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Since87 · 06-14-2003, 10:08 PM

Some more data...

I've got the pump setup in a loop that should be substantially less restrictive than any water cooling system, but I've got a ball valve in the loop.

When I say "unrestricted", I mean ball valve wide open. When I say "restricted", I mean, "Closed to my best eyeballed guess at the restrictiveness of a White Water system." How's that for vague? (If I have time and motivation, I'll setup my calibrated heatercore and some manometers and generate a rough PQ curve at lowered voltage. This particular pump runs (and even starts fine) at under 6V.

I'll get to 6V data later, right now I have the following:

11.55 Volts, Unrestricted = 1.47 Amps (Average).
11.58 Volts, Restricted = 1.15 Amps (Average).
10.18 Volts, Unrestricted = 1.26 Amps (Average).
10.43 Volts, Restricted = 1.07 Amps (Average).
8.32 Volts, Unrestricted = 1.01 Amps (Average).
8.72 Volts, Restricted = 0.88 Amps (Average).

The following scope traces are different from the earlier ones. Rather than connecting the scope to look at the voltage across the pump, the scope is connected across a 1 Ohm resistor that is in series with the pump. This allows me to "see" the current through the pump because 1 Amp through 1 Ohm produces a 1 Volt drop across the resistor. For these tests I have also changed my scope probe to be 1X rather than 10X, so when the scope image says the vertical scale is 500mV, it actually is, and it represents 0.5 Amps per division.

That image shows the current signal with an unrestricted loop and 10.18 Volts applied to the pump. Notice that you can see very clear cycles to the current draw. The number "397 Hz" on the upper right of the image shows the frequency of these cycles.

My best guess is that there are four of these cycles per revolution. That would mean:

RPM = (397/4) * 60 = 5955 :shrug:

That image shows the current signal with a restricted loop and 10.43 Volts applied. In this case the RPM is higher, and you can clearly hear the difference. The pump seems to get louder, and definitely higher in pitch when the flow is restricted. Unfortunately, I forgot to grab the soundmeter from work when I got the scope, so I can't give any objective information on noise.

The noise level is substantially lower, but still clearly noticeable at 6V.

More to come.

06-14-2003, 10:08 PM	#116
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	Some more data... I've got the pump setup in a loop that should be substantially less restrictive than any water cooling system, but I've got a ball valve in the loop. When I say "unrestricted", I mean ball valve wide open. When I say "restricted", I mean, "Closed to my best eyeballed guess at the restrictiveness of a White Water system." How's that for vague? (If I have time and motivation, I'll setup my calibrated heatercore and some manometers and generate a rough PQ curve at lowered voltage. This particular pump runs (and even starts fine) at under 6V. I'll get to 6V data later, right now I have the following: 11.55 Volts, Unrestricted = 1.47 Amps (Average). 11.58 Volts, Restricted = 1.15 Amps (Average). 10.18 Volts, Unrestricted = 1.26 Amps (Average). 10.43 Volts, Restricted = 1.07 Amps (Average). 8.32 Volts, Unrestricted = 1.01 Amps (Average). 8.72 Volts, Restricted = 0.88 Amps (Average). The following scope traces are different from the earlier ones. Rather than connecting the scope to look at the voltage across the pump, the scope is connected across a 1 Ohm resistor that is in series with the pump. This allows me to "see" the current through the pump because 1 Amp through 1 Ohm produces a 1 Volt drop across the resistor. For these tests I have also changed my scope probe to be 1X rather than 10X, so when the scope image says the vertical scale is 500mV, it actually is, and it represents 0.5 Amps per division. That image shows the current signal with an unrestricted loop and 10.18 Volts applied to the pump. Notice that you can see very clear cycles to the current draw. The number "397 Hz" on the upper right of the image shows the frequency of these cycles. My best guess is that there are four of these cycles per revolution. That would mean: RPM = (397/4) * 60 = 5955 :shrug: That image shows the current signal with a restricted loop and 10.43 Volts applied. In this case the RPM is higher, and you can clearly hear the difference. The pump seems to get louder, and definitely higher in pitch when the flow is restricted. Unfortunately, I forgot to grab the soundmeter from work when I got the scope, so I can't give any objective information on noise. The noise level is substantially lower, but still clearly noticeable at 6V. More to come.