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  • MagnusR2 commented on apapercraft's instructable Modular Honeycomb Shelves2 months ago
    Modular Honeycomb Shelves

    Quite interesting and thanks for linking to the other projects. Seeing your construction, the weakest points are probably the connections of the planks. The tape you used before the gluing should give some additional stability. Instead of the tape you could also use thin cardboard or paper and glue it there with large overlaps. That could increase the stability of these points.

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  • MagnusR2 followed Akin Yildiz2 months ago
  • MagnusR2 commented on Chris Project's instructable DC Motor Speed Controller3 months ago
    DC Motor Speed Controller

    I totally agree that MOSFET are typically not intended to be driven in linear mode, but this circuit does drive the MOSFET in linear mode. So when then the question arises how much you can scale this up to bigger motors, the data sheet does not give the answer, because the data sheet does not anticipate such a usage of the device. The SPICE model also does not give the answer to the linear operation mode. There are however a few applications where MOSFETs do need some linear mode capability, so some competitors quote a more accurate capability on their data sheets, including a DC rating and the Spirito region. Look if the lines in the save operation area figure have a kink in line determined by the power dissipation (lines which go from top left to bottom right). If the lines shows such...see more »I totally agree that MOSFET are typically not intended to be driven in linear mode, but this circuit does drive the MOSFET in linear mode. So when then the question arises how much you can scale this up to bigger motors, the data sheet does not give the answer, because the data sheet does not anticipate such a usage of the device. The SPICE model also does not give the answer to the linear operation mode. There are however a few applications where MOSFETs do need some linear mode capability, so some competitors quote a more accurate capability on their data sheets, including a DC rating and the Spirito region. Look if the lines in the save operation area figure have a kink in line determined by the power dissipation (lines which go from top left to bottom right). If the lines shows such a kink then the Spirito region was determined and you can tell if the you can use that MOSFET in that region. Still this is typically a single shot rating, so you still need to leave some margin to that line. A factor 2 is probably enough. The data sheet of IR is therefore not adequate if you want to know if you can scale up this circuit. In general I would advice against upscaling this circuit and rather use a more complex circuit, as you propose.

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  • MagnusR2 commented on Chris Project's instructable DC Motor Speed Controller3 months ago
    DC Motor Speed Controller

    When he asks for 12V I assume he is no longer using a battery as power supply. Anyway 110A is what you can get through the MOSFET if you turn it on completely (VGS=10V says data sheet), but if the MOSFET has handle a voltage drop in linear mode, that is a completely different matter. Then you reduce the VGS with your potentiometer and the RDSon rises and you cannot send 110A through it anymore... I guess you are right that the 9V block will probably not blow up the device, but you cannot be certain, just from the few information given by the datasheet. When force your device in linear mode and the MOSFET has to handle a VDS of just 9V, it will likely blow up when you drive more than 10A through it. I did not try it for this device, but I have bad experience driving MOSFETs in linear mode.

    Not sure. The data sheet of IR is missleading. Important is how much current your motor can draw. According to current and voltage your are driving the MOSFET in the linear Mode with this circuit and MOSFET then often die because of a thermal runaway in the so called Spirito region. Some manufacturers show that region on their datasheets in the Save Operation Area, but IR does not and they don't even show the DC rating. So if you want to figure out if it blows up, look for a data sheet where the linear mode performance for DC currents is shown in the datasheet together with the spirito region. I found this document explaining linear mode performance in more detail: https://cache.nxp.com/documents/technical_note/TN00008.pdf

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