Power Budgeting for Aquarium Systems
By Rex Niedermeyer
First published by The Saltwater Enthusiasts Association of the Bay Area
(SEABay)
Aquarticles
I'm going to discuss a subject that most aquarists fail to consider when they set a new
tank up, and which at times can be downright dangerous and at others quite sobering. The
subject I'm referring to is the amount of power or electricity an aquarium system
uses and how this relates to both safety, reliability and economics.
Most people don't give much thought to plugging an appliance or power tool into an
outlet and expecting it to work. The electrical outlet you are plugging the device into
has a limited capacity to provide power, and if this limit is exceeded then in a properly
designed electrical system a fuse or circuit breaker will open and prevent the system from
over loading by shutting off the electricity. If the electrical system is not designed
properly (i.e. does not meet proper electrical codes), then the wiring can over-heat and
possibly cause a fire. If you are unsure of the state of your location's electrical wiring
then have a qualified electrician examine it before you set up (or add) an aquarium
system.
When operating an aquarium in which its inhabitants are relying on electrical
power to maintain things such as temperature and circulation, it is obviously not
desirable to have power interrupted by trying to draw too much power through an outlet or
electrical circuit and risk the danger of killing all of these inhabitants (much less
setting your house on fire).
How can you prevent this potential disaster from happening?
- By properly determining the power used by your aquarium system and then budgeting that
power for your location's existing electrical capacity.
First, how do you determine the power or current (current usage is closely
related to power usage) a given piece of aquarium equipment (e.g. pump, lighting, heater,
etc.) uses?
- Most pieces of electrical equipment have printed either on the unit itself or in
accompanying literature the maximum amount of current or power it is likely to use. (If
power in watts, then current in amps is given by dividing the power by 115). For those
pieces of equipment that don't have a current and/or power rating then contact the
manufacturer (or possibly the store you purchased it from) to get this information. For
those more adventurous souls who wish a more exact operating current value for their
specific piece of equipment, they can purchase or obtain a clamp-on current probe
and line splitter to measure it themselves. However you obtain the operating currents for
your aquarium equipment the resultant maximum current usage for a given aquarium system is
determined by just adding all these individual equipment values up.
Now that we have a way to determine the total maximum current used by our
aquarium system we can see how this matches with our available electrical circuits'
capacities.
- Most electrical circuits in the home allow a maximum total current of 15 to 20 amps (to
determine which yours is, check your fuse or breaker box). Each of these electrical
circuits can have one or more electrical outlets attached to them. To determine whether a
given electrical outlet is connected to a particular circuit just turn that circuit off
and see if that outlet is still working (manually turn the circuit breaker off or remove
the fuse. If you are unfamiliar with working with electricity then get help from someone
who is). The total current this given electrical circuit is using is determined the same
way our total current usage was determined on our aquarium system, or by just adding up
the individual current usages for all the electrical devices plugged into this circuit
(include all non-aquarium related devices as well). If after determining the total current
usage we find that it is equal to or higher than what the circuit is rated for, then we
are in serious danger of overloading the circuit and causing it to trip or blow. In
practice I find I don't like to operate an electrical circuit at better than about 75% of
maximum rating ( i.e. 15 amps for a 20 amp circuit or a little under 12 amps for a 15 amp
circuit) to add an additional safety margin as well as allow operating currents to
possibly increase as equipment ages. (There's also something called power factor that
could use margin, but that's beyond the scope of this article). This 25% margin also
allows limited increases in power usage on that circuit by the plugging of additional
devices into it on a temporary basis (e.g. pumps for water changes, fans for cooling,
etc.). Though remember you still have to abide by the maximum current limit for that
circuit at all times.
What if my total current requirements for a given electrical circuit exceed the
recommended maximums?
- There are several ways of addressing this problem. The simplest though not always
practical solution is to plug some of the electrical devices into another circuit, doing
the same maximum current usage analysis on this second circuit as we did on the first
(remember another outlet, if on the same breaker/fuse, does not count as a second
circuit). If a second circuit is not readily available then your options become more
complicated. You may be able to upgrade your existing circuit to a higher capacity (please
have a qualified electrician verify this is possible if you don't know what you are
doing), or you can reduce the total current you are using by eliminating devices or using
alternate devices that use less electrical power (i.e. current). This last option can be
painful in that you may not be able to use that larger lighting system you wanted or that
chiller you planned on. It is advised that you do this maximum current analysis before you
set up any new aquarium system, since it may significantly influence both the size,
location and type of system you set up.
I wish to mention two additional safety tips on aquarium power budgeting.
- First, the exact same arguments made for limiting the maximum current used on a house
electrical circuit also apply to any power strips you may be using. Don't overload your
power strip - operate within its rated value.
- Second, whenever you have electrical devices operating around water you run the chance
of shorts and electrical shocks. To minimize any danger to both yourself and your tanks'
inhabitants use Ground Fault Interrupters (GFI's). A GFI is able to detect when
electrical current is being lost to a path other than the electrical system itself (such
as your tank or yourself) and will shut the electricity off to prevent damage or harm.
While you can use circuit breaker based GFI's, I would not recommend them as they
will shut off all power to the circuit if only one piece of equipment is shorting,
and could cause your whole system to crash. Instead, use individual GFI's or several GFI's
grouped so that if any one of them trips it will not cause a catastrophic failure to your
tank(s).
So far we have discussed the concept of power budgeting when planning a new
aquarium or operating an existing one and the procedure used to create one. We will now
put theory into practice and analyze an example system and determine some of the
implications of this analysis including projected operating costs.
The example system I've chosen to analyze its power budget for is near and dear to my
heart, in that it is a recent system I set up for myself. It is a relatively large
reef system (270 gallons) and represents one of the worst case conditions one is likely to
encounter. (If you're considering a larger or more complicated system you have my
condolences).
Table #1 shows my power budget analysis for this example system in spreadsheet format
(a simple list is fine but I have to justify my computer system somehow and this looked to
be good opportunity).
Let's now review this power budget spreadsheet in more detail:
Table #1
The first column of the spreadsheet lists the different pieces of electrical
equipment used on this system, and the second column the corresponding
peak operating currents for the devices. These currents were actually measured
with a current probe and are generally somewhat less that the maximum rated currents from
the manufacturers. These slightly lower operating currents are fairly common, in
that actual operating currents can vary slightly from device to device (even for the same
model device) due to manufacturing tolerances, and so the manufacturer normally specifies
maximum currents for worse case tolerances and operating conditions.
The third column is the devices' operating powers (in watts) and is
determined by multiplying their operating currents by 115 volts.
Column four is duty cycle and represents the fraction of a day a given
device is expected to operate. Determining duty cycles for items such as heaters and
chillers can be complicated since they do not operate on regular schedules. My duty cycle
values here are my best guesses based on past experience, but will likely be refined as I
observe my system in operation. (Duty cycle does not effect peak current levels so only
operating cost calculations will be effected by them).
The fifth column is the total energy used per day by each device and is
determined by multiplying the devices operating power by duty cycle and then 24 hours/day
to get watt-hours (actually shown in kilowatt-hours, so also divided by 1000).
The last column is circuit number and is required because this system's
power requirements are greater than 20 Amps (24 actually) and therefore exceeds any single
standard electrical circuit's capacity and has to be split between two circuits (20 Amp
circuits in this case). You will notice I have not evenly split the operating currents
between the two electrical circuits,. This is because I have other non-aquarium related
devices on circuit #2, most notably a garage door opener (6 Amps). Remember your operating
current totals must include ALL electrical devices on a given circuit, not just the
aquarium related ones. I've also limited the maximum operating currents on any one circuit
to only 75% maximum capacity as recommended earlier.
At the bottom of the spreadsheet are totals for operating currents, power and
KWH's. You will notice that operating current and power totals do not add up
properly. This is because I've arranged the system so both the heaters and chiller cannot
be on at the same time and thus reduce my total peak operating currents/powers
contribution to the larger of the two, the chiller in this case. (It is also important to
note that for this to work both heaters and chiller have to be connected to same
electrical circuit).
The last number of note on this power budget spreadsheet is the total operating
costs per month for this system of about $136/month. (This is the sobering
part of power budgeting I made mention of at the start of this article). Before you run
and hide, remember this is a large and well endowed reef system and as such likely to be
much more than your system requires. (I have a second 100 gal. reef system with 820
watts of light and a chiller, and it only costs about $55/month, a more moderate system or
fish only tank would be even less). The operating cost/month is just determined by
multiplying the total KWH/day value by your electricity cost per KWH (available from your
monthly power bill statement), and the number of days in a month.
Given the effort that went into preparing this power budget, what did it do for
me?
Several things actually:
- For one, it told me that I could not operate this system on one electrical circuit, so
wherever I set it up I would need access to at least two electrical circuits.
- It also told me that when combined with a similar budget done for my other tank,
they could not be placed in the same room. (Unless I was willing to have new electrical
circuits installed to accommodate it).
- And last, but not least, it gave me a relatively accurate estimate of its projected
operating costs, which allowed me the option of changing its design before built if I felt
it was more than I was willing to pay.
What if I did want to reduce our example's operating costs?
- By going to the power budget spreadsheet I could identify those devices that use the
most energy and see if I could eliminate them, reduce duty cycles, or find alternatives
for them which use less power.
I hope this power budget exercise has been useful and given you an appreciation for how
helpful it can be when planning a new aquarium system or optimizing an existing one.
Note from Aquarticles: The author of this article, Rex Niedermeyer, has also written a major
series of three articles about Aquarium Lighting, which explain in a straightforward
manner the operating principles of the various types of lighting systems, and their
relative advantages. These articles, "Let There Be Light", may be seen at
SEABay's website, www.seabay.org |