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What to Look for in an Inverter surge capacity

Most inverters will deliver two to three times their continuous rated power depending on the design. This surge capacity allows the inverter to deliver enough power to start large electric motors such as pump motors and power tools.

Idle current
All inverters use some power even when no loads are turned on. This is the idle current of the inverter. It is a fixed amount and is always present as a load on your battery when your inverter is turned on. Some inverters have a search mode which reduces idle current by turning the inverter on and off every second to search for a load. If no load is present the inverter stays in search mode.

Battery charger
Many inverters feature built in battery chargers. This allows the battery to be charged from an AC power source such as a generator or the utility. When an inverter is used in a back up power system the battery charger is a key feature of the inverter. If a significant amount of the power being delivered to your battery is coming from a generator, battery charger size may be very important. Having a charger that is too small will require running your generator for too long under a low load to achieve a proper charge. It is most efficient to use your generator to its maximum capacity so you can minimize the running time.

Modern inverters can achieve efficiencies as high as 95% and typically operate above 85% at full power. Efficiency varies from model to model and according to the relative load on the inverter. True sine wave inverters are usually less efficient than modified sine wave inverters. Overall efficiency may be similar due to the energy lost in the harmonics of a modified sine wave, especially when running motor loads.

Generators and inverters are an ideal match. An inverter operates small loads like lights and computers more efficiently than a generator. Large, intermittent loads like pumps, power tools and microwaves are also perfect for an inverter, but expensive to operate with a generator. Small jobs are tough on a generator. Running diesel generators under low load causes excessive carbon build-up on valves, shortening the generator's life. A generator drinks almost as much fuel for light duty as it does for heavy duty.

Installing an inverter and battery bank allows the generator to operate as a battery charger eliminating the need to run the generator all the time. When the generator is off, loads are powered by the inverter (taking energy from the batteries). Today's solid state inverters can start and run difficult motors like washing machines, submersible pumps, table saws, air compressors, etc. A small inverter can also be used to run a small load a long distance from the batteries, such as a light down at the dock, saving the cost of heavy DC wiring.

Battery and Inverter Subsystem
The heart of most stand alone alternate energy systems is a battery and inverter. If you are already using a gas or diesel generator you should consider a battery and inverter subsystem. This allows you to achieve the following benefits before making a decision about PV, wind or micro hydro.
• AC power is available 24 hours a day with the flick of a switch.
• The generator can be run at convenient times for direct AC power and battery charging.
• Generator operation is much more efficient.
• Energy costs are lowered because generator run time is reduced.
• Generator capacity is better utilized as a result of battery storage.

Chargers / Transfer Relay
Many inverters come with a built-in battery charger. This eliminates the purchase of an additional component to charge your battery bank from grid power or a generator. Most models with a charger have a built in transfer relay. This allows a unit to operate AC loads directly from an external source (such as a generator or grid power). All of the trace units are able to switch from generator or grid power to inverter power fast enough to prevent computers or electronics from crashing - allowing them to function as an uninterruptible power supplies. Most of the electronic equipment (computers, network components, phone system, web server) at Energy Alternatives is run through a Trace inverter, providing us uninterrupted usage during power failures and brownouts which happens several times a week. Our battery bank provides us enough power to keep everything running for many hours during power outages.

Stacking two inverters together allows them to produce double their rated capacity as well as 3-wire, 220 VAC power. This enables you to operate large power tools, deep well pumps and any other load that requires 220 VAC power.

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