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Registered Member #2845
Joined: Mon May 03 2010, 06:40AM
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Posts: 12
Update from something awhile ago:
A few months ago, I and someone else were both having trouble with coils that were working, but not that great. Well, I found my trouble, so figured i'd share incase anyone else has the same problem! I was glad I have the luxury of having three of the same units to swap parts between, which made isolating the problem easier. It turns out I had a diode (CR1) backwards in the current feedback area. So the circuit must have been seeing only half of the feedback and only working half the time! Probably wasn't too good for the IGBTs, but it did run for hours straight at a few shows before quitting!
Edit: and also a question: Does anyone know where to get the 5X20 mm fuse size that fits in the power sockets recommended in the kit instructions? I can't seem to find high enough amperage ones, and I've had such headaches with those that I've taken to bypassing them and using the variac fuse only.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
raysf wrote ...
Update from something awhile ago:
A few months ago, I and someone else were both having trouble with coils that were working, but not that great. Well, I found my trouble, so figured i'd share incase anyone else has the same problem! I was glad I have the luxury of having three of the same units to swap parts between, which made isolating the problem easier. It turns out I had a diode (CR1) backwards in the current feedback area. So the circuit must have been seeing only half of the feedback and only working half the time! Probably wasn't too good for the IGBTs, but it did run for hours straight at a few shows before quitting!
Edit: and also a question: Does anyone know where to get the 5X20 mm fuse size that fits in the power sockets recommended in the kit instructions? I can't seem to find high enough amperage ones, and I've had such headaches with those that I've taken to bypassing them and using the variac fuse only.
Great questions. The 5x20mm fuses are standard and should be available at most electronics distributors. I've gotten mine from Digikey, Newark, Allied. I usually use 15A, but have 20A as well.
But during testing, I think i've bypassed mine as well as just use the fuse in the variac which is rated for 20A.
But glad to hear everything is working good for you!
Registered Member #2845
Joined: Mon May 03 2010, 06:40AM
Location:
Posts: 12
Will check Newark-I had no luck at Mouser or Allied. I ordered some "25A" fuses at Mouser, but it turns out they goofed and they were actually 2.5A! And the coils are 12 feet up when installed in the sculpture and the fuses take ninja hands to reach in and change, so blowing all 3 at once didn't make me too happy! Luckily, somebody had a burrito, so I wrapped them in aluminum foil and no fuse troubles after that!
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
raysf wrote ...
Will check Newark-I had no luck at Mouser or Allied. I ordered some "25A" fuses at Mouser, but it turns out they goofed and they were actually 2.5A! And the coils are 12 feet up when installed in the sculpture and the fuses take ninja hands to reach in and change, so blowing all 3 at once didn't make me too happy! Luckily, somebody had a burrito, so I wrapped them in aluminum foil and no fuse troubles after that!
Registered Member #3093
Joined: Mon Aug 09 2010, 11:40PM
Location:
Posts: 68
I got my coil working! http://www.youtube.com/watch?v=7GRHkAaQC6A , but I had forgot to check the current limit. (my display sorta broke on my faulty soldering) So, I fixed that to 300 amps limit, and now the coil won't work any more. I investigated the cause, but I have only found out that the 5 volt regulator is getting hot and the d flip-flop is working, but running hot. Anyone have any Idea as to the problem? Everything seems to be working up until the input of the gate drivers.
Registered Member #1848
Joined: Sat Dec 06 2008, 03:24AM
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Posts: 15
I'm just about finished with the final wiring in my minibrute and have come across a question. I'm looking at the relay k!21 in Fig 2-7 of Dan's book. one side of the relay is being used ot switch in R123 as a safety bleeder. Here's where I'm confused,.
1) looks like C121 and C122 already have pretty good bleeders in R121 and R122.... That looks like a time constant of about 12 seconds.. is R123 really necessary ?
2) If so, I was planning on using short thick 8 gauge wired to connect C121 and C122 to the half-bridge.. Both side of K121:C are labeled 'DC_Supply+' do I
(a) wire the non-switched side (ie. the left) to the half bridge and just switch the bleeder in and out with K121... or
(b) am I supposed to wire K121:C in series with that connection. (I.e. wire from the plus end of C121 to the center pole on one side of K121, then wire the Normally open contact of that same contact pair in K121 to the half-bridge ? . It seems like a lot of current to stick through that tiny relay..
Any guidance much appreciated.
Also.. I just want to confirm.. the schematic on fig 2-8 shows the current sense in the secondary. I believe this is a throwback to when Dan was doing secondary current sensing.. I'm supposed to put the sense in the grounded side of the primary.. Right ?
Once get this figured out, I'm ready to begin testing.. Wish me luck ! -jc
Registered Member #1848
Joined: Sat Dec 06 2008, 03:24AM
Location:
Posts: 15
johncohn wrote ...
Folks..
Never got a response on this.. Anyone got a comment on mesh vs copper foil / Thanks !
I'm working through a minibrute build and have a couple of questions. Hopefully Dan or others can comment: - I'm fashioning the screen for the self-resonator board .. The book calls out using copper foil as the shield. Can I use copper screen instead ? Is this for electrostatic or magnetic shielding. - what do folks suggest I use for a clamp to use for tuning the primary ? Do people use an alligator clamp of some sort ? - is it really necessary to bring the top of the primary down through the base ? I have done so.. but the bends in the Cu tubing are not that beautiful. Would I be electrically OK to cut the Cu at the top of the primary ? Thanks ! -jc
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
GORT wrote ...
Regarding the fan on the film caps... Honestly, caps are not designed for heat dissipation via air flow. Blowing on them doesn't really accomplish much due to the fact that heat dissipation within the cap is not going to be affected by airflow on the outer shell.. sorry, that's just physics... design for the rms (always best practice).
Hi Gort. Actually, that is not a true statement. Forced air cooling works extremely well for these types of capacitors. It is done all the time even in well designed military applications such as pulse power supplies. Anything you can do to remove heat from the surface of the capacitor, whether its forced air cooling, direct interface (through thermal interface material) with a cold plate, etc... will allow the internal structure of the capacitor to run at a cooler operational temperature.
Also, simply designing a capacitor to meet an RMS spec doesn't necessarily mean you are operating the capacitor within its proper operational envelope. For example, the 942C 0.15uF capacitor has an IRMS spec of about 13A at 70degC. If the capacitor is operating above 70degC, you would need to derate accordingly, or if its operating at less than 70degC, the IRMS maximum current actually increases. Most capacitor vendors, including CDE, can provide you with test data and specification curves for their capacitors on request.
Registered Member #3528
Joined: Sun Dec 19 2010, 12:44AM
Location:
Posts: 14
Hello everyone. I'm an Electrical Engineering Technology student of Canada here. I'm Building the miniBrute and hoping to take a crack at designing an audio-modulation circuit for it as a technical report project in order to graduate. This is my very first Tesla coil build, so there's been lots of learning.
I'd like to thank Dan for all you've done and everything you've made available, it's greatly appreciated. This site was also very helpful. There's only a couple questions I have before completing the build:
1) In the addendum it states that the thermal sensor (LM35) is no longer suggested. What is the reasoning behind that?
2) Also, concerning the caps on the PVC pipe for the secondary support, the CAD drawings show them to have a diameter of 4.5" which would put them resting on the pipe. However, the picture diagrams all show the caps to be inserted inside the pipe. I'm figuring that the extra 1/4" added to the secondary support would make a big difference in it's position in relation to the primary. I'm not sure which way to go with that, to put them on the outside or inside the PVC pipe.
If anybody could clear those things up for me, it would be greatly appreciated.
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