On PCB spark gap? - Page 1
Forum section: electronics / repair

author: Phil1977
author_rank: Frequent Contributor
timestamp: June 27, 2024, 02:26:34 pm
content: Hi,doing a rough sanity check over a super low cost power supply I was asking myself why there is no solder stop lacquer under the Y-capacitor (see pic).Is this intended as a spark gap so that if the voltage between primary and secondary rises to high, e.g. by electrostatic charge, the current is flowing there instead of breaking the insulation somewhere else?Is this good or bad? Just asking generally, I will replace this PS anyhow.

author: ataradov
author_rank: Super Contributor
timestamp: June 27, 2024, 02:52:29 pm
content: It looks like a spark gap, but it is not clear why it would be needed in a low voltage power supply.My best guess - they just used some existing footprint with embedded spark gap.

author: wraper
author_rank: Unknown
timestamp: June 27, 2024, 02:56:54 pm
content: It's better if (say static) discharge happens there than breaks relatively thin insulation somewhere else and becomes a permanent safety risk.

author: squadchannel
author_rank: Frequent Contributor
timestamp: June 27, 2024, 02:57:19 pm
content: I don't think any number of Pikachus would be enough to spark this distance.

author: Phil1977
author_rank: Frequent Contributor
timestamp: June 27, 2024, 02:58:01 pm
content: They even put another spark gap of that kind on the other side of the PCB.Is it anywhere state of the art to build spark gaps that way? Somehow I wouldn't feel comfortable if burn marks from the sparks are generated there.

author: wraper
author_rank: Unknown
timestamp: June 27, 2024, 03:06:05 pm
content: Quote from: squadchannel on June 27, 2024, 02:57:19 pmSomething in order of 10-20kV should break it.

author: squadchannel
author_rank: Frequent Contributor
timestamp: June 27, 2024, 03:07:24 pm
content: This is a common method for low-cost switching power supplies (consumer products, often single-sided boards).It does not always spark, but rather serves to release surges when they occur due to lightning, etc., so i have not seen many blackened ones.

author: wraper
author_rank: Unknown
timestamp: June 27, 2024, 03:08:26 pm
content: Quote from: Phil1977 on June 27, 2024, 02:58:01 pmWhy would there be any burn marks unless there was a high current supply like lightening strike? Would you be more comfortable with a hidden hole in insulation between primary and secondary transformer windings?

author: coppice
author_rank: Super Contributor
timestamp: June 27, 2024, 03:10:12 pm
content: If you want a real spark gap you slot the board. Board surface is a terrible way to create a safety related gap. A little dirt and a humid atmosphere really messes up any characteristics you thought you had designed into them. Enough fluff will bridge a gap, but the scale of that issue pales into insignificance compared to board surface issues.

author: Phil1977
author_rank: Frequent Contributor
timestamp: June 27, 2024, 03:19:37 pm
content: Quote from: squadchannel on June 27, 2024, 03:07:24 pmThanks, that´s what I wanted to know. It may not be the best way to do it, but it´s obviously not the worst.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 27, 2024, 03:20:52 pm
content: I’ve seen PWB spark gaps with slots exactly as Coppice mentioned, and for the exact same reasons.Still, not a precision break over voltage by any stretch of the imagination, but essentially free.