AC shore power and inverter conflict?

[Flyview]

I have a couple AC circuits throughout my van with a breaker panel from when my van was built. There was already a master breaker and 2 more for the other circuits. I put in a third breaker and plugged an out from my inverter into that. So now I get power to my outlets from my inverter. What happens if I forget to turn off this last breaker for the inverter when I plug in shore power? My inverter is a fairly small 600W pure sine inverter, but my friend building a van with a big Victron Multiplus 3000W inverter has the same question.

Thanks!

 

[justinm001]

No clue how yours is wired up but a Victron MP has a built in auto transfer so with your friends, the power goes from shore thru the inverter to the Breaker panel. If no shore then the inverter inverts, if power over shore then it'll assist up to the inverter. The victron can limit how much power it receives from the shore, so he sets it to 15a/30a/50a

 

[seneysolar]

I have a couple AC circuits throughout my van with a breaker panel from when my van was built. There was already a master breaker and 2 more for the other circuits. I put in a third breaker and plugged an out from my inverter into that. So now I get power to my outlets from my inverter. What happens if I forget to turn off this last breaker for the inverter when I plug in shore power? My inverter is a fairly small 600W pure sine inverter, but my friend building a van with a big Victron Multiplus 3000W inverter has the same question.

Thanks!

What i think you are describing is backfeeding the panel through one of the breaker spots?
If you are still plugged into shore power you will likely trash your 600w inverter.

Your friend with the multiplus has the option to use shore power as a power assist input at the same time as the inverter is on. But thats using the input side NOT the output side.

Do not backfeed a panel while energized by shore power. Bad things will happen.

 

[justinm001]

What i think you are describing is backfeeding the panel through one of the breaker spots?
If you are still plugged into shore power you will likely trash your 600w inverter.

Your friend with the multiplus has the option to use shore power as a power assist input at the same time as the inverter is on. But thats using the input side NOT the output side.

Do not backfeed a panel while energized by shore power. Bad things will happen.

I'm curious on whatll happen though. As people with Ingrid solar systems backfeed all the time without issues. I have a grid tie system at my house and it'll backfeed into the breaker but not past the meter as it uses CTs to only handle load.

Soon my Victron inverters in my RV will do this using solar from RV to power my house, think the CT meter comes tomorrow.

Not saying you're wrong I'm just curious on whatll happen. Also it's all 240v not 120v and with Victron power feeds through inverters and it syncs the sinewave.

I'm assuming with OP the sinewave will be off and it'll get well above 120v, up to 240v but not 100% certain

 

[ricardocello]

Do not backfeed a panel while energized by shore power. Bad things will happen.

Specifically, unless by some miracle the relative phases of the shore power and inverter output happen to be synchronized, BOOM!
Most likely the inverter drive circuits will pop, magic smoke released, maybe a fuse or breaker blows, maybe a fire starts.

 

[seneysolar]

I'm curious on whatll happen though. As people with Ingrid solar systems backfeed all the time without issues. I have a grid tie system at my house and it'll backfeed into the breaker but not past the meter as it uses CTs to only handle load.

Soon my Victron inverters in my RV will do this using solar from RV to power my house, think the CT meter comes tomorrow.

Not saying you're wrong I'm just curious on whatll happen. Also it's all 240v not 120v and with Victron power feeds through inverters and it syncs the sinewave.

I'm assuming with OP the sinewave will be off and it'll get well above 120v, up to 240v but not 100% certain

The folks that feed the grid on accident have an inverter capable of doing so. The voltage and frequency needs to sync with grid power, otherwise you just have 2 different potentials, only one will win.

 

[justinm001]

The folks that feed the grid on accident have an inverter capable of doing so. The voltage and frequency needs to sync with grid power, otherwise you just have 2 different potentials, only one will win.

Thanks thst was my assumption just wasn't certain. In a DC system it would be OK, many have dual alternators or converters connected.

 

[Flyview]

What i think you are describing is backfeeding the panel through one of the breaker spots?
If you are still plugged into shore power you will likely trash your 600w inverter.

Your friend with the multiplus has the option to use shore power as a power assist input at the same time as the inverter is on. But thats using the input side NOT the output side.

Do not backfeed a panel while energized by shore power. Bad things will happen.

Thanks! Yes, although from the breaker's point of view it's not much different than the power coming in to the master breaker. So the problem stems from not being able to have multiple AC power sources because they will likely be out of sync, correct? I will have to make sure the inverter breaker is off whenever connecting shore power. Would anything bad happen if the breaker is on but the inverter itself is off (it's usually off)?

 

[seneysolar]

Thanks! Yes, although from the breaker's point of view it's not much different than the power coming in to the master breaker. So the problem stems from not being able to have multiple AC power sources because they will likely be out of sync, correct? I will have to make sure the inverter breaker is off whenever connecting shore power. Would anything bad happen if the breaker is on but the inverter itself is off (it's usually off)?

Depends on the inverter. Probably not.

Remember when back feeding breakers, (aside from it being dangerous) most are only designed to work in one direction (line/load). You should assume you don't have that breaker for over current protection when in use.

 

[robbob2112]

If you want to feed power into your AC panel you need an interlock breaker so that only grid or your inverter can be online at one time. Or buy an inverter that has a grid input. If you don't need the large power of the 3k multiplus you can get smaller ones that interact with the grid for you.

Here is an example without all the bells and whistles of the victron, but at a fraction of the price. And, bonus it also includes a charger for you battery. I have it as a UPS with a MPPT to be added that can also charge the batteries. So I have it set to DC prefered now and a timer on the AC to only turn on the charger at night when I am not around.

12V 2KW Pure Sine Wave Inverter Charger

Rated Input Voltage: 12V Rated Output Voltage: 110V Efficiency: >90%

www.expertpower.us

5ms switchover when AC is lost.

 

[robbob2112]

Note - the Expertpower doesn't have a built in MPPT to connect panels until you hit 3kw, but you can just buy a separate one and connect the output to your battery(ies)

 

[0truck0]

Easiest to just install an AB switch on the hot side instead of a breaker or in addition to.
My RV-type breaker box has two main inputs (shore and generator). The breakers are next to each other and there is a physical plate that when one breaker is turned to ON then the other breaker gets turned to OFF. This is a very good 20 cents solution, and came from an old old RV. I dont have a link to give, but the solution is a breaker or switch that can only be set to one input or the other. Usually done on the hot wire, well, all breakers are...

Yes, if you back-feed an ordinary inverter you will smoke it. This is nothing like DC power where you can backfeed it, with AC you cannot.

On that same wire system I added an inverter, so had shore, generator and inverter. On the outlet wires only I added an A/B toggle switch (selects either A or B) and put it on the hot wire from the breaker box. This now selected either inverter or breaker box (shore or generator), and the main circuit breaker still selects generator or shore by separate operation. The inverter was to only be used on outlets, not the air cond and not the heating element on the propane fridge, so this solved how to cut out those two from the inverter without messing with shore or generator. This made it impossible to select two power sources at the breaker box - all 3 could be hot, but only one selected to feed the box, and one selected to feed the outlets.
So, the generator or the shore could be powering the box therefore the air cond and fridge but the toggle isolated the outlets.
How up to code it was putting a toggle switch in IDK, but Im sure there are methods to make it code, and more sure there are devices made to do this that are code. There is no code for me wiring up my RV that I have to follow legally, but I still kept it safe.
So, with inverter running the electric the DC operation of the fridge stayed on DC. Fridge was not on the "outlets", it was on a breaker in the box.. that fed its own outlet separate. The fridge would auto switch to AC if power is present. Fridge uses way too much power on AC mode, so never run that off battery.