Author Topic: Streetlight LED driver is open to the air.......therefore needs confomal coating  (Read 1662 times)

0 Members and 1 Guest are viewing this topic.

Offline ocsetTopic starter

  • Super Contributor
  • ***
  • !
  • Posts: 1516
  • Country: 00
Hello,
We took apart a mains connected streetlight “head” from China.   :-/O   :-/O   :-/O
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”.       :scared:

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”.   :-BROKE

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 would even 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)
 8)
 

Offline TomS_

  • Frequent Contributor
  • **
  • Posts: 854
  • Country: gb
Not sure I would call that "open to the air". That seems like a bit of a stretch.
 
The following users thanked this post: ocset

Offline mdszy

  • Supporter
  • ****
  • Posts: 291
  • Country: us
  • somehow has an ee degree
    • szy.io
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?  :-DD

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.
somehow allowed to be a Pixie Wrangler in Training
eBay Store | My site | Hackaday.io Projects | my mastodon.technology profile
 
The following users thanked this post: ocset

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 13216
It depends on the size of the holes.  Mud dauber wasps or Mason bees can do a lot of damage.
 
The following users thanked this post: JPortici, ocset

Offline mzzj

  • Super Contributor
  • ***
  • Posts: 1298
  • Country: fi
"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%  :-DD
« Last Edit: August 26, 2018, 07:06:53 pm by mzzj »
 
The following users thanked this post: SeanB, tooki, ocset

Offline ocsetTopic starter

  • Super Contributor
  • ***
  • !
  • Posts: 1516
  • Country: 00
Quote
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?
Thanks, 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?
« Last Edit: August 26, 2018, 09:10:11 pm by treez »
 

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 22436
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
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
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
The following users thanked this post: ocset

Offline JS

  • Frequent Contributor
  • **
  • Posts: 947
  • Country: ar
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

If I don't know how it works, I prefer not to turn it on.
 
The following users thanked this post: ocset

Offline Kjelt

  • Super Contributor
  • ***
  • Posts: 6586
  • Country: nl
Outdoor driver electronics should be potted.
 
The following users thanked this post: ocset

Offline mzzj

  • Super Contributor
  • ***
  • Posts: 1298
  • Country: fi
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


GORE has a product for exactly this problem: https://www.gore.com/products/gore-protective-vents-for-lighting-enclosures
 
The following users thanked this post: ocset


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf