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Dummy Load II

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by jocanon, Jan 12, 2013.

  1. ()blivion

    ()blivion Active Member

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    Any issues we could come across probably all depends on what sockets you get, and how close/long the wires are.

    If the sockets add a significant length to the connections, or put them very close to each other, then you could get problems with crosstalk. There is also the issue of how much current the socketing interface can handle. The power wires will have a ton of current going through them, that's for sure. And I have seen my fair share of respectable looking sockets melt from overcurrent, so the sockets will need to be beefy. Also, more current means more magnetic field, meaning more influence on the gate wires. I think we are driving the gates with a very low impedance driver though, so this shouldn't matter that much.



    If you have some socketing options picked out that you like, link/post it and we can examine them.
     
  2. jocanon

    jocanon Member

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    This is what I ordered. I got the 4 way terminal because it is rated to handle enough current for the MOSFETs I believe. But then I also ordered the 8 way because I thought it might be easy to put the gate on it too. I got both because I don't know which option I will do and they are coming on a slow boat from China and they are cheap enough. Then I got the 34 pin headers that are only rated up to 1 amp to run everything else through like the fans in my case, the POT...I know 34 pins is overkill, but I didn't want to run out.


    4way terminal (it appears the 12 amp rating at 300V is per terminal because they all say 12A from 2 terminal blocks all the way up to 12 terminals).
    http://www.futurlec.com/Connectors/PLUGTERMS4W.shtml
    http://www.futurlec.com/Connectors/PLUGTERMV4W.shtml

    8 way terminal
    http://www.futurlec.com/cgi-bin/search/qty_price.cgi?part_no=PLUGTERMS8W
    http://www.futurlec.com/cgi-bin/search/qty_price.cgi?part_no=PLUGTERMV8W

    34 pin header
    http://www.futurlec.com/Connectors/HEADD34.shtml
    http://www.futurlec.com/Connectors/HDCONND34.shtml
     
  3. ()blivion

    ()blivion Active Member

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    Good choice. The only possible problem with those terminal blocks is they require you to screw down the terminals one at a time. That's perfectly fine if you don't mind doing this every time you want to take the system apart of course. However, do know that they make sockets that the ends can just press in/pull out of. I say that, though I can't actually cite anything in particular that would work for this application, so what you have will have to do I guess. Most proper "sockets" are very low current only anyway. It could even be said that the screw down terminals can handle more current, precisely because they screw down... but now then i'm just rambling. :)

    Those type of header connectors break down into smaller segments realy easy. And if you can get your hands on some IDE/Floppy ribbon cables, cut them up, be a little clever, put them back together, you can get arbitrary size and length connectors of decent quality fairly easily and cheaply. I have been using this for a lot of my most recent work, as I have bunches of computer equipment that is long since past it's prime.

    Finally, those headers usually won't actually handle a full 1 ampere per pin as is claimed, not with what usually connects to them. You are more than likely only going to get ~500mA or less out of them. But this is almost entirely because of the contact/wires, and says almost nothing about the actual pins of the header. In any case, I always limit my projects that use such headers to 500mA per pin/wire.
     
  4. dave

    Dave New Member

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  5. jocanon

    jocanon Member

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    I got the connectors in the mail yesterday. They actually do plug in. You screw the wire into one side but then it mates up with the pins and plugs in, so I will not have to unscrew them to take it apart. There is a lot of spacing and thick plastic insulation between each pin on the header. In looking at it in person it seems to me that I can put the gates and the source all on one header plug and still have good separation. I can make a custom cable and put a lot of insulation (i.e. double up on shrink tubing) between the wires. Do you think that will work? I am still not 100% that is what I will do, but I am leaning towards it so I just have everything on one plug (well, sort of, I will have 1 plug for 4 MOSFETs, so 4 plugs).
     
  6. ()blivion

    ()blivion Active Member

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    Interesting. . .
    Sorry, I guess I thought those plugs were of a different type. Good to know they will socket your transistors.




    As for the heat shrinking everything, if it's cheap enough there is no reason not to do it.

    Just remember we are more interested in trying to avoid electromagnetic field sharing, not electric current from jumping across a short circuit (though preventing shorts is also important, for totally different reasons). Point is, heat shrink will prevent shorts, but it will not block the EM fields that cause cross talk, obviously, because magnetic fields will go right through plastic. Only wire separation, shortest possible wire lengths, non-parallel routing, and so on will work to prevent cross talk I'm afraid.

    The wires don't actually have to be separated that much, just don't go bundling them all together for long stretches to try and make the construction cleaner or anything. Two long wires that are run together will act like a transformer. So any current through one will induce a voltage on the other. If this were to happen with say, your MOSFET ground wire and the gate wire, the massive current through the MOSFET will create a voltage on the gate pin. Since the gate pin controls the current through the device, this would cause all sorts of problems.

    To use an analogy, it would kinda be like if your car tires or axel were rubbing on your throttle or brake controls. Every time you went faster, the rubbing might either engage the brakes and slow you down, or engage the throttle and make you go even faster. Not hard to see why this might be a problem for you.
     
  7. jocanon

    jocanon Member

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    I see, that makes sense. I think there is enough space that I can keep the wires seperate enough coming off the header. So basically I won't bundle them all up together but rather have seperate wires coming off he header.
     
  8. jocanon

    jocanon Member

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    Just to let you all know, I am still here. I haven't had a chance to build the dummy load yet, but will soon. I have all the parts.
     
  9. jocanon

    jocanon Member

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    Someone commented on my YouTube video of DLI and suggested I use a radiator and reservoir pump instead of hooking up directly to the water line of my house. I will save a little money on my water bill, but would it be enough to make up the cost of the pump and reservoir AND would it provide as effective cooling as the water line running full blast. Or, if it's not as effective, would it be effective enough? These are the questions I have. Luckily I haven't started building it yet so if I want to change it up now would be the time. I would not have to change the schematic at all, just the hardware.

    http://www.youtube.com/watch?v=t5rglrH168E&noredirect=1
     
  10. ()blivion

    ()blivion Active Member

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    I could go on and on about this honestly. My philosophy is simply that the entire earth's hydrosphere makes a better coolant than recirculating a small amount of water in a radiator does. And a sealed coolant system is hard to do and costs more money.
     
  11. jocanon

    jocanon Member

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    point taken, about the cost...the only real benefits I see is that it would be portable and save a little on the water bill...I don't need portability so I will probably just stick with what I know works.
     
  12. ()blivion

    ()blivion Active Member

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    Do you use city water? I could see that being potentially pricey. Otherwise, like my house, water bill is simply a bit more on the power bill.
     
  13. ronv

    ronv Well-Known Member Most Helpful Member

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    Probably just trade the water bill for the air conditioning bill. :rolleyes:
    It might not take as much water as you have running. If you could find an easy way to restrict the output it might save a bit.
     
  14. jocanon

    jocanon Member

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    Yeah, our water bill never really high anyway. I think this is more of if it's not broke don't fix it...
     
  15. jocanon

    jocanon Member

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    I got a scope! I am excited to learn how to use it now :)...this is the one I got:

    http://www.ebay.com/itm/Tektronix-T...zsXqeD0OOESXFMegLiYP8%3D&orig_cvip=true&rt=nc
     
  16. jocanon

    jocanon Member

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    A year later - hoping to have some time soon to actually build this. Sorry for taking so long...
     
  17. jocanon

    jocanon Member

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    I am not going to be building this dummy load. In short, I started a new job as Tax Director at a large public company and I simply do not have time to continue on the power supply business. I have all the parts to build this Dummy Load II, so if anyone is interested in buying them from me, send me a message. Thanks!
     
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    Congratulations!
     
  19. jocanon

    jocanon Member

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    Thank you Ron, and thanks for all the help on the dummy loads, you've been great.
     

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