cap dialectric - Page 1
Forum section: electronics / beginners

author: p.larner
author_rank: Frequent Contributor
timestamp: January 05, 2024, 08:24:05 pm
content: i am thinking of making some fixed caps for an atu,it will be copper fr4 sandwitched with 0.36mm nomex sheet as seperators,the fr4 boards are 6 inchx4 inch,will that work for high voltage?https://www.ebay.co.uk/itm/144648265472

author: TimFox
author_rank: Super Contributor
timestamp: January 05, 2024, 08:30:47 pm
content: Why not use a well-characterized low-loss dielectric material such as polypropylene?In any sandwich construction, be careful to avoid air gaps in the stack, where the adjacent dielectric will increase the E field (voltage gradient) in the air by it’s dielectric constant.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 05, 2024, 11:12:35 pm
content: simple realy as i have a sheet of the stuff,i brought it to use the insulate the windings from the stator on an ebike hubmotor rewind,so ive a lot left over+its tough.

author: TimFox
author_rank: Super Contributor
timestamp: January 06, 2024, 12:20:18 am
content: Nomex is an electrical insulator commonly used for fire protection, but I don’t know it’s dielectric properties, constant and loss. It is often a fibrous construction.Did you look up its properties to design the capacitor?Polypropylene has excellent voltage capability, so thin sheets can be used.Polyester (MylarTM) is mediocre for loss.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 06, 2024, 11:14:42 am
content: i found this

author: TimFox
author_rank: Super Contributor
timestamp: January 06, 2024, 10:20:36 pm
content: The two Nomex dielectric loss data are mediocre, similar to polyester/Mylar at a few percent.Note that the data are at sub-RF frequencies.Polypropylene should be about 0.1%.Depends on how good a capacitor you want, which usually depends on the dielectric.

author: MathWizard
author_rank: Super Contributor
timestamp: January 08, 2024, 08:57:59 am
content: What about something like hot glue ? If you glued together some metal sheets. I have an LCR meter and calculator, I need to try some of this. Like making variable caps out of tin can's.What about if you wind some inductor and coat it in hotglue ? If the coil radius is large enough, wouldn't still be an air core inductor. I need to play around with inductors more, like putting different materials inside them.

author: TimFox
author_rank: Super Contributor
timestamp: January 08, 2024, 06:04:41 pm
content: Back in the day, we used “Q dope”, which was polystyrene dissolved in a solvent (acetone?) to exploit the low dielectric loss of polystyrene.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 08, 2024, 09:20:24 pm
content: would 2 sheets of fr4 copper clad (1.2mm thickness? glued back to back work as a cap at hf? then?.i have about 150 5"x4" sheets f it,its to make padding caps for an atu.

author: TimFox
author_rank: Super Contributor
timestamp: January 09, 2024, 02:27:24 am
content: With the data sheet values for dielectric constant and loss, and your plate area and dielectric thickness, what capacitance and Q do you calculate?

author: p.larner
author_rank: Frequent Contributor
timestamp: January 10, 2024, 11:53:15 am
content: i have no datasheet!.just wanted to know if it would work.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 10, 2024, 02:34:33 pm
content: Put a sheet of Nomex in your microwave oven for 30 seconds. Make sure you have a cup of water in the microwave alongside your sample Nomex.If the sample gets warm, it's no good for your RF antenna tuner application.

author: TimFox
author_rank: Super Contributor
timestamp: January 10, 2024, 03:24:13 pm
content: Quote from: p.larner on January 10, 2024, 11:53:15 amI’m sure you can locate dielectric data for FR4 through Google.How can anyone else answer the question if it would work without a clue about the required capacitance and Q?