charging rates

Hi Phil,

I'm basing the charging numbers on an ammeter that is between the engine and house bank. When I had all identical marine flooded jars I did see large current (up to over 70 amps) coming from the engine (if the house bank was hungry, or I placed a load (water heater) on the inverter). Now that I'm all AGM the house bank feeds the engine current. For example, if the solar panels are feeding 6 amps into the battery banks, there may be 8 amps going to the engine. I'm sure that the ecm limiting voltage to the alternator charging path is the issue.

A simple volt meter may not "tell the tale" on which way current is flowing.

The connection path is two #8 wires with solenoids. I do have the ability to turn them off. A third path is one way from house to engine via a Trik-L-Start module.

pnichols wrote:

pianotuna wrote:
I thought that might be because I had a flooded marine battery (from 2005) for the starter. I finally replaced that in 2017 in the spring with a AGM. I still get almost no charging for the house bank.

Don, perhaps your motorhome's engine alternator/engine battery/coach batteries interconnection system is different than my Itasca's.

I have two voltmeters and an ammeter mounted on the cab dash. One voltmeter shows the voltage on the engine's 12 volt system, the other voltmeter shows the voltage on the coach's 12 volt outlets, and the ammeter has it's shunt mounted in the main coach batteries' negative cable connected to the chassis frame.

The two voltmeters read within about 1/10 volt of each other all the time whenever the engine is running -> if and only if the interconnect solenoid (that activates from the ignition key) is activated AND has contacts in good conditon ... such that there is no resistance voltage drop across it's contacts (I've had to change it twice in 11 years).

As I drive down the road, both of the voltmeters track each other and slowly drop in voltage reading as the coach batteries charge up while driving. The ammeter drops down to near zero within a few hours of driving after camping - thus indicating that the coach batteries are no longer accepting charge current at whatever voltage the meters indicate.

This behavior leads me to believe that Winnebago has the engine battery and coach batteries wired in parallel with each other someway. Since the engine battery is liquid acid and the coach batteries are AGM, they're all getting charged together at the same voltage from the alternator, as indicated by the voltmeters. However as the coach batteries run down when drycamping, of course the engine battery doesn't run down - so the three batteries aren't in "hardwire/direct" parallel with each other ... BUT there is not a diode drop difference in the readings on the two voltmeters, so the engine and coach batteries are not isolated by simple diodes. Maybe there is some computer control of the engine battery charging that is separate, even though my two voltmeters show near identical voltage readings from the systems (engine 12V system and RV 12V system).

Whatever is going on it all plays together perfectly, even with mixed battery technologies. However the coach/engine batteries interconnect solenoid must have good contact surfaces for my situation. I wonder how many of these solenoids in RVs everywhere are activating all right, but introduce a voltage drop across there contacts after a few years with the RV owners not even aware of it. What this does is cause the coach batteries to never get charged adequately between campsites. The coach batteries are getting some charge, but not enough because of the reduced charging voltage on their terminals due to the voltage drop from the alternator created by the drop across the interconnect solenoid's contacts.