7v mod - safe?

[flexy]

we all know the simple 7v mod, where you exchange the GND connector on a molex with the +5V to get +12V & +5V == +7V

My question is whether this has any negative effect ?

The PSU is a 750W High Quality PSU w/ plenty amps. I just want to know whether there is a reason which would speak against using this mod?

G.

 

[The Boston Dangler]

i suggest against bucking power. you can pick up a 3-pin to 3-pin resistor pretty cheaply.

 

[Rubycon]

Originally posted by: The Boston Dangler
i suggest against bucking power. you can pick up a 3-pin to 3-pin resistor pretty cheaply.

Yep - I don't recommend the 7V mod.

 

[CallMeJoe]

I know a lot of people who swear by the 7V mod, but I have to agree with Dangler and Rubycon on this one. Cross connecting two regulated sources is just not sound practice, especially considering how many cheap, simple fan controls are available.

 

[aigomorla]

+3


Drawing from the 12V+ and 5V+ can put quite a load on your psu. Hence why its not recomended. Use a fan controller to get the voltage, thats my 2cents.

 

[DerwenArtos12]

I've done it a number of times and it's safety genuinely matters most on the PSU design. johnny could explain the reasons why but, I had an old cheapy 350W running for many years with the 7v mod with no problems what so ever. I tried it once on my seasonic S12-600 and realy thought I killed my rig but, was able to drag it back with a full cap drain and re-power. I've done it on other power supplies but, I honestly don't remember which models it's worked on and which it hasn't. I'll gladly say this, a reistor or potentiometer are much safer ways of achieving whatever voltage you want and gives you a lot more options as far as speed control is concerned. Things like this are YMMV and do carry a chance of permanent system damage.

 

[flexy]

yes..thats about what i remembered too. so, to be on the safe side i use a potentiometer now.

the funny thing is on many many articles regarding this mod noone ever mentioned the potential damage, depending on PSU of course. But since my Corsair (== Seasonic!) blew yesterday i can see this mod *maybe* having a part to do with it so i wont use the 7v mod anymore.

 

[DerwenArtos12]

Originally posted by: flexy
yes..thats about what i remembered too. so, to be on the safe side i use a potentiometer now.

the funny thing is on many many articles regarding this mod noone ever mentioned the potential damage, depending on PSU of course. But since my Corsair (== Seasonic!) blew yesterday i can see this mod *maybe* having a part to do with it so i wont use the 7v mod anymore.

were you able to fully power cycle your PSU and get it back or was it a smoke/light show?

 

[Navid]

In this arrangement (12V - 5V= 7V), current flows from the 12V rail through the fan to the 5V rail.

Each rail of the power supply is driven by a voltage regulator.
Common voltage regulators are designed to supply current, not to receive current.
The current that flows through the fan has to be less than the current that the components draw from the 5V rail. Then, as far as the supply is concerned everything is fine and every regulator only supplies current.

However, if the fan current is more than the total current your computer components draw from the 5V rail, it effectively is like the 12V rail is charging the 5V rail. The supply may not like that.
The possibility of such a problem goes up as you increase the number of fans since you increase the overall fan current.

At bootup, the components don't all turn on at the same time. So, even if you think you are OK with the overall load you have on the 5V rail compared to the current the fan draws, you may still have a problem at bootup.

As everybody else has stated already, the ease of the 7V mod is not worth the risk.

 

[flexy]

Originally posted by: DerwenArtos12

Originally posted by: flexy
yes..thats about what i remembered too. so, to be on the safe side i use a potentiometer now.

the funny thing is on many many articles regarding this mod noone ever mentioned the potential damage, depending on PSU of course. But since my Corsair (== Seasonic!) blew yesterday i can see this mod *maybe* having a part to do with it so i wont use the 7v mod anymore.

were you able to fully power cycle your PSU and get it back or was it a smoke/light show?

I posted a thread in the PSU forum, but just short:

I did a very extensive graphics benchmark (furmark) which puts more load on the card than crysis benchmark. (I get +4 degrees on the GTS with furmark over crysis GPU bench!)

PC shut down all of a sudden - then the PSU tried to re-power the PC 4-5 times in *very quick* succession (all happened in maybe 2 secs)...and finally popped and sparked and took out all power in the house

GF swears she saw a spark flying from the back across the room.

Anyway, thinking it was maybe only the fuse i went out getting replacement fuse and soldered a new one in...re-started PSU (not connected to the PC this time).....but it popped again.
I didnt see any burn-marks (except busted fuse) or smell or anything in the PSU. I got a Toughpower 750W now and got rid of the 7V mod.

As said the 7V mod having a part in this is certainly possible.

 

[DerwenArtos12]

Originally posted by: flexy

Originally posted by: DerwenArtos12

Originally posted by: flexy
yes..thats about what i remembered too. so, to be on the safe side i use a potentiometer now.

the funny thing is on many many articles regarding this mod noone ever mentioned the potential damage, depending on PSU of course. But since my Corsair (== Seasonic!) blew yesterday i can see this mod *maybe* having a part to do with it so i wont use the 7v mod anymore.

were you able to fully power cycle your PSU and get it back or was it a smoke/light show?

I posted a thread in the PSU forum, but just short:

I did a very extensive graphics benchmark (furmark) which puts more load on the card than crysis benchmark. (I get +4 degrees on the GTS with furmark over crysis GPU bench!)

PC shut down all of a sudden - then the PSU tried to re-power the PC 4-5 times in *very quick* succession (all happened in maybe 2 secs)...and finally popped and sparked and took out all power in the house

GF swears she saw a spark flying from the back across the room.

Anyway, thinking it was maybe only the fuse i went out getting replacement fuse and soldered a new one in...re-started PSU (not connected to the PC this time).....but it popped again.
I didnt see any burn-marks (except busted fuse) or smell or anything in the PSU. I got a Toughpower 750W now and got rid of the 7V mod.

As said the 7V mod having a part in this is certainly possible.

huh, typically if the 7v mod is going to short your psu it'll do it right at start-up. Sorry for your loss.

 

[toadeater]

Bah. I've used 7v mods for years on numerous PCs with all kinds of PSUs. Not a damned thing ever happened with any of the PSUs or any other components. Including after some accidental shorts due to exposed wiring (electrical tape fell off). I'm using one right now, until I get new fans. The most I've ran modded simultaneously were two fans, it's possibly that more could start to do some damage?

I'd still suggest avoiding them, they do mess with the PSU's +12v rail(s). E.g. on the PSU I'm using it on now, the voltage dropped from a steady 12v to a steady 11.37v. If I unplug the fan, it goes back to 12v. Not permanent damage apparently.

 

[DerwenArtos12]

Originally posted by: toadeater
I'd still suggest avoiding them, they do mess with the PSU's +12v rail(s). E.g. on the PSU I'm using it on now, the voltage dropped from a steady 12v to a steady 11.37v. If I unplug the fan, it goes back to 12v. Not permanent damage apparently.

That is really unusual, I don't see a particular reason for the 12v rail dropping that much with just a 7v mod. The main issue with this mod is that the 5V rail will overload. I've never designed a PC power supply but, I have designed inverters and line conditioners and votage regulation circuits and I don't see why any quality with a decent voltage regulator would drop that much just from the flowback to the 5V rail. I'll point johnny to this post and see if he can give some insight.

 

[CallMeJoe]

Originally posted by: DerwenArtos12
That is really unusual, I don't see a particular reason for the 12v rail dropping that much with just a 7v mod. The main issue with this mod is that the 5V rail will overload. I've never designed a PC power supply but, I have designed inverters and line conditioners and voltage regulation circuits and I don't see why any quality with a decent voltage regulator would drop that much just from the flowback to the 5V rail. I'll point johnny to this post and see if he can give some insight.

I admit I've never studied PC PSU designs, but switching regulators in the avionics units I repair typically have one primary voltage they regulate to with a high degree of precision (~1%); the other voltages scale from the regulated line, with secondary regulation loops that only cut in if the secondary regulated voltages vary significantly (>5%) from nominal.

If the PSU's primary regulation loop is on the 5VDC rail, the voltage bled over through the fan from the 12VDC rail could cause the PSU to pull its outputs down to hold the 5VDC line within tolerance.


edit: This type of inter-rail loading glitch is another argument against the 7V mod. As has been asked before, why risk a problem when there are so many other cheap and easily available solutions?

 

[aigomorla]

Originally posted by: Navid

The possibility of such a problem goes up as you increase the number of fans since you increase the overall fan current.

At bootup, the components don't all turn on at the same time. So, even if you think you are OK with the overall load you have on the 5V rail compared to the current the fan draws, you may still have a problem at bootup.

As everybody else has stated already, the ease of the 7V mod is not worth the risk.

What navid says here is the reason why. One fan isnt always an issue, its when you stack them, or if that fan is pushing a lot of amps.

Hence each case is a Your Millage May Vary Scenario so it should be avoided alltogether.

Just get a fan contoler and save yourself the possibility of a headache.

 

[Modelworks]

Just pick up a couple LM78xx regulators and have whatever voltage you want .
Change xx for whatever voltage you want and thats the part number, 7805=5volts.
Very easy to use, 3 pins, IN, GND, OUT.
Instant regulated voltage for whatever you want at 1Amp.
About 2 for 1.00 most places.

Or you can use a resistor but remember that voltage will change with load.
I like the 78xx though, just install one , bolt to case.
Using 7809 currently.

 

[Rubycon]

Originally posted by: Modelworks
Just pick up a couple LM78xx regulators and have whatever voltage you want .
Change xx for whatever voltage you want and thats the part number, 7805=5volts.
Very easy to use, 3 pins, IN, GND, OUT.
Instant regulated voltage for whatever you want at 1Amp.
About 2 for 1.00 most places.

Or you can use a resistor but remember that voltage will change with load.
I like the 78xx though, just install one , bolt to case.
Using 7809 currently.

Yes just make sure to adequate sink the package (TO-220) as it will get hot near full output with multiple fans.

RE: Instability - sometimes all it takes is one "out of nominal" operation to make a supply become unstable with certain areas loaded. If a feedback loop develops things will go bad in short order.

 

[Modelworks]

Originally posted by: Rubycon

Originally posted by: Modelworks
Just pick up a couple LM78xx regulators and have whatever voltage you want .
Change xx for whatever voltage you want and thats the part number, 7805=5volts.
Very easy to use, 3 pins, IN, GND, OUT.
Instant regulated voltage for whatever you want at 1Amp.
About 2 for 1.00 most places.

Or you can use a resistor but remember that voltage will change with load.
I like the 78xx though, just install one , bolt to case.
Using 7809 currently.

Yes just make sure to adequate sink the package (TO-220) as it will get hot near full output with multiple fans.

Yeah, forgot to add that part.
Thats why I just bolt it to the metal pc case, perfect heatsink

 

[DerwenArtos12]

Originally posted by: Modelworks

Originally posted by: Rubycon

Originally posted by: Modelworks
Just pick up a couple LM78xx regulators and have whatever voltage you want .
Change xx for whatever voltage you want and thats the part number, 7805=5volts.
Very easy to use, 3 pins, IN, GND, OUT.
Instant regulated voltage for whatever you want at 1Amp.
About 2 for 1.00 most places.

Or you can use a resistor but remember that voltage will change with load.
I like the 78xx though, just install one , bolt to case.
Using 7809 currently.

Yes just make sure to adequate sink the package (TO-220) as it will get hot near full output with multiple fans.

Yeah, forgot to add that part.
Thats why I just bolt it to the metal pc case, perfect heatsink

Just looked those up, they look perfect for grabbing an 05 and an 07or08 and wiring up a tptt switch with 12v on the last pole, I may have to build myself a couple of these.

 

[toadeater]

Just for future reference, could one of these regulators be found in an old broken VCR or stereo receiver, etc? If I'm going to order anything, it's going to be a new silent fan, not a voltage regulator.

 

[DerwenArtos12]

Originally posted by: toadeater
Just for future reference, could one of these regulators be found in an old broken VCR or stereo receiver, etc? If I'm going to order anything, it's going to be a new silent fan, not a voltage regulator.

Silent fans are great for purpose buit silent system. Multipurpose systems or high end systems that you just want to be quiet while you're not playing are really where fan speed adjustments are necessary. That being said, if it's only for gaming and you want it silent while you're not playing, turn it off. Some things aren't as simple as they're made out to be, others actually are.

 

[Modelworks]

Originally posted by: toadeater
Just for future reference, could one of these regulators be found in an old broken VCR or stereo receiver, etc? If I'm going to order anything, it's going to be a new silent fan, not a voltage regulator.

Its highly likely.
They are used in tons of consumer devices because they are so cheap and easy to use.

 

[Navid]

To keep this complete, it should be mentioned that another big advantage of the 7V mod is that it does not dissipate any power.

If you power a bunch of fans at 7V and they take a total of 1A, you will be wasting at least 5 Watts in heat if you use a regulator or resistor or fan controller.
You would be wasting 0W if you used the mod.

But, I still do not recommend the mod.