Inverters Shutting Down

[HarborBus]

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Last November we made a trip from Yuma, AZ to Marathon in Beaumont, CA to have our awnings adjusted. We drove from Santee, CA the 80 miles to Marathon and on that trip our inverters shut down three times. Marathon replaced the regulator thinking that it was allowing the batteries to charge higher than the 30 amps that the inverters will allow. On the test drive the inverters shut down after just 10 min. They then adjusted the regulators output test drove again, no problem. In March we headed home to Gig Harbor from Yuma by way of Prevost and Marathon. The last 150 miles of our 1800 mile trip, the inverters shut down three times. The last time we were real close to home and when I arrived I discovered that only #1 inverter had shut down that time. When we are plugged in everything operates normally with no faults. Maybe it is my imagination but I think the inverters shut down when we hit a rough section of road. I took the panels off to check and tighten the connections and found heavy corrosion on one of the posts (see pictures). Do you think the corrosion causing enough resistance to cause the inverters to shut down??

[Jon Wehrenberg]

Elliott,

When the bus engine is running your inverters are functioning to convert battery power to AC power such as you get from the generator or shore power. Your alternator supplies charging current to the batteries so their DC voltage is maintained, and the inverters are pulling from those batteries to provide power to your critical house circuits that your converter deemed necessary.

Obviously you must make sure that all your cable connections are clean and tight. Poor or corroded connections cannot deliver the required voltage to the inverter. If I were to start analyzing your problem I would start with the cable connections.

But further information is required. For your inverters to shut down when converting DC to AC voltage high voltage could be the culprit, but so will low voltage. My first question is if the tech measured the voltage output from the alternator and then measured it at the batteries and then measured it at the DC connections at the inverters. If so what were those voltages? Do you have a meter and can you get those measurements? That will be the starting point. I think you problem can be isolated and resolved by methodically doing the diagnosis. I am concerned the tech may have shot from the hip without doing a good analysis.

[truk4u]

What fault is the inverter giving you when it's shut down?

[HarborBus]

My first question is if the tech measured the voltage output from the alternator and then measured it at the batteries and then measured it at the DC connections at the inverters. If so what were those voltages? Do you have a meter and can you get those measurements? That will be the starting point. I think you problem can be isolated and resolved by methodically doing the diagnosis. I am concerned the tech may have shot from the hip without doing a good analysis.

Jon, No his diagnosis was not that extensive. He only measured the the output of the alternator at the regulator, no further comparisons were done as you suggest. I do have a good RMS meter that I can get those values. Tom, unfortunately I didn't check the fault the inverters were displaying. That would have been a good thing to do Huh.

[Jon Wehrenberg]

All inverters and their remote panels differ to an extent. If you have an inverter installation in which your remote panel tells you information such as too much or too little DC input power that is critical information to share.

Based solely on Elliott's description above one could conclude when he says he is on shore power and everything is OK that means his inverters are functioning as battery chargers and are passing shore power through to the 120V AC devices.

But since Elliott talks about shutting down when on the road I am assuming they (or one of them) is shutting down when converting DC power to 120V AC power. The analysis (regardless of what the remote panel says) has to start with measuring the DC voltage, and to do that properly we have to determine if Elliott has a 12 volt coach and a single alternator, dual alternators, or a 24 volt coach and a single or dual alternator.

Generically I believe all inverters cease functioning when input DC voltage is too high or too low and he can have either condition present. We also cannot rule out an inverter starting to go bad, but if the shut down he talks about has involved both inverters, then looking for an inverter problem would be down near the bottom of the list because of the odds against two failing simultaneously.

One thing is for certain. To properly diagnose the problem is going to involve a step by step check of the factors which could cause inverters to shut down.

Elliott, we have to assume the technician that replaced the voltage regulator did a diagnostic check that led him to conclude there was an issue. So if there was excessive voltage (not amperage) did you get an alarm on the dash from the Vanner monitor that lit an annunciator light that showed high or low voltage? (To answer this you have to also reveal if your house has a separate dedicated alternator which I suspect is the case if you got not dash indication of a voltage problem). How did you know the inverter shut down? Does it have an audible alarm or do you have a display that is easy to see to alert you.

In your conversion (tell us if it is a 12 or 24 volt house and dual or single alternator) is there a way for you to read house voltage (DC, not AC)?

I think a little time with a volt meter and the problem can be identified.

[HarborBus]

When I was writing the original post I did have momentary brain fade and stated the tech measured amps but I meant volts.............no really I did. I have two alternators one small one to charge the chassis batteries and the large on to charge the house batteries. I don't know if the house is 12 or 24 volt, How would I determine that? There is a audible alarm and light on the dash that sounds and illuminates the moment inverter power is lost. I don't think we can rule out the possibility that #1 inverter is getting weak: ("The last time we were real close to home and when I arrived I discovered that only #1 inverter had shut down that time".). I can read house voltage through the Tech Link system. Of-course if the inverters have shut down it reads zero. As soon as I get around here this morning I'll go out and take some measurements with the volt meter.

[BenC]

Did you or the technician take apart, clean and tighten/torque the battery connections after your discovery? Have you observed the inverter shut-down scenario since then? Just curious. Jon is correct. Bad connections act as high resistance (like physically putting a giant resistor in line) in the power delivery line. Resistors "drop voltage" proportional to the current flow value through them, thus the greater the current value (or load) the more voltage is dropped. These problems are not often evident to technicians, if the system is not operating under a large load condition. The effect with corroded or loose connections is that the voltage the down-stream devices "see" will be lower, and can cause invertors to shut off due to low battery. They also use more current at lower voltages to produce the necessary 120v AC power and are succeptible to shutting down on temperature as well. Corroded and loose connections are common problems with all coaches, and all battery and alternator connection inspection/tightening should be considered an annual PM.

[Jon Wehrenberg]

For those that may not know BenC he is an electrical wizard and is with Coach Worx, one of our sponsors.

Pay close attention to what he says because I cannot think of anyone better to deal with electrical questions.

No, I don't get any rewards for saying stuff like that about Ben just telling it like it is.

[Jon Wehrenberg]

Elliott, If I am screwing up here I hope Ben will jump in, but the voltage readings I would like to see are at the alternator output, at the batteries and at the DC input to the inverters. I would like to see you load up the electrical circuits in the bus that are on inverter, and make sure you are not on shore power.

As Ben described if you see a substantial voltage drop between what you see at the alternator, and what is going into the inverter that is likely your problems. If the circuit is unloaded there may be no voltage drop.

Conversely, if the voltage was high, and the inverters see voltage over some value (30 volts maybe) they will also shut down. At least my inverters will.

[BenC]

You are right on track Jon. Thanks for the kind words, by the way.