Siglent SDM and SDG Series, maximum Silent

[klausES]

Hi there,

I'm now done with my conversions of annoying ventilation noises.

It is absolutely silent now.
A rustle between fingers half a meter away dominates even when you hold your ear to the devices. 

It is the combination of speed control (everything from adjustable minimum speed, temperature control, curve of increase, maximum speed)
the fan itself (no commutation noises, no bearing noises, no wing noises), the complete decoupling of the vibration from the housing
and the geometry that creates a venturi effect of the flow (recirculated air to fresh air).

If I have some time there will be create nice PCBs.

This would be possible with all SDMs, i.e. SDM3045X, SDM3055 and SDM3065X
as well as SDG1032X, SDG1062X and the SDG2042X, SDG2082X, SDG2122X.
Probably also with the SDG6000X (I don't have one to test).

Follow pictures...

[klausES]

First an SDM.

All settings are possible through the hole in the handle without removing the housing.
My helper was sleeping instead of helping... 

[klausES]

SDG Series.

The filter is only temporarily attached (test).
A nylon that is statically charged by the rotation of the plastic wings and holds tight without great air resistance.
The concave curvature on the inside is intentional (enlarge the surface behind the holes in the lid).

Again, all settings are accessible through the closed housing (hole in the handle).

Everything can be completely dismantled without leaving any traces. no holes drilled, only existing fastening options used.
That was a lot more work (angles made of sheet metal, aluminum etc.) but I wanted it to be that way.

Oh well, there is also a LED as a stroboscope for visual control of whether and how fast the feeder is rotating.
Just hand outside, hold your finger to the case. 
The SDM got that too (unfortunately it was not on the pictures yet).

PS.
The black tape is a thicker PVC tape and is only used to prevent the outer skin hood made of sheet metal from "scraping and rattling" directly on the sheet metal of the chassis.
The hood is still shielded (contact with the locking screw below).

[klausES]

With the SDM it was particularly important to me to quickly reach a certain adjustable temperature and then to keep it exactly constant.
This is the same everywhere in the housing due to the circulation (fan at minimum speed 90% only internal airflow).
At the moment this is exactly 28 °C for the test which is kept at + - 0.25 °C.

The behavior of the SDG is the same, only the temperature is kept a little lower.
The SDG also generates more waste heat than the SDM.
There the fresh air share is higher than the recirculated air share, or the fresh air share is started up faster.

[klausES]

A few more technical data:

Since the minimum speeds (without a requirement that it would be too warm) are quite low, a safe start must be guaranteed.
The circuit starts the fans with increased voltage for the first second so that they can start up safely.
(This depends very much on the type and data of the fan, but the short increase means that you are always on the safe side).

The regulation starts as min speed (tuned for exactly this fan model) at 220 rpm (SDG) and 150 rpm (SDM).
This guarantees a flow within the device (circulating air) which, on the one hand,
keeps the temperature throughout the housing and hotspots do not remain without airflow.

If the temperature is e.g. initially very cold environment / device begins to reach / exceed the desired / set threshold value,
the speed increases proportionally (differently strong curve for SDM and SDG).

With increasing temperature (speed) the proportion of fresh air increases and displaces the proportion of pure circulating air more and more.
At maximum speed (adjustable. E.g. with the SDM 450 rpm, with the SDG 650 rpm) the fresh air portion is initially only approx. 10% then over 90% of the delivery volume.

The correct placement of the sensors took some time, measurements and tests.
For the job, the total temperature, but also the hotspots and e.g. the power supply should be included in the tests and measurements.

The mechanical decoupling of the fans is just as important.
Even very low-vibration fans generate resonances and interference in the housing at certain speeds.
The decoupling is done by extremely soft silicone.
That the fan still "stays" vertically (not sagging) is due to the tension-pressure distribution of the four positions.

There would be a lot more details to tell...

.
Addendum April 05.2020

Since the amount of heat emitted by the SDG is considerable
(on the other hand, little with the SDM and with these in a cold environment, the target temperature should be reached faster)
and keep the fan speed as low as possible for as long as possible, the proportion of recirculated air in the SDG has now been reduced, and the proportion of fresh air increased.

The fan speed at 30 ° C (test room with fan heater) now only increases to just under 450 rpm and is therefore almost inaudible with this Sunon Type even at this ambient temperature.

Nevertheless mechanically decoupled, the distance on the suction side (noise reduction to the perforated plate) remains maintained.

[klausES]

Addendum after a few months of test operation and now finally summer temperatures:

Internal temperature in the current environment >30 ° C (>86 ° F) with the SDM and SDG not higher (in truth, even lower for both)
than in the original factory condition and that in contrast to before with almost inaudible noise levels.