12v TO 120 AND BATTERY WATT HOURS

[anderson2624]

A 6 volt battery has 1,350 watt hours. When fed into an inverter does it still have 1,350 watt hours of 120 V AC?

Thanks

[Qwert66]

Yes watt hrs (in) minus a slight loss for wire efficiency in the form of heat.
Watt hrs (out) depends on the efficiency of the inverter usually in the 85-90% range for a pure sine wave type. It will be less (effective) efficiency for a modified sine wave unit. Volts x amps = watts Remember 1350/6vdc = 225 amp hrs @ 6v and 1350/120vac = 11.25 amp hrs @ 120volts

[BryanL]

All lead acid batteries have about the same energy density by weight - this comes out to about 12 watt hours per pound to the 50% discharge point. You don't want to pull all of that 1350 watt hours from your battery as a routine thing if you want best battery service and life.

One thing to note when inverters are considered: the energy rating is at a power draw of about a watt per pound (the 20 hour amp hour rate). If you draw at a higher rate than this, the available energy capacity of the battery is reduced. Search "Peukert" to find out about the guy who discovered this phenomena and what it means.

Efficiencies are always a factor. An inverter should be places close to the battery so as to reduce wiring losses. Keep in mind that much of the loss in the efficiency of the inverter can be gained back due to its wiring and loads being at 10 times the voltage, which means 1/10 of the current and wiring loss is proportional to the square of the current.

Also watch out for excessive precision. Available battery capacity is influenced by 10% or more due to such things as temperature, age, cycle to cycle variation, and use profile. That means that calculating things out to a gnat's eyelash, while it might be fun, can be misleading when it comes to actual performance.