EVA3 Dual 4028 Inlet

Why?

I'm sure your first question is why?  Isn't the stock single 4028 inlet enough?

From a purely functional stand point, I believe it is, yes. 

However, it also has the potential to be extremely noisy.  The 4028 fans default (fail) to spinning at 100%.  This means even if you wire everything correctly, it still has the potential to run at 100% unexpectedly.  How you might ask? Simple, repeated movements weaken the PWM signal cable and create a short/break.  When the printer instructs the fan to turn to any percentage you end up with the fan running at 100%.

I had this happen a number of times. So, I began looking for alternatives. A dual 5015 inlet exists, but these fans don't move enough air to be comparable to the original 4028.  It did however give me the idea of doubling up quieter fans that do move more air.  Which led to this design.

Noise

I finally got around to making a dual 4028 inlet for the EVA3 and took some noise level measurements... readings taken at my desk roughly 3 feet away from printer

• ambient = 47 dba

original 4028 fan -- dual 4028

• 20% = 47 dba -- 47 dba
• 30% = 51 dba -- 49 dba
• 40% = 56 dba -- 50 dba
• 50% = 59 dba -- 51 dba
• 60% = 62 dba -- 52 dba
• 70% = 64 dba -- 53 dba
• 80% = 68 dba -- 55 dba
• 90% = 70 dba -- 56 dba
• 100% = 72 dba -- 58 dba

Original fan:

• https://ratrig.com/fan-4028-axial-protechnic-mgt4012wb-w28-c-1-2a-12v-23000rpm.html

22000 RPM, 28.64 CFM

Dual fans:

• https://www.newegg.com/bgears-b-blaster-40-case-fan/p/N82E16835132037

9000 RPM, 17 CFM 

I don't think I can quite count the CFM as double on the dual fan setup, but each is rated at 17 CFM compared to the 28.64 CFM of the original... so I figure I'm getting somewhere near the same overall CFM with significantly less noise.

Range of Movement / Printable Area

While the ducting is wider, tests show that it doesn't interfere with the printer's range of motion.