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At low voltages there is a slight danger the pump may not start. In other words it my run at 7V but it might not start at 7V.

Ideally you need a circuit that initiall comes up at 12V then after a few seconds reduces to whatever minimium voltage you set.

That's a bad idea. If the pump stops, bad things may happen. Find a quieter pump.

NOT the proper way to do this. The way to keep the starting torque high while reducing speed:

I like Homer's **Find a quieter pump** notion.

They also used to put dot-matrix printers inside boxes.

Thanks Homer,

It's a Liang D4 -

Bios is set to shutdown at 65C which is the lowest setting, at 12V I get around 32C cpu temp at 20C ambient. The hottest I've seen it go is 41C at the height of summer here with an ambient of around 30C. I'm not too worried about it stopping.

Liang do produce a variable model (D5 Vario) with stepped settings from 7 to

Cheers

Ian

Ian, water cooling a PC is ridicululous, since the dissipate so low energy. My suggest is for you to purchase an Terrminator case, which is sold by ASUS. Right now my Terminator case ran is running at 1480 rpm, and which I even hear. The cpu fan is now running at 1222 rpm, which I cant hear either. The Pentium 4 cpu is now running after 10 hours at a temperature of 43C/109F while operating at 2800 mhz.

I am a silence freak, and have worked with water cooled systems previously in designing Navy combat controls sytems. What I would say to you is simply to update your computer system to modern technology, and the need for water cooling will vanish. My older computer dated something like 1990 sounded to me like an air-raid siren when it ran with its 4 fans, but todat's computer are essentially silent, without the need for water cooling.

The upgrade cost is not significant for many people. My ASUS T2 Terminator box, mother board and power supply cost roughly $120. The 1 Gig RAM IIRC about $80. My twin 50 Gig disk drives cost about $100 each. So here were talking about a relatively state-of-the-art system that cost roughly $400 and about 6-hours time to construct.

It runs as silent as can be. The greatest noise is that when the CD drive/burner (anoter $80 that I'd forgotten about runs at maimum RPM. Most of the time you don't hear it.)

Water cooling? Gimme a break! The water colling will produce more noise than a state of the art computer does itself.

Just sharing this with you.

Harry C.

Ian wrote:

use a 555 and a transistor to do pwm

Use a PICAXE 08M chip (has built-in PWM and can read the DS18B20 temp sensors). It would be relatively simple to program a full-speed startup for the first minute or so, then adjust the speed to maintain some do-not-exceed temperature.

The PICAXE series is designed for educational use (ages 8 and up) and programmed in a version of BASIC, so the elementary bits are relatively easy (obviously, the ability to do PWM indicates that there is much more capability than just things for elementary education projects). This chip is about $3US. The Windows IDE for programming the chip is a free download

There's an active forum at

I haven't used the PWM capabilities (yet) but do use the temp sensor interface to control a fan in an audio/video cabinet and use other features in a water level alarm:

More PICAXE info:

Think of the PICAXE as the 555 of the 21st century ;-)

John

Friday, October 06 2006, @ 2:17 PM (-0700 GMT)

Try to find a "Variac." These were once used quite a bit to lower the voltage to Christmas Tree lights to make them last longer. As you likely know, or can guess, its an "auto-transformer."