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Old 8th April 2001, 06:44 PM   #1
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Location: Columbia, SC
This is an interrim report on the water-cooled Aleph 2 I'm building. The emphasis for the moment being on the water-cooled aspect, not the Aleph circuit.
First, two disclaimers:
1) This isn't going to be for everyone. It's cumbersome, to say the least. Frankly, I'm not sure I will stay with it. It's just an idea that occurred to me since I can't get big heat sinks for a reasonable sum of money.
2) Sorry, but for those who might wish to recreate what I've got here, I'm going to be at a loss for particulars in some cases. In particular, the heat exchanger is from a dead heat pump. I don't know the make or model number. I don't know any reasonable way to measure its efficiency as a separate unit. It's part of the system here and will have to stand or fall as part of the overall system. I will provide physical measurements below.
Here are the particulars of the Version 1.0:
I have one channel of an Aleph 2 built and functional. The quiescent heat dissipation is on the order of 300W for the one channel.
The heat sink system consists of the following (for the moment--this is only a test setup to determine whether I want to proceed). Each bank of 6 output devices is mounted on an 8" long piece of aluminum L 3/16" of an inch thick, with 1" flanges. The devices are mounted on 1" centers spaced from the center line of the L. The L is bolted to an 8" long piece of 2x4" aluminum strut (not anodized) such as you see as framing around doors and windows. The aluminum is 1/8" thick. The 2x4" is capped at the ends with 1/4" thick Plexiglas. One end is tapped for two NPT brass barbs for water in/out. The Plexiglas end caps are glued in place with clear Dow Corning silicone sealant. This is *not* the best arrangement you might wish for. The sealant adheres nicely to the Plexiglas, but only so-so to the aluminum. It's good enough for the time being, but is not something I'd want to use in a 'for real' version.
Coming off of the brass barbs, I'm using braided vinyl hose. Not because the lines are under pressure, but because vinyl tends to sag and crimp when faced with heat. The braid maintains the shape so that the hose remains open at all times.
Now comes the main variable--the heat exchanger. The one I'm using came out of a heat pump. It consists of two separate heat exchangers banked together in an A shape, one on each side. Each end of the 'tent' is closed with thin sheet metal; the only opening is at the bottom. There are three individual 1/4" copper lines running up each side from a plenum (I had to build the input plenums). The three lines from each side meet at the top in a single plenum where the water comes out. Each side of the A is 2" thick, 16 3/4" wide, and 18" tall; filled with the usual thin aluminum vanes that you see on heat pumps and air conditioners. At the moment, I'm running one bank of output devices into each side of the A.
On the output side of the heat exchanger, I'm using a Little Giant 3-MDX. I don't remember how many gallons per minute the pump is specified for, but that shouldn't be hard to find out. I'll try to track that information down, as that will be the critical number. Note that the Little Giant 3-MDX is a *food grade* pump. I removed it from my brewing system. There is no reason to run such a pump in a water-cooled heat sink system; it's just what I had on hand. The water coming from the pump goes back to the aluminum struts via a T fitting to split the water into two flows, one for each bank.
Performance: Excellent. At the moment, I'm only using convection through the heat exchanger. I could easily use a fan to force air through. Moreover, there is little air moving through the heat exchanger due to the fact that it's sitting on a shelf with only the front lip over the edge. The resulting slot is about 1" by 13" compared to about a 15" by 13" opening across the bottom of the A. Obviously, I could increase efficiency considerably by allowing more air to flow though the heat exchanger, but I'm running out of space on my work bench. Add to that the fact that I wanted to 'torture test' the system to see how it would operate under less than optimal circumstances. In spite of being hamstrung in this manner the temperature at the aluminum L right behind the output devices is on the order of 108 degrees F after 2 hours of operation. Ambient temperature is about 72 degrees F.
I've spent about $30 out-of-pocket for the aluminum, the braided line, and the brass fittings. The pump was, I think, about $70 or so, although a non-food grade pump would be much much cheaper. The heat exchanger was free. Call it about $50 if you were to build such a system from scratch.
Now the interesting thing is that you could conceiveably run more than one amp off the same system. For those into solid state, it would not be a major difficulty to "T" out more lines and water cool more channels. That's a *lot* of money you could save on heatsinks.
Noise from the pump: Yes, the pump makes noise. Other pumps may be quieter. I would not want to have this pump in the same room while I was listening. My intention, both for the noise and for heat, is to put the heat exchanger and the pump in another room. I had considered the possibility of a purely convection system, but decided to go with the pump, since I had one on hand.
What I would like to do for a Version 2 is to use copper bars, perhaps 1" wide, 8" long, and 1/4" thick soldered directly to copper pipe. This should provide for far better heat transfer, as copper is superior to aluminum in that regard. It would also be more compact and sturdier than the current setup. The problem will be availability of copper bar. I'll see what I can do.
Oh, speaking of compact...it is. Compared to the size of the passive air-cooled heat sinks you'd need in order to build a circuit like this, it's positively tiny. The entire circuit, complete with aluminum 2x4's, would easily fit in a two-space (3 1/2") rack mount enclosure. The heat exchanger, obviously, is rather large, but can be put somewhere else.

Grey

P.S.: Do not fuse the individual rails going into an Aleph circuit...
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Old 8th April 2001, 11:38 PM   #2
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As an addendum to the above, it seems that the Little Giant 3-MDX is rated at about 7 gallons per minute when operated at 3' head, which is roughly how high the heat exchanger is above the circuitry.

Grey
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Old 13th April 2001, 09:52 PM   #3
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Version 2.0
I have built copper heat exchangers for the system. They replace the aluminum 2x4" exchangers described above.
The new version consists of a copper bar 1/4" thick x 1" wide x 8" long, soldered (silver solder, in case it matters) lengthways to a length of 1/2" copper pipe with fittings on each end. The resulting cross section thusly: O-
The output devices are mounted on 1" centers, evenly spaced from the center line. (Same as above.)
All else is the same as above.
Performance: On the order of .06 degrees C/Watt. The disclaimer here is that I'm still running the heat exchanger from the heat pump with the same 1" air intake. I'd be surprised indeed if the performance didn't improve with more air flow.
The cost isn't bad at all, really. The copper bars were about $8 ea. The copper pipe is nothing special, the usual stuff you'd use for plumbing around the house. Same 1/2" NPT brass barbs for fittings on the ends.
Mechanically, these are far superior to the aluminum 2x4" exchangers, as all connections are soldered or threaded instead of glued with silicone.
They are also even more compact. The limiting factor (on their sides) is the 1" diameter of the copper fitting to receive the brass barb. I confess to being tempted to place the circuitry in a single-space (i.e. 1 3/4") rack mount chassis. I probably won't--the passive air-cooled heat sinks for the IRF9610s in the front end stick up higher than the output heat sinks...and when's the last time you saw a front end with bigger heat sinks than the output section?
Of course, I could water-cool the front end...

Grey

P.S.: The copper is nicely polished and looks pretty sexy...
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Old 13th April 2001, 11:30 PM   #4
grataku is offline grataku  United States
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I had a completely different idea on how to do that (if my environmental sensitivity would allow me to throw away 300win heat). Howeverm I am curious to see pictures of your rig.
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Old 14th April 2001, 12:20 AM   #5
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grataku,
Worse yet, the 300W represents only one channel. *Sigh* And with summer coming on it's hard to justify, heat-wise, although I shall be glad of it next winter, no doubt.
Pictures...I'd be glad to post pictures, but I'm probably the only author in the known universe without a web site. Sooner or later I've got to do one. My enthusiasm level is somewhat less than low, unfortunately. I'll do something, promise. (Just not sure when. If nothing else, it will give me a way to put up a few schematics, as well.) I know it's hard to visualize things from a bare bones description, because I've run into the same problem myself.
I'll take pictures as I'm building the other channel. That way I'll sidestep all the what-ifs and why-don't-I-trys that I went through to get where I am now.
Oh, yeah...one other thing. I anticipate that the copper version will be easier to mount, mechanically, than the aluminum one.
What ideas did you have? I'm not too proud to take a good idea from elsewhere, and it's not too late to revamp the system if it were to work better and/or cheaper than what I have here.

Grey
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Old 16th April 2001, 08:43 PM   #6
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Lightbulb Take a look at this!

Hi all,

take a look at this:

http://www.benchtest.com/

This guy has DIY water coolers and even heat pipes (a very interesting subject IMHO). He's cooling PCs, but well, we can cool amps with the same technology.

One particularly cool element in his heatsink projects is that he used copper from a roofing supply and this was quite cheap. Hmm....

grataku, would you mind telling us about your idea?
GRollins, thanks for reporting about your experiments. I would also like to see a picture...

Regards
Timo
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Old 17th April 2001, 01:14 AM   #7
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Tim0,
Great site. Yes, the guy seems to be working along parallel lines to what I've been doing. However, I'm not set up to mill things--my shop is well equipped only in the woodworking category. Machining things is cool, but beyond my capability as things stand now. (Nelson got by this by buying his own milling machines...but he can justify the expense by doing his commercial product in-house. I have no intention of doing this stuff commercially.)
My goals are low expense, and KISS (Keep It Simple Stupid...). The less complicated this is, the less can go wrong. I'm already *way* out on a limb as far as complexity goes (compared to air-cooled), but I'm making a semi-successful effort to keep things under control in that department. As far as cost, I'm coming in far less than I had guessed that I'd spend. Setting aside the water pump, which I already had on hand, the most expensive thing I'll be dealing with is the braided vinyl line at about a dollar & somethin' per foot...total price determined by the distance you want between your amp and the pump noise (and, arguably, the heat, but that will depend on the season and where you live).
The only tools needed for my way are a tubing cutter (hacksaw in a pinch, but I like tidy ends on my pipes), and a propane torch; neither of which are expensive. Oh, and a wrench or two to tighten everything. Not much to it.
Speaking of computers--somewhere in another thread (X100 back engineered thread?) someone mentioned buying a mess of CPU heatsinks. I don't remember whether they specified the cost, and I know they didn't specify the degrees C/Watt. Since the ouput devices in an Aleph circuit are dropping (at idle) about 20-25W each, I don't know how practical that would be for a class A circuit. (Somebody who's current on PC hardware drop in here and tell me how many watts an average CPU has to dissipate these days. I'm sure it probably said somewhere in that site, but I didn't read the whole thing...) Now, the X runs AB--might be practical there.
I etched and populated the boards for the second channel this weekend. My intentions were to pick up parts for the second heatsink today, but Murphy's Law bit me. May not even get it done tomorrow the way things are looking now. (Grumble, grumble...won't be much longer before I start muttering about Communist conspiracies to keep me from finishing this amp.)
Yeah, I want to get pictures up to help folks visualize what I've done so they can come up with a better way to do it, but I don't have a scanner or digital camera, and I don't have a website. One way or another, I'll get something done, as this is the most economical way to dissipate lotsa watts that I've come up with so far.

Grey
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Old 17th April 2001, 02:21 PM   #8
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Gray,

modern CPUs dissipate up to 70W. Older ones, for example the Pentium II 500 Mhz, about 30W.
But the heatsinks are used with fans. Without fans i would only dissipate one tenth of the heat in these sinks. Overall i think they are overpriced. An array of them would have unpredictable properties IMHO. A single CPU heatsink has about 0.25C/W.

I'm with you on the low expense and KISS front.
Water cooling and heatpipes are not exactly KISS. ;-)
A big, slow fan is simpler and cheaper. Of course, not as silent. (OTOH maybe comparable to a pump)
I have such an air cooling system in mind for a bigger class D amp (approx 1kW) with temperature controlled fan speed.

Regards
Timo
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Old 17th April 2001, 03:44 PM   #9
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Tim0,
I considered fans, of course, but I'm trying to get rid of a fan (the one on my poor old Hafler 500, which needs to go back into my bass rig), not replace it with another. Passive air-cooled is out of the question simply because big heat sinks are made out of unobtainium.
Another unconventional option I considered was to do air-cooled heat sinks, but place the fan in another room. Huh? How you do that? Easy--use that plastic flexible ductwork that they use behind dryers and such. It should be pretty cheap. Use it to duct air in from a fan mounted elsewhere. However, I couldn't convince myself that I could completely isolate the noise of the fan. Seems to me that a fair amount of the noise would come down the duct. (Stand outside your house and listen to the sound of the dryer...) Still, I offer the idea for anyone who thinks they can make it work.
Water-cooled?
I got the idea from the big mainframe computers I work with. Although the current generation of IBMs are air-cooled, the industry has gone through alternating cycles of air-cooled/water-cooled. We used to have 3080s and 3090s which were water-cooled. They had TCMs (Thermal Conduction Modules) with water fittings going in and out. I figured that something of that nature should do the trick.
And as a buddy of mine is fond of saying: One you get it in your head, you're not happy 'till you get it in the rump. (Translating roughly as I'll pay dearly for my hubris.)
Sure enough, once I remembered having that heat pump heat exchanger on hand, I was on the slippery slope and gathering speed. The idea is to spend as little as possible so that I don't feel guilty (my Scottish blood won't let me toss money about easily) if I choose to back away and try something else.
grataku,
Where are you, buddy? What was your idea? Somebody come up with a better/cheaper way to do this, so I can slap my forehead and say,"Why didn't I think of that?"
Tim0,
I'm jealous of the guy on that website--if I had that kind of machining ability here, I'd be doing the fancy stuff regardless of cost.

Grey
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Old 17th April 2001, 05:02 PM   #10
grataku is offline grataku  United States
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Sorry Grey and Tim0,
I disable the email notifications because they fill up my mailbox so I have to check the site from time to time. Plus, I spent the weekend working on my biamp project for a change and I didn't surf the net at all. Grey, if you care to know I just finished the external transformer box (remember that post about transformer noise?) it looks great. I am getting better and better at machining stuff so I can let my imagination loose with enclosure designs.
So more to the point, I am afraid that I have little to contribute to the discussion here, my water-cooling ideas involve big hunks of aluminum and a milling machine...so nothing that would save you guys time or money.
Also, I am not sure that building costs are significant if you look at the big picture. I mean, we are talking about dissipating 600w plus the pump, double that for air conditioning as you need to get the heat out of the house in the summer (and that is assuming a 100% efficiency air conditioning system!).
If one could carry a pair of thermally insulated lines outside the house and run them through a an old air conditioning heat exchanger without a fan that would save some money on the electric bill in the summer.
So, the more I think about it, the less I know where I would put the heat exchanger, and the less I want to built it.

[Edited by grataku on 04-17-2001 at 04:29 PM]
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