anderson2624
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- Jul 28, 2011
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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
Thanks
12v TO 120 AND BATTERY WATT HOURS
- Thread starter anderson2624
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vermilye
Well-known member
Yes, less the efficiency loss. Of course the battery current will be a minimum of 10X the 120V current (has to be to keep the wattage the same...)
Tom
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The answers you've received are for a 12V battery or two 6V batteries in series, not a single 6V battery. Also realize that you won't get the full capacity out of the battery; The inverter will shut off at some (low) battery voltage. Some of us use 50% of the battery capacity in our calculations.
Gary RV_Wizard
Site Team
The inverter costs in efficiency, i.e. converts some of those watt-hours to heat instead of 120 electric, but the battery watt-hours is still the same. The efficiency of an inverter depends on the size and loading, as well as the design quality of the device, but 90% is a fair rule of thumb estimate.
Two 6V batteries in series will have double the watt-hours (same amperage at 2x the voltage = 2x the wattage).
You should also be aware that the battery watt-hours is not a fixed number. The amount of usable power (watt-hours) varies with the amp load on the battery. The lower the amp load, the greater the number of watt-hours available (Peukert's Law). Furthermore, the storage capacity deteriorates with age and use, so the spec amp hours generally apply only to a new battery in laboratory conditions.
Last, an inverter usually shuts off at 10.5v and may give an warning alarm at 11.0v The 10.5v figure is the same as the low cut-off used to calculate the 20 hR discharge rate and the 1350 watt (per 6v battery) capacity, so in theory the inverter can use all 1350 watts. However, conventional wisdom is that discharging a battery all the way to shut-down will damage it and severely reduce its longevity, so a max discharge of 50% (roughly 12.0v) is recommended. That reduces the available watt-hours substantially.
Two 6V batteries in series will have double the watt-hours (same amperage at 2x the voltage = 2x the wattage).
You should also be aware that the battery watt-hours is not a fixed number. The amount of usable power (watt-hours) varies with the amp load on the battery. The lower the amp load, the greater the number of watt-hours available (Peukert's Law). Furthermore, the storage capacity deteriorates with age and use, so the spec amp hours generally apply only to a new battery in laboratory conditions.
Last, an inverter usually shuts off at 10.5v and may give an warning alarm at 11.0v The 10.5v figure is the same as the low cut-off used to calculate the 20 hR discharge rate and the 1350 watt (per 6v battery) capacity, so in theory the inverter can use all 1350 watts. However, conventional wisdom is that discharging a battery all the way to shut-down will damage it and severely reduce its longevity, so a max discharge of 50% (roughly 12.0v) is recommended. That reduces the available watt-hours substantially.
Lou Schneider
Site Team
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- Mar 14, 2005
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- 13,231
Watts are units of power - voltage x current = watts.
So yes, you'll get the same number of watt-hours at 12 volts as you will at 120 volts, less the 8-10% conversion overhead in the inverter.
Where people get confused is having batteries usually rated in ampere-hours, not watt-hours. Since current is but half of the power equation (you have to multiply amps by volts to get watts) the voltage becomes a critical part of the discussion.
120 watts equals 1 ampere at 120 volts, or 10 amperes at 12 volts. 1 amp-hour at 120 volts requires 10 amp-hours from a 12 volt battery.
So yes, you'll get the same number of watt-hours at 12 volts as you will at 120 volts, less the 8-10% conversion overhead in the inverter.
Where people get confused is having batteries usually rated in ampere-hours, not watt-hours. Since current is but half of the power equation (you have to multiply amps by volts to get watts) the voltage becomes a critical part of the discussion.
120 watts equals 1 ampere at 120 volts, or 10 amperes at 12 volts. 1 amp-hour at 120 volts requires 10 amp-hours from a 12 volt battery.
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