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Re: [TCML] Secondary Coil Form
I suppose there always is some risk of obtaining PVC with conductive trash in it, since the industry specs don't require pristinely pure materials for the intended application. However, It seems from the collective data from fellow coilers that the actual level of risk of electrical failure is quite small and manageable. I, for one, have never had any issue with the PVC piping material that I have used in all of my TC forms over about 20 years of actual coiling. As a matter of fact, until I "knew better", I never even bothered cleaning off the printed lettering from the surface of the pipe before winding it. I am currently using gray 12" PVC duct pipe (thinner walls than sch. 40) for the sec. form of my Green Monster coil and it's been performing *pretty much flawlessly for about 8 years now. (I did have one flashover that damaged it and caused me to have to facilitate repairs, but I attributed this more to not wiping down its surface from dust or possible moisture after it sitting idle for months than to any conductive impurities in the PVC material.) I noticed that Ed Wingate would wipe down the extra coil of his huge maggie before firing her off and I've since employed a "pre-fire" wipe down as normal setup for firing off my coil now. So far, I've had no more secondary failure since doing this.
David
Sent from my iPhone
On Sep 13, 2012, at 7:44 AM, Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:
> On 9/12/12 6:24 PM, mddeming@xxxxxxx wrote:
>>
>> It comes down to this:
>>
>> White pipe -- always OK
>> Grey pipe -- usually OK
>> Black pipe -- Occasionally OK
>>
>
>
> Leaving aside green pipe (SDR, used for sewers and such) and the pinkish stuff that has UV inhibitor used for landscape watering.
>
> White pipe is NOT always OK. It is white on the surface,but might be grungy and full of particles under the surface. I learned this when turning a piece of white PVC down on a lathe to cut threads in it.
>
> Grey pipe (as in electrical conduit) has, by specification, some electrical properties at DC/50/60 Hz kinds of frequencies, but not at, say, 100 kHz.
>
>
> The problem is that plastic pipe is made by extruding shredded plastic, and that shredded plastic is chosen to be cheap and meet the *structural* requirements (e.g. burst strength) and chemical properties (solvent welding).
>
> When you get to large diameter sizes, the problem is worse: since the wall thickness is greater, the maximum "grunge" particle size can be bigger without the mfr worrying about it sticking through the wall.
>
> So ANY pipe is a take your chances, unless you're buying something specifically characterized for the application (expensive! in most cases)
>
>
> YOu couldn't even depend on cutting off a 1" slice from the end and testing it, because for all you know, that thin metal ribbon scrap is in the next inch.
>
> So, what do you do: Most folks just hope for the best. If you're winding a big coil, and are investing a substantial amount of time and money in the wire and winding, you might want to test your form before you start winding.
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