# Need wall wart with 1.5V, 1000 ma output

Discussion in 'Electronics Resources' started by ggaige, Feb 8, 2011.

1. ### ggaige Thread Starter New Member

Feb 8, 2011
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I want to power about 100 1.5 volt lights for some vehicles on my model railroad layout. The only transformer I could find with 1.5 volt output is a radio Shack unit that costs about \$30 and has adjustable outputs from 1.5 to 12 volts, but it only has 300 milli amps, and the voltage on the end of the line dropped to 1.4 volts after adding only five vehicles. All the lights will be dim by the time I hook up all the vehicles.
I have several other used wall-warts ranging from 3.9 to 12 volts each. I tried using some of them with resisters in line, and could not see any drop in voltage , according to my volt meter, so I didn't try them with the 1.5 volt lamps for fear of blowing them
I bought some diodes and they didn't seem to drop the voltage either. The ideal unit would be 1.5 volts and 800-1000 milliamps. Any idea on where I could get one of these?

2. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
Hosfelt Electronics has several pages of surplus wall-warts at attractive prices. 1.5V at 1 Amp is an unlikely combination. Good Luck

http://www.hosfelt.com/

3. ### beenthere Retired Moderator

Apr 20, 2004
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If you put your lamps in series strings of 8 bulbs, the voltage needed to drive them is 12 volts, a common figure. That gives you 12 strings pulling 10 ma each (all currents in series are the same) and one with 4 lamps also pulling 10 ma. That is only 130 ma.

So a 12 volt wall wart rated at 250 ma gives you what you need with some overhead.

4. ### magnet18 Senior Member

Dec 22, 2010
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Depending on how you measure the voltage there my be no visible drop, if there is not a complete circuit, the voltage will not appear to drop.

V=I*R, in an open circuit there is no current flowing, so 0*R=0V, or zero volts dropped across the resistor.

Last edited: Feb 8, 2011
5. ### spinnaker AAC Fanatic!

Oct 29, 2009
4,866
988

They are fairly near my home. It is a shame, he does not add to his inventory.

Their website is not up to date. They have a very dated paper catalog that is more up to date (that they have no copies foe ).

You should see the place. It is a mess stuff scattered everywhere.

That said he has pretty good prices for the little bit he carries. I have a feeling the price was set on the website eons ago and he is too lazy to change them.

Dec 26, 2010
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Are these lights definitely filament bulbs, not LEDs? You say that you want 100 of them, but expect to need only 1 Amp. This implies only 10mA per bulb or 15mW each, which seems a remarkably low power for a filament lamp.

There are some more things to consider when using LEDs, so it would be as well to be sure about this. On the other hand, the smallest 1.5V lamps I've ever seen are more like 50mA: 100 of these in parallel would need 5A.

No doubt you may be right about your bulb type and wattage, but it would be best to be sure to avoid wasting money on the wrong power supply..

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
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If you don't mind a ton of extra stuff for the supply, a computer power supply plugged into an older motherboard will give you 1.2-2.5V at 20-90 Amps (depending on how new the motherboard is).

This only applies to the motherboards that have the extra 4 wire jack that plug in next to the processor. There's usually a set of 4 or more on board switching supplies to make the 12V @20 into 1.x volt at a bunch of amps.

Probably not your first choice unless you have that stuff laying around and the room for it....

8. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
That's too bad. We bought large quantities of wall-warts 15 years ago for "Starter-Kits"