Running microwave shutting down BMS

[HRTKD]

On my older inverter, which was a Xantrex, it was old school and required a manual reset when I overloaded it. Maybe your will at least have an overload light on it?

 

[Mia]

Conservatively, the microwave is going to draw 135 amps on the DC side (1380 watts / 12 / .85 = 135) based on your Killawatt meter. The label says 13 amps AC and using that we get 152 amps DC, Which should be well within the capability of your two batteries.

It would help to know what is shutting down. Was it the inverter or one of the batteries? You'll have to look at the logs. If even one of those batteries shuts down then you lose everything on the DC side because the other battery will also shut down due to overload from trying to carry all those amps by itself.

Check all your connections. A poor connection can show great voltage, but when put under load you'll get very few amps and the voltage will drop.

For comparison, my microwave is very similar.

View attachment 158324

My inverter is a Multiplus 12/3000 (effectively 2400 watts). I've had no problems running my microwave on high for five minutes. Running continuously doesn't sound like your problem, it's the startup surge. Before blaming your inverter, we need to know if your batteries are shutting down.

I did not see anything in the logs. Everything looked fine. Nothing red or greater than 0 for logged alerts.

 

[HRTKD]

Put a meter on battery #1 and turn on the microwave. If the meter shows no voltage when the microwave shuts down, then you know that battery stopped discharging. If the meter still shows voltage then do the same test with the other battery.

You may see that both batteries shut down and you'll have to figure out which one is shutting down first. It may happen so fast that you can't figure it out with just a simple voltmeter. Either way, if you see the batteries shut down then you know it isn't likely to be the inverter.

 

[Zwy]

I’ve included what is noted on the MW for the power rating in the one attachment. (All I recall is it’s noted to be a 2002 model and LG but apparently rebranded as Dometic.) Not sure what the wiring is for the MW because it was pre wired as well as unsure what the wiring was that they used to pre wire it for the solar. It’s a 2003 Arctic Fox 990. The wires for the batteries and the inverter are using 2/0 copper wires. The batteries were at least 97% when we attempted to the MW yesterday when it kept cutting out… yet it’s odd as I’m pretty sure we had it work once before earlier this trip. Also just tried the MW again in the driveway and it’s still shutting off after 2-3 seconds and was at 98%….I just took a picture of the microwave specs inside the MW and also included a picture from the manual I found online as attached. (When I put the KillaWatt display meter on tonight, it read 1380 watts and 13 amps and didn’t seem to catch any sort of surge at startup.) ps- Sadly I was not able to get any good shots of the setup at this time.

I have a 24V system for the inverter and it will pull over 50A as it turns the mag on/off.

13A sounds about right for 120V, that is over 1500W, but that is when it is already running. It's not possibly the inverter but the battery and it's cables that are the problem. On 12V, the surge will drop the voltage and the result is the inverter shuts down. Or the BMS is shutting down the system. Add in a little resistance from a marginal connection and it will shut down also.

 

[Mia]

Unfortunately I really can’t get any good pictures as it’s pretty tight in there ….the wiring is located in the cupboard that also houses the sink plumbing (and yes, I know, electronics and water is a bad combination… but it was really the only place there was available for it as we’re in a truck camper and there’s very limited available real estate available…)

Just need to know how to determine if it’s the bms or the inverter that’s causing it to cut out at startup.

On my older inverter, which was a Xantrex, it was old school and required a manual reset when I overloaded it. Maybe your will at least have an overload light on it?

The other odd thing is that it seems to run the toaster oven fine off the inverter while it’s parked in the driveway here and no external additional power.

I’ve included what is noted on the MW for the power rating in the one attachment. (All I recall is it’s noted to be a 2002 model and LG but apparently rebranded as Dometic.) Not sure what the wiring is for the MW because it was pre wired as well as unsure what the wiring was that they used to pre wire it for the solar. It’s a 2003 Arctic Fox 990. The wires for the batteries and the inverter are using 2/0 copper wires. The batteries were at least 97% when we attempted to the MW yesterday when it kept cutting out… yet it’s odd as I’m pretty sure we had it work once before earlier this trip. Also just tried the MW again in the driveway and it’s still shutting off after 2-3 seconds and was at 98%….I just took a picture of the microwave specs inside the MW and also included a picture from the manual I found online as attached. (When I put the KillaWatt display meter on tonight, it read 1380 watts and 13 amps and didn’t seem to catch any sort of surge at startup.) ps- Sadly I was not able to get any good shots of the setup at this time.

AFAIK, we had nothing else running simultaneously … also, now that we’re home, and are trying to troubleshoot this issue, we turned everything we knew was possibly a draw off … the fridge totally off, the fans are off, the UV system for the water off, the led lights off, the phone chargers were unplugged, etc… There was nothing else we could find that could have been actively simultaneously drawing anything from the LiFePO4 batteries. And odd.y enough the 1000w toaster oven also seems to do fine plugged into it. It’s looking like possibly its a bms issue. The one battery that’s at 100% is showing as locked on the bms app, so maybe that’s also stopping the bms on that battery from discharging as well versus just locking it out from charging? I guess maybe I’ll have to call the battery company and see if that’s possibly what’s happening. They also have new BMSs available that are rated for 200a now, so maybe we will have to pursue buying 2 new BMSs and upgrade from what’s currently installed on them. If only one battery and bms is actively “available“ - due to the lock on the one that’s at 100% so that it doesn’t overcharge the battery- maybe that’s actually what’s playing into this issue and causing the trouble of it’s over the 125a limit of the single bms…i don’t think the inverter needs to be reset as other things seem to work off of it currently, the microwave is just not one of them.

 

[Mia]

Put a meter on battery #1 and turn on the microwave. If the meter shows no voltage when the microwave shuts down, then you know that battery stopped discharging. If the meter still shows voltage then do the same test with the other battery.

You may see that both batteries shut down and you'll have to figure out which one is shutting down first. It may happen so fast that you can't figure it out with just a simple voltmeter. Either way, if you see the batteries shut down then you know it isn't likely to be the inverter.

Cool! Thank you! Somehow I didn’t see this reply earlier, but I will share it with hubs in the morning and see what we can find out!

 

[HRTKD]

I've read that a toaster oven has no surge. At least nothing like the microwave. So the two appliances can't be directly compared.

A BMS usually has two locks: charge and discharge. It sounds like your charge lock is on, not the discharge. You may be charging your battery too high. A charge voltage of 14.4 volts is plenty. Yes, the battery CAN go to 14.6 volts but you don't want to do that very day.

 

[Mia]

So your microwave lists a consumption of 1500W. So let's call it a 1500W microwave, even though it only outputs 1000W.

1500w/12.8v/0.85 (inverter inefficiency) = 137A.

That 137A is the running power, but the startup surge would be more.

Let's say startup surge is 4500W. Your 3000W inverter is supposed to be able to handle twice that, for 6000W. But for how long? Not sure Renogy lists for how many seconds (or milliseconds is probably the likelihood) it can handle 6000W. Or how many milliseconds it can handle 4500W for your microwave startup surge.

But it might be your startup surge amps is more than the BMS's can handle. 4500w/12.8v/0.85= 413A

Again, your BMS's, the two together in parallel, can handle up to 250A continuously, but how much can they handle for surges and for how many milliseconds, before the BMS shuts down?

Perhaps someone can help you narrow down if it's the inverter or the BMS konking out, but my bet it's one of those.

I have also heard that microwaves can be especially difficult for some inverters to start because 1) surge is actually 5-6x, not just 3x (clamp meter could measure this, but you'd want a beefy one) and/or 2) something to do with microwaves being out of phase (this is where my electrical knowledge plummets so I'm parroting from poor memory) with the inverter (not sure what the fix is).

Well not sure what being out of phase looks like, but I would not be surprised if this MW is “out of phase“….Even with using the generator, I seem to have to ”prime” the MW by first turning on the toaster oven momentarily and then it will finally power on the MW display… so this MW has been sort of quirky for a while now actually, and have just had to endure it… thanks for your reply

 

[Tomthumb62]

And odd.y enough the 1000w toaster oven also seems to do fine plugged into it.

The toaster oven doesn’t have any startup surge.

 

[Tomthumb62]

Well not sure what being out of phase looks like, but I would not be surprised if this MW is “out of phase“….Even with using the generator, I seem to have to ”prime” the MW by first turning on the toaster oven momentarily and then it will finally power on the MW display… so this MW has been sort of quirky for a while now actually, and have just had to endure it… thanks for your reply

Hmph, that’s odd. No idea why the mw display shows only if the toaster oven is on. Again, maybe it’s that phase thing I mentioned. Hopefully someone knowledgeable about the quirks of a microwave on an inverter will chime in.

I’ve also read that some people have tried a different microwave and the second one worked whereas the first one didn’t. Might be worth trying if you have an extra one around.

 

[HRTKD]

Hmph, that’s odd. No idea why the mw display shows only if the toaster oven is on. Again, maybe it’s that phase thing I mentioned. Hopefully someone knowledgeable about the quirks of a microwave on an inverter will chime in.

I’ve also read that some people have tried a different microwave and the second one worked whereas the first one didn’t. Might be worth trying if you have an extra one around.

Agreed, odd. It's starting to sound like the microwave itself is the problem.

 

[Hedges]

Your wording implies that microwaves of any type might cook from the inside out. They do not. Microwaves of any type heat the surface of the food, and the interior is heated by conduction from the warm/hot surface.

Matter is not invisible to microwaves. Microwaves excite the first water molecules they meet. They do not jump over/past water molecules to get to others. The primary cooking benefit of inverter microwaves is the ability to heat at a true reduced power so the surface heating rate is more comparable to the rate of conduction heating of the interior.

Then explain why my 240V Advantium oven (microwave + IR from quarts lamps) can cook a whole 3.5 lb. chicken through to the inside and crispy on the outside in 20 minutes. (not that I recommend it; clean up of fat splatter took longer than the cooking.)

(Apparently now over the range model is only available in 120V)

GE Profile™ Over-the-Range Oven with Advantium® Technology|^|PSA9120SPSS

GE Appliances is your home for the best kitchen appliances, home products, parts and accessories, and support.

www.geappliances.com

2.4 GHz, 17 mm penetration according to this:

Microwave burn - Wikipedia

en.wikipedia.org

Of course, power delivered exponentially decreases with depth, so more near surface less deeper than 17 mm.

Just like PV cells, where photons don't necessarily interact with the first atom. Also for ionizing radiation of various types.

 

[Tomthumb62]

Agreed, odd. It's starting to sound like the microwave itself is the problem.

I’ve also read that certain Renogy inverters don’t play nice with certain BMS’s. I don’t recall what brand of lifepo4 batteries that OP is using. Iirc, the story I read was with a Renogy 1000W inverter and an SOK (or was it Chins?) battery. Others had reported a similar quirk.

 

[E. Cho]

FWIW,

A friend had a Xantrex 2400 Watt Modified Sine Wave inverter. He had a new 24 volt 100 AHr LiFePO4 battery, BMS inside unknown but is basic and has no input settings access. His inverter would not run his 1000 Watt microwave, nor his 1500 Watt induction hot plate nor his vacuum cleaner with a power head 1000+250 Watts. The battery BMS would shut down. We would have to open the battery case each time to reset the BMS by unplugging the wiring harness.

He bought a low cost Xija 3000 Pure Sine Wave High Frequency Inverter. It would not run his induction plate nor his vacuum cleaner but did run his 1000 Watt microwave . The battery BMS would shut down when the vacuum and power head were tried. Plus the Xija came with quite thin double cables, which seemed inadequate to me. The inverter terminals were also very flimsy and small and larger lugs would not fit and would bend the Xija terminals.

He then bought a used Aims Low Frequency 3000 Watt Pure Sine Wave inverter and we used 1/0 cables left over from his lead acid batteries to connect the inverter to the same 100 AHr LiFePO4 battery as used with the previous inverters and now everything runs as one would have expected. He hasn't had a single BMS shut down in the last year since using the Aims LF inverter and appropriate cables.

My old Xantrex 24V 4000 Watt Low Frequency inverter with a similar 100 AHr LiFePO4 battery has run everything that I've tried, such as my 1500 Watt microwave, 1500 Watt induction hot plate, dishwasher (tested but never really used due to high energy use to heat water), vacuum cleaners, compressors, circular saws, table saw, etc. It just works and runs 24/7.

So my friend had to buy 3 inverters to get to where I suggested he should have started which is with a robust Low Frequency inverter and appropriate or larger gauge cables. Sadly, even Aims isn't the most reliable brand but after 1 year, it's still working for him.

 

[JRH]

Hi all,

I built a 280AH battery using a 120amp Overkill BMS. I've got a 2200 watt pure sine inverter and I tried to run my rv microwave and it shut down the bms. Looking at the specs on the microwave, it takes a 1500 watt as input, 1000 watt as output. So that makes sense... 1500w / 12v = 125 amps. I guess the bms should shutdown. So I then tried to run the microwave on low power thinking that that would reduce the input amperage. Nope, still shutdown the bms. Strange, unless the input stays the full 1500 watt amount regardless of the output.

So, I am now considering swapping out to a smaller 1000 watt microwave in the hopes that it wouldn't shutdown the bms. 1000w / 12v = 84 amps. Do you think that would work?

Thanks so much!

When I was a boy and microwaves first came out, my granny used to always say , “ these things are the work of the devil, these things ain’t right” …

 

[Hedges]

How many watts is your microwave?

According to a quick google search, a 900W microwave can draw as many as 2700W to start up. This means it can draw about 250A from your battery for 1-2 seconds. A decent BMS should be able to handle a short burst like that, and even then your 2x125A BMS is good for 250A, continuous...in theory. Also your wiring can make a huge difference. If your wiring between the batteries or between the inverter and battery bank is too small, you WILL have voltage drop and the result is the microwave will try to draw even more amps to make up for it, resulting in more voltage drop...it can become a vicious cycle.

So as @HRTKD suggested, a photo of your wiring would help people give you more specific advice.

Since key component of a microwave is transformer, the start-up surge could be due to transformer inrush (saturation of magnetic core if hit with same phase as where it shut down, instead of alternating phase.)

Second part of inrush could be rectification through a diode (half wave) charging capacitor.

I’ve also read that some people have tried a different microwave and the second one worked whereas the first one didn’t. Might be worth trying if you have an extra one around.

Try the same microwave a second or third time. Transformer inrush is a roll of the dice. Every time.

That's interesting. We also had a 1200 Watt Panasonic inverter microwave and found that a Honda 2000 could run it on 50% but not on any setting higher than 50% which indicates that load drawn does depend on power setting. Our Panasonic may have been newer than yours, we went to a 600 Watt unit because it fits our kitchen better.

My understanding is that modern inverter microwaves run the magnetron on lower current for lower power settings whereas standard microwaves achieve lower power by pulsing the magnetron on and off to get a lower duty cycle delivered to the food.

Are those inverter type microwave ovens PF corrected? Because if not, if they just drink gulps of current only near peak of sine wave, they will overload an inverter or breaker/fuse well below what wattage would suggest.

 

[E. Cho]

When I was a boy and microwaves first came out, my granny used to always say , “ these things are the work of the devil, these things ain’t right” …

too bad there is no such thing as a "devil".

Wonder what she would have said about solar panels, electric cars, going to Mars, curing many types of cancer and so many other diseases? Things simply were not better in the "good ol' days" and the human brain's memory is incredibly flawed and inaccurate.

 

[JRH]

too bad there is no such thing as a "devil".

Wonder what she would have said about solar panels, electric cars, going to Mars, curing many types of cancer and so many other diseases? Things simply were not better in the "good ol' days" and the human brain's memory is incredibly flawed and inaccurate.

your a very considerate and gracious individual… thank you for your input… have a nice life..
J.

 

[Hedges]

Any chance the cancer we're (not) curing today, and other diseases, weren't so prevalent in the good old days?

( 's advocate here)

 

[JRH]

Any chance the cancer we're (not) curing today, and other diseases, weren't so prevalent in the good old days?

( 's advocate here)

Yea, we were healthier… and other stuff… good call.