💬 OT The (not really) official electronics workbench thread
- Thread starter Mr_Roboto
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Managed to fix the PSU to get it spewing hv again. I don't know that it is quite right but it pegs the 5kv of my volt meter. Up next is pulling the doubler to see if I can get the voltage down and actually measure it.
I tried some monostat, it didn't work. Maybe I needed to wait 7 days but I got impatient. I added the pots thinking it was an open input but in the end it was just crossed wires.
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The IC is a tl494. It has a bunch of stuff built in to make a DC to DC power supply. This includes an oscillator, 2 error amplifiers, 2 output transistors and a voltage reference.The idea is it is a complete controller for a switch mode power supply with input/output circuits and a few components besides to set the IC up.
How it works is that you set the oscillator frequency, then you set up the error amplifiers with feedback from the output based on current and voltage. You use the voltage reference to compare to and the duty cycle of the output is adjusted based on the feedback loop. The output circuit inductor holds a charge and the capacitor in the output side averages it far as I can understand. It uses a resistor in series with the output load to determine the current (the more current, the higher the drop across the resistor) and feeds it back into one error amplifier. As the voltage gets higher than reference, it decreases the duty cycle. The same thing happens with the voltage. You divide the voltage and feed it into the error amplifier. At the time the current gets too high, it starts decreasing the pulse width sent to the output transformer.
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Smaller words, crayons, construction paper. Explain it to us like we are five. Snacks would be good, and maybe then a nap.
In an SCR or Thyradron there's a cathode and anode like a diode but it has a gate (or grid in the case of the Thyratron) instead. You apply voltage in a forward way like a diode with no gate voltage and it doesn't do anything. When you go above a specific value on the gate or grid, it will conduct as a diode until the voltage falls to zero again.
The concept is commonly used in power supplies for computers among others. What is called a "crow bar" circuit. If you take a PC power supply and short it out, deep down there's an SCR that's triggering and causing the current fault protection to trigger. If you disconnect power and wait for the remainder of the capacitors to drain, it goes back working fine again.
RCA/burle 8988. Plate dissipation is 5kw should loaf at legal limit. Not even close to the biggest one I have.
Mono band or multi band? I want to build an mrf454 setup I saw in a 1985 arrl handbook. The HG mrf454s are supposed to be really efficient and really cool running. I have some parts and was tinkering with it but stopped and didn't get too far. I should breadboard out the bias circuit at least.
I wasn't overly serious, but if it can be done on a budget, just 160-10m. Don't think I need anything for 6m, it's just not that active most of the year. Even 10m is questionable, since I usually don't work that high on voice, just digital.
I like hearing on 40m and 20m, "Oh, I've just got a Delta Loop......... and 1.5kW". No wonder everyone in the northern hemisphere can hear you like you're shouting in my window.
Max power through a delta loop is bound to be a heck of a thing. From what I understand of loop antennas the capacitor in the middle has huge voltages across it potentially. As in you're talking stuff like vac variables to make it work.
https://www.powerstream.com/Wire_Size.htm
Throwing this chart here because I ordered primary and maybe secondary material for my project. An important concept to know about electricity is that the depth it travels on something is dependent on the frequency; For a given material, the higher the frequency the shallower it travels. Since my desired frequency is 40KHz, I looked decided on the thickness of 23AWG. Since I sized for 15A input, the wire is way too small. How do you fix this? You either use multiple strands of wire (called Litz Wire) or you use a piece of flat stock instead. I ordered copper strip, I'll end up having to insulate it but that's not a huge deal. masking tape will probably work for the first go, after that I'll get something a bit more formal.
I still need ferrite to put this on though. My initial project may be much simpler than I thought, which is to feed a hot plate through a fully isolated switch mode circuit. This gives me a chance to do things like calculate losses. I've also decided I need to pull apart one of my microwave oven power supplies and try to re-wind the secondary to a lower voltage, higher current winding and see if I can keep losses under control. I have resistors now so I need to make a resistor bank to load stuff up with, and figure out an easy way to make it adjustable.
Throwing this chart here because I ordered primary and maybe secondary material for my project. An important concept to know about electricity is that the depth it travels on something is dependent on the frequency; For a given material, the higher the frequency the shallower it travels. Since my desired frequency is 40KHz, I looked decided on the thickness of 23AWG. Since I sized for 15A input, the wire is way too small. How do you fix this? You either use multiple strands of wire (called Litz Wire) or you use a piece of flat stock instead. I ordered copper strip, I'll end up having to insulate it but that's not a huge deal. masking tape will probably work for the first go, after that I'll get something a bit more formal.
I still need ferrite to put this on though. My initial project may be much simpler than I thought, which is to feed a hot plate through a fully isolated switch mode circuit. This gives me a chance to do things like calculate losses. I've also decided I need to pull apart one of my microwave oven power supplies and try to re-wind the secondary to a lower voltage, higher current winding and see if I can keep losses under control. I have resistors now so I need to make a resistor bank to load stuff up with, and figure out an easy way to make it adjustable.
I am waiting on wire to show up for the secondary. I obviously printed the bobbins. The primary wire is litz wire which is a bunch of insulated strands that are made into one wire. The advantage is that at high frequency the shallower the electricity travels on a cable. This is 120 strands of .1mm wire which let's me pull 2.7A at about 1.75MHz. The wire for the secondary I got was 28ga which is a much more modest 175KHz for full depth based off the chart I have. (Still waiting on that to show up) The big down side of going higher in frequency is you don't get to use the full conductor if you run too high of frequency.
Besides that, if you look at the primary core it's got a center tap. The reason why is that in actuality only 1/2 of it is the secondary. This is what is called a forward converter. One half that coil will be used to magnetize the ferrite, and the other half will be used to de-magnetize it. This is done by having the coils turned opposing directions from each other, then having a diode coupled with it so that as the fields collapse they will act opposing one another.
Since the ferrite is mystery typed, we'll get to see what frequencies it responds to. I should probably put a chunk of litz wire on the secondary to test that out, just to be sure the wire isn't the limit. I am thinking this core is likely to be limited at 200KHz anyways, but I have no direct evidence on the material type which would be the determinant of that.
There's 3 windings there, 130V for bias, 700V for the HV and 300V for the lower voltage. In the end it will be about 300W, and I will probably use a commercial power supply for the filaments of the radio I intend to power with this. Input for this should be 170V (peak AC house voltage averaged out via good filtering) and objective is to keep duty cycle at about 40%. That means that we wind up with ratios as:
(700/170)/.4=~10.3:1
(300/170)/.4=~4.4:1
(130/170)/.4=~1.9:1
Multiplying each # times the primary turns gives the number of turns they should be. This transformer has 14 primary turns.
10.3*14=144.2T
4.4*14=61.6T
1.9*14=26.7T
I will probably go 15-20% over these numbers. It's easier for me to use the feedback loop of the controller to reduce the pulse width and in turn the output voltages than it is to rewind the core because the voltage is too low. I also need to calculate and build out inductors for the outputs as well. Just not quite there yet. That's important because it determines peak currents and ripple as well.
I stuck this coil on an IRF510 powered by 12V, after the signal generator was not generating a ton of power. This thing is LOUD at about 5KHz. Cranking the frequency up out of audible range, I get this. The load is 5400 ohms and this is the HV tap. I believe I went to about 160T on the secondary which is a ratio of about 11.4:1. I haven't measured the DC voltage of this power supply, but it may well be higher than 12V slightly. Something like 13.8V. The way that the voltage spikes up is interesting, I'm wondering if there's something about the characteristic of the ferrite. The other thing that immediately comes to mind is the IRF510's being saturated or something. I've got a few things to try here, but I need to figure out what transistor to use. I'm not sure that running this as a forward converter is going to work since the transistor has a built in diode already. This is the output of hte scope at 50V/division. Not bad for 12V.
This may seem like a silly pic to post, but it's progress. At 20V/division, that means I'm putting about .35W into a 5400 ohm load
I got it up to 55V at 21KHz, which is about .5W. Input voltage was 12V from a server PSU. I didn't get input current to measure efficiency with, which probably would have been a good idea. I also need to play with the duty cycle some, but haven't gotten there yet either. Quite frankly the setup I have arranged for the in and out circuits is extremely crude, so I want to go to a real controller instead of using my function generator which annoyingly varies the duty cycle as I vary the frequency. I'm also using an IRF510 FET as the driven transistor, and it absolutely will not do the voltage I designed this circuit for which is rectified 110VAC. I need to find another transistor to put into this. Research will be required to do that. I like the IGBTs I have but I think they won't work due to having a built in diode.
Today was a lot more mundane than my last stuff, and a lesson on why we replace capacitors. I ripped the orange ones out of my hp-13 heathkit power supply. They had an esr of anywhere from about .2 to 1 ohm. There are a couple of tiny ones that had an esr of 4 ohms by my meter.
This magnavox amplifier has caps with an esr of 11 ohms! Ewwwwno wonder it hummed. Going to replace then i will have a nice little 6v6 amp.
This magnavox amplifier has caps with an esr of 11 ohms! Ewwwwno wonder it hummed. Going to replace then i will have a nice little 6v6 amp.
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