# Help me size an LED driver--I'm confused.March 10, 2017 12:24 PM   Subscribe

I'd like to build a shop light/tinker light out of cheap LED COBs, but I'm confused about how to size the driver. COBs have wattage, voltage and amperage ratings. To my understanding, to run 3 10w COBs, I would need a driver that puts out 30 watts. The voltage seems pretty straight forward, it's represented by a single number and the driver should be capable of delivering that. The amperage is where I get REALLY confused.

I understand that I want a constant current driver because otherwise the COB will draw too much and explode. I also understand that you can run COBs at different (within reason) amps and get more or less intense light. (Under- and over-driving (generally a bad idea) according to the grow light videos on YouTube.) My question: must my driver amperage match my COB amperage? IOW, if a COB is rated as 10w 36v 700mA, does my driver have to be rated 36v and 700mA, or can I get, say, a driver that has the correct watts and voltage but 5A? I believe I understand that the watts are divisible across the number of COBs I am running but there must be enough watts for every COB in a series.
posted by OmieWise to Science & Nature (3 answers total)

You will need slightly more amperage, but try to aim close to the total so the driver is running at or just below it's rating for best efficiency.
posted by nickggully at 12:32 PM on March 10, 2017

Based on your last sentence "every COB in a series" I'm assuming you are connecting the COBs in series. Therefore each of them will get the same current, so your driver current should match the COB recommended current, but the voltage and wattage of the driver will need to be 3x the individual COB numbers (108 V, 30 W). If you are connecting them in parallel it will be different, and you'll need to worry about thermal runaway and current sharing.
posted by doctord at 12:51 PM on March 10, 2017

Note that the number you really want to match is the current rating of the driver, for the voltage/wattage of the driver you need to be above the numbers shown above, not an exact match.
posted by doctord at 1:00 PM on March 10, 2017

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