I'm sketching up the basic circuit layout right now for you guys to examine.
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When you talk about a common-mode choke on the mains wiring coming into the welder, you're talking about basically a filter to keep the high-speed switching noise from radiating back into the breaker box and interfering with other electronics in the house correct? I have an off-the-shelf mains filter that is rated for 20A that I am going to use on the input for the HF/HV arc starter, but I can easily build a simple one for use on the input for the welder's circuitry. That other inverter welder schematic I posted(the one with the absurd layout) has a noise filter on it's mains wiring. I think he's using a bifilar wound toroid with a 470n/250VAC cap on both sides of it for his noise filter. Also the 20A filter I have has the schematic with component values in the manual for it so I could copy that filter's design and just wind a new toriod capable of handling the higher current.
Also, as for the current control and OCV limiter, I've figured out a way to completely isolate the output side of the switching transformer from the controller board. I'm going to use current transformers for both the primary-side current limiting and also for the output side current control. As for the OCV Limiter, I designed a VERY simple circuit that just triggers a PS2561 optocoupler(Is this one fast enough do you think?) which then triggers the Dead-Time Control pin of the TL494. Everything simulated fine in Multisim so I think it will all work. I'm working on the drawings right now so I will post up the schematics soon.
For the CTs I did some calculations and this is what I came up with, so let me know if I did this properly.
For the primary side current limiting I can use a 200:1 CT(This gives 250mA@50A), rectified, then driven into a 2Ω 2W resistor. That should give me a 0-500mV(0-50A) signal which I can then run through a simple op-amp with a gain of 10 to give me the 0-5V signal I desire.
For the output side current controller, I can use a 600:1 CT(This gives 500mA@300A), rectified then driven into a 1Ω 2W resistor. That should also give me a 0-500mV(0-300A) signal which I can do the same as above and amplify it to the 0-5V signal that I desire.
Since the CTs are both isolated from everything, once their signals are amplified by their respective op-amps, I should be able to run that 0-5V signal directly to the TL494 and handle them that way. To set the primary side current limit and to be able to control the output current, I won't be adjusting the signals from the CTs. Those signals will always be 0-5V signals. What I will be adjusting is the reference(compare to) voltage on the opposite pin of their respective ErrAmps in the TL494. For the primary current limit I can set it's compare voltage with a 25t trimmer for very precise control and for the output current control I can set its compare voltage with a POT to set the MAX current, a foot-pedal to adjust the amperage WHILE welding between 0 and MAX(set by the knob) and then I have also designed a simple current pulsing circuit which will pulse the compare voltage between 2 set points giving a very handy current pulsing feature to the welder.
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I got a question. In this schematic that I posted (
**broken link removed**) what is the purpose of the 6R8/2W resistor in series with the 4n7/1KV cap across the secondary side of the switching transformer? I'm pretty sure that the 4K7/3W resister across the output terminals is to keep a slight load on the output to keep the voltage from spiking extremely high. Is this correct? The welder I have in my garage has a 250R/100W/WW resistor in parallel with a 25R/50W/WW resistor that is in series with a 30uF/165VAC cap. The cap is pretty large about 6" tall, 2.5" wide, 1" thick and these 3 devices are placed across the output terminals of the welder. They are used as a dummy load from what I was to understand to keep the OCV voltage down to 100V. If you unhook them the OCV jumps to ~150V. This is a transformer based welder though, not an inverter.
Anyways. Here is the layout schematic for my current and voltage sensing isolation circuits. I think they should keep the output side of the switching transformer completely isolated from the logic devices and still provide me with plenty of control over the current and OCV voltage.
View attachment Isolation Circuits.pdf