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Thread: question about usb osciloscope

  1. #11
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    Quote Originally Posted by Travis View Post
    I'll vote for Rigol.
    me to but its 310 euros (plus taxes) vs 180 euros of the Stingray (no custom taxes here).

    The Stingray is only useful for PSU testing (but good for this purpose) whereas the Rigol is suitable for everything.

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    Quote Originally Posted by Makalu View Post
    it's looking good...was wondering what type of loads did you use and what are it's capabilities? Do you have more photos? What website will you be posting your reviews at?
    Resistors are used for loads. Its capabilities are 67A in 12V1, 66A in 12V2, 22A load in 5V, 19.8A in 3.3, 2A in 5VSB and 0.6A in -12V. I used simple switches to dial the loads but in the future I am thinking of replacing the switches with relay boards that will be controlled via usb.

    I put 4 shunts (12V1, 12V2, 5V, 3.3V) and three panels to measure the Amps but unfortunately the panel meters are of very poor quality so I left them on the loader only to cover the holes I made for them To measure the Amps I drive all the differential outputs from the shunts to a rotary switch and from there to two aligator clips, where I take the mV measurements for each rail (with a DMM) and I can calculate the Amps.

    Because I don't like very much the above way I have already ordered a Labjack U3 and currently I am in the process of making a program which will handle all the Volt/Amps readings of the test PSU.

    I work for the biggest IT community in Greece, www.TheLab.gr

    some more photos








    and bellow an early sample of my program that will take the readings of the test PSU
    Last edited by crmaris; 02-27-2010 at 07:00 AM.

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    That's really slick...or going to be once you get it all setup and programmed. I toyed with the idea of shunts and panel meters for measuring current but really didn't have enough room for the number of circuits I wanted to measure so I just use a clamp meter. Messed around quite abit with my two data logger multimeters but currently I just use them manually...gives me something to do. Here's my ghetto setup in case you're curious:

    http://forums.guru3d.com/showthread.php?t=296940

    let us know when you get your first test results up ok?

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    Attach heatsinks to the resistors, or derate those resistors by half (i.e. use 5Ohm 50W resistors for 12V so its heat dissipation is limited to 28.8W each). Those resistors will get very hot, and then some will fail in a few months.

    I prefer a constant current sink circuit connected in series with a power resistor, something like xbit's equipment (and of course mine). The heat is much easier to deal with.
    It's been a hard day's night and I've been working like a dog.

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    Quote Originally Posted by Makalu View Post
    That's really slick...or going to be once you get it all setup and programmed. I toyed with the idea of shunts and panel meters for measuring current but really didn't have enough room for the number of circuits I wanted to measure so I just use a clamp meter. Messed around quite abit with my two data logger multimeters but currently I just use them manually...gives me something to do. Here's my ghetto setup in case you're curious:

    http://forums.guru3d.com/showthread.php?t=296940

    let us know when you get your first test results up ok?
    Very Nice work!!!!

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    Quote Originally Posted by Travis View Post
    Attach heatsinks to the resistors, or derate those resistors by half (i.e. use 5Ohm 50W resistors for 12V so its heat dissipation is limited to 28.8W each). Those resistors will get very hot, and then some will fail in a few months.

    I prefer a constant current sink circuit connected in series with a power resistor, something like xbit's equipment (and of course mine). The heat is much easier to deal with.
    I have used 3 Ohm, 50Watt resistors for the 12V so I am at 48W (theoretically), but every resistor is firmly attached to the base of the case and with the use of thermalpaste the whole base of the case acts as a big heatsink. Also I have 2*220V blowers on the side panel and 5*120 fans and 1*80 (12V) inside the case. If I notice that the resistors get too hot then I will use additional blowers in the side panel. Finally if you put into account the losses (in Ohms) I have in the switches and the cables the resistors draw much less current than the theoretically 4Amps (for a 3Ohm res.).

    Loading 4 of the 12V resistors for about 4-5 minutes continuously they were only warm (I could easily touch them) and this without the side panel (and the 2 blowers).

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    Several other sites have used resistor loads but the resistors failed after months of toasting. So don't underestimate cooling requirements.
    It's been a hard day's night and I've been working like a dog.

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    Travis you were right. After some more tests I did today I noticed above normal temps, in the 12V resistors. However the resistors of the other rails (5V, 3.3V etc.) run very cool, under 40 Celsius. I have in the case now about 10 Fans and 2 220V blowers (in the side).

    The base of the case, that the 12V resistors are attached, plays its role and it absorbs the heat. So I will put a lot of heatspreaders on it along with cooling fans and I hope that I will solve the heat problem of the 12V rails.

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    you can sink the tops of the resistors too if you have to...they just don't have as much surface area as the base except the Arcols there it looks almost the same

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    Tomorrow I am gonna put 8-10 heatsinks to the base and along with 4-5 extra fans I hope that I will deal with the extreme heat!

    Also I noticed your (great) work. The only thing I didnt like is the way that you measure the Amps. Look is plain easy to put some shunts and take fine reading from them, if you want some help (how to install the shunts) drop me an email to crmaris@aegean.gr.

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