12V LED lights and DC?

[ColJack]

I know that regular 12V halogens are ok on DC ( as I have one in my van and my cousin installed several for his campervan ), but do the newer LED equivalents work ok on DC?

 

[bernardgreen]

I know that regular 12V halogens are ok on DC ( as I have one in my van and my cousin installed several for his campervan ), but do the newer LED equivalents work ok on DC?

Some DO some DON'T
Some WILL some WON'T
Some CAN some CAN'T

All LEDs ( as in the basic light emitting diode element ) work ONLY on DC, whether a lighting unit using LEDs works on AC or DC depends on what the makers designed it to work on.

 

[timtheenchanter]

the better ones seem to be better at DC than the cheap ones (if your using them for lighting you will need better quality ones.

If you but them from a caravan/camping store then they will be fine (if not take them back!)

 

[ColJack]

I'm well aware that LED's work on DC ( not technically correct, they will work on AC but only on one half cycle.. ), but it was specifically the LED replacements for the halogens that I was interested in as they will obviously have some sort of rectification built in..

 

[bernardgreen]

( not technically correct, they will work on AC but only on one half cycle.. ),

But the reverse polarity voltage in the "other" half cycle is likely to slowly but inevitably degrade the diode unless there is a parallel diode to keep that voltage below the maximum permitted reverse polarity applied to the diode..

 

[ericmark]

12VDC LED,21 MR16 GX5.3 12 Volt LED lamp seen here has built-in voltage regulator - safe up to 15v but many will not work on DC.

Since the diodes will likely be powered for only 50% of the time it is likely some over driving will be done or other electronic compensation and running on DC is likely to destroy them unless specially designed for DC.

 

[bernardgreen]

Some of these use a capacitor to limit the amount of energy from the AC mains as a much cheaper alternative to a proper regulated current source for the LED. So DC is no use for them.

For battery driven LEDs a common and perfectly safe "trick" to make them look brighter is to pulse the LED with 5 times normal current many times a second. If it is ON for 10% of the time and OFF for 90% the average current is half that that would be taken if it was ON permanently at its normal current. But the eye sees the 5 times normal brightness and persistance of vision makes the LED look 5 times brighter when only using half the power.

 

[ericmark]

For battery driven LEDs a common and perfectly safe "trick" to make them look brighter is to pulse the LED with 5 times normal current many times a second. If it is ON for 10% of the time and OFF for 90% the average current is half that that would be taken if it was ON permanently at its normal current. But the eye sees the 5 times normal brightness and persistance of vision makes the LED look 5 times brighter when only using half the power.

At University we were required to do that very experiment and our lecturer expected what you have related. We used 555 timers and set it all up using the oscilloscope and a light meter to prove results.

However the results showed over driving did not produce more light and it reduced the life of the LED's. I would expect that there are some LED's that can have a mark space setting to produce more light but not with the standard red LED we all know and love. He was very upset with the result seems year before had guessed results so he had thought it would produce a brighter light.

I also found the reverse current the LED could stand varied a lot. it was a common trick to fit an LED between the common on a 7812 regulator chip and real common to raise the voltage to 13.2V to feed equipment designed for motor vehicles. And one batch would work A1 and the next batch would blow all the time.

But every time one says you can't do that one seems to be proved wrong. I have many times said you can't get ELV fluorescent lamps this being why I went for GU10 but when looking for this post I find you can buy Fluorescent 11 Watt, B22D Bayonet Cap, 12 Volt Lamp, Cold Light for use on DC so I expect soon we will get the same with GU5.3 base.

Who said there was nothing new under the sun?

 

[timtheenchanter]

Ive had a pair in my caravan for a while now, had a look this evening because I couldnt remember, and Im presuming they will work with either 12V AC or DC, because there are no polarity markings, they are a direct replecement for the MR16s

Im looking at buying some for replacements of the capsule lamps, maily because we go away with no electric for longer periods, relying on the leisure battery for all our power, and the LEDs have obvious advantages here.

we have the "warm" LEDs in the van, the normal "white" being too bluish/stark for my liking.