Gut check on transfer switch for inverter - special case

[thedavidzoo]

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.

[computermonkey]

Example of what I did. I wanted to power every 110v socket through the inverter. I added a second transfer switch making the inverter dominant, that way power from the first transfer switch would be on all the time until inverter was turned on then twenty seconds later the transfer switch would allow the power from the inverter.

I have two circuits coming off the battery. One is a 100amp BMS. The camper's 12v power and charging is done through this. Also has temp cut off so if to cold it will stop the charging from damaging the batteries. Second is a 250amp using 4/0 wire going to a 3000watt inverter with a low volage battery disconnect.

I set the refrig to propane and unplug the converter. Charging is done mostly there solar.

https://imgur.com/oO1xBRL

https://imgur.com/EK2CX1x

https://imgur.com/wKBA2SG

[2oldman]

12thgenusa wrote:
You have losses inverting 12V to 120V and then back to 12V through the converter to power the 12V items.

I don't see that.

[thedavidzoo]

12thgenusa wrote:
A much better way is to leave the 12V distribution panel connected to the batteries and disconnect the 120V feed to the converter. Another plus is that in the event of an inverter failure all 12V items would still operate.

Yes, this is now the plan!

[12thgenusa]

You are correct in that as you have it drawn there is not a charging loop between the converter and inverter however, powering everything through the inverter is very inefficient and overly complex. You have losses inverting 12V to 120V and then back to 12V through the converter to power the 12V items.

A much better way is to leave the 12V distribution panel connected to the batteries and disconnect the 120V feed to the converter. Another plus is that in the event of an inverter failure all 12V items would still operate.

[DWeikert]

Hemi Joel wrote:
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?

Since the charge controllers monitor battery voltage that would only happen when the battery is fully charged. Or at least one of the controllers thinks it is.

Once the batteries approach full charge the controller set to the highest voltage would be the last one providing current. For example, if controller A is set to 14.38v and controller B is set at 14.42v, controller A would stop providing current at 14.38v then controller B would provide the last bit of charge until the batteries reach 14.42v. But I doubt that's going to be a problem.

[Z-Peller]

A converter uses 110v power to make 12v power and feed it to the batteries. Inverter draws 12v from batteries to make 110v power. You say your converter runs on 12v??...don’t see how.....Check your 110v breaker panel for converter breaker and switch it off. No more converter producing 12v power when you are running inverter for 110v power. There is nothing at converter for 12v wires to backfeed. Wire your inverter thru generator feed which will go to 110v breaker panel then you can turn breakers on or off to select what you circuits you want on or off.

[thedavidzoo]

Thanks everyone. I have probably beaten this dead horse by now.:B

[time2roll]

I put my converter on a separate breaker to use as a switch.

[thedavidzoo]

The company is ElitePowerSolutions. Larry from Starlight Solar, Yuma, AZ is their distributor.

This system is virtually identical to Technomadia's install who were kinda pioneers with these cells in RVs. https://www.technomadia.com/lithium/

Yes, it is a complicated system (you should see the wires!). This was before the drop-in Battleborn systems and such. All these parts including the brain are necessary, it keeps tabs on undervoltage, 16 individual cell temps and voltages, etc.

I know the manufacturer installed batt kill switch should be a step earlier, but the brain has its own main kill switch that shuts everything battery related down.

I want to retain all shore power and gen abilites, so no removal of parts.

I was hoping the 3 terminals on the brain were "one way", as in the converter DC could not backflow into batteries to charge. The company confirmed that is NOT the case and I would have a loop with the inverter running the show.

So, I think the easiest answer is to disable the converting part with a switch. That way I retain all 110 on inverter and can still use 12V from battery only. If on shore power, the converter can be easily switched back online.

[Hemi_Joel]

The loop that I pointed out is all downstream of the integrated battery brain thing. That IBCS would have no effect on it. When AC power is being provided to the converter by the inverter, the converter will convert the AC power into DC power. It will sense the load that is being placed upon it by the DC side of the inverter, and send DC current to it. The inverter will convert that DC power to AC power, and send it back to the converter, and there you have your loop regardless of the brain.

[pianotuna]

If you never use shore power or a generator, simply disconnect the converter. I would leave it in place.

[theoldwizard1]

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]

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]

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.