Battery Charging: I don’t understand this

[Neemer]

I replaced my chassis batteries a few days ago. They were beyond dead, measuring 10.7V when I put them out of their misery.

I’m looking at some info available to me in the overhead cabinet. The generator is running and this is what I see:

Why wouldn’t the numbers for the chassis batteries be similar to the house batteries?

 

[Richpatty]

What type of batteries are your house batteries? And maybe the BIM is not connected…

 

[Neemer]

House batts are AGM. Chassis are lead acid.

 

[Headhunter]

That happens to me all the time. I could be wrong, but I think the chassis batteries have to hit a certain low level before the inverter starts charging them. Maybe 12.4 or 12.3.

Did you replace your batteries with wet cell or AGM enclosed batteries. It shouldn't make a difference in the rate of charge though.

HH

 

[Neemer]

That happens to me all the time. I could be wrong, but I think the chassis batteries have to hit a certain low level before the inverter starts charging them. Maybe 12.4 or 12.3.

Did you replace your batteries with wet cell or AGM enclosed batteries. It shouldn't make a difference in the rate of charge though.

HH

You know, that rings a bell. I would like to find that in writing somewhere. I’m speedreading through everything I can find in my manuals.

The replacements are wet cell maintenance free.

I have awakened once this week with dead batts and don’t care to repeat so soon. You can’t even start a generator at 10.7v.

 

[Neal]

There has been discussion of the trickle charge solar panel causing chassis batteries to boil off. Some have gone so far as checking water levels in them. They aren't expensive so I replace mine at 5 year intervals, keeping in mind when your batteries could have been installed for new RV owners.

 

[DennisT]

Yeah, the chassis batteries do charge differently than the house so the voltage can be a bit different.

At least it is that way in our Superstar with 8 lead acid house batteries and two agm chassis batteries.

Our auto gen start is set for 12.2 on the chassis and something a bit lower in the house.

 

[J&JD]

Mine often reads just like yours with the same setup. Doesn’t seem to cause any problems so I quit worrying about it after several years of ??

 

[AbdRahim]

Just left SES. They said chassis bat charges when it gets down below 12.5v.

 

[Chuggs]

This is what our Bi-directional relay action looks like over time. So, it all depends on when you look.

 

[AbdRahim]

This is what our Bi-directional relay action looks like over time. So, it all depends on when you look.
View attachment 29212

What did you use to get the graph?

 

[Chuggs]

When I installed my solar, I had chosen Victron equipment. A friend, who also installed Victon asked if there was a way to monitor things. At the time I suggested Venus GX device. Today, I believe thier Cerbo GX has some added features. GX devices connect to your Victon devices and send packets to the Victron Remote Mgmt website. Victron provides this service free. You do need a connection method...Ours uses wifi, but they make other devices that communicate on different platforms. The graph you see is a recording from my BMV-712. It monitors volts and amps on my house bank, and volts only on my chassis bank. Seeing the volts comfirms the charge being shared from the inverter charger while parked.

I didn’t think I needed it…but after seeing the data he collected…I was onboard. You can set alarms to notify you of any deviations from parameters you select. To be honest…it is also a phenomenal way to educate yourself on your your electrical system and it’s performance.

 

[Chuggs]

There has been discussion of the trickle charge solar panel causing chassis batteries to boil off. Some have gone so far as checking water levels in them. They aren't expensive so I replace mine at 5 year intervals, keeping in mind when your batteries could have been installed for new RV owners.

Hmmm…. 7/10th +/- of an amp from a 10 watt panel vs 240amp alternator running for hours each day the coach is driven?

IMHO, solar panel is insignificant. As a matter of fact, I checked my inline fuse at one point and it had blown. Our year model doesn’t come with the little solar led…so, we aren’t even aware if it is working or not.

I don’t have a representation of what the voltage at the battery terminal is while driving…but the voltage from the chassis as measured at the thru hull studs in the compartment under the drivers seat is over 14 volts with the engine running on the highway. Potentially doing the equivalent of an absorb charge rate for 6 hours each day you drive your coach. I would imagine if you set the Magnum Charger up to remain in absorb for 6 hours each day, you would blow thru water pretty fast there too.

 

[Neal]

Hmmm…. 7/10th +/- of an amp from a 10 watt panel vs 240amp alternator running for hours each day the coach is driven?

Yeah, doesn't make sense. "Read it on the Internet"