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Question regarding close proximity of PCB board to Primary Coil (DRSSTC)

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LAN_403

HV Enthusiast

Sun May 07 2006, 11:08PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Here is an interesting problem I am currently facing with one of my projects. Basically, i have a tesla coil with 6 primary polycarbonate supports which will be illuminated via LEDs (from underneath the base as shown in the attached image)

Now, i would ideally like to use a PCB board to mount the LEDs and this PCB board would then screw directly underneath the base where the LEDs would protrude through the base and up into the bottom of the primary supports. This keeps everything nice, neat, and compaq with out having six million wires all over the place.

However, the problem is that i am not quite sure how the board would act in close proximity with the primary coil which is only about 2-3 inches above this PCB board.

Option 2 and 3 both seem to be the worse of the group since they will couple with the primary like a shorted or partial turn, respectively.

Option 1 seems like a possible alternative, but i'm not sure how that would work. And Option 4 with the flying leads may be the only feasible option.

Anyways, what are your thoughts on Option 1?

Any other thoughts or ideas you may have???

Again, my concern isn't how the PCB board would affect performance of the coil but rather it is the concern of induced noise onto the PCB board which would screw up the control voltage powering the LEDs.

Thanks!!

Dan

ragnar

Mon May 08 2006, 12:56AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

I'd be under the impression flyleads are the worst thing you could do and might result in some exploding LEDs =P

But in any case with Option1 (which can't have too bad a voltage gradient across the board), how are you going to shield the leads from the board itself? STP?

Instead of the large disc/plane each side for the LEDs, how about something like this:
(pic attached)
1147050222 63 FT1630 Evrleds2

quasi-star formation for anode/cathode both sides, then e.g. shielded-twisted pair back to your power supply for each "flower"..?

I guess with Option1, the compromise between voltage-gradient-on-PCB and induction/efficiency effects on the coil depends on the size of your star...

More circular plane in the middle and less tracks is a greater load on the primary... but induced currents wont flow so easily in longer spindly tracks, but then again, since these are higher impedance do they form an aerial and overvolt the LEDs...

Suck it and see, I guess. ^^

Flyleads could be done with about the same hassle as your filled-in disc board... use an 8-pin DIN with some shielded cable to connect to the board, and hope those few centimetres of tracks don't pick up too many volts...

Hazmatt_(The Underdog)

Mon May 08 2006, 02:01AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Option 5: Let the RF power the LED. This will require some experimentation, but the strong field im sure would do it. Just use the shorted turn concept and a voltage divider, whichever you like, capacitor/resistor or resistor/resistor.

=P

Steve Ward

Mon May 08 2006, 05:30AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I think id actually vote for option 3, because you dont have as big of a loop area. Or, why not just make the PCB mostly non-copper, and run power and ground in close proximity, and not in a full loop. It would offer the neatness of a PCB, and the actual loop area (assuming your power and ground do not complete a full "turn") should be very low, so id expect only common mode noise (which is easy to filter). Twisted wire pairs is probably even better i would think. I dont think 12 wires is *too* bad, since you can tie them all together remotely and just run a pair back to the power supply.

Marko

Mon May 08 2006, 09:13AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Option 5: Let the RF power the LED. This will require some experimentation, but the strong field im sure would do it. Just use the shorted turn concept and a voltage divider, whichever you like, capacitor/resistor or resistor/resistor.

Simplest would be just ot series all the LED's in the circle (that can be the board) put some fast diodes backwards (for protection and AC conduction) and then limit the current using a small capacitor (high brightness (blue) LED's usually need current in microamp range to start glowing, and few mA for a full shine. You'l have to choose the cap by the frequency of the coil.

Only problem I see is that leds will 'flash' if you lower the modulator frequency under ~24Hz (ever)

That can be solved using diode bridge and rectifying cap, so it makes a little more mess.

HV Enthusiast

Mon May 08 2006, 11:54AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Thanks for all the comments guys! After much thought, i have decided to go with option 3 and will power from a small aux. transformer from the 120VAC side. This way, i can isolate and filter from my 5V or 15V control electronics. So i'll run a half-semicircle, with outgoing and returns directly on top of each other (tightly coupled) and provide some good common mode filtering.

Thanks much!

Dan

Marko

Mon May 08 2006, 12:04PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I would also like to see if '5' is feasible.

I once got arcing between too-close ends of strikerail so I presume you have more than enough voltage there for LED fun. YOu actually need to limit the current not to blow them up.

Good luck with anythyng you choose

GimpyJoe

Mon May 08 2006, 02:46PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

You could just put neon bulbs in there, or glue small ccfl tubes along the bottoms of the primary supports. Either way you wouldn't need to power them.

HV Enthusiast

Mon May 08 2006, 03:30PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

thanks again for the additional comments.

After much consideration, my final proposed solution will be the following . . .

LED power will be tapped from the primary using a small current transformer. This will then power the LEDs and possibly also a resevoir capacitor
so the LEDs remained lit even after power is decreased or turned off. Simulations look promising, so i'll build up a prototype and give it a whirl. Then i will proceed to wire this up as in option 3.

Thanks again!
dan

Steve Ward

Mon May 08 2006, 04:40PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I think that would give a really cool effect as you increase the power, the primary glows brighter and brighter

. Might be difficult to get linearity with the setup, but maybe there are some tricks you could use.

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