• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Why is my 5V so low? Read this

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.
It's not so much how much higher in frequency you can clock, but how much higher you can take the core voltage, if needed to achieve a stable overclock. Of course, you have to also have good cooling to dissipate that additional wattage. Without the modification, when I ran my core above about 1.75V, I could see the +5V start dropping. By the time the core voltage was at 1.9, the +5 was down to 4.85 and at a core voltage of 2.0, it was down to 4.75. Both of those drops even though the PSU output only went from 5.10 to 5.05.
So, to answer your question. If you have adequate cooling for 100+ watts of heat, then increasing the core voltage will allow you to increase your CPU speed, up to the point where your other system components, even the motherboards characteristics start to be a limiting factor. Keep in mind that every CPU has a sweet zone where increasing the voltage allows you to increase the speed. Once you are outside that sweet zone, it takes a lot more voltage to get a small additional gain in performance. I strongly believe you should not operate your CPU in that region, but rather hang around the top of the sweet zone. I typically test a setup for every additional mhz increase I can squeeze out of it, to find the absolute maximum it can obtain. I look at how hard everything is working to achieve that. Then, with an eye on reliability and longevity, I usually back it down a little bit and leave it there. To some overclockers, that may sound like heresy, but I don't run my car at the Red Line continuously either.

Hoot
 
I measured the Voltage on my MOSFETS and a ground and it says 6.06v

but my bios and my HWMonitor say I have 4.66at high speed.

I measured it at molex 4 pin and I get 6.16v and about 17v!!! no wonder my deltas screamed that high!!! jejejeje I use a rheostat and it lower to 11.5v!!!!

Anyways...


WHy is this happening?

the reading on the 5v regulators seems to be MORE THAN ADEQUATE...
 
That doesn't sound right. Are you sure you're measuring the Mosfets associated with your core voltage regulator or the Vagp regulator?

Hoot
 
YESSS i did that but you were also right it sounded strange... I bought a new 9v battery to my voltimeter... and guess what.. my PS is throwing now 4.99V vs 4.73 on the mosfets now...

My other question is... I did the volt mod with just one cable...
it had no effect... Must I do it with all 3?
I checked with the volt meter on that mosfets and I was getting 4.99v but my bios and HW mon kept saying 4.73.

Let me know.. Thanks
Thanks
 
Hoot: Now I understand why my +5V line drops again.
Will try to fix it at 1.85V and then see what the +5V line does. Right now I modded it to 1.95V.

I'm just so irritated that I can't get 1705Mhz stable under load!

Little thought. Would it be a nice idea to take 2 small PSU (125W from an old 486'er) and use those +5V on each of the mosfets gates of my mobo? that way there is no problem when using the main PSU for it.

What do you people think about it?
 
The Highlander said:
YESSS i did that but you were also right it sounded strange... I bought a new 9v battery to my voltimeter... and guess what.. my PS is throwing now 4.99V vs 4.73 on the mosfets now...

My other question is... I did the volt mod with just one cable...
it had no effect... Must I do it with all 3?
I checked with the volt meter on that mosfets and I was getting 4.99v but my bios and HW mon kept saying 4.73.

Let me know.. Thanks
Thanks

Assuming you have a good battery in it, :D always trust your voltmeter above the on-board monitoring circuit. I must confess that I've never seen that large of an error in an on-board monitoring circuit. It's usually on the order of .05V or less, not .26V. One additional 5V conductor to the Mosfets should be sufficient.

Hoot
 
Ok... So i did the voltage modification to another mosfet of those... Now I have 2 of them wired...

My system is again stable... Something happened that the 5V dropped to 4.60... I had removed the 5v mod... Now I did the mod again to 2 and it raised to 4.71 under seti...

Everything stable again...

But ... I think I'll have to do it to the 3rd one to get to the 5.00v mark..
 
stupid question maybe, and maybe also already answered, but with multiple mosfets do you take mutiple wires too or just one single wire and split them to the various mosfets?
 
Hoot said:


If you dont have access to a voltmeter, find someone with an 8KHA+ who does and have them determine it for you.

Hoot

Which brings me to this, for all to whom it's relavent:
 
I measured the mosfet on my shuttle ak31 with a analog multimeter it's showing a little over 5 volts under load the same as psu is putting out so there isn't much of a voltage drop. mbm is reporting +5 volt line at 4.81-4.87 the only thing I can figure is multimeter isn't reading too accurate but since there isn't any drop I'm thinking my problem is I need a bigger psu right now I'm using a enhance 300w.
 
Re: What do you think?

ElectricMan said:
I checked out my system , I hooked up the multitester like this. one lead going to a blk wire from one of my drives and the other lead going to the center lug in the mosfet. I had 5.09volt's. I then played a music cd and put a dvd movie in and them ran 2001 mark and it went down to 5.02 .I am a electrician (Building's) but I think from what you guys are saying that is good and needs nothing, no mod like hoot did is needed. I have a Aopen Case and power supply 300 watt. What do you all think????

I've been doing the figuring too, and as best I can figure out the resistance can't be in the connector (at least not the most of it). This mod may do enough to work, but I think the effective resistance of the PSU itself may actually be the primary culprit. If it really is that much of a problem for some people, maybe they should shell out the money for a PSU from PC Power and Cooling. One of the nifty things their powersupplies do is flatten that voltage/load curve so it is always 5v.

Any way I had some Ideas of my own on the subject though I started them on a thread on AthlonMB

Anyone want to check my math for me?
 
I think I just figured out the flaw in my reasoning. When the motherboard or other devices are trying to draw more power in most cases it is probably an act of flipping on a switch to power something creating anothe path for current and thereby DECREASING the resistance across the five volt rails. Since the resistance of the PSU and the cables remains the same this means that the devices alonf the five volt rails have become a lesser portion of the total resistance and thereby drop a lesser portion of the total voltage. This means that my logic that most of the resistance can't be in the cabling is false (sorry, wrong side of the curve).

Still my idea might work for those who are borderline and merely suffer from rebooting and such when other devices briefly draw more power. The tapping of a capacitor onto the circuit would help stabilize the line voltage and might prevent problems from all but the lenthiest drains.

My suggestion would be to try a number of things before this mod:

Remove some of the possible oxide layer from the power connector pins by disconnecting and reconnecting it several times.

Try the screwdriver trick previously described where you re-narrow the recpeticles for the pins on the connector to make the friction conection less resistive.
 
HOOT!!!!

I did the voltage mod to all my mosfets...
Now I am using a KR7A instead of a KG7.

The 5V at stock VCore was 4.95v now is at 4.84v under load with the modification... why???

MY PSU is delivering... but why dont I see it near 5v on the MBM5?
 
The Highlander said:
HOOT!!!!

I did the voltage mod to all my mosfets...
Now I am using a KR7A instead of a KG7.

The 5V at stock VCore was 4.95v now is at 4.84v under load with the modification... why???

MY PSU is delivering... but why dont I see it near 5v on the MBM5?

I think I'd get another opinion on what that resultant voltage is, like from a multi-meter. That is not what should happen. I take it you were thorough in determining which Mosfets to tap in to, or else you system would not be running. You did not say what the voltage was you read at one of the unused molex connectors. That would give you the voltage present at the output of the PSU, before it makes the journey to the Mosfets.

Hoot
 
5.05v on the power supply

on the multimeter it says 5. but Its a direct connection with the system, so... I think its a bit obvlious that it will show 5v on the multimeter...

Let me know!!!
 
Pardon me if these questions have been asked already- I looked thru the rest of this and the other PSU thread but I cannot find what I seek! Maybe I missed 'em- sorry if I did.

First- how low is your 5V line allowed to drop? I see folks with it at 4.9, 4.8, 4.7.... what is an acceptable drop, and what would be considered 'dangerous'?

Second- what are the symptoms of a too-low 5V line? If your 5V is too low, it's gotta have some effect on your system. Does it reboot itself, does it lockup alot, would it get 50+mhz more OC if it had the right voltage, what? Basically- how do you know for SURE that you need to up your 5V?

I just want to get this straightened out before I even think about modding my mobo. I'm not worried about frying it, I just want to be sure it is worth doing.
 
Monster of Rock said:
Pardon me if these questions have been asked already- I looked thru the rest of this and the other PSU thread but I cannot find what I seek! Maybe I missed 'em- sorry if I did.

First- how low is your 5V line allowed to drop? I see folks with it at 4.9, 4.8, 4.7.... what is an acceptable drop, and what would be considered 'dangerous'?

Second- what are the symptoms of a too-low 5V line? If your 5V is too low, it's gotta have some effect on your system. Does it reboot itself, does it lockup alot, would it get 50+mhz more OC if it had the right voltage, what? Basically- how do you know for SURE that you need to up your 5V?

I just want to get this straightened out before I even think about modding my mobo. I'm not worried about frying it, I just want to be sure it is worth doing.
reboots or lockups are common with low 5v line. Don't know what you would call acceptable mine is 4.78 and I can't overclock any higher 1618 and if I raise vcore past 1.85 it won't boot into windows. As long as your happy with your stablity at whatever speed you have your cpu running then your fine but if your running into problem a low 5v line might be the cause. I'm sure I could go higher if 5v line was a little higher.
 
ok that makes sense, thx res0r9lm

my situation is this- my celeron 566 is super happy at 961, very slightly flaky at 975, and very unhappy at 995, even when boosting vcore to 2.05. It flakes out by rebooting or jumping straight to the W2K blue screen at odd times- it will run folding fine for hours then crash hard as you open notepad, that kind of thing.

Does this sound like a power supply issue? The C566 stepping I have usually runs out of juice right around there, so I am unsure if it is my CPU or PSU holding me back.
 
Back