Frequently Asked Questions - SW sine wave power inverters

I heard that operating refrigerators or water pumps can be critical from a non-sinewave power inverter. What do I have to know about this?
It is worth to mention that these loads are typically those types (inductive loads which incorporate a motor inside) which would require a true sine wave inverter. Otherwise the motor in these units would easily overheat, could give out a humming noise and eventually would get damaged when operated continuously. Chosing the right power inverter for a so called absorbtion refrigerator could not be a problem, as they do not draw high start-up current. We could encounter a problem though when powering a normal fridge if we are not familiar with this subject. In a normal fridge there is an electric motor which powers the fridge's compressor. The compressor needs to overcome various compression values (just like a piston in a combustion engine of a car) during operation. The current drawn by the electric motor gets higher as the compressor requires more power in order to be turned properly under all compression values. This current draw can be up to 10 times higher than the nominal value which gradually falls back to normal. It is very difficult to calculate the inverter's power using the Watt-values of a data plate at the back of the fridge (e.g. a 300W power inverter will not start a 100-150W fridge). Generally we recommend to use a min. 600W or better 1200W inverter for starting a normal fridge in all circumstances. The situation is similar with water pumps - they take high surge current, often for several seconds. Pulling the water up from greater depths would also make the pump's work more difficult and it would take higher start-up currents. It is not at all impossible that e.g. a 1000W power inverter won't start a 500W water pump.

What does a battery deep-discharge mean?
One of the main components of an inverter power system is the battery, the most widespread type from all of them is the lead-acid battery. After considering the early replacement of an old battery bank an expensive and environmentally not friendly process, it is important to make sure that our battery would remain fit during many years of service. Deep-discharging is the condition which deteriorates most badly the capacity and shortens the expected lifetime of the battery. When the battery is discharged more than allowed (usually below 50% of its capacity) we can talk about deep-discharging. This process intensifies the sulphation of the lead battery plates and this results in drastically reduced battery capacity. The inverter's built-in DDP (deep-discharge protection) function won't allow the user to operate any connected AC load when the battery is discharged enough. The output of the inverter will be switched off automatically at this stage and will only be restarted (automatically) when the battery is sufficiently recharged.

What will happen if I connect a higher load to the inverter than its nominal power?
Loading an inverter is unfortunatelly not like connecting a load to the wall socket of the mains. While you can connect practically any domestic equipment to the wall socket, you can only connect loads to the inverter's output which do not exceed the nominal power of the inverter (e.g. you can not connect a 300W computer to a 150W power inverter). If you erroneously tried to connect a load higher than the nominal power of the inverter, it would get damaged without protection. But with a built-in overload protection the inverter will just simply won't start or stop operating within any damage. After a few seconds the inverter will try to start again automatically - if the overload condition is gone, the inverter restarts, if it is still present, it will switch off again. After a certain number of attempts the inverter will shut down, restarting is only possible by resetting it by the main switch manually. There is a difference between continuous and short time overload where the latter means that the overload condition is present during a very short period (few milliseconds or second). Typical examples are the following loads: computer monitor, water pump, fridge, microwave, power tools which require a much higher current upon startup than their nominal power. In order to be able to start such difficult loads, our inverters can take up to 200% overload for a short time.

There was an accidental short-circuit at the inverter's output, will the inverter get faulty?
Short-circuiting the output of an inverter could not only damage an expensive equipment but it could represent a fire hazard. Therefore there is a fully electronic short-circuit protection incorporated in our SW pure sinewave power inverters which protects the inverter from short-circuiting its output. After the short-circuit is lifted, the inverter remains fully operational.

Why do you call the cooling system of the SW sine-wave inverters "intelligent"?
The 600W inverter models (SW600, 1200, 2000) and above have a built-in fan cooling system. The fan's operation is controlled by a microprocessor depending on the power the inverter is loaded at. If the load uses only a small percentage of the inverter's power, the fan cooling in not yet necessary and the processor won't start the fan. This helps to reduce the power consumption of the inverter to the minimum. The inverter's microcontroller recognizes when the load requires considerable power from the inverter and it switches on the fan before the inverter would overheat.

Why is it so important chosing the right cross section and the length for the battery cable?
To obtain and install a suitable battery cable is essential and require attention. Even a 1200W inverter can only render a few hundred Watts if it is connected to the battery by a small diameter or too long cable. This is because of the so called "voltage drop". At 230Vac mains voltage you can use a long 30-40 metre extension cord without having to worry about voltage drop, but when talking about low voltage (12 or 24V), you will have to calculate with this phenomenon. The smaller the cable diameter, the larger the voltage drop gets. Also, the longer cable you use, the more voltage will drop between the two end of the cord. So here is a simple rule: just use a thick and short cable to connect the inverter to the battery terminals. For your reference you can find exact length and diameter values in the users' manual of the SW inverters.

Can the SW power inverters be installed on the wall?
Yes, they can be mounted table-top or on the wall as well, using the holes at the rear side of the inverter units.