2000W Inverter won't run microwave

[Go-red-car]

OK so I thought that I had the perfect solution so that we wouldn't have to take a generator along to run the microwave. I inherited a solar panel from the previous owner which I believed to be the Go Power Overlander kit which is 190W. The charge I am getting is only 7amps in full sun so my guess is that it is the 110W panel. It is a huge panel so that is why I guessed it was the 190W.

Batteries - 2 Renogy 100AH, with Renogy smart battery monitor to monitor the actual state of charge (not just voltage). It takes it forever to get to 100% so I am guessing that the charge rate is insufficient. I have ordered a Renogy 200w panel which I was going to connect in parallel with the existing one. Is this OK since the panels are very different in the output?

Solar controller was upgraded to the new Go Power GP-PWM-30 UL which has a lithium charging profile.

Inverter: 2000W Renogy

Go Power 30 amp transfer switch.

Everything seems of work and all plugs are energized. My Nespresso machine rated at 1500W runs no problem. When I attempt the microwave it will run for 5 seconds, then the inverter gives an audible alarm and shuts down. I looked up the power consumption for the Dometic microwave and it is 1100W output and 1500W consumption.

So why will the coffee maker run but not the microwave? Power usage is the same. I know that there are parasitic losses as some things like the converter are always on. I have also read that most inverters will tolerate a surge and that a 2KW will be ok at 3KW for a short burst.

Is a 3KW inverter in my future? I wish I would have thought this through a bit more.

So my two main questions are:
- Why will the coffee maker run while the microwave won't as they are both 1500W
- Can I combine dissimilar panels in parallel? (my past setup was a 110W in parallel with a 100W. All worked fine and I would get 15A of charge in full sun).

[craigav]

While I am not a Microwave technician, I am a certified electronics technician (retired). In any case and to keep it high level. A microwave oven creates a nonsinusoidal wave on the electrical circuit (distortions in what would normally be a smooth wave pattern). Inverters do not like this and have problems providing enough power to overcome the distortions. This is particular to microwaves and also occurs but less so for AC motors and some other electrical items. In any case, you need roughly double the inverter capacity than what the Microwave says it needs, and that is with a pure sine wave inverter. This doesn't occur with resistance loads like a heater element, toaster, incandescent light bulb, etc.. Also, just fyi, even with a stronger inverter, the microwave will take longer to cook when powered from an inverter vs shore power. ~CA

[EJH]

7 amps for the 190W Go Power in full sun with a PWM controller sounds right. If you tilt the panel, and are on the equator, you could see a max of 9 amps.

I added a second 200W Rich Solar panel, in series to my stock 190W Go Power. That setup is great (the specs for both panels are close enough it is ok to mix). However, I also upgraded to a MPPT controller. If you use the Go Power PWM controller, you will need to parallel the panels. You will be happy with the second panel. In full sun, I will see 16-18 amps charging my battery.

My guess is your microwave is pulling more the 1500W. You can measure it when on shore power and find out. I have a 700W Renogy inverter and it definitely pouches about its rating. It will run my wife's hair dryer, which makes her happy I also think craigav hit the nail on the head. You probably need a 3000W inverter.

[DonBr]

I have run microwaves on 2000 watt inverters many times, and the only failures have been with modified-sine-wave units. Microwaves hate those, and even if they run they sound like they are doing it under protest! Renogy makes both Pure Sine Wave and Modified Sine Wave models. What model do you have?

[XoXSciFiGuy]

Just my two cents worth. I agree microwaves are a problem when trying to run them via batteries and an inverter. You don't have lead acid batteries I see. This is good because if you put too heavy a load on those batteries you will shorten their life substantially.

The best way to avoid problems is to switch to a pure sine wave inverter and go to at least 3,000 watts. Later, you might want to consider running four batteries at a time, as well. With 400-800 amp hours to work with (depending on whether you go with 100 amp hour or 200 amp hour batteries) your problems will be over.

We boondock a lot and my policy is that you can never have TOO much available power. I have a pure sine wave inverter, but it only runs to 750 watts right now. I will be going bigger at some point. We run the portable generator to do the microwave for now. Generator is dual fuel but we always run it on propane tanks. Easier to store propane than gas, of course.

[Go-red-car]

Originally Posted by craigav

While I am not a Microwave technician, I am a certified electronics technician (retired). In any case and to keep it high level. A microwave oven creates a nonsinusoidal wave on the electrical circuit (distortions in what would normally be a smooth wave pattern). Inverters do not like this and have problems providing enough power to overcome the distortions. This is particular to microwaves and also occurs but less so for AC motors and some other electrical items. In any case, you need roughly double the inverter capacity than what the Microwave says it needs, and that is with a pure sine wave inverter. This doesn't occur with resistance loads like a heater element, toaster, incandescent light bulb, etc.. Also, just fyi, even with a stronger inverter, the microwave will take longer to cook when powered from an inverter vs shore power. ~CA

Thanks Craig for a plausible explanation. My background is in electronics so this does make sense to me. Would you think that a 3K inverted would work?

[Go-red-car]

Originally Posted by EJH

7 amps for the 190W Go Power in full sun with a PWM controller sounds right. If you tilt the panel, and are on the equator, you could see a max of 9 amps.

I added a second 200W Rich Solar panel, in series to my stock 190W Go Power. That setup is great (the specs for both panels are close enough it is ok to mix). However, I also upgraded to a MPPT controller. If you use the Go Power PWM controller, you will need to parallel the panels. You will be happy with the second panel. In full sun, I will see 16-18 amps charging my battery.

My guess is your microwave is pulling more the 1500W. You can measure it when on shore power and find out. I have a 700W Renogy inverter and it definitely pouches about its rating. It will run my wife's hair dryer, which makes her happy I also think craigav hit the nail on the head. You probably need a 3000W inverter.

EJH, thanks you for the confirmation on the panel being 190W. So adding a 200W Renogy panel should not present much of a mismatch.

[Go-red-car]

Originally Posted by DonBr

I have run microwaves on 2000 watt inverters many times, and the only failures have been with modified-sine-wave units. Microwaves hate those, and even if they run they sound like they are doing it under protest! Renogy makes both Pure Sine Wave and Modified Sine Wave models. What model do you have?

DonBr, I have the pure sine wave as I need to run computers also

[Go-red-car]

Originally Posted by XoXSciFiGuy

Just my two cents worth. I agree microwaves are a problem when trying to run them via batteries and an inverter. You don't have lead acid batteries I see. This is good because if you put too heavy a load on those batteries you will shorten their life substantially.

The best way to avoid problems is to switch to a pure sine wave inverter and go to at least 3,000 watts. Later, you might want to consider running four batteries at a time, as well. With 400-800 amp hours to work with (depending on whether you go with 100 amp hour or 200 amp hour batteries) your problems will be over.

We boondock a lot and my policy is that you can never have TOO much available power. I have a pure sine wave inverter, but it only runs to 750 watts right now. I will be going bigger at some point. We run the portable generator to do the microwave for now. Generator is dual fuel but we always run it on propane tanks. Easier to store propane than gas, of course.

XoXSciFiGuy... yes I have thought about 4 batteries as we are off-grid a lot as well. The trouble is the lithium price tag. I came from 2x100AH 6v batteries. I figured that the 2 lithiums would give me double the capacity as I am not restricted to just going down to 50% charge. My go power charge controller at last reading stated that I had 660 amp hours. I don't know how it can calculate that it is not in communication with the BCM. I believe that it can only extrapolate from battery voltage, which is OK for lead-acid but not correct for lithium. I like the idea of dual fuel for the generator... unfortunately I am already committed with a Yamaha 3000.

[craigav]

Originally Posted by Go-red-car

Thanks Craig for a plausible explanation. My background is in electronics so this does make sense to me. Would you think that a 3K inverted would work?

I suspect you are already very close to having enough inverter power based on your statement that it would run ~5 seconds. So with that, I would expect even 2500w would be enough and with running the microwave only, but I would go with a 3000w inverter anyway and have a little more overhead than needed.

Also, keep in mind that while others report that their microwave will run off of a 2000w inverter, many RV microwaves are less powerful than yours, for example mine is ~950w power output and likely requires 1250w~1350w input (it doesn't show the input power on the label). Some RV microwaves are even less powerful and around the ~700w range.

One other thought, when I mentioned earlier that an inverter should be ~twice as powerful as the microwave input power, that is subjective and simply my recommendation. However, I suspect it would be more accurate to say that the inverter would need to be at least twice the microwaves output wattage as the bare minimum inverter size although that sizing suggestion may not be enough for some microwaves (just like motors, A/C's, etc) some are more efficient than others. ~CA

One other thought to share, if your DC input cables to the inverter are not large enough to carry all of the current needed for the maximum inverter output, then that could cause a low voltage shutdown scenario and appear to be similar to having an undersized inverter.

[Go-red-car]

Ok, a funny story... we wanted to warm up our cinnamon buns a little so we ran the microwave in 5-second increments four times. They were perfect!

I think you are right that trailer microwaves come in different powers. I had heard that the 700W was common so when I saw mine spec'ed at 1100 output and 1500 consumption I was a bit surprised. I should have done my homework as that is way too close. I have also heard that inverters work much better if you don't rum them at close to their maximum.

I'm using the 4ga 3 foot cables that came with the inverter. I deliberately placed the inverter close to the batteries. I notice that the 3000W Renogy inverters do not come with cables. Do you think that 4ga on a 3 foot run would be sufficient for 3000W?

I did a quick search and 4ga is rated for 195 - 260 depending on temp. 2000w will draw 167A while 3000w will draw 250A. The other consideration is the duty cycle. This will have very intermittent use and not be in continual use... LOL or the trailer would have to be full of batteries

[craigav]

Interesting points you have and information.

I should have asked earlier on about your wiring size, 4awg isn't enough for a 2000w inverter (under a full load). I suspect the inverter companies provide the minimum size cable (if any cable) to reduce costs or just to verify it works. The good news is that now that I realize you are using 4awg I believe that you may find that by either adding another 4awg cable parallel for each cable you have now, or better yet replace them all with 4/0 awg cables that your existing inverter may actually be able to run your microwave as long as there is no other usage occurring at the same time.

The charts you looked up were likely like this one, but you really need to size your cabling for the cooler temps (60\75c degree which is 140\167f degrees) as what happens is not just that the cable gets hot, that heat is similar to adding an electric heater in series into the circuit and that lowers the voltage at the end of the cables while also pulling more amps which is what is creating the heat. Check out table 1 in this chart for example.
https://www.southwire.com/medias/sys...aper-LO-1-.pdf

I would suggest this, replace the cables with 4/0awg cables as that is what you would want to have anyway when moving to a 3000w inverter. I suggest you replace them prior to purchasing a new inverter as you may find that your existing inverter is powerful enough after all for your microwave and with having larger cables, and if not, then you are not out anything as you needed to purchase larger cables anyway for a larger inverter.

If you can't find 4/0awg cables, the minimum I would suggest would be 2/0awg.

~CA

[Go-red-car]

Originally Posted by craigav

Interesting points you have and information.

I should have asked earlier on about your wiring size, 4awg isn't enough for a 2000w inverter (under a full load). I suspect the inverter companies provide the minimum size cable (if any cable) to reduce costs or just to verify it works. The good news is that now that I realize you are using 4awg I believe that you may find that by either adding another 4awg cable parallel for each cable you have now, or better yet replace them all with 4/0 awg cables that your existing inverter may actually be able to run your microwave as long as there is no other usage occurring at the same time.

The charts you looked up were likely like this one, but you really need to size your cabling for the cooler temps (60\75c degree which is 140\167f degrees) as what happens is not just that the cable gets hot, that heat is similar to adding an electric heater in series into the circuit and that lowers the voltage at the end of the cables while also pulling more amps which is what is creating the heat. Check out table 1 in this chart for example.
https://www.southwire.com/medias/sys...aper-LO-1-.pdf

I would suggest this, replace the cables with 4/0awg cables as that is what you would want to have anyway when moving to a 3000w inverter. I suggest you replace them prior to purchasing a new inverter as you may find that your existing inverter is powerful enough after all for your microwave and with having larger cables, and if not, then you are not out anything as you needed to purchase larger cables anyway for a larger inverter.

If you can't find 4/0awg cables, the minimum I would suggest would be 2/0awg.

~CA

Hi Craig... just wanted to close the loop with you. My son had a piece of 4/0 kicking around and made me up a set of cables. They are massive! Tried the 2KW inverter with new cables and we got 30 seconds instead of 5 before it shut down. So cable gauge was definitely a factor.

So we switched out the 2KW with the 3KW inverter. It works but it works hard and the fan comes on in the inverter. That microwave must draw a lot of power. I looked at the Renogy site and they recommend 3x100 AH batteries. I just have two so I guess I will have to be careful. I now have an almost new 2KW boat anchor.

[EJH]

2x 100AH batteries probably can't source enough current to power a 3k inverter at full load.

[craigav]

Originally Posted by Go-red-car

Hi Craig... just wanted to close the loop with you. My son had a piece of 4/0 kicking around and made me up a set of cables. They are massive! Tried the 2KW inverter with new cables and we got 30 seconds instead of 5 before it shut down. So cable gauge was definitely a factor.

So we switched out the 2KW with the 3KW inverter. It works but it works hard and the fan comes on in the inverter. That microwave must draw a lot of power. I looked at the Renogy site and they recommend 3x100 AH batteries. I just have two so I guess I will have to be careful. I now have an almost new 2KW boat anchor.

Thanks for the follow up. Here is a thought to share not that it matters for many cases, an inverter has its highest efficiency numbers at around 30~50% of its capacity. In other words a 2000w inverter would require more input amps to produce 2000 watts than a 3000w inverter would require to produce 2000 watts. You were very close to being able to run the microwave continuously with the 2000w inverter but for sure the 3000w inverter along with the heavier cables will serve your needs better.

As far as adding a 3rd battery, as long as the 2 batteries will allow you to run everything you want to run, then I suspect you will be just fine. Certainly 3 batteries would allow the 3000w inverter to produce more output current than 2 batteries and for a longer duration, but if you don't need more inverter output current than your highest appliance load (microwave) then all should be fine. In either case, 2 or 3 batteries, there will be a lot of current flowing through the inverter which will kick in the cooling fans to their highest ability when running your microwave.

Are you using the Renogy Lifepo4 batteries or Renogy's AGM batteries? I think their LifePo4 batteries are limited to 100a current output each (as that is common with LifePo4 batteries), and the AGM batteries likely could output more than 100 amps each at any point in time.

For another thought, there is a classified section here in the Jayco Owner's website and a 2000w inverter would be more than enough for RV's with a lower wattage microwave. I suspect you could find someone here interested in purchasing a lightly used good condition 2000w inverter.

~CA

[craigav]

One other thought to share which certainly may already be known by many, but for others as well who may read this thread.

When you power your RV with an inverter, be sure to turn off the breaker to the converter if it would also be powered by the inverter otherwise. Not that failure to do so would necessarily create an electrical failure, but there would certainly be a loop that would cause very high inefficiencies. ~CA

[Go-red-car]

Originally Posted by craigav

Thanks for the follow up. Here is a thought to share not that it matters for many cases, an inverter has its highest efficiency numbers at around 30~50% of its capacity. In other words a 2000w inverter would require more input amps to produce 2000 watts than a 3000w inverter would require to produce 2000 watts. You were very close to being able to run the microwave continuously with the 2000w inverter but for sure the 3000w inverter along with the heavier cables will serve your needs better.

As far as adding a 3rd battery, as long as the 2 batteries will allow you to run everything you want to run, then I suspect you will be just fine. Certainly 3 batteries would allow the 3000w inverter to produce more output current than 2 batteries and for a longer duration, but if you don't need more inverter output current than your highest appliance load (microwave) then all should be fine. In either case, 2 or 3 batteries, there will be a lot of current flowing through the inverter which will kick in the cooling fans to their highest ability when running your microwave.

Are you using the Renogy Lifepo4 batteries or Renogy's AGM batteries? I think their LifePo4 batteries are limited to 100a current output each (as that is common with LifePo4 batteries), and the AGM batteries likely could output more than 100 amps each at any point in time.

For another thought, there is a classified section here in the Jayco Owner's website and a 2000w inverter would be more than enough for RV's with a lower wattage microwave. I suspect you could find someone here interested in purchasing a lightly used good condition 2000w inverter.

~CA

CA, thanks for your great suggestions! I feel fortunate to have you to bounce ideas off. Yesterday I was a bit distressed as the batteries went from 96% SOC to zero overnight. The Smart monitor gave the voltage at 11.6. I confirmed this reading with a voltmeter. The solar panel controller was showing a small charge of 0.3A (heavy overcast), but the monitor showed zero. I checked the fuse between the solar controller and the battery and it was melted. I checked the pigtail connection and it was corroded so that might have presented a resistive load. Disconnected the solar and isolated the batteries by removing the + from the trailer and also the inverter. Put the batteries on a charger overnight.

This morning the batteries are 100% SOC on the smart monitor. I reconnected the trailer + and also the inverter + (which produced a spark, which I hope is normal). Inverter is off... trailer is on shore power, so I will leave it for a while to see if there is a loss. The only thing that is on is the clock on the stereo. I can't imagine it drawing much.

Thanks for the info on turning the breaker on the converter off when running the inverter. I had no idea you were supposed to do that. So that would be the main breaker?

[Go-red-car]

Oh, and I am using the Renogy Lifepo4 batteries. 2x100AH

[craigav]

Originally Posted by Go-red-car

CA, thanks for your great suggestions! I feel fortunate to have you to bounce ideas off. Yesterday I was a bit distressed as the batteries went from 96% SOC to zero overnight. The Smart monitor gave the voltage at 11.6. I confirmed this reading with a voltmeter. The solar panel controller was showing a small charge of 0.3A (heavy overcast), but the monitor showed zero. I checked the fuse between the solar controller and the battery and it was melted. I checked the pigtail connection and it was corroded so that might have presented a resistive load. Disconnected the solar and isolated the batteries by removing the + from the trailer and also the inverter. Put the batteries on a charger overnight.

This morning the batteries are 100% SOC on the smart monitor. I reconnected the trailer + and also the inverter + (which produced a spark, which I hope is normal). Inverter is off... trailer is on shore power, so I will leave it for a while to see if there is a loss. The only thing that is on is the clock on the stereo. I can't imagine it drawing much.

Thanks for the info on turning the breaker on the converter off when running the inverter. I had no idea you were supposed to do that. So that would be the main breaker?

It is common when connecting an inverter that hasn't had power to it recently to have what is called "inrush" current. This inrush of current can cause issues with blowing fuses along with burning small spots on the cable connector or the battery post and only lasts for a second and commonly seen as a big spark when connecting the power. If you run into problems with the inrush current (such as blown fuses or damage to the battery cable\post) then there are options that you could use such as using an resistor in the circuit when first connecting (and reconnecting) the power to the inverter. I wouldn't be overly concerned though unless that inrush current causes issues. (what is happening is that the transformer, capacitors and perhaps other electrical components in the inverter momentarily pull all the power they can, which only lasts for about a second or less in time). Here is an example of a resistor that would work (8 ohm 100w), and what (the simplest method) you would do is prior to connecting the last battery cable that feeds into the inverter is to connect the resistor between the battery and the cable for a few seconds and that will taper the inrush current and then you can connect the battery cable as it should be connected without having a big spark.

https://www.amazon.com/Tulead-Resist...al&sr=1-1&th=1

btw, if you use a resistor to "pre-charge" the inverter, be aware that the resistor could get very hot very quickly, so using gloves may be a very good idea.

Because I don't know how your inverter is wired into your RV, having the converter on or off while on inverter power may have been already addressed. Many inverters are wired to provide power to only a certain circuit in the RV, and others wire the inverter to provide power to all of the circuits. If the inverter is wired to provide power to all of the circuits then it is more likely that one of those circuits would also be the charge\power supply converter's circuit as well. On mine (and many RV's), there is a breaker specific for the converter that could be turned off so you wouldn't need to shut off the main breaker, just the breaker providing power to the converter. If you have any details regarding how your inverter was installed and connected then I could provide more specific thoughts.

As a side note, the LifePo4 batteries don't have issues with fully discharging them (as the internal bms protects them), so other than the inconvenience and the understanding that something you are not aware of depleted the batteries, there would be no harm to the batteries. If your batteries continuously run down when you believe that there is little to no load on the batteries, then certainly that is something that will need to be addressed and something that will likely become apparent in short time.

Best wishes, ~CA

[Go-red-car]

Originally Posted by craigav

It is common when connecting an inverter that hasn't had power to it recently to have what is called "inrush" current. This inrush of current can cause issues with blowing fuses along with burning small spots on the cable connector or the battery post and only lasts for a second and commonly seen as a big spark when connecting the power. If you run into problems with the inrush current (such as blown fuses or damage to the battery cable\post) then there are options that you could use such as using an resistor in the circuit when first connecting (and reconnecting) the power to the inverter. I wouldn't be overly concerned though unless that inrush current causes issues. (what is happening is that the transformer, capacitors and perhaps other electrical components in the inverter momentarily pull all the power they can, which only lasts for about a second or less in time). Here is an example of a resistor that would work (8 ohm 100w), and what (the simplest method) you would do is prior to connecting the last battery cable that feeds into the inverter is to connect the resistor between the battery and the cable for a few seconds and that will taper the inrush current and then you can connect the battery cable as it should be connected without having a big spark.

https://www.amazon.com/Tulead-Resist...al&sr=1-1&th=1

btw, if you use a resistor to "pre-charge" the inverter, be aware that the resistor could get very hot very quickly, so using gloves may be a very good idea.

Because I don't know how your inverter is wired into your RV, having the converter on or off while on inverter power may have been already addressed. Many inverters are wired to provide power to only a certain circuit in the RV, and others wire the inverter to provide power to all of the circuits. If the inverter is wired to provide power to all of the circuits then it is more likely that one of those circuits would also be the charge\power supply converter's circuit as well. On mine (and many RV's), there is a breaker specific for the converter that could be turned off so you wouldn't need to shut off the main breaker, just the breaker providing power to the converter. If you have any details regarding how your inverter was installed and connected then I could provide more specific thoughts.

As a side note, the LifePo4 batteries don't have issues with fully discharging them (as the internal bms protects them), so other than the inconvenience and the understanding that something you are not aware of depleted the batteries, there would be no harm to the batteries. If your batteries continuously run down when you believe that there is little to no load on the batteries, then certainly that is something that will need to be addressed and something that will likely become apparent in short time.

Best wishes, ~CA

Hi CA... ok some good news for a change. After about 4 hours of being reconnected there is no loss as I am at 99.8%.

To answer your question on the inverter wiring, I am going through a GoPower 30 amp transfer switch as it was my intention to power all plugs in the trailer. So the main shore power feed to the converter is interrupted and run to the transfer switch. The converter is powered by either the shore power or the inverter. With this wiring configuration I don't think I can exclude the converter. https://www.google.com/search?q=go+p...HBI0H4Lg4p9JcM

The transfer switch is not much more than a 30A relay, but I do believe that it has some logic to give priority to shore power if both shore and inverter power is detected.

Thanks for the link to the resistors! Good to know that the inrush surge is pretty normal. I don't think that would have affected the fuse from the solar controller to the battery though as the current path would be from the battery to the inverter. I picked up a switch to turn off the stereo completely so that it is not a source of drain.

So quick question on converter charging. I had assumed that a small charging current would be supplied to the batteries when connected to shore power. But when I measure the + lead from trailer to battery I read no voltage. Now that I think about it when I have the inverter on will it attempt to charge the batteries? That is a scary loop. Battery power to inverter to converter and back to charging batteries???

I now also have the LED lights flickering in the trailer and I am sure they did not do that before. This is happening on shore power.

I have the fridge on Auto. Just realized that when I power the converter with the inverter it will also run the fridge. That could be a big drain. When I test the inverter again I will switch the fridge to LP.