How bad are cheap Chinese resistors? - Page 1
Forum section: electronics / projects

author: samocamo123
author_rank: Newbie
timestamp: February 01, 2017, 10:47:28 pm
content: I don't do much electronics projects, but I had to use a resistor to get 5v (usb) down to LED voltage. I basically just went on ebay and typed in 100 ohm resistor and bought the cheapest one. I was wondering how bad they are and would they be fine for a simple usb to led? These are the ones I boughthttp://www.ebay.com/itm/New-100pcs-1-4W-Watt-100-ohm-100-Resistance-Metal-Film-Resistor-0-25W-1-/131882768987?hash=item1eb4d35a5b:g:GwEAAOSwdzVXjmwP.

author: Seekonk
author_rank: Super Contributor
timestamp: February 01, 2017, 10:54:45 pm
content: Those 1% are likely better than those in most of the products you buy. It is rare you need better quality than those in most projects.

author: calexanian
author_rank: Super Contributor
timestamp: February 01, 2017, 10:56:51 pm
content: for resistors in this kind of use that would be perfectly fine. I am a little concerned however that 100 ohm may not be the right value. What led are you using and how many, or just one.

author: law_freak
author_rank: Contributor
timestamp: February 01, 2017, 11:12:06 pm
content: Quote from: calexanian on February 01, 2017, 10:56:51 pmYeah, I would consult one of the myriad LED-resistor calculators to check that value. It is very likely that you will experience no issues with your project, but you may be driving the LED harder than it is specced for.As far as problems with cheap resistors, I would imagine that they are the least problematic of the cheap components. Cheap caps are where disaster can be found quickly in even basic designs. My experience is limited and someone more knowledgeable will be along shortly with better information.

author: samocamo123
author_rank: Newbie
timestamp: February 01, 2017, 11:18:57 pm
content: Quote from: calexanian on February 01, 2017, 10:56:51 pmIt is a singular red led. I am going to be using it in a keyboard. Will it be fine?

author: mmagin
author_rank: Frequent Contributor
timestamp: February 01, 2017, 11:33:07 pm
content: Probably fine. I've run across some really cheap 1/8 watt metal film (I think) resistors from china and they seem to be fine and within spec, though I hadn't tested them extensively (power rating, tempco, etc)The only thing I hate is the tiny package and blue color makes the color code nearly unreadable. Also the tiny thin leads are terrible with a solderless breadboard.

author: Seekonk
author_rank: Super Contributor
timestamp: February 01, 2017, 11:41:29 pm
content: 30ma is certainly bright and near the limit of many small LED depending on color. If just a simple indicator I would use 220 or 330 ohm. Hey, you got a hundred of them!

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2017, 11:46:39 pm
content: They work fine, however the thing I don't like is the leads of the through-hole type are very thin and feel flimsy. It doesn't *really* matter, but I still prefer thicker leads. I've had those cheap resistors get broken off of bare boards.

author: BBBbbb
author_rank: Unknown
timestamp: February 01, 2017, 11:50:19 pm
content: Quote from: mmagin on February 01, 2017, 11:33:07 pmFor prototyping they worked fine, but like you, I've never went close to the power ratings.I've given up on color code reading because of the bad contrast and just read the value on the strip and double check it with the DMM, and so far the value has always been within specs.

author: samocamo123
author_rank: Newbie
timestamp: February 01, 2017, 11:53:44 pm
content: Would using two 100 ohm resistors in a row make a 200ohm resistor? Or should I just use a singular resistor for 1 RED led.

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2017, 11:58:15 pm
content: Yes, for resistors in series the values are simply added. For resistors in parallel it is the product of the values divided by the sum of the values.

author: bson
author_rank: Unknown
timestamp: February 02, 2017, 04:05:58 am
content: The resistors are probably fine, but the leads are likely very thin which can sometimes make them difficult to use with a breadboard.

author: varghese
author_rank: Newbie
timestamp: February 02, 2017, 04:45:39 am
content: Chinese stuffs are fine , as long as you can fully test and certify them at your side ..( load ,power, heat range,burnin) .. now a days its hard to say who is getting from where ..

author: RogerRowland
author_rank: Regular Contributor
timestamp: February 02, 2017, 05:37:50 am
content: Quote from: james_s on February 01, 2017, 11:58:15 pmPedantic but, the product-over-sum thing is only for two resistors in parallel. Although if there are more than two, you can still do this pairwise in an iterative fashion.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 02, 2017, 06:13:55 am
content: They should be fine, I've got a number of values from similar Chinese sources and they haven't been an issue. It's worth noting that 100 1% resistors of the same value through digikey is only like $2.50, if you really were worried about part sourcing.I'd agree that 100 ohm is a bit small for an LED off a USB power supply. If you're looking for an indicator lamp, I'd go with 680 or 1k in most cases, a little brighter would be 470, and especially if your LED is a 3mm smaller one... I probably wouldn't go much below that. If you want a lot of current and are using a 5mm, maybe a 330.... but for prolonged use I wouldn't push the LED too hard - you shorten their lifespan when running closer to maximum rated current, and if you don't have the datasheet for the LED, I'd stay away from much over 10mA to be sure.They're cheap and you'll run into this problem in the future, though, so why not get a couple values. Especially if you have several colors, to get approximately matched brightnesses, you'll need different values anyways.

author: dimkasta
author_rank: Regular Contributor
timestamp: February 02, 2017, 08:54:34 am
content: For a single DIY led project they are probably fine.I would get something closer to 300-500 Ohm for a relatively bright led.I like mine dimmer so I usually use something closer to 1K

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: February 02, 2017, 12:35:48 pm
content: These components usually have plated ferrous leads. I'm not sure if this causes any issues but I have found them corroded through after contamination with fluids/vapour.BT

author: karoru
author_rank: Regular Contributor
timestamp: February 02, 2017, 12:50:18 pm
content: Quote from: bson on February 02, 2017, 04:05:58 amUsual solution for this problem is not trying to buy 1/8 W ones;)For author of this thread - 99% consumer products is built using whatever cheapest resistors they could find at the date of manufacture, so don't overthink it.

author: DBecker
author_rank: Frequent Contributor
timestamp: February 02, 2017, 01:33:10 pm
content: Quote from: BurningTantalum on February 02, 2017, 12:35:48 pmYou'll quickly find out which of your wire cutters are magnetized.Initially I thought that the steel leads were harmless -- only a trivial additional resistance when it was already a resistor. But even a tiny exposed cross section of steel from the cut-off leads will produce orange rust stains. If your board may get wet, even from imperceptible condensation, touch the soldering iron to each joint after trimming the leads closely. That should cover the exposed steel with solder.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: February 02, 2017, 02:14:30 pm
content: I have a big issue with cheap Chinese resistors when using them on abreadboard.they simply float around and they dont make contact, 99.9% of projects that I do on breadboard and they arent working is because the resistor isnt making good contact with the breadboard traces.Maybe it's better to say fuck it and order common values from vishay for example because they have much much thicker legs that are great for breadboard stuff, and they are fairly cheap, about 0.8$ for 10 vishay resistors 1/4W 1%.you would probably need like 30 values so for 10pcs each value it is about 24$. not bad, but maybe a better breadboard is a good solution!

author: pieman103021
author_rank: Contributor
timestamp: February 02, 2017, 05:51:18 pm
content: Quote from: ZeTeX on February 02, 2017, 02:14:30 pmWhen you can get a thousand Chinese resistors for under $10, it would likely be worth it to try better breadboards before resorting to getting better resistors. That being said, I don't think a new breadboard would solve the problem too well, the thin legs are much better suited to perfboard prototyping.

author: james_s
author_rank: Super Contributor
timestamp: February 02, 2017, 05:53:07 pm
content: Even good quality resistors are dirt cheap, I usually buy 100 of any value I need. I don't use a lot of through hole resistors anymore but they're handy for prototyping.

author: TimFox
author_rank: Super Contributor
timestamp: February 02, 2017, 09:07:19 pm
content: For digital purposes, the only important concern is connection reliability, including the above statements about lead diameter and composition, as well as internal quality of the end cap or other termination connection to the lead.For critical analog purposes, including audio, "crummy" resistors will show excess noise at low frequencies when there is substantial voltage across them. Carbon tends to be the "crummiest", while wirewound and expensive foil are the least crummy. The normal choice is metal film, but again the internal termination can degrade the performance.With zero DC voltage across the part, the noise voltage depends only on the resistance value (broken connections excepted).Also note that operating a resistor close to its power rating can result in the resistor itself reaching a high temperature, which can burn your finger or the circuit board touching it. This tends to be important for high-power wirewound resistors, which are capable of operation at elevated temperatures.