" "for starting motors you need to use every trick in the book"....Hi Flux ,.....I would like to see that list...
is it possible it exist's??......sorry for the interuption........artv "
Possibly that was a misleading statement as there really is no book.
Induction motors are pigs to start, 3 phase are easiest and they have starting currents from 1.5 to 3 times running current and it is at low power factor during start.
Single phase motors of any size can pull 5 times full load current during starting and at power factors as low as 0.5 . Small alternators in particular have great difficulty starting them as the kVA available is not much more than the full load kW rating before the volts start to collapse.
Inverters do tend to be able to handle the higher kVA a little better but only for a fraction of a second. few motors start in such a short time. Those with an inertia load can often take several seconds to start.
With alternators adding capacitors will power factor correct the lagging current of the motor during the start and often make a big improvement but you need to be careful to have the capacitor connected to the motor, otherwise adding a high capacitive load to the alternator will cause it to produce excess volts and saturate the core, both of which are damaging to the alternator and anything connected to it.
With inverters ,adding a bit of capacitance as pf correction may work with a pure sine inverter, it is very risky with modified sine as these really don't tolerate capacitive loads and if you must try it, again make sure that the capacitor is in parallel with the motor before switching to the inverter. If the input cable is totally inadequate for the inverter you may gain a little with a monster capacitor directly on the input terminals of the inverter as this question was originally about but with proper input leads it will do little good.
I can't go into this in much more detail but any further tricks normally rely on reducing the starting requirements of the motor itself, mechanically or electrically. Resistance in the line ( long extension leads) may reduce the starting current to something the inverter can handle but sadly motors tend to take more current as the volts are reduced to try to maintain the starting torque unless you can reduce the frequency at the same time ( possible with an alternator but not many inverters).
Fridges and freezers are a bad case and unless you can get a start in about 3 turns before the compressor builds up pressure you won't get it away. If you fail then wait several minuted for the pressure to drop before trying again.
High inertia loads such as fans can be eased by removing the fan load during the start ( block the air in or out) once the motor is running let the air flow. There are other tricks such as a pilot motor running light before the main load motor is added but not so effective on single phase, it works far better on 3 phase . You can also play with changing the starting capacitor on single phase motors during the start but it is near impossible to give any real guide on this as each case behaves differently.
Shall have to be more careful about these throw away remarks in future but if it does help someone then all to the good.
Flux
