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Old 02-28-11, 07:02 AM   #611
okpiddler
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I do not know Drake. My under pressure on the low side protection and over pressure on the high side is all mechanical. I did not check into going electonic. By first glanced it looks like the cost would have been the same or less to go elec. I have enough ways to collect data and am not really interested in logging it. I have a Fluke logging thermometer and an elec meter so I know how it is performing and it will perform that way for yrs. to come.

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Old 02-28-11, 10:38 AM   #612
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OK, the question was referring to some of the technical electronics discussed earlier in thread, which at times(I'm not complaining) can become fractured as topic jumps around to include important information as it comes and people with useful knowledge expand on it. Get the info any way you can, it can be organized later. There are many pieces to the puzzle being laid out not yet in perfect order or is the HP we want it to make. Throw in we all don't want or probably correctly require the same HP system its a very variable subject yet. I greatly appreciate all who are sharing information on this subject. Someday this maybe the source the DIY HP book may be written from. I wish I had more knowledge than questions to share at this point.
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Old 02-28-11, 03:58 PM   #613
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Default The Power-Up Delay Scenario...

Quote:
Originally Posted by Drake View Post
OK, the question was referring to some of the technical electronics discussed earlier in thread...
On the electronics front, there are a few things that really need to be addressed in order to protect the compressor from destroying itself...

The most important is a delay period that begins when the compressor is powered up...

The scenario is this:
The compressor has been running for a while and there is a brief power loss of maybe a few seconds, to maybe 30 seconds. It is easily possible for the 'compression chamber' (if there is such a term) to become filled with liquid. If power is applied at this moment, the compressor will be trying to compress an incompressible liquid, and lock up with full power being applied to the compressor motor windings. This could burn and ultimately short out the windings, it is also conceivable that mechanical parts of the compressor could be damaged.
The power-up delay fixes this condition by allowing enough time (usually a couple of minutes) for the liquid in the 'compression chamber' to 'bleed down'.

I knew about the delay thing and only later learned why the delay is there. But on my prototype unit, I bypassed the whole delay circuit and wired power directly to the compressor (the starting cap was there, of course). During my testing, and experimenting with the unit, I accidently did replicate the scenario above, and the compressor locked up under full power, at which time my hand was instinctively flying to the power cord to turn the damn thing off... no harm done. But the scenario is real and it can kill your carefully crafted heat pump.

I have also had the experience, as has probably anyone who is reading these words, where I was sitting in a room, and for no apparent reason, the lights blinked, went off for some small fraction of a minute, then came right back on... this is the killer scenario.

This is what the power-up delay is there for. There is probably some cheap 'off the shelf' component that will do this for you, but I don't yet know what it is.

So, if you are building your own heat pump, and you wire directly to the compressor (with the starting capacitor in place of course), you need to know that there is a risk of intermittent power taking out your compressor..

I have made and used an Arduino-like microprocessor to do the delay task for me, and it's working just fine. If there's anyone interested, I can put the schematic and code on line. The Arduino has plenty of spare processing power so I'm still working on that part of the Arduino controller project.

Quote:
Originally Posted by okpiddler View Post
...My under pressure on the low side protection and over pressure on the high side is all mechanical...
Can you tell me more about this? What are they called, and where do you get them?

-AC_Hacker

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Old 02-28-11, 04:53 PM   #614
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Makes good sense and probably explains why an AC man once told me to not turn a running AC off and on again within I think he said 5 min(very old AC without probably modern electronics inside). Is any electronic delay stuff recoverable from an AC dissemble? Our dehumd works off humidistat control does it have delay?
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Old 03-01-11, 02:15 AM   #615
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Default HX Brazing - The setup...

I finally bit the bullet and began brazing up copper tubing to my Brazed Plate Heat exchangers.

This brazing project that I'm sharing with you is to attach short lengths of 3/8" copper tubing to the gas ports of the heat exchangers, to which the bent refrigeration tubing will be later brazed, this will keep the heat exchangers safely away from subsequent brazing steps.


Tool set up

Here's a shot of most of the tools I used for this round of brazing.

On the right is my tourch, in the photo, I have the green propane bottle still on my tourch, but I have found that using MAPPS gas which comes in the yellow bottles is more expensive but very much nicer to work with. Compared to soldering, brazing results in much stronger joints than soldering but requires more heat than soldering too. In refrigeration work, you shouldn't ever consider using solder, as the vibration from the compressor will fatigue solder. I tried propane when I first started brazing, I found that it could work, but it took quite a while to get the copper to the required cherry red that is needed for proper flow in brazing, then I discovered MAPPS gas, and life is good again. I'm really sold on the piezo trigger type torch, not only because it is easy to light, but also because it is so much more convenient to turn off the torch when it is not needed. Because of this, the cylinders last much longer.

I am an insufferable tightwad and a real gas welding setup isn't in my future. If you happen to have acetylene already, that's the Cadillac setup.

In the foreground is a long tube of Siphos 5% silver rod (the HVAC trade seems to prefer Silphos 15%), that is really the greatest thing since sliced bread. If you are brazing copper to copper, it is ideal and doesn't call for any flux. It also flows really nice and is very strong.

If you are brazing dissimilar metals, you'll need to use brazing flux and high-silver (40% or more silver, I'm using 55% silver) brazing rod. Close to where the torch crosses over the Silphos tube is my little bottle of flux (also Silphos brand) and a small coil of high-silver rod. I don't braze dissimilar metals much, so the small coil ($$$) has lasted me quite a while.

Also shown in the photo are a couple of my Brazed Plate Heat Exchangers. The smaller one I got for a prior project, that is on hold and the bigger one is what I ordered for this current heap pump project.

The considerations I went through for sizing the larger exchangers can be found here.

Frankly, I was initially hesitant to braze the exchangers because I was fearful that I would un-braze the exchangers that I had spent so much money on. Then I happened to come across a blog where a formerly frustrated HVAC guy told the new way he was doing it (thank you Al Gore for inventing the Internet!).


Rag is saturated, not just damp.

What he did was to wrap a saturated (not just moist) rag around the heat exchanger close to the place where the brazing would happen. Another key was that he applied heat to the copper tube, got it glowing cherry red, and then moved the cherry red area down to the heat exchanger and fed in the high silver rod as he did so (he had pre-fluxed, of course). I followed his method and it worked out great.

But I started, I made up some purging tubing so that I could displace the oxygen inside of the copper tubing that would otherwise cause copper-oxide flake contamination. The purging gas most usually used in the HVAC trade is nitrogen, while carbon dioxide has been use successfully also. In fact, Daox did a test using CO2, and it worked just fine. Argon would also be good, if you have it around but it is a tad expensive. I have even heard of some mindless idiots using propane as a purging gas, but I wouldn't recommend it if you expect to live to see tomorrow.


AC_Hacker's penny-wise purging tube

Here is a shot of my purging tube, I bought some small PVC tubing and super-glued some latex tubes to the ends because the PVC was much cheaper than the latex and I am such a penny-pinching miser. The latex streatches nicely over copper tubing from 1/4 to 3/8 and worked out really well.


Purging tube with rubber band to seal in the purging gas.

So before the brazing started, I fed some purging gas through the heat exchanger until I could see it coming out... it kind of looks like a little mirage. When I saw it coming out, I waited for it to purge a bit longer, and reduced the flow of purging gas, but made sure it was still flowing.

If I had been a completely brain-dead idiot, and had used propane for my purging gas it might have looked something like this:


Please ignore flame.

...but since nobody in their right mind would actually do this, please ignore the flame.

NEXT POST: TURNING UP THE HEAT


Regards,

-AC_Hacker
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Old 03-01-11, 12:54 PM   #616
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Default Turning Up the Heat...

Gathering up the tools and materials is really most of the job, and once that is done, you might as well pack up and go home (just kidding).

Here is a close-up of the gas port. Note that I have already put brazing flux on the joint. I put a liberal amount of flux on the tube (which I had lightly sanded with very fine sand paper), then I slowly rotated the tube into the gas port, taking the flux down with it.


brazing flux on joint, saturated rag

Also please note that I really wasn't kidding about the rag being saturated and not just damp. In fact just before I put heat to the joint, I drizzled a bit more water into the rag just to make sure...

Here is a picture of the tubing getting cherry red. Sorry about the picture, it was tough snapping photos and working the torch at the same time... The brazing was perfect, the pictures, not so good... probably best that way.


hotter than the tongs of hell...

So, shaky as it is, here's what it looks like when you really put the heat to it. I'm using the yellow bottle of MAPPS gas here and the tubing heats up pretty quick, compared to propane. Now that I look at the photo, and remember what color the hot copper tube was (the photo color is pretty accurate), I'd have to say that "cherry red" is maybe too mild a term. Probably more accurate would be "hotter than the tongs of hell".

I wasn't able to photograph the next step, which was moving the torch and the glowing red area down to the stainless steel gas port on the heat exchanger, because I needed to use both hands... One hand to hold the torch, the other to apply the brazing rod. This is really the most critical moment, and you'll want to get a good, smooth braze flow and then back the heat out as quickly as possible.

I had the luxury of having two heat exchangers from the project that is on hold, that I started on first, to get my technique perfected (and possibly destroy the heat exchanger in the process), not a bad idea really. But in this case, it wasn't needed and the described procedure yielded perfect results...


insufficient heat for good braze flow

...with the exception that when I brazed the second gas port, I was a bit cowardly in my application of heat and didn't get good flow. This I can easily fix by repeating the procedure only turning up my heat (and courage) slightly higher.



Below is a photo of a proper joint after everything is cooled down and buffed up just a bit with a fine wire brush.


what a proper joint should look like

Nice, smooth braze flow, no pinholes, no discontinuities.

So I did my small exchangers first and by the time I was working on the second set, it was very smooth sailing.

Here's a shot of all the finished heat exchangers...


brazing all finished

Once I got going, all the brazing took maybe 30 minutes.

Regards,

-AC_Hacker

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Old 03-01-11, 01:15 PM   #617
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Came across this very interesting article wherein solar heating panels (sun boxes) are used to "charge the earth" during the summer, for subsequent heat extraction during the winter.

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Old 03-01-11, 07:16 PM   #618
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Default Dual pressure controller

Hey AC, I need to learn how to put a delay on my compresser. It is relatively safe now being a rotary compresser with a hard start kit on it. I have stopped and started it many times with it only off for a second with high compression ratios, but, it is not right. I'd like to learn some of the electronic logging and controls anyways. Probably would have been cheaper to do my high and low side that way too.
Dual pressure controller for high and low side protection

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Old 03-01-11, 07:26 PM   #619
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Dual Pressure Control, 1/4 In Flare Nut - Dual Pressure Controls - HVACR and Appliance Controls - HVACR : Grainger Industrial Supply
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Old 03-01-11, 08:02 PM   #620
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Default Beam Me Up...

Quote:
Originally Posted by okpiddler View Post
I'd like to learn some of the electronic logging and controls anyways.

So you're interested in the Arduino stuff, are ya?

OK, there's a hardware part and a software part.

I can point you in the right direction, but you're going to have to do some homework on your own.

The lucky part is that the Arduino stuff is very popular, so you'll have so many places to get information that you won't know whether to shift or go blind.

So, if you get into this stuff, you need to realize that you'll need to talk to some experts along the way, and they will probably be 13 years old and will know more about this stuff than you or I ever will, so keep your humble hat close by, you're gonna need it.

[* EDIT (11-11-11): Since this post, an inexpensive controller with a web interface has been found. Xringer has posted a thread where he gives a pretty good introduction to the controller including sources of interface devices that make it very useful. *]

Regards,

-AC_Hacker

P.S.: Once you get your sea legs, Strider3700 is doing a great data logging project over here.

P.P.S.: I could post the schematic and the source code to the delay control here, but you probably wouldn't know what to do with it quit yet.

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