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Old 07-25-2021, 12:40 PM   #1
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Microwave on batteries?

We'd like to use the microwave for short periods without starting the generator. We are rarely on shoreline.


I ran a separate 120v power line to near the microwave so we can plug into the inverter or regular coach 120v by changing which one it's plugged into. I have plenty of battery and a 3000/6000 inverter but the even with all of that power is microwave fails to start sometimes and sets off the inverter alarm. Other times it starts and runs well drawing about 1750w. I was sure that a 6000w surge inverter would be enough to get it going but it's iffy.


I replaced the 1100w microwave/convection with a plain 1000w microwave but the problem remains. Is there a trick to handling the surge without and even bigger inverter?



Thanks all - the forums have made being a newbie much easier!
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Old 07-25-2021, 01:00 PM   #2
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Is your inverter wired to the distribution panel such that it runs all 110vac outlets and appliances? If yes, you should be able to run the microwave if you turn off all other ac loads. My inverter is 2000w with 3000w surge, and is wired direct to panel. Runs microwave fine as long as I’m not running any other big loads. If you’ve connected your microwave direct to the 110vac outlet on the inverter, it should work as well, as long as there aren’t any other big loads. Additionally, your battery bank needs to big enough to service a big load for a certain amount of time. If you’ve got enough dc output from your batteries and it still fails, you probably have a problem with the inverter. Conv/micro = 15a x 110v = 1650 watts peak
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Old 07-25-2021, 01:09 PM   #3
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Your inverter is probably the modified sine wave type (MSW). These sometimes have problems with microwaves and other appliances. It sounds like your inverter has plenty of electrical capacity for a microwave but the stepped, squared off waveform may be the problem.

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Old 07-25-2021, 02:41 PM   #4
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Your inverter is likely tripping due to the battery voltage dropping below the low voltage set point for your inverter. Probably around 10.5 volts, but you will need to check the setting from the manual for your inverter. There are a number of questions here. What brand and model is your inverter? Are the 12 volt cables from the battery to the inverter large enough (at least 3/0 AWG) and short enough (maximum of about 5 feet long)? You said you ran a separate wire for a new outlet for the microwave. Did you use a minimum of 12 AWG wire? Did you test the outlet using a different load like a lamp or some other device. Depending on the quality of your inverter, it may not actually be capable of supplying 3000 watts and a surge of 6000 watts. Most inverters can only support their surge rating for milliseconds and many of the cheap china made inverters have inflated power ratings. Your said you a plenty of battery. What is the actual amp-hour capacity of your batteries?
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Old 07-25-2021, 02:56 PM   #5
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Thanks

Thanks DavidM and Marine359! The inverter is a Kinverch 3000W Pure Sine Wave with 6000 watt surge. It replaced the Kinverch 2000W Pure Sine Wave with 3000 surge. You can imagine how my heart sank when the new 3000 did the same thing that the 2000 did.


I'm using 2 100Ah battleborn Lithiums along with the Sprinter battery and even tried adding a 4th battery with jumper cables to the back of the inverter.



The brand is well reviewed but is nothing special. We buy non-Chinese whenever possible but the Victron version is almost 4 times more.


The only other thing plugged in is the fridge. It may be pulling current but it idles at around 70 watts so it would seem to be irrelevant. I'll unplug it and test some more.



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Old 07-25-2021, 03:22 PM   #6
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Opened the checkbook for good batteries eh? Then slammed it shut when buying the inverter. Good inverters like Xantrex and Victron don’t cost a lot more than not so good ones relative to the cost of your BBs.

Actually, the inverter may be working properly. And since you’ve got great batteries, there must be something wrong with the wiring.
1. Most Inverters should be grounded separately to chassis. Is yours properly grounded?
2. Are the dc input cables tight?
3. Is the inverter properly fused?
4. Are any cables or wires warm to the touch when you try to use the microwave?
5. Is the inverter ac output connected to a gfci?
6. Is the inverter connected directly to the battery +/- or is there something in between, like a disconnect switch, a bus bar, a shunt, or a fuse block?
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Old 07-26-2021, 09:58 PM   #7
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I found that a 3000 watt pure sine wave inverter worked well with the residential microwave in my Winnebago ( I ditched the OEM junk one from HiPointe and replaced with a LG ). Note that the 3000 watt size just helps deal with the large in-rush current a microwave oven draws for a split second when the microwave generation device starts up.

I bought an inexpensive one with remote on/off switch on Amazon for under $ 400 in 2017 and it has worked great since. The one I bought is no longer for sale but many similar ones are listed on Amazon. I feed the inverter 120 VAC output thru a 20 amp slo-blow fuse (old screw in type) and ran # 12 Romex to three 120 volt 20 amp transfer switches and the inverter can power both 120 V convenience outlet circuits and the microwave oven 120 V outlet ( I put the third transfer switch between the EMS box and the microwave ). The 20 amp AC fuse is to protect the AC wiring when the inverter is supplying power to the 3 circuits.

Don't believe anyone that says you have to buy a $ 2,000 inverter/charger system to do this.
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Old 07-27-2021, 06:07 AM   #8
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Nobody has suggested OP buy a $2,000 inverter charger. The issue here is OP’s inverter won’t run his microwave. If he first determines there is no problem with the wiring or installation, it means the problem is with his inverter. And, yes you can buy a 2000w PSW Xantrex on Amazon for $364. Optional remote. The value to buying a US brand is they have a customer service dept.
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Old 07-27-2021, 07:50 AM   #9
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So I have a tip since experienced in the electro mechanical trades 4 over 30 yrs. The new Dodge promaster has easy access to its automotive battery (not coach) by drivers side floor location. I personally purchased the smallest size microwave and it still has a total wattage draw inclu the the losses incurred from a 1500 watt pure sine inverter of aprox 1100 watts-100 amp draw on the 12 volt supply connecting to the battery. I custom assembled and electronic soldered/ double insulated all 4 foot cable w inline 150 amp circuit breaker near the positive/red alligator clip and connections to easily alligator clip on to the battery. Simply start the vehicle and carefully attach the jumper cables. My intent is to just use my microwave for a short duration of maybe 2 minutes max to reheat food. There is no way around the enormous power consumption of a microwave unless you get involved W a complex setup for safe operation (heavy #2 wire size, circuit breakers etc.)
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Old 07-27-2021, 09:39 AM   #10
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I have 400 amp hours of AGM batteries and I have a first rate Magnum 2000w PSW inverter. I can run my microwave for 30 secs before the LVCO alarm sounds and trips the inverter.

Microwaves are very tough loads requiring a LOT of amps to start up.

We just don't do it. If the microwave is needed we start the generator.
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Old 07-27-2021, 09:00 PM   #11
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I have four 200 amp hour Interstate 6 V Golf Cart Flooded Lead Acid Batteries sold by Costco sold for under $ 100 each for a total of 400 amp-hour of 12 volt capacity and can use microwave for up to about 10 minutes in the afternoon after solar has charged batteries to 100%. In morning with batteries discharged to 80% or more I can always get a couple of minutes in without getting the inverter low voltage shutdown, plus power for the toaster and the Keurig coffee maker.

This is still happening after the batteries are over 3 years old. I do have an on-board On-Board Desulfator. Battery Minder OBD-12, under $ 100. It runs whenever charging voltage is present across the batteries.

So, I don't have to wait for the end of quiet hours to use my microwave or run my high power draw Keurig coffee maker in the morning.

Generally, AGM does not do as well as flooded golf cart batteries for heavy amp loads.

If you have a large inverter doing a large load it helps to have two pairs of 6 volt golf cart batteries in parallel to split the amp draw across more batteries and greatly extend the microwave run time.

The same holds true for LiFe04 each 100 AH one is only rated to deliver a max of 100 A DC so to do a microwave or Keurig type AC load you need at least 2 wired in parallel.
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Old 07-27-2021, 09:38 PM   #12
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I should add that I have the LVCO set at 12.1v and the microwave would sag the batteries to that briefly at start up. But rather than set it lower like 11.9v I've kept it at 12.1v and just decided to use the generator.

But my point was the microwave uses a lot of power.

But perhaps the 6v battery setup is able to pull it better.
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Old 07-28-2021, 02:50 AM   #13
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Quote:
Originally Posted by dhodgesnvl View Post
We'd like to use the microwave for short periods without starting the generator. We are rarely on shoreline.
Why? Are you wanting to microwave at a place with no shore power but enforces a quiet time with the Generator? Do you ever use your generator otherwise? Seems like a hefty investment thus far for popcorn

My daughter has been known to start the genny when he had shorepower connected to pop her popcorn , but I ain't mad her.
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Old 07-28-2021, 04:53 AM   #14
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The same holds true for LiFe04 each 100 AH one is only rated to deliver a max of 100 A DC so to do a microwave or Keurig type AC load you need at least 2 wired in parallel.
My battery rated for peak output of 350adc for 6 sec. Battery LVCO 9.8v. Inverter LVCO set at 11.5v Anything over 300a would trip my in-line fuse. We have only used our microwave 3 times on inverter only. Twice for defrosting meat, and once for melting butter. Seems to do ok with those chores without having to fire up the genny. We wouldn’t consider using it for anything else without SP or genny.
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Old 08-01-2021, 04:34 PM   #15
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Run 850 Watt Microwave or 1400 Watt convection on battery.

I have a sharp convection microwave that is 850 Watt of microwave and 1400 Watt of convection.

I have run it on AGM and LiFePO4 batteries using our Magnum 2800/12 inverter. No problem at all. I have run the convection long enough to bake cakes or meals at 1400 Watts. It takes 10 or more minutes of full 1400 watts to preheat. Typically we microwave things at full power for 10 minutes or less. We can do this with a coffee pot and the refrigerator running. During testing I have run the system at near maximum with over 250A of power for 30 minutes.

The high current put a hurt on the AGMS due to Peukerts effect but the LifePos just shrug off high current.

Your battle born batteries specify 100A continuous discharge. If you have 2 you should be ok there for the microwave of 1800 Watts assuming 85% inverter efficiency and 12.5 volts at the inverter input.

Your going to have to measure your voltage at the inverter under load. To figure out if this is an inverter or battery/ wiring issue. When you get in to dc currents of 150A or more things have to be wired correctly with correct materials or you get big voltage drops and dangerous heating.
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Old 08-01-2021, 04:38 PM   #16
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I installed 3x100 amp hour Battle Born lithium batteries and a Victron 3000w inverter along with a 1000w of solar. The batteries are connected to the + busbar with 4/0 cable, as is the inverter. Photo included. As you can see from the photo, the inverter has pretty short cable runs. I built the busbar from a 1"x 1/4" copper bar. The inverter is connected to the breaker box under the bed with #6 wire, as I recall. (I had a Winnebago dealership do that part for me because I wanted to separate the breaker box into two circuits.) We did not run new wiring from the breaker box to the microwave. Over-engineered? Maybe, but it works.

We run our microwave daily while boondocking without the generator and with no problems (unless my wife forgets and turns on her hair dryer at the same time, which usually, but not always, trips the breaker).

So, it is possible to make it work.

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Old 08-01-2021, 04:55 PM   #17
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I run a 1100 watt microwave with two Battle Born, 100 amp hour battery. I use the Victron 2000/80/50 Mulitplus, and Victron 702 monitor. I have the remote for the inverter. No problems running microwave. BUT. I use 2/0 cables from the battery to the inverter, and distance of about 2 feet!

I suspect that the OP does not have adequate cables from batteries to inverter. The cables which come with his inverter are 6 AWG! Good for about 500 watts! Then there is a mention of combining the Sprinter house (House?) or (Chassis?), and jumper cables with a 4th battery.

In my humble opinion there is a danger combing a FLA or AGM battery directly to the LiFePO4 batteries. Mine are isolated from the house circuit. I charge with the Victron Multiplus @ 80 amps off the generator or mains power. I also have a Sterling 12 DC to 12 DC 30 amp charger off the engine start battery.

I would recommend that the OP check his cables to the battery to be sure that they are rated at adequate size (and short distance). I am a bit dubious about that Chinese inverter.
Yes the Victron inverter/charger is about $1200. But that is a high quality inverter which is definitely PSW and has a charger which has the profile and power to charge the BB batteries. Also I didn't see any mention of monitoring the battery. I also strongly suggest that the LiFePO4 batteries be isolated and never connected directly or indirectly to any other batteries (Jumper cables are often relatively small gauge, and even connecting to the inverter power intake poles, it is connected directly to the Li battery--potentially a dangerous situation.
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Old 08-01-2021, 10:03 PM   #18
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Quote:
Originally Posted by dhodgesnvl View Post
Thanks DavidM and Marine359! The inverter is a Kinverch 3000W Pure Sine Wave with 6000 watt surge. It replaced the Kinverch 2000W Pure Sine Wave with 3000 surge. You can imagine how my heart sank when the new 3000 did the same thing that the 2000 did.


I'm using 2 100Ah battleborn Lithiums along with the Sprinter battery and even tried adding a 4th battery with jumper cables to the back of the inverter.



The brand is well reviewed but is nothing special. We buy non-Chinese whenever possible but the Victron version is almost 4 times more.


The only other thing plugged in is the fridge. It may be pulling current but it idles at around 70 watts so it would seem to be irrelevant. I'll unplug it and test some more.



RVing is fun but modifying and upgrading is BIG fun.

Likely the cables provided with the inverter if used were undersized and not capable of providing the inverter with enough current to carry the load of starting the microwave however since it does not appear to be an RV specific inverter with a built in converter you would likely need to manually turn off the converter/charger when running on the inverter or you will have the charger running trying to make up for the load being taken off the battery by pulling power from the inverter to try and charge it which will be running at somewhere around 85% to 90% efficiency which is just going to generate additional loading and heat to no real purpose.

The surge capacity of most 1,200 watt inverters should be able to handle the microwave regardless of if being a convection model or not. I have run an 800 watt Maytag Convection Microwave without issues on an 800 watt Harbor Freight inverter as long as the batter cables were heavy enough to carry the load.
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Old 08-02-2021, 12:59 AM   #19
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NeilVL: You make a very good point... The cables need to handle the current over time!


moabdds: That's a nice setup. Can you post more picture of your system? ..It looks like you have also installed some specialized current monitors.

====

Personally, I have not run my microwave on inverter power that often, but I have come to trust "THE INVERTER TEST."

What is "THE INVERTER TEST?"

I basically run my microwave for 1.5 minutes and heat up a bowl of water. And if my FLA house batteries do NOT bounce back to within -0.1V of where I started then I know my FLA batteries are sulfated and need replacing if the volt meter registers below 12.0V.

===

Note: I was replacing my 4-6V-GC2 Golf Cart Batteries every 2 years, but ever since I STOPPED charging my batteries with my Dimensions 12X20B3R4T "charger" and started using a Victron 17A charger (#BSC IP167 Victron Charger) I don't even put water in it and I hope my house battery life will reach 4-5 years. (TBD)

In addition, this Victron is my battery maintain when I put my RV in storage and this prevent "battery freeze" in sub-32F weather. (At least in Texas anyway.)

I highly recommend you stop using the Dimensions Charger and start using the Victron (Bluetooth) charger and with a KeyLine VSR your alternator will charge your house batteries when you drive!

I also have 400W of solar power, but first I would by the Victron, then the VSR, then the solar panels, then the LiFe04 batteries in this order.
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