Vishay Dale CMF vs. RN Resistors (Wattage, Price and Size)

• Vishay Dale CMF vs. RN Resistors (Wattage, Price and Size)
  Posted by Philipp F. on 01 May, 2018 09:58
• Hey,
  
  I was in the market for some decent quality resistors when I found the Vishay Dale CMF series. They seem to be highly regarded and look quite funky.
  Since I am very new to the whole electronics design aspect of things, I have some questions regarding the differences between the regular CMF Industrial and the mil-spec RN version.
  
  What I'm looking for are the 6.1x2.29mm sized ones so either CMF55 or RN55. What threw me off were the wattage ratings and prices.
  
  I see them rated as 0.5W@70°C and 0.25W@125°C and in other datasheets as 0.125W@70°C and 0.10W@125°C.
  
  Mouser has the CMF55 rated as 0.5W and the RN55 as 0.1W or 0.125W.
  
  So my question is, are they the same thing? To me it looks like the only difference are the larger wattage and voltage margins to meet the mil spec of the RN, RN has no RoHS and maybe tighter QC?
  So if I want 1/4W resistors could I just go for the RN, since in some cases they are quite a bit cheaper on Mouser?
  
• #1 Reply
  Posted by bd139 on 01 May, 2018 10:07
• I think they are same. RN's are derated heavily and with extra QA I assume. I have had both together and they look identical.
  
  I bought a load from RS here in the UK as 0.1% tolerance reference resistors.
• #2 Reply
  Posted by CopperCone on 01 May, 2018 14:55
• The military and the industry have different definitions of the same resistor type, i heard.
  
  I have 1/4 watt resistors, they are the size of like 1/8 watt resistors, military probobly rate for 1/16 lol
• #3 Reply
  Posted by Cerebus on 01 May, 2018 15:49
• Yes, it's just down to a different basis used for the power rating for commercial and military specifications.
  
  The CMF55 are available in an industrial rating with a power rating of 0.50W @ 75C ambient and 0.25W @ 125C ambient, and military rated with a power rating of 0.125W @ 75C ambient and 0.10W @ 125C ambient. They are essentially the same part, but the military spec ones use a different rating scheme and are guaranteed subjected to the full MIL-R-10509/MIL-PRF-55182J test procedures.
• #4 Reply
  Posted by bd139 on 01 May, 2018 15:50
• Just a point on these. I've seen a couple of people in the past use them because they are colour blind and have numeric value written on the resistors.
  
  Then they go and solder them in value-side down. Something to remember when you are using them: make sure the value is pointing up