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Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
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Posts: 16
Thanks for the responses!
So I had another learning experience........ I didn't leave the scope probe floating when looking at the gates of my transistors, which blew traces off of my gate circuit boards. So currently the coil is out of commission. Hopefully I can get it working next week again though......
To measure the primary current I have EVRs current monitor board hooked through a 12 ft BNC cable to my scope. I'm getting about 200 amps peak. It is very difficult to get a stable trigger with my scope, I need a faster one..... Well anyways I have not been able to adjust phase lead because of the above problem. Here is my primary current waveform, I honestly am not entirely sure about what I'm looking at, but it doesn't seem normal....
So I had another learning experience........ I didn't leave the scope probe floating when looking at the gates of my transistors, which blew traces off of my gate circuit boards. So currently the coil is out of commission. Hopefully I can get it working next week again though......
To measure the primary current I have EVRs current monitor board hooked through a 12 ft BNC cable to my scope. I'm getting about 200 amps peak. It is very difficult to get a stable trigger with my scope, I need a faster one..... Well anyways I have not been able to adjust phase lead because of the above problem. Here is my primary current waveform, I honestly am not entirely sure about what I'm looking at, but it doesn't seem normal....
Did you forget to attach the waveform (also what burden resistor did you use for the CT)? I'm not sure why it would be difficult to get a trigger off the waveform, but you can instead trigger off a separate input such as from the gates or the inverter output. You'll need to scope that for phase lead adjustment anyway. The primary current should look like a growing sinusoid which decreases after cut-off. Here's an example of the primary current overlaid with the bridge output: . For taking measurements, it is best to isolate your entire inverter power circuit with an isolation transformer. A good investment to get one in my opinion :)
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
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Posts: 16
Picture didn't attach for some reason...... I'll try it again.
I'm not sure about a burden resistor for my CTs, but my GDT's are 10 ohms.
This measurement is with the secondary in place making 8" sparks. It looks like it rings up a bit, rings down, then back up again.... Doesn't look like other waveforms I've seen.
About the isolation transformer, sounds like a good idea but my funds are very limited (high school student) so it sounds like eBay for me... What should I look for?
Stancor isolation transformers are great, but you can also get a huge variety of other brands such as cheap isolation transformers from amazon as well. What other parameters are you currently running the coil at, such as bus voltage etc? Have you done any tuning with the primary coil? I find that usually tuning the primary such that it is the same as the secondary with a long wire on it (so that it's about 10-20% lower than the secondary depending on your coil) is usually a good place to begin setting the primary tap at, before fine tuning. It looks like your coil is exciting both pole frequencies resulting in the beating envelope (I suppose you have set both pri and sec to the same frequency?), or just out of tune, but I might be wrong! Would like to hear the opinion of others as well. Also 10R is probably too large a gate resistance. See my drsstc 3 page linked previously on how to select a good gate resistor. I found 5.1R to be generally good for CM300s.
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16
Thanks for the info on the isolation transformers!
For the bridge power I'm using a 140v variac through a rectifier. I've planned to double that eventually...
I did a little tuning with the primary, but probably not sufficient. Your tuning method sounds much better to start with... I'll replace the resistors and see if that improves things...
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
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Posts: 16
I have replaced the gate board that I fried and wound a new gate drive transformer (some of the wire had burnt...)
New GDT has 14 turns of CAT5 cable and still 10 ohms of burden resistance. I haven't gotten around to replacing those yet....
When I went to test the phasing with no power to the bridge and a function generator as feedback, I found that my UD 2.5 was putting out some sort of weird square wave.
I was wondering if anyone had ever seen this on theirs or had any pointers on troubleshooting the board and where to look... Im fairly new to troubleshooting.......
Is this the output of the gdt secondary? If so it looks like you have a core which is not suitable, such as powdered iron. You'll need a proper ferrite core.
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
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Posts: 16
That's what I thought too, but I found that odd because I got that core from EVR, so I scoped the output of the UD. That is the waveform on the GDT pins with the GDT connected.
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