LED light problem

loades · Post by **loades** » Fri Dec 11, 2020 12:10 pm

I have a picture light on a lighting circuit. The on/off switch is built into the light - no dimmer. The bulb type is G4. I replaced the 20W halogen bulb with a 3.5W G4 capsule LED bulb which was fine except it sometimes flickered a little. I read that to cure this I should replace the transformer with an LED driver/transformer which I've now done. No more flicker ..... it now flashes like a strobe light! Full on, full off etc. What's the problem?

ericmark · Post by **ericmark** » Fri Dec 11, 2020 2:51 pm

Mark/space regulation, to control the output of any power supply there are two methods, one is a variable resistor of some sort, which produces a lot of heat, the other is to switch it off/on and adjust the on time (mark) compared with off time (space) so the average is the energy required, and with a tungsten bulb this works well, however the time with a LED bulb of combined mark/space needs to be a lot shorter, or you need some thing to damp the pulses like a capacitor.

However it is very hard to design a power supply from zero to y watts output, so more normal is x watts to y watts, so a MR16 G5.3 electronic transformer will be typically rated 20 - 60 VA (VA can be considered as same as watts) so it needs at least a 20 watt load. Using a toroidal lighting transformer you can go to zero output, most MR16 LED's are marked 50 Hz so are designed for AC, but other LED packages are designed for DC, and a smooth DC at that, in a caravan or boat we will have 12 volt DC LED lights rated 10 - 30 volt and inside the lamp is a little switch mode chip which controls the output, it is a little regulator, so it does not matter if the battery is on charge or not, light output is the same, but it needs supplying from a smooth output, but the little strips of LED lights have a simple resistor, so must be supplied to spot on 12 volt average, but it can be an average it does not matter if the power supply sends out pulses or a smooth supply.

So if the lamp says DC it needs a smooth supply, if it says AC/DC then a switch mode supply is good enough. If it says 50 Hz then may be using a capacitor to limit current, so must be a toroidal lighting transformer, in the main drivers are smooth DC supply output, however the word driver for lighting means current control not voltage, they were used with the likes of air port run way lights so every light was same brightness, so when buying a driver some times they are current regulated and voltage can be 5 to 50 volt, and some times voltage regulated and fixed volt and variable current and with the aircraft lights they were AC so it does not even mean they are DC.

It seems the lighting industry just swap names around, some times they will put electronic in front of the name but ballast, transformer, driver, all seem to have no real meaning, you have to read the spec sheet to find out what they do.

kellys_eye · Post by **kellys_eye** » Fri Dec 11, 2020 3:14 pm

What voltage was the halogen bulb? I'm assuming it was 12V since you state there is (was) a transformer in there. Thing is, LED's should be run on DC and the transformer outputs AC so the LED will only conduct (light up) on the positive half cycles the output voltage which means it will flicker at 25Hz (half the AC mains frequency of 50Hz).

Putting in an LED driver is straightforward but you need to match it to the power of the LED - a 3W LED needing a driver that can deliver 3W (or more) but as Eric stated (a bit long windedly) some systems require a MINIMUM load.

Just get the right driver for the LED and all will work.

loades · Post by **loades** » Fri Dec 11, 2020 7:12 pm

Sorry, I don't have a degree in electronics. I'm a simple DIY'er who thought an LED Driver Transformer would power an LED bulb. What has been said goes over my head :-(

This is the specification of the driver transformer I fitted:
Power: 0.5W – 6W
Input: 170-260V 50/60Hz
Output: DC 12V 500MA
Dimension: 45 x 30 x 23 mm
Max case temperature: 75°C
Max ambient temperature: 40°C
The 6w maximum rating for this LED driver must not be exceeded – generally one per light
These LED drivers/transformers are suitable for all G4, MR11, MR16/GU5.3 LED bulbs and also most LED strip lights, just make sure the maximum wattage of the strip light does not exceed the 6w max output power of the LED driver.

This is the bulb which flashes like a strobe light:
Brand Diall
Bulb type Capsule
Cap fitting G4
Colour rendering index (CRI) 80
Colour temperature 2700K
Equivalent wattage 20W
kWh per 1000hr life 2kWh
Lamp lumen maintenance factor (LLMF) ≥ 70%
Light technology LED
Lumens 200lm
Model name/number 1101100035
Pack quantity 2
Power output 1.8W
Product diameter 14.5mm
Product length 43.5mm
Switch cycles 30000
Voltage 12V
Warm up time 1sec
Product code 3663602907886

Both items are new. Which needs replacing and if so by what?

Someone-Else · Post by **Someone-Else** » Fri Dec 11, 2020 8:17 pm

Believe it or not, in theory what you have should work, the fact that it doesn't is "interesting"
Unless we can test it all anyone can do is guess.

Since the lamp flashes, my money is on the driver, either duff or incompatibility, I would suggest you have This one

kellys_eye · Post by **kellys_eye** » Fri Dec 11, 2020 9:22 pm

Change the LED. Using it on an AC supply (as you did originally) will damage it on the negative cycle of the supply which may be the reason it is 'flashing' - it's effectively got a short circuit internally which overloads your new driver circuit and causes it to 'reset' constantly.