Building Cooling Controllers, CNCs, LED Lighting, and more!

Discussion in 'Electronics & Electrics' started by IMtech, Aug 21, 2011.

  1. IMtech

    IMtech (Banned or Deleted)

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    Hi All,

    I have been toying around with the idea of building a TEC-Cooled Water-Water Heat Exchanger for my PC for a while now. I have pretty much got the design down pat for the exchanger itself, but I am seeking advice on building a suitable controller. :)

    I have found a lot of different ones on the net, but decided to design my own PCB for the job. I am trying to drive 2x or 3x 136w 12V Peltiers per board, which will be supplied by the 12v from a molex or PIC-E connector, straight to the PCB and then fed to the TEC from the relay.

    Now, the only thing I am not sure about is how much current I can put through the PCB traces. I have designed the PCB now, with 3.81mm traces from the PSU connector to the relay, then back from the relay to the TEC PCB connector. I am thinking of using either 16awg or 14awg wires to connect both the power and TECs to/from the PCB. The TECs will be wired in parallel.

    My questions are: Is my PCB design good enough for 2 TECs @12v at full tilt? That would be around @272w of power going through the PCB traces/relay. Can it take it? What about 3 @ 408w total? I guess what I am trying to see is what is the safest maximum amount of power I can get through the PCB I designed. :)

    I am planning on making a small batch of the PCBs, and may even give a couple away to anyone willing to help out on this! :thumbup:

    The PCB will be used in my upcoming PC build, where I may go as far as using 5 of them, as I need to pull at least 1200w with the TECs to make the project worthwhile, so I figured a maximum of 5 boards would be okay space-wise in my project.

    Before anyone points it out, I have looked at phase changing, but I need something with a good fail-over, cooling multiple point not easily accessible, which only water cooling can give me with my design... ;) :leet:

    Thanks in advance guys! :thumbup:

    EDIT:

    Testing for the TEC water-block design & general TEC mischiefs will be done in my other thread: Peltier Porn (Or how to have some cheap fun!) :)
     
    Last edited: Jan 24, 2012
  2. Goth

    Goth Grumpy Member

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    Check out the calculator here:

    http://www.pcbco.com.au/tracecalc.html

    Note that the above site measures the width in "mil", i.e. thousandths of an inch. When you design PCBs you have to get used to working in thousandths of an inch.

    Basically, the copper track is a resistor with a small amount of resistance.

    If you know its length, width, thickness, and the resistivity of copper, then you know the resistance, and how much power it will dissipate at a given current.

    You don't want it to dissipate too much power, otherwise it gets too hot, and eventually will burn the track if the overload is too extreme.

    Some things to think about:

    - Run the same track on both the top layer and the bottom layer, if you've got a two layer board and nothing is using that space on the top layer. This essentially gives you double the track width in the same area.

    - Use thicker copper, eg. 2 oz. (PCB copper thickness is usually measured in "ounces of copper per square foot". 1 oz., which is the most common, equals about 35 microns.)

    - Apply a thick layer of solder over the high-current track after the board is assembled to boost its current-carrying capacity.
     
  3. mtma

    mtma Member

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    One other option is use non-PCB mount relays (e.g spade terminal relays) and have the power wired to them separate to the control.

    Additionally, you might not really want to always be using the same PSU for control and power output (for example for the 1200w system they may as well be seperate) so you might benefit from separating the control and TEC power rails anyway.

    As a result, I'd be inclined into optioning the boards so that at least the two supplies can be split and a removable link to allow you to share them if that's the most convenient (e.g lower power).
     
  4. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Thanks for the tips Goth! :thumbup:

    So I guess with my design ends up being 150 Mils. With a 3oz PCB, over a max distance of 2cm, this gives me 17.5A with a temp rise of 20c, ambient @ 25c.

    So I could run 2 136w/9A peltiers of the one PCB then, with solders on the traces between the PSU plugs, the relay and the TEC plugs... right? :thumbup: :)
     
  5. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Thanks for that mtma... I didn't even think of using a relay out of the PCB! :lol: :o

    What is the maximum power a relay can do on 12V? Something that would be easy to find & cheap...cheap is nice, as always! :lol: :thumbup:

    So with the relays outboard, I shouldn't have trouble getting like 3 or 4 of them switching off the same PCB right? As in, they don't really use much power each? :confused:

    This would make the project so much easier, with just the one board controlling all the TECs! :thumbup: :) :)
     
  6. mtma

    mtma Member

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    10A per contact is generally very common. Beware that the DC contact rating is normally lower than the AC contact rating though.
     
  7. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Thanks man really appreciated! :thumbup:

    So with around 10A per relay, that only means I can run 1 Peltier per relay then. Which is not optimal, but it can do! ;)

    Would I be able to run like 9-10 relays of the one relay output from my PCB? I guess the relays themselves would be very low current? :)

    Edit: I'm using a 2N2906, fed by a LM7812 in my design to supply current to the relay. Would that be enough for up to 10 relays?
     
    Last edited: Aug 21, 2011
  8. mtma

    mtma Member

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    Well you need to choose a relay you're comfortable with in terms of price and etc.

    So for example with this the coil will use 75mA normally. There's plenty of other options to choose from from other places like WES, rs components, element14 etc.

    According to the current specs of the 2N2906 this should be 8, but you need to consider the power dissipation of the transistor, which is only 400mW so in reality you can only run about 6 because of the transistor's saturation voltage.

    I would go with a TO-126 or TO-220 size package transistor. Something like a BD140

    ED- the above linked is also double pole which means you have 2x10A current switching available from a single relay
     
    Last edited: Aug 21, 2011
  9. Goth

    Goth Grumpy Member

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    If you're bringing in current from the PC supply, via a molex or PCIE connector or similar, is there really any point to using a 7812?

    The PC supply is already well regulated, and even if it is a little bit above 12V, it won't matter for the circuit, and there won't be enough head room above 12V for the 7812 to regulate properly anyway.
     
  10. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Thanks guys! :thumbup: :)

    I think I found one that is reasonably priced. This one

    Available here

    It's less than $9, and can do 8A at 250VAC, so I should be safe to assume it will be ok for 9A @12V loads right? :confused: :)

    I have now changed the circuit to reflect mtma's suggestions. I can now drive 4 groups of 3 relays from the one controller board. I was limited by Eagle PCB's Light edition restrictions, but am looking at now buying it, since it would allow me to have a mega TEC controller card with a half dozen relays on a PCI form factor card! :shock: :) ;)

    I realise now there may be some potential in my idea, as I have not really seen anybody else doing one, bar a couple of people on Xtrem Systems which don't really share much in the way of schematics... :p

    I have designed a heat exchanger cooled by 6 136w peltiers, which is good for about 816w worth of peltier action :leet: This should be enough to get both a single CPU and a single VGA card below ambient, maybe even close to freezing the water if it's a very light load if wanted, hence the reason for the controller :thumbup:

    I am thinking of building 1 controller with 4 slave relay board (3 relays on each board), for a total of 12 peltiers and 1632w. This will be cooling an 8 core CPU (come on already AMD! :p) and 4 HD6950 2GB video cards. Hopefully I should hit sub-ambient with the whole system once it is all complete! :D

    I will be cooling the hot side of the peltiers with a big Ford Falcon radiator, so that should be ok for I anticipated to be 3Kw worth of heat all up. I have devised another board to control valve that will control the flow between the heat exchanger and a normal WC loop, to offer both redundancy and a way to cool the system without having to run the peltiers 24/7 :p

    I am finalizing the boards in the next couple of days, in case I think of anything to add, and then I will be ordering in a few boards to get this project kick started. I may even make a few more if people here are interested! :thumbup:
     
    Last edited: Aug 21, 2011
  11. dakiller

    dakiller (Oscillating & Impeding)

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    Jaycar have plenty of high current relays, a bunch that will do 30A, and this one :shock: - http://www.jaycar.com.au/productView.asp?ID=SY4073

    Don't put the relay on the PCB, just run the wires for the relays coil from the PCB to the relay and hard wire the TEC's to the relay.

    Are you going to be switching these on and off to try and limit their power? (aka PWM) Because that is a bad idea to use relays to switch repetitively like that, MOSFET's will do a better job and not go *click clack* all day long

    Hope you got enough power and cooling for these things, 1600W @12v is nothing to scoff at

    And aren't TEC's better run at higher voltages, around 15V? Or was that only for the ones around years ago when I was curious about them
     
  12. Goth

    Goth Grumpy Member

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    You can get relays that are PCB mounted, and have PCB legs for the coil, but have spade terminals on the top of the relay for the contacts, so the higher-current or higher-voltage contact wiring doesn't need to be wired through the board.
     
  13. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Wow that is a monster of a relay. You guys may be right about not getting the relays on the board. I can barely fit 3 on the one board anyway, and would have to build a little tower or relays to get what I needed to do.

    I'm gonna go to my local Jaycar tomorrow and see if they have one of those monsters in stock. Cheers! :thumbup: :)

    I won't mind the noise of the relays I guess, as it will only be used for benching, so only after hours really. The PC is also in another room to were I sit, so the noise won't bother me. Unless I can find a mosfet that can do 108A or more on 12V for the whole lot, or at the least 27-30A for a group of 3 Peltiers... :D

    I have not seen anything like that tho. Do you have a link handy for a high rated one? :)

    That could be even better, with only the one PCB with the one relay on-board (or at the worst 2 on a separate board mounted on top of the controller)! :thumbup:

    Thanks again guys! :thumbup: :)
     
  14. Goth

    Goth Grumpy Member

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    There are all kinds of neat things available when you move outside the box of simply using what you can buy at Jaycar.

    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PB304-ND

    Start shopping at somewhere like Digi-Key or Mouser or element14 and you'll realise just how expensive Jaycar is, too. But that's the price you pay to have a chain of local retail shopfronts.
     
  15. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Cheers for the heads up! I was aware of Element14, but not the other 2. :)

    I am up to Mark 4 on my design now. I have 2x 6Pin PCIE plugs on board the main controller board for power, and a 8Pin PCIE plug for connecting to the relay wiring harness I found at Jaycar. This way, I can use 6 pins for power (2 8AWG wire worth for each peltier unit, more than enough I think!), and keep 2 pins for the relay on/off power signal.

    I think I am really heading in the right direction now. I will be able to have everything on board except for the wiring harness/relay, which will off course be offboard, but it is actually good, as I can snatch it away somewhere in the case and forget about it... :thumbup:

    I will be sleeving all the plugs and leads too, so as to make it look as good as I can! :)

    Now to make 1 of the little beasts, then if the proof of concept works I will make 3 more. I do not anticipate any problems but you never know, my electronic skills haven't been used for the best part of a decade... :Paranoid: :lol:

    I also think that with a beefy relay, like the 150A one mtma pointed out, and the 12V bypassed from the PCB, I could also use the same circuit later on to control a Phase Change unit or two, which is one of my longer term project...

    I have also made an "ACCessories" PCB, with a simple PCB mounted relay, that controls 10 plugs total for power. 5 on/5 off when relay is not powered, and the opposite when it is powered. I will use those PCBs to power the fans for the TEC Heat Exchanger on one side when TECs are on, then turning those off and powering the WC gear fan that will cool the system down when not using the TECs, or in case of any failure in the TEC system. The 10A relay should give me plenty of juice for a few fans & lights! ;)

    One of the ACC PCB will also power valves on/off to regulate the coolant flow from the traditional WC gear to the TEC Heat Exchanger as needed.

    Now I have a few Amps to power the relays it makes the project so much broader in it's use. Thanks again guys! :thumbup:

    EDIT: PCI-E 8Pin plugs, and especially connectors, seem impossible to find, so I substituted them with 8Pin EPS PCB connectors & matching plugs ... rated at 7A per pin! :)

    Not cheap tho... the EPS connector are $2.04ea if I buy 10 and plugs are $0.702 if bought by 10 also. PCI-E 6Pin connectors are a big cheaper tho, at $1.08 if I get 10. So $40 worth of plugs so far, and that's maybe 2% of the parts I need... :p
     
    Last edited: Aug 22, 2011
  16. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Didn't get around to Jaycar today, as I had to rush to HN to get a TouchPad! :lol: ;)

    But the 150A relays looks damn tasty, as I could run all 12 off the one relay/controller, which means only one "brain" for the whole cooling system! :thumbup:

    If I run the peltiers in parallel, I would only need 14awg wire from the relay to each peltier right? I was thinking of getting an electrical bridge to get it all looking neat and also safely secured, but I don't know what kind of wiring would take 108A+... :confused:

    I have made more changes to the PCB, but I'm not sure if it will all work out.

    I'd be happy to show the PCB schematics to someone that knows their electronics to make sure it all works... Happy to shout out a couple of beers for the effort too! :) :thumbup:
     
  17. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Well I have now finished one of my projects.

    Let me introduce the IMtech CONTROLFAN PWM MK1! :D


    Click to view full size!

    (Please note the Thermistor in this picture is actually 2 pin headers for the temperature sensor)

    It is a 3x fans or 1x TEC PWM controller. It has a MOSFET power capacity of up to 33A peak :shock: and I rate the board for 10A continuous at 12V, so enough to drive a 136w peltier easily with heaps of headroom for an additional fan if needed. The temperature sensor can be placed anywhere in your PC as needed, and it plugs into a standard PC Molex 4-Pin plug.

    The temperature is set once via the build-in variable resistor, but can be changed later on with a small flat-head screwdriver. ;)

    It has a big capacitor to reduce ripple/drooping on the 12V input, so it does not over-strain the PSU when connected to a high powered load, and the MOSFET is definitely over-sized for this controller, which will allow it to run pretty cool during normal operations.

    The whole board itself, excluding the hanging part of the MOSFET (which needs to be attached to a heat-sink for normal operation), is 33x44.5mm, which is very small for the power rating and feature set.

    The beauty of the design I think is the size and ability to drive a fairly large load on the one mini board. :thumbup:

    I have bought all the parts today to build a prototype on the week-end, and have got quotes for getting some build in small quantity. I can get the whole thing down to about $25 a piece fully built, using high grade components (including temp sensor on 1m cable and Molex power cable). I can order a few PCBs at once if needed, so if people here are interested I can have a few more PCB done at the same time for that, or if people want just the board itself it should work out under $5 easily for a naked 3oz board silkscreened. :thumbup: :)

    This is only part one of my series of controller. I have it's big daddy the CONTROLTEC PWM pretty much done, at MK4 stage already. ;) This will be a board about double the size, maybe 50x90mm or so, but it will control outboard relays up to 150A for BIG peltier(s) action! :leet:
    It will also have a daughter board, of about the same size, with 12x 12V outputs of varying on/off switch state depending on the motherboard controller's states. :thumbup:

    Watch this space! ;)
     
    Last edited: Aug 26, 2011
  18. andrew_bg

    andrew_bg Member

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    Hi mate,

    I would be interested in your heat exchanger design.
    I have been running twin pelts for beer fermentation temp control and have been building custom water blocks that take both the peltiers, and having a water block top and bottom acting as my heat exchanger.
     
  19. OP
    OP
    IMtech

    IMtech (Banned or Deleted)

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    Hi Andrew,

    That is exactly how I am going with one of my designs! :thumbup:

    A series of 3 peltiers sandwiched between 2 waterblocks - one hot and one cold loop. I have also done another design with only one waterblock for the cold side and a heatsing design for the hot side dissipation, which 2 controllers, 1x for the TECs and one for the hot side's fans.

    I am still battling with designing them in SketchUp, as I have never used it before and the push/pull concept is doing my head in... :lol: :p

    I should have some more free time this week-end to finish the designs tho... :thumbup:

    What are your thoughts on the controller tho? :)
     
  20. andrew_bg

    andrew_bg Member

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    I can speak from experience and say that you want to try and keep your HOT side with the biggest dissipation.
    This was tricky for me as I am heating AND cooling with my setup, however the bottom line was that outside of my cabinet needs to have the most heat dissipation as it is mostly going to be hot on the outside and cool on the inside.
    When it runs in the reverse, well, the heating is much more efficient and it doesnt really matter if the outside is cod or not, the inside will always heat up with little effort.

    Sorry, I havent had a super detailed read of your controller plans as I have built a 1-wire interface and specific computer controller, meaning that I have full logging and web control over my setup :)

    I'll have a read of your controller soon.

    What are you using for water blocks?

    cheers

    Andrew
     

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