General > General Discussion
Minatronics 1.5V Incandescent Bulbs
Alan:
You could use two of your 1/2 watt resistors in parallel. Use 1K paralleled to equal 500 ohms.
TwinStar:
I might if space weren't an issue and I have enough. There are 4 bulbs in each nose and I think I'm correct in assuming that I'll need a resistor for each bulb.
Alan:
4 bulbs changes the equation drastically. Don't order those resistors just yet.
If you wire the bulbs in series then the total resistance is 200 ohms. Let's do the math...
Hold on. Wife is calling me to dinner. Back in about an hour.
TwinStar:
No worries.
There are:
1 clear Mars light
1 red emergency application light
2 headlights in the lower housing
No rush, enjoy the dinner.
I will add that 3 may be on at the same time, or just two, or just two on dim.
Alan:
And we're back. With a full tummy!
I'm glad you listed the lights. So much for wiring them in series.
Yes, since you will be operating the lamps individually you will need a resistor (or resistor parallel pair) for each lamp. The headlights are the exception since both are operated together. If you wire the headlamp bulbs in series then the math for them looks like this:
Combined bulb voltage = ( Supply voltage x Combined bulb resistance ) / ( Unknown Resistor + Combined bulb resistance )
( 1.5 + 1.5 ) = ( 14.8 x ( 50 + 50 ) ) / ( R + ( 50 + 50 ) )
3 = ( 14.8 x 100 ) / ( R + 100 )
3 = 1,480 / ( R + 100 )
3 * ( R + 100 ) = 1,480
300 + ( R * 3 ) = 1,480
( R * 3 ) = 1,180
R = ( 1,180 / 3 )
R = 393
The series resistor needs to be 393 ohms to create a 1.5 volt drop across each 30mA bulb when two bulbs are in series at 14.8 volts.
In the end it doesn't change things since the next standard value above 393 is our original 470 ohms. Wiring the bulbs in series just means they will be ever so slightly less bright but you need only a single resistor instead of one for each. Should you go the parallel resistor route then you can use two 810 ohm resistors in parallel to get 405 ohms. That will make your series wired headlights full brightness and you can use 1/2 watt resistors.
You should wire up a bulb and a resistor outside of the loco. Turn it on for 15 minutes. Check to make sure the resistor isn't so warm it will melt plastic.
BTW Unless you are a devout Amazon fan, it is the last place you want to buy electronic components. Very expensive. eBay from China will be a fraction of the cost but last I checked Beijing doesn't offer free 2 day shipping! :D
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