What are those? - Page 1
Forum section: electronics / beginners

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 05:52:54 am
content: I know the second (at least) is probably burned, but it's weird both have an "1WJ" identification mark.PS. They are both from an HP Laptop PSU.

author: kars
author_rank: Contributor
timestamp: September 27, 2019, 06:10:40 am
content: i think they are power resistors probably used as a current shunt to measure the current input/output in the psu

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 06:13:48 am
content: Quote from: kars on September 27, 2019, 06:10:40 amI noticed the PCB has R051 and R051-1 for them which made me think they are resistors (but they didn't look like resistors I know of).To replace those is there a safe alternative or do I need the exact ones? (e.g. regular resistors)PS. I'm not sure what the original models of those are to begin with.

author: TomS_
author_rank: Frequent Contributor
timestamp: September 27, 2019, 06:17:50 am
content: Quote from: epigramx on September 27, 2019, 06:13:48 amYou can measure the voltage across a resistor of a known value to determine the current flowing through it.

author: Warhawk
author_rank: Frequent Contributor
timestamp: September 27, 2019, 06:21:07 am
content: Quote from: epigramx on September 27, 2019, 06:13:48 amThese are typically low-value resistors. Current through the resistor creates a voltage drop across it as per Ohm's law. A followup circuitry then treats the voltage drop as a current information.https://www.powerelectronictips.com/measuring-current-shunt-resistors/The magic google formula would be "shunt based current measurements".Such resistors are also known as "shunts".If I read this correctly, the A sample is 0.22 ohm (220mOhm) and the B sample is 0.13ohm (130mOhm).You shall replace them with the same power rating (they can get hot).

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 06:25:13 am
content: Quote from: Warhawk on September 27, 2019, 06:21:07 amQuestion is, what rating do they have, and can they be replaced with some kind of contraption of regular resistors (e.g. a few of them in parallel).

author: Jwillis
author_rank: Super Contributor
timestamp: September 27, 2019, 06:32:16 am
content: Quote from: epigramx on September 27, 2019, 06:25:13 amThey look like 1Watt . I've come across ones like these before and always seem to find out they are silicone coated wire wound flame resistant .I suppose it could be different from one manufacturer to another.

author: Warhawk
author_rank: Frequent Contributor
timestamp: September 27, 2019, 06:32:55 am
content: 1WJ could theoretically mean 1W of power dissipation. You can find exact components on e.g. Farnell.comYou can use a bigger one, if you can fit it in you circuit. Here is an example:(cheap but with higher tolerance)https://uk.farnell.com/tt-electronics-welwyn/w31-r12-ji/res-0r12-5-3w-axial-wirewound/dp/9497218Alternatively, you can use standard resistors (0.5W metal film resistors) and put them in paralel. Finding the combination can be bit tricky.Could you share more details on the circuit you're repairing? Ideally with pictures.

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 06:39:52 am
content: By the way, I bet HP were useless when designing them and rating has to be double. However, I also found 2 dead transistors near them so eh, I don't know what died first.It'd be a bit hard to make sense of photos right now since it's not even fully disassembled and they are taken out of it but they are probably put in parallel themselves.PS. I suspect any resistors that look gigantic would end up with good dissipation (well obviously it wouldn't hurt to not do it randomly but with specs)

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 06:51:39 am
content: Also when I first opened it, the first one was not even connected at all; my first reaction was that the wire could have burned off or something.Now I suspect that's what killed the 2nd. Probably the 1st not being connected at all at the factory.PS. This would be the 2nd time I find something not connected at all at the factory. Last time it was a small laptop that didn't have its fan connected at all to power! (it worked "great" for years, but at ...0.5X speed?)

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 09:56:24 am
content: I just found I have an assorted bag of resistors that are rated 1/4W. I guess 4 of them in parallel do 1W?PS. Or also in series?..if they are identical I guess.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 27, 2019, 10:02:45 am
content: Quote from: epigramx on September 27, 2019, 09:56:24 amYes, only if all 4 of them have the same resistance value.

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 10:08:21 am
content: I'd better do it with at least 5 identical then if I attempt it. If the design failed for that it wouldn't hurt to be more dissipative.(then again, it was probably because 1 of them wasn't even connected so ..yeah)

author: madires
author_rank: Super Contributor
timestamp: September 27, 2019, 12:11:15 pm
content: 1WJ means 1W and 5% tolerance.

author: epigramx
author_rank: Regular Contributor
timestamp: September 27, 2019, 01:03:15 pm
content: So, I need 0.08Ω apparently since they appear to be in parallel (and 0.13+0.22) but I don't have any around (to parallel) (not even near, those assorted-resistors bags appear to be usually >=10Ω).Would a sufficiently long cable that is exactly 0.08Ω suffice? Or at least if it's not kept right on other electronics..

author: Zero999
author_rank: Super Contributor
timestamp: September 27, 2019, 04:31:42 pm
content: There are two potential problems with using a long cable:1) The resistance of copper is more temperature dependant, than a resistor, which is designed to be temperature independent.2) Cable has more inductance and capacitance, than a resistor, which could cause the circuit to oscillate.

author: epigramx
author_rank: Regular Contributor
timestamp: September 28, 2019, 07:44:34 pm
content: Yeah I ordered a few 0.15Ω high power resistors and left it aside. I don't have resistors to parallel and a cable will probably turn to a weird antenna at least.It's a project for fun and learning mainly, it's not worth much repairing it if it's about money only, though it takes a lot of waiting for shipping.