Okay Guys, I need some help. I’ve got 5 light bulbs of unknown wattage that I want to hook up to battery power. I don’t have access to look at the bulbs and that is also the reason why I don’t want to blow them out by applying too much voltage. Objective is to figure out if they can handle 12 volts of battery power. So can any one help me with a test to figure out a safe voltage?
Got an old power pack laying around and a voltage meter?
Yup - I’d go with Ken’s suggestion. Start out at Zero and bring them up slow. Don’t let them get too bright or they go POP 
Be careful with a power pack - with no load they can put out higher than expected voltage when you first turn the knob. Another safe way is to start with a 1.5 volt battery and a couple of alligator clips. add a couple fo cells at a time to see what brighness you get at a specifc voltage.
“Be careful with a power pack - with no load they can put out higher than expected voltage when you first turn the knob. Another safe way is to start with a 1.5 volt battery and a couple of alligator clips. add a couple fo cells at a time to see what brighness you get at a specifc voltage.”
I was thinking about just adding batteries to a series to get the right power, hadn’t thought of a power pack. I think I’ll try the adding batteries test. This is good timing, because I’ve got a number of battery packs that I planned to hook together today. I’ll test light bulb voltage first.
Another question - see any reason I can’t use a DPDT switch on two different circuits? Use the one side for one circuit, say a power supply and the other side for a light circuit. On and off together, but not powered from the same sources? This may turn to more of just a theory question, but it has occupied grey matter for awhile. 
Not a problem to use a DPDT for two different circuits. Biggest thing to watch in the sub-minature size ones is the current capacity. some look alike, but one will be very low current capacity, the other higher. I always use the higher current ones, unless they are only carrying light circuits or something similar with small current draw.
Okay, so I’ve wired the lights in series (plus to minus) and planning on putting a 1.5 volt battery in the chain. If that works and is dim, I’ll try 3 volts. Using the lights of a Bachmann rail truck and if (big “If”) they are equal in size (totally unknown) what would be the susspect right voltage 3, 4.5, 6, 9 volts? Any clues?
Now if this works, to keep it from being like the old Christmas tree lights of one going out - they’ll all go out, I plan to eventually hook them parrallel ( all plus’s together and all minus’s together). Am I on the right track?
I think the series type Christmas tree lamps are 2.5 volts each — 125V/50bulbs in a string = 2.5V each.
Not sure of the wattage. Guess a half watt each?
(Others more knowledgeable, please chime in.)
Joe
Worked up to 6 volts and never got a blink, oh well. Thanks for the advice.
I was cleaning up my work bench(believe it or not!) Found an Aristo incandescant, so hooked it to the transformer to see what voltage it took and it was 12 volts before it would light up.
Dear Ric,
You could have (a) burned out bulb(s).
Do you have an Ohm-meter? If you don’t, you really should buy one.
You can purchase Multi-meters at Harbor Freight or some other discount tool store for very reasonable cost.
I’ve seen them on sale for about $2 with coupon, once.
The ohm-meter will tell you if you have a burned out bulb: Any resistance less than 400 Ohms means there still is a filament.
If there is a broken filament, the reading on the meter won’t change from “no continuity” (meaning “no connection”) or “open circuit” or “over-range” or “infinity ohms”.
Hope this helps.
Sincerely,
Joe Satnik
Joe,
Thank you for the assitance. Yes, I have an ohm meter. Actually a fairly good one. I’ve soldiered everything together in parrallel at this time and moved on. I’ll go back to the lights at a later date. I’m not sure what course I’m going to take at this time. Once again, thanks.
Be careful with christmas set lights, I fine they have 2 sets of series circuits and that gives 5 to 6 volts per bulb.
Best supply I have for checking bulbs is my home built DC source which never outputs a high start up voltage and I keep a DC voltmeter permanently attached.
For my Aristo TE’s I keep a light bulb on the track to limit the ‘mosfet leakage’, plus it tells me that my power pack is working and supplying the rails.
Dan,
Talking battery power on this project. I also keep a light on the track power just to let me know it is on.
Put your light bulb across the track. Put your volt meter across the track. Grab your remote and hit the Fast button. When the bulb is glowing nicely, see what the voltage is.
(Helps if you don’t have a train on the track at the time)
Thanks Tom, your’s, along with many others are great ideas. I’ve closed this project up for now and have moved to other stuff. Daylight only running for now.
There may be a way to guestimate the limit of applied power by using a digital ohm meter, and a bit of math. Wattage is unknown, available voltages can be assumed and tested.
Oh never mind…
After reading the Curmudgeon in Garden Railways, I’m thinking I want to hook up the backup lights on my engines again.