First off Happy Hollidays to all.
What type of resistors should I be ordering for MR electronics? I am referring to whether they should be carbon, carbon film , wire film etc. Looking at the Mouser catalogue they ask the type & it is confusing to me.
Thanks
Bob D
It doesn’t matter. What is important is the wattage rating.
I have used carbon and carbon film for many years. I use 1/4 watt.
Rich
The real difference, at a given wattage, is precision. But it’s not that critical for installing a dropping resistor for LED headlights. 10% tolerance is fine. Carbon film is usually the cheapest - you want the cheapest ones. For headling dropping resistors, for LEDs, 1/8 watt is fine.
–Randy
Mouser, Digi-Key are big firms selling stuff to specifications far more demanding that what we would ever require.
LION buys his resistors in several common resistances, all at 1/4 watt. True 1/8th Watt will do, but the 1/4s are far cheaper. LION buys his from All Electronics (an MR advertiser) and these people deal with seconds and closeouts and their customers are hobbyists of all sorts. They will not have the confusing variety, And these will be far cheaper. LION buys the 1KΩ resistors by the 1000 and are a penny each.
ROAR
Depends on what use they are for. Carbon are usually low wattage and low current, wire wound are for high currents and wattages (Wattage is Volts X Current). For MR applications, usually use a wire wound for track current and carbon for most other apps.
Hope this helps
There are also sand resistors which are very good for track currents.
LION uses 1/4W carbons on his trackwork, but this is a specialized service and are resisting current for only a few seconds at a time. Our building engineer said they would be good enough, and indeed they are unless a train derails right on top of one, in which case I have had a couple of small trackside fires. Maybe I will try to adjust station voltages with diodes instead.
ROAR
Wattage and application usually drives the choice of resistor.
1/4 watt metal or carbon film resistors are the normal choice on a layout, but as I also do a lot of engine and car lighting, the tiny PC board resistors which are 1/8 or 1/10 watt are used in all DCC conversions and lighting situations. All my lighting is LED only. For holding back a low voltage incandescent lamp, you need more wattage.
Richard
For 1.5 volt, 15 maa light bulbs, 1/4 watt work just fine. I use the 1.2mm, 1.5 volt, 15ma bulbs.
Below is some info about LED’s and light bulbs. He says, 1/4 watt for 15 ma light bulbs.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
Rich