1/4 watt vs 1/8 watt resistors. - Page 1
Forum section: electronics / beginners

author: LiftedTrace
author_rank: Regular Contributor
timestamp: March 18, 2025, 10:41:41 pm
content: I just ordered a bunch of 1/4 watt resistors amd one pack came and looks like they are 1/8 watt.Any chance the resistors on thr right could be 1/4 watt or was i given the wrong product?Thanks.

author: coppercone2
author_rank: Super Contributor
timestamp: March 18, 2025, 10:48:01 pm
content: that shit depends on the construction I have 0.4 watt rated real brand name resistors that look tiny

author: BillyO
author_rank: Super Contributor
timestamp: March 19, 2025, 12:14:18 am
content: Yeah, some 1/4W resistors are pretty tiny.

author: PGPG
author_rank: Frequent Contributor
timestamp: March 19, 2025, 12:23:53 am
content: Quote from: LiftedTrace on March 18, 2025, 10:41:41 pmI don't know what have happened to wattbut when I was young each power value resistors (if remember well so called metalized) were two times bigger than later.May be to specify higher watt for resistors they changed the method of measuring them. May be in past resistors were tested not mounted and now mounted with very short wires at enough big copper fields at PCB. May be in enough detailed datasheet you are able to find that information.

author: wraper
author_rank: Unknown
timestamp: March 19, 2025, 12:29:37 am
content: Resistors on the left are very likely 0.6W, not 1/4W. 1/4W resistors also exist with dimensions as on the right, examplehttps://www.tme.eu/Document/666e7778b38636d265b3a73aa901cb81/LR.pdf. Power rating depends not only on dimensions but also on temperature resistor can safely work at. Look into actual datasheet, it's not the first such thread where OP ordered something without checking any spec, then publicly fumes he was sent a wrong part, still not checking any spec.

author: floobydust
author_rank: Super Contributor
timestamp: March 19, 2025, 03:06:06 am
content: OP what mfgr/series are these resistors, so we can look at their datasheets.I dislike these "little bastard resistors". They are 1/2 to 1/3 the size of "the usual" having similar power rating.There are several threads about this but they unfortunately descended into mud slinging and personal attack, instead of a discussion on thermodynamics and how to properly design-in the parts, and how resistor manufacturers are misleading us. I contacted them and asked WTF are these "little bastard resistors" and got the explanations and yup it's a trap.To avoid surprises, you have to dig in and look at the datasheets instead of blindly trusting the i.e. "1/4W" parameter on websites.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 19, 2025, 03:12:34 am
content: Quote from: floobydust on March 19, 2025, 03:06:06 amCan I ask why?Not trying to argue with you, just curious about your antipathy here.I actually like smaller resistors for the sake of making more compact circuit boards (but then I'm a hobbyist, not a production person).

author: ME
author_rank: Frequent Contributor
timestamp: March 19, 2025, 07:50:43 am
content: Are they chinese watts?, The ones i hate are blue ones as i find the colours a twat to read/see.

author: LiftedTrace
author_rank: Regular Contributor
timestamp: March 19, 2025, 09:32:30 am
content: Quote from: floobydust on March 19, 2025, 03:06:06 amLeft ones are MFR25FTE523K6Right ones. MFR25SFTF522K7Got them from digikey. Im on my phone writing the part numbers, i forget what brand they were.

author: factory
author_rank: Super Contributor
timestamp: March 19, 2025, 10:18:19 am
content: They are Yageo, the S after MFR25 is the smaller package size (normally 1/6W size), but with same power rating, of course it will run hotter. Note the voltage ratings differ for the smaller package.https://www.yageo.com/upload/media/product/app/datasheet/lr/yageo-mfr_datasheet.pdfDavid

author: LiftedTrace
author_rank: Regular Contributor
timestamp: March 19, 2025, 07:46:04 pm
content: Quote from: factory on March 19, 2025, 10:18:19 amThank you for pointing that out.Not guna lie, i completely missed that. I dont look at these sheets all the time and some can be a bit confusing.