Led Lighting Problem

[musszzy]

Hi,

I have an odd problem with Led lighting and would appreciate if anyone had a theory on what i am doing wrong (nearly said can someone shed any light on this!).

I have 6 off 12v MR16 7W LED lights wired in a pelmet with a maximum cable run of approximately 6 feet using 1.0mm T+E. The transformer is a 1-10v dimmable led driver rated
at 12v 5 amps i.e 60W.

When i switch the transformer on only 3 bulbs light.

If i remove a single light bulb (any one) all 5 light and it works fine.

When initially powered up the current draw with all lights is 5.14 amps (too much)
If i remove one lamp 5 light up at the expected 3.14 amps and if i then reconnect the 6th lamp
they all work and the current increases to the expected 3.8 amps. However as soon as i switch
the transformer of either by shorting the 1-10v input or at the mains then the problem returns and its again drawing over 5 amps.
Any info appreciated.
Thanks.

Read more: //www.diynot.com/diy/threads/led-lighting-issue.453821/#ixzz40orHGQA8

 

[Midas Man]

1-10v on 12v lamps?

 

[musszzy]

Hi,
No the led driver has an input for dimming which is 1 - 10v. Not using this yet but basically using it as a switch if you short it then the output for
the led is on, disconnect it for off. You can use a special dimmer to achieve dimming of the lights by varying the voltage on the input.

Sorry i did not make this clear

 

[333rocky333]

However as soon as i switch
the transformer of either by shorting the 1-10v input

if you short it then the output for
the led is on, disconnect it for off

Is it me or does that not make sense



Is this a constant voltage driver, could it be that 6 leds are playing havoc with the drivers internal electronics somehow, I seem to recall some lamp makers telling you to limit how many lamps per circuit.
maybe try 2 drivers with3 lamps on each

 

[stillp]

No the led driver has an input for dimming which is 1 - 10v. Not using this yet but basically using it as a switch if you short it then the output for
the led is on, disconnect it for off

Surely if it expects to see 1 - 10V and you short it, it will see 0V and go into fault mode?

 

[bernardgreen]

The transformer is a 1-10v dimmable led driver rated
at 12v 5 amps i.e 60W.

Sound like a LED driver ( the "transformer" ) that is supplying LED drivers that are buiilt into the lamps.

Two points.

1..... The LED drivers in the lamps take 12 volt supply and use it to supply a controlled current into the LED elements.. If the lamps are not dimmable then the driver in them will endevour to put the same current through the element whatever the input voltage is. When the supply voltage is reduced below 12 volts the current taken from the supply will increase to ensure that 7 watts of power is supplied to the element. If the "transformer" is providing only 6 volts then to get 7 watts the LED driver will be taking over an amp.

2..... The "transformer" and the LED drivers in the lamps will all be using some form of Pulse Width Modulation. PWM is switching a high voltage on and off very rapidly to achieve an average voltage that is lower than the supply voltage and is the required output voltage. The frequency of switching will be different for each unit and these "chopped up voltages" can disrupt the operation of equipment they are supplying.

 

[Lectrician]

Incompatibility. Makes/models?

 

[musszzy]

Hi,
Stillp: 1-10v refers to the dimming range. Grounding/shorting switches the output off.

Lectrician: powerpax driver and Samsung dimmable mr16. If I realised the minefield I was getting in to then I would have been more careful. However information on the subject seems quite scarce.

I think Bernardgreens point 2 is most likely reason although I have no way of testing this. Will try dimming next with 3 of the 6 lamps and if successful purchase another driver as per 33rocky333 suggested.


Thanks

 

[ericmark]

If there is a PWM driver inside the lamps then likely it takes a surge of power on switch one to charge the capacitor if designed for AC/DC this is putting the power supply into overload mode until the power is removed. This is a problem with LED lighting one has not got a clue how the lamp controls the current and so the two controllers one built into lamp and one to reduce to 12 volt may not hand shake as they should.

Some lamps as shown on this page are designed for DC only clearly with PWM drivers built in as they give full 100 lumen per watt. Others are designed for AC only and still more are designed for AC/DC but other than that page linked to it is hard to find any information as to what is inside the lamp. The fact that many lamps give only 60 lumen per watt shows the internal electronics are rather simple and cheap.

Using proper DC bulbs you could use less watts as more lumen per watt, however I would not expect them to dim. Basic thing is power supply and bulb need to be compatible best is to use same make it would seem your bulbs do not match power supply. It is possible if you start dim then increase the power it will work, but I avoid 12 volt LED's except for caravan as it is so hard to match up, and what I want is to be able to pop to local supermarket to get replacement bulbs not have to send away for specials. I don't want to stock bulbs so want cheap and cheerful 230 volt.

 

[stillp]

Stillp: 1-10v refers to the dimming range. Grounding/shorting switches the output off.

1 - 10 v is commonly used in instrumentation, and anything outside that range can only occur as a result of a fault. Otherwise if no fault detection they could use 0 - 10V.
What's the model of the LED driver?

 

[Lectrician]

Lectrician: powerpax driver and Samsung dimmable mr16. If I realised the minefield I was getting in to then I would have been more careful. However information on the subject seems quite scarce.

I think your lamps are "retrofit" types, meaning they just require a 12v AC/DC supply. They have their own current limiting driver in them.

Is the driver you have constant current or constant voltage? Powerpax do both. You need constant voltage. What model is it? If you have constant current, odd things will happen.

1-10v dimming is very standard. Why this thread is querying this is odd. 1volt is the dimmest, 10v the brightest, 0v is off (so shorting should kill the output).

 

[musszzy]

The Driver is a
PowerPax UK LPF-60D-12 60W 12V 5A Single Output Switching LED Dimmable Driver
On closer inspection of the PDF you are quite correct this is constant current and my led`s are Samsung 12v ac/dc dimmable ie rectifier built in.
Think i have been given some duff information by the supplier who i asked for a suitable driver from.
At least this has been quite an education for future projects.
I am particularly interested in the 1-10v control because i wish to integrate this in to a home automation system but think this may
have also confused things for me.
onwards and upwards thanks for help reaching this conclusion.
Dave

 

[bernardgreen]

Most LED lamps have LED element(s) and a Pulse Width Modulation driver to control the current through the LED element(s)

Using Pulse Width Modulation to control the current through the LED element(s) is a low cost way to alter brightness but does not give the best dimming.

The PWM current control is a series of pulses of current many hundred times a second which average out to be the required current. This works well with incandescent lamps as the filaments smooth out the pulsing effect ( they cannot heat up and cool down as fast as the pulses ). An LED element can and does vary in brightness almost as fast as the pulses so the eye sees and retains the pulses of bright light emmitted during the current pulse. Although the average current in the LED element is reduced to half the LED elements still emit full brightness during the pulses of current. The human eye does not average this out to be half brightness.

Some of the better quality dimmable LED lampdo control the current in a way that smooths out the pulses of current to reduce the effect of pulsing light and these emit continuous half dimmed light when the current is half.

The best option for dimming LED lighting is to use lamps that have nothing in them other then the LED element(s) and a resistor in series and supply them from a voltage controlled supply.

The resistor value is chosen such that the current through the LED element(s) is the rated maximum ( or less for longer life ) when the supply voltage is at the top limit.

Then as the voltage is reduced the steady current through the LED element(s) reduces.

The reduction is not linear and the LEDs will be very dim when the supply voltage is close to the forward voltage of the LED element(s) Typically about 3 volts for white LEDs

So with 3 LED elements in series ( forward voltage = 3 x 3 = 9 volts ) good dimming can be achieved with a supply varing from 12 volts (bright) to 9 volts (dim)

 

[333rocky333]

I stand to be corrected but my understanding of drivers, which is still new to me, is that constant CURRENT output drivers, dont actually put out 12volt, the voltage varies around that, depending on the load connected, in your case the lamps.
As you say it is a bit of a minefield and more so when dimming.

In retail we tend to use sealed lamp fittings which come with there own drivers, each lamp tends to be built in clusters of leds in series and I take it if part of the lamp fails, the constant CURRENT driver voltage adjusts to compensate to keep the current at 750ma or whatever the leds are rated at, downside once a few leds go, you lose the whole lamp,
the 1-10 volt dimming via data cables linked from management box, to fitting to fitting.

Afaik, constant VOLTAGE drivers are better in applications like signage where a lot of fixed led lamps are in Parralel so if leds fail you tend to still have some working, not tried it personally, but I dont see a reason why this would not also work if you was not dimming them 12 volt lamps, but as bernard says the problems arise once you opt to dim them

 

[JohnW2]

I stand to be corrected but my understanding of drivers, which is still new to me, is that constant CURRENT output drivers, dont actually put out 12volt, the voltage varies around that, depending on the load connected, in your case the lamps.

I don't think one really has to have any understanding of 'drivers', since it's so basic an issue. It is obviously impossible, by definition, to have any sort of constant-current source which delivers any specific (or even constant) voltage, regardless of the load it is supplying.

Kind Regards, John