Different isolated offline SMPS? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: April 17, 2023, 08:19:56 pm
content: Hi,Are there any examples of products which feature an offline 100-265VAC isolated SMPS in a plastic case which has vent holes for an internal fan? Also, with no earth connection. Also, the case being entirely plastic.To what isolation voltage are they tested?, and what creepage/clearance do they need to exhibit between primary and secondary nets?

author: temperance
author_rank: Super Contributor
timestamp: April 17, 2023, 08:26:16 pm
content: 1 April was about two weeks ago.

author: alm
author_rank: Super Contributor
timestamp: April 18, 2023, 01:13:04 am
content: No, no SMPS has even been built in a plastic case. Only solid gold or tropical hardwood.

author: Faringdon
author_rank: Super Contributor
timestamp: April 18, 2023, 05:57:48 am
content: Thanks, i have seen offline isolated SMPS in plastic case with vent holes, i just cant remember where?

author: mzzj
author_rank: Super Contributor
timestamp: April 18, 2023, 07:36:04 am
content: Quote from: Faringdon on April 17, 2023, 08:19:56 pmHi,As you probably still wont be able to afford the standards that specify the creepage distances I'd say go for 1 thumb of clearance and use high voltage. About 10 strokes of dry cat fur.https://www.eevblog.com/forum/projects/how-do-you-find-out-that-8mm-is-min-creepage-distance-in-offline-isolated-smps/Time for yet another new nickname?

author: temperance
author_rank: Super Contributor
timestamp: April 18, 2023, 09:13:38 am
content: They measure horses in hands in the UK.

author: f4eru
author_rank: Super Contributor
timestamp: April 19, 2023, 05:24:51 am
content: Not really practical for this use, as the horses get scared from the high voltage.

author: dmills
author_rank: Super Contributor
timestamp: April 19, 2023, 09:27:51 am
content: Wait, horses have hands?Learn something new every day.

author: temperance
author_rank: Super Contributor
timestamp: April 19, 2023, 11:58:52 am
content: https://www.britannica.com/science/hand-measurementhand, ancient unit of length, now standardized at 4 inches (10.16 cm) and used today primarily for measuring the height of horses from the ground to the withers (top of the shoulders). The unit was originally defined as the breadth of the palm including the thumb. A statute of King Henry VIII of England established the hand at four inches. Units of various lengths were used by the ancient Egyptians, Hebrews, Greeks, Romans, and others.So it seems that a creepage/clearance about 5/4 of a hand will do fine in most cases.For completeness:https://en.wikipedia.org/wiki/List_of_obsolete_units_of_measurement

author: alm
author_rank: Super Contributor
timestamp: April 19, 2023, 12:07:36 pm
content: Quote from: temperance on April 19, 2023, 11:58:52 amThanks for the history! This is the first time I'm actually learning something from one of these threads

author: temperance
author_rank: Super Contributor
timestamp: April 19, 2023, 11:03:16 pm
content: A little more related to switching power supplies is the way the English used to define flux density:1T (Wb/m²)= 64520 lines inch²I don't know who has been involved in counting those lines (as if it is/was something countable) because you can't really shove the all ready counted lines to one side it seems.

author: johansen
author_rank: Super Contributor
timestamp: April 19, 2023, 11:57:27 pm
content: Quote from: temperance on April 19, 2023, 11:03:16 pm120 years ago when electricity was 10 to 100 times more expensive than is now, they ran transformers at 40,000 lines of flux per square inch to get the iron losses down.