Help identifying power rating of THT Carbon Resistors - Page 1
Forum section: electronics / repair

author: danielbriggs
author_rank: Regular Contributor
timestamp: June 17, 2024, 07:17:02 pm
content: Hi all,I wondered if I could get a quick opinion of what power rating these old carbon resistors are? I'm repairing an old board, mid-90's era, and I've not used this sort of high power old carbon resistor before so difficult for me to gauge.I know they're 22Ω, 5%; all connected in parallel.They measure 17.5mm long, and 8mm in dia.Would anyone hazard a guess at what possible power rating something in this size package of that era would likely be?I'm tempted to put these 3W ones in, but just thought I'd check in with the collective-experts, if I'm way off. Can't harm to up-rate them, eh?https://uk.farnell.com/bourns/w3m22r0j/res-22r-5-3w-axial-wirewound/dp/2530207Unfortunately I have no way to know the design spec of the rated current for this PCB.Thanks in advance!Dan

author: McMax
author_rank: Newbie
timestamp: June 17, 2024, 07:30:42 pm
content: I think you're good to go with the 3 watts you linked, but you can fit the 5Watts of the same series.At the end resistor are dissipating heat and it's just a matter of thermal mass, the bigger, the better

author: fzabkar
author_rank: Super Contributor
timestamp: June 17, 2024, 08:39:21 pm
content: Take care with wirewound resistors. Your application may not tolerate the standard inductive types.https://4donline.ihs.com/images/VipMasterIC/IC/BOUR/BOUR-S-A0008961256/BOUR-S-A0008961256-1.pdf?hkey=6D3A4C79FDBF58556ACFDE234799DDF0Quote

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 17, 2024, 11:08:13 pm
content: HiA better question to ask is why have have four out of five burnt up and fifth has not?G Edmonds

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 18, 2024, 08:28:20 am
content: Yeah, I'd be figuring out why they burnt first. Then when replacing them, space them a few millimeters off the PCB for good airflow for good measure.

author: danielbriggs
author_rank: Regular Contributor
timestamp: June 18, 2024, 09:18:44 am
content: Thanks all for your replies; appreciated!I'll get to the bottom of the overcurrent situation + swap out.

author: factory
author_rank: Super Contributor
timestamp: June 18, 2024, 07:46:31 pm
content: The dimensions in this datasheet would suggest the old parts are 2W;https://www.hificollective.co.uk/sites/default/files/allen_bradley_data_sheet.pdfWe don't know what the application is, so can't advise the best replacement, something from the 1990s would have very few carbon comp resistors, they would be using them for the pulse rating, or non inductive properties.Beware wirewounds can burn up badly in certain failures and make a right mess of your board.David

author: danielbriggs
author_rank: Regular Contributor
timestamp: June 18, 2024, 07:49:17 pm
content: Thanks all, that's really useful to know.I'm not 100% as I don't have the part it was connected to, but it looks like they were part of a stepper motor driver.The board was large and had lots of other things going on, but I think these resistors were responsible for that.All the best,Dan

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 18, 2024, 08:59:21 pm
content: HiThe resistors are 1W Carbon Composition from the data givenG Edmonds

author: factory
author_rank: Super Contributor
timestamp: June 19, 2024, 06:19:28 am
content: They are 2W, look again, they are the third from the bottom of the table in the AB datasheet, dimensions A & E.David