• Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
    Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.

Do rails drop under load?

N

Nakamori

Gawd
Joined
Jun 11, 2005
Messages
530
When completely idle my 3.3V rail shows 3.17V (This is a software measurement; I borrowed a multimeter a while ago and the actual measurement was 3.26), but when running firefox + itunes it drops down to 3.15. It tends to stay at 3.14-3.15 when gaming. I assume this would be around 3.22-3.24 with the real multimeter measurement.

Is this normal?
 
When under load it is quite common for a rail to change voltage. So long as it remains in spec (+/-5%) it is dfine. Be sure to check your rails under load with a multimeter also.
 
Even if the rails are within spec, sudden drops could cause a lock up, etc. The 5% tolerance is good over longer period of time.

That's a pretty drastic drop for a 3.3V rail. That's more like something I'd see out of a 12V rail with a pair of 7800's! :D

What kind of board is this?

*fortune cookie guess* Asus A7N8X? */guess*
 
JG- you consider a drop from 3.17 to 3.14 while gaming serious? that's only ~ 1%.

Something to consider is that the drops may not be as dramatic when viewed with DMM this is the my case. My sensor readings as measured by MBM high low logs consistently drop from 3.43V idle to 3.39V under full load and 12V drops from 12.30V to 12.10V. But when watching the same 12V on a DMM shows a less dramatic drop of 12.30 idle to 12.23 load
 
I will clarify: I do NOT think a 1%.. or even a 5% drop serious. It's the rate at which the drop occurs.

A "gradual" drop would not be a concern.

Also, it's not normal for such a drop to occur on a 3.3V rail. Yes, even if it's within spec.. I'm not used to seeing drops in the 3.3V rail.
 
Drop rate isn't a problem.

What matters is that voltage is high enough so chips will function - and almost all 3.3V-powered chips in existance are speced to run at 3.0 - and low enough so shit doesn't blow up, you're fine.

And you'd be surprised how little stuff on a motherboard actually runs off 3.3V...
 
If gee says so. :D :D

What runs off of 3.3V these days: Umm... RAM. Anything else? ;)

The only time I've seen a 3.3V rail drop that much during use (not the drop from post to boot. Any drop is normal there.) was an Asus A7N8X... and I've seen that a couple times!

I'm curious to see if the OP has that type of board. :D
 
DDR is normally 2.5V, which is derived from 3.3V (or 5V in some situations) using a LDO. As long as the 3.3V rail doesn't drop too much, the DDR should remain at 2.5V.

3.3V powers things like IDE controllers, PCI slots, etc. Beyond that, almost everything is run off lower voltages that are regulated down from 3.3V or 5V.
 
Does this info apply to the Asus p4p800 "droop problem" or is it a different topic ? I keep finding references, but no hard info on this.


 
I have an MSI K7N2M-V mATX board with nforce2. I'm going to get another stick of ram, so we'll see how the 3.3v handles that.
 
gee said:
Drop rate isn't a problem.

What matters is that voltage is high enough so chips will function - and almost all 3.3V-powered chips in existance are speced to run at 3.0 - and low enough so shit doesn't blow up, you're fine.

And you'd be surprised how little stuff on a motherboard actually runs off 3.3V...
Click to expand...

...are you saying that the 5% drop limit doesnt really apply to the 3.3v rail anymore, because current cpus run more from the 12v rail these days? That anything significantly higher than 3.0v is fine?

just wanted to make sure i understood you correctly, so that I don't panic over a couple of .02-.03 volt drops.
 
gee said:
DDR is normally 2.5V, which is derived from 3.3V (or 5V in some situations) using a LDO.
Click to expand...

Correct (although I wasn't aware of any boards that regulated RAM voltage off of the 5V, why not, right?) and I do remember you saying something about the LDO having it's own built in tolerance that can compensate for any voltage fluctuations, is that correct?

If so, then I guess fluctuation on the 3.3V is really a non-issue. But whenever I see radical drops like that (ok, ok, it's not really radical) I'm suspect since a power supply should be able to hold it's rails.

Of course, we didn't get any info from the OP about what kind of PSU it is. Given that the board is a K7N2M, it may be just a crossload characteristic of the power supply.
 
Its the stock psu that came with the aspire qpack. They apparently improved the psu that come with it, as it gives 26A on the 3.3, 38A on the 5.0V, and 30A on the 12.0V.

my other rails are rock-solid.
 
You must log in or register to reply here.
Back
Top