On 10/19/18 2:28 PM, David Speck wrote:
Doug,It's polite to change the subject of a thread if you are going to a different topic.There is no way to predict the voltage rating of your cap without knowing the thickness and dielectric ratings of the plastic material of the food tubes that you are using.If the cap works and doesn't show signs of puncturing, then it's apparently rated high enough for your application. How long it will continue to work is unpredictable.The buzzing indicates that the foil electrodes are not firmly attached to the dielectric material. The metal flexes as the potential changes across the capacitor, making the noise.To eliminate the buzzing, you want to use a uniform layer of adhesive to glue down the dielectric on both the inside and outside of the tube. Air bubbles under the foil will permit the development of corona discharge which will attack the dielectric material and eventually lead to its failure.People who have built their own capacitors have used rolled layers of Mylar Teflon, or polypropylene dielectric sheet and aluminum foil coated liberally with mineral oil, and tightly compressed to exclude air bubbles. It's a messy and difficult process to make caps that will last for any extended period of operation.I'm pretty sure that your capacitance value is overly optimistic. 14 uF would be a very high value of capacitance for the sort of device that you have described, unless I'm missing something. A value like 0.0014 uF might be more in the ball park, would be my guess.Dave On 10/19/2018 3:15 PM, doug11642@xxxxxxxxxxx wrote:I have been experimenting with home rolled Caps and would like some help with values please?Using food saver tubes as the dielectric, dielectric is 36" X 8", foil inserted in the food saver tubes is 32" X 6", uf measures 14uf as rolled. What would be the voltage rating? So far I have used one in a small TC [7.5k NST] and have not destroyed it! All-tho it buzzes loudly.Doug J.
Are you talking about the vacuum sealer thing? so you cut a 36" length, put foil in it, then vacuum seal it?
Where are the two plates? do you have another piece of plastic between the foils, or do you stack a pair of "sealed" electrodes?
probably more like 14 nF, as Dave pointed out.Historically, air has been a problem in rolled caps. A food sealer might be a good way to pump it down, with oil. My FoodSaver has an attachment that lets you pump down an arbitrary container, and for "degassing", it's not like you need pump down to a micron.
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