LED driver - critical match?

[Lionel44]

Hi guys, can you tell me how critical it is to match the wattage of an led driver to the down light it is driving. Can I match a 7w lamp to a 15watt driver? or 2 x 7watt lamps to a 15watt driver? what is the tolerance of these things?

 

[Harald Kapp]

The driver max. power needs to be higher or equal to the load power. SOme headroom, e.g. 10 %, is a good idea.
Do not provide too much headroom as the driver's efficiency will be reduced if the load is too small (compared to a drievr that matches the load better).

what is the tolerance of these things?

hat should be stated un the datasheet - or at least the max. values.

 

[(*steve*)]

Many led drivers are constant current supplies. It is important that you match the load to the power supply.

Such power supplies will typically have a minimum voltage output (that defines the minimum load that can be correctly driven), and a maximum voltage that represents the maximum load.

A 10W driver could deliver 300, 700, or 1000mA, and have a maximum voltage of 33V, 14V, or 10V respectively.

The first consideration for the load (the LED) is it's rated current. A device rated for 300mA will not be suitable for any driver other than the first. However, one rated for 1000mA may be able to be used on any of these drivers.

A 300mA 5W lamp may operate correctly on the first driver, presuming that the driver can cope with the lower voltage output. The driver may specify this as a voltage or a minimum power.

A 10W lamp rated for 700mA may operate from the first driver, but with a lower output power sure to the lower current.

A 20W lamp designed for 700mA could only be used on the first driver.

Determining what LED devices can be used with which driver is not trivially simple, and it is best to go with a recommended driver and LED pair rather than trying to cobble something together yourself.

 

[Lionel44]

The driver max. power needs to be higher or equal to the load power. SOme headroom, e.g. 10 %, is a good idea.
Do not provide too much headroom as the driver's efficiency will be reduced if the load is too small (compared to a drievr that matches the load better).

hat should be stated un the datasheet - or at least the max. values.

Thank you

 

[Lionel44]

Many led drivers are constant current supplies. It is important that you match the load to the power supply.

Such power supplies will typically have a minimum voltage output (that defines the minimum load that can be correctly driven), and a maximum voltage that represents the maximum load.

A 10W driver could deliver 300, 700, or 1000mA, and have a maximum voltage of 33V, 14V, or 10V respectively.

The first consideration for the load (the LED) is it's rated current. A device rated for 300mA will not be suitable for any driver other than the first. However, one rated for 1000mA may be able to be used on any of these drivers.

A 300mA 5W lamp may operate correctly on the first driver, presuming that the driver can cope with the lower voltage output. The driver may specify this as a voltage or a minimum power.

A 10W lamp rated for 700mA may operate from the first driver, but with a lower output power sure to the lower current.

A 20W lamp designed for 700mA could only be used on the first driver.

Determining what LED devices can be used with which driver is not trivially simple, and it is best to go with a recommended driver and LED pair rather than trying to cobble something together yourself.

Thanks Steve.
the mr16 lamps I buy on ebay (china) only give specs as 7w,9w, 12w etc and all at 12volts dc.
I am confused with this 'constant current' thing. is there any connection to Ohms law?
How does your 10watt constant current driver vary the current dependant on the wattage of the lamp?.

 

[Bluejets]

Can you provide a link to the particular lamp you are using.
If it is the particular MR16 lamp I'm thinking of with inbuilt control, it can be simply run off the old MR16 dichoric transformer.

 

[(*steve*)]

I am confused with this 'constant current' thing.

This type of driver is used for LEDs without inbuild controllers

the mr16 lamps I buy on ebay (china) only give specs as 7w,9w, 12w etc and all at 12volts dc.

These are likely to have their own internal driver. All you need for these is a 12V power supply as mentioned above. In this case, the voltage needs to match and the total of the current (or wattage) must be less than or equal to the maximum current (or wattage) of the power supply.

Many MR16 type LED bulbs will work from a variety of voltages, but it is best to stick to something as close as possible to what is recommended.

 

[Lionel44]

Can you provide a link to the particular lamp you are using.
If it is the particular MR16 lamp I'm thinking of with inbuilt control, it can be simply run off the old MR16 dichoric transformer.

Thanks, sorry I haven't got that far yet

 

[Lionel44]

This type of driver is used for LEDs without inbuild controllers



These are likely to have their own internal driver. All you need for these is a 12V power supply as mentioned above. In this case, the voltage needs to match and the total of the current (or wattage) must be less than or equal to the maximum current (or wattage) of the power supply.

Many MR16 type LED bulbs will work from a variety of voltages, but it is best to stick to something as close as possible to what is recommended.

Thanks again