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Unread 06-15-2003, 12:32 AM   #117
Cooling Neophyte
Join Date: Jan 2003
Location: gmt -6
Posts: 21

Very nice...

i would have to say the RPM estimate's pretty close. i don't remember exactly, but i would say there are around 8-10 brush conctact patches within the motor (and there's no way in hell i'm going to take it apart again), so 6000rpm is probably within ~20% of actual speed at that voltage.

Not that it matters so much though -
I did some casual (very casual) testing with an adjustable power supply after reassembly, and noted a couple of things.

First, the pump was noticeably noisier and slightly less powerful after reassembly. I assume all of the pushing and prodding i did to get the brushes back into place scraped the contact areas up a little. (this would be my third warning so far in this thread to anyone who would consider disassembly out of curiosity...)

Second, the free-flow output capacity seems to correlate (loosely - as i said, this was very casual testing) with the square of the voltage applied. Ohm's law would seem to predict that, but a motor such as this is not a static resistance, and other factors come into effect....

Anyway, what i observed was that voltages below about 10v gave a rather severe performance hit (1/3 to 2/3 of 12v flow), without reducing noise levels much. This may be due to the abnormal brush wear I put on mine, but the whine that makes up the most noticeable noise from the pump was not significantly decreased (i.e. not more than a few db) at lower voltages, just reduced in frequency.

On a whim i cranked it up to 18v for a bit, seeing dramatic (2-3x) increases in flow rate over standard 12v. I would certainly not recommend running the pump over 14v (nor does the manufacturer) but it was interesting to try.

Well, the cap-filtered scope trace is encouraging. I was previously going to run my pump off of a separate power supply, but that doesn't seem necessary anymore. Now i just need to wait for Cathar to start selling his new block...
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