DIY Doctor

LED woes after fitting LED driver

Postby CaliTrav » Sun May 03, 2020 12:19 pm

Hi all,

Have inherited a house where the last owner was a bit of a halogen spotlight fanatic.

We decided to start moving these over to LEDs - we've had the learning curve, experiencing flickering without the trailing edge switches etc. Even with those we still had some flickering issues so the wisdom seemed to be to fit an LED Driver.

I've test fitted those on one bank of lights and can't get any life out of them. To see if it was me being thick I put just one into another bank of halogen lights. They all work fine, but the LED I fitted has a very slow, rhythmic pulse on and off.

Any ideas what I'm missing? Hopefully something simple!
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Postby Mr White » Sun May 03, 2020 9:56 pm

Missing information.

What were the lamps you are replacing.
Information regarding the driver
What are the new LED lamps
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Postby CaliTrav » Mon May 04, 2020 8:44 am

The halogen lamps in situ are Osram Decostar 51s for the most part aside from a few replacements. 12v / 35w with GU5.3 base. Connections into the wiring were just terminal blocks in nice cases.

Trying to replace with Lap MR16 LED bulbs (same GU5.3 fitting, 5w / eqv 35w) replacing the terminal block with a Lowenergie driver (240v AC in, 12v DC out up to 12w)

Thanks
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Postby ericmark » Mon May 04, 2020 10:43 am

Since replacing quartz, there should be no dimmer involved, you should not dim quartz, but you talk about trailing and leading edge so seems there is a dimmer involved?

So two types of electronic switch be it dimmer or simple on/off, those with a neutral connected and those without a neutral connected, the latter needs a small amount of current to flow through the bulb when switched off to work, this current needs leaking through the bulb without lighting it, and there is normally a resistor or capacitor in the bulb to leak this current away, but where there is some thing between the switch and the bulb, then this device needs to leak this small current away.

So the bit between the bulb and the switch comes in four flavours.
1) The true driver variable voltage fixed current, normally feed LED directly not normally used when the LED is in the form of a bulb.
2) The DC power supply, fixed voltage and variable current, often incorrectly called a driver, tends to be used with small LED lights.
3) The transformer, no frills, just a simple toroidal transformer, 50 Hz in means 50 Hz out, and is the normal power supply for most G5.3 MR16 compatible bulbs, can't be used with a dimmer switch in most cases because of the in-rush, it has no minimum output and not heard of any problems with them, I have a 200 VA version running 4 x 3W LED MR16 compatible lights in pods, and has been like that for 4 years, so 12 VA load on a 200 VA toroidal transformer.
4) The electronic transformer, not really a simple transformer although there is one inside, it uses a frequency in the kHz range, and because of the high frequency the transformer is a lot smaller, it uses the switch mode principle, that is the on and off ratio (mark/space ratio) is altered to produce an average voltage, but since there is a lower limit to the on part, often they will not start from zero output, so typical rating 35 - 105 VA, some can be dimmed although they should not be dimmed when powering a quartz bulb. So with the example given if using LED bulbs and dimming to 50% you need 70 watt of LED bulbs for it to work, clearly a problem.

There are some electronic transformers today that will work 0 - 50 watt, but we have a further problem, because of the frequency adding diodes can mean they become a transmitter, it will depend on internals they are not all the same, but even with quartz bulbs there was often a warning not to use over 1.5 meters of cable, some times even less, as the cable could become an aerial.

Now the bulbs, many bulbs are marked 50 Hz, clearly using with a toroidal transformer this is OK, but as said toroidal transformers tend to kill any dimmer switch. We don't know why they say 50 Hz, we can only guess, and we know they have been used with DC but this could over load the rectifying diodes, unlikely but we don't know, and if they use capacitors to current limit, then they will only work with 50 Hz. I would guess in the main they will work on 12 volt DC, but we don't know. The same goes with kHz supply, if a capacitor is used the current will be wrong going through the capacitor, unlikely a capacitor is used on 12 volt more likely three LED's plus a resistor, a white LED is about 3 volt so x 3 = 9 volt so a resistor to sink the last 3 volt and control current seems favourite method, but we simply don't know what is inside the package.

With the MR16 compatible (not really a MR16 as they don't have a multifaceted reflector and that is what MR stands for) with the G5.3 version there are some designed for boats and caravans with a voltage range of 10 - 30 volt DC, your not likely to find these in the local supermarket, but to make statements like all G5.3 are AC is clearly wrong, some are even made at 230 volt, although rare.

Even with the GU10 we have a problem, although 230 volt 50 Hz AC so no transformer or driver involved, electronic switches with no neutral can cause them to flash when switched off, and you have to fit load capacitors around 4uf across the lamp, but these should be built into any driver or electronic transformer, and a toroidal transformer should not need them.

So as said we don't know what you have, but if you want a dimmer switch then don't use extra low voltage lamps, go to low voltage (230 volt) it's hard enough getting them to work as it is without fitting dimmer switches. Likely an electronic transformer with a output 0 - xxVA will work, but really you should use a toroidal transformer with most G5.3 lamps. Same with 12 volt DC power supply, likely they will work if 0 - xxVA, but can't be sure.

Oh as a note, volts x amps x power factor correction = watts, and in the main power factor correction = 1, so VA and watts are in the main the same, but technically there is a difference, so a 35 - 105 VA electronic transformer will run two 50 watt bulbs.
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