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Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14
Thanks for the reply Dan,
I believe I'll end up having to tune it, as My torroid isn't quite to spec. Besides the torroid I believe everything else is bang on the money. I'm actually at a standstill right now. I'm trying to track down the fuses I need locally, I figured they would be standard physical dimensions, but apparently not. I think I may end up having to order some online.
Once, I get the fuses I'll start testing, and if the results are good enough to present the project, I won't bother about fine tuning until after I'm out of school.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
BryanD,
The fuses are standard 5x20mm. BTW, if you are using an external variac with a built in fuse, you can simply short out the fuse connection on the power outlet cord. Or you could use an external fuse using a standard BUSS fuse. I think most people just short out the built-in outlet fuse and use an external fuse. Just make sure you use a fuse.
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14
Well turns out nowhere in town carries them. I'll have to be ordering them online I suppose. Yet another shipping fee :P Thanks for the advice about the variac fuse. Since I'm ordering fuses, I'll order a dew the proper dimension for it, however I'll keep that in mind if I end up blowing a few.
While we're on the business of fuses. There's a fuse on the variac (20 A) and a fuse just down the line on the input of the coil (20A). Should I synchronize them at all, meaning make one slightly larger, one with longer inverse-time characteristics, or it doesn't matter.
BTW I'm using a variac rated for 10A with a 20A fuse in it, aas this seems to be common practice to save a few pennies. However, it should be only used in short intervals. What is considered short intervals? Guess it depends on the specific variac eh?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
BryanD wrote ...
Well turns out nowhere in town carries them. I'll have to be ordering them online I suppose. Yet another shipping fee :P Thanks for the advice about the variac fuse. Since I'm ordering fuses, I'll order a dew the proper dimension for it, however I'll keep that in mind if I end up blowing a few.
While we're on the business of fuses. There's a fuse on the variac (20 A) and a fuse just down the line on the input of the coil (20A). Should I synchronize them at all, meaning make one slightly larger, one with longer inverse-time characteristics, or it doesn't matter.
BTW I'm using a variac rated for 10A with a 20A fuse in it, aas this seems to be common practice to save a few pennies. However, it should be only used in short intervals. What is considered short intervals? Guess it depends on the specific variac eh?
BryanD, Just contact me via my website email and let me know what you need. I'll send you some new fuses out free of charge. Not sure if i have 20A, but i definitely have 15A in stock - at least i think i do.
But if you're using a variac with a fuse in it, you should be fine. Just make sure the control 3A fuse is in place. Also, running a 10A variac at 20A is okay. Just keep in mind that if you do have a short circuit event, you may get some "pitting" in the variac core as peak current could get pretty high until the fuse blows.
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14
So I got the fuses, thanks Dan. I started testing, but ran into a little problem, or I guess more of a misunderstand. When I checked the voltages coming off the low voltage transformer LP-575 I got 12V on either lead in reference to ground, but 24V from lead to lead. Is this right? If so, once I connect it to the driver board I get double the voltages I'm supposed to get everywhere. I'm wondering if I wired the xformer wrong or something.
I tried connecting the primary in series rather than parallel to get half the voltage on the secondary, thinking I'd get the right voltage levels on driver. Instead I got the same voltage levels as when I was applying 12V.
No matter what I seem to do I'm always getting about 36 V on pin 1 of LM7805 and LM7815 which is above the maximum rating for their input.
I attached a drawing of how I got the xformer wired. Can somebody clue me in on what's happening here please.
EDIT: Wow, I really wish I could delete this post, but since I can't I guess I'll explain what I did in case someone else does the same thing :P I was using my bench meter rather than my meter I typically use which auto differentiates between AC/DC. I checked the voltage level off the xformer which is AC, but then forgot to switch my meter to DC when measuring on the board after the diodes. The reading I was getting was the metering error, which worked out to be 2.2 times larger.
I woke up this morning and with a fresh head rechecked the voltages and everything was fine. I was baffled for a while, untill I realised what I must have done.
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14
I hope this isn't considered a double post, since it's a different topic. I made a bit of progress today on testing, however once I came to check the signal coming from E1 & E2 I got stuck. I had no idea how to take a differential measurement, so I researched it. What I came up with was, I needed to take the two probes and attach one to E1 and the other to E2 without connecting the grounds to anything. I then need to set the scope to add and invert CH2. So that's what I did. I got the driver board completely isolated, the only thing connected is the power, 5V to the ext Mod, and 100kHZ to the current FB. What I'm getting is this funny wave.
I hope it's not something like my last problem. I know I'm asking for lots of help, but please remember that I am a student after all and have no real experience :P
EDIT: So I get the proper input to U4 & U5, however I keep getting that on the on the outputs or E! & E2 rather. I'm wondering, could the ICs be fried, or am I just taking the reading wrong?
Registered Member #3263
Joined: Sat Oct 02 2010, 04:43AM
Location: Sydney, Australia
Posts: 34
The MiniBrute secondary is specified as 12" winding length, 1140 turns (=95TPI)
using AWG30, single build insulation (0.01009), javaTC is reckoning only 1017 turns @84.75 TPI. Simple math would suggest 1189 turns are possible in 12" so obviously some factor is being included to account for imperfect winding.
What are the turn counts and winding lengths you guys have actually built? Both seem to effect Fres.
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
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Posts: 14
Hello Ruben,
Since your not getting a definite answer, I'll tell you what I did :P Now mine isn't up and running yet, so no idea on performance. However, I just wrapped it at exactly 12".
Registered Member #1848
Joined: Sat Dec 06 2008, 03:24AM
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Posts: 15
Good news / Bad news... First the good news.. I got my minibrute all tuned and boxed in the other day... With current limit set to 400A I was able to get a good hot 26-30" spark.. It was beautiful.. (see low quality attached vid)
Now the bad news.. I say was because it failed the very first time I took the coil out of my lab to show folks at work.. . I set the thing up in my office and arraigned for a nice unplugged wall lamp with a ground as a target.. The thing worked fine for a few multi-second bursts.. then on one of the strikes to the lamp I hear a loud pop and the thing went dead.... . So much for first public demo. All I can assume is that the arc jumped form the lamp back to the primary.. . though I never saw it.
I took the coil home and pulled it apart and found both IGBT's were shorted between gate, emitter and collector (grrrrr) and the 20A fuse in the bridge supply plug was blown. .. I plugged in the control supply and turned on the advanced modulator and noticed that I could not hear the self resonator board buzzing the pulse transformer. So.. I replaced the IGBT's with spares I'd ordered just in case. I also spot checked all the components on the bridge port with a DVM.. everything seems OK. I put on the control supply and the modulator and was pleased to hear the resonator buzzing. I cautiously turned on the HV supply and slowly began turning up the voltage. I noticed at low setting that the florescent tube in the room started glowing... a little more juice and I stared to hear a corona at the breakout point.. but.. as I turned the variac up to 40% I still got no appreciable breakout, even though I noticed the LED ammeter registering about 200A. Before the thing failed 40 % would have generated a lout, hot 25" spark...
So.. I'm a bit stumped.. the bridge seems fine.. the pulse transformer is buzzing merrily, but no good spark. One clue is that I put a scope on both IGBT's gate and saw a pulse train, but I measure nothing on the emitter of either device. Is it possible that I fried one of the U4/U5 gate drivers ? I originally thought not since I could hear the resonator board buzzing the transformer.. Any clues ?!? One other question I have since I'm at it.. When the coil was working well, I noticed it was very sensitive to where I placed the advanced modulator.. and where my hands were in relation to it. For example.. just reaching my hand down to change the modulator frequency would cause the coil output to drop almost to nothing.. I'd turn the pot... then withdraw my hand.. as soon as my hand was clear the thing coil would go back to full output.. I noticed the same thing when I tried to do the demo in my office before the coil failed. Does anyone know why the output would be so sensitive to my hands proximity to the modulator ? Is there anything I can do to make this more robust ?
Thanks for any feedback ! -jc
Here's a lousy cellphone recording of a recent test ]tesla2.wmv[/file]
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
Location:
Posts: 14
Hello guys,
Sorry to hear that Johncohn, wish I could help you out there.
I'm about to ask one of those simple questions again. I'm having an issue with my DC power supply. I have everything the same as the diagrams, the only difference is that I'm using a bridge rectifier rather than CR121 and CR122. No matter what I try the circuit is not amplifying the voltage. Whatever comes out of the rectifier is what I get off the output of the Dc supply. I'm using the same values as in the schematics (2800uF caps and 6k resistors), I also have them connected the same as in the schematics. I don't understand what's going wrong here.
I tried simulating it using a Multisims type program, but got no results.
I have one week left before I need to have it complete it. I was hoping to have it audio modulated, but since time won't allow for that, I was hoping to at least have a working coil to present. Any help would be greatly appreciated.
EDIT: I included a picture showing how I wired it, and how I'm testing it in case that helps
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