1.Inverter power supply
The continuous output power of the inverter indicates the power that the inverter can provide during standard operation. This is very important for inverter selection. Under operating conditions, the peak load requirements of the system at external rated temperature shall be met. The inverter used in Australia shall indicate the continuous output power and surge output power at 40 ℃. The inverter shall be capable of providing stable AC load at the highest temperature. Considering the variable nature of China’s load, large electrical equipment is often used in a limited period of time. Therefore, the rated power of 30min is available.
- Surge capacity
Most inverters are allowed to operate beyond their rated power for a period of time. This function is very necessary because the equipment may absorb multiple rated power during startup, especially when starting the motor with load. Generally, the surge capacity of the inverter is at least three times of the continuous rating, but when selecting a suitable inverter, it should be considered whether it can start all motors connected to it.
- Inverter rating
When the manufacturer publicizes its inverter, the unit is w or va. when the power factor is 1, the two ratings are unified. For example, an inverter with a rated value of 1000W can also be considered as 1000VA. Therefore, when selecting the inverter capacity, it is very important to determine the total apparent power of all loads as the minimum rating requirement of the inverter. This is especially important when the inverter is rated for small loads.
For example, a customer wants to run their TV and two indicators. The rated power of TV is 150W, but its apparent power is 200va. The customer bought a 200W inverter to supply power to the TV and two 15W indicators. It was found that the inverter tripped after 15 ~ 30min. AS4509. 2 point out that the inverter should be 10% higher than the rated capacity. If the customer plans to expand the system in the future, or the load will increase significantly than expected, it will be very beneficial to choose a larger inverter capacity. It is equally important to ensure that the inverter can provide the surge apparent power required by the equipment.
- Automatic start / demand start function
When there is no load, the inverter will stay in standby mode. The inverter will stay in this ready mode with a small amount of pulse power and constantly monitor the load circuit to “find” the load. Once the load is connected, the inverter needs to give a response within 0.5s. In standby mode, the inverter usually uses 20 ~ 60mA current to maintain operation. If the inverter does not have this characteristic, additional energy demand needs to be considered when the system is rated. Another option is to turn off the inverter when there is no load. However, this means that the inverter will have to be turned on manually whenever a load is turned on.
- Isolation
The input (DC side) and output (AC side) shall be electrically isolated internally. However, the inverter without transformer does exist in the market and may be dangerous when installed in a neutral or DC grounding system. Before installing the inverter, be sure to refer to as / nzs5033-2012 photovoltaic array installation and safety requirements, as / nzs3000-2007 wiring rules and other relevant standards.
- Radio frequency interference (RFI)
Because the switching speed of the power devices used in the inverter is very fast, no matter what type of wave they output, they will send out some form of RFI. According to different design schemes, the number of RFIs transmitted varies among inverters. The most significant RFI range generated by the inverter is 500KHz ~ 30MHz, which has the greatest impact on AM radio, marine interphone, wireless telephone and other transceivers. In Australia, the inverter shall meet the requirements of c-tick for RFI.
Some inverters can be generated from DC battery leads, which means that any wire connected to the battery will also radiate electrical noise. In order to minimize the impact of this noise, DC cables should not be indoors or close to communication equipment. Noise suppression equipment and technology will facilitate battery and DC circuit wiring. The interference of some inverters comes from the inverter itself. The best way to minimize this interference is to place the inverter as far away from the house or communication equipment as possible. RFI can also be transmitted from AC lines. RFI should not be confused with 50Hz buzzing, i.e. low-frequency buzzing in audio equipment or noisy motors, such as ceiling fans. These problems can only be solved by installing a high-quality sine wave inverter.
Read more: What factors affect battery life?