2000 watt inverter question

[DannyLori]

I have a 2000 watt sine wave inverter connected to a separate fully charged 12 volt deep cycle battery. My issue is my 900 watt microwave will only run for a few minutes before the inverter begins beeping. I don't understand why it won't run longer? I don't have anything else plugged into the inverter and all wires are tightly connected. I tested it on My T.V. with dvd player and it runs for over an hour. Am I doing something wrong or is the microwave just too much for my inverter? I tried this when boondocking. The trailer has two more identical batteries but I dont have them hooked up to this inverter. Would it help if I connected all three batteries in parallel to the inverter.

[KMP44]

What are the specs on the battery? If you have a typical lead acid battery, you might only have something like 50 usable amp hours. A 900 watt microwave pulls 7.5 amps at 120 volts, but you are creating that 120 volts from your 12V battery. So at 12 volts, you are more like 75 amps to run the microwave. In theory you might have 40 minutes of microwave time, but in actual use it could be less. Not sure what you have for existing batteries, but for sure a bigger battery bank would help. Microwaves, toasters, and coffee pots are big draw items when running on battery power.

[DannyLori]

The only information on my battery is Duralast Marine Deep Cycle 840MCA 180RC 27DC.
I'd be happy if the microwave would run for 10 minutes. I also tried running a simple 750 watt air fryer but it wouldn't last more than 5 minutes. In your opinion Would a LiFePO4 Lithium Battery 12V 100AH Rechargeable BMS work better for this application?

[roadster]

If you google it, a 900w microwave could require 2700 watts of starting power. Your 2000 w inverter is not enough.

[tomkatb]

A common issue is the wire size between the inverter and battery. Chances are you are several sizes too small.

Then too, a single battery is being taxed too much with an over 1000 watts from the battery.

Lithium single batteries have bms’s that limit the outflow. Generally 100 amps for one battery. That is 10 amps ac. Not a lot. Plus you know inverters loose 20% in the conversion. So really you need 1200 to get 1000.

Several batteries will work better,

[carguy4471]

On a lead acid battery you may be dealing with voltage sag as well. If the draw on the battery is high enough the voltage will dip, if it dips below the inverters minimum input voltage it’s likely shutting off due to low voltage. Could be this.

[TitanMike]

Lead acid batteries suffer from voltage sag at hugh current levels. My microwave causes my 2,000 watt inverter to draw ~120 amps while running. Not a huge amp hour draw but a single 12v battery will struggle to maintain sufficient voltage for 10 minutes and avoid shutdown.

Will probably take two 12v batteries in parallel OR. 2 - 6 volt golf cart batteries in series. OR 2 - 12 v LiFePo4 batteries in parallel. The LiFePo4 batteries don't suffer the same voltage sag but most 100 ah LiFePo4 batteries have a BMS internally that limits continuous output to 100 amp thus the requirement for two.

Simply put, you need more battery capacity.

[TitanMike]

Originally Posted by roadster

If you google it, a 900w microwave could require 2700 watts of starting power. Your 2000 w inverter is not enough.

I run a 1350 watt (input) microwave regularly on a 2,000 watt Renogy Pure Sine Wave inverter with zero issues. I feed it with two 100 ah LiFePo4 batteries which provide plenty of current and voltage.

[jimmoore13]

Your answer is here:
https://www.rapidtables.com/calc/ele...alculator.html

Your 900 watt microwave is likely the OUTPUT rating. Input power requirements are on the data plate. But a 900 watt micro may require 1300 watts or more to run, and significantly more to start.

Nonetheless, plug 900 watts (power) and 12 (volts) into the calculator, and you get 75 Amps.

Lets assume your stand-alone 12 volt battery is a Group 24 marine battery. A group 24 has a rated capacity of about 70 to 80 amp hours (AH) on a good day. You get to use half. This means you have 35 or so AH at your disposal. Yet, your micro is sucking power at the rate of 75 amps, so you're all done after about 30 minutes. Worse, battery capacity ratings are based on modest loads that drain the capacity over a period of 20 hours...not half an hour. Those high current draws deplete the battery much more quickly.

So, yes, you're asking too much of a single, stand-alone 12 volt battery to be running your microwave. And forget about bundling your other two batteries into your microwave torture chamber...you'll drain them dead in no time, too. Fire up your generator for heavy 120 volt loads. Just absolutely have to have popcorn after quiet hours? Make it on the stove.

[TitanMike]

Originally Posted by jimmoore13

And forget about bundling your other two batteries into your microwave torture chamber...you'll drain them dead in no time, too.

They won't be drained as fast as a single lead acid 12 volt battery.

The great benefit of wiring batteries in parallel. Capacity grows as a multiple of the batteries connected.

I agree that just firing up the generator is best but one's neighbor may not agree if someone is doing so around midnight to warm a baby bottle or make a cup of hot chocolate.

[lckeehne]

Originally Posted by DannyLori

I have a 2000 watt sine wave inverter connected to a separate fully charged 12 volt deep cycle battery. My issue is my 900 watt microwave will only run for a few minutes before the inverter begins beeping. I don't understand why it won't run longer? I don't have anything else plugged into the inverter and all wires are tightly connected. I tested it on My T.V. with dvd player and it runs for over an hour. Am I doing something wrong or is the microwave just too much for my inverter? I tried this when boondocking. The trailer has two more identical batteries but I dont have them hooked up to this inverter. Would it help if I connected all three batteries in parallel to the inverter.

DANNY / LORI, I had to increase my battery bank to around 450AH. Now we can use M/wave - hair dryer and coffee maker. no problems, just not at same time. If you boondocks think about lithium battery... You could get by with two or three since they can be depleted further than my AGMs.

[TitanMike]

Originally Posted by lckeehne

DANNY / LORI, I had to increase my battery bank to around 450AH. Now we can use M/wave - hair dryer and coffee maker. no problems, just not at same time. If you boondocks think about lithium battery... You could get by with two or three since they can be depleted further than my AGMs.

I've been using two Lithium batteries with my Microwave for a full season (which for me is pretty much year round) and every once in a while I consider adding another. Inverter was added last year.

Then I look at my Victron BMV-712 use log and see my deepest discharge was only 162 ah out of 200 ah capacity. That was after three days with no charging so I pass on adding another battery.

[rk06382]

Originally Posted by DannyLori

The only information on my battery is Duralast Marine Deep Cycle 840MCA 180RC 27DC.
I'd be happy if the microwave would run for 10 minutes. I also tried running a simple 750 watt air fryer but it wouldn't last more than 5 minutes. In your opinion Would a LiFePO4 Lithium Battery 12V 100AH Rechargeable BMS work better for this application?

What AWG are your battery cables to the Inverter? You can lose power if you do not the right cable. The chart below is a guide. I am using 4/0 AWG.

[jimmoore13]

Originally Posted by TitanMike

<<SNIP>>
I agree that just firing up the generator is best but one's neighbor may not agree if someone is doing so around midnight to warm a baby bottle or make a cup of hot chocolate.

My popcorn comment covers these, too. Use the gas range to heat a pan of water...or a few cups of milk...and heat the bottle or make the hot chocolate. We are, after all, camping. And it's possible to respect quiet hours and achieve any number of goals without a microwave.

[DannyLori]

Thank you all for your great advice. I am going to try the simple suggestions first. Increase my battery cable size and then wire in my other two batteries in parallel. I can always use my generator if I really need to. Thanks again.