HX650 vs RM750

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davidshbaek

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Nov 19, 2013
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Hey guys, I ended up with HX650 and RM 750 on hand (yes, there is 100W difference between the two, not a typo!). Both of them are Gold certified and only differ by $10. I am looking into refunding one but after much research into both of them, couldn't really come to a conclusion.... I don't have much plan for OC'ing my computer, probably only up to 4.2GHz. I know HX is top-notch series for PSU so I know I can't go wrong with that. On the other side, RM is claimed by Corsair to be an ultra-quiet PSU. But they only released it recently and am wondering if it will be reliable for my computer.... so anyone who has experience of using RM or know much about it to compare against HX, please help me out. Don't forget the 100W difference (HX650 vs RM750) but I don't think it will matter much for my build - either gives me plenty power right?

For your reference here's my spec,

CPU: i7-4770K
Motherboard: Asus Z87-A
Graphic: MSI Radeon HD7870
RAM: Kingston HyperX 8GB 1600/CL9
HDD: Seagate Barracuda 1TB
SSD: Samsung EVO 250GB
Cooler: Corsair Hydro Series H60
Case: Corsair Carbide 400R
 
Solution
ko888
For a system using a single AMD reference design Radeon HD 7870 GHz Edition graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 28 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.

For a system using two AMD reference design Radeon HD 7870 GHz Edition graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 40 Amps or...
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ko888

ko888

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Feb 18, 2009
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For a system using a single AMD reference design Radeon HD 7870 GHz Edition graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 28 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.

For a system using two AMD reference design Radeon HD 7870 GHz Edition graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 40 Amps or greater and have at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.

Overclocking of the CPU and/or GPU(s) may require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.

The Corsair HX650 (SKU# 75-001217 / CP-9020030) power supply unit, with its maximum combined +12 Volt continuous current rating of 54 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with a single Radeon HD 7870 GHz Edition graphics card. It is also more than electrically sufficient to power your system configuration with two Radeon HD 7870 GHz Edition graphics cards in 2-way CrossFireX mode but it lacks the extra two 6-pin PCI Express supplementary power connectors that will be needed. This HX Series PSU model is of higher quality than the RM Series. This specific PSU model uses Seasonic as its OEM.

The Corsair RM750 (SKU# 75-001937 / CP-9020055) power supply unit, with its maximum combined +12 Volt continuous current rating of 62.5 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with a single Radeon HD 7870 GHz Edition graphics card. It is also way more than sufficient to power your system configuration with two Radeon HD 7870 GHz Edition graphics cards in 2-way CrossFireX mode. There was a reported thermal problem with this model and it has been revised. Make sure your model has a serial number that starts with 1341xxxxx or later because they would be the revised model. This specific model uses Chicony Power Technology (a.k.a. HIPRO) as its OEM.
 
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davidshbaek

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Nov 19, 2013
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Hey thanks for the quick reply. 400W seems a little underestimated but i do understand that 650 is already more than sufficient for my build. But if I were to choose between between HX650 and RM750, which one would you recommend? I just need to get rid of one by Monday for full refund.
 
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davidshbaek

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Nov 19, 2013
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One thorough review! Much appreciated... I was aware of RM750 being manufactured by Chicony and that it failed to pass a test, making it one of the first kind in Corsair series. But I didn't know I could check the serial number to get the improved version. Based on your explanations, it appears that RM is better than HX but I'm sure Corsair had reasons to put it below HX.
 
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ko888

ko888

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Feb 18, 2009
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RM uses lower quality Taiwanese electrolytic capacitors on the PSU's secondary side. RM is rated for up to 40°C ambient.

HX uses all higher quality Japanese electrolytic capacitors and is rated for up to 50°C ambient.

All of the professional test reviews rate the HX Series models higher than the RM Series.
 
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davidshbaek

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Nov 19, 2013
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Again, thanks for that!

Now even with my H60 AIO liquid cooler, I'm sure the temperature on my PSU will easily go over 40'C when playing games (Starcraft 2, LOL, Diablo). How important do you think the difference between 40'C and 50'C up to which their rating stands is?

Also, what would you do if you were in my situation? Stick with HX650 and for graphics upgrade, just get a better single graphics card few years later or stick with RM750 for possible CrossFireX with a second 7870 few years later? On second thought, maybe CrossFireX will not be a good idea at all given that it will put more load on the system and raise the PSU operating temperature more...

Thanks for your thoughtful input in advance!
 
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ko888

ko888

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Feb 18, 2009
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As long as you mount the PSU with the fan facing down so that it draws in cool air from outside of the computer case you shouldn't need to worry about high ambient temperature. That's assuming that the surrounding air that the computer is in isn't at a high temperature like a room during a hot summer day with no air conditioning.

How far in the future would you be looking at crossfire? Hopefully not so far that it would be difficult to even find a second card with the same GPU.
 
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davidshbaek

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Nov 19, 2013
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To be honest, I have only been using laptops with crappy graphic support (I've been using the laptop mostly for work-related tasks; powerpoint, word, image J....) that what I am jumping into (and this is my first computer build) will be enough of amusement for me to last for awhile. So yes, I am not looking into crossfiring for at least 3-4 years at least, or possibly not at all until I feel the need to replace my whole computer perhaps 7-8 years down the road.. I just left a number of options open for me in case I might realize I want to go for crossfire.

So based on what I am understanding, I feel that you are willing to suggest that I can go for either HX650 or RM750 if I don't have any plans for crossfire. HX650 is $10 cheaper than RM750 so in this case, I am guessing that it will be a battle between $10 saving and quiet operating PSU. On the other hand, if I were to go for crossfire or leave possibilities open for going crossfire, you would be willing to suggest RM750 over HX650. Please correct me if I am wrong.

I have to say you've been amazingly helpful in this case. I've been much appreciating all your comments and support. You bet I am going to choose one of your aforementioned answers as the solution. I just want to arrive at the final decision before closing this forum.
 
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ko888

ko888

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The fan in the HX650 doesn't even turn on until you draw more than 40% of the PSU's capacity. When your system configuration is running at load you will be at the HX650's 40% power draw level.

If quiet is what you want then get the RM750. Its fan also doesn't turn on until the system draws more than 40% of the PSU's total capacity but its fan is quieter over all than the HX650.
 
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davidshbaek

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Nov 19, 2013
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Thanks, just as a last question...

I might get Club 3D 7950 Royal King instead of MSI7870. I tried to read through the requirement for this graphics regarding the Volts and Amps as you outlined for 7870. Unfortunately, the numbers and terms don't make much sense to me....

http://www.club-3d.com/index.php/products/reader.en/product/radeon-hd-7950-royalking.html

Could you please take a look and see whether the same explanation you gave for 7870 applies for 7950?
 
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ko888

ko888

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Feb 18, 2009
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For a system using a single AMD reference design Radeon HD 7950 graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 30 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.

The Club 3D Radeon HD 7950 royalKing is a non-reference design, factory overclocked card so its power consumption is higher. That's why the card requires one 75W 6-pin and one 150W 8-pin PCI Express supplementary power connectors.

When www.ht4u.net reviewed an AMD Reference Design Radeon HD 7950 they reached a power draw of 266.79 Watts during their over clock test using the Boost Clock BIOS Update when running FurMark stability testing.

If the PSU has at least a maximum combined +12 Volt continuous current rating of 37 Amps or greater then you shouldn't run into a problem with insufficient power.
 
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