Transformer for LED Lighting

Did you used the correct formula to calculate the transformer current ?.

What exactly is written on the transformer ?

Did you actually measure 5A in the primary? If so, I'd be very surprised.

Your math is correct, more or less. But the amount of current delivered by the transformer will depend on the load. To get 100A out of it, you would need a 0.12Ω, 1200W load on the output, which I'm guessing you don't have.

If you're getting 500ma, you probably have a 24Ω load.

If you are actually measuring 5A going into the primary and 0.5A on the secondary, you have a bad transformer, and you need to get a new one, because this one is about to catch on fire.

Are you sure the transformer says 5A and not 5W? Because 5W would be just about right for what you are describing.

The resistor will blow up I have done it. LOL

5 amps is the rated input current that transformer can handle without any burnout at 230volts input, from there you came to figure of about 100amps at 12 volts of output.

Where as 500mA you measured is the actual current drawn from transformer by lighting.

This means you can put about 200More similar light on the same transformer and it will serve you without any trouble.

Or in other word you should choose a much smaller transformer for this light.

Note 500 mA is the drawn current and 100 A is the maximum current you can draw from it.

Think of a your home water line that is connected to main water line passing out side of your house.

Regards.

Replies from Mr. rajeshbhanushali123 awaited to all the replies by posters.

Indeed ... As long Mr. or Ms. rajeshbhanushali123 does not give us more info, we can assume anything !... Maybe he read wrong and there is not 500mA on the label, but 500MA .. In that case ....

All the LED lighting systems I have see or installed use a constant current driver rather than a transformer with multiple LEDs wired in series up to the maximum driver voltage drop. If you allow the current to rise above the rated value for the LED you will destroy it. Be very very carefull you will not get a second chance.

Good luck

But which driver is used? I connected four leds in series with 12v stepdown transformer directly & it is working also.But the current from transformer is 500mA.Input 230v/5A

It all depends as usual the devil is in the detail. To illustrate the point I have a new installation of 11 off 9W LED assemblies, each one has a light output better than a 35W and approaching the that of a 50W Halogen Diachroic, driven by 4 off constant current drivers rated at 36VDC at 0.7amp These are expected to last 25 years. I also have another smaller lower cost installation of 3 off 1.8W LED units suitable for under unit lighting in kitchen driven by a single driver rated @12VDC and 1.25amp which are expected to last 10years. The manufacturers of both sets insist on constant current drivers to maintain the warranty conditions i.e. if you don't use one they won't replace when they fail. The life times are both based on the same operating regime, same hours/day, same days/year etc.

Without knowing the spec of the LEDs being used it is to possible to advise further.

Comment like this got good reply

The current for LED should not be more than 15mA if you want LEDs to last long(50000hours?).

I understand in LED lighting, the current is designed upto 50mA, but then life is reduced. If your measurement shows 500mA, the life should be very low. What is your observation? Please let me know, since I am also interested in this and want to install at my house.

I was desided to install the whole circuit using bridge rectifire & RC Filter.And also got the current 20mA In out put.But my one friend told me it can work without that circuit. My another que. Is in the list of my topics.Its xformer & xformer1.Can u plz answer that.

I did not get your other question, what was that?

U just go to my profile & check my posts u will get it.

Actually, this is for common garden variety LED's, i am using some at work that run off 350mA, with 500mA recommended and 750mA burst.

These LED's don't light at 20mA.

Another consideration for LED's is that they are not cold light sources, some generate alot of heat, and this heat must be catered for in your designs

Thanks, this is news to me. Somehow I thought that all white LEDs are same. Any more details available on these LEDs like light output Vs power consumption, voltage drop, heat generation would be useful to design LED lighting.

Rajesh

The device I'm using is a Osram LW W5SG - Golden Dragon

Am now at work, I can read the datasheet ;o)

Forward Current (T_a=25 Deg C) = 500mA

Surge current t<= 10uS, T_a=20 Deg C = 1500mA

Thermal Resistance (Junction/Solder point) = 9 K/W

Forward Voltage (I_F = 350mA) =3.8V (typ.)

Optical Efficiency = 21 lm/W (typ.)

Oh great, cut/paste, the top cells shifted left 1 place.

Thanks for the information, I will try to procure these. Sorry for the delay in response. Could not go through personal mails for quite few days.

Rajesh Salaskar