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HDD migration/exchange between Gen8 and other hardware


BlueThing
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Aren't those LNA cables just regular cables with a resistor in-line? If so, I don't think they will work because I believe the Gen8 uses a PWM fan.

 

They do work with PWM fans, they just reduce the power to the fan.

 

However, the HP fan isn't just PWM, I'm convinced there's a temp sensor in there too, which is why there's a 6-pin connection on the fan, and why there's an 'exhaust temp' reading in the Sea of Sensors.

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They do work with PWM fans, they just reduce the power to the fan.

 

However, the HP fan isn't just PWM, I'm convinced there's a temp sensor in there too, which is why there's a 6-pin connection on the fan, and why there's an 'exhaust temp' reading in the Sea of Sensors.

 

That's interesting. From other posts in the forums, I'd concluded that simply reducing power to a PWM fan won't slow it down. Someone, who obviously has knowledge of electronics, made quite a few posts about his efforts to control the speed of the fan. He had to come up with a custom circuit to do it. I'm not familiar with these LNA cables. Do they have something more than a resistor? Perhaps this "temp sensor" you mention is what made it so difficult for him? He didn't mention anything about there being one.

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I have several of the LNA cables, if I remember when I get home I'll open one up and let you know, but going by feel (squeezing the rubbery braiding), it feels like it's just got a 1 or 2W resistor on the 12V feed.

 

A PWM fan has 4 pins - 12V power, Ground, tacho, and speed control (which from memory is a TTL signal around 2kHz).  That's why you can run a PWM fan off a 3-pin connection, and why you can run a 3-pin fan off a PWM connection.  It stands to sense that if you supply 9V to the fan, it can only go 3/4 the speed no matter what the PWM controller is telling it.  Does that make sense?

 

The problem with the Gen8 in particular is that it expects a certain speed from the fan, and if it doesn't get it, it huffs.  Its not slowing the fan down that's the problem, it's tricking iLO in to thinking the fan is running faster than it actually is.

Edited by HellDiverUK
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According to the other poster's statements, no. From what I recall, he said the tachometer signal would cause the fan to spin at the designated speed despite the voltage drop. That said, I presume that, if you drop the voltage low enough, there is going to be some significant effect on the fan.

 

But I'm wondering, if PWM tries to keep the fan running at a specific speed, and it only has 9 volts to work with instead of 12, couldn't that be detrimental to the fan?

 

It will be interesting to see your results.

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Guys/Girls, I think you better take this discussion to a new "Fan" thread please

We apologize. It's easy to get us off topic, and .... I seem to be really good at starting that.

 

My subjective impression is that it was pretty similar in both modes.

The nose is indeed noticeable when everything else is quiet but during the day i don't mind that.

When we have guests staying over in the living room i can still turn off the server for the night once in a while.

After all, it's just a family server

Also, does the bios has the option to set the fan speeds? If so, that would help curb the noise.

Also, apps like SpeedFan may help you control that, or even set profiles IIRC.

That is ... if it likes the fan controllers.

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