# Att: kernel devs! Usb-fast charge!



## joemagistro

So its cool that we have native call recording support, however one feature I really miss from my nexus is usb fast charge mode... I can't take how slow DC charging is....... Is this possible to accomplish?

Sent from my SGH-T999 using Xparent Blue Tapatalk 2


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## RMarkwald

I will note that on the Galaxy Nexus with this enabled, it wouldn't mount MTP right, so you'd have to disable it. Also it seemed that people who had this enabled and used it quite a bit it was killing their phone's USB port.


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## jbzcar

RMarkwald said:


> I will note that on the Galaxy Nexus with this enabled, it wouldn't mount MTP right, so you'd have to disable it. Also it seemed that people who had this enabled and used it quite a bit it was killing their phone's USB port.


First part is correct. Never heard of the second problem at all.


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## RMarkwald

jbzcar said:


> First part is correct. Never heard of the second problem at all.


There was a trend for a little bit where users who enabled it seemed to have that issue more than the users who did not. Not wanting to run that risk, I never used it and never had an issue. It may have been completely unrelated, but just seemed odd.


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## joemagistro

Never had a problem either... That option is huge for me since I can charge my phone relatively fastttt

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## afmracer6

Now imoseyon test kernel has force fast charge

Sent from my SCH-I535 using RootzWiki


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## joemagistro

damnn... guess im SOL since i dont have verizon! lol


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## yarly

it's very possible to fry a faulty is usb port with fast charge enabled. it's why cyanogen didn't add it, despite risk being low.


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## joemagistro

yarly said:


> it's very possible to fry a faulty is usb port with fast charge enabled. it's why cyanogen didn't add it, despite risk being low.


im just curious how this is possible??? Im not doubting you, but rather curious.... if it puts out the same current as if AC was plugged in, why would that have any negetive effects on the usb port??? i could understand if it put out moreee draw, but its the same as ac current right??


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## yarly

Short answer is bad wiring in the usb port mostly. It's not an issue with the phone getting fried, just the charging port on the other device.

Actually, I can do better than just explain, here's the original link where they rejected it in CM's kernel if you're interested:

http://review.cyanog....com/#/c/17802/


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## joemagistro

yarly said:


> Short answer is bad wiring in the usb port mostly. It's not an issue with the phone getting fried, just the charging port on the other device.
> 
> Actually, I can do better than just explain, here's the original link where they rejected it in CM's kernel if you're interested:
> 
> http://review.cyanog....com/#/c/17802/


i can see where that makes sense on the other device...... my only primary major use for fastcharge is with a DC charger in my car or motorcycle anyways... I love the feeling of riding my motorcycle for an hour knowing that when i park it and take my phone out, my battery is significantly more charged then a standard dc charge


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## PhantomGamers

yarly said:


> Short answer is bad wiring in the usb port mostly. It's not an issue with the phone getting fried, just the charging port on the other device.
> 
> Actually, I can do better than just explain, here's the original link where they rejected it in CM's kernel if you're interested:
> 
> http://review.cyanog....com/#/c/17802/


i read through that but i really can't see this being harmful.
as one of the dudes in there said: you never see people complaining about external HDDs frying USB ports.


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## yarly

T1 is a Galaxy S2 variant. No idea if the S3 has the detection abilities built into it to determine if it's charging from a regular usb port or one that can pump out more ampage.


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## PhantomGamers

yarly said:


> T1 is a Galaxy S2 variant. No idea if the S3 has the detection abilities built into it to determine if it's charging from a regular usb port or one that can pump out more ampage.


even if the s3 is attempting to pull more power than the usb port can handle, what usb port would actually GIVE it that power?
i'm sure the usb port itself has some sort of hard limit, I can think of many usb devices that would fry if it didn't.


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## yarly

PhantomGamers said:


> even if the s3 is attempting to pull more power than the usb port can handle, what usb port would actually GIVE it that power?
> i'm sure the usb port itself has some sort of hard limit, I can think of many usb devices that would fry if it didn't.


It says why if you read the comments. If you're really interested, it's worth reading them just for the insightfulness. Most of them are the main CM team guys.


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## PhantomGamers

yarly said:


> It says why if you read the comments. If you're really interested, it's worth reading them just for the insightfulness. Most of them are the main CM team guys.


I did read them and it seems like the main reason it got rejected was because they didn't want to risk breaking 0.1% of USB Hosts...


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## yarly

The ports can't give it more voltage, but the charger can pull out more electricity than the port can handle. Electrical current it just the flow of how much electricity goes over an area at once. Too much too quick and it'll fry it if it can't handle it.


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## Jaxidian

EE (among other things) here. One problem is precisely with this statement:


> if the s3 is attempting to pull more power than the usb port can handle, what usb port would actually GIVE it that power?


The spec for the battery is precisely 5V (+/- 0.5V) at 500mA-1500mA (completely going by memory, maybe I have something wrong but it's really not important.

So what does this mean? This means that the source can provide a voltage as low as 4.5V or as high as 5.5V without risking damage to your device. While providing these voltages, it must push 0.5 to 1.5A in current. The way electricity works, if you try to pull too much amperage, then your voltage drops. So if the USB Port isn't capable of pushing 1.5A but the devices tries to pull it, it may actually receive 1.5A but at 3.5V. This is a HUGE problem both for the phone and for the USB port.

Why is this a problem? This means that in order to keep either the phone or the USB port from being damaged, you are relying 100% of the time on failsafe devices to protect them. While this may sound fine (I mean, what are failsafe devices for anyways?), in reality it's not. Failsafes are designed for emergency situations and not for ongoing use. I mean, could your Sedan tow a broken-down pickup truck 400 feet to get it in your driveway? Sure. Do you really think that same sedan could get 200k miles while pulling the pickup truck every single one of them? No way!

Analogy time:
Think a garden hose and a pool. Your goal is to fill up the pool. The pool is 110 feet away from your spigot and you can never have more than 100 feet of hose. So this means that your hose must spray the water 10 feet out in order to reach the pool that you're filling up. So you turn the water on and stand there holding the hose while it fills. After a while, you think, "Hmm, if only I could get a thicker hose that could spray more water, this would go much faster!" Well, this works if you had a fire hydrant behind the hose but if you take a 100 foot fireman's hose and hook it up to your spigot on the side of your house, you'll be pretty hard-pressed to have it spray 10 feet. In this analogy, the amount of water (per unit of time) the hose sprays is like current while the distance the hose is able to spray it is like voltage.

Now all of this still may not be enough to convince you, so let me throw out one more thing out there. Many many MANY USB ports out there are inferior and actually do not conform to specs. USB Hubs, case ports, LCD ports, and even some motherboard ports - they simply do not comply with all USB specifications. The area that they usually are deficient in are with power. Go google a little bit real quick with what USB hubs work and do not work with Raspberry Pi devices. Or actually, I'll save you the work. This is just the tip of the iceberg of devices that need to be considered and this is a very well-documented area where failure to conform to USB specifications has rendered MANY USB components incapable of handling "standard" scenarios. And you want to throw something that demands even MORE than the standard at them without any ill-effects? Hah, good luck! It WILL cause problems. There's no maybe about it. If I were the CM team, I too wouldn't have wanted to be responsible for burning up several peoples motherboards, monitors, and phones just because I wanted to help somebody who was in a rush. Sorry but it's the right decision.


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## Jaxidian

yarly said:


> The ports can't give it more voltage, but the charger can pull out more electricity than the port can handle. Electrical current it just the flow of how much electricity goes over an area at once. Too much too quick and it'll fry it if it can't handle it.


Too little can equally fry it as well. It's usually less risky than too much, but it's still risky. Go plug in a fridge to an old house where the power fluctuates due to old/bad wiring and you'll see a fridge that dies in 6 months because it's constantly dealing with brownout situations (i.e. the power is good then not enough then good then not enough, etc). You'll have the same thing with phones. Hopefully the circuitry is more advanced and can tolerate it a bit more but it will still suffer. It's just a matter of when.


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## joemagistro

Jaxidian, that aside, running the usb to a 12volt dc source is fine right? Just a risk with usb devices?

I just wanna fast charge my phone using dc power from my car or bike

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## Chakra

Imo's kernel has fast charge enabled.


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## joemagistro

unfortunately his kernel isnt for t-mobile :-/


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