway in use I will keep to the manufactures limits.
The 5V output easily provided more than the 1.5A it is rated to.
The 12V output easily provided more than the 0.5A it is rated to.

The testing I am doing is to prove the Sunflower is performing to manufacturers specifications. The other forum post was about a Sunflower that seemed not to work.

The Sunflower should work well for your logger. Just be sure to use it as designed.
The USB in & Solar in are to charge a LiPo, not to power the outputs. It needs to have a LiPo connected to work properly.


EDIT: If you are running something continuously, the battery charging might be a problem if the pump and sensor are drawing more than the charging current. Yet to test that situation.

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Hi James

A little bit of Math (and testing) will in show that the battery will indeed go flat eventually. The charging system must provide enough POWER to run the load AND replenish the battery after a zero charge period like at night if using solar alone.
Cheers Bob

1 Like . I am glad to hear the exclamation @Robert93820. This logger developed in Australia draws 7-10uA, while counting pulses, its will draw about 5mA for 50ms every 15 minutes to totalise the pulses and resume sleep. Once per day it will wake for 1-2 minutes and transfer its data over cellular using 80mA (both dependant on Signal). This version has the 19AH battery, so its warranted for 5 years.

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Thank you @James46717. I am glad to hear that, on the bench for 3 days with nothing connected, I note the same. I also note the PCB draws about 2.5mA, with no Solar.
All you’ve said is good and fine and what we intend doing.

Your last comment. If the battery is full and in full sunlight, the PCB will be consuming my continuous current (Sorry didn’t mention - about 25mA at 12V) plus self discharge and PCB draw 2.5mA plus a bit of battery self discharge. Were you concerned that we could be up in the 1-2 A continuous?

Is a rough calculation that the 20AH battery I chose will survive about a month of zero sun?

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Yes, I was concerned that the Sunflower may think nothing is attached, but this is sorted later in the discussion.

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You could test the drain on the battery with no solar connected to get accurate figures. But from what you have provided I think a 20AH would not last a month with no sun. The 25mA at 12V would equate to 3 to 4 times that at 3.7V. (rough calculation) The board drain is significant and most of it would be by the 3 small LEDs. The logger drain would eventually drain the battery but it is pretty small compared to the constant board and pump drain.

Yes. If the drain is higher than what the solar panel can provide then the battery would not charge. But the battery and solar would contribute to the current supply meaning the battery would last longer.

Side note: I built a clock temperature sensor. Micro wakes every 30s and records the temperature on a SD card. I calculated the battery should last about 6 months, actual it lasts 4 to 5 months. Nothing like real world figures to show what will happen.


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OK thank you, " If the drain is higher than what the solar panel can provide then the battery would not charge" this is what occurs when there is no sun, so it makes sense. I will do some real world testing.

Principle aim of this whole exercise is to reduce the weight of my package that currently uses Lead acid batteries.

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last comment. The boot button, is it likely to only be needed on battery change? I am wondering if I need to regularly boot with my logger, so that we don’t ever have to physically visit except when a battery is end of life. It looks like it only has 2 terminals so not impossible to solder

The following is from the DFRobot web page.
From this I gather the “boot” button is used to activate the protection IC and would only be needed when the unit has been turned off or the battery replaced. I use LiPOs that have built in protection ICs, such as those sold by Core Electronics. The Sunflower protection would just be an extra level for me.

I intend to use the Sunflower as a Bench Top power supply while projects are in the development and testing phase. The voltage and current available is more than I need for most of my projects. I have a 20W Solar Panel on the roof to recharge the LiPO. The LiPO & Solar Panel will be disconnected when not in use and the Solar Panel connected only when necessary to charge the LiPO.


Build a solar powered system

  • Connect the Li battery to BAT IN.
  • Connect the solar panel to SOLAR IN.
  • Connect USB OUT of the module to Arduino with USB cable.
  • Switch one bit of the MPPT SET to ON (others remain OFF) according to the nominal (maximum power point) voltage of the solar panel.
  • Connect USB OUT of the module to Arduino with USB cable.
  • Connect all the VCC and GND pins of the peripherals to the regulated power supply headers or terminals according to the nominal voltage.
  • Press the BOOT bottom for once to activate the the Li battery protection IC.

EDIT: My guess is; the “boot” button has been included by DFRobot probably due to the following note in the datasheet. (the only one I could find in English, others are in Chinese)

From the schematic.


This board arrived a few days ago. It worked perfectly; as per the specification by DFRobot. I was unable to generate the same conditions as the original post.

It was tested with a 20W Solar Panel and 2000mAH LiPO battery. The board will work with just the Solar Panel or the battery or both. Solar output depends on the level of sunlight.

The quiescent current is around 2.7mA, meaning the battery will drain in about a month with no charge.

The protection circuit worked well; overloading caused it to disconnect the battery. Removing the overload condition and pressing the ‘Boot’ button reset it. Unsure if it is necessary to press the ‘Boot’ button when installing a new battery. Pressing or not pressing it when connecting and reconnecting the battery didn’t change anything, the overload cut-out work either way.

The protection circuit activated a little over the rated current for the 5V / 12V supplies. Tested separately, did not test together.

With a Solar Panel connected in full sun and a full battery the Sunflower will output much more than the rated amount. The Solar Panel will output 1.16A at the MPPT of 17.4V. The Sunflower circuit is designed to supply up to 2A.

There was an interesting side effect.
I have a small digital radio on the bench, which could probably do with a better antenna.
The Sunflower switch mode regulator must generate a significant EMI field. The radio cut in and out when testing with high current levels. Something to consider if using it to power a RF system. Probably shielding it would be enough.

I put the board in a case and will use it to power small projects in the development phase. Having 3 supplies is much better than what I currently have. The Solar will remain disconnected until the battery needs a charge. The battery has a switch for when it will not be used for a while.

A concern I have with these kind of systems is trickle charge. LiPO batteries are not designed to be trickle charged. They last longer if discharged to 30% and recharged to at least 80%. This applies to mobile phones as well. A Galaxy S5 I had lasted 5 years before the battery began to show signs of not charging fully. Friends have experienced this in a little over a year, they had been putting their phone on charge every night. Anyway, a pet concern I have.


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