Newbie..... Batteries?

philo111 wrote:
Thanks everyone but it sounds like a bunch of "educated guesses".
Isn't there some precise math?

Sure

2 is weak and marginal at best for a 2000 watt inverter. Minimum recommended by Xantrex is 400 amp hours.

3 don't go there.

4 is about minimum and should work fine. They work fine for me. 15 full minutes will still be a heavy discharge especially in one swoop. My MW draws about 1650 watts and 150 to 170 amps from the battery. So the 1000 should be easier. But is that cooking power or input power?

6 if space and money are easy this is the way to go.

philo111 wrote:
Isn't there some precise math?

Not really, not with the Peukert effect, soc, temperature, wire size, type of inverter... We've been through this before with you.

Can you answer my question?

1000 watts/12 V = 84 amps

84 amps X 0.25 hours = 21 amp-hours

21 amp-hours/0.8 inverter efficiency = 27 amp-hours

As you can see it's not a huge total amount of energy. BUT it is a huge current drain in a short period of time. You need a huge battery bank and super-heavy wiring to pull 84 amps in 15 minutes.

Listen to those with experience in such matters.

I would find some other way to heat the item in question. Try the range top or oven. People have cooked without microwaves for thousands of years, you can manage it too.

Thanks everyone but it sounds like a bunch of "educated guesses".
Isn't there some precise math?

I can't imagine that you will ever be able to do that successfully with any reasonably sized RV battery bank. The inverter size is "OK" but your microwave may use at least half of that and if the inverter is not a True/Pure Sine Wave (TSW, PSW) it's possible you would burn up the microwave even if the battery bank was large enough.
This is not a realistic goal and you should be looking at other power sources when using the microwave for such a long period of time.

i have a decent size 5 battery AGM bank, 675 Amhrs , thats equal to 6 or more golf cart batteries, these weight 102# EACH

and i still prefer to run the generator, 6 minutes to bake a potato

i might give it a 1 minute shot late at night, so as not to disturb anybody
15 minutes MW on batteries never, well maybe if i had a 2000 ampHr bank of batteries

in lead acid that about (1) ton aka 2000# of batteries

if you need 15 minutes at 2 AM, try eight batteries
if this is during daylight normal hours, save the batteries, use the generator

you would need several hours of generator run time with a Beefy converter, for a recharge anyways, better to use the generator for minutes instead of several hours

BTW we full time and have a residential 120v compressor fridge and a large MW
i know about heavy amps and battery recharging

been there tried that
just a 6min potato is a really hard battery drain

15 minutes continuous? You probably can't carry that many batteries. Usage divided up into 1-2 minute increments? 6.

Probably at least 4 to be safe.
I would run a generator instead.