Raspberry P(s)i

I read up on BLDC phase current and agree that it's not possible to get power to the compressor from the phase current. So it would be interesting to know the battery current.

The P2 compressor curve is fairly flat and doesn't fall off until you get to higher flow rates. Below is the data for discharge pressure at 30,000 impeller rpm. On a small engine like a 2.8L, the manifold pressure is going to be essentially constant at any engine rpm. The mass flow of air into the engine (which highly correlates to HP) will depend on the manifold intake, the air temperature, engine rpms and the engine's volumetric efficiency. On fuel injected engines that use speed-density for fuel control, volumetric efficiency data is available by reading the EPROM. If the engine does not flow at least 1080 lbs/hr, the P2 will surge (and make some real noise). Because the curve is flat at lower flows, you can't tell if you are getting near surge from the manifold pressure.

If I know the orifice diameter, orifice thickness, pipe diameter, and discharge pressure, I think I can calculate the flow within 10%.

lbs/hrpsig
12006.3
18006.7
24006.7
30006.5
36006.2
42005.1
45603.6
 
I 3d printed the restrictor plate so the dimensions are within 0.05mm. Apologies in advance for the mixed units but the hole is exactly 0.999 inches ID (25.4mm). The plate itself is 20mm tall. The OD is 3" (76.2mm). Maybe the thickness of the restriction is contributing to the differences between alex and our measurements?

On another note, I'm trying to get my hands on a DC clamp meter to measure battery current under load. Should be easy to find in a lab full of equipment but we'll see!

restrictorPlate.PNG
 
FYI, an orifice with an thickness to diameter ratio of 0.2 will indicate about 8% higher flow at the same pressure drop than an orifice with a T/D of 0.93. Not huge but the orifice thickness does make a difference.
 
I calculated the flow for a 1" orifice based on 6.3 psig discharge pressure and got 175 cfm. This is right on the surge line for a Vortech with Si trim. I assumed the discharge temperature was 155 'F based on the compressor map and 72 'F inlet temperature. Since the system is at ambient temperature to start with and the test is short, the discharge temperature may not get to 155 'F. If so the flow may be a little higher than calculated. Based on a 68% compressor effciency the calculated compressor power is about 5 kW.
 
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