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  1. D

    3-phase pump on/off detection

    On one of my CNC mills I'd like to make a circuit that can detect when the coolant pump (3-phase, 200v) turns on so that I can turn a solenoid valve on/off (basically the solenoid valve will control the air that goes to the spindle's positive pressure "seal"). The circuit will also do a few...
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    3-Phase Back-of-the-envelope Calculation Check

    Hi All, My small consulting company is moving into an industrial location since we are getting a used CNC milling machine. The machine takes 208V 3-Phase power, and the required current rating is 40 amps. I know that actual current usage depends on the load, but I'm trying to estimate the worst...
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    Low Side Current Sense amplifier

    Sorry, I missed that post! It makes more sense to me now. When I get off work I'll go simulate/build that circuit and see if I can further my understanding. Thank you very much FvM. If I want to give you points, what kind of points should I give you?
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    Low Side Current Sense amplifier

    is the ADC referenced (ground reference) to j1.1 or j1.2?
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    Low Side Current Sense amplifier

    Being right or wrong doesn't really matter to me (although eventually it'd be nice to know the right answer). What I'm trying to do is measure a positive or negative current using a single sided ADC. I'd like to amplify a +- 0.1v input signal, for example, so that it outputs a 0-3v signal with...
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    Low Side Current Sense amplifier

    I see. This makes sense to me now. However, I would still like to build a bidirectional current sensor so that I can put it inline with the motor windings. I guess the way to do that would be to use a differential amplifier and then just read the voltage with an oscilloscope. I am still curious...
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    Low Side Current Sense amplifier

    I understand this, but what if the Back EMF on the motor (when all transistors are in the "OFF" state) causes current to flow through Q3 and Q2. If the motor is modeled as an inductor, and you turn all switches off after having one pair of switches on, then the motor will try to force current...
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    Low Side Current Sense amplifier

    Won't current go from both drain-to-source (MOSFET "ON") of Q3/Q4 and also from source-to-drain (MOSFET "OFF", current flowing through the MOSFET body diode) when driving an inductive load? Thanks, Matt
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    Low Side Current Sense amplifier

    Hi everyone, I want to create a low side current sensing circuit. The goal is to sense a 0-5 amp magnitude current by using a kelvin resistor, differential op amp, and a 0-3v ADC (from a microcontroller). The problem I have is that the direction of the current is not guaranteed. This is a motor...
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    90V DC Power Supply Sanity Check

    Thanks, I bought some 100uF 450V capacitors from a local surplus electronics supply store. Can't wait to see how it goes! Matt
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    90V DC Power Supply Sanity Check

    Thanks Mister_rf. Yes, my units were wrong on the current rating! 11pm... How do you determine the upper capacity limit for the capacitors? I Have some 20000uF 400V capacitors here, can I use them? Since I will slowly raise the voltage, they shouldn't draw too much current. I can probably put a...
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    90V DC Power Supply Sanity Check

    Hi All, I need a roughly 90vdc power source for a brake on an AC motor. At this stage, I'd just like to simply release the brake. The resistance of the brake at room temperature is 1.2kohm. At 90v, this corresponds to a current draw of 75mOhms, correct? I'm not sure the best way to make a 90V...
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    Power Supply Failure during Testing

    Yes, there is feedback control. The failure didn't happen right away. It sort of happened over time. The 24V Meanwell supply was making a humming noise for awhile when the motor was under load (I'm modulating PWM at 20khz). Then it started intermittently working. Finally it gave up completely. I...
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    Power Supply Failure during Testing

    Hello, I've recently made a motor control board. Rather simple, it has an H-Bridge run with 4 N-channel MOSFETs and half bridge drivers from fairchild, microcontroller from TI. Anyways, I was testing the H-Bridge circuit with a motor (after doing a LOT of tests with both high, and then lower...
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    High Voltage Caps Insulation

    What is an isolating base plate? I'm assuming it isolates electrically but what are the requirements for this? We have silicone o-rings/air gap, is this sufficient?
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    High Voltage Caps Insulation

    What does 2000v/60sec mean? That means a 2000v potential for 60 seconds before the insulation breaks down? If there is an air gap and the caps sit there floating, will this be okay? What would I do if I had 40 caps in series and 15000 volts? Thanks, Matt
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    High Voltage Caps Insulation

    My friend is building a high voltage vacuum tube amplifier. Part of the design is some 6000uF (500V rating) Nippon caps. Four of these caps are in series. The network is charged to 1500V. My question is regarding the mount for these capacitors. Are the outside of the caps well isolated from the...
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    3v MCU to N-Channel MOSFET gate

    Thanks for the help! This makes sense. It looks like in the SPICE simulation the resistor only case is only about half as efficient as the transistor gate drive case. What program did you use for simulation? This looks different than LTSPice but at the same time has a lot of similarities.. Matt
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    3v MCU to N-Channel MOSFET gate

    The MOSFET has a gate capacitance (Input capacitance) of around 1 nF. If I drive the MOSFET by using a pull up resistor at 5V, say 1kohm, and pull it down using an npn transistor, then I could drive the MOSFET w/a higher gate voltage. However, this will limit my switching speed... To have a 5V...
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    3v MCU to N-Channel MOSFET gate

    RdsON is only given for 4.5V and 10V. There's a graph of Vgs curves (3-10V, in 1V increments) vs Vds and Ids. Ids for 3V is only given up to a Vds of 3V, but Vds should never get THAT high, right? Matt

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