bigal_scorpio
Active Member
Hi to all,
I recently bought some 3R9 and 4R7 resistors from a seller on ebay that were listed as 1/2w.
I only bought these because the only ones I had were 1/4w or 1/8w which is what the vast majority of my collection are (or were bought as) and I needed some 1/2w ones for a new project where the resistors are used in a LM317 regulator to keep current to a certain level and the calculations meant that the resistors would possibly carry 1/3w.
When the new resistors arrived I was a bit taken aback to see one set labelled as 1/2w carbon film 4R7 and the other as 1/8w carbon film 3R9!
Now that wasn't the only thing that struck me as strange, the resistors were both the same physical size and looked suspiciously like the thousands I already have that were bought as 1/4 and 1/8w.
Now I am wondering what they are and don't want to wait until I have built the circuits just to see if the resistors get too hot as at the moment I am waiting for some parts and if they do fail I would have to wait again for bigger resistors.
Is there any way I can tell what watts(pun intended) the resistors are? Is there a way to determine the wattage by the physical size? Are there differently made carbon film resistors that have higher or lower wattage capacity?
BTW I already contacted the seller only to be told that they are both 1/2w and mislabelled!
My problem is now that I don't trust what he says and would like to know for sure. Many years ago I worked with large resistors and they certainly did get bigger for more watts then. Has this changed? Are my thousands of resistors all mislabelled? Or are these two wrong?
Any info either way appreciated guys.
Thanks. Al
PS the resistors measured with my vernier calipers are (body)6.25mm x 2.2mm at thickest to 1.7mm in the center. Leads measure (3R9) 0.49mm (4r7) 0.51mm.
I recently bought some 3R9 and 4R7 resistors from a seller on ebay that were listed as 1/2w.
I only bought these because the only ones I had were 1/4w or 1/8w which is what the vast majority of my collection are (or were bought as) and I needed some 1/2w ones for a new project where the resistors are used in a LM317 regulator to keep current to a certain level and the calculations meant that the resistors would possibly carry 1/3w.
When the new resistors arrived I was a bit taken aback to see one set labelled as 1/2w carbon film 4R7 and the other as 1/8w carbon film 3R9!
Now that wasn't the only thing that struck me as strange, the resistors were both the same physical size and looked suspiciously like the thousands I already have that were bought as 1/4 and 1/8w.
Now I am wondering what they are and don't want to wait until I have built the circuits just to see if the resistors get too hot as at the moment I am waiting for some parts and if they do fail I would have to wait again for bigger resistors.
Is there any way I can tell what watts(pun intended) the resistors are? Is there a way to determine the wattage by the physical size? Are there differently made carbon film resistors that have higher or lower wattage capacity?
BTW I already contacted the seller only to be told that they are both 1/2w and mislabelled!
My problem is now that I don't trust what he says and would like to know for sure. Many years ago I worked with large resistors and they certainly did get bigger for more watts then. Has this changed? Are my thousands of resistors all mislabelled? Or are these two wrong?
Any info either way appreciated guys.
Thanks. Al
PS the resistors measured with my vernier calipers are (body)6.25mm x 2.2mm at thickest to 1.7mm in the center. Leads measure (3R9) 0.49mm (4r7) 0.51mm.