# Requirements for dimmable LED driver

I bought a new LED aquarium light and the driver that came with it is not working. I want to buy a replacement driver but I need a better understanding of the driver requirements before I can make an informed purchase.

The driver that came with the light has an output of 48v/700mA and it's dimmable via a 1-10v input, all that's written on the light is that they are 45W (15*3W).

1. The original driver only outputs 33,6W, isn't it best to have a driver that is working at no more than 80% capacity?
2. If I wanted dimmer light could I buy a driver that has say an output of 48v/500mA or would that stress the driver? Isn't that how a driver with a dimmer works anyways; lowering the amps?
3. I connected the light to the strongest power supply I have at hand which is 12v/5A, when I connect this the light only barely lights up. In terms of wattage this power supply should be sufficient so obviously voltage is important here, why is that?
4. Do I need 48v minimum?
5. I found a driver with dimmer that outputs 30-36V/0-1,5A does that mean the knob will adjust both voltage and ampere simultaneously?
6. If I want a dimmable driver do I need one with constant voltage that only adjust the amps?

Feel free to only answer the question(s) you want.

• @TonyM Done. Someone has already given a seemingly complete answer anyway so my fears are probably unwarranted.
– pipe
May 21, 2017 at 15:07

1) LED drivers work differently, not with power but with current. I expect that the old 33.6 W driver outputs 1 A (of current) and up to about 36 V. You have to use it with LEDs which can handle 1 A or more. If the LED is 1 A, 20 W then the driver will supply 20 W to that LED since the current is limited to 1A. Both LEDs and drivers should operate below their maximum rating (of course).

2) Correct, halving the current to 500 mA will indeed lower the power. Now that 1 A 20 W LED would run at 0.5 A and use about half the power. That does not mean the light output is also halved, many LEDs are more efficient at lower currents so you might get 60% of the light instead of the 50% you'd expect. Powering a 20 W LED at 10 W will increase its lifetime and reliability a lot assuming you keep it cool that is. Heat is a LEDs enemy !

3) LEDs need a certain voltage, in this case much more then that 12 V. So your "powerfull" 12 V 5 A supply cannot deliver the power to the LEDs. The voltage is too low for the LEDs. This supply is constant voltage (12 V), for LEDs you need constant current. Constant voltage supplies are very much unsuitable for most LEDs. Only 12 V LED strings (for decoration) can use a 12 V supply.

4) Depends on the LEDs. Most LEDs modules I've seen are 36 V nominal, that's about 10 LED chips in series. Don't pay too much attention to the maximum voltage, the current is more important. I expect that 44 V max is often enough.

5) Depends on the driver. But controlling the voltage with LEDs is impractical, like mentioned above, LEDs need to be driven by a current, the voltage is largely irrelevant. A LED can be dimmed by controlling the current. But a nicer more controlled way of dimming a LED is done by using PWM (Pulse Width Modulation). It means switching the LED on and off quickly, for example 400 times per second. Human eyes are too slow to see that but some animals can see that. I would avoid a PWM based controller for an aquarium.

6) see 5) as I said, forget about the voltage, it is the current (which is measured in Ampere) which matters.

If you'd use a voltage to dim a LED, the light output would vary over temperature, age and whatnot of the LED. When using current control this is much less an issue, light output is much more predictable and controllable. This has to do with the Voltage/current behaviour of a LED.

• Thanks for the reply, I'm less confused now, however, if you could clarify a few things in reference to your answers: 1) The original driver had rating of 48V/700mA, I assume you missed this and used 1A/20W as an assumption? Did you mean to write 20V and not 20W? As in the driver will supply 20V (out of 36V) since usage is max 20W (at 1A)? Perhaps we can guess from the original driver that the LED's can handle max 1A/45V (45W) but is limited to 700mA as to not run LED's at maximum capacity and this will also keep voltage below 45V even though the driver is rated for 48V (see 3)). May 21, 2017 at 10:46
• 1&2) "Both LEDs and drivers should operate below their maximum rating (of course)." Isn't this a paradox? If I use a high output driver the LEDs will run at maxiumim capacity and if I get a low output driver the driver will run at maximum capacity. May 21, 2017 at 10:46
• 3) I think I understand this: The 12V/5A driver can't light the LED's because even though it's rated for 5 Ampere it can't supply this current because of it's maximum voltage of 12? And reversly if current is capped then the voltage is descreased as well? Perhaps this is the difference between constant voltage and constant current, i.e. what is capped/the bottleneck: voltage or current? May 21, 2017 at 10:46
• 5) So constant current means the driver will always supply X amount of current and the voltage is simply adjusted as a means to reach that X amount of current? Hence ratings like "18-33V". May 21, 2017 at 10:46
• I did not miss the 48V driver, my 1A/20W was just an example. Did you mean to write 20V and not 20W NO as I wrote many times: the voltage does not matter so I wrote 20 W and I meant 20 W. No there's no paradox. It just how LEDs work, A LED is rated for a certain power which it will have at a certain current. Forget about capacity !! It is the current which matters. the driver will always supply X amount of current and the voltage is simply adjusted Yes, that is very important ! Remember that and forget about capacity/voltage etc. They're not relevant. May 21, 2017 at 15:59