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Adafruit USB Li-Ion/LiPoly Charger - v1.2
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Apr 03, 2019 9:58 am

okay thanks @Mike. Is there mention of the fact that the Adafruit's charger controller has set the voltage VREG to be 4.2? For references purposes.

Another challenge that i am having is with the Charge/Charge complete status LEDs (and as such the STAT pins) of the charge controller:
When my project is ON (the charger controller load is connected to the project via a switch) and i apply a voltage to the DC+ and DC- inputs of the charger controller to charge the battery, the LED to indicate that the battery is charging is lit immediately (great!). With the project ON, however , the charger controller NEVER indicates a charge complete status. Now my project only draws 70mA at most and the supply current of this charger controller is 200mA so I am sure the current consumption is not the problem. It seems as if charging is locked in the CHARGE state even after the battery is fully charged. The reason i say this is because if after a sufficient time has passed with charger charging the battery and simultaneously powering the project (the project is ON) then if i switch OFF the project, the charge complete LED on the charger controller INSTANTLY lights up.
I don't have this indication issue when charging the battery with the project switched off the entire time. Is this normal? is there a way to work around it.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Fri Apr 05, 2019 12:53 am

Alli wrote:okay thanks @Mike. Is there mention of the fact that the Adafruit's charger controller has set the voltage VREG to be 4.2? For references purposes.

Not particularly. It's an inherent part of being used with LiPos whose full-charge voltage is 4.2aV.


Alli wrote:With the project ON, however , the charger controller NEVER indicates a charge complete status. Now my project only draws 70mA at most and the supply current of this charger controller is 200mA so I am sure the current consumption is not the problem.

The MCP738x series of LiPo chargers only terminate a charge cycle when the current flowing out through the VBAT pin drops to 5% of the constant-current level. If your constant-current level is 10mA, it will have to drop below 10mA.

If you have a 70mA load connected to the VBAT pin while the LiPo is charging, that will never happen. In effect, the load always draws 70mA from the LiPo and the LiPo always draws at least 70mA from the MCP73833.

The power system design for the Feather connects the 5V USB line directly to the input of the 3.3V regulator, and connects the LiPo to the regulator's input through a diode. When you plug in a USB cable, the diode reverse-biases and there's no load on the LiPo. That way the MCP7383x can do a complete charge cycle if you leave the USB cable plugged in long enough.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Fri Apr 05, 2019 3:20 am

The MCP738x series of LiPo chargers only terminate a charge cycle when the current flowing out through the VBAT pin drops to 5% of the constant-current level. If your constant-current level is 10mA, it will have to drop below 10mA.

ah, i see. I did not realize. Well at this late stage in the design adding new components will not be possible. I will try monitoring the battery voltage and with the use counters and timers to see if i can work around this problem. Thanks Mike. Again, is there mention of the 10mA threshold for STAT pin changes anywhere on the adafruit site or did i miss mention of this in the manual, for reference purposes.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Fri Apr 05, 2019 4:42 am

It isn't in any of our documentation, but it's in the MCP73833 datasheet.. page 4, 'Charge Termination' lists the percentages for the different variants of the device.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Fri Apr 05, 2019 6:36 am

Okay I see. Thanks alot.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Jul 03, 2019 10:57 am

Hello @adafruit_support_mike

Another quick question. Can I charge my luthium ion battery and power my load with a 1 Watt solar panel (which is rated at 5V with a maximum current draw of 200mA) through this charger controller ? Does the charger controller require or does it have the necessary protection circuitry in order to operate with a solar panel as the power source ? Can I connect the output terminals of the solar oanel directly to the input of the charger controller ? Thanks in advance Mike.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Wed Jul 03, 2019 2:24 pm

The basic charger doesn’t work well with solar panels. Solar power is notoriously uneven, and LiPos want a nice, reliable charging supply.

What you want is the Solar LiPo Charger:

https://www.adafruit.com/product/390

It uses the solar panel efficiently while charging a LiPo. The tutorial explains how it works, and why a solar panel isn’t very efficient at charging LiPos:

https://learn.adafruit.com/usb-dc-and-s ... y-charger/

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Jul 03, 2019 3:47 pm

Okay thanks alot. I will take a look at those links.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sun Jul 14, 2019 5:07 pm

Hello Mike

Noticing something strange. As you recall you mentioned that the charge controller will never change from a charge status to a charge complete status when the charge controller is powering the load and charging the battery? i found this to be true many times before. However lately this does not seem to be the case. The charger controller is charging reaching full charge then changing status and after the voltage of the battery drops its changes status and starts charging again. i have been logging the battery voltage and so i was able to verify this aside from visually seeing the LEDs on the charger controller changing. Have i somehow damaged my charger controller?

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Mon Jul 15, 2019 12:33 am

What voltage are you seeing on the LiPo?

If it’s reaching 4.2V, the charger might be able to complete a charge cycle. The solar panel will have to put out enough current to power the load and charge the LiPo, but that’s physically possible.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Mon Jul 15, 2019 2:15 am

Hello Mike.
Yes it is reaching 4.2V as it was reaching 4.2V before. I haven't implemented the solar panel addition as yet. I think it's reaching a complete status due to the fact that I'm cycling my hardware on a power saving mode. The current consumption drop in the load seems to be significant enough to allow the status indicators to change. I was only abke to confirm this a few moments. Sorry, i should have actually thought to check this before posting to the forum. Thanks Mike.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Fri Jul 19, 2019 4:30 am

Hello Mike

I read through the tutorial and also had a look at the solar charger you have available. Keeping these in mind, and in a bid to be avoid adding another charger controller in conjunction with the adafruit charger controller i already have, i have the following question:
The real issue with charging the li-ion battery with the adafruit USB Li-ion charger V1.2 using a solar panel is that a stable input voltage, above the thresholds specified in the datasheet, is required and a solar panel's voltage varies with light intensity which will result in cycling of the charger controller. If i were to use a switch mode voltage regular where the output voltage will be stabilized to for e.g. 5V, but the current produced by the panel were to be less than what is needed by the charger controller to charge the battery at any given time, will this Li-ion/Lipoly Charger v1.2 charger controller still charge the battery with the lower available current?
From my understanding the solar charger you mentioned in the link basically maintains the voltage applied to the battery and draws as much current as available without throttling that voltage. I am trying to achieve similar results without needed to buy another charger controller if i can achieve this results alternately.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Sat Jul 20, 2019 7:55 pm

Connecting a switching controller to a solar panel would create a whole new category of problems.

Switching converters are constant-power devices: to get 1W out, you have to send at least 1W in. In practice no real converter is 100% efficient, so the power coming out will always be less than the power you send in.

Boost converters need to draw bursts of relatively high current to charge the inductor's magnetic field, and it's unlikely that a solar panel will be able to provide that current efficiently. If you try to draw too much current from a solar panel, its output voltage falls dramatically, so instead of getting 1W of input you might only get 100mW. The converter's output voltage will be too low for a LiPo charger, and the instability will be worse than trying to power the charger from a solar panel alone.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Mon Jul 22, 2019 7:47 am

Oh okay i see, thanks for the advice.

A comment/concern on a previous comment i made:

Alli wrote:Hello Mike.
Yes it is reaching 4.2V as it was reaching 4.2V before. I haven't implemented the solar panel addition as yet. I think it's reaching a complete status due to the fact that I'm cycling my hardware on a power saving mode. The current consumption drop in the load seems to be significant enough to allow the status indicators to change. I was only abke to confirm this a few moments. Sorry, i should have actually thought to check this before posting to the forum. Thanks Mike.


Now since the charger controller is cycling in/out of power saving mode, the battery reaches full charge status and the batteries charge is not kept at the maximum i.e. it appears that the battery's voltage is not maintained at the maximum. The battery voltage drops to approx 4.09V, after reaching the 4.2V maximum, before the battery is recharged by the charger controller. When my hardware does not cycle in/out of power save mode i.e. the current draw of my hardware is not reduced low enough for the charger controller's charge status LED to change to fully charged, than the battery continues to stay topped up at 4.2V. My concern is if the battery is being overcharged when the charge status is not allowed to change to charge complete? And also if it is normal for the charger controller to behave in the manner described above or have i damaged my charger controller?

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Mon Jul 22, 2019 12:24 pm

LiPo chargers have entire sections devoted to making sure they don’t overcharge a cell.

The full-charge voltage limit is a big part of that protection. It’s physically impossible for a 4.2V source to send more than a certain amount of current into a LiPo whose plate voltage is also 4.2V. Zero voltage difference implies infinite resistance.

A LiPo that’s charging may have 4.2V in the polymer directly in contact with the plates, but the polymer farther between the plates will still be at a lower voltage. As charge diffuses from the plates farther into the polymer, the plate voltage will drop slightly. That’s what keeps a LiPo charging during the constant-current phase, abut the amount of current that flows into the LiPo decreases until it’s only a few milliamps. Chargers define the point where the current flowing into the LiPo falls to 1% of the constant-current level as ‘fully charged’.

Even if a LiPo charger continues to provide current to the LiPo after that point, it can’t overcharge the LiPo. It just finds the amount of current necessary to replace the LiPo’s self-discharge current.

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