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thedavidzoo's avatar
thedavidzoo
Explorer II
Aug 27, 2020

Gut check on transfer switch for inverter - special case

A few years back we DIY installed our current lithium/solar system which is charged only through roof solar. We initially rewired a few 110V outlets dedicated to the inverter, including the microwave. We "never" plug into shore, do not have a generator, and do not charge the batteries via truck (disabled with switch at converter just in case). The generator compartment is prewired into an existing automatic transfer switch (shore or generator). Converter is standard dealer WFCO type.

We are now relooking all our outlets and USB charging ports to make them a little more logical for our uses. We would like to again rewire so that all 110V outlets run from the inverter. I hear that you do not want a loop where the inverter draws on the batteries, feeds back into the converter (using an automatic or manual transfer switch), and charges the batteries.

Now our system is a little different, I think. Our lithiums have individual cell BMS and an integrated battery control system "computer" (the brain) which regulates all battery in and out power among other things. We have no direct positive connection between converter and battery as would be the usual way. Any charging source (only solar now) comes through the C+ connection on the brain. All loads (to inverter, converter) go out through L+ on the brain. Therefore, I conclude that there is no way the converter can feed back into the batteries with the inverter powering the converter. Confused yet?

Plus, I think I can just wire the green manual transfer switch after the existing one so I can select the inverter or shore.

Also, our fridge is 110/12V compressor. I think I could just unplug its 110v cord and force it to run 12V when the inverter is on.
Wouldn't affect the furnace, only 12V.
Would only affect propane WH for initial spark? Wouldn't use electric WH on inverter anyway.
Wouldn't try to use AC air on inverter either, might have to rig thermostat switch against accidental bumps.

So many questions. My sketch, don't laugh. Thanks.
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17 Replies

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  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 27, 2020
    If you never use shore power or a generator, simply disconnect the converter. I would leave it in place.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Aug 27, 2020
    The system you have loos OVERLY COMPLICATED !

    thedavidzoo wrote:
    We would like to again rewire so that all 110V outlets run from the inverter.


    So no shore power or generator. Get rid of the automatic and manual transfer switches.

    With on external AC power, you do not need a converter at all ! You diagram shows the DC is connected directly to the batteries (via the positive bus bar) so that is fine.

    Your "battery kill" switch should be on the line between the battery and positive bus bar.

    I don't understand the purpose of that "Integrated Battery Control System". IMHO it is not required at all as good solar charge controllers will handle charging the batteries.

    What is the make and model of the "Integrated Battery Control System" and the batteries ?
  • thedavidzoo's avatar
    thedavidzoo
    Explorer II
    Aug 27, 2020
    I need to be able to run all 110 outlets and appliances off inverter while simultaneously running all 12V system off batteries.

    The converter is there top left.

    My 2 solar controllers are master and slave, they are meant to run like that. Technically, I could add several more slave strings. Initially it was an amp sizing issue vs cost vs space. I kinda like having 2 different strings.

    My batteries power the converter like everyone else's, although mine are first routed through the iBCS "brain" which does its own magical switching and regulating.

    Since it looks like you are using the WFCO 120v/12v distribution panel I am fairly certain if you power up the 120v side of the panel the converter will put 13.6 volts onto the DC side. Something will need to be disconnected to disable the converter."
    Is the problem that both the batteries and the inverter-fed-converter will want to power my 12V system at the same time? But how is that different than just plugging in shore power? Both remain connected. Since I have no direct charging feedback to my batts from the converter, I don't think I have a loop (because iBCS brain).
    One option is to just use the batt kill switch (after inverter connnection), then my inverter will power converter will distribute 12V to system. But I don't want to run my fridge, lights, USB, fans, furnace, etc. on inverted to converted power.

    Yes, my GFCI outlets branch also includes my fridge, but I can unplug it. I don't want to have to do too many switches for each case and get it all confused.

    I see a loop if the battery disconnect switch is closed. The inverter powers the ac side of the converter. The ac side of the converter powers the dc side of the converter. The dc side of the converer powers the inverter. Loop complete.
    Again, loop not complete because of iCBS brain?

    Yeah, direct wiring the inverter to the generator transfer switch input would be simpler than another switch. But the switch would favor inverter power over shore, but I'd never turn on inverter when on shore anyway.

    I have emailed the company to have them confirm that power cannot come back through the load output L+ terminal to the batts as it would with normal RV wiring.

    Makes my head hurt..
  • Hemi_Joel's avatar
    Hemi_Joel
    Explorer
    Aug 27, 2020
    I see a loop if the battery disconnect switch is closed. The inverter powers the ac side of the converter. The ac side of the converter powers the dc side of the converter. The dc side of the converer powers the inverter. Loop complete.
  • Hemi_Joel's avatar
    Hemi_Joel
    Explorer
    Aug 27, 2020
    I didn't think you could run 2 solar charge controllers in parallel? Doesn't one sense the output of the other and interpret that as a fully charged battery, cutting 1/2 your solar array out?
  • time2roll's avatar
    time2roll
    Nomad
    Aug 27, 2020
    Since it looks like you are using the WFCO 120v/12v distribution panel I am fairly certain if you power up the 120v side of the panel the converter will put 13.6 volts onto the DC side. Something will need to be disconnected to disable the converter.

    Not sure why you would not just feed the generator side of the OEM transfer switch.

    If you want to power just the outlets you can get a small transfer switch to power just the branch circuit(s) with outlets. Although sometimes the branch circuit that feeds the outlets also feeds the converter and fridge. Adjustments for that would have to be made.
  • 2oldman's avatar
    2oldman
    Explorer II
    Aug 27, 2020
    I'll try.

    First, I don't see any converter in your schematic. Perhaps I don't know what an IBC is.

    If you "never" (not sure what that means) plug in, and don't have a generator, how could you power a converter?

    Running the entire house on inverter is a nice way to go, but you may be tempted to run large appliances like toaster and MW. If so, I suggest you up your battery voltage (and inverter) to at least 24v. Gets rid of the fat wire.

    I don't know why you have 2 solar controllers. You could series your panels, get rid of the combiners and more fat wire, and just have one.

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