# Undervolting



## partychick64 (Nov 5, 2011)

First of what's the lowest you have ever undervolted? Second how do you know how much to undervolt? Does it depend on the governor? And lastly what are signs that tell you your voltages aren't stable?

My question comes from the fact that I got a random reboot. It hadn't happen at all it was probably my fourth day with those voltages. I set up voltages (not on boot ) and for 350MHz I had it set up to 975mV just like the previous voltage, but idk if the other voltages matter. Basically I wanna learn how to undervolt correctly without just making up numbers and such. The current voltages are the original ones that always appear and saved ones are the ones I came up with.

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## Ianxcom (Jun 29, 2011)

I've been as low as

1200
1100
1000
900
800

For me it works for a while but I get a freeze up every once in awhile. I think it has more to do with the upper frequency voltage since I run fine on morfics kernel with a stock min of 800.

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## monky_1 (Aug 26, 2011)

Ianxcom said:


> I've been as low as
> 
> 1200
> 1100
> ...


I get no reboots(;
Galaxy


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## Jubakuba (Sep 8, 2011)

Stability is the problem with undervolting.
Personally, I use:
850 1050 1150 1200 (for now).
On lean kernel.

However, I have gotten quite a bit lower...
BUT at lower values it would bog down quite a bit once the battery got low. This seems to be about the sweet spot for me.
Testing is really the only way to set them.
So any value that works for me or someone else may not work for you.


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## icanhazdroid (Jun 24, 2011)

Lean kernel

100% stable. On the stable version so I get SR1.5 but it seems to not be able to calibrate lower than this anyway.

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## partychick64 (Nov 5, 2011)

Thanks for the help guys!

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## brkshr (Jun 16, 2011)

I use Imoseyons kernel and his checkv script in terminal emulator. I'm at 830, 1020, 1120, 1240, 1240. Yes, for some reason checkv says that I can run 1200mhz & 1350mhz at 1240mv & I have never had a problem.

Flash Imo's kernel.
Open Terminal Emulator (download if needed, it's free)
type 'su' (without quotes)
type 'checkv' (without quotes)

It will tell you how low you can go. Change your voltages to what it says, then repeat the process and it may say you can go lower. Repeat until it says voltages stay the same. I've never had a problem with these settings.

Edit: I have gone much lower, but there was an article that did extensive checks for battery drainage and it said that lower voltages really doesn't do anything for battery life (I don't know what happened to that article). So I just play it safe it with this now.


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## creaky24 (Jan 13, 2012)

Great info here but one thing that has been really helpful is to do things in increments. I pretty much use Jakebites UV settings for Imo's kernel bit if I want to go lower just change one frequency at a time so if I have trouble I know exactly where to go first to try and fix it. As was said, everyone's going to have their own sweet spot. Good luck.

Sent from my Liquified Nexus


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## throwbot (Jan 2, 2012)

Yeah, I've gone pretty low before and he's right, do it in increments and give each "profile" (or set of voltages or whatever you want to call it) at least a day, or one good battery discharge to gauge them.

Sometimes, tho, I think you're best off just re-flashing the kernel and going with their stock settings. Developers spend a lot of time fine tuning their kernels and the voltages. I personally think that a lot of times, if a kernels not giving you the best battery then you are better off switching kernels as opposed to undervolting. Everyones device does differently with different kernels/settings, but I've personally had better luck with stock voltage settings (at least with 95% of the kernels I've used). Just an opinion from my personal experience, take it for what it is.

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## Metallice (Jan 27, 2012)

Be careful not to undervolt too much. It may appear and act stable, but excessive undervolting can actually cause the battery to drain more trying to correct errors. Some guy on xda did a bunch of battery tests with the nexus s and this was one of the conclusions.

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## partychick64 (Nov 5, 2011)

Thanks man. So it basically telling me what voltages to run?

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## brkshr (Jun 16, 2011)

partychick64 said:


> Thanks man. So it basically telling me what voltages to run?
> 
> Sent from my Galaxy Nexus using RootzWiki


Yep. Change your voltages, then run it again. It may give you lower voltages. Change, repeat, until the voltages stay the same

Swyped from my Galaxy Nexus


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## partychick64 (Nov 5, 2011)

Thanks I found out I could go even lower haha. ... think this voltages are safe from this?

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## brkshr (Jun 16, 2011)

partychick64 said:


> Thanks I found out I could go even lower haha. ... think this voltages are safe from this?
> 
> Sent from my Galaxy Nexus using RootzWiki


I would definitely say your safe with those. I used to have mine lower than what checkv says, with no problems. So i think checkv stays on the safe side.

Swyped from my Galaxy Nexus


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## partychick64 (Nov 5, 2011)

Sigh I had to a little bit up cuz it froze and rebooted. Good thing I don't have set up at boot haha

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## creaky24 (Jan 13, 2012)

For some reason my checkv calibrated results are all 0. What am I doing wrong?

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## Metallice (Jan 27, 2012)

brkshr said:


> Yep. Change your voltages, then run it again. It may give you lower voltages. Change, repeat, until the voltages stay the same
> 
> Swyped from my Galaxy Nexus


What you SHOULD do is once you find the point where calibrated = set voltage, you should go back up to the previous value that calibrated to this "lower limit" you just found. That way your phone will be running at this lower limit due to smart reflex, but it will have the ability to scale up if needed.

Any lower than these calibrated values and you might end up consuming more power to correct for errors. I'm assuming of course that smart reflex won't calibrate to a voltage that would give errors and consume more power. However I feel that's a pretty safe assumption to make.

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## brkshr (Jun 16, 2011)

partychick64 said:


> What you SHOULD do is once you find the point where calibrated = set voltage, you should go back up to the previous value that calibrated to this "lower limit" you just found. That way your phone will be running at this lower limit due to smart reflex, but it will have the ability to scale up if needed.
> 
> Any lower than these calibrated values and you might end up consuming more power to correct for errors. I'm assuming of course that smart reflex won't calibrate to a voltage that would give errors and consume more power. However I feel that's a pretty safe assumption to make.
> 
> Sent from my Galaxy Nexus using RootzWiki


What exactly is smart reflex? Sounds like you know a little more than me. Does that have anything to do with throttling or 'checkt'

Swyped from my Galaxy Nexus


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## tiny4579 (Oct 21, 2011)

As far as I know this phone runs at the calibrated voltages, calibrated and nominal aren't like min and max on HAVS implementations. When I undervolted on leankernel and ran checkv i didn't see any difference in the calibrated voltages.

IMO smartreflex takes away the need to custom undervolt. As another user said on page 1, it's not really worth it. The best way to save battery is cut screen brightness but I don't as I like auto brightness and it seems pretty good on CM9.


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## wellsey1126 (Dec 10, 2011)

Running Franco lastest kernel. Only running 700 Max 350min so far so good. Also I'm on milestone 4. If I ran anything lower my phone would reboot .

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## wellsey1126 (Dec 10, 2011)

Correction on previous post. After posting it about 5 min later the phone stalled. I went up 25 on 700 and have not touched 350 . Hopefully it works better. I've seem to always had an issue undervolting Franco kernel

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## Burncycle (Aug 6, 2011)

tiny4579 said:


> As far as I know this phone runs at the calibrated voltages, calibrated and nominal aren't like min and max on HAVS implementations. When I undervolted on leankernel and ran checkv i didn't see any difference in the calibrated voltages.
> 
> IMO smartreflex takes away the need to custom undervolt. As another user said on page 1, it's not really worth it. The best way to save battery is cut screen brightness but I don't as I like auto brightness and it seems pretty good on CM9.


+1 I agree that it isn't worth it. All you guys are doing is creating instability for your phone and I highly doubt that undervolting is going to do anything to actually make a difference in battery life.

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## ERIFNOMI (Jun 30, 2011)

brkshr said:


> What exactly is smart reflex? Sounds like you know a little more than me. Does that have anything to do with throttling or 'checkt'
> 
> Swyped from my Galaxy Nexus


You're CPU will undervolt itself, basically.


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## midknight (Feb 1, 2012)

creaky24 said:


> For some reason my checkv calibrated results are all 0. What am I doing wrong?
> 
> Sent from my Liquified Nexus


Are you using Imoseyon's Lean Kernel? If you're using an experimental version of his kernel, Smart Reflex is disabled and I'm assuming that's why you're getting checkv calibrated results of 0.

In response to the OP, here are the undervolt settings I'm using:

350 MHz - 765 mV
700 MHz - 915 MV
920 MHz - 1005 mV
1.2 GHz - 1190 mV
1.35 GHz - 1245 mV
1.52 GHz - 1340 mV
1.65 GHz - 1440 mv

I don't use the 230 MHz setting. Edit: I've been stable for days at these settings. No plans on changing them. I'm using Lean Kernel 2.5.0 exp2


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## partychick64 (Nov 5, 2011)

I made up my own and little bit higher seems to be working fine no reboots

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## Metallice (Jan 27, 2012)

If your using any values below 800 for 350 your probably doing much more harm than good. Trust me I was one of you. I had my 350 slot at 725 mv and thought it was great. Never had a random reboot, never had a SOD. Must be working great right?

That is what I thought until I did my own testing. Setting min and max both to 350 and streaming music with the screen off, I had greater drain at 750mv than I did at 840mv (smart reflex'd down to 830mv). Starting at 100 both times, 840/830 took about 15 minutes longer to drain to 50%.

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## ERIFNOMI (Jun 30, 2011)

Metallice said:


> If your using any values below 800 for 350 your probably doing much more harm than good. Trust me I was one of you. I had my 350 slot at 725 mv and thought it was great. Never had a random reboot, never had a SOD. Must be working great right?
> 
> That is what I thought until I did my own testing. Setting min and max both to 350 and streaming music with the screen off, I had greater drain at 750mv than I did at 840mv (smart reflex'd down to 830mv). Starting at 100 both times, 840/830 took about 15 minutes longer to drain to 50%.
> 
> Sent from my Galaxy Nexus using RootzWiki


That's not a horribly accurate test, but I'd believe it. Maybe not 15 minutes, but better off at the high voltages.


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## partychick64 (Nov 5, 2011)

830mV made my phone freeze but yet 840mV was completely fine so I am keeping it at that. Voltages help with battery a lot at least I think so

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## ERIFNOMI (Jun 30, 2011)

partychick64 said:


> 830mV made my phone freeze but yet 840mV was completely fine so I am keeping it at that. Voltages help with battery a lot at least I think so
> 
> Sent from my Galaxy Nexus using RootzWiki


I could run the maths for you but 10mV isn't going to come out to anything meaningful in the end. You'd be better off turning the screen off every time you paused while texting or a web page loaded or something like that







. But sometimes the placebo effect is as good as the real thing.


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