Backup Sump Pump Systems - Choosing the Right Battery

For years, I have been advocating the necessity of battery backup sump pump systems for homeowners serious about waterproofing their basements. A backup system by itself, however, is not the only necessary measure. Another factor that may be just as important, if not more is the battery. The best backup system in the world may be completely useless if the actual battery is one of poor quality.

Deep-cycle, no-maintenance marine batteries are the best designed battery for supplying DC currents to battery backup sump pump systems. Most large rechargeable batteries are lead-acid type, as opposed to NiCads, which are generally more expensive. The acid in a lead-acid type marine battery will generally contain 30% sulfuric acid at a full charge. Through my 22 plus years experience as a supplier of battery backup sump pump systems to contractors around the United States and Canada, the most effective battery is AGM - Absorption Glass Mat.

Most typical gelled batteries contain the combination of acid and silica gel. AGM batteries provide all the advantages that come with gelled batteries. They do not, however, exhibit the disadvantages of gel batteries. The acid in an AGM battery is contained by the fiberglass mat, and yet is still available for the battery's plates, resulting in faster migration of acid. This gives the battery a higher rate of delivery and absorption of amperage. Most typical gelled batteries must be charged at a slower rate to prevent cell damage from excess gas.

AGM batteries can be charged at normal voltages, without the need to recalibrate, or purchase special chargers. There are no charge or discharge current limits. With AGM's low internal resistance, the buildup of heat is almost non-existent, during normal and heavy charged and discharged currents. Other gelled batteries have the potential to lose capacity if overcharged due to voids developing in the gel.

With the AGM battery's low self-discharge of one to three percent average per month, they are able to be stored for a longer period of time without charging versus other batteries. Even if discharged for more than 30 days, an AGM battery can be recharged to almost full capacity.

Through electrolysis, AGM batteries preserve water as they charge. This is possible because of the recombining of hydrogen and oxygen, thus converting to water while inside the battery. Water loss in other gelled batteries, especially in hotter climates, is quite common and often leads to the premature death of a battery after a few short years. With the AGM battery, water loss is not a problem, making it maintenance-free.

Because of the mounted plates, acid will not leak or spill from AGM batteries. Because the plates are packed tightly, they can withstand shock and vibration. AGM batteries are completely non-hazardous, making them a more viable (and cheaper) option for shipping.

When considering the purchase of a battery backup sump pump system, insisting that the pump uses an AGM battery would be the wisest choice in order to maximize the effectiveness of the sump pump.

AC Versus DC Powered Battery Back-Up Systems

Power outage can be a common occurrence during a severe rain storm. The sump system in a home typically relies on a heavy duty AC primary pump to discharge water entering the home through its drainage system. To compensate for the possibility of a power outage, the sump pit may include a battery-operated DC or AC driven pump in addition to the primary pump. How do these AC/DC pumps differ in function and performance?

A DC based back up system typically consists of a DC pump, a 12 volt deep cycle battery (2 batteries if a 24 volt system), and a charger. Most DC pumps used as part of a back-up system were initially designed to be bilge pumps for boats and are not heavy duty, but some work well. A characteristic of a DC system versus an AC system is that the rate that it discharges is related to the degree that the battery power source is charged. A fully charged 12 volt battery will power the DC pump to its maximum capability. As the charge of the battery is consumed, the pumping rate of the DC pump diminishes. For example, a given pump will discharge at the rate of 30 gallons per minute with a fully charged battery, but may only be pumping at 15 gallons per minute when half of the charge is still left with the battery. At the end when the battery is about to be depleted, the pump may be discharging at less than five gallons per minute. DC systems efficiently consume DC current and can run continuously for several hours (up to 10 hours continuously and intermittently for several days).

An AC based back-up system typically consists of an AC heavy duty pump, a 12 volt deep cycle battery (or two batteries if a 24 volt system), and an inverter with a battery charger). An inverter converts the DC power of the battery to its AC counterpart. Unlike a DC pump, an AC pump will run close to its maximum potential capability until the battery charge is depleted. For example, if the AC pump can pump at a rate of 50 gallons per minute, it will continue at close to this rate (with minimal loss over time) until the battery power source is depleted. It is important to select an AC pump with efficient amperage rating (3-7 amp hours), otherwise the system will not run long enough before the battery source is depleted and the system shuts down. An efficient AC pump can discharge as much as the best DC system because it is discharging at a greater rate than most DC systems even though it shuts down faster than a good DC pump system. The key advantage of going with an AC system is that it is easier to match it up with its primary pump counterpart. Since the AC system requires an inverter, it is typically more expensive than DC systems which do not require an expensive inverter for its operation.

The best way to compare different available systems is to compare the total amount of gallons discharged with a given battery (beginning with a fully charged battery recommended by the manufacturer) and that the data, ideally determined by an independent testing agency, represents the time and performance until the system shuts down). The values should have been generated at an 8-10 ft. head. The head is the distance that the pump discharges vertically (in a basement, it is usually 8-10 ft).

For the most part, A DC system will discharge at a rate less than the primary pump can discharge. Whether this is good enough is something that the homeowner and/or contractor must make a judgment call on. An AC system can be matched more effectively to the performance of the primary pump. The best scenario is that the homeowner has determined how effectively his primary pump has performed during a major storm and matches that performance with that of the back-up system, whether it be an AC or a DC system.

Direct Grid-Tie vs Battery Based Home Solar Energy Systems

The direct grid-tie solar system is the simplest system to install and will meet the needs of most people since the majority of the population lives on a very reliable grid. In areas where commercial power is unreliable, or power is required for critical situations, battery back up and gas or diesel generators can be added to the system. Another fairly simple system is for off grid use where all electrical appliances and lights are 24 volt DC. This is common for boats and trailer homes, but won't support most folks. The other type of off grid system will have an inverter that converts current to AC and stores power in DC batteries.

Direct Grid-Tie Residential Solar Systems

Direct grid-tie systems need only the solar panels, an inverter and a disconnect switch to shut off power if the grid goes down. The inverter connects to the disconnect and then directly to the main electrical panel. Thus when the sun is shining, the electric meter spins backward when the solar power system is producing more electricity that the home is using. Often the meter needs to be replaced by the power company because older meters weren't designed for reverse operation and do not read accurately. Of course you want an accurate reading since the electric company will be crediting you for the electricity returned.

Once installed, this system is almost maintenance free and will operate for many years. A promising new type of system uses a micro-inverter which is wired directly to each panel. This makes your system even simpler since your wiring is for AC current, and you can use standard electrical wiring components. This also has the advantage that each panel is wired separately so if one solar panel is shaded, or broken, the rest of the system will work just fine.

battery-Based Systems

As soon as we add batteries to your system, we complicate the design and add extra maintenance. We need a special inverter which in addition to converting to AC power, must feed some DC to charge the batteries, and must be able to instantly switch to battery power if the grid loses power. Batteries also will add 4-5,000 dollars to your system cost, and will add maintenance if you go with less expensive wet cell batteries. You should wire your system so that the backup batteries don't supply the whole house with power or your battery expense will be even higher. Keep power flowing to refrigerators, furnace, some lights, computers, and other equipment that you must have running..

An off-grid home basically requires the same equipment as the system above designed for battery backup. The only difference is the inverter does not require the circuitry to manage the grid power, and feeds all excess power to the battery charge controller. Depending on the amount of sun you get, you may want to integrate a generator into you system so batteries can get extra charging in winter or periods of bad weather.