Magnum inverter shutting down.

kkesp · February 18, 2023

Magnum MS2012 inverter/charger. 4- L16 AGM batteries (4 yr old and have all load tested good), and I've run out of things to check. The AC power is run through 6/3 Romex with ground, all connections have been properly torqued and rechecked. Battery cables are all 2/0, and are located only about 3 ft from the inverter. Here the story, I gave my previous (aforementioned) inverter and batteries to my sister for her 5th wheel after upgrading my MH to lithium. Now it won't run the microwave for more than a minute then everything shuts down, (inverter, and remote) the remote shows no faults, and has no faults stored. While running the microwave the remote shows about 130 amps dc and battery voltage gets drawn to about 12.2 vdc and if shut off will immediately rebound to 13.6 vdc if it continues to run after about a minute everything quits. LBCO has been lowered to 9.0. It is really only a few outlets, the microwave, and a coffee maker that will be run, so other than not having to run the genset it's really not worth her spending much money fixing. I have called Magnum tech and they couldn't come up with anything, So I'm reaching out hoping someone can point out that I'm just missing something simple.

Thank you

Jaydrvr · February 18, 2023

Have you physically tested the input of the inverter under load? Sounds like low voltage cutoff, but perhaps your remote readings aren't reflecting what's going on. Jay

hemsteadc · February 18, 2023

So it's your sister having the problem?

Edited February 18, 2023 by hemsteadc

kkesp · February 19, 2023

I have not checked the voltage at the inverter inputs, I guess I was relying on the accuracy of the remote, but I will check it tomorrow.

Wrknrvr · February 19, 2023

I would check the batteries fluid level. Feel if any batteries are warm. That is a crude test for a bad battery. Separate each battery and check for voltage. They need to be 12.2 or above.

Also check incoming 120 vac.

Just a start.

oldjohnt · February 19, 2023

Not being there to test and troubleshoot and IFFFFFFFFFFF the Inverter itself is all ok???

ONE PURE GUESS the Inverter is shutting down due to low voltage........

ONE POSSIBLE CAUSE Is voltage drop across a resistive terminal or connection.

ONE POSSIBLE CAUSE is weak batteries causing excess voltage sag under load

If the current is 130 amps and there's as little a 0.1 Ohm across a cable end or connection THATS A 13 VOLT DROP

I have seen what look fine to the eye cable ends still be bad under the surface or under the crimp or end still be bad and resistive

Check battery levels and run a load test,,,,,,,,,,,suspect bad cable ends or connections etc

NO WARRANTY only a few guesses, there could be all sorts of other problems but this is all for now

John T

hemsteadc · February 19, 2023

2/0 may be a bit undersized for heavy loads.

Randyretired · February 19, 2023

I agree with most of the previous posts. If the inverter and battery are good then it is most likely a wiring problem. 2/0 should easily handle the load so it most likely is a voltage drop caused by a bad connection. Measuring the voltage at the inverter during the load should either confirm or not if this is the problem. Another way to check things is to see if one or more connections or the wire gets hot. I assume there is a fuse in the line and that could also be a problem spot. In any case the voltage at the inverter is what I would check.

After rereading your description you indicated the voltage returns to 13.6v. That would indicate there is a charger of some type connected. Is that correct? That measurement might be more meaning full without the charger.

Edited February 19, 2023 by Randyretired
Additional text

kkesp · February 20, 2023

6 hours ago, Randyretired said:

I agree with most of the previous posts. If the inverter and battery are good then it is most likely a wiring problem. 2/0 should easily handle the load so it most likely is a voltage drop caused by a bad connection. Measuring the voltage at the inverter during the load should either confirm or not if this is the problem. Another way to check things is to see if one or more connections or the wire gets hot. I assume there is a fuse in the line and that could also be a problem spot. In any case the voltage at the inverter is what I would check.

After rereading your description you indicated the voltage returns to 13.6v. That would indicate there is a charger of some type connected. Is that correct? That measurement might be more meaning full without the charger.

It is an inverter/charger, without an AC source the charger does do anything. My first thought was improper wire size but 2/0 is supposed to be rated for 175 amps, and the run is only 3 ft. All connections have be checked. I was busy today and didn't have the chance to check the voltage drop at the inverter.

oldjohnt · February 20, 2023

8 hours ago, kkesp said:

All connections have be checked. I was busy today and didn't have the chance to check the voltage drop at the inverter.

Sounds like you're on top of this. Not too long back my Inverter (2 KW, 2/0 30 inch cables) was dropping out due to low input voltage............. My cables were new and just made at Interstate Battery..........The hydraulic pressed on type terminals Interstate Battery made looked perfect to the eye.............HOWEVER upon further testing ONE OF THE TERMINALS THAT LOOKED PERFECT was dropping voltage !!!!!!!!!!!!!!!!!! I cut it off and manually installed a copper screw down terminal suitable for 2/0 THEN ALL WORKED PERFECT... Again as V = I x R a small 0.1 ohm resistance drops 13 volts at 130 Amps !!!!!!!!!!!!!!! That coupled with the voltage sag of your batteries especially at high current discharge can reduce voltage enough to cause drop out. One thing I like about my new Lithiums is the voltage sag is less under load as well as they can charge up faster !!!!

NOTE to measure voltage drop ACROSS a resistive connection (or Inverters input) may be tricky as it may not last long. My meter has a min max memory setting which can remember/hold what was there briefly...

Of course the Inverter could be the problem or all other sorts of causes such as weak batteries (have they been load tested??) This is ONLY one guess and what happened when my Inverter dropped out due to a bad terminal that still looked perfect grrrrrr

Let us know what you find

John T In the RV from Florida Flywheelers in Fort Meade Florida

Edited February 20, 2023 by oldjohnt

Anawilliam850 · February 20, 2023

It sounds like you've done a thorough job of troubleshooting so far, but there are a few more things you might want to check:

Check the wiring to the microwave and coffee maker to make sure it's properly sized and in good condition. If the wiring is undersized or damaged, it could be causing voltage drop and preventing the appliances from running properly.
Check the inverter's output voltage when the microwave is running. It should be around 120 volts AC. If the voltage is too low, it could be causing the microwave to shut down.
Check the battery voltage under load with a digital multimeter. If the voltage drops significantly when the microwave is running, it could indicate that the batteries are not able to deliver enough power to the inverter.
Check the inverter's cooling system to make sure it's working properly. If the inverter is overheating, it could be shutting down as a safety measure.
Check the settings on the inverter to make sure they are configured correctly for the batteries and loads. If the settings are not optimized for the system, it could be causing issues.

If none of these steps resolves the issue, it's possible that there is a problem with the inverter itself or the wiring in the RV that is not immediately obvious. In that case, it may be best to have a professional RV technician take a look at the system to diagnose the problem and provide a solution.