I build a set of "grow shelves" for growing cacti on a budget

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Download
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I build a set of "grow shelves" for growing cacti on a budget

Post by Download »

Over the last few weeks I have been putting together some new grow lights for my cacti. I have previously built grow lights before, and having encountered several pitfalls previously decided to incorporate that into this new build.

Concept:

Grow shelves, being a shelving unit with lights fitted to each shelve and then suitably enclosed to trap heat and reflect light. This better utilises space given that cacti don't normally grow tall very quickly. Most grow lights are orientated towards "other plants" where having extra heigh and space for bushiness is desirable.

The lights:

For this I used COB LEDs.

COBs (chip on board) are small ceramic or metal chips on which large arrays of LEDs are mounted. They are some of the most efficient lights sources available on the market, with some stretching past 180 lumens per watt. For comparison, the best incandescent bulbs do less than 20 lm/W, the best fluorescent tubes do 50 to 100 lm/W and household LEDs normally do about 100 lm/W. The higher the luminous efficiency, the more light you get for every unit of electricity consumed.

The problem is that packing all these LEDs into a little square causes heat issues, and LEDs do not like high temperatures. So, the COB LED must be mounted on a suitable heat sink. There are many heat sink designs out there and the LED must be paired with a heat sink that has sufficient cooling capacity. Previously I purchased new heat sinks, but they were costly. This time I went on eBay and found a store selling used computer parts. From them I purchased 6x 1U server heat sinks for $5 each.

For LEDs, I decided to pic LEDs made by Cree, who are generally regarded as producing quality high-power LEDs. For low cost, pick a larger COB size. Smaller COBs are advantageous for things like studio lighting, but offer no benefit here. I chose Cree's CMU2236 series of LEDs, which are 28x28mm in size and rated for 95 W each at 184 lm/W. For cacti you want as close as possible to real sunlight, so I picked the highest temperature COBs in stock, which are 4000 K with a CRI (colour rendering index - how closely they replicate natural light) of 90%

You also need a COB holder to secure the LED to the heatsink, a fan to cool the heatsink and a suitable mount. Mine are slightly ugly, but functional. In future I think I'll get myself a 3D printer and make nice looking mounts for everything.

Image

The Shelves:

I went to my local Bunnings (the Australian equivalent of Home Depot) and purchased a 540x1200mm five tier shelving unit. But at 2100 mm high, five shelves would have been a bit tight, so I assembled it with four shelves (only three usable for this project). I then purchased 3mm HDF sheeting and used PVA glue to attach household alfoil to it. These were then attached to the shelves to make sides. The soil helps reflect light, reducing wasted light.

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(Ignore the strange middle shelve. The way the shelve is assembled requires some modification to convert from 5 to 4 tier which I won't cover here.)

Electronics:

If you don't know what you are doing with electricity, seek expert advice. I have a note down below for doing this without any electrical wiring, that is far safer. It is also more expensive and less neat looking, but I strongly recommend that route if you do not have experience with mains electricity.

You can't generally run LEDs direct on mains electricity. Instead, you need an LED power supply that carefully controls the voltage and current supplied. I personally recommend power supplies made by Mean Well. They are very popular among the normal grow-light using crowd, are well priced, are very efficient (above 95% in larger models) and come with a seven year warranty.

For this I selected the HLG-240H-36C power supply. It takes 90 to 277 V in, and outputs 33 to 40 V in both constant current and constant voltage mode (I won't explain how that works or what that means as it's covered in the manual) at 240 watts. For this I chose to purchase two 240 W models instead of a single, larger HLG-480H-36 (480 W) as this allows me to have two separate lighting circuit and control the brightness of each circuit separately.

I should note that you probably won't be able to purchase the HLG-240H-36C PSU as it's normally a made to order product with a minimum order quantity of 200. I just got lucky and managed to grab the last two available on Mouser. Not sure how they got there, but I assume someone ordered them and then cancelled. If you decide to replicate what I have here, you can purchase the HLG-240H-36A (or other "Type A" HLG series power/voltage combination), which is identical except that it has wired connections instead of terminal connections, or purchase the Type AB which is the same as the Type A except with external dimming.

I also required a 12 V power supply to run the heat sink fans and other items. For this I purchased a small, 25 W chassis mount PSU.

As cacti don't like 24 hour daylight, I needed a suitable timer. I also required a thermostat to turn on/off heaters. The issue with both of these items is that they were single pole devices (i.e. they switch on/off only one wire, when I need to switch on/off two connections; one for the live and one for the neutral wire). So I also required two double-pole 250 V, 10 A relays.

I had a suitable electrical box laying about, so I decided to put everything in the box. Here is is partially assembled:

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The silver boxes left and right are the LED PSUs. Top is the chassis 12 V PSU. Bottom right is one of two relays. Left is the timer module.

Here is the final assembly:

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The front with the timer and thermostat:

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Assembly:

I personally recommend attaching the LEDs and doing most of the wiring with the shelving boards upside down, and then flip them over. This is way easier that trying to wire everything upside down. Once that is done you can wire from each shelve to the PSU etc.

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In this image you can also see the silver cable of the thermocouple for the thermostat. As there was already a hole in the back of the box it seemed convenient to put the thermocouple through there. The power board going out of the box is for the shelve heaters. As they are 250 V mains, I decided that they would use standard plugs with mains compliant cables.

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This is the thermocouple. It's 300mm long, and that's because I had a bunch of 300mm thermocouples laying about. I'd suggest a smaller thermocouple if you are buying one.

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For heaters, I use underfloor heating cable which I have suspended from the roof of each shelve. It's cheaper than heater mats and they don't break easily like those ceramic heater globes do.

Final Result:

I used 0.5mm vinyl sheeting to waterproof each shelve (not easily seen in the image). There are also front covers made from the same 3mm MDF with alfoil on them. They have pins that go through the shelving holes and are then bungee corded to keep them in place, but you could easily make proper doors for them if desired.

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Parts and Calculations:

Each COB is running at 80 watts and produces 180 lm/W, or 14400 lm, with two per shelve. Each shelve has an area of 1200 mm x 540 mm, or an area of 0.648 m^2. This produces an average of 44000 lm/m^2 (or 44000 Lux).

Power is ~30c/kWh where I live. At 12 hours per day and 480 W total power, this setup costs ~A$1.70 per day in electricity. I can probably reduce costs by taking advantage of a floating power cost billing, as the shed where this grow shelve is is on a separate meter, which is something I am investigating.

LED parts and prices:

Mean Well HLG-240H-36C - A$115 - A$230 for two.

BJB 47.319 Series COB holder - A$4.24 - A$25.44 for six.

Cree CMU2236-0000-000N0U0A40G - A$11.08 - A$66.48 for six.

Qualtek DC FAN 60x20mm 12VDC Fan - A$6.90 - A$41.40 for six.

MEAN WELL 25.2W 12V 2.1A PSU - A$18.93

A$410 total

These were all purchased from Mouser.

The timers and thermostats I already had, but can be purchased on eBay or Aliexpress for ~$10 each. Relays came from a local electronics place and cost ~$15 each. The miscellaneous electrical parts I already had on hand probably cost $50 to purchase new.

The shelves were A$110.

All up, it was about A$600 to A$650.

The Safer Way:

I chose to do it the way I did because I am familiar with Australia's electrical code and have previous experience doing this. I have chosen not to provide a wiring diagram because if you need one, then perhaps you shouldn't be doing mains electrical work.

Instead, I will point out that you can buy LED power supplies with cords and plugs already attached to them. You can also buy timers that you can just plug into the wall and plug your PSU into. You can also buy similar thermostats designed for reptile enclosures and the like that you can plug heater mats (or other heater devices) into. This allows you do do this without any mains voltage wiring involved. Yes, you will need to do low-voltage wiring, but that's generally quite safe.

If you have questions about the low voltage side of the wiring, I am happy to help. If you need help with the mains side, please don't. At the very least, hire a local professional.
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jerrytheplater
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by jerrytheplater »

Yikes, I'm taking a break from working outside and started your post, but see I'll have to come back to it. Very detailed, is very good.
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
keith
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by keith »

interesting. Is it one COB per Shelf ? AU voltage is twice USA voltage so 220V to your Power supplies ? Whats that glass bulb bottom of electrical box that looks like a cord is plugged in ?

I just finished a low voltage power supply design very low power compared to a House wired circuit like your setup. Looks very neat all the wires nicely arranged and crimped to terminals I think ? I would probably just use the power cords option attached to the regulators ( power supplies) but I guess that depends on where the shelf goes.

LED lighting is pretty amazing
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jerrytheplater
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by jerrytheplater »

Really great. A friend of mine that is a member of the Aquatic Gardening club I belong to made a bunch of LED lights for his aquariums before they were easily available for purchase. He also used CREE LED's. At that time, you could buy them directly from CREE. Now you have to go to suppliers. He ended up selling his home and moving to Arizona, so he sold all of his equipment. I bought a 4 foot long light from him. He has a nice build article on our club website for the light I bought from him. This is the link http://www.njagc.net/wp/articles/cree-x ... ium-light/

A few questions.

What about heat in your electrical box containing the LED power supplies? Concerns? Fan needed?

What is the purpose of this build? To provide an overwintering place for tender cacti?

If I understand your write-up correctly, you have a cover/door to totally enclose the area containing the cacti. Correct? If so, what about air circulation in there?
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
Download
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Location: Adelaide, Australia

Re: I build a set of "grow shelves" for growing cacti on a budget

Post by Download »

keith wrote: Sat May 21, 2022 5:17 pm Is it one COB per Shelf ?
6 COBs, 3 shelves.
AU voltage is twice USA voltage so 220V to your Power supplies ?
Almost everywhere is 220V/240V/250V. The North America is the odd one out there.
Whats that glass bulb bottom of electrical box that looks like a cord is plugged in ?
A plug socket.
jerrytheplater wrote: Sat May 21, 2022 9:43 pm Really great. A friend of mine that is a member of the Aquatic Gardening club I belong to made a bunch of LED lights for his aquariums before they were easily available for purchase. He also used CREE LED's. At that time, you could buy them directly from CREE. Now you have to go to suppliers. He ended up selling his home and moving to Arizona, so he sold all of his equipment. I bought a 4 foot long light from him. He has a nice build article on our club website for the light I bought from him. This is the link http://www.njagc.net/wp/articles/cree-x ... ium-light/
Those are some real old-school LEDs for sure. You might want to look at replacing the LEDs. You'd probably look at something like 50% greater efficiency just from that alone.
What about heat in your electrical box containing the LED power supplies? Concerns? Fan needed?
The PSUs are rated up to 90 degC ambient with derating, and 60 degC without any derating if run at 240V input (110 V input requires 50 degC ambient for no derating). The box is warm and I might have to add vent holes come summer, but for now it's not a problem.
What is the purpose of this build? To provide an overwintering place for tender cacti?
Some of it is for overwintering (Melocacti and some cacti I paid too much for to leave outside, as it gets to about 2 degC overnight in winter where I am) but most of the space is for seedlings. I have about ~800 seedlings that need a month or two of long days and bright light and then I will be able to sell them. Once those are done I will be putting lots of takeaway containers in so I will have plenty of seedlings ready for outside come summer.
If I understand your write-up correctly, you have a cover/door to totally enclose the area containing the cacti. Correct? If so, what about air circulation in there?
The heat sink cooling fans run 24/7 which circulates air. The door is not perfectly sealed. Without the heater and with an outdoor temp of about ~14 degC, the internal temp is ~26 degC. The thermostat is set to 18 degC and so far only comes on at night. I will probably need to add a ventilation fan for summer or maybe leave the doors ajar.
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MrXeric
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by MrXeric »

Excellent guide! I've been considering building something larger for seed raising than my storage 'prop' box setup. I will bookmark this for future reference.
RorBurg56
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by RorBurg56 »

Just wondering if you could explain the risks of powering led setups with plugs directly from a mains socket?
Growing some succs and cacs in mid/coastal Scotland.
Download
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by Download »

RorBurg56 wrote: Mon May 23, 2022 1:11 pm Just wondering if you could explain the risks of powering led setups with plugs directly from a mains socket?
Besides the fact few LEDs are designed to run at 120 or 240 V?

LEDs are electronic devices with a positive power to temperature relationship. As they heat up, they draw more power, causing them to heat up more, and so on, until they fail.

You also need accurate voltage and current control to get the most out of your LEDs.
RorBurg56
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by RorBurg56 »

OK, thanks. Suppose it must have been a slightly obvious answer. Oh well.
Growing some succs and cacs in mid/coastal Scotland.
keith
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Re: I build a set of "grow shelves" for growing cacti on a budget

Post by keith »

Just wondering if you could explain the risks of powering led setups with plugs directly from a mains socket?

LED light bulbs have a circuit built in to convert AC to DC . This custom design uses the power supplies to convert the AC to DC. And the heat sinks and fans to cool the LED COB this is quite a design . I design COB often not with LEDS but amplifier chips using epoxy and wire bonds they are very small and can easily be FAT fingered so a cover is needed. And a heat sink. The power converters are like a fraction of this design.
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