What would happen if two inverters feed the circuit breaker box?

softdown · December 2015

My 48 volt solar array is working very well. So far, it rarely needs help from the generator. The problem with the diesel generator? It doesn't like to start when it is very cold. That is also when it is most likely to be needed. The fumes also work their way around a little bit.

The giant 24 volt forklift battery seems to be a good one. What would happen if the circuit breaker box was fed by two different inverters? In my case, a 48 volt inverter and a 24 volt inverter. Of course both of them are putting out ~120 volts.

My guess is that the circuit breaker box may simply use both sources of power? In essence, doubling the size of the battery array? Or....disaster awaits the eager "explorer"?

FWIW: the 48 volt inverter is part of an Outback MATE system. The 24 volt inverter is a pure sine wave Cotek that costs much less money. And...I am broke and in debt...before someone tells tell to simply cough up a few thousand dollars.

Dave Angelini · December 2015

Right up there with letting a bear get into your home.

softdown · December 2015

Thanks for the input....I'll try to avoid that. Have another couple options:
1) Feed one side, with the lower demand, of the circuit breaker box with the 24 volt inverter.
2) Feed the freezer with the 24 volt inverter. This may be the soundest idea.
3) Set up a switch. Use the 24 volt array for a day or two when the main 48 volt array needs more time to recuperate.

Dave Angelini said:

Right up there with letting a bear get into your home.

stillchillin · December 2015

add a second breaker panel and split the loads how you please. The neutral also carries current, you do not want to share that between two uncompatable inverters, I'm sure someone in the forum can tell you exactly why but I would say no.

vtmaps · December 2015

softdown said:

Thanks for the input....I'll try to avoid that. Have another couple options:
1) Feed one side, with the lower demand, of the circuit breaker box with the 24 volt inverter.
2) Feed the freezer with the 24 volt inverter. This may be the soundest idea.
3) Set up a switch. Use the 24 volt array for a day or two when the main 48 volt array needs more time to recuperate

Do not run both inverters into the same circuit breaker box unless you use a transfer switch so that only one inverter at a time is connected to the breaker box. I am presuming that the bond between neutral and ground is in the breaker box.

By the way, what are you using for a battery in the 24 volt system? How do you charge the 24 volt battery?

How difficult will it be to separate the loads into two breaker boxes so that you can run two systems simultaneously?

--vtMaps

softdown · December 2015

Have a 1652 pound forklift battery for the 24 volt system. Seller thought it was 48 volt. Got it for scrap value since it showed 22.2 volts. He also paid scrap value so nobody got hurt.

I charge it with a couple extra 190 watt panels. I'm not an electrician so I'll just run a wire to the freezer and hope it handles the chest freezer. For now anyway.

I bought so many panels that I don't know what to do with all of them. My solar guy said he could easily sell them but that has not materialized. I may just sell them on Craigslist. Went to California and bought 48 used panels a few months ago.

vtmaps said:

softdown said:

Thanks for the input....I'll try to avoid that. Have another couple options:
1) Feed one side, with the lower demand, of the circuit breaker box with the 24 volt inverter.
2) Feed the freezer with the 24 volt inverter. This may be the soundest idea.
3) Set up a switch. Use the 24 volt array for a day or two when the main 48 volt array needs more time to recuperate
Do not run both inverters into the same circuit breaker box unless you use a transfer switch so that only one inverter at a time is connected to the breaker box. I am presuming that the bond between neutral and ground is in the breaker box.

By the way, what are you using for a battery in the 24 volt system? How do you charge the 24 volt battery?

How difficult will it be to separate the loads into two breaker boxes so that you can run two systems simultaneously?

--vtMaps

mike95490 · December 2015

> Or....disaster awaits the eager "explorer"?

You can only feed 2 inverters to a single panel, if they are a matched pair with a sync cable. Otherwise, it will be "exciting".

Skip · February 2016

I have a similar question to this thread, I have 2 Cotek SK 1500 - 124 PSW Inverters, I have 2 sub panels, one in the garage and one in my bonus room, is it possible to connect 1 of the inverters to each of the 2 sub panels without any damage to the inverters, or anything else? as I have a 3500 watt grid tie stand alone system and would like to use the Coteks for for backup power during outages. I have an AC Disconnect switch to disconnect the power company from the main load center.

zoneblue · February 2016

If the sub panels are isolated. Which they tend not to be! And no relying on a breakers to isolate, is not enough you need a full transfer switch.

Skip · February 2016

Thanks for the reply Zoneblue (nice website BTW), I am still wondering what it would take to make this work.
I totally disconnect the juice from power company using my AC Disconnect switch on the main electric panel, and using the AC disconnect switch in the off position on my 220 vac PV Watts 3500 GT Inverter so the only possibility of any current running in the house would be power supplied by the Cotek PSW inverters wired into the sub panels, hooked to a battery bank and charged by my 1600 watt secondary set of solar panels. At this point will the inverters power up the 110vac portions on the house circuits without blowing the inverters, as they are NOT stackable?

vtmaps · February 2016

You really need a transfer switch, even if you are using only 1 inverter. It is extremely poor practice (and illegal) to power your house from either a generator or an inverter unless you have a transfer switch.

--vtMaps

Skip · February 2016

OK so lets say I add a Transfer switch would it matter if the transfer switch was automatic or manual? what will it take to get a answer to this question? using 2 inverters? I really don't want to spend more money on a transfer switch if my 2 inverter plan won't work. Yea I know that using a 3000 watt inverter would work but I don't have one on those yet.

WaterWheel · February 2016

Skip said:what will it take to get a answer to this question? using 2 inverters

Using 2 inverters on the same line that are not in sync with one another is a disaster even with the local utility totally disconnected. I guess you could be unhooked from the grid and use one inverter tor L1 and the other inverter for L2 but their shared neutral would probably still make it an unusable setup. And the shared earth ground would probably trip GFIs.

In addition you could not use them to run 220v since they would be out of sync.

There are more knowledgeable people than I here but no way would I be foolish enough to try it.

zoneblue · February 2016

Skip said:

OK so lets say I add a Transfer switch would it matter if the transfer switch was automatic or manual? what will it take to get a answer to this question? using 2 inverters? I really don't want to spend more money on a transfer switch if my 2 inverter plan won't work. Yea I know that using a 3000 watt inverter would work but I don't have one on those yet.

Its important that you understand what people are trying to tell you, as what you are proposing is fraught with hazards.

You can not / should not:
- connect any separately derived system to the house without a UL listed transfer switch that categorically prevents the SDS and the grid (and your GTI) becoming connected.
- connect the output side of 2 or more off grid inverters (or other SDSs) together unless those devices are specifically engineered to do so, (read stackable inverters).

To achieve what you want, you will need several transfer switches (manual is ok), one for the grid, one for each sub panel that you want to power (possibly minus one), (to prevent the subpanels ever becoming connected accidentally.).

There are of course easier ways, like using an hybrid inverter specifically designed for this application, or a single bigger off grid inverter and a single transfer switch.

You should also ideally:
- use quality off grid inverters, that are UL listed for hard-wire.
- get an electrician involved

zoneblue · February 2016

In case the issue of two inverters and two subpanels isnt clear from the above, if you connect one inverter to one subpanel, and a second inverter to a second subpanel, and the subpanels arent safely isolated, you will likely destroy one or both of the inverters. This is because they will be out of phase, and fighting each other.

Skip · February 2016

OK I would like to thank you zoneblue and foolami for taking the time to answer this question, so if I get you both, I need a transfer switch and one large off grid inverter, to be safe and legal and I like that plan, so again Thank You both the this information.

brianbk1 · December 2016

I have a similar type question. My 5th wheel is designed to operate in 30 or 50 amp. For 50 amp I can plug in 1 50, or use a second plug on the RV to do a 30 and 20 connection. Would this work with 2 inverters?

Estragon · December 2016

Why do you want to use 2 inverters?

As I understand it the 50a plug is 120/240v split phase shore power source. If using two inverters in that setup I'd want them set up to duplicate that (stacked for phase sync). Don' t quite understand what you're trying to do though.

bill von novak · December 2016

brianbk1 said:

I have a similar type question. My 5th wheel is designed to operate in 30 or 50 amp. For 50 amp I can plug in 1 50, or use a second plug on the RV to do a 30 and 20 connection. Would this work with 2 inverters?

Short answer - no. You cannot get one inverter to deliver 20 amps and a second to deliver 30 amps and have them, together, produce 50 amps. If they are the same brand AND they support parallel operation you can do it - but from your question I have a feeling you are looking to do this on the cheap, and such parallelable inverters are not cheap (nor are they the best way to accomplish what you want to do.)

What would happen if two inverters feed the circuit breaker box?

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