Protecting LED lights from overheating on
low-voltage (12/24) solar systems

 

Some LED lamps can overheat when used on 12 or 24 volt solar systems.  After a while the LEDs may start flickering or stop working entirely.  Fortunately, there are zero-EMF solutions available.

 

Keywords:   LED lamps, LED lights, hot, dead, overheat, flicker, 12 volt, 24 volt, off-grid, solar

 

The basic problem

LED lights are designed for a specific voltage, such as 12 volts or 24 volts.  Low-voltage solar systems operate at variable voltages, which for a 12 volt system goes above 14 volts when the batteries are nearly fully charged.  If the batteries are cold, the voltage may even exceed 15 volts before the batteries are fully charged.  This will also happen during equalization of the batteries.

 

When LEDs are run at a higher voltage they become very hot.  The heat can damage the LEDs, or the soldering around them, so they either start flickering, go dim or die entirely.

 

One dim and three burned-out LEDs in a lamp converted from use
with a 120/12 volt power supply.

 

This is both a problem for some LED lamps designed for off-grid use, as well as lamps that are converted.  The converted lamps are typically intended for grid power and have a little 12 volt transformer.  The conversion consists of cutting off the transformer and connecting the lamp directly to the house’s 12 volt system.

 

Solutions to the problem

Some LED lamps have built-in voltage controls which protect the LEDs and may also allow the lamp to work at lower voltages.  These types of systems use rapid switching of the electricity, which generates radio-frequency (RF) radiation from the lamp itself and from the wires (dirty electricity).  These technologies are not suitable for a low-EMF home.

 

A simple solution is to never run an LED light during the daytime, when the batteries are charged at the higher voltages.  At night, the voltage will be 13 volts or less and not a problem.

 

This author lost an LED porch light that was accidentally left on all night and through the next day, where equalization of the batteries raised the voltage above 15 volts.  Some of the LEDs then started flickering, even at normal voltages.  This lamp was designed for off-grid use and was not a conversion.

 

A better solution is to modify each lamp to limit the voltage going to the LEDs.  There are various methods to do that.

 

Insert a resistor

A resistor can be soldered into the electrical cord going to the lamp.  It can be done on either the positive or the negative wire.

 

You may need to try a few resistors to see what works.  I have used a 4 ohm 5 watt resistor for a few years on an LED lamp that has 42 LEDs and consumes about 10 watts.  The resistor gets quite hot, and needs air around it for cooling.  A resistor of a lower wattage would burn out, higher wattages will work but are more bulky.

 

 

 

A 4 ohm 5 watt resistor protecting an LED lamp.

 

A simple way to decide on how many ohms are needed is to buy a set of 5 or 10 watt resistors with a range of resistances, say from one to ten ohms, and try them out.

 

Check that the lamp is not too dim when the system voltage is 12.5 volts at night.  Check that the voltage across the lamp, with the lamp turned on, is no more than 13.0 volts.  This is measured with a multimeter, with one probe on minus and the other probe on the plus side, and on the lamp side of the resistor.

 

Using a linear voltage regulator

Another option is to use a linear voltage regulator.  They come as a single three-legged chip that is soldered onto the wires.  They cost a few dollars and are available from online electronic component sites.  I use the “7812” types, which are very easy to use and do not emit any EMF or dirty electricity (unless overheated).

 

The “7812” linear voltage regular.  The left leg takes the 12-16 volt
input from the battery.  The middle leg goes to minus and the right leg provides
12 volts for the LED lamp.

 

A 7812 chip mounted on the back side of the metal base
of an outdoor LED lamp.

 

The front side of the same outdoor LED lamp.  The screw holding the 7812
chip in place, and also transferring the heat, is seen on the base.

 

The voltage regulator may need a heat sink for cooling, depending on how much current runs through it and at which voltage.  In the pictures, the metal base of the lamp acts as the heat sink, though it never gets warm.

 

There are versions for 24 volts (“8624”), 9 volts (“8609”) and other voltages.  They can be used for lamps and other small electronics; just to be sure not to overload the chip, they can handle only an amp or so (12 watts).

 

There are general-purpose linear voltage regulators available (such as “LM317”) which can be programmed for any voltage with two resistors.

 

Linear regulators cannot create a higher voltage than the input.

 

2015