How does shore power work for the 12 volt system?

Generally the converter/charger and the batteries and the 12V distribution system are all tied together (at least when the battery disconnect is not disconnected). You can think of it as power coming from the converter to both the 12V system in the coach and to charge the batteries, at least up to its current capacity. If you're consuming more current than it's supplying, the batteries will supply the excess.

What happens with the battery disconnect switch turned off is a bit more variable. On my particular unit, the converter and battery stay connected, but the 12V distribution is disconnected from both of them (so the lights, etc. don't work but the battery charges). I would guess that some have the converter on the other side of the disconnect switch, and probably some more complex variations exist as well. Some (mostly older) converters don't work properly with no battery attached, and others operate but provide very unclean DC power, relying on the battery to act as a filter. Incidentally, some solar controllers also have a similar need to be connected to a battery.

To summarize, the answer to your second question is "maybe."

"Most Class A motorhomes today have a manufacture installed device called a converter/inverter/charger."

Could you give the manufacturers name for one of these? I have never heard of such a thing

paintedtugboat wrote:
Most Class A motorhomes today have a manufacture installed device called a converter/inverter/charger. This device receives power from shore power, a generator, the engine alternator and storage batteries. If there is no shore power, the engine is not running and the generator is not working, the coach will get power to run 12 volt lighting and 12 volt systems from the deep cycle coach batteries. The inverter part of the device will also use some of the 12 volt battery power to make 120 volt alternating current (AC) for TVs, entertainment system and some outlets. When hooked up to shore power, the coach ahs 120 volts AC for all the AC appliances like air conditioners, washer/dryers, TVs and microwave; also the inverter stops working and the converter changes 120 volt AC power into 12 volt direct current(DC)for 12 volt lighting, vent fans and other 12 volt appliances and the charger part of the device replenishes the batteries. (The batteries can also be replenished by the engine alternator, the generator and solar panels,if any).

this 100% correct. To clarify the OPS original question. In any RV converters or converter/iinverter units are designed to be operated with batteries hooked up. The conveters put out dirty power. The batteries absorb the spikes and noise and prevent damage to 12 equipment. It is also hard on converters to run without batteries because they have very little capacitance. This can lead to voltage sags and overheating of the converter. Always have a battery hooked up.

draboo wrote:
I am curious as to how the 12 volt system works when plugged into shore power.

Does the inverter keep the batteries charged, and directly power the 12 volt stuff on the motorhome, or do the batteries provide the power and the shore power keeps the batteries charged?

Maybe this will be a clearer question than the one above: Is it necessary to have the house batteries hooked up to provide 12V power to the motorhome?

Clear as mud? :)

draboo,
It would be nice if we knew the make/model/year/engine etc. of your coach. We could give more accurate answers to your question. But, as has been stated, if you have a gas coach, most of those came and come with, a "Converter/charger". That is, the converter takes incoming A/C voltage and, changes it to 12VDC for coach component operation if and when, plugged into shore power. It will also charge the house batteries. Some, depending on how they're wired etc., will also charge the chassis batteries.

But, if it's a Diesel coach, most of those come with an "Inverter/Charger". And, many of those do not have a converter. The 12V from the batteries cruises right through the system and supplies all the house components. The Charger section of the Inverter/Charger will charge the house/coach batteries. Many DO NOT charge the chassis batteries. There are additional systems/wiring setups that will utilize some of the coach battery charging, to charge the chassis batteries, when the coach is plugged into shore power or, running the generator. Hope this helps some.
Scott

Most Class A motorhomes today have a manufacture installed device called a converter/inverter/charger. This device receives power from shore power, a generator, the engine alternator and storage batteries. If there is no shore power, the engine is not running and the generator is not working, the coach will get power to run 12 volt lighting and 12 volt systems from the deep cycle coach batteries. The inverter part of the device will also use some of the 12 volt battery power to make 120 volt alternating current (AC) for TVs, entertainment system and some outlets. When hooked up to shore power, the coach ahs 120 volts AC for all the AC appliances like air conditioners, washer/dryers, TVs and microwave; also the inverter stops working and the converter changes 120 volt AC power into 12 volt direct current(DC)for 12 volt lighting, vent fans and other 12 volt appliances and the charger part of the device replenishes the batteries. (The batteries can also be replenished by the engine alternator, the generator and solar panels,if any).

Whether a CONVERTER or an INVERTER/CHARGER, they work in conjunction with the Coach batteries. In real terms, the Converter is supplying the needed 12 volts and is trickle charging and keeping the battery/s fully charged. An Inverter/CHARGER just charges the battery bank and all 12 volt loads come from the batteries. The more 12 volt loads and the Inv/Charger may increase its charge output. An Inverter/Charger CANNOT operate without batteries connected. MOST Converters (with a few exceptions) can operate without batteries connected. Whether you can operate your Converter with or without batteries connected, it is BEST to have a battery connected to help the Converter to do its job better. Doug

All depends on how the rig is wired, some need to have 12 volt batteries in the circuit, some do not.

Lots of info here: The 12 Volt Side of Life

When plugged in to shore power your 12V system is powered by the on-board CONVERTER. The converter also charges the battery(s). If you have an INVERTER it is used to provide 120V AC power, usually for a few outlets or devices when not connected to shore power. The house battery(s) should be connected even while on shore power for everything to work properly.