I was wondering if anyone knows a formula or has general knowledge of how many decorative lights/lamps a 12 volt- 18 volt transformer can run. I have blown up 2 tranformers in the last 2 weeks trying to run approximately 40 lights on my layout. Both the tranformers were your basic christmas light type which converts 240 volt (australia) into a 12 to 36 volt output. I sacrificed these 2 after my previous tranformer blew. I have tried using the standard DC controller bit not enough power gets to all the lights and they are dull. Ideas/suggestions ??
I'm not sure about these bulbs. The Miniatronics 16-volt bulbs draw about 30 milliamps each. 40 of those would run 1.2 amps. Most small power supplies are 1 amp or less, so you are probably over that limit. The Christmas lights are brighter, too, so they may draw more current.
It takes an iron man to play with a toy iron horse.
Your problem is that you are pulling too many amperes (amps) through the transformer. If all the lights are connected in parallel (e.g., if one burns out the others still stay on), the amps are additive. If you have 40 lamps, each using 100ma (that's milliamps), then the total amp load (or current) is 4. If you have a short somewhere, then the current is a lot more.
I don't know what the transformers cost, but I would think a fuse and fuse holder, placed in line (series) with one leg of your circuit is less expensive.
Co-owner of the proposed CT River Valley RR (HO scale) http://home.comcast.net/~docinct/CTRiverValleyRR/
You may want to purchase a more robust transformer from an electrical supply house. There is no need to run DC through then lights either. You can use an AC power supply for lights. Amperage is one of the reasons LEDs are so well liked. Much lower current draw and no heat generation as well as almost never burning out.
The details of your transformer and lamps are a little scarce.
The rule is that the current draw cannot exceed the capacity of the transformer. The draw is the sum of all the lamps. The solution is to make sure the transformer is rated for that amount of load, and to be on the safe side, a bigger transformer won't hurt.
Pull too much power, the transformer saturates and begins to overheat.
seanclarkeI was wondering if anyone knows a formula
First I don't know that anyone has ever calculated the output of all transformers in order to get an average. So read the specifications on the thing and record its output.
Assuming all the voltages line up. That is voltage rating of the lamps equals voltage of the supply. Then it is easy.
sA = maxium constant output of supply in AmpsbA = current draw of each lamp in Ampsn = number of lamps
Then choose n such that n * bA < sA
So if each bulb draws 40 mA and the power supply can supply 1 A then:
n * .04 < 1 or 1 / .04 = 25 bulbs
If all the bulbs are not the same, then each one must be measured so that:the summation of bAx where x = 1 to n must be less than sA
or expanded: bAx + bA(x+1) + bA(x+2) + bA(x+3) + ... + bA(x+n) < sA
can you use a sadering gun? i found a simple plan of the internet that i made from some parts that youll need to get from radio shake and a old charger from a phone it said i can run up to 20 or more lights off 1 power sorce
when you use LEDs and micro balbs you need to be aware of the voltage and amps going through them or you might end up with dead ,to bright, or to dim lights this seemed to take care of all of that worked for me ill look it up for you if you wan just let me know
First of all, get yourself a multimeter. Make sure it can read AC amps. Some cheaper meters cannot read AC amps, Learn how to use it. If you do not know how much current a lamp draws, you can find out with a meter. Some people use AC voltage, some use DC voltage. Since you know the current rating of the transformer, you can easily calculate the amount of current a bunch of bulbs will draw.
Don't forget, the more load you put on a transformer the lower the voltage will be to a point. A transformer with no load might be 18 volts AC, Full load maybe about 12 volts AC. I would never draw more than 75 percent of what a transformer is rated for. A safety margin, read ,no burn out. As an example, a 1 amp transformer, do not draw more than .75 amps. A 2 amp transformer, not more than 1.5 amps. For the amount of lights you are using, I would go with a 12 volt, 3 amp transformer.
If you ever use LED's for lights, only DC voltage will work.
By the way, there is no such thing as an "average" transformer.They come in different voltages and current ratings.
Below is a good online calculator I use a lot.
http://www.opamplabs.com/eirp.htm
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.