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Adafruit USB Li-Ion/LiPoly Charger - v1.2
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

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

by Alli on Mon Jul 22, 2019 1:10 pm

So are you are saying is that when the battery is fully charged by the charger controller and the voltage is measured to be below 4.2V, the battery is still fully charged ?
I see the charger controller indicate a charge complete status and thereafter a few minutes (approx 30 mins) the battery voltage drops to 4.09V and the charger controlller's charge status changes to 'charging' and then reaches complete charge etc. This only happens when my hardware is cycling in and out of power save mode. When the hardware's current draw is maintained i.e. no power save mode cycling, then the charger controller's charge indication remains on charging and the voltage of the battery remains fixed at the maximum voltage i.e. 4.2V. With power save cycling, it seems as if the battery is reaching fully charged status and then the charger controller is cutting the charging process off and the battery is feeding into the load in spite of the fact that the charger is connected to charger controller?

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

by adafruit_support_mike on Mon Jul 22, 2019 10:06 pm

Alli wrote:So are you are saying is that when the battery is fully charged by the charger controller and the voltage is measured to be below 4.2V, the battery is still fully charged ?

The LiPo won't be fully charged when the cell voltage is less than 4.2V, but another part of the overcharge-protection circuit lets the LiPo discharge slightly before starting another charge cycle.

You mentioned to voltage dropping to about 4.09V, which is about where a new charging cycle would start. The cycle wouldn't last long, but would take the LiPo back to 4.2V.

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

by Alli on Thu Aug 01, 2019 6:48 am

The LiPo won't be fully charged when the cell voltage is less than 4.2V, but another part of the overcharge-protection circuit lets the LiPo discharge slightly before starting another charge cycle.

You mentioned to voltage dropping to about 4.09V, which is about where a new charging cycle would start. The cycle wouldn't last long, but would take the LiPo back to 4.2V.



This is not the case when the hardware is not cycled in/out of power save mode. It doesn't allow that drop but keeps the voltage at 4.2V. This is normal?

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

by adafruit_support_mike on Fri Aug 02, 2019 12:04 am

If you have a continuous current load on the LiPo, and that load is more than 1% of the constant-current charging level, the charger won't be able to terminate its charging cycle.

The charger will provide enough current to take the LiPo to 4.2V, then will hold the voltage at 4.2V while it provides all the current necessary to run the load.

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

by Alli on Fri Aug 02, 2019 5:17 am

Thanks Mike

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

by Alli on Tue Aug 04, 2020 9:57 am

Hello @Mike. I trust you are well. I would like to expand the capabilities of my project and this will require a little bump up in power. I would to know if you have an alternative lithium charger to the Adafruit USB Li-Ion/LiPoly Charger - v1.2 which is capable of charging 2 x lithium ion cells and whilst charging those cells, also able to deliver power to the load the way that the Adafruit USB Li-Ion/LiPoly Charger - v1.2 does. I noticed you had a USB/DC Lithium Polymer battery charger 5-12V - 3.7/4.2v which has been discontinued unfortunately. Do you have a device like this?

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

by adafruit_support_mike on Mon Aug 10, 2020 1:27 am

It depends on what you mean by 2x cells.

There are two ways to combine a pair of cells in any battery: in series, making what's called a '2S' battery, or in parallel, making a '2P' battery. You can also buy combined versions, like an 11.1V 3S-2P battery, with three pairs of parallal cells in series.

We only carry 1S chargers, and I strongly suggest against trying to make a 2P battery from individual cells selected at random. It's easy for those to explode.

The problem comes from one of the big advantages of lithium chemistries: they have low internal resistance.

Every battery can be modeled as a perfect voltage in series with a resistor. As you draw more current from the battery, the voltage across the resistor increases and the output voltage seen by the load falls. For batteries with high internal resistance (9V batteries and coin cells), drawing a lot of current can create more than 1V of voltage drop. Batteries with low internal resistance like lithium only lose a small amount of voltage under heavy current loads.

No two cells have exactly the same voltage though, so the model for a pair of lithium cells in parallel is two perfect (but different) voltages with a pair of low-value resistors between them. If both cells have an internal resistance of 50mOhm, a voltage mismatch of 100mV will make 1A flow from the higher voltage to the lower one.

Lithium chemistries really don't like to see that kind of back-power. Their correct operating range is just below the 'about to catch fire' point, so exposing them to the kind of backflow that comes from using a mismatched pair in parallel just makes it a question of when things will go bad.

The only cost-effective way to make a safe nS or nP LiPo pack is to select cells from the same production lot whose test results shows nearly identical charge and discharge behavior. Those get welded together and spend their whole lives in nearly identical operating conditions, so it's safe to assume they'll age in nearly identical ways. Cells without that kind of match get sold individually, so to a first approximation, it's safe to assume that no other cell in the world is a good match.

It's statistically inevitable that some individual cells will match well enough to work in a 2S or 2P pack, but finding them requires extensive testing under different load conditions, not just to see how well the cells match now, but how well they stay matched over time. It's far simpler to use a battery control system that charges and monitors each cell individually.

We do carry 1S-2P and 1S-3P LiPo packs:

https://www.adafruit.com/product/354
https://www.adafruit.com/product/353

and those work with all of our chargers. We don't carry anything for 2S or higher, or any battery management systems that can handle random cells.

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

by Alli on Mon Aug 10, 2020 6:03 pm

Hello Mike thanks for the insightful reply. I guess I will have to replace my original battery with a higher capacity battery to be safe. However, I am curious, what if i required a battery back up supply that is double the cell voltage of a single lithium ion cell. If I connected 2 lithium ion cells in series to achieve this than how would I charge both cells? Is there a lithium ion battery charger that is able to safely charge the lithium ion cells in series? Or will the cells need to be charged seperately, using two BMS to charge the series lihtium ion cells individually in circuit?

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

by adafruit_support_mike on Tue Aug 11, 2020 8:43 pm

You can charge a 2S pack matched and assembled at the factory as if it was a single 7.4V cell with a full-charge voltage of 8.4V. Most places that sell 2S packs will also sell compatible chargers.

For 2S packs that aren't factory-matched, you'll need a more complex battery management system that controls the connections between the cells, charges them individually, monitors each cell during discharge, and shuts off output when any cell hits a limit. There are battery systems for quadcopters and other RC gear which do the job.

I'm afraid we don't have any recommendations, as we don't carry or use them.

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Please be positive and constructive with your questions and comments.