Please add a low voltage battery disconnect to your lipo chargers

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niteris
 
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Please add a low voltage battery disconnect to your lipo chargers

Post by niteris »

Hi there, I'm an engineer making small batch wearables for festivals. I want to thank Adafruit for making all the fantastic and affordable products that you do. It's really pushed the needle forward for wearables.

I want to talk about a problem that no one has solved in the wearables space: LIPO chargers with a low voltage battery disconnect. I think this would be very popular product with your customers.

For example:
https://www.adafruit.com/product/5397

As many know, LIPO's hate going under 3 volts. The Lilypad series, also the Adafruit micros with integrated LIPO chargers, none of them have an undervoltage battery disconnect (that I've been able to find). This means that unless the user hits the off switch, each wearable device will bring the battery to 0 volts, which will render the battery completely useless after 10 cycles.

I've lost amazing jewelry pieces because the battery was embedded directly inside not knowing that this was an issue. Additionally, many of the Arduino compatible devices have large parasitic loads. For example the USB -> Serial FTDI chip common on the 328p's are listed as having a 4mA load. The only solution to this is to get an Arduino that requires an external FTDI chip to program it through the ISCP headers.

The only solution at this point is to buy chargers off of amazon like these: https://www.amazon.com/dp/B08F7QSLN7?ps ... ct_details and now I'm going to try to re-work them to bring the charging rate down from 1A to 100mA.

This issue must plague every single wearables designer. I've tried to do things like switch to NIMH batteries but learned that they will get wrecked too unless perfectly balanced, which doesn't really happen in the real world.

My wish list is for Adafruit to be the first one to offer such a device. Either as a refresh to their Adafruit LiIon or LiPoly Charger BFF. Or as an Arduino designed with an onboard lipoly charger, like an upgraded gemma or Lilypad with this feature. The 328p running at 8mhz has more than enough processing power for most wearables and has a well tested low power library to shut down the chip. I'm not sure what the story is of the m0 as I haven't tried it. But given that the gemma m0 is about the size of a 2450 or 2432 cell, I could imagine a product offering where a future gemma device could have it's battery pins positioned to perfectly fit a custom LR2450 cell, or a pouch cell of about the same size which could plug into an onboard JST connector.

A custom board would be the best option because all of the parasitic loads during low power state could be eliminated so that the board runs at micro amps during it's deep sleep state.

If you've read all the way here, then I thank you. If your team produces such a board I will be the first one to buy it in bulk and I am sure it will be a top seller.

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adafruit_support_bill
 
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Re: Please add a low voltage battery disconnect to your lipo chargers

Post by adafruit_support_bill »

Thanks for the feedback. I will forward your request to our design group.

Most of the rechargeable cells we stock have battery protection circuits which have a low-voltage cutoff as well as overcurrent protection. But coin cells like the LR2450 don't have that kind of protection.

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niteris
 
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Re: Please add a low voltage battery disconnect to your lipo chargers

Post by niteris »

Oh wow, yes you are right. I just found them. Thank you so much. I just bought 8.

For anyone else running into this problem, you here are two products that have this feature:

150mAh: https://www.adafruit.com/product/1317
500mAh: https://www.adafruit.com/product/1578

This will work with the Lilypad USB quite nicely. The only issue here is that the Lilypad has to be switched to charge mode, which will be counter-intuitive to users.

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niteris
 
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Re: Please add a low voltage battery disconnect to your lipo chargers

Post by niteris »

One final thing. You might want to update your text copy of the Adafruit non protected batteries and let buys know about the versions with the under voltage protection circuits. I've been searching for two days and Google doesn't readily show this one of the results.

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adafruit2
 
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Re: Please add a low voltage battery disconnect to your lipo chargers

Post by adafruit2 »

it sounds like you're talking about a specific charger just for LR lithium cells because all our batteries have low-voltage disconnects. we do stock a charger but personally we think its best to just go with
https://www.adafruit.com/product/1317
which is very petite and has the cutoff built in!

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niteris
 
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Re: Please add a low voltage battery disconnect to your lipo chargers

Post by niteris »

adafruit2 wrote: Wed May 03, 2023 12:33 pm it sounds like you're talking about a specific charger just for LR lithium cells because all our batteries have low-voltage disconnects. we do stock a charger but personally we think its best to just go with
https://www.adafruit.com/product/1317
which is very petite and has the cutoff built in!
Thanks! Good to know!

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