MR16 LED what is 12 volt?

27 Jan 2008
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Llanfair Caereinion, Nr Welshpool
United Kingdom
Seems odd question but not as daft as it seems. With GU10 lamps often the voltage is given as 85 - 265 volt showing the range they will work on but with 12 volt it just states 12 volt it does not even say AC or DC.

Two issues one is 12 volt transformer seems the bulbs do not last very long and wonder if should be DC?

Second is caravan 12 volt nominal is anywhere between 11 and 14.8 volt mine is not at stage charger so 13.8 volts. Some do say will work with electronic transformer so clearly AC however my transformer is not electronic in any way.

Looking for 1 or 2 watt but can find halogen rated 13.8 volt (85W so would not really want these) but not LED and it would seem likely that with 12 volt a simple resistor is used but with 230 volt a switched mode power supply.

A 2W 12V lamp with AC supply would likely be driven to well over the 2W limit on the peaks tested LED's over driving at 2kHz pulse and worked OK but at 100Hz likely two long of a time to stand over driving.

But can't find any data. So question is has anyone used MR16 12v rated LED lamps at 13.8 volt DC and did they last? And have any other found using 12v LED in 12v RMS AC supply has caused failures or was I unlucky?
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Some of the drivers in low cost lamps using LED elements are very badly engineered.

There is nothing wrong with running LED elements on pulses of controlled current where that current is several times the normal continuous current for the element provided the average current is significantly less than the maximum continuous current for the element. This gives pulses of light that make the LED appear brighter than it would with a continuous current.

It goes wrong when the pulses of current create an average of the pulsed that is close to the maximum continuous current. At this point thermal conductivity and molecular migration effects become significant and the element degrades rapidly.

Some drivers use pulses that are greater than the maximum peak ( pulse ) current for the element and these will degrade the element resulting in a very short lifetime. The element gives a lot of light and looks good but only for a short life.

One driver I came across puts rectified mains directly onto a string of LED elements via a semi-conductor switch which controls the pulse width. Very cheap and nasty. The elements have a a very short life time.

Another driver has a switched mode current source with the pulses of 6 times continuous that are one tenth duty cycle. Lamps using this design of driver have been in continuous use for over 5 years.

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