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Old 08-28-2019, 01:17 PM   #1
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Inverter and Microwave

Couldn’t find an answer in search so here’s my question. I have a 2000watt inverter, 2 six volt GC batts powering it, and want to run a 900 watt (7.5 amp) small microwave (.9 cubic ft). Will it work?
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Old 08-28-2019, 01:35 PM   #2
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I have run a MW on an inverter for years. Used to be an old modified sine wave that made the MW buzz a bit. Last year, I installed a Xantrex Pure Sine Wave 2000W inverter and MW runs like normal.
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Old 08-28-2019, 01:41 PM   #3
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Originally Posted by Gulf Comanche View Post
Couldn’t find an answer in search so here’s my question. I have a 2000watt inverter, 2 six volt GC batts powering it, and want to run a 900 watt (7.5 amp) small microwave (.9 cubic ft). Will it work?



Is that 2000 watts peak or running watts? If it's a modified or true sinewave then probably. The older square waves I found had a harder time dealing with powering the microwaves capacitors and transformer. I had an 1100 watt micro on a 2200 running watt squarewave inverter. It would shut down as soon as the microwave started up. I don't remember the brand right off but it was a quality RV unit made in the 90's and in my camper. It shouldn't hurt to try it. The inverter has protections in place to prevent an overload.
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Old 08-28-2019, 01:47 PM   #4
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It will work. The inverter will be fine but he batteries won't last long. If your GC batteries have 200 Ah capacity, you can use 100Ah before they are 50% discharged. The microwave will use roughly 100 Amps. So, if the batteries are fully charged, fairly new and you have no other power consumers, you can run your microwave for an hour.
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Old 08-28-2019, 02:00 PM   #5
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It works fine for me. The only thing to be aware of is the amount of power than they draw. Your inverter can handle it, but can your battery bank. Isn't 900W of power 75amps at 12 volts? That doesn't take into account the 10-20% loss at the inverter. So your microwave would be drawing 80 amps from your battery bank? That may be a bit much for just 2 GC batteries that may have 120Ah capacity. You might double check that with someone that actually understands electricity.
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Old 08-28-2019, 02:09 PM   #6
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Your inverter can handle it, but can your battery bank. That may be a bit much for just 2 GC batteries that may have 120Ah capacity.
If its a decent PSW inverter, it can handle it no problem. A friend is building an off-grid cabin in Wyoming. I just set him up with a solar panel, my old Xantrex 2000W inverter, and two Costco GC 6V batteries. Amazingly, it happily drives an old 15A Skil worm drive circular saw through 2x12 lumber without a hiccup. All day long. I believe the PO said his MW was rated at 7A.
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Old 08-28-2019, 05:23 PM   #7
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Couldn’t find an answer in search so here’s my question. I have a 2000watt inverter, 2 six volt GC batts powering it, and want to run a 900 watt (7.5 amp) small microwave (.9 cubic ft). Will it work?
Yes your inverter can handle it if your batteries are good but, watch your amp meter..... I keep one 120vt light. If it goes dark, time to shed some loads and close the breaker again.
My 1800 watt inverter has saved more than my bacon, a number of times. Pun intended.
On a 30 watt boat, it can mean juggling the loads.........
#1 shut off the HW heater.
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Old 08-28-2019, 05:26 PM   #8
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Not all microwaves work on modified sine wave. Make sure you choose a pure sine wave inverter or know that your microwave will work with modified sine wave.
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Old 08-28-2019, 06:56 PM   #9
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Who runs a microwave for an hour, even on and off for an hour a day. I will be using a convection oven with a 2000 inverter, 1300 watts but remember the oven cycles on and off in an hour but the small fan is on full time. I won't be using this oven at anchor much unless I run out of propane - BBQ and propane stove/oven.

I have 4 Firefly batteries, total 464 amps, but you can take Firefly's down further than other batteries. I also have Efoy 210.
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Old 08-28-2019, 07:22 PM   #10
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Apologies for just getting back to this. 4000 surge, 2000 continuous, modified sine wave. Specs say the mw draws 900 watts, thus 7.5 amps (900/120=7.5) unless my math is wrong. I’m good with it, thanks to all for the help. Now, FL, GA, AL MS, and LA batten down the hatches, big dose of weather headed this way. Good luck to all.
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Old 08-28-2019, 08:15 PM   #11
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Apologies for just getting back to this. 4000 surge, 2000 continuous, modified sine wave. Specs say the mw draws 900 watts, thus 7.5 amps (900/120=7.5) unless my math is wrong. I’m good with it, thanks to all for the help. Now, FL, GA, AL MS, and LA batten down the hatches, big dose of weather headed this way. Good luck to all.

7.5 amps at 120v. However at 12v that is 75amps. 75 ampss of current will come (not counting inverting loss) will have to come from your battery bank.

I use a microwave all the time on pure sine wave inverter, but I have over 750Ah in my battery bank.
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Old 08-29-2019, 12:09 AM   #12
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900W at 12VDC is a 75A current draw, plus inefficiencies.

GC batteries are about 200AHr each, and in parallel to make 12V, 200AHr in all.

If you are willing to discharge to 50% you've got 100AHr to use.

That's about 1 hour and 20 minutes of microwave time if you do nothing else.

But, more realistically, That's four cups of tea, two frozen dinners or meals of leftovers, and a bag of popcorn....and your batteries are still at 86%, meaning that you've only used 28% of your available capacity.

Realistically, you'll probably consume more of your capacity than that since batteries drain faster at a higher discharge rate than a slower one. But, there is also not really that big a difference in lifetime between discharging to 50% and 30%, depending upon how you look at it and how often you do it.
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Old 08-29-2019, 05:55 AM   #13
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The modified sine wave may be an issue, but only one way to find out. Otherwise is will work fine, but with limited operating time. Keep in mind that you will be draining the battery at about the 1h rate, not the nameplate 20hr rate, and consequently will have a bunch less capacity.
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Old 08-29-2019, 06:01 AM   #14
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Works for me, but I have a pure sine wave inverter (Magnum).


On my 4 6v Lifelines (220a of usable before charging). Make coffee, heat something 2 or 3 x in the micro (small, 1000w), run my computer for a few hours. In additional to the batteries running two fridges, LED lights, etc.


Works fine.
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Old 08-29-2019, 06:37 AM   #15
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"Amazingly, it happily drives an old 15A Skil worm drive circular saw through 2x12 lumber without a hiccup. All day long. I believe the PO said his MW was rated at 7A."

Older power tools usually have universal motors , brushes, and are rated AC-DC.

These (if you can find them) are by far the best tools to operate from an inverter!

If fed low voltage their amperage does not soar , they simply are a bit weaker , which is seldom noticed as few folks task them to the limit.

Tag sales are a great source for tools with universal motors.
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Old 08-30-2019, 07:30 PM   #16
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Inverter and Microwave

We use the microwave, vacuum and coffee grinder all the time but, only one unit at a time and for short periods and with the battery bank well north of 50% SOC. These things use lots of juice. 1125 amp hour battery bank and a Magnum 2812. We usually only use the vacuum on the Inverter when we are travelling, or on strong solar and expecting to fully charge the bank at some point during the day. Also we shut the Inverter off when we aren’t specifically needing it. The parasitic loads can be significant over a full 24 hour cycle.
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Old 08-30-2019, 07:52 PM   #17
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My small 750watt microwave when used with the inverter draws 10 amps AC (because the microwave has inefficiencies) and at the same time about 100amps from the batteries because the inverter has inefficiencies. My inverter is a modified sine wave unit with a max output of 1800w.

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Old 08-30-2019, 09:28 PM   #18
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I have a 3000 watt MSW and it runs a big MW that takes close to 14 amps when running.
It is a small bit different sounding, but not bad. Not all MSW inverters are the same.

i got a 3000 watt because the MW is not the only thing that will be running, I also have a fridge, etc...

I had a poor MSW 3000 watt that blew up, it caused the MW to be very noisy and fans were very noisy. I am glad it failed, cause now I have a better one. The stink they make when burning is very unpleasant.
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Old 08-30-2019, 09:56 PM   #19
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I just used my inverter for the microwave while on shore power.

I got back to the boat for the weekend, it was hot and I was hungry. I kicked on both AC units and the hot water tank (so so wouldn't forget and end up with a cold morning shower).

Then I tried to zap some food. No love. Over my 30A limit. Microwave kept running on inverter, but main breaker blew. I shut the breaker for the inverter/charger, turned the main back on, and all was good -- microwave finished uninterrupted on inverter. As soon as I was done zapping, turned the charger back on.

(Yes, I probably could just have turned thebhotbwatwr heater off instead of the charger -- but I'd rather risk forgetting the house charger than a cold shower. The genset can instantly cover house...but not warm a shower).
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Old 08-31-2019, 07:34 AM   #20
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I just used my inverter for the microwave while on shore power.
Good point. It never occurred to me to use the inverter for power management.

I could see myself connected to 30A shore power and running both air conditioners plus one other major load like the water heater, and wanting a quick bite to eat from the microwave.

Rather than shut off one of the big loads, I could cut power to the inverter, so the circuits connected to it (which include the microwave outlet) would pull from the battery. Then switch it back on when done. The charger would replace what I'd drawn out, but spread it out a bit so I don't exceed 30A.

It's always good to have options!
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