Help with a design

Thread Starter

dplumley2

Joined Sep 23, 2022
5
Hi guys, I am new here. FYI before I get started, I am not an engineer, designer, programmer, or anything of that nature. I’m just a dude who loves a challenge, and I love diy home projects. Now, I hope this is the right forum to ask this kind of question!

So let me get started:
I have lately been thinking of a way to create a charge limit on my iPhone, because I try my best to limit degradation/long term damage of the battery. I have read articles and found that the lithium ion battery in your phone shouldn’t regularly be charged above 70-80ish percent, and certainly couldn’t be stored that way.

I try not to put my phone on the charger at night, as leaving the phone at 100% for a few hours over and over each night will eventually degrade the battery further. I also try to keep my battery in the 25-75% range as letting it die is also not good for it. This is pretty inconvenient, so I have thought of a solution. My idea is to create a small USB flash drive sized device with a male to female usb input/output. This device would plug into your phone’s power cube, and then you would plug your charging cable into the other end of the device.

I would implement Bluetooth so that the device can connect to your phone and know when your charging limit has been achieved to cut off power. It would also sense the internal temperature of the phone and cut off power if the battery temp gets too high during charging (heat and Lion batteries=quick degradation).

I have no idea where to start with this, so I figured I’d ask someone who knows a lot more than me! I am curious if there is a good (cheap) board/chip to use that can be connected to the phone via Bluetooth that is around the size of a flash drive. I need to be able to program it to perform these tasks. I am also trying to think of a good circuit for this design. For example, the board/chip would have to toggle some kind of switch/gate when either charging level is achieved or temperature is too high, and also be able to toggle the switch again once temps decrease or charge level decreases by a certain amount.

know this all sounds quite complicated and messy as I don’t know electronics terms/lingo, but it’s just a start for me and any help is appreciated! Gotta start somewhere, right? I’m just asking for input and ideas!

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MrChips

Joined Oct 2, 2009
27,196
I leave my iPhone, iPad, and all devices charged from a USB charger plugged in for very long times.

The charging controller is in the device. There is no harm in leaving it plugged it. It will not overcharge.
 

AlbertHall

Joined Jun 4, 2014
12,162
I leave my iPhone, iPad, and all devices charged from a USB charger plugged in for very long times.

The charging controller is in the device. There is no harm in leaving it plugged it. It will not overcharge.
Agreed, but charging to only 80% will extend the lifetime of the battery.
 

Thread Starter

dplumley2

Joined Sep 23, 2022
5
Agreed, but charging to only 80% will extend the lifetime of the battery.
I agree with you. Even if phones have built in charging controllers charging to only 75 or 80% will increase battery life. I’ve personally experienced this before with older devices!
 

Thread Starter

dplumley2

Joined Sep 23, 2022
5
Another thing I wanted to add. There is a device called a “Chargie” that does exactly what I want, but it’s from a company out of I believe Romania and also it’s very expensive! Also, I just want to make my own because I like making things, lol.C77401C1-F86B-4FDA-BDEB-ADAC3A9F7240.png
 

AnalogKid

Joined Aug 1, 2013
10,127
Agreed, but charging to only 80% will extend the lifetime of the battery.
I've seen this before, but nothing that explaines it at the charger circuit or battery chemistry level. Today's chargers are pretty smart, and I'm wondering if this concern is left over from 5-10 years ago; you know, the "old days".

Link to article(s) that explain this?

ak
 

Thread Starter

dplumley2

Joined Sep 23, 2022
5
I've seen this before, but nothing that explaines it at the charger circuit or battery chemistry level. Today's chargers are pretty smart, and I'm wondering if this concern is left over from 5-10 years ago; you know, the "old days".

Link to article(s) that explain this?

ak
There is a lot of recent research that still explains that charging a lithium ion battery above 75-80ish percent drastically decreases the amount of charge cycles that it can go through. Also, temperature is huge. The hotter the battery, the more damage will be caused. Also, slower charging is better than fast charging. Here’s a few recent articles explaining this:

https://www.frontiersin.org/articles/10.3389/fenrg.2022.905710/full

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries
 

Alec_t

Joined Sep 17, 2013
13,160
I believe some phones have a built-in function to do wahat you want. Doesn't the iPhone? If it doesn't, then does it have a sneaky function to prevent an external device doing what you want?
 

Thread Starter

dplumley2

Joined Sep 23, 2022
5
Yes, post #8.
iPhone’s “optimized charging” is a very unreliable way to do this, as it chooses its own time for when to charge to 80%, and then proceeds to charge the phone fully after that set time. You don’t get to choose when it charges to 80%. Also, the whole point of this is to prevent my phone from charging to 100%. Optimized charging still brings the phone to 100%.
 

Berninia

Joined Nov 21, 2015
19
Not all devices when reporting 100% charge actually reach the 4.2 V threshold for li-ion. In particular EVs. They often quit at 4.15 or 4.1 V. That is what my li-ion cell charger does for the 18650 and the 2170.

If this is an issue with your smartphone, then it should have a function to selectively limit charging to 80%. I would not worry too much about this in modern li-ion packs, especially if the charging is slow, which it generally is over 80%.
 

Audioguru again

Joined Oct 21, 2019
5,211
Battery University and some Lithium Charger IC datasheets say that a Lithium battery cell is about 75% to 80% fully charged when its charging voltage reaches 4.2V.
It is fully charged when its charging current has dropped to about 5% of its mAh rating.

I store my Lithium cells at half-charge (3.7V to 3.8V).
 

Alec_t

Joined Sep 17, 2013
13,160
I agree with Jon. Is there an iPhone app which allows you to read and export the exact state of charge? Cell voltage alone isn't an accurate measure. Coulomb-counting is better.
 

MisterBill2

Joined Jan 23, 2018
13,206
How about a simple in-line timer for the mains power to whatever charger you want to use? Then set the time to charge at night and it can charge for an hour or three or however much, depending on what you want. Simple and easy and no mystery about what it willdo.
 
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