My First (Simple) Project

Discussion in 'The Projects Forum' started by Pet0r, Mar 28, 2012.

  1. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Hi,

    Basically I've done no electronics work before at all (except for a little in school), but I have a little project which I'd love to work on.

    Laptop cooling pads that I've bought (with the fans on) have been completely inadequate, so I'd like to make my own. Now, I can make the actual base no problem with a couple of bits of wood, but my main concern is the fans. I know that I can strip the end off a 12V DC transformer and as long as it has enough amps, rig up as many fans as I need to the positive/negative ends and they'll be powered, but that means... stripping the end off a DC transformer and the plugs of all the fans.

    What I'd really love to do is have a little circuit with a proper socket for the transformer to plug into, and then sockets for the fans to plug into as well, and probably a switch to turn them on/off. So the whole circuit can be put together without damaging any components (say I want to use the fans later, it would be annoying if I've stripped the plugs off).

    So I have a couple of main problems, I don't think one of them is actually wiring the circuit, but they are:
    1) What components to buy, and where from (I'm in the UK)? I found a site called rapidonline.com which seems to sell what I might be looking for.
    2) How can I mount the circuit (especially the sockets) in such a way that they actually work? I had a look at a few sockets and most of them seem to say they're for PCBs, and I have no idea how to use them.
    3) What's the best way to "cover" to circuit to avoid it just being open on the bottom of the cooling pad and allowing people to touch it while it's turned on?

    Many thanks,
    Peter
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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    Rapid are good, I get most of my components from them.
    I just tried and PC fans plug nicely into PCB headers (order code 22-0515 or similar). They can be easily cut to the right number of pins.
    You can solder them directly to stripboard (also anything else with a 2.54mm [0.1 inch] pin spacing).
     
  3. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Thanks, it's good to know that I at least found a supplier for the stuff.

    Thanks for the info on the PCB headers too, it seems like they would be perfect (I would ideally like the headers like you get on a motherboard, that stop the fan being inserted the wrong way), but I'm having a lot of trouble finding my way around component numbers and such.

    It seems I need these for the 3 pin fan headers:
    http://www.molex.com/molex/products...cHome##-1##-1~~ncPCBHEADERS##0##1pa&Itemlist=

    But there seems to be about 10 of the same kind on that page with the only difference being some say "11 Circuits" or "19 Circuits" or whatever. What does this mean? And any idea where I could source some?

    Secondly, what kind of wire would be suitable for this? I'm a complete novice and I imagine the current wouldn't exceed 1A, I presume the connections on the stripboard will be fine with this, and I should be good with pretty much any kind of equipment wire?
     
  4. Markd77

    Senior Member

    Sep 7, 2009
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    I found just the thing:
    http://www.rapidonline.com/Cables-C...415/?sid=10066c8e-bac1-48f8-9f22-0ddcfa020888
    You want the "3 way" version.
    The photos on the page you linked to are just for show, I think 11 circuits means 11 pins.

    Pretty much any wire will do, I like solid core because it stays where I put it, so I'd recommend the first one on this page or the single core equipment wire pack further down. The stripboard is also OK for at least a couple of amps.
     
  5. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Thanks for the help, you're right, circuits does mean pins, I found that out a little after I posted.

    I think the perfect one is this:
    http://uk.rs-online.com/web/p/headers-pcb-receptacles/6701721/
    (the 4 pin version would also work, but I'll only be using 3 pin fans).

    The only difference between the one I just listed and the one you did is that yours has a friction grip which I think is for a slightly different kind of connector than a fan one. I don't suppose it would matter a huge amount, the connector would probably fit either way.

    Any idea where I could buy a suitable transformer and the socket for it?
     
    Last edited: Mar 28, 2012
  6. Markd77

    Senior Member

    Sep 7, 2009
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    I think you want the 2.54mm version, not the 5.08mm unless your fans are different to mine.
    I found RS a bit odd, some bits of their terms and conditions say that you must be VAT registered, other bits seem to say that private customers are OK. I just put N/A on all the company related boxes on the registration form and seem to have got away with it.
     
  7. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Ooh, well spotted, you're right, I need the 0.1" spacings.

    In that case I'm not sure where to get hold of ones without the friction lock, as I'm struggling to find the part number on Molex's website.
     
  8. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Looks like these might do the trick:
    http://uk.rs-online.com/web/p/headers-pcb-receptacles/4838477/

    The one you posted should also be fine. I didn't realise the fan connector had a very small friction grip lower down, I was looking at the top. :rolleyes:

    I wouldn't mind some suggestions on where to obtain a good transformer though (I'm thinking 12v DC and maybe up to 1500mA). I also need a socket although those seem easy to just grab on either of the sites we've linked to here.
     
  9. Markd77

    Senior Member

    Sep 7, 2009
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    Not really sure where to get the supply. You might already have one, if you have kept the supplies from old printers, routers, laptops, etc.
     
  10. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    I have one which is 12V, 1A, but the fans I'm going to use, I want four of them, and the documentation says they can hit 0.23A when starting up, so I thought going with a 1500mA supply might be better?

    EDIT: I don't mean "better", I mean, safer? I guess. Just to make sure there's some leeway.
     
  11. Markd77

    Senior Member

    Sep 7, 2009
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    If that's the startup current and not the normal running current then a 1A power supply should be fine. It would supply more than that for a short while.
     
  12. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Thanks, I guess in that case it should be fine.

    I was thinking of instead of having a switch, having a potentiometer so I can adjust the speed of the fans if I want to. I would kind of like one which has a "click" off, I've seen some speakers that have a similar setup, the knob "clicks" on which completes the circuit and then as you turn it up, volume gets louder.

    A few things though:
    1) Can you buy a potentiometer like that? I've found it difficult to tell from the websites I've looked at.
    2) Don't they start at 0Ohms and go up to X? Which would mean the fans start at full speed and then reduce as you turn it?
    3) I don't really understand the wattage ratings, they seem way too low so I think I'm doing something wrong. Like this one, it seems to only be rated for 3W. Now I thought Watts = Amps x Voltage, so assuming 12V and 1A, that seems to be 12W?

    Thanks!
     
  13. Pet0r

    Thread Starter New Member

    Mar 28, 2012
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    Also (I can't seem to edit my post), I just measured the voltage of my existing transformer with my multimeter and it seems it provides just shy of 15v when unloaded, will this be ok for the fans? The ones I'm looking at say "Voltage Range: 12v", will they just draw what they need or is this not recommended?
     
  14. Markd77

    Senior Member

    Sep 7, 2009
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    It's unfortunately not quite that simple.
    Usually a potentiometer would be used to control a transistor to vary the current or the duty cycle of PWM, which is why potentiometers are not commonly available in high powers. Using PWM is efficient, the other ways are not.
    Using the pot as an example, the fan will probably only spin at around 7 volts or more. At that point the current will be fairly low and there will be around 5V across the pot, which is what you would use to calculate the power. With the fan voltage at 11.5V there will be 0.5V across the pot and around 1A. At some point in between is the most inefficient point, which is pretty hard to guess, but could be over 3W in the pot.
     
  15. Markd77

    Senior Member

    Sep 7, 2009
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    It's probably OK, the voltage will drop the instant the fans are switched on. It's hard to guess how much current will make it drop all the way down to 12V, but the 4 fans should do it.
    I was going to suggest instead of variable speed, switching on 1,2,3 or 4 fans, but maybe 1 fan wouldn't be enough load to get the power supply to drop down in voltage enough. I don't think a few seconds will do the fans any damage if you want to check what happens with the voltmeter.
     
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