Edinburgh Hacklab

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====== COB Grow Light ======

**Status**: Complete\\
**People**: River\\
**Last Update**: 21 May 2022

{{ :cob_grow_light.jpg?600 |}}

I bought a COB LED module from aliexpress for 1.45. It claims to be a "full spectrum" grow light, and 50W. 

I soldered some wires onto the aluminum board using the hot plate as a preheater and finishing with a soldering iron. Earth connected to heatsink with an anti-shake (jaggy) washer to get some bite through the aluminium oxide. Earth is critical as live only separated from heatsink by microscopic dielectric layer on board.

I fitted it to a heat sink with thermal tape and laser cut a cover which slotted into the heatsink.

It appears to contain an array of 8 x 9 = 72 LEDs. If they were 3V each, that would require 216V. The integrated driver is a bridge rectifier and linear current limiter. It draws about 200mA when turned on, which declines as it heats up. I got bored watching at 165mA. Voltage was 238V, power factor unknown. Multimeter not True RMS. It was sold as 220V, so probably getting hotter than ideal because we can have up to 253V here by spec., and I often see 250V. Considered using a capacitive dropper to save power / heat, but it would need about 27uF X2 cap to take 240V down to 220V, which exist, but are rather expensive.

I've been using the light for a week or so now. It gets hot - too hot to touch, at about 75C with ambient ~25C, but not too hot for the electronics I think. Efficiency seems questionable.

Otherwise it seems to work well. It is pink. I thought there might be a selection of LED colours in the array, but they all look the same.

{{ :cob_banding.jpg?600 |}}

The camera shows the flicker from the unfiltered bridge rectifier. You can also see some of the LEDs in this image.