Sunlu S2 70°C Circulation Air Duct

Update - V2

One of the expected benefits of this approach, from keeping the fan on the outside of the case, should be the life of the fan. Only the impeller is constantly subjected to the set 70°C. The electronics in the fan should be at a lower temperature, cooled by the outer fan body which is cooled by ambient air. Actually measuring that temperature is problematic. So time will tell how long the fan lasts. In addition, I have the 24V fan running on 12V so the electronics are not at maximum stress.

The model has been updated to provide larger seating pads where the ducts return the air into the S2. This was done to allow the use of thin double-sided tape to hold the pads in place and seal the air junction. Note that the positions of the air duct entry holes are further out than the original version.

Initial operation exposed the limits of the S2 heating system. With no circulation other than convection, I measured 15°C difference between the top and bottom of the air space. With the fan on, set at 12VDC on the 24VDC 5015 fan, the temperature difference was negligible. I have not tested the newer S2 version which has a small fan. It must provide some circulation but not to the level of this ducted 5015 fan.

The ducts have been optimized to have minimal wall thickness. This allows more room to insert heat insulation around the ducts.

Further testing showed this was necessary as there is sufficient heat loss from the S2 to prevent it from cycling at 70°C with the fan on. Simply wrapping the S3 in a blanket was sufficient to reduce the heat loss to a point where the S2 would cycle at 70°C.  

So I progressively added self-adhesive aluminum bubble wrap around the air ducts and on the outside of the S2case until operation at 70°C was achieved.

The final result is a toasty S2 in a puffer jacket, much like a skier.

Drilling the S2 case

A challenging part is making holes in the S2 case to align with the return air ducts.

I made a “single-use” drilling template which provides for 3mm right angle pilot holes to be drilled as a precursor to drilling larger 8mm holes at the correct angle. The template provides guides for the correct angle.

What worked for me was to avoid the use of powered drilling, instead using a hand chuck to ensure the drilling did not wander off center.

There are sufficient rings on the S2 back to center the drilling template. There is a round section which should be aligned with the S2 power socket.  Once that is done, the holes for the M3 mounting screws can be drilled.

Three m3x16 cap head screws can then be used to secure the drilling template onto the S2 into three M3 nuts to hold it in place while creating the air holes.

Once secured, I drilled 4 x 3mm pilot holes at right angles to the S2.

Then I drilled another set of 4 x 3mm holes in the larger tubes which are set at the correct angle.

This made it much easier to use an 8mm drill to open up the four return air holes.

Fan Air Intake Gasket

The 5015 Fan requires a gasket to seat the fan flat face onto the sloping S2 center profile. 

I printed it in PETG but it would probably seal better if printed in TPU.

The fan gasket assembly is better left until the air duct is fully mounted. In this way the 5015 fan and its gasket can be positioned correctly against the air duct and used to mark the positions of the M3 fan mounting holes.

Once the fan gasket is secure, it can be used to mark the extent of the intake hole.

Fan Control

There are numerous options for controlling the fan, from wiring directly to the S2 power socket to a switched arrangement with fan speed control.

Thermal Management

I used a thermal camera to identify where the major heat loss was.

The junction of the fan and air duct, and the wire entry hole were smeared with silicon, along with a dab on the wire entry hole into the fan case. This made those areas revert to background levels. 

I avoided covering the viewing section of the lid but covered most of the case outer faces. Given the thermal camera results, the hinge area was also covered. 

For anyone thinking of any modifications, a STEP model file is provided.