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Simple DC System for
Hydroponic Watering

 By James Dunn

With today’s technology, a
simple watering system for
hydroponics can be built with a battery and direct current pump. This makes
setting up a hydroponic garden possible in remote areas such as deserted
islands, deserts, mountain or forested areas far from the electrical power grid
system.

A water pump is considered
crucial to a hydroponic system unless you intend to hand water the plants once a
day. Using a water pump reduces risk associated with hand labor and allows the
garden owner some freedom from work and worry. A hand watering system can also
be boring if it is desired to water the plants four times a day. The system
should be automatic and allow the garden owner to leave for three or four day
periods and let the garden continue to grow and flourish.

When you use electric devices,
pumps, timers and lights, there are two basic choices, AC or alternating current
or DC direct current.

AC is the 110 volt power we
have in our homes. It is usually delivered through power lines that deliver the
power to the home and costs money from the local supplier.

DC power is the type of power
we have in our cars and boats where electricity is delivered by a battery. In
cars this is most often a 12 volt battery.

There are lights, timers,
fans, and pumps designed for a 12 volt DC battery system. These items can
usually be found in a local hydroponic store, a marine supply store, an auto
parts store or a store specializing in aquarium equipment.

Pumps – The most economical
submersible pumps for hydroponic systems are the bilge pumps ranging in costs
from 20 to 40 dollars. They are used to pump excess water out of boats and can
be attached to a timer. There is also a more expensive DC pump used to pump
water in RV plumbing systems. It costs about $80.00 and can be outside the water
tank.

Timers – There are many DC
timers available from aquarium supply stores and a few have their own battery
power supplies. One of the best ius a 12 volt seven day programmable timer,
usually costing about $60.00. This timer can be set to run the pump a few times
a day for a set number of minutes. Other DC devices – There are also DC light
bulbs, heaters to heat air or water, and fans to circulate air. All of these
devices are available through recreational vehicle supply stores although most
require quite a bit of energy to run and are expensive to purchase.

Our car batteries are 12 volt
batteries called cranking batteries that retain enough charge to start the
engine. Once the car engine is started the alternator continues to keep the
battery charged and supplies power to the DC electrical devices in the car. The
power is stored by the battery and if any lights or electrical devices are left
on when the car is not running, they will use battery power and perhaps reduce
the power in the battery so low that it will no longer start the car.

There is another type of 12
volt battery called a deep cycle battery. These batteries are usually built
differently and can withstand being drained low more often. While a cranking
battery may only be effective after being drained 30 times, a deep cycle might
be able to continue after being drained 100 times or more. Deep cycle batteries
are used in solar power systems, or systems built for boats and recreational
vehicles.

A 12 volt deep cycle battery
is used as the basic source of power. One battery is sufficient for a simple
system, but there is a wide range of effectiveness of deep cycle batteries. When
purchasing a battery, there should be a rating called amp hours, and for many
this is about 100 amp hours. That means the battery can be used for 100 hours to
power a device that uses one amp per hour of operation.

The Pump Battery System

Each DC electrical device uses
a number of amps (or current) per hour. A power hungry device like a heater or
refrigerator might use five or six amps per hour, and a DC light might use a
single amp per hour.

The DC pump used in your
system uses about 1.5 to two amps per hour of operation. In this time these
pumps will deliver a certain amount of gallons per hour, usually about 400 to
500 gallons. A two amp pump can be run for 50 hours before draining a 100 amp
hour battery. The DC pumps have different levels of height they can reach, but
the typical bilge pump will pump water four feet high. A system designed where
the reserve tank is three feet below the system and the watering tank is six
inches above will allow for efficient operation.

That is of course, the theory.
In reality, it is best to recharge the deep cycle battery before it is reduced
to 50% of charge. This allows the battery to last longer and offers insurance
that the pump will have power to work. So the actual operation of the pump
should be no more than 25 hours.

Depending upon the size of the
hydroponic system being watered, most systems only require the pump to be run
three to six times a day, for periods of 10 to 15 minutes. For a 500 GPH
(gallons per hour) pump that means 80 gallons will be delivered to the system
for a 10 minute cycle and 120 gallons for a 15 minute cycle. That is if the pump
is allowed to pump with full strength for the running time. Any valve between
the pump and the system will allow that flow to be reduced.

If a hydroponic system is run
four times a day for 15 minutes, the amount of power used should be two amps per
day, and allowing the battery to reduce charge should allow a system to run for
25 days without requiring a recharge. This is in theory and it would be less if
the timer in the system requires energy from the battery also.

In fact, the battery systems
can be problematic and should be monitored every four or five days, and the
hydroponic system itself should be designed to have that much residual water for
each plant. That is a safer system, so even if the pump and battery system do
not work, the plants will have enough water to last the times between being
checked.

The plant container in a
remote system should contain enough water for the plant to survive for four or
five days without receiving any additional water. Even if the plant used up most
of the nutrients in the water, the extra may help them survive until the
mechanical system can be restored.

Another option to increase the
reliability of the system is to place two or more batteries in parallel, that is
hook positive poles to positive poles and therefore increase the time available
for the hydroponics system, or increase amp hours. But even using this option,
it is safest for your plants to design a system that will keep the plants alive
even if the pump does not work, at least for some time.

Recharging the Deep Cycle
Battery

The battery can be
continuously recharged by a power producing device. There are several options
available.

A battery recharger – There
are battery rechargers on the market that can be plugged into the household AC
system that will then recharge a battery. A few of these costing about $80.00
have voltage regulators in them which will prevent overcharging the battery. The
drawback is that they have to be plugged into an AC system. This can be used to
charge batteries that are then transported to the remote site.

Solar power – There are
photovoltaic panels that use the sun the produce electrical power. These range
in size from 60 watts to about 140 watts and cost about $300 to $400.00. They
can be used to power the battery but need a voltage regulator in the circuit to
prevent overcharging the battery.

One drawback to solar power is
that it needs sunshine to work. Cloudy days and rainy days do not provide power
and if a shadow falls on any part of the panel it may work very poorly or not at
all. Even when the solar cell works well it may only deliver two to three amps
per hour to the cell, and may not keep up with battery use from the pump.

Wind power – A wind generator of 60 to 400 watts
can be used like the solar cell to produce power from the wind. These cost about
$300 to $400 and have a similar drawback to the solar cells that they work only
if there is wind from five to 15 miles per hour.

Generator – A gas or diesel
powered generator can be used to provide energy for the battery. These also
require a voltage regulator and cost from $500 to $1500 for small systems. The
drawback is they use fuel, are usually noisy and are really oversized for a
small system. Most of these generators need to be started by hand, some even
requiring a pull cord to start. They are not usually easily or cheaply set up
into automatic systems providing recharge when needed.

Perhaps a system that combines
methods of recharging is best, such as a system with both a wind generator and a
solar panel.

Hydroponic System to

Attach to the Pump

Whatever type of hydroponic
system is used to deliver water to the plants, it is probably safer to have two
water tanks for the nutrient water, one with the water and pump at ground level
and one four foot or less above the ground level pump.

This tank will then use
gravity and a valve to deliver the nutrient water to the plants that will then
go through the system and then through gravity flow back into the ground level
tank.

A system that is provided 120
gallons of nutrient water four times a day can probably supply about 200 plants
that use a liter of water a day. The amount of water required per plant varies
according to plant type and size, and the temperature and sun conditions of the
day.

On a sunny hot day the plants
will require twice the water as on a cooler cloudy day. The plants transpire
this water to keep themselves cool. So a system should be sized to have enough
water for the plants on a very hot day.

A three times a day system
with 240 gallon of water being delivered to the plant system should easily
supply 200 plants with enough water to last the day. Of course the water supply
tank would also have to be sized to have enough water in reserve.

Once a pumping operation is
established the hydroponic system can be pvc tubes, black plastic bags, or other
plant holders. The water supplied to the plants can be either pumped to the
plants with any excess being allowed to go to soil, or the extra waters gathered
and returned to the watering tank.