# Led dimmer circuit project

Discussion in 'General Electronics Chat' started by parthabar, Dec 22, 2017.

1. ### parthabar Thread Starter New Member

Dec 22, 2017
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Hello,
I am new to this forum and this is my very first post.Hope you guys will help me.

I currently have a led light that has 25 fixtures ,each containing 6 white leds.So in total 150 leds.There are two drivers each has a output DC voltage range of 93 to 140V and current of 300mA and power 40W.I suppose the leds are connected in series as the voltage of the drivers are very high.
My project is to make the leds dimmable with a dimmer.For that I bought a dimmer with output voltage 12 to 24 V and current 8 Amps. Max power 90 Watt.
I want to achive the dimming buy converting the circuit to parallel.
Since total current is 8A or 8000 ma each led fixture will get 8000/25 =320 mA of current. The voltage of each fixture will be i guess 3*6=18 volts.But I am not sure of the registor that should be added to the circuit.I hope 40 ohm should be fine.

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2. ### Audioguru Expert

Dec 20, 2007
11,167
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LEDs should never be connected in parallel unless you buy thousands and test and sort them into groups having the same voltage. Each LED will probably have a different forward voltage then the one with the lowest voltage will hog all the current and quickly burn out, followed by the next one then the next one then ....

Are you guessing that your LEDs are 3V? No, they might be any voltage from about 2.5V to about 3.5V.
You forgot to add the voltage across the current-limiting resistor.

Your 90W dimmer might be made to give AC to incandescent light bulbs. LEDs need current-limited DC. You could connect back-to-back LED strings to AC. But the dimmer might cause LEDs to be abruptly on or off. Back-to-back LEDs powered from AC will flicker when they are turned on.

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3. ### parthabar Thread Starter New Member

Dec 22, 2017
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Thanks Audioguru for your inputs .

4. ### parthabar Thread Starter New Member

Dec 22, 2017
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Hello Audioguru

Can you please check this diagram and suggest if I will be able to do this connection.
One of my friend suggested 12W driver on a 15W load. Is it ok or I should use a driver with higher power than the load.

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5. ### AnalogKid AAC Fanatic!

Aug 1, 2013
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Please post information about the dimmer. It might not be appropriate for what you want to do no matter how it is connected. Photo, datasheet, website link, etc.

ak

Dec 22, 2017
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7. ### parthabar Thread Starter New Member

Dec 22, 2017
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Also the specs of each led panel will be as below

Item specifics
Emitting Color: Warm White
Electric Current: DC 300mA
Model Number: YP-753-3W-26MM
Power: 3W
LED Type: SMD 5730
PCBA Diameter: 26MM
VF: 9.0V - 9.9V
Item Type: Ball

8. ### Audioguru Expert

Dec 20, 2007
11,167
1,317
The very cheap electrical products are missing important safety certification. I would never buy uncertified junk online that could easily cause my home to burn down.
I buy Name-Brand electrical products from a local store and they have CSA, UL and European safety certification labels.

Did my government run electricity provider give away safe certified compact fluorescent light bulbs for free?
They thought so. The light bulbs dripped flaming melted plastic and they all were recalled then replaced.
The no-name-brand Chinese manufacturer stole the certification number from a competitor so the light bulbs were extra cheap and never inspected to be safe.

The driver has a 45V minimum output and five of the 3W LEDs in series would have a minimum voltage of 45V. Then the driver will get very hot and might cause a fire unless it is vented for cooling. I doubt you will vent them. The LEDs will also get very hot. How will you cool them?

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9. ### parthabar Thread Starter New Member

Dec 22, 2017
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I was not going to buy the items in the link i.e the drivers and dimmer. I just gave them as a reference as was asked by analogkid. But for the leds , i have the same leds.For the drivers i have chosen philips .I don't have the picture now,but have talked with the vendor.The important point is the connection that i wanted you to check.Will that work ?
Do I need to change the specs of the driver,if so what should be ideal specs of the driver for this project. I cant change my leds as i have made the fixture according to them.Please suggest.

10. ### Audioguru Expert

Dec 20, 2007
11,167
1,317
I do not know if you can trust the manufacturer of the LEDs who say their minimum voltage is 9V each. Then five in series need at least 45V but get a driver that works down to 40V to be sure.The LED is rated for 9.9V max so five makes 49.5V but get a driver with a max voltage of 55V to be sure.

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11. ### parthabar Thread Starter New Member

Dec 22, 2017
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Thanks. What about the power ?
Should I go with a 3*5=15 watt driver or a higher one.One of my friend suggested 12 Watt as he said it will make the leds last longer (I am not sure about that),or should i select the 18Watt driver .

12. ### Audioguru Expert

Dec 20, 2007
11,167
1,317
The spec's for your LEDs are 3W and a voltage from 9.0V to 9.9V. Then the current is 3W/9.0V= 303mA to 3W/9.0V= 333.3mA. You are looking for a 300mA driver that might be +/-5% so from 285mA to 315mA. 315mA is too much current if the LEDs are actually 9V or a little more.

I think you are trying to operate the LEDs at or a little more than their absolute maximum power that depends on how you cool them. Liquid Nitrogen? I never run anything at its absolute maximum power so that they last a long time and I do not need to worry as much about their heating.
Pick a driver with a 285mA output or less so that 285mA + 5%= 299mA is not more than the 9.0V LEDs 303mA.

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13. ### parthabar Thread Starter New Member

Dec 22, 2017
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Hello AG,

I connected 13 of my leds in series to this driver to test , but one of my leds burnt out.
Was it because of the higher voltage, as I was not unable to get a 55v Driver. But this is a constant current driver, with power 40W.

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14. ### Audioguru Expert

Dec 20, 2007
11,167
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The Philips "LED Driver" does not say it limits the current to 280mA, maybe that is the max allowed load current that your LEDs exceeded. Its 142V output is much more than you need.
Maybe you did not cool the LEDs properly.