Question Two Systems in One Case (Lian Li DK07) - Sharing Fans

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Small_Town_Gamer

Mar 20, 2025
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I'm planning a two-system build in a Lian Li DK07 desk case, with an AMD system on the left and an Intel system on the right.

My airflow will be from front-to-back and left-to-right. For this to work, I need all case fans on at all times, regardless of which system I am running. I may even want to leave the fans on for a bit when both systems are off. I need to be able to turn case fans on and off (and ideally, to adjust their speed) from outside the case.

How can I do this?
 
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You could run a separate 12V power supply for the case fans and use a fan controller to ramp up or down the speeds. IMO something like Altronix already set up for things like camera or door controller power would be great but significant level of overkill. You could technically use something like a plug in (box) transformer if you calculate the required amperage.
 
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The "fly in the ointment" here is that there is NOT just ONE PSU. That desk / case system holds TWO completely separate systems, each with its own PSU, and hence each with its own power switch. If OP wants ALL case fans to operate at all times (with or without speed control), then he / she needs a separate power supply (and speed control?) independent of either mobo. For that one needs a 12 VDC power supply able to supply a max current more than the expected total max current of all case fans used. IF speed control is required, too, then that output of that power supply module should be capable of changing the output VOLTAGE based (probably) on a MANUAL control knob. Then the FANS can be simpler 3-pin (older style) Voltage Control fans since they will NOT ever receive a PWM control signal. Some custom wiring may be needed to connect the output of this power supply to standard computer 3-pin fans. Such a system will NOT be able to display the actual speed of any of the fans. But if it has (or OP can connect) a Voltage meter, that info can be used as a guide to manual settings. NOTE that such fans normally can STALL if supplied with a Voltage less than 5 VDC, so some way to limit the minimum power supply module output might be needed.

This has NOTHING to do with cooling systems on each mobo for the repective CPU's. Those each SHOULD be connected to the mobo CPU_FAN header since they are used solely for cooling one mobo's CPU and SHOULD be controlled only by the tempertature sensor inside each CPU.
 
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In my opinion, this is being over thought on.
From my perspective, as long as there is constant airflow and positive pressure to facilitate the intended direction of dust filtration. --Of which could be controlled by either system's fan headers, using a flat curve for a static speed or run them off of SATA power and add resistors accordingly. It doesn't matter which system is assigned the case fan duty. If the case was split into two separate chambers, it wouldn't be any different than having two PC's.
Then each system's CPU fan/s can have their own separate fan curves, as usual.
 
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Small_Town_Gamer said:
I'm planning a two-system build in a Lian Li DK07 desk case, with an AMD system on the left and an Intel system on the right.

My airflow will be from front-to-back and left-to-right. For this to work, I need all case fans on at all times, regardless of which system I am running. I may even want to leave the fans on for a bit when both systems are off. I need to be able to turn case fans on and off (and ideally, to adjust their speed) from outside the case.

How can I do this?
Click to expand...
Maybe a relay. If power supply 1 is active the relay is energized and the output of the relay is switched to power supply 1. If power supply 1 is not active, then the output of the relay is power supply 2. If it is active, then the fan controller connected to the relay is fed from power supply 2.
A single pole double throw relay.
 
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I think the intent of the design is for each system to be setup mirrored so you don't actually have to run all fans at all times. From looking through the manual it's clear the sides are intended to be intake with exhaust at the back. I can't imagine the front being used for anything other than intake.

I'm not sure what the goal of the left to right air flow strategy would be since the sides are very far apart and the fan RPM required to push that far would be extremely high not to mention all the turbulence being caused.

As far as controlling all fans from each system I can't think of a simple way to do this without some sort of independent power supply and fan controller.
 
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Paperdoc said:
This has NOTHING to do with cooling systems on each mobo for the repective CPU's. Those each SHOULD be connected to the mobo CPU_FAN header since they are used solely for cooling one mobo's CPU and SHOULD be controlled only by the tempertature sensor inside each CPU.
Click to expand...


Keeping in mind that the OP stated "case fans" specifically. From first post:

"I need all case fans on at all times"
 
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thestryker said:
I think the intent of the design is for each system to be setup mirrored so you don't actually have to run all fans at all times. From looking through the manual it's clear the sides are intended to be intake with exhaust at the back. I can't imagine the front being used for anything other than intake.

I'm not sure what the goal of the left to right air flow strategy would be since the sides are very far apart and the fan RPM required to push that far would be extremely high not to mention all the turbulence being caused.
Click to expand...
This was my initial thinking. But that would mean 5 intake fans and only 1 exhaust fan per system. The case has plenty of holes for positive air pressure to escape, but that still seems unbalanced.

Is a 5-to-1 intake-to-exhaust fan ratio OK?
 
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The "relay idea" can do only part of the job. A SPDT relay with power to the coil provided from a 12 VDC output line from Mobo #1 could select power for ALL case fans from that same 12VDC line when #1 is on, or from a 12 VDC line from the PSU of Mobo #2 when #1 is off. But this provides NO control of fan speeds. Probably it is not reasonable to try to control those fan speeds according to the "normal" method of using temperature sensors on the mobos as guides, so MANUAL control is the better choice. You might accomplish that by simply connecting a variable resistor in series between the output of that relay and the collection of fans. It would take some experimentation to select the right resistance and power rating of that unit. The max resistance should not be high enough to drop Voltage to the fans below 5 VDC - otherwise the system might cause fans to stall and not start up. Personally I do not know how to calculate the max power dissipated in the resistor for all of its range of settings (Voltage drop and amperage all changing) but some experimentation and measurement could figure that out.

williamjeremiah said something to consider. This desk / case does NOT separate the two halves into separate chambers because it CAN be used for a single system. But you could mount a simple metal sheet baffle between the halves in a 2-mobo system and thus create two separate chambers. Then mount and connect and control case fans for each system as if they really were two separate computer cases. Air flows in each half would be front to back and side. I do not see how doing that would cause any problems, and it would make all of this unnecessary.

Regarding balance of intake / exhaust, I think OP has assumed the wrong fan directions on the SIDES. Whether or not you install a central baffle, the two SIDE fans BOTH should be exhausts, as well as the two rear fans. Then there is no left-to-right air flow. In each half (with baffle or not) there are 2 or 3 intake fans (maybe on rads?) at front and two exhaust fans (side and rear). Pretty close to balance.
 
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Small_Town_Gamer said:
This was my initial thinking. But that would mean 5 intake fans and only 1 exhaust fan per system. The case has plenty of holes for positive air pressure to escape, but that still seems unbalanced.

Is a 5-to-1 intake-to-exhaust fan ratio OK?
Click to expand...
It's definitely unbalanced, but it does seem to be the design for dual system. I think it mostly depends on components and how you're cooling for what you can get away with. If you were liquid cooling I could see radiator on intake then using side exhaust as a potential option. Using air cooling though you don't want to be pulling cool air immediately out.

If you could figure out a simple way to wire up just both exhaust fans to operate at all times that would probably make it a bit better. I still can't think of a simple way to do this aside from making them separate from the systems.
 
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