If you are going to use these pumps, you do not need to buy or build anything special, just get yourself an off-the-shelf general purpose laptop supply rated at 24V with a max current of 6 amps as Brewzone suggests.
Just miss out all the waffle about getting a variable PSU going.
But this is what I did:
Firstly, find a power supply,
Monday am, great joy! The spares box yields a couple of PSUs I did in a previous life that I had forgotten about. Originally designed for 24/15/5V with an input switching down converter rated at up to 40V out at 4 amps – perfect. Chop out a couple of bits, remove a single resistor and replace with a pot and another fixed resistor. If anyone is interested, http://www.datasheetcatalog.org/datashe ... s/1333.pdf tells you how to do it, but the L296 is probably obsolete now and there are much better ways to do it if it was for production.
If only all life was that easy…
Find a box to stick them in, ah, that’ll be up in the attic with all the spiders – it’s now that you regret the big chuck out of most of the “useful†stuff which had been up there for 15 years or more.
But all is not lost – total overkill but what the hell.
Offered up the PSUs on their brackets, fine, and then decide that I might as well put the thermostat and PID controllers in here as well – Monday 11.00 and more delay, but no point in doing the job twice.
Find a bit of ally for the front and back panels, jump all over the guillotine because its Birmabright, probably left over from a Series 1.
Then tragedy strikes – I have to do some proper work (lose most of the next 6 hours).
Once that is out of the way I draw up the front panel on squared paper – well it’s quicker than doing it on the CAD – stick it on the front panel and centre punch through, scribe the lines.
But now it’s too late to annoy the neighbours with cursing from the garage so it’s on with the electronics, do the modifications above and re-build onto the heatsinks.
Tuesday am, punch out the holes, linish (Bill Gates says that isn’t a word) with the belt sander and lacquer.
The Mashmaster on the mash tun has a weep, so I fix that prior to the tests while waiting for the panel to oven, then work intrudes again for a few hours.
Controller box is now part finished; the wiring of the PID and thermostat can come later because I am become desperate to get some actual results after having hand the pumps for nearly a week.
I’m using a couple of DMMs and a ‘scope so that I can look out for any instability. The ‘scope is very noddy and cheap but very portable and able to catch events if necessary.
First the pump setup: That is self amalgamating tape around the pipe to provide a bit of give but good support. There is an olive crimped onto the pipe but this is doing very little. Two o-rings are pushed onto the pipe and then the first is located in the grove in the pump. The second is to stiffen it up a bit.
I have decided to JB-weld a bit of 15mm onto the second pump, using the o-rings again as belt and braces and to ensure that no goo gets inside the pump.
But that is where it ends for tonight. It is now after 21:00 and for the last 4 hours I have been trying to work out why it is “huntingâ€.
My first quick test was with a brutish 20V 10A jobby had seemed to go very well. I did not check current but 16-21V seemed smooth and stable. Today, with either the new PSU or the brute, I am getting this slow hunting at about every few seconds. I first put it down to an airlock or cavitation, so I changed the orientation of the pump (pain in the proverbial because its all copper pipe) – but no change. So now I am thinking sucking in air at the inlet. Either way or something else I have had enough for now.
I just JB-welded a bit of copper into the second Speck, it’s going to need 15 hours, less a bit if I stick it in the oven at about 50C.
(opens another bottle of Youngs London Special...)
