Inverter kicks out when microwave is started

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

PJ Stough

Well-known member
Joined
Sep 20, 2009
Posts
2,336
Location
Central Iowa
Sharp voltage cutoff like that could indicate a BMS over current trip, that's a lot of instantaneous current and some BMS controllers will not tolerate it.
Would that indicate that one battery is having more that the 100 amps max that the BMS is set for being drawn from it?
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
602
Location
Texas
Would that indicate that one battery is having more that the 100 amps max that the BMS is set for being drawn from it?
It's certainly a consideration, differences in cable, connection and internal cell resistance will define the available voltage and therefore current at load. no two batteries will ever be the same and likewise, no two bms systems will be either unless precisely calibrated.

my thinking here is that if one battery bms is more sensitive at close to full load conditions then it could trip, causing the second battery to overload and trip also, the unknown here is how the current limit is implemented. if the limit is set to reduce current to a safe value, then the voltage on load will also drop, hence the measured 7.8 Volts value.. that's just one theory, it could also be a malfunctioning bms...
 
Last edited:

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
75,871
Location
Looking to buy a new home
I have to agree with those who think the 7.8v reading is a huge clue (assuming the reading is accurate). That just shouldn't be with a properly functioning BMS and LiFePO4 batteries. If it were mine, I think I would start experimenting with taking one battery at a time out of the bank to see if one BMS or battery might be the culprit.
 

Ernie n Tara

Well-known member
Joined
May 16, 2009
Posts
4,202
Location
Ft Myers, FL
You should be measuring across the fuse under load, not to ground! Should be less th 0.1 Volts (probably not even close to that), not greater than 1.5V! If you reported an accurate reading, you have identified a problem. Note that the 13V plus reading is likely a surface charge only or the battery is being charged.

Ernie
 

JayArr

Well-known member
Joined
Jun 13, 2020
Posts
1,258
Location
Mission British Columbia Canada
Personally I think your microwave is bad. A huge clue is that it takes 28 seconds before the trip. That's quite a while and sort of rules out any surge currents or instantaneous anomolies. It could be that the magnetron in the microwave heats up at about that point and starts drawing much more power. A partially shorted winding will do this when hot, the magnetron would keep running but at a much higher current.

To make a current measuring jig on the cheap: Take a short extension cord and cut about a foot of the sheathing off without cutting the inside wires. Next cut just the black wire in the center of the exposed section. Connect a current meter between the black wires. Tape everything up so you don't get electrocuted. Plug the microwave into the extension cord and then the extension cord into the outlet. Heat a cup of water and read the current, see if it starts to creep upwards as it goes along, maybe even spiking just as it trips.
 

CharlesinGA

Well-known member
Joined
Oct 6, 2017
Posts
1,032
Location
50 miles south of Atlanta, GA
Personally I think your microwave is bad. A huge clue is that it takes 28 seconds before the trip. That's quite a while and sort of rules out any surge currents or instantaneous anomolies. It could be that the magnetron in the microwave heats up at about that point and starts drawing much more power. A partially shorted winding will do this when hot, the magnetron would keep running but at a much higher current.

To make a current measuring jig on the cheap: Take a short extension cord and cut about a foot of the sheathing off without cutting the inside wires. Next cut just the black wire in the center of the exposed section. Connect a current meter between the black wires. Tape everything up so you don't get electrocuted. Plug the microwave into the extension cord and then the extension cord into the outlet. Heat a cup of water and read the current, see if it starts to creep upwards as it goes along, maybe even spiking just as it trips.
What Jay is describing is a home brew version of one of these, which are only about $15 or so. A lot of MW units have a flat cord that is easily split also.

3ZH94_AS01


Separate hot, neutral, and ground conductors without opening the line cord by using this 3-wire AC line separator for clamp-on meters. It also has points to insert meter probes to measure voltage.

I read thru this entire thread and I too am suspecting the microwave, or its circuit from the breaker panel. As the RV was originally built, the microwave would have been given a dedicated circuit and circuit breaker with nothing else on it.

Its possible the Microwave shared the circuit with a water heater via a load shed device. We do not know if anything else is on the same circuit or not.

I have a conventional High Pointe 900 watt MW that draws 1350 data plate watts and I also have a Panasonic 1250 watt Inverter MW that draws 1525 data plate amps. I think the inverter microwaves are more efficient than others (and weigh a whole lot less), but I'd be surprised if that 1000 watt MW of the OP is rated to draw over 1500 watts and possibly not quite that if working properly.

Charles
 
Last edited:

JayArr

Well-known member
Joined
Jun 13, 2020
Posts
1,258
Location
Mission British Columbia Canada
I like that! Thanks Charles, my local parts supplier (Digikey) has them in stock so I've thrown one in my cart for my next order. I've made a half dozen of the quick kind by cutting up cords but then I lose them or repurpose them.
 

Isaac-1

Well-known member
Joined
Dec 3, 2016
Posts
5,752
Location
SW Louisiana
I have one of those that I bought off Amazon a while back, mine is a made in China cheap one though, and the 1X and 10X loops are marked backwards.
 

racatk

Member
Joined
Dec 18, 2021
Posts
13
Location
Arizona
Well after Much time and several tests I believe the problem is with one of my three batteries. I was able to run the microwave successfully on two batteries but has cut out with a combination of #1 + 3 or 2 & 3.
Called Brattleborn today and they are sending a box and RA# to ship it back for them to do additional testing.
Thanks to all who responded with great thoughts.
 

racatk

Member
Joined
Dec 18, 2021
Posts
13
Location
Arizona
Received battery back from Battleborn yesterday, they said the positive post was loose and caused a mod frame to over heat.
Also bought a Kill a Watt meter and tested the microwave. At start the 1000w microwave pulled over 1500w and didn't drop below 1480w.
 

Latest posts

Forum statistics

Threads
123,312
Posts
1,250,470
Members
128,888
Latest member
grammargirl
Top Bottom