Forum Discussion

draboo's avatar
draboo
Explorer
May 08, 2015

How does shore power work for the 12 volt system?

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? :)
Class A
  • Hosehosea's avatar
    Hosehosea
    Explorer
    May 28, 2024

    Shore power is 120v AC which goes into the converter which then outputs 12v dc to power the 12v DC panel and also charges the battery. An inverter takes 12v battery power and turns it into 120 v AC

    • way2roll's avatar
      way2roll
      Navigator II
      Dec 09, 2024

      Helpful information I am sure, but this thread is almost 10 years old and the OP hasn't been on here in years. 

  • sch911's avatar
    sch911
    Explorer
    May 08, 2015
    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.
  • dougrainer's avatar
    dougrainer
    Nomad
    May 09, 2015
    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
  • paintedtugboat's avatar
    paintedtugboat
    Explorer
    May 09, 2015
    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).
  • FIRE_UP's avatar
    FIRE_UP
    Explorer
    May 09, 2015
    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
  • msturtz's avatar
    msturtz
    Explorer
    May 09, 2015
    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.
  • dons2346's avatar
    dons2346
    Explorer
    May 09, 2015
    "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
  • DrewE's avatar
    DrewE
    Explorer II
    May 09, 2015
    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."
  • dons2346's avatar
    dons2346
    Explorer
    May 09, 2015
    Since you ask about an inverter, I assume you have one. On shore power the inverter charges the house batteries and the house batteries supply the 12 volt systems. The inverter has a "pass thru" system that allows 120vac to supply power to some of the 120vac stuff such as tv, microwave, and some wall sockets.

    When not on shore power, the inverter can supply 120vac to the same circuits by using battery power to do so.

    Even with an inverter, without the batteries, you will have no 12vdc even when plugged into shore power.
    • Hosehosea's avatar
      Hosehosea
      Explorer
      May 28, 2024

      You got this all backwards. The inverter doesn’t charge the battery. The converter does. When on shore power 120V AC is supplied to the converter which converts 120V AC to 12v DC which then powers the 12v distribution circuits. The converter also charges the battery. If you shut off the converter the battery takes over powering the 12V system. That’s how you test for a good battery: turn on 12v lights and then shut off the converter. If your 12v lights stay on that means the battery is doing its job and powers those lights when the converter is off. This is also what happens when shore power is removed…. You’re back to being battery powered only. An inverter however, takes 12v DC and changes it to 120v AC.

      • rshellhammer04's avatar
        rshellhammer04
        Explorer
        Dec 09, 2024

        There is power loss when 120 v is converted to 12 v. Would you use less electricity if you ran the 12 v system on the batteries and just use the converter to charge the batteries?

About Motorhome Group

38,705 PostsLatest Activity: Jan 14, 2025