PSU single or multirail?

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it is
drawing 175 watts, I have no video card, am running Intel UHD630 CPU
graphics.
Is there any preference in running the PSU in Single or Multi-rail mode?


Rene

Rene Lamontagne wrote:
My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it is
drawing 175 watts, I have no video card, am running Intel UHD630 CPU
graphics.
Is there any preference in running the PSU in Single or Multi-rail mode?


Rene

PSU single or multi-rail is likely to be a current limiter mode.

This explanation isn't helping me.

http://www.jonnyguru.com/forums/show...f-the-12V-rail

You could do a supply like this. Each output being independent.

AC ---- DC 300V+ --+-- SW ------ ATX12V1
|
+-- SW ------ ATX12V2
|
+-- SW ------ ATX12V3

Or, you could monitor the current flow on each
output, yet use a single source.

AC ---- DC 300V+ ----- SW ----+--- OCP (20A)-- ATX12V1
|
+--- OCP (20A)-- ATX12V2
|
+--- OCP (20A)-- ATX12V3

Now, if you turn off overcurrent monitoring, the
thing "behaves" like a single rail supply. You could
draw 60A through one of the cables, burning the cable.

When the current limiters are turned on, then no
rail can go past its limit (20A), or the PSU switches off.

When a unit has a whizzy way of switching modes, the
box is not likely to be "doing something active to
change how the 60 amps flows". That takes expensive
MOSFETs to actually interrupt the current flow path.
They're not likely to be doing it that way.

Instead, disabling a digital control path with some
logic chips, changes the current monitoring from 3x20A
to a single 60A sensor elsewhere. The 60A sensor
would be closer to "SW", or it might even be
implemented as a "thermal element". I've seen
some supplies making all sorts of claims, that
are backed up by a thermistor bolted to a heatsink :-)

*******

In any case, if the unit was something like this,
the "transformer count" would give it away. For
example, a quad output device years ago, when they
opened it up (it was about three inches longer than
a regular supply), you could count the four transformers.

AC ---- DC 300V+ --+-- SW ------ ATX12V1
|
+-- SW ------ ATX12V2
|
+-- SW ------ ATX12V3

And there's no convenient way of "combining" such
a device such that the outputs are combined into
a single rail. Such a separated design, remains
separated.

Any time you short such outputs together, current
hogging can happen, and one "channel" provides more
of the current than the others. That's why "true"
multi-rail supplies are a nuisance, as they're
not allowed to be shorted together like that.

The biggest problem with true multi-rail supplies,
was the lack of documentation concerning the wire
loom(s) and where stuff was connected. I've seen
cases where it was all too easy to short things
together (like mixing PCIe connectors from
different looms and have them short through the
video card common copper plane). It might not
be obvious to the user what was going on,
except for the "squirrel-like" behavior of
the computer. Something is wrong, but you can't
put your finger on it.

So enjoy your "pseudo-multirail" mode, which is
just a current monitoring option as far as I know.

In the picture here, I think the item with "Corsair"
printed on it, is the common 12V transformer. the
stuff on the left is inlet filtering and active PFC
stuff. I saw the words "resonant mode controller"
somewhere in the review, so perhaps the "hunk" in the
upper left corner is a resonant transformer or coil
for PFC purposes.

The loom distribution has polymer caps and is the
assembly on the right (where the modular connectors
are located). I can't really spot something that
looks definitely like a 3.3V&5V board. There should
be one.

https://www.jonnyguru.com/wp-reviews...750i-027-s.jpg

( https://www.jonnyguru.com/blog/2015/...-power-supply/ )

Whatever mode it ships in, is likely "safe enough".

Paul

Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all loads or
separate your loads across multiple rails. Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load. Your PSU won't run cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup. Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later. At first, retrofitting to multi-rail was about connectivity, not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations. Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each. As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W. While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you will
place on each rail in a multi-rail setup. Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup. I got the Corsair RM750 but the x suffix since I saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W). That has additional power
inputs from the PSU, but my PSU is single rail. Well, Corsair says
nothing about multi-rail in their description or documentation for their
RM750X PSU, and I don't remember anything on the PSU's label or box that
led me to believe it is multiple rails. You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode. I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)? Nope. The in-cable
capacitors are a bitch for routing the cables. Modular is supposed to
make routing easier by using only as many cables as needed. However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility. The cables won't flex for about 2-3 inches from the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning. That's too low a load. In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning. That's a
40% load with no spinning PSU fan. You're running at a 23% load (175W
of 750W). That's assuming you are using default cooling mode instead of
some minimal RPM threshold to cool more than needed.

VanguardLH wrote:
Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all loads or
separate your loads across multiple rails. Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load. Your PSU won't run cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup. Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later. At first, retrofitting to multi-rail was about connectivity, not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations. Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each. As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W. While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you will
place on each rail in a multi-rail setup. Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup. I got the Corsair RM750 but the x suffix since I saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W). That has additional power
inputs from the PSU, but my PSU is single rail. Well, Corsair says
nothing about multi-rail in their description or documentation for their
RM750X PSU, and I don't remember anything on the PSU's label or box that
led me to believe it is multiple rails. You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode. I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)? Nope. The in-cable
capacitors are a bitch for routing the cables. Modular is supposed to
make routing easier by using only as many cables as needed. However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility. The cables won't flex for about 2-3 inches from the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning. That's too low a load. In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning. That's a
40% load with no spinning PSU fan. You're running at a 23% load (175W
of 750W). That's assuming you are using default cooling mode instead of
some minimal RPM threshold to cool more than needed.

The purpose of multi-rail, was intended to meet
one of the SELV requirements. No more than 240W per
DC output. Which is 12V @ 20A. The purpose of that
safety requirement, was a perception by someone in
a standards body, that this reduces the possibility
of fire. The power supply already has a requirement
not to catch fire, but there have been reports from
users, of flames actually exiting via the fan hole.
Which is bad, if you have draperies next to the PC.
A combination of flammable drapes (which were supposed
to have their own chemical safety features added), plus a PC
with "bad table manners", could lead to a catastrophe.

Over the years, the reports of fires have decreased.
Maybe the protection features now, actually work.

Now, there are single rail supplies, where we can't tell
what they are enforcing. It may look like the unit offers
12V @ 60A on any yellow wire (yikes!), but there are likely
OCP setups per loom to prevent such a thing from happening.

I've seen similar rating screwups on older supplies. There
were a few supplies with a 5V @ 40A rating. The product of
those two numbers is still less than 240W (i.e. passes 60950
or whatever the spec is), but the wiring itself is unlikely
to be all that safe if you run 40 amps through it. If you
had a short on the Molex feeding your video card, it
would likely burn the connector clean off.

Paul

On 2019-08-02 1:05 p.m., VanguardLH wrote:
Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all loads or
separate your loads across multiple rails. Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load. Your PSU won't run cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup. Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later. At first, retrofitting to multi-rail was about connectivity, not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations. Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each. As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W. While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you will
place on each rail in a multi-rail setup. Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup. I got the Corsair RM750 but the x suffix since I saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W). That has additional power
inputs from the PSU, but my PSU is single rail. Well, Corsair says
nothing about multi-rail in their description or documentation for their
RM750X PSU, and I don't remember anything on the PSU's label or box that
led me to believe it is multiple rails. You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode. I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)? Nope. The in-cable
capacitors are a bitch for routing the cables. Modular is supposed to
make routing easier by using only as many cables as needed. However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility. The cables won't flex for about 2-3 inches from the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning. That's too low a load. In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning. That's a
40% load with no spinning PSU fan. You're running at a 23% load (175W
of 750W). That's assuming you are using default cooling mode instead of
some minimal RPM threshold to cool more than needed.


Thanks Paul and VanguardLH for the very informative write ups,
The fan never runs and the temp stays at about 44 deg Celsius So at
the light loads I am running means I just as well leave it in multi rail
mode, Only have 1 spinning drive and no Video card means very little
load on a 750 watt unit

Rene

On 2019-08-02 3:26 p.m., Rene Lamontagne wrote:
On 2019-08-02 1:05 p.m., VanguardLH wrote:
Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all loads or
separate your loads across multiple rails.Â* Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load.Â* Your PSU won't run cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup.Â* Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later.Â* At first, retrofitting to multi-rail was about connectivity, not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations.Â* Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each.Â* As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W.Â* While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you will
place on each rail in a multi-rail setup.Â* Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup.Â* I got the Corsair RM750 but the x suffix since I saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W).Â* That has additional power
inputs from the PSU, but my PSU is single rail.Â* Well, Corsair says
nothing about multi-rail in their description or documentation for their
RM750X PSU, and I don't remember anything on the PSU's label or box that
led me to believe it is multiple rails.Â* You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode.Â* I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)?Â* Nope.Â* The in-cable
capacitors are a bitch for routing the cables.Â* Modular is supposed to
make routing easier by using only as many cables as needed.Â* However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility.Â* The cables won't flex for about 2-3 inches from the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning.Â* That's too low a load.Â* In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning.Â* That's a
40% load with no spinning PSU fan.Â* You're running at a 23% load (175W
of 750W).Â* That's assuming you are using default cooling mode instead of
some minimal RPM threshold to cool more than needed.


Thanks Paul and VanguardLH for the very informative write ups,
Â*The fan never runs and the temp stays at about 44 deg CelsiusÂ* So at
the light loads I am running means I just as well leave it in multi rail
mode, Only have 1 spinning drive and no Video card means very little
load on a 750 watt unit

Rene


should have added Pic.

Rene


https://postimg.cc/Wt5Jv4Xh

Rene Lamontagne wrote:
On 2019-08-02 3:26 p.m., Rene Lamontagne wrote:
On 2019-08-02 1:05 p.m., VanguardLH wrote:
Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all loads or
separate your loads across multiple rails. Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load. Your PSU won't run cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup. Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later. At first, retrofitting to multi-rail was about connectivity, not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations. Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each. As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W. While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you will
place on each rail in a multi-rail setup. Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup. I got the Corsair RM750 but the x suffix since I saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W). That has additional power
inputs from the PSU, but my PSU is single rail. Well, Corsair says
nothing about multi-rail in their description or documentation for their
RM750X PSU, and I don't remember anything on the PSU's label or box that
led me to believe it is multiple rails. You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode. I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)? Nope. The in-cable
capacitors are a bitch for routing the cables. Modular is supposed to
make routing easier by using only as many cables as needed. However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility. The cables won't flex for about 2-3 inches from the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning. That's too low a load. In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning. That's a
40% load with no spinning PSU fan. You're running at a 23% load (175W
of 750W). That's assuming you are using default cooling mode instead of
some minimal RPM threshold to cool more than needed.


Thanks Paul and VanguardLH for the very informative write ups,
The fan never runs and the temp stays at about 44 deg Celsius So at
the light loads I am running means I just as well leave it in multi
rail mode, Only have 1 spinning drive and no Video card means very
little load on a 750 watt unit

Rene


should have added Pic.

Rene


https://postimg.cc/Wt5Jv4Xh

That's a pretty efficient supply. I don't think any
of mine are that good.

Paul

On 2019-08-02 4:45 p.m., Paul wrote:
Rene Lamontagne wrote:
On 2019-08-02 3:26 p.m., Rene Lamontagne wrote:
On 2019-08-02 1:05 p.m., VanguardLH wrote:
Rene Lamontagne wrote:

My system is running a RM750i psu, At idle with windows 10 on the
desktop it is drawing 53 Watts, At full 100% load running Prime 95 it
is drawing 175 watts, I have no video card, am running Intel UHD630
CPU graphics.

Is there any preference in running the PSU in Single or
Multi-rail mode?

Efficiency doesn't change whether you use a single rail for all
loads or
separate your loads across multiple rails.Â* Because efficiency doesn't
change, and you don't get 100% efficiency, neither does the amount of
heat produced change for the same total load.Â* Your PSU won't run
cooler
under the same load whether you set it to single- or multi-rail mode.
With 2 rails of 40A max with each having a 20A load or a single rail
with 40A load, the PSU still has to supply the 40A load.

https://www.youtube.com/watch?v=rC-ImSeYn2A

That author references Jonny Guru (works for Corsair) who speaks in
this
next video:

https://www.youtube.com/watch?v=PWtKSHT2od8

It isn't about reducing how much heat from the PSU produced the total
load (well, in a way, yes it is) but about the safety feature of
limiting how much of a load can be placed on a rail in a multi-rail
setup.Â* Multi-rail was initially poorly implemented and just slicing
apart the single rail to provide the power connectors for video cards
that drew more power than the PCI bus could handle, but the separate
rail for PCI card didn't get more power (which caused shutdowns) until
later.Â* At first, retrofitting to multi-rail was about connectivity,
not
supplying enough juice on each rail.

Multi-rail is more popular in Europe because of their safety
regulations.Â* Whether you can use multi-rail mode depends on the load
each rail can handle and what max load you will place on each.Â* As 2nd
video notes, you end up with a max of, say, 40A on a rail in multi-rail
mode instead of 83A on a single rail, so a short (that's not caught by
the PSU's logic) would dissipate 480W or 996W.Â* While 480W is safer in
preventing fires, a 100W incandescent bulb laying against your wood
sided house is still going to scorch the siding and maybe start a fire,
so even 100W is safer but doesn't prevent fires, either.

I saw no advantage to single- versus multi-rail mode unless you're a
jobber that disregards or doesn't check what load the video card,
drives, mobo, and other devices will draw to know how much load you
will
place on each rail in a multi-rail setup.Â* Getting the full load spec
for each device can be daunting to impossible, and using multi-rail can
result in unexpected PSU shutdowns, so it is easier to build using a
single-rail setup.Â* I got the Corsair RM750 but the x suffix since I
saw
no advantage to paying another $20 for a multi-rail PSU that I'd be
running in single-rail mode, anyway.

I'm using an AMD RX580 video card (185W).Â* That has additional power
inputs from the PSU, but my PSU is single rail.Â* Well, Corsair says
nothing about multi-rail in their description or documentation for
their
RM750X PSU, and I don't remember anything on the PSU's label or box
that
led me to believe it is multiple rails.Â* You're using the onboard video
controller embedded in the CPU on the motherboard, so it's getting its
power from the 24-pin ATX connector (and optionally from 4-pin ATX or
8-pin EPS12V connector if your mobo has that connection).

If each load for each connection to the PSU is under the lowered
amperage limit for that connection in multi-rail mode, you can see what
happens going from single- to multi-rail mode.Â* I don't expect you'll
see any change in how much heat is produced by the PSU because the PSU
still has to source each and every rail, and the efficiency of the PSU
doesn't change.

Would I buy another Corsair RM750 (x or i)?Â* Nope.Â* The in-cable
capacitors are a bitch for routing the cables.Â* Modular is supposed to
make routing easier by using only as many cables as needed.Â* However,
Corsair putting the ripple voltage capacitors in the cables result in
losing flexibility.Â* The cables won't flex for about 2-3 inches from
the
connector, and this can result in having to do some creating routing to
use those cables without making a mess (visibly and for airflow) inside
the case.

Even at 175W, tis likely the fan inside the Corsair RM750i is even
spinning.Â* That's too low a load.Â* In the 2nd video, Jonny had a 1000W
Corsair PSU running at 400W and the fan wasn't yet spinning.Â* That's a
40% load with no spinning PSU fan.Â* You're running at a 23% load (175W
of 750W).Â* That's assuming you are using default cooling mode
instead of
some minimal RPM threshold to cool more than needed.


Thanks Paul and VanguardLH for the very informative write ups,
Â* The fan never runs and the temp stays at about 44 deg CelsiusÂ* So
at the light loads I am running means I just as well leave it in
multi rail mode, Only have 1 spinning drive and no Video card means
very little load on a 750 watt unit
Rene


should have added Pic.

Rene


https://postimg.cc/Wt5Jv4Xh

That's a pretty efficient supply. I don't think any
of mine are that good.

Â*Â* Paul

Yes, Good unit, about $165.00 I like a good PSU when I build, THE PSU

is often downplayed but I feel it is the foundation of a good system.

Rene

Rene Lamontagne wrote:

Yes, Good unit, about $165.00 I like a good PSU when I build, THE PSU
is often downplayed but I feel it is the foundation of a good system.

When I bought the RM750x from Newegg (might've been on sale), its cost
was $129 (and is that price today). As I recall, the RM750i was $20
more. I see the RM750i is now on sale from Corsair for $115 ($110 from
Newegg after rebate). Argh!!! Of course, if I waited another couple
years to do my new build, I would save lots more. Tis the price of
having now instead of waiting for later.

The $20 difference (at the time) would not have been enough for me to
forego the RM750i and instead get the RM750x. There was something back
then about the RM750i that veered me away from that product. I can't
remember why I chose the RM750x over the RM750i. Likely I didn't give a
gnat's fart about the glitzy extra features that I wouldn't use and
decided not to pay for.

However, from what I see of the pics for the cables for both the RM750i
and RM750x, both use those those damn in-cable endpoint ripple
capacitors that result in impossible to bend cables at their ends. For
those that like to keep neat their case inside, especially when using a
case where the 2nd panel comes off and there's room behind the mobo
plate to hide cables, those endpoint capacitors can make routing a
challenge both for routing and keeping down the curse word count.

On 2019-08-02 5:55 p.m., VanguardLH wrote:
Rene Lamontagne wrote:

Yes, Good unit, about $165.00 I like a good PSU when I build, THE PSU
is often downplayed but I feel it is the foundation of a good system.

When I bought the RM750x from Newegg (might've been on sale), its cost
was $129 (and is that price today). As I recall, the RM750i was $20
more. I see the RM750i is now on sale from Corsair for $115 ($110 from
Newegg after rebate). Argh!!! Of course, if I waited another couple
years to do my new build, I would save lots more. Tis the price of
having now instead of waiting for later.

The $20 difference (at the time) would not have been enough for me to
forego the RM750i and instead get the RM750x. There was something back
then about the RM750i that veered me away from that product. I can't
remember why I chose the RM750x over the RM750i. Likely I didn't give a
gnat's fart about the glitzy extra features that I wouldn't use and
decided not to pay for.

However, from what I see of the pics for the cables for both the RM750i
and RM750x, both use those those damn in-cable endpoint ripple
capacitors that result in impossible to bend cables at their ends. For
those that like to keep neat their case inside, especially when using a
case where the 2nd panel comes off and there's room behind the mobo
plate to hide cables, those endpoint capacitors can make routing a
challenge both for routing and keeping down the curse word count.


Yes it do make the cables hard to manage, A couple days ago I took out
the redundant Video card 12 volt cable with the dual plugs, that
cleaned it up quite a bit.
Now with no Video card and cables and 2 small NVMe drives I have plenty
of open space now, Sorta like a small dance hall. :-)

Rene