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Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Instead of starting a bunch of posts, I'm just going to put everything in here...
I have tried searching for answers here and on google, but can't seem to find anything that fits.
1. Regulating a MOT @ ~600V. 120V mains to 2.25A Variac to MOT to Half-Wave or Full-Wave rectifier. With the DMM connected to either the full or half wave rectifier, I turn up the Variac till my MOT output sits at 600V. At irregular intervals, the voltage spikes to anywhere between 1.2 and 1.8kV. The MOT is NOT ballasted. I understand that a MOT is self-regulating at a full 120V input, 2.2kV output by saturating the core. I have yet to find a VReg at my local shops that will do the trick. Anyone here have some advice?
2. Scoping a Full-Wave Rectifier. I would expect that any 60Hz full wave rectified output would look exactly the same. Like this - . But not so when "I" scope it. Every-other wave appears to be compressed, and at a higher voltage. Scoping the un-rectified output is fine, scoping FETS, 311's, TL072's and 555's all work fine with the expected output. WTF did I do? It's not like a rectifier is difficult to understand or build... Apparently that's not a safe assumption. FWIW the rectifier is made from sixteen 1N4007 diodes. Each segment is 2x2.
3. LC DMM's - Anyone here have experience with one? I have a bunch of unlabeled inductors which I pulled from various pieces of equipment. Specifically I'm looking for one @ 40uH. I expected the DMM to measure L with the same "results" I get from measuring C. That appears to be too much to ask. If I measure a bunch of caps with known capacitance, it's accurate to within a few uF or nF, depending on the cap. Measuring known and unknown inductors, the display never settles on any value. It just spikes and zeros out, and the spikes are never the same. Are any DMMs which measure inductance reliable or accurate?
Registered Member #1819
Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137
Zenador wrote ... 1. Regulating a MOT @ ~600V. 120V mains to 2.25A Variac to MOT to Half-Wave or Full-Wave rectifier. With the DMM connected to either the full or half wave rectifier, I turn up the Variac till my MOT output sits at 600V. At irregular intervals, the voltage spikes to anywhere between 1.2 and 1.8kV. The MOT is NOT ballasted. I understand that a MOT is self-regulating at a full 120V input, 2.2kV output by saturating the core. I have yet to find a VReg at my local shops that will do the trick. Anyone here have some advice?
2. Scoping a Full-Wave Rectifier. I would expect that any 60Hz full wave rectified output would look exactly the same. Like this - . But not so when "I" scope it. Every-other wave appears to be compressed, and at a higher voltage. Scoping the un-rectified output is fine, scoping FETS, 311's, TL072's and 555's all work fine with the expected output. WTF did I do? It's not like a rectifier is difficult to understand or build... Apparently that's not a safe assumption. FWIW the rectifier is made from sixteen 1N4007 diodes. Each segment is 2x2.
1. Check for spikes on your household voltage. If that's not the problem (which it likely isn't), the transformer's residual stored enegy might be reacting with itself or the variac.
2. What do you mean by compressed? Is it higher frequency, lower voltage, clipping, bottoming out, or some combination of the above? A schematic would also help.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
1 and 2: Something wrong in the connections, contacts, or the instruments, or sparking somewhere. What are you using to measure kV voltages? Be very careful with MOTs. Errors can be very destructive, to you too. 3. 40 uH may be too low inductance for your meter. Some inductors (with core) are nonlinear, and a regular meter may produce nonsense. You can always measure the resonance frequency with a known capacitor, and then calculate the inductance (for linear inductors, of course).
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Some General HV questions...
