Everything you need to know about the Pax Bellum A.R.I.D., Part2 LED and maintenance

How long will the LED’s last?

The LEDs are rated by the manufacturer for 50k hours. We suggest replacement after 40k. Make sure your heat sink is able to radiate heat to room temperature air. LED life can be cut short by inadequate cooling. Placing the ARID inside a cabinet without ventilation will put unnecessary thermal stress on your light assembly, and reduce its service life.  While LED’s are much cooler to run than other light bulb technologies, they do still produce some heat and need room to expel that energy safely.

 

What voltage are the LEDs?

The LEDs are designed to run using only the 12VDC power supply provided with the ARID. Running the ARID on higher voltage will cause them to burn out.

 

How are the LED’s cooled?

The LEDs are attached to a vapor heat pipe that carries the heat evenly away from the LEDs to the heat sink located above the lid where it is released into the air. 

 

Will heat from the LEDs raise my tank water temperature?

LEDs waste about half of their input energy as heat. Therefore our smallest model the, “ARID N18” would give off approximately 7 watts as waste heat, of this at least 3 watts is taken away by the heat pipe, leaving at most 4 watts of heat to transfer into a 40-120 gallon system. Basically, an insignificant amount of heat is transferred into the aquarium.

 

Why is the light tube plastic and not glass?

The heat pipe in the ARID extracts heat so efficiently it allowed the use of high output LEDs and a plastic light tube that is impact and thermal cycling resistant. The heat pipe also cools the lights sufficiently that carbonates will not precipitate out of the saltwater and build up on the light tube, obstructing light transmission. The heat pipe will also protect the macro-algae from cooking should the pump supplying water to your reactor fail. Proper thermal management is necessary for optimal life expectancy of LEDs that are designed to be cooled from the underside.

Simply encasing LEDs inside a glass tube and submerging them in saltwater is not a good idea for the previously mentioned reasons. Glass also tends to break along thermal gradients, especially ones that rapidly change temperature, like the one found at the point the light tube passes through the lid. Glass sleeves work in UV sterilizers because they’re always on. The temperature is relatively constant 24/7, and it’s chosen because glass is UV stable. UV sterilizers are generally not opened up on a regular basis. This is not the case in an ARID macro-algae reactor.

Glass is not impact resistant or resistant to external forces placed on it especially when undergoing a rapid thermal change. If you have ever taken a hot glass aquarium heater out of your tank without letting it cool first and then accidentally tapped it on something you’ll know the heater can shatter instantly.

Even if we used glass with our heat pipe cooling system we would be limited to the height the reactor due to the deflection strength of glass. Glass failure is also abrupt unlike plastics.

 

Why not place the LEDs on the outside of the chamber?

Efficiency is the main reason the ARID doesn’t use LEDs on the outside of the chamber shining in. Many more LEDs are required to penetrate the algae mass when illuminated externally. The LEDs would also require the same intensity to penetrate the algae mass the same depth. This may work for a small reactor but scaled up it would be very cost prohibitive.

For this illumination strategy to work the transparent chamber wall will need to be kept free of any bioaccumulation to maintain light transmission, and would require frequent acid washing and scrubbing. After time the chamber will become scratched and light transmission will be degraded, resulting in the entire chamber needing to be replaced.

Heat is another issue, more LEDs means more heat. The entire chamber will be heated and transferring a good portion to the water, more so if the chamber wall is thin. Many transparent plastics have residual internal stresses from to rapid of cooling during production and are not able to take thermal cycling and will eventually crack. If the LEDs are to be cooled from the underside to avoid this problem, a heat sink the entire surface area of the chamber would need to be used.

 

What periodic maintenance should I perform on the reactor itself to keep it operating efficiently?

We recommend an acid wash of the chamber every 6 months to keep the chamber walls reflective. Either acetic acid (white vinegar) or hydrochloric acid (muriatic acid) can be used. This involves filling the unit with straight store bought white vinegar or making a dilute solution of 5% HCL acid and letting it sit for a few hours until all carbonate buildup is dislodged,or dissolved. Then drain and rinse with freshwater and put it back into operation. A white poly pad made for scrubbing plastics can be used to aid in dislodging any stubborn buildup.

The light tube should be replaced every 10-12 months due to aging and scratches that will accumulate from cleaning.

The flange seal may need replacing yearly due to dimensional changes from aging and compression set. 

Wipe dust from the heat sink on a regular basis to keep it transferring heat efficiently.

Clean the gland that the flange seal seats into of any foreign material to ensure a proper seal.

Check plumbing fittings leading to, and on the reactor for blockages during routine algae harvests. Low flow is the number one reason for algae collapse.