12V electrical problem

[Pete'sMH]

My motorhome is SOB (2019 Newmar Bay Star Sport) but I’m hoping the wonderful folks here can offer me some generic direction to assist me In diagnosing my issue.

My 12V coach power occasionally just disconnects with no apparent pattern. My house batteries are new, clean, full and test at 12.7 volts at the posts. When it disconnects it shows 0.0V on my hardwired, dash mounted voltmeter. This can happen whether I’m on shore power or not. Today it happened when I was doing my monthly generator exercise and, when the 12V disconnected it turned the generator off as well. I tried the emergency battery start switch to connect to the house battery to the chassis battery but apparently that doesn’t work if one of the batteries is showing zero volts so my problem is upstream of that relay. The only possibly useful clue is that when I started the engine the house system came back on line at 14.1V on the alternator. I turned off the ignition after a few minutes and the house Voltage was 13.1. I suspect I’ve got a bad relay somewhere but I could use some collective wisdom here.

Thanks in advance for your help.

[javelin]

After reading your post you said that even when on shore power your “disconnect event” makes the voltmeter reading drop to 0 volts if I understood correctly? Do the 12vdc loads (lights/fans) in the coach keep working or not during the “event”, when on shore?

My first thoughts on your situation is that it is not a DC breaker tripping since your 12vdc comes back without resets (unless the breaker is not sitting in a panel correctly etc)........might be a relay that is dropping out for some reason......but I thought a bad/loose or dirty electrical connection somewhere that makes (works) sometimes and breaks (opens) other times is more likely the problem.....maybe temperature or motion sensitive?

The gen probably stopped when the “event” killed he 12vdc supply feeding the gen control unit. If 12vdc is lost from the coach DC fuse panel during these outage events I would start by checking all DC connections from output of converter to DC fuse panel. Also use a voltmeter to test where the 12vdc is good and where it fails during the failure event.

[TurnerFam]

sounds like an infrequent loss of 'ground'... maybe due to corrosion, or just a plain 'loose' connection.

When the wires are in 'use' by the 12v system, they create some heat, which can create interesting situations(loss of power/connection) when they 'expand' or 'contract' during this time. Corrosion can probably creates some similar scenarios.

I could only suggest to check every possible connection upstream from the batteries. Yes, a relay or solenoid could be going bad, or 'unlatching'. Another idea is to check the wires behind the 'Use/Store' switch, itself, if you have one.

[lwmcguire]

Originally Posted by TurnerFam

sounds like an infrequent loss of 'ground'... maybe due to corrosion, or just a plain 'loose' connection.

When the wires are in 'use' by the 12v system, they create some heat, which can create interesting situations(loss of power/connection) when they 'expand' or 'contract' during this time. Corrosion can probably creates some similar scenarios.

I could only suggest to check every possible connection upstream from the batteries. Yes, a relay or solenoid could be going bad, or 'unlatching'. Another idea is to check the wires behind the 'Use/Store' switch, itself, if you have one.

Agreed and double check all the wires to and from the inverter

Look for a possible terminal loose that appears to be tight, don't trust anything by looks, physically check and tug the wires

[Pete'sMH]

Thank you for your help. I am coming to the conclusion that it’s probably just a bad connection at the batteries or chassis ground. Spent an hour today checking and found one suspect ground connection at one of the batteries. Nothing definitive but possibly. And when I left today everything was working properly. We’ll see. Take home point is to check the simple things first, be methodical and don’t overthink the problem!