# How to keep amperage in serial and parallel?

I have a 2000mA AC adapter and also I have the lights that I show here:  Each of these lights consume up to 300mA.

If I make a circuit with 3 lights in serial, ¿will the amperage of each light decrease?

If I make a circuit with 3 lights in parallel, ¿will the amperage of each light decrease?

I am asking it because I don't want the lights to decrease the luminosity. I want the maximum luminosity in each light.

The lights are for growing lettuces. Now I am using a low consumption light but are not efficient: You haven't said what the voltage rating of your Power Supply is, but if we assume it is a "constant voltage" regulated supply, then it will attempt to maintain a constant voltage up to the rated current capacity (2000 mA).

If you put your LEDs in series, then the voltage from your power supply is distributed across the LEDs, and is therefore lower on each LED. This would cause your LEDs to be less bright.

If you put your LEDs in parallel, then the voltage remains constant.

• The power supply convert from 220v to 12v. Your answer confirm what I was thinking about voltage, but I would like to know about the amperage. Oct 28 '16 at 14:27
• The other answers by Gerben and Majenko correctly note the requirement to limit current to avoid destroying your LEDs. If you don't limit the current on purpose, the LEDs will dissipate more power than they are designed to and will die. Oct 28 '16 at 14:33

The simple answer to that is "No, and stop right now whatever you are doing."

Those LEDs, because of their high current requirements, need a constant current driver.

First a little theory:

• LEDs in series sum the voltage, the current stays the same.
• LEDs in parallel with no form of current management split the current unevenly and LEDs start dying (or even exploding when you have high currents involved).

If you don't want any control over the brightness then the simplest constant current driver is to use an LM317 voltage regulator wired in constant current mode.

It is also possible to make a constant current sink (the same as a constant current source but between the LED and ground instead of positive) using discrete components.

If you want control of the brightness then the best solution is to use something like the CAT4101 PWM LED driver.

Why don't you use a simple resistor like you would for any other small LED? It's quite simple. Both resistors and LEDs characteristics change with heat. When you are using higher currents like this both the resistor and the LED give off heat (more so the LED than the resistor unless you pick too small a wattage). That means you get changes in the characteristics, which means the current you originally calculated for is now wrong - typically the current increases above what you had originally calculated. More current means more heat. More heat means more current. The result: a cascade. Worst case? The LED dies.

If you put them in series the they require 300mA, but you'd need to have a higher voltage (around 10 Volt).

If you put them in parallel, you could keep the same voltage as a single led (around 3.3 Volt), but you'd require trice the amount of current (i.e. 900mA).

You however need to add proper current regulation, of you'll burn out the leds. The advantage of having the leds in series, is that you only need a single constant current driver.

You could use resistors, but since these leds require that much current, the leds will have to dissipate a lot of heat. Which is both wasteful, and requires special high wattage resistors.