Comparison between inverters and UPS and calculating how long a battery can last
What are Inverters
inverters are adapters to convert and amplify battery dc power into ac. a question may arise about the difference between inverters and ups - uninterrupted power supply. the answer can be simply illustrated in a couple of points:
Inverter vs. UPS Comparison
|Switching time is slow comparing to UPS, i.e. > 20 milliseconds, a typical inverter takes 500 milliseconds to switch making it reasonably unsafe for high tech electronics like computers.||Switching time is relatively high 2 - 10 milliseconds, typically 8 milliseconds which is why we use them for computers.|
|External battery is required||Internal battery is installed|
|Supply time can be controlled by the amps of the battery||Supply time is restricted|
|Power transfer is not necessarily automatic||Automatic power switch|
|Last but not least, it doesn't beep your head out||Beeps the heck out of you|
博趣彩票手机app下载ups/inverter power is measured by the volts/amps, i.e. watts.
Watts ÷ 240 = Amps
Amps x 240 = Watts
Note: For calculations, you may want to replace the voltage values in this article to match with your country voltage. Here in Yemen, we are powered with 240 volts "hardly J".
You also have to keep in mind the startup watts which are consumed at the start of most appliances, as a general rule, most would consume twice as much at a startup, i.e.,
Watts x 2 = Approximate starting load博趣彩票手机app下载. This formula yields a close approximation of the starting load of the appliance, though some may require an even greater starting load.
Note博趣彩票手机app下载: Induction motors such as air conditioners, refrigerators, freezers and pumps may have a start up surge of 3 to 7 times the continuous rating.
Most often, the start up load of the appliance or power tool determines whether an inverter has the capability to power it. You may find the wordings "continuous and peak surge" on the back of an appliance.
Example: continuous - 2000 Watts, peak surge - 4000 Watts
If you don't find it, you can simply multiply Amps x Volts, i.e.
(Amps x 240 AC voltage) = Watts博趣彩票手机app下载. For example, you have a freezer with a continuous load of 4 amps, and a start up load of 12 amps:
4 amps x 240 volts = 480 wattscontinuous
12 amps x 240 volts = 1,440 wattsstarting load
to convert ac watts to dc amps:
AC Watts ÷ 12 x 1.1 = DC Amps
博趣彩票手机app下载(this is the size vehicle alternator you would need to keep up with a specific load; for example, to keep up with a continuous draw of 1000 watts, you would need a 91 amp alternator)
Pumps and Air Conditioners
|Well Pump 1/3 HP *||750||1400-3000|
|Well Pump 1/2 HP||1000||2100-4000|
|Sump Pump 1/3 HP *||800||1300-2900|
|Sump Pump 1/2 HP *||1050||2150-4100|
|7000 BTU to 10000 BTU *||1000-1500||2200-5000||A/Cs are a very difficult load because of the high start-up surge. Use the Locked Rotor Amps to determine the start up surge requirement.|
Appliances and tools with induction motors (marked * in tables) may require from 3 to 7 times the listed wattage when starting. The start-up load of the appliance or tool determines whether an inverter has the capability to power it. Be sure to check the specific wattage requirements and operating instructions for appliances / tools to be used.
How Long Can My Battery Last?
to calculate the time a battery can last, use the following formula:
T = ((AH / 2) / (L / BF)) x C
T- Time in hours
AH- Ampere Hours the battery is rated for
L- Load in Watts
BF- Battery factor (10 for 12V & 20 for 24V)
C- Discharge rate.
博趣彩票手机app下载going to the manufacture curves you can get accurate figures, for this article, let us assume that a battery lives about a year of continuous consumption and use a straight line depreciation factor @ 1/12, i.e. 0.083
1 - (0.083 * M)
M博趣彩票手机app下载 = Months passed
the only accurate method is by measurement as all batteries lose capacity with age, charge/discharge cycles and temp variations.
博趣彩票手机app下载it is also obvious that the more ampere hours you can get from a battery, the more time you will get, batteries come in the following sizes:
|Battery Type||Voltage||Ampere Hours|