With accordance to defined objectives for thermal management the following experimental development of Cooling COB LED was fulfilled.
In spite of big numbering of standard heat sink there are many difficulties to incorporate it in the LED fixture design with regard to right combination of efficiency, size, weight, shape in the fixture construction. Unfortunately just in a few simplest cases standard heat sink can be fitted to LED fixture without any customizing. This is reason why so many experiments have been done to figure out right solution in LED thermal management of MP Lighting Company.
The intensive prototyping for development satisfactory temperature regimes of LED fixtures was performed in different combination, for example:
- with different metal for heat sink (aluminum or copper),
- with various combination of dimensions and square of heat sink, shapes, height and interval of fins,
- with different kind of thermal interfacing between LED PCB itself and heat sink (thermal grease, thermal gaskets, etc),
- with compare passive and active (with fan) cooling system for LED fixtures with the same wattage,
- with variation of speed of fan for optimization of cooling efficiency and negative noise effect,
- with fitting and combination housing of LED fixture as integrated part of cooling system,
- with temperature sensors (thermistors) for measurement and controlling temperature regimes of LED fixtures.
All these experiments were performed on the solid base of temperature measurements on the main elements of LED fixture: LED PCB itself and mostly hot spots of LED lamp housing. Thermo couples were used as temperature sensors and 8-channel data logger OMEGA was used as recorder. All temperature changing during of experiments were monitored and recorded in real time in OMEGA format files. The creation of data base of thermal management was started as 50 OMEGA files represented LED.
The main conclusions from thermal management experimental development are followed as:
- The packaging on the base passive cooling system could be done only for the lighting fixture with low wattage (3 – 5)Wt, but even in this case the extending metal elements contacted directly with LED PCB is highly recommended. In such a way of additional dissipation of heat we can expect to keep LED PCB temperature at least (50-55) degree Celsius.
- Having analysis of LED we can say that minimal surface square per 1 Wt for dissipated heat could be roughly specified as 20 (cm x cm) so that passive cooling system for the lighting fixture with wattage (12 -50)Wt and up to 100 Wt requires very extended metal surface with good heat contact with LED PCB. This requirement could be satisfied not only by means of appropriate heat sink (with reasonable size and weight) but with right combination heat sink itself with extended metal elements of housing of power LED fixture. So, the design of metal housing for powerful LED fixture is becoming very significant .
- On the base of information (i.e. 2) the new profile of aluminum extrusion has been designed in our company. This profile will be used in manufacturing LED lamps (linear type) with wattage (30 – 40)Wt per each unit and it should be provide the integration LED PCB itself with extended metal parts ( covers, conductors, etc) of housing of fixture.
- Another way for improving thermal management of power LED fixture is active cooling system on the base intensive heat transfer from LED PCB (fan, heat pipe, thermo electric battery). Series of experiments in these directions were performed in our R&D Lab.
- The fan in combination with heat sink increases the efficiency of cooling system dramatically (for example, fan with wattage just 5% of output wattage of LED lamp capable to reduce the temperature of LED PCB on 24 degree Celsius to compare with passive cooling system). However some actions have to be done to avoid negative noise effect from fan.
- As a results of our LED we have found that noise effect from fan can be reduced by means of its speed automatic controlling. The control loop with thermistor as temperature sensor capable to run fan with lower speed (and noise also) depend on temperature regime of LED PCB. This cooling system has been prototyped and tested in our company and its realization was recognized as patentable.