Compare CPAP fans: WS7040 vs WM9290 vs WM7575
You've probably all heard that the 7040 are not the strongest kids on the block, the 9290 are their bigger and stronger siblings that can significantly outperform them. The last months there have been talks about a third option, the WM7575, a 400W 220VAC all metal monster that promises an enormous performance jump, with a static pressure 4x higher than the 9290. But how do they all stack up used with some standard CPAP ducts?
Simulated CPAP fans comparison
Three sims have been done, with the only variable being the fan, and the results are shocking:
- WS7040-24-V200 in last place, with 5.2dm³/s flow rate and average outlet speed of 29.6m/s ( baseline )
- WM7575-220VAC only second, with 8.9dm³/s flow rate and average outlet speed of 50.7m/s ( +71% )
- WM9290-24V in the lead, with 9.7dm³/s flow rate and average outlet speed of 55.4m/s ( +87% )
Two key takeaways:
- The mighty 400W compressor is let down by its relatively low maximum flow rate, that is less than that of the average 9290, and in a low restriction scenario like this one it means that the high max pressure is not useful.
- There is a lot of apparent variance between 9290 specs. Wonsmart (WS) has different P/Q curves and lists different specs in different pages, while Steady Motors (WM) has a different P/Q curve altogether. For this simulation I chose to use the P/Q curve of the Steady Motor version because it's in the middle of the others, to have a simulation that is not biased to either side of the performance curve.
Real World CPAP fans Comparison
After the last post about simulating the relative performance of three CPAP fans, Kaifas kindly helped bring the comparison to the real world. A 7040, a 7575, and a 9290 were tested with a short tube attached and an anemometer put in line. The experiment was repeated both without obstructions and with the same ducts of the precedent simulations, to have results that matched as close as possible. The tests were conducted at multiple flow rates, while measuring the spectral distribution of the noise with the Decibel X app.
7040:
Free:
- 25% 3.2 dm³/s
- 50% 4.6 dm³/s
- 75% 5.5 dm³/s
- 100% 6.5 dm³/s
Ducts
- 25% 3 dm³/s
- 50% 4.2 dm³/s
- 75% 5.1 dm³/s
- 100% 5.8 dm³/s
7575:
Free:
- 7% 2.3 dm³/s
- 25% 4.1 dm³/s
- 50% 7.1 dm³/s
- 75% 9.6 dm³/s
- 100% 12 dm³/s
Ducts:
- 7% 2.2 dm³/s
- 25% 4.2 dm³/s
- 50% 6.8 dm³/s
- 75% 9.3 dm³/s
- 100% 11.6 dm³/s
9290:
Free:
- 25% 1.1 dm³/s
- 50% 4.5 dm³/s
- 75% 7.3 dm³/s
- 100% 9.8 dm³/s
Ducts:
- 25% 1 dm³/s
- 50% 4.2 dm³/s
- 75% 6.9 dm³/s
- 100% 9.2 dm³/s
Comments:
The 7040 outperformed the sim by 12%, the 7575 outperformed it by 30%, while the 9290 underperformed it by 5%. This put the 7575 in the lead for peak performance. The 7040 was surprisingly the least adjustable of the group, showing the highest flow at 25%, making it less suitable for low cooling scenarios, while the 9290 showed itself capable of the widest performance range, reaching the lowest flow rate at 25%, even less than the 7575 at 7%, making it the best all rounder. The 7575 increased the air temp.
Noise:
The 9290 was the quietest, and the 7575 the loudest, also considering that it was loud at low speeds too. Both the 7040 and the 7575 had a bias to the high frequencies, giving them a more annoying sound signature, while the 9290 had a more uniform frequency spectrum, making for a fuller and less bothersome noise.