LED dimmer

[ninja.turtle007]

I'm thinking of installing a 27w 12v LED light. If I use a remote dimmer will the watts drawn be constant or will they decrease as the light is dimmed?

Dimmer m.ebay.co.uk/itm/360837477632?nav=SEARCH&sbk=1

[billybigspud]

The only thing that can be affected in a dc circuit is amps or volts and if one goes up, the other goes down keeping the wattage the same.

[nicq]

Ohm's law states v x a = w
V volts
A amps
W watts
27 w led is massive be like a search lamp

[itchyfeet]

LEDs are semiconductors and so don't behave the same as resistive dc devices
They need a certain amount of voltage to illuminate and they are usually dimmed by varying the current on a constant current power supply (voltage stays approximately steady)

Another method of dimming is pwm or pulse width modulation where they are pulsed at a fixed current and the ratio of on to off pulses dictate the dim level

To complicate things there are 12v LED devices, these have sets of LEDs in series with a resistor which acts as a current limiting device, these are dimmed by pulse width modulation with the fixed voltage pulsed on and off

So in short yes it should reduce the power consumption or watts drawn

[ninja.turtle007]

Thank you for the replies.

So basically with the light dimmed my batteries will last longer?

[itchyfeet]

Yes

[nicq]

I have an led dimmer and the total current draw changes insignificantly with light output, in fact it draws more connected up than if its not in line. Maybe the unit is not efficient. All you can do is try it.
If you are using modern ribbon Led,s they draw so little current you really do not need to worry.

[itchyfeet]

I have an led dimmer and the total current draw changes insignificantly with light output, in fact it draws more connected up than if its not in line. Maybe the unit is not efficient. All you can do is try it.
If you are using modern ribbon Led,s they draw so little current you really do not need to worry.

Oh dear that's not good
Do you have a link to this dimmer?

[nicq]

No bought on eBay over a year ago.
Draws 50ma. Without any load.
Strips of leds draw less
I am sure if you bought a good quality unit it would be different but to get cost down I don't think efficiency is high on the list of priorities.

[itchyfeet]

Yes all electronics will have an inefficiency 50 mA at 12v is 0.6w that's to be expected even without load

If your leds use less then they must be very low power op is talking about diming 27 w so the odd watt for the dimmer is worth it

[nicq]

The point is how much power are you going to save if any.
You have to have Mega amounts of leds if you reduce o/p by 25% to cover a 50ma loss in the box.
Its still nice at night if you want a dim light in the early hours.

[CJH]

The point is how much power are you going to save if any.
You have to have Mega amounts of leds if you reduce o/p by 25% to cover a 50ma loss in the box.
Its still nice at night if you want a dim light in the early hours.

LEDs are good, but not THAT good. Even the lower power SMD3528 strips seem to be rated at about 5W per metre, which is about 400mA. So a 25% saving would be 100mA. Per metre.

[California Dreamin]

I was going to add that a dimmer is basically a resistor, resistors get hot....the heat is wasted electrical power.

Martin