High Voltage Episode 21 - Inductive Current Limiting To Control Current Draw
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- Опубликовано: 17 ноя 2021
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Also a perfect demonstration of why MOTs are such terrible transformers. About 500 watts of power dissipation with no load! They are designed very cheaply with not enough copper and iron to operate out of saturation at their intended operational EMF of 120 volts. If you reduce the input voltage to about 90 volts they are much more linear and efficient.
Take some red sharpie or nail polish and paint the part of the toggle switch that gets covered when it's off. That way if you see red you know it's on.
I just repeated part of this experiment and got puzzling results. I have two MOTs. First I measured the resistance of the coils. MOT A had a resistance of 0.6 Ω across the primary and 89.5 Ω across the secondary. MOT B's coils were 1.2 Ω and 100.8 Ω, respectively. I put a clamp meter around one secondary lead of MOT A and set peak hold. I connected 120 V across the secondary. Let's see, 120 V / 89.5 Ω = 1.34 A. Allowing for impedance, I expected about 1 A. I got zero detectable current. I tried the same thing with the primary. 120 V / 0.6 Ω = 200 A. I expected peak hold to catch something before the breaker tripped. The breaker didn't trip, and I got zero again. I left the primary connected for several minutes, and it didn't even get warm.
I had saved the bulb from the microwave's interior light (20 W incandescent). I clamped the meter around one lead and applied 120 V. The bulb lit brightly, but no current detected.
I wondered if there were a problem with my clamp meter. I (nervously) tried connecting the 10 A port on my more expensive DMM in series with the secondary and applied 120 V. Again, nothing. Switched ports and range to mA. Nothing. Connected one meter to measure voltage and the other current. Voltage fluctuated between 122-123 VAC rms with zero current. Tried the primary with the same result. Disconnected the power and measured the resistance on each coil. No change. I repeated all the above with MOT B, and got the same results. At one point, two of my test leads accidentally touched. The breaker tripped immediately. Any clue what's happening here?
Maybe also include an advanced version of this class in a future episode for us adults with some moderate resources and theory knowledge, if you have time. I'm good for some donations.
I think the average hobbyist should be able to handle Ohm's law. When the current is low, there must be some resistance. But then it's alternating current. so it's not only the wire resistance, it's the coil's impedance, and then there's imaginary numbers that have real effects and ... yeah, I can see why you don't want to scare them away with circuit theory.
I remember kidwell saying “they’re going to get warm” when referring to MOT’s with shorted secondaries
My ballast transformer doesn’t have a secondary I removed it. Will it still limit the current of the transformer I intend to use? Thanks pls lmk
I have 2 MOTs with inputs in opposite phase parallel and outputs in series. It sits idle at 15 Amps and goes to 60 Amps for short duration loading. What inductance would I need to keep it under 20 Amps?
Here's a good place to start. This is the 10A version of the one you saw in the video. amzn.to/3MUxo9J
Hello, Tesla Coil builder here. I am currently using a 12kV/30ma NST. I'd like to move up to a dual anti-parallel MOT setup with voltage doubler/peak detector. What I'm unclear about from this video is how one correctly sizes an inductive current limiter. Do I go by the 60Hz impediance of the limiting coil and my mains voltage? How do I know what is an appropriately sized reactor? Thanks.
Damn i never thought a mot could draw 47 amps! Did you removed the shunts of the transformer? Back to a couple years ago when I was a noob and didn’t known about inductive current limiting i was drawing arcs straight off unballasted mots and the breaker was rarely popping (15a breaker)
47 amps was the initial maximum current. The (unloaded,) steady state current would, necessarily, be less than 15 amps or the breaker would always disconnect.
i want to see a mot meltdown. what's another way they could build mots?
Cant you just use a second mot in series as a current limiting inductor?
Cant you also limit current by using different cores? As in Less iron, adjustable shunts?
Yes (to both), it all depends on what you're trying to accomplish, and swapping out cores is a serious pain, just get a choke.
Been working on a project got a questioin, I made a solar power charging station for a 48v scooter. I now have 2x 48x lituim power packs for my scooter and I see people use a simple parallel wire to double the amp hours but it seems a lot of them catch fire, how can I limit two batterys in parallel to equal the amps of just higher then one battery?
the more I think its better two get a two way switch and use one at a time so im not feeding energy to the atmosphere, AC stuff is so wastfull lol