Questions about inverting DC to AC

[kettaneh]

Hello,

I have a question, How can I calculate the working time for the following scenario:

I have 12V 7.2AH LEAD ACID SLA DEEP CYCLE BATTERY
Then I used DC 12V to AC 220V Power Inverter USB 1000W to give me AC

I connected one 100w lamp .. For how long it will work ? how can I calculate it


another question .. How can I calculate the watt of the inverter (to know which one I should buy) .. is it 220v x amp ? or 12v x amp ?

thanks

 

[mfb]

I connected one 100w lamp .. For how long it will work ? how can I calculate it

You will need the efficiency of your converter to find the power needed as input.
Assuming your battery is designed to deliver ~100-150W (check this!), it can store 12V*7.2AH = 86,4Wh, so it will run for something like 30-50 minutes.

another question .. How can I calculate the watt of the inverter (to know which one I should buy) .. is it 220v x amp ? or 12v x amp ?

The power rating of the transformer is probably for the output, so you should use the 220V-side. If the losses in the converter are small, the other side should give a similar result (the current will be much larger there, to account for the lower voltage).

 

[RBTO]

For power inverters, the rating is always for the load. If you have 1000W of light bulbs (a resistive load), you need at least a 1000W inverter (can be larger but not smaller).

Something else to consider besides the efficiency of the inverter is your battery. The faster you discharge a battery, the lower the Ah rating becomes. Usually the Ah rating is taken for a 20 hour discharge period. If you discharge over a longer time it actually goes up slightly, but if you were to discharge your battery in say 5 hours, the Ampere-hours you realize can decrease considerably (plus you can damage the battery if the drain is too high).

In your example of a 7.2 Ah battery, the 20 hour rating would result in a 360 milliampere drain (for 20 hours), but with a 100W load, the current drain would be over 8.3 Amperes so the 7.2 Ah battery rating would be diminished substantially. Lower ambient temperatures will also decrease the Ah rating.

Lastly, the Ah rating of a given battery usually falls with the age of the battery and how it has been treated during that lifetime (rate of discharge, depth of discharge, number of discharge cycles, etc.)

 

[RBTO]

Here's an addenda to my last post about loss of Ah capacity with increased discharge rates (Peukert's Law). This website might be of interest to you.

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-fundamentals/peukerts-law-and-exponent-explained/

 

[alphy]

Hello,

Calculating the working time for a battery connected to a power inverter is dependent on several factors, including the efficiency of the inverter and the power consumption of the connected device. In this scenario, the 100W lamp will draw approximately 0.45A (100W/220V) of current from the inverter. Assuming the inverter has an efficiency of 90%, the power consumption from the battery would be 0.5A (0.45A/0.9). Therefore, with a 7.2AH battery, the lamp should work for approximately 14.4 hours (7.2AH/0.5A). Keep in mind that this is a rough estimate and actual working time may vary.

To calculate the wattage of the inverter, you would multiply the output voltage (220V) by the maximum current that the inverter can supply. In this case, if the inverter can supply a maximum current of 4.5A, then the wattage would be 990W (220V x 4.5A). It is important to note that the wattage of the inverter should be higher than the wattage of the device you plan to connect to it, to ensure it can handle the power demand.

I hope this helps answer your questions. If you need further assistance, I suggest consulting with an electrician or doing more research on specific inverter models to determine the best fit for your needs.