I postponed continuing my current discussion because I was concerned it might obscure Wolf_n_Kat's post, as well as Leeann's response. I felt it was important to make sure this thread's community had a good opportunity to read and respond to those posts. Then, I got busy using nice summer weather to work on the house.
Before continuing, I'd like to clarify and amplify some elements in my previous post on typical motorhome electrical systems. The following is a "top level" block diagram, reflecting the totality of most motorhome electrical systems.
The diagram contains two "black boxes" with each representing one of the two (sub)systems typically found in recreational vehicles. The diagram also has three lines/arrows representing the connections between the (sub)systems.
For completeness, I decided to add two lines/arrows depicting two external connections for the 120/240VAC (sub)system. which were not discussed in my previous post. I chose to add these because shore power cords are usually physically attached to the motorhome and many motorhomes have onboard generators
I probably could have added an external connection line/arrow, also labelled "Battery Charger(s)." to the 12VDC (sub)system, to show that battery chargers could be plugged into external outlets, as well as internal outlets. However, I decided, in this case, external outlets (and battery chargers) aren't part of a motorhome's overall system.
You may have notice my repeated use of "(sub)system" in this text while the diagram simply uses "system." I did this to maintain a degree of continuity with my previous post. The diagram's labels are technically correct and the repeated use of "(sub)" is, at this level, superfluous. (The use of "system" and "subsystem" is a judgement call, usually related to how autonomous a component is within the overall system.)
The use of black boxes is a means of avoiding getting bogged down in details. In general, black boxes represent subsystems, circuits, and components, with each having specific characteristics and function(s). By obscuring the details existing within the black box, we're able to focus on a specific section of the overall system and how it relates to (connects to or interfaces with) other sections.
My previous post on this topic was written on-the-fly, which results in not always choosing the most appropriate terms. Specifically, I used transformers and bridge rectifiers when power supplies would have been a more appropriate term. On the other hand, I was specifically thinking about our older motorhomes and power supplies consisted of transformers and bridge rectifiers back in those days. Modern power supplies typically use electronics and are, to varying degrees, more sophisticated than old skool transformers/rectifiers.
(This is the reason I recommend upgrading to a new, more modern power supply if you're still using the power supply that originally came with your motorhome.)
As noted in my previous post, we are going to ignore the motorhome's 120/240VAC system, at least for the time being, and focus on the 12VDC system.
Just as with the typical motorhome's overall electrical system, we can break down the typical motorhome's 12VDC system into two distinct, cohesive parts: The coach system and the motor vehicle system.
Unlike the higher level breakdown, where the dividing line between the two systems was the voltage and type of current in each system, what we're looking at now is partitioned based on function. (The criteria for dividing up a system is also a judgement call, based on a variety of factors, such as functions, locations, characteristics, etc. In complex systems, it's sometimes necessary to have multiple diagrams, each reflecting a different aspect or view of the system.)
The coach system includes the components and circuitry that supports the motorhome's living quarters role. On the other hand, the motor vehicle system includes the components and circuitry needed for the motorhome to operate as a legal motor vehicle.
Note: I prefer "coach" over "house" because house is a somewhat ambiguous term with multiple meanings and interpretation. More important to our discussion, the electrical system in most people's houses is (at least in North America) exclusively 120/240VAC systems. (If their houses have a 12VDC system, it's usually because they're living off the grid.)
(Following the same train of thought, I prefer "auxiliary battery" over "house battery" in boats.)
The only connection between the two systems is the desirable but problematic means of charging the coach battery bank and powering the coach circuits when the engine is running.
Both systems show external connections, refined and carried over from the higher level diagram.
The motor vehicle system shows a single external connection, consisting of a single battery charger for charging and maintaining the motorhome's SLI (engine) battery. (Part of the details hidden by the black box is the alternator's role as the other SLI battery charger/maintainer.)
The coach system has three external connections, which are the three connections between the 120/240VAC and 12VDC systems in the higher level diagram/breakdown. In this case, they're shown as external connections because what they're connected to is outside this diagram.
I should also note this diagram slightly modifies the definition of battery charger(s) to include both onboard chargers connected to the motorhome's 120/240VAC system and external outlets. In addition, the "(s)" indicates the possibility of more than one charger for multiple batteries/banks.
In my next post on this topic, we'll look at the coach system in more detail, largely because it's relatively simple and provides a good opportunity to address some basic concepts, such as what a circuit is and so forth.
BTW - It's raining today, which is why I managed to finish this ...
