DIY Conformal Coating - Page 1
Forum section: electronics / projects

author: 8163jb
author_rank: Contributor
timestamp: September 04, 2017, 12:21:55 pm
content: Hi Guys,I'm currently working on a project which involves fairly high voltage (180-200V DC), and it's gonna end up in the hands of makers/hobbiests. Obviously there are alot of safety warnings on the project about the HV, but to mitigate a little bit of the risk I was considering using a conformal coating on the PCB. I have found this aerosol based conformal coating online (http://www.ebay.co.uk/itm/PRO-POWER-PPC121-PRO-POWER-CONFORMAL-COATING-400ML-/171329872497) and I was wondering if anyone here had any experience with products like this. How easy is it to implement - and have it still look nice - and how effective a barrier will it present etc?Cheers!

author: fourtytwo42
author_rank: Super Contributor
timestamp: September 04, 2017, 01:01:14 pm
content: I have used the aerosol version for moisture protection but never thought of it as a way of touch proofing! The resulting coating is very thin although it does resist DVM probes quite wellMaybe you need it to help prevent tracking too as you say your board is high voltage. As for looks the stuff I use from RScomponents (569-313) is shiny!

author: jpanhalt
author_rank: Super Contributor
timestamp: September 04, 2017, 01:02:55 pm
content: I use this:http://www.ebay.co.uk/itm/Mg-Chemicals-Acrylic-Lacquer-Conformal-Coating-340G-12-Oz-Aerosol-Can-Clear-/253108378900?epid=668265674&hash=item3aee6f5d14:g:es4AAOSwz2tZm4GoDidn't pay anywhere near that price (USA) when I got it. Descriptions seem to be similar. Have heard that Krylon Clear (if available) is also an acrylic clear that might be cheaper. Just read the label.I use mine for protection from corrosion, and it works. Looks OK. Your spray technique will control how bad it looks. Acrylics usually dry quickly from solvent evaporation, which causes them to cool substantially. If done in a humid environment you will get a cloudy result from condensed water.Never tested it for HV protection, though.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 04, 2017, 02:10:51 pm
content: Acrylic coatings are not touch safe.It's just to prevent moist air from damaging the board. They aren't even splash proof! And you can still use blunt banana plugs to make contact.You will need polyurethane potting compound for reinforced isolation and touch safety.

author: 8163jb
author_rank: Contributor
timestamp: September 04, 2017, 02:53:31 pm
content: Quote from: Jeroen3 on September 04, 2017, 02:10:51 pmThis is useful to know, the dielectric strength of 80kV/mm was misleading me a little. I will make sure to still keep all the warnings and other preventative measures in place, but would you say having it is still better than not?

author: Gyro
author_rank: Super Contributor
timestamp: September 04, 2017, 06:11:57 pm
content: Go and have a look at RS or Farnell (and CPC). You'll find a better selection, certainly more product data, and probably a better price than ebay too.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 04, 2017, 08:55:39 pm
content: Quote from: 8163jb on September 04, 2017, 02:53:31 pmYes.It's a question of film thickness, not the chemistry of the polymer. An acrylic coating is only a few mills, if that, thick. If you search on conformal coatings and high voltage, you will find responsible manufacturers (e.g., Silicon Labs) recommending various conformal coatings to improve corona resistance and HV board designs.The dielectric strength is real. The "blunt probe" test needs more detail before it can be relied upon for guidance. For example, I can easily drive a "blunt nail" through 1 cm of polyurethane. That doesn't mean a thing in real life electrical safety.

author: jbb
author_rank: Super Contributor
timestamp: September 05, 2017, 12:28:28 am
content: If you want some kind of formal safety protection, you'll need a lab to evaluate it to a particular standard. This will be expensive (several thousand $).If you're selling it as test equipment for informed users (with warning labels etc.) then you can probably get away without formal testing.If you want physical protection, I would suggest a thick conformal coat (>0.4mm) or even potting that section if the board. If you can clump the HV stuff along one side, you can dip-coat one edge of the board (without filling up all the connectors...).Alternatively, have you considered soldering a grounded shield can over the area?Whichever way you go, be careful ofVIAS- you don't want to cover up the top side and haveLIVEcontacts on the back. Solder mask will not *reliably* stand off high voltages.All that being said, it might be possible to avoid the coating issue alltogether. Can you do all three of the following:- strictly limit the stored energy at any HV node? Even in the face of a single component failure?- strictly limit the continuous current available at any HV node (considering single component failure)?- detect erroneous conditions (eg over voltage, over current) and shut down?Then you might be able to provide a good level of safety even if someone touches it.Edit: sub 'potting' for 'pitting'Edit: I hate autocorrect. Stupid mistakes fixed and now italic...

author: joeqsmith
author_rank: Super Contributor
timestamp: September 05, 2017, 01:53:26 am
content: My idea of HV and yours differ. That aside, I have done some home conformal coating of some of the Dow Corning products using a paint gun for a car. Data sheets will tell you what you can use for a thinner if you decide to spray it. We used HumiSeal seal products that were available in aerosol.

author: jbb
author_rank: Super Contributor
timestamp: September 05, 2017, 02:21:55 am
content: He he!There is indeed!I certainly wouldn't sell anything >= 25kV (with any real current or energy) to a hobbyist :-)

author: Jeroen3
author_rank: Super Contributor
timestamp: September 05, 2017, 05:33:35 am
content: You will have to spray the aerosol coating multiple times to get a sufficient layer for your purpose. It won't be pretty.

author: Pitrsek
author_rank: Regular Contributor
timestamp: September 05, 2017, 08:01:04 pm
content: what about potting the whole thing? I would be quite nervous about just thin layer of coating... Vacuum chamber and custom mold would go a long way. And it doesn't need to look bad either. If you have a wound component manufacturer(transformers/coils etc.), they might be of help.