LM301B herb garden build

[Daisy Van Donk]

Hi guys, great forum! Thanks also to LEDGardener for his dedication to the cause. I don't grow weed but I'm surprised folks aren't converting to LED in their droves(!!)

Anyway this will be a fairly low powered, 70W rig as I want to use it to grow some lovely herbs for my kitchen through the long, dark Scottish winter months and the running cost can't exceed what I would pay per-month in the supermarket.

I plan to use Mean Well HLG-120H-C1400B (1400mA, 54-108V)

with 4* Samsung LT-Q562A , 2ft, 40 diodes, 4000k.

These will be USD 75 from arrow.com (including the 20% new customer discount).

I found these 300mm*25mm*12mm heatsinks for USD 2.30 each which seems pretty good. I wish I could find 600mm ones but no one sells them.

https://www.aliexpress.com/item/COTS-Al ... eLevelAB=0

I plan to drive the strips at about 700mA, so not the most efficient but pretty good and will give about 79 lumens per diode or
12,600 lumens total output (I suspect you can't just add them all up but I don't know how else to show it).

I chose the driver as it will allow me to run the light in 4S2P in the future if I want to expand my set-up. Until then it is a bit risky as I will use a potentiometer with the Mean Well "resistance dimming" to vary the current output and it would only take a slight overenthusiastic twist of the pot to blow the Samsung strips' 900mA limit.

So my question is...is it possible to wire a fixed-value resistor in series with a variable resistor to achieve the dimming? The fixed value to limit the driver's output to 900mA and then the variable-resistor to vary the output between 140mA-900mA? If so do you know how I might calculate the resistor values or is it a case of trial and error?

Here is the ghetto shelf I'll be using once I clear it out. It's the one with the ruler, 18 inches of vertical height which should be OK for a wee grow.

[LEDG]

Hi guys, great forum! Thanks also to LEDGardener for his dedication to the cause. I don't grow weed but I'm surprised folks aren't converting to LED in their droves(!!)

Anyway this will be a fairly low powered, 70W rig as I want to use it to grow some lovely herbs for my kitchen through the long, dark Scottish winter months and the running cost can't exceed what I would pay per-month in the supermarket.

I plan to use Mean Well HLG-120H-C1400B (1400mA, 54-108V)

with 4* Samsung LT-Q562A , 2ft, 40 diodes, 4000k.

These will be USD 75 from arrow.com (including the 20% new customer discount).

I found these 300mm*25mm*12mm heatsinks for USD 2.30 each which seems pretty good. I wish I could find 600mm ones but no one sells them.

https://www.aliexpress.com/item/COTS-Al ... eLevelAB=0

I plan to drive the strips at about 700mA, so not the most efficient but pretty good and will give about 79 lumens per diode or
12,600 lumens total output (I suspect you can't just add them all up but I don't know how else to show it).

I chose the driver as it will allow me to run the light in 4S2P in the future if I want to expand my set-up. Until then it is a bit risky as I will use a potentiometer with the Mean Well "resistance dimming" to vary the current output and it would only take a slight overenthusiastic twist of the pot to blow the Samsung strips' 900mA limit.

So my question is...is it possible to wire a fixed-value resistor in series with a variable resistor to achieve the dimming? The fixed value to limit the driver's output to 900mA and then the variable-resistor to vary the output between 140mA-900mA? If so do you know how I might calculate the resistor values or is it a case of trial and error?

Here is the ghetto shelf I'll be using once I clear it out. It's the one with the ruler, 18 inches of vertical height which should be OK for a wee grow.

Hey, another veggie grower

This should be a neat little project. Rather than run series/parallel in the future with the HLG-120H-C1400, I'd do either of the following instead:

1- Get a constant voltage 24V driver that can produce enough current to run all 8 and connect them all in parallel. If you got a big enough driver, you could run the initial 4 first, then slap the remaining 4 in parallel with them when you get 'em.

OR

2- Grab an HLG-120H-C700 and run your first 4 in series, then add the rest in series when you get the other 4. This way, you don't have to worry about overpowering them. I know the constant current region minimum for the 120H-C700 driver is 107V and you would likely only be around 96V with 4 in series, but I have found that these drivers are extremely forgiving on the lower side of the constant current region.

I was actually just messing with this yesterday and was running a single 36V COB on an HLG-480H-C2100 which is rated for a minimum voltage of 114V. The driver was providing 2100mA bang on the money without issue... WAY under its rated minimum.

If you decide to go with your original plan, the way you could set this up is to use less resistance. The driver needs to see at least 100K ohms on the dimmer circuit in order for it to put out full power, so if you wanted to limit it at say 50%, you would use a 50K ohm pot instead.

[Daisy Van Donk]

Hi LG, thanks for your explanation! I completely missed the fact the resistance of the pot will need to be less to run the PSU at half power.

Also fascinating that the Mean Well CC drivers perform WELL under their rated minimum voltage! I wonder why the rated minimum is so high then? Do you think it's possible that the efficiency of the driver might drop-off steeply below the rated voltage? If not it completely changes the game in selecting a PSU. It might be worth mentioning that in your article on driver selection if you haven't already as it's so handy to know.

Part of the reason I wanted the 1400mA driver is to be able to test the strips at 900mA. I'm worried that 4* strips at 700mA each will be too dim for growing. What do you think? I really just want to grow a few pots of herbs- basil, coriander/cilantro, parsley, and maybe some leafy veg. Also...I think my final question. If it were you, what spectrum would you run the 4 strips for leaf growth?

Thanks!

[LEDG]

Hi LG, thanks for your explanation! I completely missed the fact the resistance of the pot will need to be less to run the PSU at half power.

Also fascinating that the Mean Well CC drivers perform WELL under their rated minimum voltage! I wonder why the rated minimum is so high then? Do you think it's possible that the efficiency of the driver might drop-off steeply below the rated voltage? If not it completely changes the game in selecting a PSU. It might be worth mentioning that in your article on driver selection if you haven't already as it's so handy to know.

Part of the reason I wanted the 1400mA driver is to be able to test the strips at 900mA. I'm worried that 4* strips at 700mA each will be too dim for growing. What do you think? I really just want to grow a few pots of herbs- basil, coriander/cilantro, parsley, and maybe some leafy veg. Also...I think my final question. If it were you, what spectrum would you run the 4 strips for leaf growth?

Thanks!

Yeah - I'd imagine efficiency won't be amazing at only 50% load but the same goes for any driver. I'd mention it in the calculator but I don't want to get in trouble by making a blanket statement and telling people to go against the manufacturer's recommendations. In this case, however, I'm certain it'd be fine.

Here's an example of what these drivers can really do. I pulled up Mean Well's published test reports for a couple drivers and check this out. The 240H-C2100 is rated for a constant current region of 59V to 119V. The unit they tested was able to hold the rated current all the way down to zero volts!

MWCCR.png (175.93 KiB) Viewed 988 times

As for whether or not it'll be enough light, you're going to be running all 4 strips in the one shelf, correct? If so, I guarantee you that 700mA is going to be loads of light. You could flower under that much light in that small of a space. You'll need to turn it down even at 700mA because your plants are going to be right up in the lights in no time with only 18" of height. By the time you have little pots in there, they're going to be pretty pressed for space.

I'm running a shelf that's comparable in size to yours on about 65 watts and I'm growing bell peppers on it. Your lights should be running at the same power as me so I assure you that it'll work. I took a few measurements for shits and it looks like 12" from the sensor to the lights is a PPFD of about 450 which is more than you'll need for greens.