Any issue with powering 12V MR16 lamps with DC voltage?

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Mustwin351

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Wanting to power one landscape light (12V MR16 10w lamp) with a simple dc adapter. Am I correct that the lamp will operate just fine with 12V DC as it is equivalent in power to 12V AC the lamps normally run off of?

The smallest landscape transformers in town are 120 watts and with such a small load the voltage to the lamp will be too high and shorten the lamps life.
 
Mustwin351 said:
Wanting to power one landscape light (12V MR16 10w lamp) with a simple dc adapter. Am I correct that the lamp will operate just fine with 12V DC as it is equivalent in power to 12V AC the lamps normally run off of?

The smallest landscape transformers in town are 120 watts and with such a small load the voltage to the lamp will be too high and shorten the lamps life.
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Yes, except for the absence of a strobe effect the behavior and light life should be the same.

You can put back-to-back diodes in series with the transformer output to drop the voltage to the lights by about .7V per diode pair.
 
a 10w MR16, is it a halogen? i would switch to a LED MR16.
its a very common question. its not really the bulb that dictates this. if the fixture has a control circuit that relies on 12vac input then using 12vdc may or may not work.

just a bulb, then 12vac(rms) = 12vdc


i always add buts to these. using 12vdc on a 12vac filament bulb are in fact different operating methods. when switching to DC you lose the inductance component that is in the filament, thus DC power will flow more amps. will this matter for your bulb? probably not.
 
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gar said:
Standard tungsten filament lamp life is less when powered from DC vs AC for the same power input. See "Reducing filament evaporation" at https://en.wikipedia.org/wiki/Incandescent_light_bulb
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"which may cut lifespan in half compared to AC operation; different alloys of tungsten and rhenium can be used to counteract the effect"

Following the footnotes, the research appears more related to long-life low-current indicator lamps than general-use lamps. OTOH it also appears that over-voltage is a greater cause of failure than AC/DC.
 
zbang said:
"which may cut lifespan in half compared to AC operation; different alloys of tungsten and rhenium can be used to counteract the effect"

Following the footnotes, the research appears more related to long-life low-current indicator lamps than general-use lamps. OTOH it also appears that over-voltage is a greater cause of failure than AC/DC.
Click to expand...

but you can inline a resistor to lower the DC amps therefore counter-balance the effect.

a well made halogen rated for 12vac can go what, 10yrs. if i switch to dc then i get 5yrs? still ok under the scenario given.
or, switch to LED.
 
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