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Unread 06-15-2003, 02:17 AM   #118
Pro/Guru - Uber Mod
Join Date: Sep 2002
Location: Indiana
Posts: 834

I decided to test at 7V instead of 6V.

1. It gives some margin above a voltage I know the pump will start at. I didn't actually find the minimum voltage, but I'm done testing now.

2. 7V is a rather convenient voltage to get.

3. It gave better resolution on my manometer.

I only took one pressure vs flowrate point. After I'd taken it I decided to check the noise difference by shorting out the voltage dropping resistor. This wasn't a real bright thing to do, since it blasted water out of one of my manometer tubes, while sucking air into the system through another. My brand new PSU was just inches away from getting a shower.

Anyway, the one set of data I took, had the pressure drop across my heater core at 0.12 mH2O, and the pressure drop across the 'block' (nearly closed ball valve) at 0.48 mH2O. Because BillA measured the flowrate vs pressure drop curve of my heater core, I know that 0.12 mH2O drop across the heater core equates to about 4.9 lpm flowrate. Knowing the flowrate and that the pressure drop across the 'block' was about 0.48 mH2O, I can determine that the 'block' was about as restrictive as Bill's "462-U w/ 3/8" Cu tubing". (As shown in this article.) The ball valve that was simulating the block was closed about as much as in my earlier testing.

I also measured the current draw at 7V with my DMM as being 0.68A. (average) So, the pump was consuming 4.76 Watts while giving enough performance to be useful. In the brief interval before spraying water all over, I noticed that the pump was 'substantially' louder at 11.5V.

I also captured the current draw on the scope:

The cycle rate is only 270 Hz at 7V. (It was 397 Hz in the 10.43V restricted case.)

It would be fairly easy to design a circuit to generate an RPM pulse that could be connected to a fan header. This would allow MBM to shutdown the system in the event of pump failure.

An Op-Amp, some caps, and resistors would provide a bandpass filter that would eliminate irrelevant components of the signal. That could be followed by a comparator with an open collector output, which could drive the fan header directly. (It might be necessary to install a counter or flip-flop to divide the frequency down to a range the motherboard can read. I don't know what max pulse rate the components on the motherboard can cope with.)

Last edited by Since87; 06-15-2003 at 10:53 AM.
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