24V Inverter and 12V system

ZoNiE
ZoNiE Solar Expert Posts: 100 ✭✭
in Off Grid Solar & Battery Systems #1
Hi, I acquired a Sensata Dimensions 24/2200 mil spec pure sine inverter which I want to use with my RV. As usual, the RV is 12V. I currently have two 6V GC's in series, and will add two more. I was thinking of putting them in a switched arrangement where Mode A is 12V, two parallel connected banks of series connected 6V batteries, and the Coach is powered normally by the batteries, Shore Power, or the Honda EV4010, and Mode B where the Batteries are in series for 24V output to the inverter only, then the inverter powers the existing charger in the coach, which powers the 12V appliances, but is not connected to the batteries, naturally (that is if the converter will work without a battery load). I fully realize that there will be double efficiency losses going this route, but I got this $1,600 inverter for next to nothing. I will be doubling my battery capacity from what I have so I can live with the losses even though I will be using more power.

One reason is to go to a 120VAC Compressor refrigerator as the Gas units just don't keep the food cold during desert camping. I don't want to run the Genny just for the fridge, but do run it during the day for Air Conditioning when needed so it will keep the batteries up.

My question is, has anyone done something like this? I have the relay switching figured out, but there may be other methods I am not aware of? I'm new to this, but am an EE so the circuitry is a no brainer. Just wondering if it is worth it

I may add solar in the future, I have three 200 series 173 Watt Solyndra panels that may find their way on to the roof
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Comments

  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #2
    Re: 24V Inverter and 12V system

    You could also use a 24V to 12V DC-DC converter. Or some smart switching arrangement that would frequently move the larger 12V loads to whichever half of the string has the highest SOC. No conversion losses this way.

    I am available for custom hardware/firmware development

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  • ZoNiE
    ZoNiE Solar Expert Posts: 100 ✭✭
    #3
    Re: 24V Inverter and 12V system

    Yeah, I was thinking the same, but on another forum, switching between banks was suggested as a way to fry my batteries. And then there is the charging of two different banks at different charge levels.

    small 24-12 DC-DC converters at the individual appliances makes more sense. One for lighting, One for the Ignition on the water heater and refer, and one for the furnace.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: 24V Inverter and 12V system

    My advice would be to avoid trying to switch batteries from parallel to series configuration. It is not simple, and involves changing wiring that will be carrying heavy current. Go up to the 24 Volts the inverter needs, and use the DC to DC converter for any 12 Volt loads just as jonr suggests. That would be the most practical way to handle the requirements.
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  • ZoNiE
    ZoNiE Solar Expert Posts: 100 ✭✭
    #5
    Re: 24V Inverter and 12V system

    Yeah, the more I look at my schematic, the more I think that is the way to go. I have the switchgear already that can handle the current, but the WEIGHT will probably kill me!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Re: 24V Inverter and 12V system
    ZoNiE wrote: »
    Yeah, the more I look at my schematic, the more I think that is the way to go. I have the switchgear already that can handle the current, but the WEIGHT will probably kill me!
    Two 12V batteries in series weigh the same amount as those same two batteries in parallel. It is only if you use two 12V batteries in place of one of the same size that you get increased weight. :)
    SMA SB 3000, old BP panels.
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  • ZoNiE
    ZoNiE Solar Expert Posts: 100 ✭✭
    #7
    Re: 24V Inverter and 12V system

    I was jokingly referring to all the weight of the contactors, etc.. To further complicate my wiring, I have 6V batteries...:roll:
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