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Feather or solar charger, which batt port?
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Feather or solar charger, which batt port?

by IoTAll on Wed Jul 24, 2019 4:14 am

Hi,

I have a project using a feather where I have a Lipo battery connected to the battery port of the feather.

I would like to have the battery charged by the Solar charger V2 connected to a solar panel.

I am thinking about connecting the batt/ground port of the solar charger to the batt/ground pins of the feather with 2 wires.

I also have the TPL5111 breakout connected to the batt/ground pin on the feather.

Would this work?

Is there a preferred place to connect the battery? On the feather batt port or on the solar charger batt port? Is there an impact on the stability of the power for the feather if you put it at one place or the other?

Thank you!

IoTAll
 
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Re: Feather or solar charger, which batt port?

by adafruit_support_mike on Sun Jul 28, 2019 3:13 pm

Connect the TPL5110’s input to the Sola Charger’s BAT port, and its output to the Feather’s BAT and GND pins.

It’s also possible to use the Solar Charger’s LOAD port and the Feather’s USB and GND pins, but that can be risky. The Solar Charger passes power straight to its LOAD port while the panel is active, and under high-sun conditions, the output on LOAD can reach 6V.

That’s enough to damage the Feather’s LiPo charger if you connect power to the BAT pin, and pushes the limits of the charger’s maximum input when connected to the USB pin.

Using the charger’s BAT port is safer, but a little less energy efficient. Any power the Feather doesn’t use or the LiPo doesn’t absorb while charging is wasted.

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Re: Feather or solar charger, which batt port?

by IoTAll on Sun Jul 28, 2019 3:37 pm

Ok thank you very much for your answer!

I will connect then the Lipo battery pins, TPL5111 vcc/gnd pins, the solar charger batt/gnd pins and the feather batt/gnd pins together then to be safe.

Is there any difference if i physically connect the Lipo battery to the solar charger battery jst port or to the feather battery port?

Thank you!

IoTAll
 
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Re: Feather or solar charger, which batt port?

by adafruit_support_mike on Mon Jul 29, 2019 1:48 pm

You’ll want to connect it to the Solar Charger. That way the LiPo can charge while the TPL5110 is sleeping and power to the Feather is cut off.

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Re: Feather or solar charger, which batt port?

by IoTAll on Tue Jul 30, 2019 3:16 am

Ok thanks and in the case of TPL5111 that I am using, utilising the enable pin?

Does it have any incidence at all if the Lipo battery is connected to the solar charger or the feather batt/ground pins?

As I see it is "just" more length of wire at one place or another.

Thanks!

IoTAll
 
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Re: Feather or solar charger, which batt port?

by adafruit_support_mike on Tue Jul 30, 2019 1:37 pm

Sorry, my mistake. I read ‘TPL5110’ instead of -111.

If you’re only controlling the Feather’s EN pin, you can connect the LiPo to either the Feather or the Charger. You’re right that the only difference is a short run of wire.

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Re: Feather or solar charger, which batt port?

by IoTAll on Tue Jul 30, 2019 2:20 pm

No worries thanks a lot! Great then.

By curiosity is there any difference for the project to run on a battery which has wires of let say 5cm Vs wires that are 10cm long? Any impact at all?

Thanks!!

IoTAll
 
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Re: Feather or solar charger, which batt port?

by adafruit_support_mike on Wed Jul 31, 2019 11:27 am

There is, but it’s usually small enough to ignore.

All wire has resistance, and resistance is a property of matter. Making a wire twice as long doubles its resistance. 22-gauge wire’s resistance is about 56mOhm per meter, so a 10cm piece would have a resistance of 5.6mOhm and a 5cm wire would be 2.8mOhm.

To put that in context, a red LED running at 1.7V and 20mA uses 34mW of power. A 10cm 22-gauge cable carrying that power would have a voltage drop of about 112uV on each wire (positive and GND), and would dissipate about 2.25uW per wire. A 5cm cable would drop about 56uV per wire, and dissipate about 1.12uW per wire. The values aren’t even large enough to be serious rounding errors in the power calculation for the LED.

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Re: Feather or solar charger, which batt port?

by IoTAll on Mon Aug 19, 2019 1:51 pm

Ok clear thanks a lot!

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