will 12dc led spotlights work on a 12v ac supply

[crowbono10]

Hi. I've seen some cheap led spots, supposedly CE and ROHS stamped. They are mr16 12v dc 3watt. Will I be able to replace my 35watt spots which run off a 12ac transformer? If they will work will it shorten their lifespan? Thanks.

 

[ban-all-sheds]

Hi. I've seen some cheap led spots, supposedly CE and ROHS stamped.

Sounds like you might doubt the authenticity or validity of those marks.

They are mr16 12v dc 3watt. Will I be able to replace my 35watt spots which run off a 12ac transformer?

No.

If they will work will it shorten their lifespan?

How about not working AND shortening their lifespan?[/quote]

 

[crowbono10]

O.k. So much for that idea. Thanks for the prompt reply.

 

[333rocky333]

Even if the lamps were AC, its likely your transformers require a minimum load to operate properly, most likely 20 watt/VA for each transformer

 

[Gees]

Even if the lamps were AC, its likely your transformers require a minimum load to operate properly, most likely 20 watt/VA for each transformer

I HATE the word transformer being used to describe a switched mode power suppy

 

[ericmark]

Even if the lamps were AC, its likely your transformers require a minimum load to operate properly, most likely 20 watt/VA for each transformer

I HATE the word transformer being used to describe a switched mode power suppy

I agree I have a transformer which ran 4 x 50W 12vac spots and I swapped them for 4 x 0.58W LED without a problem.

There are even some types of LED (Philips) designed to kid the inverter and even though well below the minimum rating will still work.

However using a switched mode power supply or inverter which ever name you fancy to supply lamps below the minimum rating marked on the device will in the main not work.

However the posted did not call it a power supply, or inverter so the answer to the question asked must be yes it would work OK.

 

[ban-all-sheds]

So cheap LED spotlight lamps will be OK with 12V reverse polarity, and will work fine?

OK.

 

[ericmark]

I did some research as to if 12V LED lamps would work on a AC supply and it would seem they contain full wave rectifiers and work OK. I am sure there must some where be an exception to the rule but all the ones I found with rated AC/DC.

No LED is 12 volt normal around the 1.5 volt mark so they must have some circuit included in the package to reduce voltage.

 

[ban-all-sheds]

Were they marked/described as DC?

 

[ericmark]

MR 16 lamp holders are not polarised in any way how could you have a lamp the is not able to be inserted either way around?

 

[bernardgreen]

No LED is 12 volt normal around the 1.5 volt mark so they must have some circuit included in the package to reduce voltage.

Being pendantic...... the circuitry has to control the current flowing through the LED element and not the voltage applied to it.

 

[ban-all-sheds]

MR 16 lamp holders are not polarised in any way how could you have a lamp the is not able to be inserted either way around?

MR16 defines the size of the envelope, it has nothing to do with the base.

 

[ericmark]

No LED is 12 volt normal around the 1.5 volt mark so they must have some circuit included in the package to reduce voltage.

Being pendantic...... the circuitry has to control the current flowing through the LED element and not the voltage applied to it.

After the zener threshold agreed but before the zener threshold no. I have used a red LED on the common of a 12v voltage regulator (7812) to raise the output voltage to 13.2v not my idea copied from a commercial power supply for a CB radio.

I do also remember experimenting in university at over driving an LED but stopping it from burning out by switching the current on and off using a 555 timer. It in fact caused quite an argument as I had spent extra time to finish the project and found it did not behave as expected and as the current was increased past a certain limit the light output when down however other students had not completed and guessed the results and I was asked to explain why my results were different. Although I knew I could not really say why so I put it down to using a different batch of LEDs.

As to what is in a MR16 unit I don't know and even if I did reverse engineer one the next one could be different. If the LED's are over driven then a rectifier, and capacitor would be needed to get a smooth DC and yes BAS could be right that the ripple could effect the operation when run on AC however I think it unlikely that a MR16 package would be marketed which would not run AC or DC. This question was raised in a previous post and I was arguing that it would need DC but after following links and reading specs it would seem all I could find data on were AC or DC.

 

[bernardgreen]

It isn't a zener effect. The zener effect is when the reverse voltage reaches a point at which the diode changes from high resistance to to low resistance. A zener diode always conducts on forward voltage. An LED element illuminates on forward voltage and not on reverse voltage.

When the forward voltage is below the forward junction voltage Vf no current flows, when the voltage is at the Vf some current will flow and the internal resistance will control it over a very small range of voltage. Because the internal resistance is very low ( can be less than 0.1 ohm ) an applied voltage that is 0.1 volt above Vf will result in a current high enough to destroy or seriously damage the LED element.

The LED in the 0v line to a regulator is adding its forward voltage to the regulator's output voltage. The current through the LED is set by the amount of current the regulator uses internally and the optional resistor from regulator output to the LED.

Over driving an LED element with pulses of high current is a way to achieve an apparent increase in brightness and works well provided the average current is below the maximum continuous current limit. Some LED lamps use that to make the lamp appear brighter but the strobe effect can be noticed when the lamp moves across the field of vision.

 

[Gees]

I did some research as to if 12V LED lamps would work on a AC supply and it would seem they contain full wave rectifiers and work OK. I am sure there must some where be an exception to the rule but all the ones I found with rated AC/DC.

No LED is 12 volt normal around the 1.5 volt mark so they must have some circuit included in the package to reduce voltage.

light emitting DIODE !! Its a bit of a give away?