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Old 13th March 2013, 09:55 PM   #71
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I think I will probably use copper tape, it's not very humid here in the UK
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Old 14th March 2013, 01:28 AM   #72
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Quote:
Originally Posted by portreathbeach View Post
I think I will probably use copper tape, it's not very humid here in the UK
The white PVA glue used as a binder in some DIY diaphragm coatings has an affinity for water, which I think would facilitate (and accelerate) corrosion of the copper foil charge ring. My first panels used a non-PVA coating (not Licron), and when I dismantled one after two years, I saw very little oxidation and no actual corrosion on the charge ring. My latest panels, which use Licron Crystal on the diaphragms, have been playing for three years now with no problems. Since you will be experimenting before making your full-up panels anyway, rather than placing the charge ring on the opposite stator as shown on my blog, I suggest you purchase the type copper foil that has a conductive adhesive, and then place the foil directly onto the diaphragm, adhesive side contacting the Licron coating. I think this would provide a more intimate contact less prone to coronal erosion of the Licron, and any oxidation would likely be limited to the bare opposite side of the foil. I haven't tried this myself, but I will if I ever have to rebuild my current panels.
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Old 14th March 2013, 02:08 AM   #73
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What is "charge migration" and how would I know if I have it or not? The mylar diaphragms in my Lucas ESLs are graphite coated ( I made them in the 20th century) and they seem to sound OK, or don't they?
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Old 14th March 2013, 06:59 AM   #74
Calvin is offline Calvin  Germany
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Hi,

Just another word about safety. In no. 67 you wrote that You told Your wife about the functioning of th panel and safety due to low currents. This is true as long as there's no insulation breakdown. In case of playing music and touching a faulty stator one may get shocked. The amplifier driving the Stat may push serious amounts of power through the transformer.
The impedances on the HV side may be low enough to allow for possibly lethal high currents!
If you want an optically open system, I'd suggest to build a wire stator, especially if You have not extensive experience with coating metal sheets.
Accepting a small minor in optics and acoustics, I'd suggest to build a optically closed system in which the stator is either covered by a thick layer of acoustic foam, or shielded behind PE grounded metal sheets. I'D also cover the whole front and backside with acoustic cloth to optically hide that there are holes in the metal sheet where the enterprising baby may poke through.
We want the baby to grow up and enjoy Barbecues not becoming Babycue.

Jauu
Calvin
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Old 14th March 2013, 09:05 AM   #75
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Yes, this is very true and since this are basically huge capacitors one should never ever touch either/or both stators at the same time while they are playing becuase they will/do conduct when AC voltages are present.

Especially at the higher frequency's.

As for an example a typical panel of 12" X 48" with a D/S .0625" will present a capacitance of at least .001uf with reactance of about 8000 ohms at 20Khz.
Let us consider an ideal transformer at 1:100 step up ratio and with a 10Vrms input we get 1000Vrms output.

At 1000Vrms/8000 ohms =.125 amps of ac current and 1000*1000/8000=125 watts of power.

Providing your amp has the power maintain 20Vrms input to the transformer this would mean .250 amps of AC current and 500 watts of power.

At this level it would be very loud and you would be hard pressed to get close enough to the panel to even touch it.
But, if you could,DON'T DO IT !!!!!

When I burned up my last wire mesh panel I had an amp capable of maintaining this type of voltage and more at a full 625 watts at the least.
I was also using a 1:256 setup up ratio and when the coating failed it formed a solid continuous arc.

The current that was flowing through the now short circuited panel was high enough to turn the aluminium wire bright orange and cherry red in about a .75" diameter spot.
I left it to run like this for about a good minute before I decided shut it down.

It is because of these much higher currents at high frequency's is when you will find your weakest points in the stator coating.
Remember, Your Impedance gets lower as the frequency goes up!
And because there is more current available to over come the resistance of the coating and heat it up.
Simple Ohms Law here and nothing special.

Yes, I have been nailed by the the voltages coming out of the transformer using only a 100 watt amp and it is not for the ill fated.

They do pack a serious Walup!!!!

Just the same as you should never mess around with the speaker leads coming out of a 150watt and bigger amplifier while it is playing.
There is a potential of over 100V p-p coming out of the thing!!!

The last time I got nailed was with the full 13.6KV output of my HV supply and I can a test to you that I wouldn't be sitting here telling you this story had I not kept one hand in my pocket while I was working with them at such levels.

I'm very serious about this and I am not joking here!!!

Although I am working with voltages 2 to 3 times more that what is necessary to make them work, THE SAME RULES APPLY!!!

FWIW

jer

Last edited by geraldfryjr; 14th March 2013 at 09:13 AM.
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Old 14th March 2013, 11:43 AM   #76
Bazukaz is offline Bazukaz  Lithuania
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Quote:
Originally Posted by Calvin View Post
Hi,

Just another word about safety. In no. 67 you wrote that You told Your wife about the functioning of th panel and safety due to low currents. This is true as long as there's no insulation breakdown. In case of playing music and touching a faulty stator one may get shocked. The amplifier driving the Stat may push serious amounts of power through the transformer.
The impedances on the HV side may be low enough to allow for possibly lethal high currents!
If you want an optically open system, I'd suggest to build a wire stator, especially if You have not extensive experience with coating metal sheets.
Accepting a small minor in optics and acoustics, I'd suggest to build a optically closed system in which the stator is either covered by a thick layer of acoustic foam, or shielded behind PE grounded metal sheets. I'D also cover the whole front and backside with acoustic cloth to optically hide that there are holes in the metal sheet where the enterprising baby may poke through.
We want the baby to grow up and enjoy Barbecues not becoming Babycue.

Jauu
Calvin
Hi,

One could also build stator from three metal sheets(1-2-3), two of them(1-2) used for driving the membrane and one placed on the back as a shield.
Front and back sheets are connected together and grounded.This way the system is quite safe to touch from both sides. A step further is to add an additional diaphragm between 2-3 and use two bias supplies with reverse polarities(two-membrane sandwich).
I fully agree about wire stators for safety reasons. If the wire is of good quality the insulation is quite robust and will need a sharp knife with some force to be damaged. One of my old panels has had received impacts that caused wires to bend considerably and elongate, but the insulation was intact.
One can cover wire stators with a thin, partially transparent synthetic cloth.
1) Adds up in dampening the fundamental resonance
2) No need to make construction optimized for optics
3) Acts like a dust cover


Lukas.
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Old 14th March 2013, 07:51 PM   #77
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Quote:
Originally Posted by geraldfryjr View Post
Yes, this is very true and since this are basically huge capacitors one should never ever touch either/or both stators at the same time while they are playing becuase they will/do conduct when AC voltages are present.
Just to be clear, the potentially dangerous high voltages Calvin mentioned are present on the secondary side of the step-up transformer. The current is limited only be the current capability of the amplifier and the impedance of the transformer windings or any impedance put in series with the transformer primary or secondary.

It has nothing to do with the ESL panel being a large capacitor. The potential danger from the voltage on the secondary is the same no matter what the size of the ESL or even if the stators are hooked up. Granted, stators are easily accessed by anybody in the household where as the secondary connections would hopefully be safely covered in a case.

Another take-away from this is that no matter how well insulated your stators, always be careful poking around your ESL step-up transformer wiring if an amplifier is hooked up and music is playing.
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Old 14th March 2013, 08:14 PM   #78
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Yes, I meant physically huge meaning that you can lay your hand on them and this is enough surface area for the AC high voltage to conduct to your hand and through your body if you were to grab the other side while they are playing.

I know this is true because Mavric told me he did this once, After I told him not too!!!! Ahhh,ha,ha,ha

The times I got nailed was from accidently touching a bare wire connection.
Also a wire that had a rather thin insulation covering on it.
And in the one case coming too close to the bias feed as it was charged to 12Kv.

Sorry for the confusion!!

jer

Last edited by geraldfryjr; 14th March 2013 at 08:38 PM.
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Old 14th March 2013, 09:04 PM   #79
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I get your point, and I will definitely be careful when building and experimenting. I am aware of high voltages as I am a SAP (Senior Authorised Person) on our 11KV networks at our larger sites at work. These systems are not to be messed with, 11KV ring main systems with the capability of carrying 200-300 amps!

I like the idea of using extra mesh on the front and back which are grounded, very good idea. I suppose mesh could be used with a much larger open area so as not to disturb the response too much.
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Old 14th March 2013, 09:54 PM   #80
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Quote:
Originally Posted by portreathbeach View Post
I get your point, and I will definitely be careful when building and experimenting. I am aware of high voltages as I am a SAP (Senior Authorised Person) on our 11KV networks at our larger sites at work. These systems are not to be messed with, 11KV ring main systems with the capability of carrying 200-300 amps!
Sorry, I understood from checking out your other projects that you are not a newcomer to electronics.
Clarification was mainly for others who might read this thread at a later date and don't have your background.

Quote:
I like the idea of using extra mesh on the front and back which are grounded, very good idea. I suppose mesh could be used with a much larger open area so as not to disturb the response too much.
This is an excellent solution.
Attached pic shows high % open area mesh used as grounded safety shields on some models of King Sound ESLs.


Concerning HV bias contact corrsion:
Back when I was building stacks of test panels and Licron didn't exist, I come up with the following solution. I applied coating to the diaphragm leaving a 1/8" border inside the spacers. Copper tape was run around the panel in the middle of the spacers. Patches of Dag graphite were painted on to join the copper contact strip and coating.

This minimized leakage currents across spacers in humid conditions and avoided any possibility of corrosion. One of my favorite coatings at the time was Ivory dishwashing liquid soap thinned 1:3 with water and air-brushed on. Even that has shown no corrosion tendencies with the graphite after 15+ years.
Attached Images
File Type: gif Safety_Mesh.gif (135.0 KB, 91 views)
File Type: gif Contact.gif (20.6 KB, 90 views)
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