House battery charging by alternator

I will collect more data and look for trends....

CA Traveler wrote:
Most likely problem is the solenoid as significant amps are involved and DC is prone to pitting the contacts.

Yes, battery isolator solenoid failures are VERY common.

Easiest way to troubleshoot them is to temporarily connect a 12 volt test light or voltmeter across the "coil" terminals on the solenoid to confirm that the coil is energized, and measure the DC voltage across the two high-current terminals on the solenoid (while the engine is running).

If you measure any significant voltage across the high-current terminals (i.e., more than a few dozen millivolts), the contacts inside the solenoid are no longer conducting current like they should - and the solenoid should be replaced.

ramsaymike wrote:
As it happens, I monitor and record battery voltages continuously. This is what I got on the last drive. On start, the chassis batteries go to (about) 14.2 and slowly drift down to 13.6 over the 90 minutes of driving. The house batteries are at 12.0 and slowing increase as solar builds in the morning. After 20 minute break, the chassis batteries go to 13.7 but soon settle at 13.2 where they stay. The house batteries continue to build and are at 13.2 at engine off. It appears that at this point the solenoid is activated. From this point on the voltages of both sets of batteries are the same and it is obvious that they are connected. It now appears that the solar charge controller is controlling the voltage as both sets now start increasing. It is difficult to see what is going on as solar is variable but both are held at around 13.6. At the end of the drive the solenoid is deactivated - can't be sure exactly when but before final switch off. Trying to understand what is going on.....maybe just faulty solenoid?

Need to disconnect solar and just watch what alternator charging alone does to see if there is a problem.

Two chargers at different charging voltages will have the higher voltage charger raising the battery voltage up past the voltage of the other charger so it does not provide any more amps, leaving the higher voltage charger doing it all.

Your results are confusing for their timing when the solar would take a long time to get the battery voltage higher so the alternator should be still providing amps early on. Best thing to do is take the solar right out of the picture temporarily to remove all confusion

theoldwizard1 wrote:

CA Traveler wrote:
X2 I'm not aware of any MH that doesn't charge both banks from the alternator. Most likely problem is the solenoid as significant amps are involved ...

This has been discussed MANY times. It is NOT just about amps, volts are an issue.

For about 20 years, auto manufacturers have been installing "smart charging" systems on vehicles, even motorhomes.

AND it's high DC amps that cause more solenoid pitting on the contacts which causes them to fail including intermittent failure.

AND the OP has a 2007 Class C so very doubtful that he has a smart charging system.

AND I would hope that RV MH mfgs don't install smart charging systems becuause there are 2 battery banks to charge or they install a DC to DC charger for the house battery. But yes they may indeed install smart charging systems as battery discharge and failure are not their problem. And what about lithium batteries that can take a high level of charge until fully charged?

Although not Class C, for many years (15) my older Dodge Rams charged the TT battery without fail on road trips. Not a heavy duty alternator and standard truck and TT wet cell batteries were used. Cheers to the brave.

As it happens, I monitor and record battery voltages continuously. This is what I got on the last drive. On start, the chassis batteries go to (about) 14.2 and slowly drift down to 13.6 over the 90 minutes of driving. The house batteries are at 12.0 and slowing increase as solar builds in the morning. After 20 minute break, the chassis batteries go to 13.7 but soon settle at 13.2 where they stay. The house batteries continue to build and are at 13.2 at engine off. It appears that at this point the solenoid is activated. From this point on the voltages of both sets of batteries are the same and it is obvious that they are connected. It now appears that the solar charge controller is controlling the voltage as both sets now start increasing. It is difficult to see what is going on as solar is variable but both are held at around 13.6. At the end of the drive the solenoid is deactivated - can't be sure exactly when but before final switch off. Trying to understand what is going on.....maybe just faulty solenoid?

CA Traveler wrote:
X2 I'm not aware of any MH that doesn't charge both banks from the alternator. Most likely problem is the solenoid as significant amps are involved ...

This has been discussed MANY times. It is NOT just about amps, volts are an issue.

For about 20 years, auto manufacturers have been installing "smart charging" systems on vehicles, even motorhomes. These systems limit the voltage out of the alternator a few minutes after the engine starts, down to about 13.2V ! You will never fully charge a depleted house battery at that voltage.

Prove this to yourself. First, run your house battery down at least 10%. Start our engine. Immediately check the voltage at the vehicle battery and at the house battery. Drive for about 10-15 minutes and with the engine running check both voltages again.

If you are not getting >14V at the house battery, you will never fully charge that battery.

Fwiw, if needing a new relay, I’ve been using a Blue Sea ACR in our boat for over 10 years. Automatic voltage sensing. Never touch it.

IAMICHABOD wrote:
When I had the same problem as yours when the engine was running it was not charging the house batteries,after some testing I noticed that the continuous duty solenoid would click but not lock in which is a loud clunk.

After replacing it the problem was solved.

This is where I’d look first. Don’t know much about Cs, nor you switch on the dash, but the intermittent charging (you must have a gauge or display to tell you it charging?) sounds like a loose ground or a disconnect in the charging relay.

When I had the same problem as yours when the engine was running it was not charging the house batteries,after some testing I noticed that the continuous duty solenoid would click but not lock in which is a loud clunk.

After replacing it the problem was solved.