determine voltage of street lights.

[bmeup]

I have a friend who has asked me to wire his newly finished layout. Unfortunately he has included 36 street lights. He glued these down and left the wires hang below the table.

My problem is, I don't know what voltage they are.  Does anyone have a definitive way to determine the voltage?

Bmeup

[Jim Banner]

Many such lights intended for model railroading use have 12 volt incandescent bulbs in them.  However, this is not universally true.  They could have bulbs with a different rating and they could have LEDs.  Here is what I would do:

First test to see if the manufacturer used LEDs.  Connect one of the streetlights in series with a 1000 ohm resistor and a 9 volt battery.  If the streetlight does not light, reverse the battery.  If the streetlight still does not light, it does not have an LED inside it.

Second, connect one of the streetlights in parallel with a voltmeter and a variable power supply.  The supply can be ac or dc and should be able to output from 0 to about 12 volts.  A cheap old power pack will not do as they typically cannot produce voltages less than 3 or 4 volts into small loads like the streetlights.  And an electronic voltmeter will usually have problems reading a pulse type power pack.  A lab type power supply with built in volt meter is ideal.  An alternative is a pocket full of AA or AAA cells.**  Slowly turn up the power supply and see when the streetlight looks right.  If using the cells, start off with just one and keep adding cells in in series with it until the streetlight looks right.  Looking right is more a matter of the colour of the light than its brightness.  If you are not used to doing this, then a reference light to compare the streetlight to will help you.  Buy a single 12 volt grain-of-wheat bulb from the hobby shop and connect it to a 12 volt source.  Then adjust the streetlight to the same colour of light.  If it is yellower/browner than the reference, it is below its rated voltage but will last longer time.  If it is whiter than the reference, it is above its rated voltage and will put out more light but will not last as long as it should.  If you have problems comparing the colours of the lights by looking at the bulbs, let them both shine on or through a piece of white paper.  And if you have a sting of clear miniature Christmas lights, you could use that for your colour reference by hiding all but one of the bulbs from view.

Once you have figured out the rated voltage by the light colour, you and your friend can decide if that gives the effect he wants or whether you can run them at a lower voltage.  Dropping the voltage by just 10% will increase the life of the bulbs by 4 times without affecting the apparent brightness very much.

Once you have figured out the best voltage to use, you can measure that voltage and then measure the current that one streetlight draws at that voltage.  Then you can start looking for a transformer with about that voltage rating and a current rating at least 34 times the current you measured for one light.  If the voltage is in the range 7 to 14 volts, a used Lionel or Marx 0-gauge transformer is a good choice as you can adjust them to the voltage you want and the 50 and 100 watt ones can put out about 2.5 and 5 amps respectively.

** "A pocket full" is just an expression.  You could need as many as 16 cells, but don't put them in your pocket.  Having your pants catch fire is no laughing matter.

Jim

P.S.  Or do as Hunt said - ask the manufacturer.  Trust Hunt to get right to the point while I babble on forever.

J.

[mf5117]

Jim I learned alot from you ,you don't babble sir

[Doneldon]

 You could need as many as 16 cells, but don't put them in your pocket.  Having your pants catch fire is no laughing matter.

Jim-

That depends on just what it was that set the pants on fire in the first place!

                                                                                -- D

[bmeup]

Thanks Jim.  That was extremely thorough and should be helpful.

I can't ask the manufacturer as these are installed and any paperwork has been thrown out.  He apparently thought all lights were the same.

Bmeup

[NarrowMinded]

A pocket full" is just an expression.  You could need as many as 16 cells, but don't put them in your pocket.  Having your pants catch fire is no laughing matter.

I once dropped a fresh 9v in my pocket with 2 pennies, my pocket about caught fire.