Resistor Size Deceiving

[ampbldr2]

I ordered a bunch of resistors for a rocket build. 15 total line items and 3 of those line items were 1/4 watt instead of 1/2 watt yet the package labeling is marked correctly for 1/2 watt. Just sighting the size of the resistors was enough to tell they were not correct but I also took some caliper measurements and sure enough the numbers do not add up to Manufacturer specs.

Has anyone else run into trouble ordering parts and getting the wrong stuff?
I am also questioning the size of one of my Pf Caps I ordered from Mojo as it looks a bit small to be 500v rated.

[gui_tarzan]

I get all of my resistors from DigiKey. I had some 2w resistors come in looking like 1/2w so I contacted them and spoke to their tech dept. They said the rating is true (on mine) and the size in this case isn't the important part. I'll use them in some of my projects first before I put them in customer amps but if that's the rating it should be right.

[Phil_S]

Stuff keeps getting smaller. I suspect the sight test is no longer a good measure. The last time I bought resistors I was totally disappointed at how puny they were. I didn't really care about the resistor body, but along with the small body came flimsy leads that were a little short for my taste. At about 10¢ each, I've learned to keep my expectations low. Going forward, I am inclined not to order anything less than 1W rated. The same goes for caps, though even those itty-bittty 500pf silver mica caps still seem to have decent leads. OTOH, larger 22uF 450v and 600V rated electrolytic caps are now more compact, which is a very convenient thing (unless you can't peel yourself away from the Atom caps.)

[John_P_WI]

I doubt mouser is wrong. In the last year i have ordered over 1000 different line items from them without error. With resistors, especially MF, one must refer to either the data sheet or physical description for sizing. It is too easy to be fooled that x watt MF will be the size that y CF was etc... Always refer to the data sheet.

[M Fowler]

From Mouser I just received Vishey MF 1W 150k, 100k and 221k resistors and all are the size of 1/4w resistor though they are all marked 1w.

Mark

[ToneMerc]

I doubt mouser is wrong. In the last year i have ordered over 1000 different line items from them without error. With resistors, especially MF, one must refer to either the data sheet or physical description for sizing. It is too easy to be fooled that x watt MF will be the size that y CF was etc... Always refer to the data sheet.

Ditto
Human error is always possible, but I generally agree. The only times that I have had issue with Mouser is an error in quantity, where I was shorted a resistor.

Got to check the datasheets and also realize that manufacturers specs are always subject to change.


TM

[Structo]

Yeah Mouser has 1w resistors that look like 1/4 w.

I accidentally ordered some of those before.

[ampbldr2]

I doubt mouser is wrong. In the last year i have ordered over 1000 different line items from them without error. With resistors, especially MF, one must refer to either the data sheet or physical description for sizing. It is too easy to be fooled that x watt MF will be the size that y CF was etc... Always refer to the data sheet.

Yeah your right. I am definitely fooled by the size of MF KOA Spear. Why would you have the same size spec'ed between 1/4w and 1/2w?

http://www.mouser.com/ds/2/219/MF-MFS-RK-18760.pdf
The datasheet shows overall dimension and construction and lists 1/4 and 1/2 with the exact same size. Just stupid in my opinion as I populate my parts drawers for example and cant tell what power rating is by looking at the part.

[Structo]

Yeah, I pretty much stick with full sized 1w resistors when building.
I like the bigger size and leads.

If you look at most schematics they say, all resistors 1/2 w unless
otherwise noted.


Besides, bigger resistors sound better.

[ToneMerc]

Yeah your right. I am definitely fooled by the size of MF KOA Spear. Why would you have the same size spec'ed between 1/4w and 1/2w?

Because an automatic parts feeding and or insertion machine could care less about what size the body of the resistor is.

TM

[John_P_WI]

I usually buy the largest wattage resistor for the given physical size allowable. What is more important than the wattage for the size is the working voltage. Just because it may have the same power rating as larger bodied resistors doesn't mean that the working voltage rating is the same. Again, the data sheet is your friend.

[David Root]

+1 on that. Just ask John Suhr or Andy Fuchs about tiny resistors, especially anything the size of older 1/4W. I just won't use them.

They have a strong tendency to fail under high voltage eg plate loads and similar duty. Regardless of what the data sheet says.

Having said that, the Speer KOA CF 2W are fine, even though only the size of vintage 1/2W. But these are not cheapies made in India or China.

I've also used some import CFs using the Stackpole name, 2W about the size of a larger vintage 1/2W with success. Price is right at ~20 cents, even if they do have mostly steel leads and magnetic caps.

[ampbldr2]

I changed the title of the post to be closer to my problem.

I was taught you could identify the power rating of a resistor based on size and shape. Not true today as things are not what they seem. I wonder what they are teaching in the schools today then. I think it is wrong to spec 2 different power ratings with the same size resistor. There is no logical explanation for this.

Mark mentioned Vishay 1w looking the size of a 1/4 watt which is similar to my problem. What do you do send them back because you will never use them in any build.

[M Fowler]

I could give them to my pedal building friends on TAG.

I have a shit load of CF 1/2w resistors I'll never use I got them in resistor kits before I realized I only want larger size 1w or higher in my amp builds.

They would work on Dumble FET boards too.

Mark

[Leo_Gnardo]

I'm also annoyed at the trend to tiny resistors. Larger resistor = more surface area to distribute heat. Granted, new materials may allow resistors to run at hotter temps & still work but there are limits. And if you're trying to keep noise minimized in an audio circuit, resistors heating up increases the noise, who needs that.

One limit illustrated, a couple years back there were complaints here and on MEF about 1 ohm resistors used as current sensors in output tube cathode circuits. Some folks got resistors that were tiny. And though it's theoretically impossible, those resistors would fuse open in use. No. good. for the application. Hundreds of posts later, resistor fans divided into two camps: those that thought the "fuse" aspect of modern resistors in this application was a good thing & an extra "free feature." Others, like me, just as soon have fuses if we want 'em, and install 1% 3 watt wirewounds not likely to flame out. More costly, but so is my time replacing dodgy resistors. And dodgy is NOT what I want to install.