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It seems like it should be possible to have a variable rate phone charging cable with just a simple switch and a few resistors. Instead of hastening the demise

It seems like it should be possible to have a variable rate phone charging cable with just a simple switch and a few resistors. Instead of hastening the demise of a phone battery by fast charging all the time, select fast, regular or slow charge, depending on your circumstances, with the selector switch. Just looked around, but couldn't find anything already existing though. Seems like something that would already exist on Aliexpress.

brookst 4y ago
Most (all?) modern phones manage charging speed based on battery health, charge state, and temperature. I'm not sure you could force one to charge faster at e.g. 2% charge in 120 degree heat with any kind of cable. Mabye? But that seems like a software thing.
- sillystuff 4y ago
  The hope is to force it to charge slower. Fast charging all the time shortens the battery life.
  - Dylan16807 4y ago
    > Fast charging all the time shortens the battery life. How much? It's a widespread claim but without specific numbers it's not very helpful, and there are suggestions that the numbers are pretty small. Limiting max charge, on the other hand, has known strong effects.
    - sillystuff 4y ago
      > Limiting max charge, on the other hand, has known strong effects. Yes, and you used to be able to do that on a rooted android phone. But, Google required the removal of debugfs in recent android versions, so need to run a custom kernel too now to get back that functionality. Maximum charge, and percent charge where charging begins should be user accessible settings on any device with a lithium ion battery. Charging rate should also be a user accessible setting. The cable idea is just a hacky work-around for crappy software, that addresses one of the reasons lithium ion batteries prematurely fail, and doesn't require modifying the device to be charged.
      - Dylan16807 4y ago
        Charge control should be standard, but at least samsung puts in the option for 85% charge.
    - Robotbeat 4y ago
      Well if you do it every time at like 2-3C, you’re talking maybe 500 cycles compared to 1000 cycles at a slower charge rate. Depends on other stuff, too. Depth of discharge and max charge voltage are both even larger effects, but it still matters. (Knowing the exact chemistry of your phone’s battery can make a difference here, of course.) https://www.mpoweruk.com/life.htm https://www.mpoweruk.com/life.htm Fast charging from, say, 10% to 50% probably is a fairly small effect compared to trying to fast charge to 100%.
      - Dylan16807 4y ago
        Even that much is aching for more numbers. How about .5C versus 1.5C? What if my phone is one of those fancy ones rated for 6C or even 10C? Unless someone gives some precise scenarios it's so hard to guess how my phone might be affected.
  - deleted 4y ago
    [deleted]
rolenthedeep 4y ago
I don't recall if this is "standard" or not, but some devices have mode where it slowly ramps up the current until the voltage starts to drop. IIRC, this is a fallback mode on some TI charge controllers. If it can't detect a capacity signal on the D+/- lines, it reverts to this mode of testing the charger. This was intended to support sketchy Chinese trash chargers that leave the data lines disconnected, and whose real power capacity is a mystery. This strategy lets you pull as much power as the charger will suffer
- LoganDark 4y ago
  > This strategy lets you pull as much power as the charger will suffer Some chargers will allow you to pull enough power to melt the thing or catch it on fire if they don't have sufficient protections, but it's likely those would have data lines (+ protections) anyway
  - rolenthedeep 4y ago
    Well, that's kind of the point of the check. Except in the most extraordinary conditions, the voltage will drop as you approach the supply's current limit. It takes significant effort to design a circuit that can sustain large amounts of current while keeping voltage constant. There's basically no overlap between that sort of design and cheap Chinese fire hazards.
    - LoganDark 4y ago
      The point of my comment is that some chargers will melt or catch on fire even if you are pulling "as much as it can handle without voltage drop".
frosted-flakes 4y ago
My Samsung Galaxy S10e allows me to disable fast charging, and also to set a max charge of 85%.

brookst 4y ago

Most (all?) modern phones manage charging speed based on battery health, charge state, and temperature. I'm not sure you could force one to charge faster at e.g. 2% charge in 120 degree heat with any kind of cable. Mabye? But that seems like a software thing.

sillystuff 4y ago
The hope is to force it to charge slower. Fast charging all the time shortens the battery life.
- Dylan16807 4y ago
  > Fast charging all the time shortens the battery life. How much? It's a widespread claim but without specific numbers it's not very helpful, and there are suggestions that the numbers are pretty small. Limiting max charge, on the other hand, has known strong effects.
  - sillystuff 4y ago
    > Limiting max charge, on the other hand, has known strong effects. Yes, and you used to be able to do that on a rooted android phone. But, Google required the removal of debugfs in recent android versions, so need to run a custom kernel too now to get back that functionality. Maximum charge, and percent charge where charging begins should be user accessible settings on any device with a lithium ion battery. Charging rate should also be a user accessible setting. The cable idea is just a hacky work-around for crappy software, that addresses one of the reasons lithium ion batteries prematurely fail, and doesn't require modifying the device to be charged.
    - Dylan16807 4y ago
      Charge control should be standard, but at least samsung puts in the option for 85% charge.
  - Robotbeat 4y ago
    Well if you do it every time at like 2-3C, you’re talking maybe 500 cycles compared to 1000 cycles at a slower charge rate. Depends on other stuff, too. Depth of discharge and max charge voltage are both even larger effects, but it still matters. (Knowing the exact chemistry of your phone’s battery can make a difference here, of course.) https://www.mpoweruk.com/life.htm https://www.mpoweruk.com/life.htm Fast charging from, say, 10% to 50% probably is a fairly small effect compared to trying to fast charge to 100%.
    - Dylan16807 4y ago
      Even that much is aching for more numbers. How about .5C versus 1.5C? What if my phone is one of those fancy ones rated for 6C or even 10C? Unless someone gives some precise scenarios it's so hard to guess how my phone might be affected.
- deleted 4y ago
  [deleted]

rolenthedeep 4y ago

I don't recall if this is "standard" or not, but some devices have mode where it slowly ramps up the current until the voltage starts to drop. IIRC, this is a fallback mode on some TI charge controllers. If it can't detect a capacity signal on the D+/- lines, it reverts to this mode of testing the charger. This was intended to support sketchy Chinese trash chargers that leave the data lines disconnected, and whose real power capacity is a mystery. This strategy lets you pull as much power as the charger will suffer

LoganDark 4y ago
> This strategy lets you pull as much power as the charger will suffer Some chargers will allow you to pull enough power to melt the thing or catch it on fire if they don't have sufficient protections, but it's likely those would have data lines (+ protections) anyway
- rolenthedeep 4y ago
  Well, that's kind of the point of the check. Except in the most extraordinary conditions, the voltage will drop as you approach the supply's current limit. It takes significant effort to design a circuit that can sustain large amounts of current while keeping voltage constant. There's basically no overlap between that sort of design and cheap Chinese fire hazards.
  - LoganDark 4y ago
    The point of my comment is that some chargers will melt or catch on fire even if you are pulling "as much as it can handle without voltage drop".

frosted-flakes 4y ago

My Samsung Galaxy S10e allows me to disable fast charging, and also to set a max charge of 85%.