Lighting resitor question

[seod]

I just put a NCE DA-SR board in my Athearn SD45T-2 (HO). I replaced the Athearn lights with Miniatronics 1.5 volt 15 MaH light bulbs. I also have some 1.5 volt 30MaH bulbs. The NCE documentation says I need a 1/2 watt resistor instead of the 1/4 watt resistors I used with the 15 MaH bulbs. I have a lot of 1/4 watt resistors but no 1/2 watt. Can I use a 1/4 watt or would it get to hot or blow up or something else bad?.

 The NCE sheet also said I needed a 830 ohm resistor with the 15 MaH bulbs and they were way to dim so I ended up using 560 ohm resistors. The brightness is about the same as the bulb on 1.5 volt battery. So if I need a 1/2 watt resistor I would need like a 270 or 300 ohm resistor to get the same brightness?.

I did not think I was buying 30MaH bulbs but I was not paying close enough attention and that is what I got so I will use them.

Thanks for any help

Scott

[JoeinPA]

seod

I just put a NCE DA-SR board in my Athearn SD45T-2 (HO). I replaced the Athearn lights with Miniatronics 1.5 volt 15 MaH light bulbs. I also have some 1.5 volt 30MaH bulbs. The NCE documentation says I need a 1/2 watt resistor instead of the 1/4 watt resistors I used with the 15 MaH bulbs. I have a lot of 1/4 watt resistors but no 1/2 watt. Can I use a 1/4 watt or would it get to hot or blow up or something else bad?.

 The NCE sheet also said I needed a 830 ohm resistor with the 15 MaH bulbs and they were way to dim so I ended up using 560 ohm resistors. The brightness is about the same as the bulb on 1.5 volt battery. So if I need a 1/2 watt resistor I would need like a 270 or 300 ohm resistor to get the same brightness?.

I did not think I was buying 30MaH bulbs but I was not paying close enough attention and that is what I got so I will use them.

Thanks for any help

Scott

Scott:

I think that there is some confusion here.  If you needed 560 ohm resistors to get the brightness you want then you need 560 ohm resistors regardless of the wattage.  You  need the higher wattage resistors to efficiently dissipate the heat generated.  Larger wattage means better heat dissipation. Don't "cheat" on resistors they're necessary and cheap.

Joe

[seod]

Hmm OK what I am going by is page 6 of the DA-SR manual. So it could be wrong eh!. Looks like I will be getting some 1/2 watt resistors of off that site. I looked and they are real cheap.

http://www.ncedcc.com/images/stories/manuals/dasrv35_d.pdf

 

Thanks for the answer.

 

Scott

[rrinker]

 The resistence rating determisn how much voltage will be dropped through the resistor. The current times the voltage will determine the power in watts being dissipated. You should not run a resistor right at its maximum rating, but leave some head room. SO if the result is more than .2 watt, use the next larger size, a half watt resistor. Excessive power will make the resistor get hot and eventuall (or if greatly exceeding the rating, quickly) fail as the heat builds up and can;t go anywhere and instead melts the resistor.

 For just 1 or two, Radio Shack is a worthwhile source. To buy quantities of the same value for converting multiple locos, you're better off with a supplier like Mouser and ordering in quantity.

                              --Randy

[hon30critter]

I am absolutely not an electronics expert, but I thought I read that putting 2 - 1/4 watt resistors in parallel would equal a 1/2 watt resistor. Please correct me if I am wrong.

Dave

[rrinker]

 Yes, but they will each have to be double the desired value, for example if you want 1K you would need to parallel two 2K resistors.

Two 1/4 watt resistors in parallel will occupy more space than a single 1/2 watt resistor though.

                    --Randy

 

[Hamltnblue]

They're right about the resistor size if you're running 12 volts

12 volts minus the 1.5 of the light equals 10.5 volts

10.5 volts times .030 (30 miliamps) equals .315 watts

That requires a half watt resistor.

 

[richg1998]

Here are some links for this issue.

http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm

http://members.optusnet.com.au/nswmn2/ResColour.htm

http://www.opamplabs.com/eirp.htm

http://www.raltron.com/cust/tools/parallel_resistance.asp

Everyone, store the links if you do not have them.

Rich