The original Grow Light project is reportedly working very well. It’s encouraging enough that I’ve gone ahead and designed and ordered the parts for another one. This time, I’ll use a new driver chip that can handle the full amperage that the Led Engin LZ1 5-watt LEDs can use.
Here’s the expected artwork, this image is generated from the design files:
The colors represent the ENIG (immersion gold) plating, white soldermask paint drawn slightly translucent so you can see the copper traces underneath, and black silk screen paint. The beauty of this design is that it’s on a single layer of copper with no jumpers. This is possible as I’ve scrapped the non-working soft-start circuit. It does include the power supply for the heat sink fan. Here’s the board as designed in Eagle CAD:
Here is the schematic. Not much has changed other than the STCS2A driver. There’s plenty of ESD protection, and a couple of optional diodes in case I want to change some of the LEDs.
It will use 5 LedEngin Deep Reds, and 2 LedEngin Blues for each of 4 strings. That’s 28 LEDs, 20 red, 8 blue. This is different from the first grow light in that I’m going straight color, the first one used a white LED in each string to give the light a little more ‘human’ color. The strings will run at (0.1 mV/0.068 Ohms) 1.47 amps each, or 6A total. That’s top end for these LEDs, so I’m running right up to the red line. The red LedEngin LZ1-00R205 LEDs drop 3.1V at 1.5A, the LZ1-00B205 blues drop 3.8V, so each string will need 23.1V. Add 1 volt for the power diode, and 0.5 volt for the STCS2A overhead, and the circuit
will should run optimally at 24.6V. The circuit board contains test harness connectors for each of the strings so I can try out my new test wand. The whole thing should use just under 150 watts.
The spare parts were $35, the LEDS were $240, the boards are $220, the heat sink will be a Scythe Big Shuriken at $40, the power supply will run $40, altogether about $600 in parts and machining. The LEDs are over $8 each, but they are right on the frequencies for horticultural usage and there really isn’t a substitute. Sure, there are other blue and red LEDs available, but the purpose isn’t just to make a purple lamp… this is to make one that plants will eat. So far the reported results are very encouraging, but this lamp will add another 50% amperage to the LEDs, which should correspond to a 17 – 25% increase in luminosity. I can dump the 0.068 ohm current sense resistors for slightly higher values if the lamp does in fact get too hot, or it doesn’t appear that the difference is worth the extra risk.
I got heat sink for new lamp and it’s nearly perfect . Slightly modifying the clips holds the board firmly to the PC board.
PCB Cart will ship the boards on the 21st, and all the parts are here, so just have to wait a week.
The boards arrived on Tuesday the 22nd. This is the real thing as manufactured per specs in the image above:
It took me until yesterday to figure out the problem with the Laser Engraver so I could make a soldermask stencil.
This shot came out cool (IMHO):
It works. It’s only taking 75 watts at calculated voltage, but if I turn the power supply up all the way to 26.x volts, the holding voltage on the source pin goes up a little and it takes 120 watts. The LEDs are dropping a little more voltage than I thought and the power supply needs to be a little higher. Switching out one more blue for a red should make this circuit work well. I’m burning it in a bit while I think up a housing.
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