Recommended pcb clearance for 180V DC - Page 1
Forum section: electronics / projects

author: teslinius
author_rank: Regular Contributor
timestamp: November 08, 2021, 06:15:25 pm
content: What's the recommended pcb clearance without air slot just the pcb for 180V dc, is 1mm enough?Also what's the max voltage that will be in the point marked?, if the max current will be 10A, then the max voltage will beU=I*R->U=10A*0.1=1V?The rest of the voltage will be dropped by the mosfet?

author: bob91343
author_rank: Super Contributor
timestamp: November 08, 2021, 06:47:26 pm
content: When in engineering school I was taught that arcs cannot start below about 300 VDC. At high frequencies we were not told anything but of course dielectric heating could cause problems.

author: tooki
author_rank: Super Contributor
timestamp: November 08, 2021, 06:54:47 pm
content: This page has a calculator based on various industry standards. It’d put it at 1.25-1.5mm for 180V.

author: Gyro
author_rank: Super Contributor
timestamp: November 08, 2021, 07:43:33 pm
content: Quote from: bob91343 on November 08, 2021, 06:47:26 pmThat depends on several factors - pollution degree, humidity, solder resist (or not) etc.In practical terms, the as much spacing as you can sensibly achieve by eye approach usually exceeds the absolute calculated minimum.

author: bob91343
author_rank: Super Contributor
timestamp: November 08, 2021, 11:27:19 pm
content: Perhaps I should clarify. My engineering school taught me that about 70 years ago.

author: ANTALIFE
author_rank: Frequent Contributor
timestamp: November 09, 2021, 01:10:22 am
content: It would depend on the standard you are building your device to, but if it's just a hobby thenSaturn PCB Design calculatoris a good place to startFor example, with B2 case you get 1.25mm, and if you want to be extra careful then you could apply B3 case which is 6.4mm

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 01:24:39 am
content: Quote from: bob91343 on November 08, 2021, 11:27:19 pmIt's still true, but it applies to airclearance, not PCBcreepage.

author: Jester
author_rank: Frequent Contributor
timestamp: November 09, 2021, 01:28:00 am
content: It depends......Under normal circumstances, pollution degree 2 Material Group III etc. 1.8mm minimum, for Reinforced safety double it so 3.7mm"I was taught that arcs cannot start below about 300 VDC."....... tell that to the arc welder

author: coppercone2
author_rank: Super Contributor
timestamp: November 09, 2021, 05:29:59 am
content: well I imagine usually it happens like high frequency start on a tig, a surge sets it off. A well regulated power supply might be fine at some arbitrary voltage but the mains will bring it about.

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 05:40:32 am
content: Quote from: Jester on November 09, 2021, 01:28:00 amThe key word is 'start'. Thus the phrase 'strike an arc'.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 09, 2021, 06:11:37 am
content: A Jacobs ladder is another clear demonstration that starting an arc is not the same as maintaining it.But also: that 300V limit comes from paschens law which is useful and true in the right set of circumstances but comes with a bunch of caveats. It's not something you would use to set a safety clearance by itself.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 09, 2021, 09:12:57 am
content: Arc welder generates many kilovolts by shorting the leakage inductance of the transformer, initiating energy storage in that inductance, then releasing the short. This starts the arc. Then arc is maintained at lower voltage because ionized air becomes a conductor.

author: Jester
author_rank: Frequent Contributor
timestamp: November 09, 2021, 02:01:42 pm
content: In the 80's I worked at a couple of power utilities and they used redundant 250Vdc battery banks to power the critical equipment.250Vdc can be really nasty when it gets started.This video gives a feel for it, and this is a pretty small supply.https://www.epanorama.net/blog/2013/06/27/dc-circuit-breakers/

author: coppercone2
author_rank: Super Contributor
timestamp: November 09, 2021, 02:05:51 pm
content: try to find the video on youtube, if its still there, of the large lead battery bank (like a costco shelf) going up. Throws some sparks and then shortly after the inch thick wires start smoking, dripping fire and melting before you can't see anything from smoke.

author: Gyro
author_rank: Super Contributor
timestamp: November 09, 2021, 02:27:34 pm
content: When we moved into our last office (part of an old Xerox building), the unlocked server room on the vacant floor downstairs still had its big UPS LA battery bank (I think it was pushing 400V iirc) sitting there, with all the series connecting jumpers still in place, waiting to bite the unwary. I warned the landlord and stuck a warning notice up but there wasn't much else I could do - I certainly wasn't going near the jumpers with a spanner!

author: McBryce
author_rank: Super Contributor
timestamp: November 09, 2021, 03:03:11 pm
content: Quote from: teslinius on November 08, 2021, 06:15:25 pm180VDC is pretty much what a vacuum tubes works with. Their pins are 3mm apart, but the solder pads have just 1mm between them.McBryce.