40 Amp draw from batteries to run Microwave?

No, 40 amps does not seem correct less it's one very small Microwave. 100 amps is more what I'd expect a Microwave to draw.

how to estimate battery draw for 120 volt appliances

Watts = Volts times Amps times Power factor
Volt-Amps (if listed) = Volts times Amps
For a Microwave the power factor can approach ONE so we will use that
Assume a battery voltage at the inverter of 10 (this is not correct but there are several things that need to be factored in like conversion efficiency and Inverter "overhead" and such and using 10 volts is an easy way to factor them in at currents less than 100 amps it's fairly close)

Watts/10

So your Microwave must be about a 400 Watt model

MEXICOWANDERER wrote:
I bought a high wattage "kettle" off Amazon that boils a liter of water in under 2 minutes. Starting from 25c

Jeez, you running it on 240V AC?

In Europe, you can get close to 3kW kettles, but with only 120VAC and 15A outlets here and in Mexico we're pretty much limited to 1800W.

Oh, I bet you're doing something tricky ...

I bought a high wattage "kettle" off Amazon that boils a liter of water in under 2 minutes. Starting from 25c

rjsurfer wrote:
When running my microwave on high I noticed the battery voltage dipped to 11.6 and the input side of the 2,000 Samlex inverter was only drawing 40 DC amps or so.

I didnt think that 4 T105's voltage would drop that much.
...

How long does it take to get down to 11.6VDC?

At 900W AC pull my 4 GC2s will eventually drop at least a full volt after a full charge (12.7 -> 11.6). Takes a while though. I can heat up but not boil a litre of water at 900W before the 1000W PSW inverter starts complaining about the low DC voltage.

So we're cooking/heating low and slow when using the batteries. And it just amazes me how much energy it takes to heat up water. We fry eggs rather than boil them.

My amps are ~86A at ~900W. Maybe you missed a digit and it's actually 140A?

Forget the 40 amps, doesn't seem right at all.
But the 11.8 on 4 6'ers sounds about right.
I used to do a micro off a 1500 watt prowatt, and the voltage held 10.8 on 2 6'ers,......never a problem w/ those 1 and 2 minute warmups. But after a few yrs, the MSW prowatt took its toll on the micro, had to replace it. Since then I learned that for myself, micros and converters don't go together,.....or, just not worth it, IMO

Thanks guys....

I'm going back to the trailer and recheck the amperage going into the inverter with my clamp on.

Ron W

Tis true with thick plate batteries. A trade-off: less CCA in exchange for lifespan and ruggedness. With my monster bank my 1875 watt microwave sucks voltage to 23.6
But from there on volts per amps gets a stiffer lip.

I recently burn't up my samlex 2000 watt pure sine wave inverter using a 1500 watt 1.5 quart water kettle. I have 4ea full river 250 ah 6 volt agm batteries wired for a 12 volt system. It was pulling 145 amps.
I replaced it with a 3000 watt inverter/charger and wired my batteries for a 24 volt system. It was 95 degrees ambient temperature outside when I done this so that didn't help since the samlex 2000 is only rated for about 120 degrees.

The 11.6v is quite reasonable on four 6s. The 40 amps reading is faulty. Use the 10 to 1 rule for inverter draw.

Say the MW is "1000w" then on the back it will say input required is say 1400 watts. So that means it will draw about 140 DC amps. This will create a goodly voltage drop to that 11.6v.

MW "on high" will draw the same as "on low" because it draws the same but cycles on and off with more time off at low. An exception to that is the Panasonic Inverter which will draw fewer amps at a lower setting according to owners posting on here.

Note also if you have a MSW inverter, it will take less power from the MW even on high, so it will take longer to heat something, but also will draw fewer amps than a PSW inverter would with the same MW.

That does not apply to resistive loads such as a kettle or toaster, which will have the same amps draw from PSW or MSW inverters

My little A/C at 450w pulls 33 amps.