Inverter kicks out when microwave is started

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racatk

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Microwave test
V at batteries at start 13.5
Low battery and shut down at 32 seconds at 7.8 V

V at Inverter at start 13.49
Low battery and shut down at 32 seconds at 7.8 V

Ran coffee maker, (900watts), 3 times, in the same outlet with no issues at all. Voltage at batteries during coffee test dropped to 12.9 and at Inverter it dropped to 12.7.
 

Isaac-1

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Ok, lets go about this systemically, did you take voltage measurements at the batteries as well as at the inverter?

Also is there a fuse in this circuit and if so what type is it?
 

docj

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The OP doesn't say whether or not he has a generator onboard. I've never assumed that my inverter was designed to handle loads >1kW. That's when I fire up the generator. We often do that just to heat up food for lunch. The fact that modern Li batteries make it possible to power a microwave off of an inverter doesn't mean that it is a sensible use of battery power. JMO
 

DonTom

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Low battery and shut down at 32 seconds at 7.8 Volts
Lead Acid batteries? Lith batteries will keep the voltage higher. 7.8 VDC on the batteries is too low for your inverter under load. And 32 seconds is too soon for that much drop.

But the coffee test makes me wonder if your MW oven is drawing excessive current. But I think that is somewhat unlikely.

-Don- Okeechobee, FL
 

DonTom

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The fact that modern Li batteries make it possible to power a microwave off of an inverter doesn't mean that it is a sensible use of battery power.
It's very sensible when boondocked at midnight next to others and you want to use the MW oven.

-Don- Okeechobee, FL
 

Ex-Calif

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If you want to "know" you probably put a shunted ammeter in the line to the microwave and read the current draw.

I would be tempted to replace the MW with a less powerful unit.

One could argue that the battery capacity is a bit down and one could replace the batteries. One could also argue that the MW is drawing higher than expected for some reason. The V-drop makes it clear that the MW is drawing the batteries down excessively.
 

Mark_K5LXP

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For the voltage to drop that far will be either a bad connection, batteries not charged, or bad batteries. Since the batteries are new we'll put bad on the bottom of the list. Going by the OP's post the voltage under load at the batteries and the inverter was the same. Not specifically mentioned was how the batteries are wired together per SeilerBird's post, and if the voltage was the same on each battery. Provided that's OK the next thing I'd check is that thay're actually getting charged. Since lithium has a very flat discharge curve they could be almost dead and show 'good' no-load voltage, and no mention was made of how these are getting charged.

Mark B.
Albuquerque, NM
 

Gary RV_Wizard

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I don't see a Low DC Voltage Cut-out setting in the Victron manual, but review your set-up parameters and make sure there isn't a too-conservative setting. The Victron spec says it accepts voltage from 9.5-17.0, but that's an unusually broad range for an inverter. Maybe contact Victron to verify. I note that Victron recommends 400 AH to support the 3000W inverter, but it seems 300 AH ought to be adequate to produce 1800 watts (the max for a 15A appliance)

Then, if you are convinced everything in the wiring is perfect, only two possibilities will remain:
  1. The microwave is drawing much more wattage than you stated. Check the rating plate on the back of the microwave - it should show the peak amp draw (not the cooking power). Get a Kill-A-Watt type device to measure the microwave draw when connected to shore power.
  2. The Battle Born batteries simply cannot deliver the necessary amperage. Contact Battle Born to ask how long 3 of their fully charged batteries can deliver 150+ amps.
 

Gary RV_Wizard

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Ran coffee maker, (900watts), 3 times, in the same outlet with no issues at all. Voltage at batteries during coffee test dropped to 12.9 and at Inverter it dropped to 12.7.
That coffee maker is a little over half what the microwave draws. As I stated earlier, a 1000W (cooking power) microwave typically draws around 1500 watts and has a start-up surge as well.
 

Isaac-1

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The issue here is that you should never see 7.8VDC with LiFePo4 batteries, you should either see around 10.0VDC or 0VDC as the BMS should cut out on Low Voltage Disconnect at between 10-11VDC.
 

DonTom

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Ran coffee maker, (900watts), 3 times, in the same outlet with no issues at all.
I just remembered something about coffee makers. Those 900 watts is only when the coffee is being made. It's nothing near 900 watts when it's only keeping the coffee hot, perhaps then around 250 watts or so.

Unless you were making coffee at the time, it was not 900 watts.

BTW, when the issue is with the MW oven, you need to test with the MW oven.

A Smartshunt would be very helpful for such testing. It would remove a lot of the guesswork.

I have to wonder if your batteries are fully charged.

IAC, the voltage should not drop down that much right on the batteries. Now you need to find out why. Sounds like it's a battery problem of some type, most likely, even if the issue is they are very discharged.

-Don- Okeechobee, FL
 

racatk

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Batteries are wired correctly, I'm going through all connections, again, in hopes of finding something.
I ran three pots of water through the coffee maker with no issues.
I'm leaning more and more towards a bad microwave.
Thanks for everyone's help, I'll keep you posted.
 

Henry J Fate

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We had a similar problem even when plugged in. We dealt with it for years and finally figured out it was the microwave drawing many more amps than it was supposed to.

Replacing the microwave fixed the problem.

Its a good idea to make sure the microwave is functioning within spec. Testing becomes a little complicated so if you have access to another microwave (Preferably 1000 watts) you could use that as a comparison.
 

Gary RV_Wizard

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If it was drawing too much power (amps), odds are it would trip the branch circuit breaker, even when on shore power. A 1000W micro is designed to work nicely on a 15A branch circuit, which means it will have a max amp draw of 15 (1800 watts). The typical wattage consumption is 1500-1700, which converts to 12.5-14.1 amps @ 120v. The inverter draws 10x those amps from the batteries (@ 12vdc) to produce the power. Add 10-20% for the inverter conversion overhead and you have a hefty draw without any malfunction at all.
 
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Mark_K5LXP

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Still hasn't been answered if the batteries are charged or not. That's a more likely possibility than a microwave drawing more than it's source breaker is rated for.

Mark B.
Albuquerque, NM
 

PJ Stough

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The issue here is that you should never see 7.8VDC with LiFePo4 batteries, you should either see around 10.0VDC or 0VDC as the BMS should cut out on Low Voltage Disconnect at between 10-11VDC.
I believe that the 7.8 volts is the key piece of evidence. I would say that the problem is a defective inverter.
 

PJ Stough

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I think you mean converter. I doubt the inverter is drawing too much if it works okay with the coffee.

-Don- St Cloud, FL
The microwave draws more than the coffee pot, and at some point there is a fault in the inverter. I dont believe that the inverter is actually drawing the batteries down to the low voltage cutoff, as the three Battleborn batteries can produce well over 3000 watts of power, but since the circuit breaker is not kicking out, that tells me that the inverter is not actually drawing more than 1800 watts, but because it does kick out, leads me to believe the problem is in the inverter.
 

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