Looking for help with AC power question

[SemperBadger]

I am driving a 2021 Class A diesel pusher. A couple of trips ago, I realized that the small fan in my inverter compartment was running almost continuously. Soon after, I started experiencing "brown out" conditions under AC electrical load, but only intermittently. During these instances, the RV control panel would show a loss of AC power, no pass through from the inverter/charger, and an indication that the draw was all falling on the 12V house batteries.

Following our return trip, we parked back in our RV garage and hooked back up to 50A house power. I started receiving notifications from my Marcel monitoring system that I was losing AC power several times a day, all for 5 minutes or less. I had our local RV tech follow the power from the pole, through the onboard transfer switch, through the Magnum inverter/converter and into the onboard AC electrical panel. I replaced the Magnum inverter, but the condition continues.

The RV tech says that the house batteries (4) are reading 6V each at rest, but just over 1V under load. He thinks that might be the issue. I can imagine a situation where a 12V failure would prevent your air conditioning thermostat from operating - thus preventing your AC from coming on. I am just not sure that a loss of 12V power would cause the conditions I described, or why that might happen on an intermittent basis. That said, I can imagine that running your microwave on 12V power is going to do significant damage to your house batteries.

I appreciate any thoughts from the collective wisdom and experience of the RV community. Thanks in advance.

 

[IBTripping]

Welcome to the Forum. Electricity is not my area of expertise. But, I'm sure other more knowledgeable members will respond soon.

 

[OldWEB]

If your "RV tech" is OK with a 1V battery, then I would find a real RV tech.

 

[gwinger]

If connected to shore power, you should be able to disconnect the batteries. The converter will still supply 12 volts to the system. If one or more of your batteries is bad, it may be drawing and excessive charge current.

 

[workinonit]

If your "RV tech" is OK with a 1V battery, then I would find a real RV tech.

I missed where this was stated. What I read is the tech said it might be the issue.

 

[rvlifer]

I was thinking the 1v was a typo. Mine go into shutdown mode at around 11.4v or 11.5v

 

[Gary RV_Wizard]

When plugged to shore power your batteries shouldn't be involved at all, except maybe receiving a charge. For further problem isolation, I'd disconnect the battery bank and observe how the system functions without it. It should be unaffected as long as plugged to shore or generator power.

I'll also state that 6.0v on a 6v battery is only about 50% charge, so not indicative of a healthy battery status. And 1v is far beyond "dead". Yeah, 1v would be an "issue" (nothing works!), but it's probably a separate problem than what you are experiencing with loss of AC power. Like Oldweb, I'm skeptical of your RV tech's knowledge of RV 12v systems and batteries in general.

During these instances, the RV control panel would show a loss of AC power, no pass through from the inverter/charger, and an indication that the draw was all falling on the 12V house batteries.

Your first goal should be to figure out why you are intermittently losing external AC power. Start with a possible faulty shore power cord or Auto-Transfer Switch (ATS). An intermittent wire connection anywhere in the shore cord would explain most of your symptoms and it's not unusual o have a wire break loose at the plug-end of a shore cord. Less usual but still not rare is a failing ATS relay.

 

[Kirk]

the small fan in my inverter compartment was running almost continuously.

That probably is an indication of high current demands from the charger section if it is happening when you have 120V power available.

A 6V battery that reads only 1V might be a factor in the brown outs if it has a shorted cell as that might draw excessive power but it should not remove the 120V-ac power from the entire coach.

Your first goal should be to figure out why you are intermittently losing external AC power.

If you have a power monitor such as Progressive's EMS or Southwire's Surge Guard, check that first to be sure that it isn't shutting off power for some reason.

 

[John From Detroit]

He thinks that might be the issue. I

MIGHT... I'm with Old Web.
However how did he meausre.. That kind of voltage drop indicates one of two things.
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Battery is TOAST. - or - Current path is very high resistance.

The load tester I have is a 12 volt device so I do not test a 6 volt battery. I test a 12 volt battery (two sixes in series make 12) and if the connecting cable connections are not very clean. >Well at 200 amps it only takes 0.06 ohms to lose 12 volts fast.

Of course when I tested by slices of Toast... I only drew a few amps before they hit near zero.

(Very high internal resistance = Toast)

They went to recyclers and new LiFePO4 for my back up power system... But that's another story.