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Hallowing full charge indicator?
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Hallowing full charge indicator?

by Doryen on Wed Oct 31, 2018 11:17 pm

Blah! (^V^)

How can you tell when the Hallowing has completed charging the lipo via micro USB?

It seems the light is yellow (charging) for a long time....does it turn green?

I didn’t see if there was a status color to indicate a complete charge in the documentation I viewed...

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Re: Hallowing full charge indicator?

by adafruit_support_mike on Thu Nov 01, 2018 3:36 am

The yellow LED shuts off when the charging cycle ends.

What's the milliamp-hour rating of the LiPo you're charging?

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Re: Hallowing full charge indicator?

by Doryen on Thu Nov 01, 2018 7:58 am

Thanks Mike!

It’s the 400mAh lipo that’s in Adabox 009. I’ll see if I can locate the charging current and do the math. Just thought an hour of charge would do it and since I couldn’t find that feature, thought I’d ask... did I miss it somewhere?

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Re: Hallowing full charge indicator?

by adafruit_support_mike on Fri Nov 02, 2018 2:07 am

It will take longer than an hour.

The LiPo charging cycle has two phases: constant-current and constant-voltage. During the constant-current phase, the charger sends a fixed amount of current into the LiPo (100mA for the charger on a Feather) and lets the LiPo voltage rise. When the LiPo is about 80% charged, its voltage reaches 4.2V, which is the maximum safe voltage for the LiPos we carry.

At that point the polymer directly touching the cell's plates is fully charged, but the polymer further between the plates is only partially charged. If you disconnected the charger as soon as the voltage hit 4.2V, you'd see the LiPo's voltage droop to about 3.8V over the next few hours as energy diffuses evenly through the polymer.

The constant-voltage phase sends the last 20% of energy into the LiPo, with the charger holding the plate voltage at 4.2V and tapering off the current as the deeper layers of polymer approach full charge. When the current flowing into the LiPo drops to 1% of the constant-current rate (1mA for a Feather), the LiPo is considered fully charged.

You can estimate the length of the constant-current phase from the charger's current limit and the size of the LiPo.. for a 400mAh LiPo, it would last a little more than 3 hours. The constant voltage phase takes between 2 and 4 times as long as the constant-current phase, depending on a bunch of factors like the LiPo's internal energy diffusion rate. LiPos charging below their 1C current (400mA for a 400mAh LiPo) will have a shorter constant-voltage phase because the energy has time to diffuse pretty well during the constant-current phase.

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Re: Hallowing full charge indicator?

by jgiles on Tue Nov 13, 2018 10:37 pm

That was very helpful info. Thanks Mike.

Does the Hallowing have a voltage divider connected so that we can monitor the battery level? I know this is usually a standard feature on feathers but this board is a bit different. I did check the schematic and I can see what looks like one (VBATT) but I can't tell if it's an accessible pin.

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Re: Hallowing full charge indicator?

by adafruit_support_mike on Wed Nov 14, 2018 3:34 am

Yep, it's connected to PB02, which is known as A6 in code.

That doesn't seem to be called out in the HalloWing tutorial though. I'll talk to the folks who handle that and we'll add it.

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Re: Hallowing full charge indicator?

by jgiles on Wed Nov 14, 2018 9:46 pm

Awesome! Thank you so much!

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Please be positive and constructive with your questions and comments.