KNOW YOUR LOAD POWER FACTOR AND PROTECT YOUR OFF GRID INVERTER!ok sir gawa ako ng feedback mamaya... so far ok naman yung inverter... nasubukan ko na sya sa automatic washing machine at ref... yung isang ref na pang tindahan yung ref ng coke namatay yung inverter pero nung nilipat ko sa medyo mababang wattage na ref ayun napagana nya yung ref.. meron syang meter dun sa gilid na nag iindicate ng load pero di naman umakyat yung meter..
by Rogel Naval, EE, Mar 31, 2017
AC power supplied by Meralco has 2 components. True Power and Reactive Power. The combination of which is called Apparent Power. We only pay for the True Power which is expressed in watts and KWH. The other component, the reactive power, which is expressed in VAR or KVAR, we dont pay for this.
But it will be much different if you are using off grid inverter. Your inverter must supply the apparent power, the combination of true power and reactive power.
For example: Inverter is rated at 1kw. The load is 700w. You may think that it is ok because load is about 70% of rated power. If the power factor of the load is only 50% or 0.5, the total apparent power supplied by the inverter is already 1400VA (volt-amperes)
Power factor = True power/Apparent Power.
Apparent power = True power / Power factor (700w/0.5 = 1400VA). This means also that reactive power is 700var.
Battery does not supply reactive power. It only supplies true power. It is the inverter components like inductors and capacitors that received and delivers reactive power to and from the load.
If load power factor is low, it must be corrected using a capacitor (same as power saver that you can buy at the mall) . But the value of capacitor must be computed. (Computations are available in the internet). If power factor is low say 50%, the inverter will draw 50% more current and increase internal loss in the inverter. This waste can easily be avoided if you can correct the power factor. Power factor dictates the efficiency of inverters also.
RULE OF THUMB:
Power factor limits the capacity of your inverter. Hence if you dont know the power factor, stay at 50% of inverter rating. For example 1kw inverter, run only at 500w.
But power factor can go down to a very low number so BEWARE! This is one major reason why that high frequency inverter easily failed. Use transformer type inverter for mixed loads. Its big transformer can handle reactive power much better than those high frequency inverters. But BEWARE also! Not all low frequency inverter are created the same. Cheap toroidal models have lower efficiency, which have the same performance characteristics of EI core transformer. Same as not all EI core low frequency inverter are the same. Mosfets quality alone can lower the performance characteristics of an inverter.