Hi, any inductor or switching power supply experts here?
I salvaged a toroidal core from a transformer. The transformer had markings of 115/230 volts AC in, and various outputs totaling about 25 watts. The core is about 3" outer diameter, heavy like metal, painted solid green, and a magnet easily sticks to it.
With 12 turns of #12 wire wound around the core, my inexpensive LCR meter read 234 uH. It was more than I would have liked, but was what it was. The turns must be a multiple of 12, for reasons that would take another thread to explain. I then put the inductor, L1, into the test circuit below:
SOLAR_POSITIVE is a +24 volt supply relative to ground, with a large stiffening capacitor. You can ignore the unconnected parts of L1, just consider it to be a single inductor. Also disregard Q2 and C1, they not important to this question. The PUMP signal pulses high for 20 uS, once a second, causing Q1 to apply voltage across L1. With an inexpensive oscilloscope, I monitored the voltage on both sides of R1 with 10 meg probes.
While the circuit was running, I saw 12 volts develop across R1 during each pulse, suggesting that 12 amps were flowing through L1, and that the inductance was really more like 30 to 50 uH. There was also a soft clicking sound at a 1 Hz frequency coming from the inductor. I turned off the lights in the room, but couldn't see any arcing. At one point, the clicking stopped, and when I looked on the oscilloscope, the current was only developing to about 2 amps during the pulse, implying the original 240 uH or so inductance. I let that run some more, and eventually, the clicking started again, and the 12 amps were back.
At that point, I unsoldered the inductor and reversed the leads, so that current would flow in the other direction through it. When I looked at the scope again, I saw 0.3 volt developed across R1, implying that the inductance was now more than 1000 uH.
Okay, here are the questions. Opinions and guesses are welcome. Thanks in advance.
Q1: What material is the core likely to be made of? Could it just me a solid piece of iron or iron alloy?
Q2: What happened to drive the inductance down? Did the toroid get magnetized, like core memory? If so, is that normal?
Q3: I would love to use the lower inductance in my design. Is it ok to intentionally magnetize the inductor in this way (assuming that's what caused the change), and will there be more losses of any kind if I use an inductor operating in this way?
Q4: What's my next move? Should I just buy a new toroidal core of known material? I dislike spending money as much as the next guy, but do have the resources to buy a brand new core if I have to.
I salvaged a toroidal core from a transformer. The transformer had markings of 115/230 volts AC in, and various outputs totaling about 25 watts. The core is about 3" outer diameter, heavy like metal, painted solid green, and a magnet easily sticks to it.
With 12 turns of #12 wire wound around the core, my inexpensive LCR meter read 234 uH. It was more than I would have liked, but was what it was. The turns must be a multiple of 12, for reasons that would take another thread to explain. I then put the inductor, L1, into the test circuit below:
SOLAR_POSITIVE is a +24 volt supply relative to ground, with a large stiffening capacitor. You can ignore the unconnected parts of L1, just consider it to be a single inductor. Also disregard Q2 and C1, they not important to this question. The PUMP signal pulses high for 20 uS, once a second, causing Q1 to apply voltage across L1. With an inexpensive oscilloscope, I monitored the voltage on both sides of R1 with 10 meg probes.
While the circuit was running, I saw 12 volts develop across R1 during each pulse, suggesting that 12 amps were flowing through L1, and that the inductance was really more like 30 to 50 uH. There was also a soft clicking sound at a 1 Hz frequency coming from the inductor. I turned off the lights in the room, but couldn't see any arcing. At one point, the clicking stopped, and when I looked on the oscilloscope, the current was only developing to about 2 amps during the pulse, implying the original 240 uH or so inductance. I let that run some more, and eventually, the clicking started again, and the 12 amps were back.
At that point, I unsoldered the inductor and reversed the leads, so that current would flow in the other direction through it. When I looked at the scope again, I saw 0.3 volt developed across R1, implying that the inductance was now more than 1000 uH.
Okay, here are the questions. Opinions and guesses are welcome. Thanks in advance.
Q1: What material is the core likely to be made of? Could it just me a solid piece of iron or iron alloy?
Q2: What happened to drive the inductance down? Did the toroid get magnetized, like core memory? If so, is that normal?
Q3: I would love to use the lower inductance in my design. Is it ok to intentionally magnetize the inductor in this way (assuming that's what caused the change), and will there be more losses of any kind if I use an inductor operating in this way?
Q4: What's my next move? Should I just buy a new toroidal core of known material? I dislike spending money as much as the next guy, but do have the resources to buy a brand new core if I have to.