Inverters

Plucka · August 2020

Is there a difference -Using a 1500 watt inverter to produce 240 volts to power a 1000 watt kettle or a 3000 watt inverter to produce the same.Is the 12 volt consumption the same or one uses more than the other.

mcgivor · August 2020

There may be slight difference depending on the efficiency curve but that shouldn't be of concern,, the greater issue, when using high capacity inverters with 12V nominal, is, the high DC current encountered and the associated voltage drop, which in turn requires substantial conductors. For example if a 3000W inverter was at full capacity the DC current demand would be ~ 250A, which only iincreases as the battery voltage drops under such a load.

BB. · August 2020

Power = Voltage * Current

So, in theory, a 1,500 Watt inverter will use the same amount of DC power for a 1,000 Watt kettle, as would a 3,000 Watt AC inverter.

In practice, the 3,000 Watt inverter has larger switching transistors and such... So there is a fair amount of energy loss in the conversion from 12 VDC to 240 VAC...

There are "curves" of inverter efficinecy... When using a only a few Watts of AC load, the 6-20 Watt "Tare" loading of the AC inverter just to "turn on" can swamp small AC loads and give you very poor efficiency (10 Watt load and 10 Watt Tare = 50% efficiency

At higher loading many inverters can be in the 85% to 95% efficiency level.

Other issue... For example it is very hard to get 3,000 Watts of energy from a 12 volt battery bank. Because of the high currents and voltage drops (using very heavy copper cables), I would suggest that you not try to pull much more than 1,200 to 1,800 Watts from a 12 volt battery bank. A 3kWatt inverter on a 12 volt battery bank at full AC loading would draw:

3,000 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage = 336 Amps (12 volt bank) maximum continuous current draw.

4/0 or heavier wiring would be like 0.46 or 11.6 mm in diameter (or thicker if using heavier cable):

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Example of 4/0 cable

WG gauge	Conductor Diameter Inches	Conductor Diameter mm	Conductor cross section in mm2	Ohms per 1000 ft.	Ohms per km	Maximum amps for chassis wiring	Maximum amps for power transmission	Maximum frequency for 100% skin depth for solid conductor copper	Breaking force Soft Annealed Cu 37000 PSI
0000	0.46	11.684	107	0.049	0.16072	380	302	125 Hz	6120 lbs

If you want more Watts, look to a 24 or 48 VDC battery bank instead.

-Bill

Plucka · September 2020

thanks Bill

Inverters

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