12v inverter draw on batteries with microwave

Much better to run your generator for micro and coffee pot.

DAS26miles wrote:
I calculate about 100amp draw. That's per hour, right?

Well, sort of. It's 100 amps if it's one second, or 60 seconds, or 2 hours. If you draw 100 amps for 1 hour, that's 100 amp-hours, or ah.

DAS26miles wrote:
if I run the microwave for about 15 minutes, I am using about 25amp hours.

Yes, 25 ah is correct. Using an MW for that long is hard on batteries unless you have about 20 of them. Best to just use it to warm stuff up, not cook.

What we did here with our OFF-ROAD camping trips with our 255AH (3EA 85AH Interstate in parallel was to purchase a el-cheapo white faced manual knob controlled 600WATT microwave from WALMART. We like to use this just to quickly warm up coffee and maybe a few minutes to do a quick frozen TV dinner type snack. Baked POTATO with our steaks is a must have for us as well and this microwave works ok for a couple of baked potatoes with my 1500WATT pure sine wave Inverter.. We probably only use our microwave maybe 10 minutes total during one day/night run off the batteries.



I tried running my big 1500WATT microwave and it eats up my battery power rather quick...

The small microwave solved this problem for us...

Roy Ken

160 amps to start and climb to 175 amps as the battery voltage drops.
This is why you need four plus batteries. Small group 24 you should have six or more.
Good luck running 15 minutes on the pair.

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.

Hi,

Rule of thumb is divide input watts by 10. An 1100 watt micro might have an input of 1500 watts, so demand may be on the order of 150 amps. Unfortunately there is another factor called a Peukert Calculation so apparent draw may be a heck of a lot larger.

On a 170 amp-hour battery bank a 150 amp draw jumps up to 354 amps after the calculation. Your batteries will unlove you at that level of discharge.

Basically you can probably get away with heating up a cup of coffee, but a 15 minute run time may take the battery bank down below 50% state of charge. It may be possible the batteries would be permanently damaged.

Your calculations are basically correct. But, the faster the rate of discharge, the fewer amp-hrs a battery bank can put out.

http://en.wikipedia.org/wiki/Peukert%27s_law