# Recent content by dksoba

1. ### 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...
2. ### 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...
3. ### 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?
4. ### Low Side Current Sense amplifier

is the ADC referenced (ground reference) to j1.1 or j1.2?
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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
9. ### 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...
10. ### 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
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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?