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Potential thermal issue with RM750 and RM850


RAM GUY

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  • Corsair Employees

The Corsair RM series power supplies are designed to run without active cooling for up to 40% load at typical room temperatures (25°C, or 77°F) and are capable of continuously outputting 100% of output capability at ambient temperatures of up to 40°C (104°F). We have found that our power supplies are typically used in environments much lower than 40°C and tend to have some natural aspiration within the chassis that allows for some air movement, such as from a nearby graphics card or chassis fan, within the PSU housing, when temperatures exceed normal room temperatures. We have found that this normal aspiration can maintain Corsair’s Zero-RPM fan-less mode even at temperatures as high as 35°C (95°F) when only at 40% load for durations of up to 15 minutes.

 

Thanks to recent feedback provided by an early reviewer, we have discovered a PSU fan operation issue that can be triggered with the RM750 and RM850W under highly unusual operating conditions. For the issue to occur, the PSU must be run for more than 15 minutes at:

 

  • Ambient temperature 35°C (95°F) or higher
  • Zero ambient airflow, i.e. no airflow provided by system fans or by fans on other components

 

Under these conditions, impacted PSUs may shut down before the cooling fan starts spinning. This shutdown will cause no damage to the PSU or the system. As these conditions are extraordinarily harsh, we believe most users will not be impacted. If you feel you have a unit that has been impacted, we are offering advance replacement returns for the PSU, with Corsair paying all freight costs. Please click here for instructions on how to obtain a replacement unit, or to ask any questions.

 

Thank you for choosing Corsair; we are committed to making sure you are completely satisfied with your purchase.

 

Update - November 14, 2013:

In an effort to improve our products for all of our users, we have updated the RM750 and RM850 to resolve this issue. The thermistor circuit that is used to measure the temperature for the fan controller and OTP has been changed in all RM750 and RM850 PSU’s moving forward. An additional resistor has been added that will result in the fan turning on prior to the condition that causes the PSU to shut down in the event that temperatures exceed 45°C.

 

The affected units are in lot codes < 1341 (the first four digits of the S/N.)

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Just had this exact issue happen to me with an RM750 purchased last week.

 

Room isn't even close to 35c ambient, more like 25c. Machine is built in a quiet 330r Corsair case, low airflow.

 

Disappointing to say the least.

 

Tried to make a ticket and couldn't because it isn't even in the system, but luckily had a chat support person assist with things so far and start a ticket on your end.

 

Hopefully this goes smoothly.

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Just had this exact issue happen to me with an RM750 purchased last week.

 

Room isn't even close to 35c ambient, more like 25c. Machine is built in a quiet 330r Corsair case, low airflow.

 

Disappointing to say the least.

 

Tried to make a ticket and couldn't because it isn't even in the system, but luckily had a chat support person assist with things so far and start a ticket on your end.

 

Hopefully this goes smoothly.

 

If the room is only 25°C and internal temps are 35°C, the PSU shouldn't shut off. What are you powering with that PSU and how is the PSU oriented in the chassis (fan up or fan down)?

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PSU is installed fan down. Had a few shut downs while gaming the past week and couldn't understand why, but seems this is the likely cause. Had to flip the switch on and off in the back to get it going again.

 

Haven't heard the fan spin up (Not supposed too I know) that I'm aware of, even while gaming.

 

Powering an i5-4570, 2x4gb Vengeance Ram, a single GTX660, Asus Xonar Soundcard, 2 hard drives, 3 fans (one on Hyper 212 CPU cooler) spinning really (400 rpm) slowly. Nothing too elaborate.

 

I don't imagine it gets over 50% load much, if ever. Bought the 750w to have way more than I needed right now....keep it quiet.

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"we are offering advance replacement returns for the PSU"

 

That's a quote from the above post, yet my RMA was just approved and says the following....

 

"Once Corsair physically receives your item, your replacement will be processed and shipped"

 

Looks like I have to wait for you to physically receive my PSU before you'll send me another one..or am I reading this wrong?

 

In other words I'd be better off returning it to the store and buying an alternative so I'm not with a machine for a considerable amount of time.

 

Any way we can make this not the case? My RMA # is 6252667, if anyone from corsair needs it.

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I want to post here and thank whoever is responsible for taking care of me today.

 

Received a tracking and confirmation of a replacement being shipped out, as well as a prepaid return label.

 

Very happy with how things are going now, and really appreciate the great customer service.

 

Thanks again.

 

 

Quick question to add....

 

I'm curious on how the update and fix will work out. Any insight from the PSU guru?

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Hi,

 

I registered here to ask a question on these PSUs. I purchased an RM850 PSU on the 7th Nov from Dabs.com in the UK. The PSU was sent direct from Corsair so I would like to know if my PSU is an updated model that has this issue resolved.

 

Is there a way I can check to ensure it is the updated model?

 

Thanks

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Well, an 850W is quite a lot of power for the rig you're powering, but you can try running Furmark and Prime95 together at the same time to put a load on the PSU and if the fan turns on, you're good. The problem occurs when the OTP trips the PSU off PRIOR to the fan turning on.
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Well, an 850W is quite a lot of power for the rig you're powering, but you can try running Furmark and Prime95 together at the same time to put a load on the PSU and if the fan turns on, you're good. The problem occurs when the OTP trips the PSU off PRIOR to the fan turning on.

 

Thanks for the very prompt reply and the advice. While an RM850 might seem a lot for my system I do plan on overclocking and going SLI soon. So regardless of the fact the PSU can handle my system without problems now, i am thinking of the future.

 

Is there is a way to tell by looking at the PSU if it has the fix applied? If not I will simply do the prepaid RMA to get a replacement regardless.

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If you have no way to test it because your load is so small that it would never trigger the fan or trip the OTP, then the best advice I can give you is to RMA it regardless just so you don't have to deal with it once you do get the second card and start overclocking.

 

The affected units are in lot codes < 1341 (the first four digits of the S/N.)

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If you have no way to test it because your load is so small that it would never trigger the fan or trip the OTP, then the best advice I can give you is to RMA it regardless just so you don't have to deal with it once you do get the second card and start overclocking.

 

The affected units are in lot codes < 1341 (the first four digits of the S/N.)

 

Thank you again for the advice and the help. My serial begins 1355 so I missed out by a few :(

 

I submitted an advance return request ticket number 6261275. While this is a design flaw that should have been avoided, I must say the way Corsair are handling this and your support is excellent.

 

Thanks again

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Thank you again for the advice and the help. My serial begins 1355 so I missed out by a few :(

 

Well, actually 1355 is greater than 1341, so if that were your serial number, you'd be ok. ;)

 

But also, that can't be your serial number. Can you take a pic? Reason being: The first two digits are the year (13 = 2013) and the next two are the week (52 = last week of the year), so 1355 is impossible. ;)

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Well, actually 1355 is greater than 1341, so if that were your serial number, you'd be ok. ;)

 

But also, that can't be your serial number. Can you take a pic? Reason being: The first two digits are the year (13 = 2013) and the next two are the week (52 = last week of the year), so 1355 is impossible. ;)

 

Doh! My apologies on the typo, the number starts with 1335.

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The affected units are in lot codes < 1341 (the first four digits of the S/N.)

 

So it is 100% sure that PSUs with LOT number > 1341 are NOT affected?

I ordered this kinda product, and cancelled my order :(

The serial number couldn't be said by the shop, doh!

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1341 and below have one thermistor while serial numbers greater than 1341 have the two (separate one for the fan).

 

The first four digits of the serial number correspond with the date of manufacturer, so if a change is made in production, those numbers are going to be the best way to track it.

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We have found that our power supplies are typically used in environments much lower than 40°C and tend to have some natural aspiration within the chassis that allows for some air movement, such as from a nearby graphics card or chassis fan, within the PSU housing, when temperatures exceed normal room temperatures. We have found that this normal aspiration can maintain Corsair’s Zero-RPM fan-less mode even at temperatures as high as 35°C (95°F) when only at 40% load for durations of up to 15 minutes.

Is this (apparently fan-driven) "natural aspiration" assumption still valid when many chassis are designed to isolate the PSU airflow from the remainder of the components and draw and eject their air directly from/to the outside of the case? This may (or may not) still provide sufficient aspiration (due to heat convection) where the PSU intake vent is on the top of the case, but would almost certainly provide insufficient aspiration where the intake vent is on the bottom.

 

Some direction on appropriate orientation of the PSU may be appropriate in the product documentation for this series.

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Is this (apparently fan-driven) "natural aspiration" assumption still valid when many chassis are designed to isolate the PSU airflow from the remainder of the components and draw and eject their air directly from/to the outside of the case? This may (or may not) still provide sufficient aspiration (due to heat convection) where the PSU intake vent is on the top of the case, but would almost certainly provide insufficient aspiration where the intake vent is on the bottom.

 

Room temperatures are typically much lower than internal PC temperatures, so there shouldn't be a problem unless the room temperature is unusually high (say, over 35°C). The fault was discovered when ambient temps were much higher (45°C) and without airflow, thus creating a smaller delta between ambient and operating temperature. Since the fan operates on both temperature and time delay, the temperatures raised too quickly for the fan controller to operate the fan. The ambient temperature of the room alone should be enough to maintain a lower operating temperature, so even prolonged operation at higher loads should give the fan controller adequate time to turn on the fan.

 

Some direction on appropriate orientation of the PSU may be appropriate in the product documentation for this series.

 

Actually, no. While some fanless units have orientation requirements, the RM Series can be mounted in any position just like any other actively cooled power supply.

 

Some fanless PSUs require a certain mounting orientation because they use the housing as a heatsink that needs to be exposed to the aspiration within the case or have vent holes that need to circulate air to/from the outside of the chassis. But keep in mind, these PSUs are made to run at 100% load without a fan. The RM cannot and should not operate anywhere near 100% without the fan turning on.

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