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Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN and Bl
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Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN and Bl

by phillip_kujawa on Thu Nov 14, 2019 12:56 pm

Hello Guys,

I have an issue where I have lots of bright sunlight but my adafruit solar charger is blinking slowly. I have a 2500 mAh battery connected to the MCP73871 chip. When the battery is dead the powerboost 1000 does not charge my phone. It will cycle charge on and charge off when I plug my phone in. My understanding is that if the voltage drops below a certain threshold the solar charger (MCP73871) will load balance and not charge the battery to avoid damage.

Did I get a defective board?

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by adafruit_support_bill on Thu Nov 14, 2019 1:13 pm

If you disconnect the load, is the charge light steady?

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by phillip_kujawa on Thu Nov 14, 2019 1:42 pm

adafruit_support_bill wrote:If you disconnect the load, is the charge light steady?


No it still flashes even with the powerboost 1000 disconnected.

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by adafruit_support_bill on Thu Nov 14, 2019 2:00 pm

Please post photos showing your soldering and connections to the board.

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by phillip_kujawa on Thu Nov 14, 2019 4:20 pm

adafruit_support_bill wrote:Please post photos showing your soldering and connections to the board.


Here is the photo. I only soldered on the cap
f0feb412-8de0-468d-ad36-7947db5adad2.jpg
f0feb412-8de0-468d-ad36-7947db5adad2.jpg (77.91 KiB) Viewed 243 times


3763807d-52ac-4153-bf9f-d55437922952.jpg
3763807d-52ac-4153-bf9f-d55437922952.jpg (105.39 KiB) Viewed 243 times

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by adafruit_support_bill on Thu Nov 14, 2019 4:46 pm

What solar panel are you using? What voltage do you measure between the capacitor leads when the panel is in full sun?

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by gadgeteer on Wed Mar 25, 2020 10:27 pm

I have the same behavior also, with nothing connected to the solar charger except the solar panel. I added the 4700 uf electrolytic, and it is in the right way around. Under a strong desk light, the charge and power lights flash simultaneously, flashing faster as the light intensity increases. Is this normal behavior? The panel output voltage reaches about 4.5 4.75 volts. Plugging in the battery slows the rate of flashing and lowers the panel output voltage, as would be expected.. I have yet to try it out in strong sunlight, it's been raining the last couple of days. When hooked the board up to USB power, alone, the lights are steady.

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by adafruit_support_bill on Thu Mar 26, 2020 5:27 am

Under a strong desk light, the charge and power lights flash simultaneously, flashing faster as the light intensity increases. Is this normal behavior?

Yes. That is normal. Under full sun your panel output should increase to the point where it can charge continuously.

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by gadgeteer on Thu Mar 26, 2020 2:36 pm

Thanks for the fast response!

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by toby380 on Mon Sep 07, 2020 4:00 pm

Hi guys,

Sorry if this revives an old thread. I've recently been setting up a 6V 2W solar panel (Prod ID:200) with this charging board and have seen the same behaviour. I've gone through the data sheet and from what I understand, the charging board operates as follows when it starts a charge cycle:
1) Check the supply voltage to make sure its above a minimum level, if not then the board goes into Shutdown mode
2) Check the battery voltage
If the bat voltage is higher then the regulated voltage + 100mV then go into Standby mode
If the bat voltage is below a pre determined threshold voltage then go into Preconditioning mode (trickle charge)
If the bat voltage is above the pre determined threshold voltage (but below the regulated voltage) then go into Fast charge mode

I think what's happening is, the board is checking the supply voltage and seeing approx 6V from the panel and going into either preconditioning mode or fast charge mode. But when the board tries to draw the charging current (Approx 500 mA in fast charge and 50 mA in preconditioning) the panel can't supply it because the light level isn't generating enough current and the board shuts down, only to immediately restart and try the same thing again.

If this is correct then it's a bit confusing, as the board describes itself as optimised for solar panels. It's my understanding that solar panels are more or less constant voltage, so when the charger board checks the power levels, won't it almost always see a "good" supply, even if it can't power anything. So should we be checking the supply current of the solar panel as well as the voltage?

And if not then that raises the two follow on questions:
1) Is it ok for the chip to be constantly power cycling trying to charge batteries? In a bad case scenario (winter/overcast conditions) this could go on for a while.
2) Might this be bad for the battery to see charge current (albeit very small amounts) at a frequency rather than constant supply?

Thanks for getting through this long ramble!

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Re: Solar Lithium Ion/Polymer charger V2 - Blinking DC-IN an

by adafruit_support_bill on Mon Sep 07, 2020 4:42 pm

That is normal behavior and is not a problem. In marginal lighting conditions, the panel will produce less power and will not be able to generate enough current at a voltage sufficient for continuous charging of the LiPo. So charging stops and the panel output is used to charge up the large capacitor on the board. When the capacitor is sufficiently charged, the stored energy is used to incrementally charge the LiPo. Once the capacitor is discharged, the cycle starts again.

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Please be positive and constructive with your questions and comments.