You have a point.
Regarding it being adjustable - I suppose it would be fine as a fixed PSU setup for 18V, however the voltage feedback circuit would have a potentiometer to allow slight over-voltaging. As long as the components are rated high enough, I don't think that it would cause a problem ? (Other than efficiency.)
Regarding feeding the computer from the pump's feed: Good point, but I really don't want the mess of feeding mains cables in and out of the back. How do you recon the sizes would compair of a linear regulator Vs a DC-DC converter ?
Also heat output is an issue - If the unregulated DC supply was 30V (To allow headroom for over-voltaging to 24V), then the regulator would have dissapate 30Watts of heat. If I need to add a fan I want it to be very slow to reduce the noise to nil. That would require a reasonable sized heatsink - I don't think I'd have enough space.
Regarding the computer's powersupply. Very true, however I already have a 12V pump running off it, which is rated at 18Watts continuous. (1.58A @ 12V) Based off this new pump's startup current, let's say it requires 6A at startup. A lot of people run two of my old pumps. That's 12A of startup current required based off my previous guess.
On that note, the pumps that I'm running now have a delayed start. They also have a soft-start, however it's bugged and doesn't actually work. :c
A simple RC timer could hold the converter in a standby state for 1-2 seconds, then the converter would start up. By putting a capacitor across the Voltage Feedback line and Ground, the regulator will have a slower rise which should help things out, no ?
Thanks, I'll get doing some calculations from this book.
Edit: Just did some calculations from my book.
The expected peak inductor currents worry me:
Boost-mode converter
Startup Peak Current: (24V, 10A load) 110A
Running Peak Current: (24V, 10A load) 27.5A
Half-Bridge converter
Startup Peak Current: (24V, 10A load) 56A
Running Peak Current: (24V, 10A load) 14A
Looks like I'm going to be winding a transformer ! Fun.
Edit 2:
The book shows an "XMFR" on the base of the top half-bridge transistor, what is an XMFR ?
From what I can tell (Google), it's an inductor of some sorts, but what's it for ?
Edit 3:
Okay, I think you're right about using an AC-DC converter.
After more calculations, the input requirements are: (Assuming 70% eff)
At startup: 28.6A (343Watts !!)
While running: 7A (86Watts)
I'm using a 580Watt PSU, which can supply 420Watts on the 12V rail. It says on the side 12V @ 35A, which would leave 6.4A on the 12V rail for my computer at start-up. (76.8Watts) My processor alone takes more than that.
I'll have a look around for a pre-build SMPS, if not I'll have to use a linear PSU I guess.
On the other hand - This is all just startup current, I wonder if I could get away with it ......
Thanks everyone.