Treatment of surface to eliminate or reduce static charge? - Page 1
Forum section: electronics / projects

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 30, 2013, 07:35:03 pm
content: I built a insulated chamber for temperature measurements out of styrofoam. It works very well but I am afraid that it will build up a charge and zap whatever I put in it.What can I do to mitigate or eliminate this risk? Is it possible to maybe dissolve those static dissipative bags in a solvent and paint the box with it? Or paint the inside with something like zinc paint?I even heard of applying laundry softener to surfaces, but for how long does this solution work and how good is it?I am using pink house styrofoam as a building material.

author: wraper
author_rank: Unknown
timestamp: July 30, 2013, 07:45:16 pm
content: http://uk.farnell.com/kontakt-chemie/antistatik-100-200ml/coating-antistatik-100-200ml/dp/828002

author: IanB
author_rank: Super Contributor
timestamp: July 30, 2013, 07:49:32 pm
content: Why don't you just line the inside of the box with shiny aluminium foil? It will make the inside electrostatically safe (acting like a Faraday cage) and will also increase the insulating properties of the box.

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 30, 2013, 08:38:49 pm
content: Quote from: IanB on July 30, 2013, 07:49:32 pmIt seems kind of flimsy for a coating. I suppose I can cover it in spray on adhesive and fit some of the heavy duty kitchen foil in there.Do you think that the spray on stuff or gluing foil in there is a better idea?

author: wraper
author_rank: Unknown
timestamp: July 30, 2013, 08:45:34 pm
content: I think it will be completely OK with that spray from the link I gave. I you want permanent coating there are also conductive paints.http://uk.farnell.com/kontakt-chemie/graphit-33-400ml/coating-conductive-400ml/dp/836606http://uk.farnell.com/kontakt-chemie/emv-35-200ml/coating-conductive-emv-35-200ml/dp/827988But they are more expensive and IMHO overkill.

author: free_electron
author_rank: Super Contributor
timestamp: July 30, 2013, 09:00:42 pm
content: Quote from: IanB on July 30, 2013, 07:49:32 pmclueless... go read my exhaustive post on ESD ...

author: IanB
author_rank: Super Contributor
timestamp: July 30, 2013, 09:18:48 pm
content: Quote from: free_electron on July 30, 2013, 09:00:42 pmYou think I've made a giant Leyden jar? But what's to charge it up, especially if wrapped round to the outside, or grounded?

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 30, 2013, 09:24:38 pm
content: Quote from: wraper on July 30, 2013, 08:45:34 pmI might go for the paint because I don't like spraying weird crap around frequently, I don't want a tumor in 20 years.But won't this graphite stuff have the same problem as the aluminum foil (it is conductive but not dissipative?) The manual says it does not, I guess I need to find your post. Can you direct me to it free electron?Can I maybe buy some conductive foam (like the black stuff IC's come in) and line my box with it?

author: wraper
author_rank: Unknown
timestamp: July 30, 2013, 09:54:53 pm
content: Quote from: SArepairman on July 30, 2013, 09:24:38 pmDepends on what is frequently for you. Looked in datasheet, seems that it will last for at least couple of months if you are not going to wash it.

author: wraper
author_rank: Unknown
timestamp: July 30, 2013, 10:00:14 pm
content: Quote from: SArepairman on July 30, 2013, 09:24:38 pmJust spray it all around, inside and outside. And you are 100% safe, it would be like metal chamber.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 30, 2013, 10:48:01 pm
content: I can tell you that cold galvanizing spraypaint (ie - zinc paint) does not have any residual conductivity.There are special paints with carbon in them, however, that do provide a moderately durable and conductive surface and moderate conductivity is ideal for static dissipation (too high of a conductivity just zaps the parts).EDIT: yes, you need to connect the surfaces coated with the graphite/carbon conductive paint to a good ground, just like any other anti-static mat, wristband, etc.

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 30, 2013, 11:24:02 pm
content: Well, in that case, the static dissipative spray seems like a better idea then making it conductive and having it require a ground.I would rather have it not build up a charge then accidentally forget to plug it in.

author: free_electron
author_rank: Super Contributor
timestamp: July 31, 2013, 03:39:02 am
content: Quote from: IanB on July 30, 2013, 09:18:48 pm1) every time you cycle temperature the whole mess contracts and expands = friction = knocking electrons loose = build charge2) the basics of ESD protection boils down to 1 rule : equalize potentials and limit the equalization current between two objects. you do this using resistance ... not using metallic conductors like aluminum foil !

author: JoeyP
author_rank: Frequent Contributor
timestamp: July 31, 2013, 04:41:28 pm
content: Quote from: free_electron on July 30, 2013, 09:00:42 pmClueless sayeth the Wizard!!! Thou shalt read and commit to memory my every spoken word before thee make any foolish declarations!!! (Seriously?)Considering that every commercially produced temperature chamber I've ever seen was lined with metal - grounded directly to earth through its power cord, seems to me that lining his chamber with a grounded layer of aluminum foil is a very reasonable idea.

author: free_electron
author_rank: Super Contributor
timestamp: July 31, 2013, 05:59:14 pm
content: Quote from: JoeyP on July 31, 2013, 04:41:28 pmcorrect. but that was not the question !the Ts question was : how to avoid ESD problems.so for your commercial temp chamber my answer still stands ! you need to take ESD precautions. such chambers are a nightmare

author: JoeyP
author_rank: Frequent Contributor
timestamp: July 31, 2013, 06:22:48 pm
content: Quote from: free_electron on July 31, 2013, 05:59:14 pmIn the mind of the Wizard, perhaps. Meanwhile, the rest of the world has been using metal-lined chambers for 50+ years. I've used them with ultra-sensitive devices rated for static damage at <100v (known as "class zero" devices in some circles). Experienced no nightmares - not even bad dreams or restless sleep. I suspect OP is quite competent to get the same results. And if you're really worried about limiting current flow, ground the shield through 100K or more.

author: SArepairman
author_rank: Frequent Contributor
timestamp: August 01, 2013, 01:55:33 am
content: Well I just wanted this box to put analog electronics that don't get hot into to try to minimize the effect of room temperature changes.