Streetlight LED driver is open to the air.......therefore needs confomal coating - Page 1
Forum section: electronics / beginners

author: ocset
author_rank: Super Contributor
timestamp: August 26, 2018, 09:51:35 am
content: Hello,We took apart a mains connected streetlight “head” from China.The head had a hole which was for sliding onto the vertical pole (lamp post).This hole was quite a tight fit to the pole, but obviously not an absolutely perfect seal…so in other words, air and moisture and small dust particles would be able to get inside the head through this tiny gap between pole and “head-hole”.Now, inside the streetlight head was the LED driver inside a plastic enclosure. We noticed that the plastic enclosure was not totally enclosed, but had air gaps around the connectors at each end of the plastic box….so in other words, the LED driver PCB and electronic components were in fact “open to the air”.Given this “Open-air” nature, do you think that the LED driver PCB would need to be conformal coated?I mean, for example, we noticed that there was a TO220 switching FET in the LED driver enclosure which had straight legs into its PCB footprint (and so not much clearance between drain and source pins)Or do you think that it wouldeven need potting to prevent dust and moisture from ingressing into and around the PCB and electronic components?(obviously some way would need to be found to prevent the potting compound from escaping while it cures during the potting procedure)

author: TomS_
author_rank: Frequent Contributor
timestamp: August 26, 2018, 06:07:55 pm
content: Not sure I would call that "open to the air". That seems like a bit of a stretch.

author: mdszy
author_rank: Unknown
timestamp: August 26, 2018, 06:13:14 pm
content: Like TomS_ said, it's definitely not "open to the air" - are you under the impression that electronics used outdoors are all hermetically sealed or something?Conformal coating is definitely inexpensive and an easy way to protect things, but from how it sounds it's not totally necessary in this case. I'd go so far as to call potting it overkill.

author: Ian.M
author_rank: Super Contributor
timestamp: August 26, 2018, 06:28:53 pm
content: It depends on the size of the holes.Mud dauber waspsorMason beescan do a lot of damage.

author: mzzj
author_rank: Super Contributor
timestamp: August 26, 2018, 07:05:19 pm
content: "Nobody in our company has any electronics design experience and we built a led streetlight for antarctica based on random tips over eevblog forums.Now the ceramics are cracking, case is filling up with condensing water and police is complaining that the lights flicker""and the germans don't want to buy our streetlights for their antarctic submarines because the streetlights are not manufactured in Germany"If you pot the LEDs with Electrolube ER1448RP250G potting compound it helps to reduce the visible flicker by 100%

author: ocset
author_rank: Super Contributor
timestamp: August 26, 2018, 09:07:53 pm
content: QuoteThanks, the thing is, all the off-the-shelf LED streetlight drivers are in totally sealed plastic enclosures….like this….http://www.docs.lighting.philips.com/en_gb/oem/download/xitanium/Datasheet_Xi_LP_70W_0_2-0_7A_S1_230V_C150_sXt.pdf…..so if , as I describe in the top post, you have an enclosure which is actually open to ambient air, (ie , not in a totally sealed plastic enclosure) then you are going to have electronics which runs a lot cooler…..and this means that all those off-the-shelf LED streetlight drivers are going to be far inferior in comparison. So what I am saying is, are there any disadvantages to not having a totally enclosed plastic enclosure?I mean, this could put all those off-the-shelf, totally enclosed LED streetlight drivers into extinction…Do you agree?..and if not, why not?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2018, 03:42:21 am
content: A sealed plastic enclosure isn't the be-all-end-all. Moisture diffuses through plastics, slowly but surely. Eventually the humidity inside rises to match the average ambient humidity. If that level is high enough that, at the lowest ambient temperature, water condenses: the game is over, you've lost.Potting isn't impermeable either, but it does take up space. Liquid water can't condense on a corrodable surface if there's no surface exposed!Closed (but not sealed) enclosures are typical where dripping water is expected. Where a sealed enclosure will trap moisture, a vented one allows the humidity to equalize with ambient humidity. This doesn't prevent condensation -- ambient conditions can certainly become condensing -- but it does mean it's unlikely for humidity inside the box to be much greater than the ambient, day-to-day level. Add some conformal coating to take care of the occasional condensation, and you have a pretty good box.This construction is probably typical of lighting fixtures, automotive components and so on.IP67 and such -- sealed enclosures -- are used where water under pressure is expected. Pressure washing (often automotive and industrial), submersion and so on, are typical conditions. Condensation is usually less of a priority. All you need is a sealed box, and sealed connectors; a regular board can be placed inside. If long life and condensation is a concern, then it should be potted as well.Tim

author: JS
author_rank: Frequent Contributor
timestamp: August 27, 2018, 07:09:12 am
content: Also, street lights are on during night, so worm in the most likely co densation scenario.If you have a kind of sealed box as you described, tight fit to the pole, and some water might come inside in a windy rain, for it getting out will be even harder, so you have another problem, I've found sealed enclosures filled with water much more than you imagine, so I prefer holes on the bottom and protected top, conformal coating and if possible good air ventilation in places rain can't get inside.JS

author: Kjelt
author_rank: Super Contributor
timestamp: August 27, 2018, 09:14:48 am
content: Outdoor driver electronics should be potted.

author: mzzj
author_rank: Super Contributor
timestamp: August 27, 2018, 11:02:08 am
content: Quote from: JS on August 27, 2018, 07:09:12 amGORE has a product for exactly this problem:https://www.gore.com/products/gore-protective-vents-for-lighting-enclosures