Limiting Charging When Cell Phone is Tethered to Computer by USB Cable?

Thread Starter

honda.lioness

Joined Apr 10, 2018
8
With a USB Cable, I am tethering my Moto G Play phone to my chromebook. This is so I can connect my chromebook to the internet via my phone. The cell phone's software does not reliably respond to alleged options to limit charging.

To limit charging, one internet site reported this hack:

"... on my Moto G Power phone, there is a current level where the battery stops charging but the data still works.

... I got [B06Y5KZC9W and B08D68JW4K from Amazon]

I cut the VCC power wire and inserted a 1N4004 diode and 1 ohm, 1 watt resistor in series. The idea is that the resistor provides a convenient way to measure the current by measuring the voltage. The diode is a known voltage drop of 0.6v.

With just the resistor, I measured 480 mV across it which means 480 mA current charging the battery. Then I inserted the diode and got 56 mV across the resistor. It's not zero but the important thing is that the phone battery is slowly discharging. With two diodes there is too much drop because the phone doesn't recognize when the cable is plugged in.

You could probably just use a suitable resistor."
What do people here think of this solution?

Could I just cut into the USB cable, cut the red wire, and splice a resistor into it?

I welcome suggestions.

 

Ya’akov

Joined Jan 27, 2019
9,167
Welcome to AAC.

Could you explain why the phone’s battery management is not sufficient? Why do you need to do this instead of just letting the phone charge the battery if it needs to, or stop if it doesn’t?
 

Thread Starter

honda.lioness

Joined Apr 10, 2018
8
Ya'akov,

I have tried many times to use the phone's software to slow down charging. None of the features appear to work reliably. Some of them seem to work somewhat. While tethered, sometimes the charge goes to 100% and I see no signs of the charging being turned off. No doubt this has something to do with power needing to be on to operate the tethering feature.

I will continue to experiment, since I realize using the phone's software would be preferable.

I also see reports on the net that hours of being tethered is not advisable.

Thank you for weighing in.
 
Last edited:

MrAl

Joined Jun 17, 2014
11,487
With a USB Cable, I am tethering my Moto G Play phone to my chromebook. This is so I can connect my chromebook to the internet via my phone. The cell phone's software does not reliably respond to alleged options to limit charging.

To limit charging, one internet site reported this hack:

What do people here think of this solution?

Could I just cut into the USB cable, cut the red wire, and splice a resistor into it?

I welcome suggestions.
Hi,

I've encountered issues like this also.

The best bet is to get a wall wart that has the limited current you seek to use.
For example, if your 'normal' wall wart provides 1.5 amps of current to the phone and you just want 500ma (a reasonable value) then buy a wall wart that puts out only 500ma. It would probably be very cheap. So it would be a 5vdc 500ma wall wart in this case, probably with a female USB-A connector.
If you want lower you'd just get one that only puts out that lower current level.
500ma should be low enough though, and I would think that 100ma would be too low.
 

Ya’akov

Joined Jan 27, 2019
9,167
Ya'akov,

I have tried many times to use the phone's software to slow down charging. None of the features appear to work reliably. Some of them seem to work somewhat. While tethered, sometimes the charge goes to 100% and I see no signs of the charging being turned off. No doubt this has something to do with power needing to be on to operate the tethering feature.

I will continue to experiment, since I realize using the phone's software would be preferable.

I also see reports on the net that hours of being tethered is not advisable.

Thank you for weighing in.
I have to admit that it is very strange the BMS in the phone would overcharge the phone—under any circumstance. I feel there is something missing here. Modern phones should never overcharge the cell, and the cell’s own protection should prevent it from being charged past ~4.2V.

If this was really a problem (and solution), I would expect Motorola to offer a cable designed to do this.

So, I did a little searching—Motorola’s article on charging the Moto G Power says:

NOTE: The moto g power 5G (2023) always charges the battery with the device powered on. This is normal behavior and is not an problem with the device.
Is there a reason to think this is not true? Where did you get the information that there could be “excessive” charging?
 

Ya’akov

Joined Jan 27, 2019
9,167
Hi,

I've encountered issues like this also.

The best bet is to get a wall wart that has the limited current you seek to use.
For example, if your 'normal' wall wart provides 1.5 amps of current to the phone and you just want 500ma (a reasonable value) then buy a wall wart that puts out only 500ma. It would probably be very cheap. So it would be a 5vdc 500ma wall wart in this case, probably with a female USB-A connector.
If you want lower you'd just get one that only puts out that lower current level.
500ma should be low enough though, and I would think that 100ma would be too low.
This won‘t work because he is not trying to charge, he’s tethering his computer to the phone and the charging is a side effect. Apparently, in the absence of the power signal, the phone won’t tether so it ends up charging—or indicating charging anyway. According to Motorola, this isn’t a problem but maybe the TS has more information…
 

Thread Starter

honda.lioness

Joined Apr 10, 2018
8
Where did you get the information that there could be “excessive” charging?
From the net. I have been aware for some years that for maximum cell phone battery life, numerous sites say try not to charge over 80%. Try not to discharge to less than 30%. Googling as follows turns up many sites that say as much:

overcharging cell phone battery

On the other hand, I now see some sites saying it is not that big a deal.

I think I will abandon the idea of trying to reduce the charging while tethering. It's time to buy some real internet service.

Thank you for the input Ya'akov and MrAl. I think I am good to go at present.
 

Ya’akov

Joined Jan 27, 2019
9,167
From the net. I have been aware for some years that for maximum cell phone battery life, numerous sites say try not to charge over 80%. Try not to discharge to less than 30%. Googling as follows turns up many sites that say as much:

overcharging cell phone battery

On the other hand, I now see some sites saying it is not that big a deal.

I think I will abandon the idea of trying to reduce the charging while tethering. It's time to buy some real internet service.

Thank you for the input Ya'akov and MrAl. I think I am good to go at present.
The problem with the advice about 80% and 30% is that is is an impractical ideal. The cells in mobile phones are barely adequate when used fully, in particular in the charge phase. To try to limit the charge to 80%, which will increase the cell’s useable life is a burden that—for the overwhelming majority of users—doesn’t bring benefits to offset it.

The best thing you can do is let the phone’s battery management do its job, and charge whenever you get the chance to avoid the high current charging that happens when the cell is depleted. The higher current means more heat and heat is the enemy here, not the charging per se.

You will probably get better performance with a home broadband connection in any case, and it will be always on, and can have no usage caps. Enjoy it!
 

MrAl

Joined Jun 17, 2014
11,487
The problem with the advice about 80% and 30% is that is is an impractical ideal. The cells in mobile phones are barely adequate when used fully, in particular in the charge phase. To try to limit the charge to 80%, which will increase the cell’s useable life is a burden that—for the overwhelming majority of users—doesn’t bring benefits to offset it.

The best thing you can do is let the phone’s battery management do its job, and charge whenever you get the chance to avoid the high current charging that happens when the cell is depleted. The higher current means more heat and heat is the enemy here, not the charging per se.

You will probably get better performance with a home broadband connection in any case, and it will be always on, and can have no usage caps. Enjoy it!
Hi there,

Samsung has a limit setting in maybe all of their more modern cell phones. It's under battery management.
You can limit the charge to 85 percent (not 80 as we would expect) and also turn off fast charging.
 

MrAl

Joined Jun 17, 2014
11,487
This won‘t work because he is not trying to charge, he’s tethering his computer to the phone and the charging is a side effect. Apparently, in the absence of the power signal, the phone won’t tether so it ends up charging—or indicating charging anyway. According to Motorola, this isn’t a problem but maybe the TS has more information…
Oh yes I see that now.

In that case, the only way would be to try the resistor trick unless the phone itself can be modified. If there is a small value resistor in series with the battery inside, that would limit the charge current, but it would have to be small enough such that the phone still functions properly. Even a very small value like 0.1 Ohms would probably do it, and that would probably mean an SMD part could be used. 1 amp through a 0.1 Ohm resistor only dissipates 100mw.

Oh wait, I almost forgot.
It might work to simply plug the phone into a USB 2.0 port not a USB 3.0 port. There's a chance that would lower the current to a more acceptable level, although I have no idea what the level is now and what the target level is.
If I remember right, the USB 2.0 port will only put out 100ma unless the connection is negotiated, and then the max current can only be 500ma.
If 500ma is too high for the phone, connect a resistor across the 5v to ground line, which will draw some current leaving only the remainder for the phone.
If the resistor draws 250ma, I would think the max current to the phone would then be just 250ma, but I have never actually tried this so it would have to be an experiment to see if it works.
 

Jon Chandler

Joined Jun 12, 2008
1,051
Could you explain why the phone’s battery management is not sufficient? Why do you need to do this instead of just letting the phone charge the battery if it needs to, or stop if it doesn’t?
In my case, when I tether my phone to my laptop, the laptop insists on charging the phone. The problem with this "helpful" feature is that my phone battery will power the phone for far longer than the laptop battery will power the laptop. I'd rather not shorten the laptop's run time by it charging the phone when it's not needed.
 
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