CHFAN2 of 800 G4 SFF

[pseudomk7]

Hi,

I want to add a NVIDIA Tesla P4 to my 800 G4 SFF running an i7-8700 (65W TDP) and I need install cooling fans for the GPU. I tried using the CHFAN2 for power, but fans just don't work. (The fans do work normally when they are plugged into the CPU cooling fan power supply.) So I suspect there are some conditions needed to be fulfilled to enable it. (I've checked there is no relevant BIOS setting.)

According to manual, CHFAN2 is used in 95W models to power a rear cooling fan. Is there such a possibility that it's enabled/powered by the motherborad only when the CPU installd has a TDP of 95W? If so, is the only possible way to enable it using a 95W-TDP CPU? Having to switch to an i7-8700K of 95W TDP (which I don't actually need) to use the CHFAN2 seems funny to me.

Any idea?

Thanks

[NonSequitur777]

@pseudomk7,

Welcome to our HP Community Forum!

I have had plenty of experience upgrading HP EliteDesk 800 G3/G4/G5 SFFs, and what I found in all cases was that the secondary system cooling fan 'CHFAN2' connector should provide PWM power no matter if you got a 65-watt or 95-watt processor installed.  In other words, it should work regardless, as long as you make sure you connect it to a 12V, 4-pin PWM fan.

It is true that when you install a 95-watt processor, the system does want you to have a second cooling fan installed, and it will beep upon starting the PC without a second fan, but it is sort of optional as you can hit enter to continue starting up your desktop.

Make sure you got your BIOS updated to the latest version (v. 02.18.00 Rev.A) as found here: HP EliteDesk 800 G4 Small Form Factor PC Software and Driver Downloads | HP® Customer Support.

Hope this was helpful.

Kind Regards,

NonSequitur777

[pseudomk7]

Hi @NonSequitur777,

Thanks for the important information that CHFAN2 should work regardless of CPU TDP.

The fans I used to connect to CHFAN2 are indeed 4-pin 12V PWM fans. That's why I'm confused.

1. When the "increase fan speed when idle" setting in BIOS is set to 0%, the CPU fan works, but the CHFAN2 fans don't rotate.
2. I tried setting the "increase fan speed when idle" to values greater than 0% and I could hear an obvious speed-up of both CPU fan and the PSU fan, but the fans connected to CHFAN2 still don't work at all.
3. I also tried adding load to CPU to increase its temp to trigger the cooling, but the CHFAN2 fans are still motionless.
4. I moved a fan from CHFAN2 to use the CPUFAN, it worked ok. So I'm sure my own fans can function.

What do you think might be the problem based on the information above? The CHFAN2 on my motherboard may be dead?

Given that when 95W-TDP CPU is installed the motherboard would insist a CHFAN2 fan, I probably do need to get one such CPU to test if CHFAN2 is broken.

(I have my BIOS updated to the most recent version using the built-in online update feature.)

Thank you very much

[NonSequitur777]

@pseudomk7,

Perhaps a faulty motherboard header?  -I hope that is not the case, though (at least here in the US) you can purchase a replacement HP EliteDesk 800 G4 SFF motherboard for less than $25 via eBay.  But, come to think of it, you should be able to get a similar deal via AliExpress (Alibaba).  One way to find out -and recommending this high performing 95-watt processor: install an i7-8700K.

Kind Regards,

NonSequitur777

[NonSequitur777 · Accepted solution]

@pseudomk7,

Come to think of it, another solution would be to use a 4-pin PWM Fan Hub or 4-pin PWM Splitter cable on your "CPUFAN" 4-pin PWM power connector:

This should work just fine, providing that the total CPUFAN Cooling Fan amperage doesn't exceed 1-Amp (12 watt).

Kind Regards,

NonSequitur777

[pseudomk7]

@NonSequitur777,

You are the best. The 1A limit seems reasonable. But is there any document mentioning this? Just want to make sure.

[NonSequitur777]

@pseudomk7,

The generally accepted maximum is about 1 Amp spread across all your 4-pin PWM fan headers.

Kind Regards,

NonSequitur777

[pseudomk7]

I see. Thank you very much for all your help!

[NonSequitur777]

@pseudomk7,

You are very welcome -glad I could assist.

Kind Regards,

NonSequitur777