12v inverter draw on batteries with microwave
If I get a 2000w inverter for my MH and use my 1100w microwave, what will be the draw off the house batteries? Using Ohm's Law I calculate about 9 amps draw at 120v. Then converting from 120v to 12...
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Use the "divide by 10" to get the inverter's amps draw from the 120v wattage of what is running. So 1500w would be 150 amps.
Now look at the label on the microwave for its wattage rating. That will be about 1500w for a "1000w" microwave. MWs are named for cooking watts not for the watts they need to run them.
Next, when running microwaves inverters are different when MSW or PSW. The MSW type (if it will run the MW at all--many do just fine, some don't) will run the MW at lower power and draw fewer amps as a result. So you can run a 1000w MW on MSW and it will draw 110amps say, instead of the full 150 amps that a PSW will draw. However the MW will run slower, take a little longer to cook/heat up something.
Next is the battery bank to handle that big draw. First any battery bank will have an immediate voltage drop on that load, so when you turn on the MW, you want the battery voltage to stay above 11.0v, the inverter's alarm off. That means if the voltage drops 1.0v , you have to start off above 12v. Then voltage wil,l fall slowly while the load is on, so you need some room for that, so let's say you need 12.2v to run the MW for a couple minutes before the alarm goes off.
If battery voltage is already down from the TV/DVD being on and the furnace while you watch a movie, and you decide to make some microwave popcorn, that means you need the batteries to be up even more at the start.
So to get that ok, you need good wiring between the inverter and battery bank, and you need a big enough battery bank to hold up that voltage above 11v so you can get the job done.
Think in terms of four Wet batteries of about 440AH and wire maybe two three foot lengths of #2. However, AGMs can hold up their voltage better under load, so you could get away with two of those, depending on just how big the load is and for how long. That means if you have a small rig with room for only two batts and you want to do microwaving, you should make those two batts AGMs.
Now look at the label on the microwave for its wattage rating. That will be about 1500w for a "1000w" microwave. MWs are named for cooking watts not for the watts they need to run them.
Next, when running microwaves inverters are different when MSW or PSW. The MSW type (if it will run the MW at all--many do just fine, some don't) will run the MW at lower power and draw fewer amps as a result. So you can run a 1000w MW on MSW and it will draw 110amps say, instead of the full 150 amps that a PSW will draw. However the MW will run slower, take a little longer to cook/heat up something.
Next is the battery bank to handle that big draw. First any battery bank will have an immediate voltage drop on that load, so when you turn on the MW, you want the battery voltage to stay above 11.0v, the inverter's alarm off. That means if the voltage drops 1.0v , you have to start off above 12v. Then voltage wil,l fall slowly while the load is on, so you need some room for that, so let's say you need 12.2v to run the MW for a couple minutes before the alarm goes off.
If battery voltage is already down from the TV/DVD being on and the furnace while you watch a movie, and you decide to make some microwave popcorn, that means you need the batteries to be up even more at the start.
So to get that ok, you need good wiring between the inverter and battery bank, and you need a big enough battery bank to hold up that voltage above 11v so you can get the job done.
Think in terms of four Wet batteries of about 440AH and wire maybe two three foot lengths of #2. However, AGMs can hold up their voltage better under load, so you could get away with two of those, depending on just how big the load is and for how long. That means if you have a small rig with room for only two batts and you want to do microwaving, you should make those two batts AGMs.
