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variac transformer & 12 volt incandescent blubs

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  • Member since
    February 2010
  • 160 posts
variac transformer & 12 volt incandescent blubs
Posted by banjobenne1 on Friday, August 11, 2023 7:38 AM

I have about two dozen 12 volt Incandescent lights (ho scale) and a 300 volt (0 to 130 volt) 3 amp variac transformer. Most of these lights are in flood light towers and railroad signels. I would like to run them at 8 volts max so they will last longer. So can I use the variac for this? 

  • Member since
    May 2021
  • From: Northern Colorado
  • 86 posts
Posted by CharlieM on Friday, August 11, 2023 8:33 AM

Best to start with a 12 volt transformer. Then use the Variac on the primary of the transformer to reduce the transformer output to 8 volts. This would put the Variac output at abpout 80 volts; a very comfortable value. Setting the Variac output directly at 8 volts is not practical.

BTW, incandecent lamp life varies approximately as the fourth power of applied voltage. A little reduction goes a long way to extend life.

Charlie - Northern Colorado

  • Member since
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  • From: lavale, md
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Posted by gregc on Friday, August 11, 2023 2:30 PM

banjobenne1
So can I use the variac for this? 

presumably you have a 12V power supply and want to use the Variac to reduce the 110VAC to the 12V supply to reduce it's output.   is this what you're suggesting?

or could you possibly be suggesting to drive the lamps from the Variac, reducing the 110VAC to 8VAC??

there are inexpensive adjustable step down converters from ebay that can be used with a 12V wall wart or any other DC wall wart > 8V lying around that can safely be used to adjust the lamp voltage

greg - Philadelphia & Reading / Reading

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Posted by banjobenne1 on Friday, August 11, 2023 2:34 PM

And then I run the 80 volts to the lights??????

  • Member since
    May 2021
  • From: Northern Colorado
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Posted by CharlieM on Friday, August 11, 2023 2:45 PM

"And then I run the 80 volts to the lights??????"

NO!

The Variac output must be connected to the primary of a 120V to 12V stepdown transformer! Then the transformer secondary is connected to the lamps. Greg's approach will also work but it must be used with DC supplies only. The Variac will only work with a true transformer, preferably a 12V transformer. The Variac cannot be used with DC supplies.

Charlie - Northern Colorado

  • Member since
    September 2004
  • From: Dearborn Station
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Posted by richhotrain on Friday, August 11, 2023 3:37 PM

Yikes!

That guy better hire an electrician before he kills himself.

Rich

Alton Junction

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    January 2017
  • From: Southern Florida Gulf Coast
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Posted by SeeYou190 on Friday, August 11, 2023 3:53 PM

banjobenne1
Most of these lights are in flood light towers and railroad signals. I would like to run them at 8 volts max so they will last longer. So can I use the variac for this? 

I would never do this. 8 volt power supplies that are modern and safe are not expensive.

Yes, I am the guy that prefers 40 year old Troller power packs.

-Kevin

Living the dream.

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 21,483 posts
Posted by MisterBeasley on Friday, August 11, 2023 4:51 PM

I agree with Kevin.  KISS Keep It Simple, See?

You can get an 8 volt supply for a few dollars off eBay.  Add a fuse holder and a small fuse for a dollar or so, and you have a simple, robust and pretty much failproof system.  I run all my incandescents off 12 volt supplies.  The 16 volt bulbs I use glow happily and will last forever with the lower voltage.

It takes an iron man to play with a toy iron horse. 

  • Member since
    February 2010
  • 160 posts
Posted by banjobenne1 on Friday, August 11, 2023 7:07 PM

So this 8 volt supply will have enought juice to push my 2 dozen lights? Look I am asking these questions first so I don't kill myself. It's those who don't ask that are looking up at dirt. Cut me some slack.

  • Member since
    July 2009
  • From: lavale, md
  • 4,678 posts
Posted by gregc on Friday, August 11, 2023 7:46 PM

banjobenne1
So this 8 volt supply will have enought juice to push my 2 dozen lights?

don't know how much current the lamps require without knowing the type.   this T-3 type draws 0.33 A at 13V

don't know what power supply you have and how much current it can supply

these step down converters can handle 3A

2 dozen lamps drawing 0.33 A requires ~8A

greg - Philadelphia & Reading / Reading

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