# Battery Inverter + Inverter Generator for surge power?



## Browse Deweb (Jan 16, 2021)

I'm curious if it is possible to have a setup that could marry a battery inverter system with a standard inverter generator in order to address temporary surge conditions that would otherwise prevent a standard inverter generator from meeting a large inrush demand like an AC condenser unit? For example, I have a Honda EU7000is generator that is setup to run on natural gas. It can run the entire house with the exception of the main HVAC unit. It would be a waste of fuel and money to get a second EU7000is just to overcome the AC inrush demand.

If I had a battery inverter setup that could assist the Honda for the inrush spikes, then go idle and recharge while the Honda is running, that would solve the issue. I'd rather not have the battery system be the main power provider since that would unnecessarily cycle the batteries and shorten their life. An inverter with a high surge ability would be required.

Seems like this would be a no brainer and possible, but I'm not sure. Any thoughts?


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## FlyFisher (Jun 30, 2018)

Grid tie inverter used in alternative energy systems. 

Grid tie = can synch with existing AC power. 

If you don't have grid-tie you can not synchronize the AC waves.


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## iowagold (Jan 22, 2020)

large ups is what i use here.
get the expensive version.

and yes there are special inverters that will sync to almost any power source.
but they are higher priced than the cheep units...

if you are not selling power back
then a grid tie would work if the gen is the secondary power
and then make the battery charger as the sell point.

charge the battery bank with the left over power from the solar.

there is a way to impulse charge from a electric start gen set...
you can set the threshold for charge call in the controller for the inverter charger setup.

easy to do if you are into all the programming...
not for the novice.


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## FlyFisher (Jun 30, 2018)

iowagold said:


> large ups is what i use here.
> get the expensive version.
> 
> and yes there are special inverters that will sync to almost any power source.
> ...


There is a video, I can not locate it at the moment, from EVTV (Jack Rickard - he passed away last fall, I believe). It showcases a Sigineer inverter (12kw or 15kw, it was before they came out with their 18kw) running in conjunction with grid-tie inverters.

*EDIT:*
I think this is the video. They have the grid tie inverters operating in conjunction with the large inverter. Rather long video, but I found it very informative. 





The shop that EVTV uses has solar power on the roof. They use micro inverters at the panels then feed several large grid-tie inverters that are what power the shop.

The point of the video I recall was that Jack was proving a critic wrong. The Signeer inverters have the ability to be "chargers" also. They can be set up in conjunction with batteries and utility power, or generator power. As what ever is deemed as the "utility power" comes and goes the inverter can switch from drawing from the batteries to provide AC power when the "utility power" is off; or charging batteries when "utility power" is on.

What the critic was trying to prove Jack wrong over was that you could not use "grid tie" inverters in place of the "utility power" so as to charge the battery bank.

Of course, Jack proved the critic wrong and did a fantastic demonstration of the functionality of this set up - using the Signeer inverter as the initial power, drawing from a Tesla car battery as his "battery bank". Then he turned on the grid tie inverters from the solar set up. The grid tie inverters were turned on one at a time. The reason for this was as each grid tie inverter coming on line would add more power back in to the "grid" (local - only between the large inverter and the grid-tie inverters - no commercial power or generator power). You could watch the power going back in to charge go up on the large inverter with each added grid tie unit powering up (and the feed from the solar panels coming in - each grid tie inverter had its own feed from an array of panels).

Going back to the original question asked herein -



Browse Deweb said:


> I'm curious if it is possible to have a setup that could marry a battery inverter system with a standard inverter generator in order to address temporary surge conditions that would otherwise prevent a standard inverter generator from meeting a large inrush demand like an AC condenser unit?


Yes you can.

However, I agree with Paul - it would not be a cheap system.

In looking over the idea again - something that catches my attention is the grid-tie inverters I recall that were used in the referenced video were fed from solar - the arrays fed the grid-tie inverters AC from the micro inverters. In the generator example here - you would have to have a DC source powering your "grid tie inverter".

In being very open, just thinking out loud here, I am not sure if there are commonly available inverters that allow powering from a battery bank that also allow for "grid tie" - the idea of synchronizing AC waves to meet an existing AC power source (whether it is grid power, generator power, inverter power, what have you - it doesn't matter - and that was the point of the video I am thinking of - to prove that).

When you look at the idea of "grid tie" as it is commonly used in the sense of home solar systems - there is no battery bank. The solar system feeds your home power - which is commercial power. Your existing power source is the utility grid. If you produce more solar power than you consume then some power is "fed back to the grid". It doesn't "charge a battery".

If you have an off-grid solar install that does run on batteries there is no need for "grid tie" because there isn't commercial power anyway.

I would be curious if such an inverter exists, however - one that allows for both "grid tie" feeding of a commercial power grid (or generator, or...) at the same time offering stand-alone operation off a battery bank.

The idea, then, would be to charge the battery (or battery bank) off the generator and power the grid tie inverter off the battery, sync the grid tie inverter to the generator power, and see what happens.

The question is - how do you tell the power to draw primarily from the generator until start up load hits? You can't support a heavy wattage draw off the "grid tie inverter running off the battery" by the charger running off the generator. For a short boost of start up power I could see that working - but how do you regulate it?

Interesting question.

2 last points:
1. I understand the paralleling of the Honda inverter gens (can't parallel rotaries) requires one to be on and running, then the 2nd one you power up becomes a "slave". It meters the power from the "master" (or 1st unit) to synchronize the power. Once the power is synchronized then the 2 gens' inverters run in tandem.

There was a report on the forums a while back about 2 units swapping loads. One would seem to take all the load while the other was at low RPM's. Then they would flip every 20-30 seconds or so. That isn't normal for there to be such a large difference in the loads on the units, however I could see where there would be some sense of wattage so one unit leads a bit over the other.

2. The "grid tie" inverter would have to be large enough to run 240v split phase, assuming that the AC that is in question is central AC that runs on 240v. The large Sigineer units are 240v units, however I don't see them described as themselves being "grid tie", only that they can be used to simulate grid power with OTHER grid-tie inverters (the reference, again, to the video and the purpose of that video).


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## iowagold (Jan 22, 2020)

the big issue with grid tie is if you are using the national grid..
you will have contracts and rules...
and in some areas of the country you cannot use the system as a stand alone system during an grid failure..

lol
ask any one in florida about this!
they found out the hard way after one of the BIG hurricane events that their super expensive grid tie solar system left them with no power as it is designed as the grid sets the cadence for the system....
and BIG fines if you have a generator on your property!
no kidding...

and same if you do grid tie in some other states...
BIG rules for how to use the grid tie system...

for me the best system would be to be able to choose your power provider..
grid or
other alt power. wind, solar. hydro. or fuel generator etc.
and be able to sell back to the grid on your terms when you want to...

the farm systems here in Iowa they see saw the power 
BIG production and sell power during the day. 
and no production at night and buy power from the grid when the power is cheaper
due to the time of use is not needed for commercial industrial users.
they have a TOU meter system here... (time of use)
it does cost, but if you are on a timer with electric items and not at home during the day.
you can save 15-30 bucks a month on the electric.
pretty cool!


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## pipe (Jun 27, 2021)

iowagold said:


> ask any one in florida about this!
> they found out the hard way after one of the BIG hurricane events that their super expensive grid tie solar system left them with no power as it is designed as the grid sets the cadence for the system....
> and BIG fines if you have a generator on your property!


Little more details or an online article to read on this ?


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## drmerdp (Apr 10, 2018)

I’ve seen a guy on YouTube parallel a regular 12v inverter with an inverter generator. So in theory it seems possible.


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## iowagold (Jan 22, 2020)

pipe said:


> Little more details or an online article to read on this ?


just google it @pipe it should show up in your search.

the copies of contracts I have here, have folks real personal data on them.
not for web publication.

in your area contact the utility company ask about grid tie and have them send over the paper work.
make sure to real all of the fine print.

most utilities are going the way florida did on the contracts in the name of crew security.
they claim a chance of power out of the homes generation system.
so they have an interlock that will not let the slave set inverter produce power if the master grid power is not live.
and yes there is tags on all of those boxes so you cannot bypass or change anything with out the risk of the diversion charges and BIG fines.


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## FlyFisher (Jun 30, 2018)

iowagold said:


> the big issue with grid tie is if you are using the national grid..
> you will have contracts and rules...
> and in some areas of the country you cannot use the system as a stand alone system during an grid failure..


Paul I think you missed the boat with all of the following discussion regarding the rules and regs.

You may be correct for a "grid tie system" *WHILE CONNECTED TO THE GRID. *

However, the idea of a "grid tie" inverter/system in the thread was for a *NON-GRID CONNECTED SYSTEM *- IE - stand-alone, and not feeding power back to the grid.

Your reference of the regs requiring that the "grid tie" system use the grid to set cadence so that if the grid is down it doesn't back-feed is valid, however that has no bearing on a generator setting cadence in a grid-down situation.

*IF* the owner of such a system would want to set up a solar system that *IS grid-tied (back feeding the power grid) THEN* what you are suggesting may come in to play. But we never were discussing a solar system grid-tied. We were discussing using a grid-tie inverter to synch with the AC power from a generator so as to get more peak wattage (for the start up load of an AC compressor), and not synching with the power grid.

Interesting to note, also - the power system in the video I posted earlier is off-grid. They are using the inverter to set cadence of the grid-tie inverters (again, that is what someone stated couldn't be done so the demonstration was set up to prove it would work). That was the point I was trying to get across with the generator + inverter scenario - have the generator set cadence and synch a grid-tie inverter to it to provide the additional power. Though, I do question how you would regulate the loading on what device - especially with the fast hitting start up load of an AC compressor.

I'm sure I am in the same boat as a lot of people on this one - the strictness of the regs you describe seem wacked. Why would you fine someone for having backup power when the grid goes down? How else are they going to keep their refrigerators going, fans, etc if the solar isn't going to do it?Then again, given the current political climate that doesn't surprise me. Hopefully that gets straightened out with time. Even more reason to go off-grid.


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## FlyFisher (Jun 30, 2018)

drmerdp said:


> I’ve seen a guy on YouTube parallel a regular 12v inverter with an inverter generator. So in theory it seems possible.


Thinking...

The EU7000 is a 240v generator.

Most inverter generators are 120v.

Does anyone know if the 240v from the EU7000 is generated at 240v in-phase at the inverter then split to 2x 120v legs with a center tapped transformer? Or is it 2x 120v transistor decks 180deg out of phase against neutral?



FlyFisher said:


> 2 last points:
> 1. I understand the paralleling of the Honda inverter gens (can't parallel rotaries) requires one to be on and running, then the 2nd one you power up becomes a "slave". It meters the power from the "master" (or 1st unit) to synchronize the power. Once the power is synchronized then the 2 gens' inverters run in tandem.


Taking the above in to consideration - swapping 1 gen for an inverter as @drmerdp suggests would mean the inverter would be the "standard" waveform the generator is synchronizing to when paralleling, or that the inverter is the "master" and the generator is the "slave".

If the inverter is 120v and the generator is 240v I am not sure that would work. If the generator had 2x transistor decks 180deg out of phase then, perhaps, a 120v inverter could be used to synch to one of the 120v decks. That would boost the wattage on that leg alone, not across both for 240v though. If there is only 1x 240v transistor deck then I don't see how it would be possible to synchronize to a 120v source???

Interesting ideas/questions/theories here. If I had an EU7000 to mess around with I would be curious to try it.

On edit:

Interesting discussion from another thread that directly relates:


StormReady said:


> Do all generators that produce 240V have two separate power producing circuits, each feeding a bus bar? I ask as my Honda has two power producing circuits and was surprised to read that.





iowagold said:


> what model?
> 
> if it is a eu7000is there is also a switch on the front that will make the gen set a 120 vac only gen set.
> kinda cool if you only run 120 vac items.





StormReady said:


> Yes, it's an EU7000is. But when running 240V, the two power producing circuits are separate and produce 2750 watts each, no more for running.


If there are 2 separate "power circuits" that would mean there are 2x 120v transistor decks as I was trying to get at - either that or a center tapped transformer. 

So as far as the question of getting an inverter to be the initial power AC signal the gen would synch to - it may be possible for the EU7000 to synch to a 120v inverter on one leg, but that wouldn't be able to offer a power boost across 240v. It would, however, lower the loading on the one leg (if it is able to do this at all). If that leg is heavy on loading, and not balanced very well with the other leg, then, perhaps, the heavily loaded leg having the benefit of the inverter power on top of the gen power would allow more head room for a 240v load to hit both legs - as the inverter would give more head room on what was the heavily loaded leg.


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## Robh (Aug 19, 2019)

How big is your A/C unit? All this sounds more complicated than simply buying one of these.
EasyStart™ 368 Soft Starter

*Edit:* I just saw your previous thread where you tried one and your A/C unit was pulling 76A?! I'm not sure anything can tackle that easily.


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## Browse Deweb (Jan 16, 2021)

Robh said:


> How big is your A/C unit? All this sounds more complicated than simply buying one of these.
> EasyStart™ 368 Soft Starter
> 
> *Edit:* I just saw your previous thread where you tried one and your A/C unit was pulling 76A?! I'm not sure anything can tackle that easily.


Yeah, I have the EasyStart and due to my TXV, the inrush is still pretty high. I have seen videos of an EU7000is mated with other Honda inverter generators...both 120V and 240V and it appears to work fine. This is what made me think that it could also theoretically work paralleled with a battery inverter setup. Some off grid inverter setups can work in conjunction with a generator to charge the batteries when they go below a certain threshold level. What I haven't seen is an inverter controller that can parallel a battery inverter with a second inverter like a generator, where the battery inverter acts as a slave to the generator. Seems like it could solve a lot of problems with under-powered portable gen setups.


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## iowagold (Jan 22, 2020)

Browse Deweb said:


> Yeah, I have the EasyStart and due to my TXV, the inrush is still pretty high. I have seen videos of an EU7000is mated with other Honda inverter generators...both 120V and 240V and it appears to work fine. This is what made me think that it could also theoretically work paralleled with a battery inverter setup. Some off grid inverter setups can work in conjunction with a generator to charge the batteries when they go below a certain threshold level. What I haven't seen is an inverter controller that can parallel a battery inverter with a second inverter like a generator, where the battery inverter acts as a slave to the generator. Seems like it could solve a lot of problems with under-powered portable gen setups.


hey Browse Deweb can they mod those txv ac units to free wheel the start up?
some of the inverter air con units feather the valve on restart...
ramp up on the pressure orifice restriction.


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## iowagold (Jan 22, 2020)

FlyFisher said:


> Thinking...
> 
> The EU7000 is a 240v generator.
> 
> ...


hey fly spend the bucks and go to a honda gen repair school.
best money you will ever spend for sure.
boot camp style school.

and at the least go buy the $50.00 usd service manual!
most of the questions you are asking are in the service manual.
not going off... just stating take the time to study the 7000i gen...
it might convert you to honda red!

it is a brilliant setup at the least...
basic a dual inverter setup that can be switched to internal parallel for a single 120 vac.
or ran in the 240 mode...
pretty slick design at the least.
the cool part is you can run 2 of the 7000i gens in parallel for the 14kw start and 11kw run..
nice for when it is super hot out to run the air con units...
then in winter switch back to one gen set...
or get a little 2200i gen set for winter if you do not have BIG pumps for water.


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## drmerdp (Apr 10, 2018)

FlyFisher said:


> Thinking...
> 
> The EU7000 is a 240v generator.
> 
> ...


The inverter on the eu7000 consists of a master and slave, L1 and L2. A 120v inverter can sync with one of the Honda’s 120v legs. I was able to start and run my central air effectively by syncing an eu2000 with my eu7000. Possible Long term heat and degradation due to neutral cross currents lead me to almost Buying a predator 9500 inverter and eventually actually buying another eu7000.


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## Browse Deweb (Jan 16, 2021)

Hmmm....after thinking about this for a bit and reviewing one of those new inverter battery kickstarter offerings, I think one way to address the surge requirement would be to buy two of these which can supply up to 14.4kw of surge power at 240V when connected in parallel:









Buy EcoFlow DELTA Pro Portable Power Station - EcoFlow US


Official EcoFlow DELTA Pro: ✓ Capacity：3600Wh ✓ Battery Cell Type: ‎Lithium Ion (LFP). Click to learn more!




ecoflow.com





Review:





The Honda could keep the inverter batteries charged while the Ecoflow units are powering the house via the interlock. These battery units aren't cheap, but it looks like they could do it. In my case, my house usually only draws between 1-3 kW when the main HVAC unit isn't running, so I'm guessing the generator running on natural gas would be able to keep the batteries charged.

The only down side to this is that purchasing two of the Ecoflow units is about what a second EU7000is would cost, so ultimately it would be a wash.


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## iowagold (Jan 22, 2020)

Browse Deweb said:


> Hmmm....after thinking about this for a bit and reviewing one of those new inverter battery kickstarter offerings, I think one way to address the surge requirement would be to buy two of these which can supply up to 14.4kw of surge power at 240V when connected in parallel:
> 
> 
> 
> ...


so they are about 2k each on the battery setup?


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## Browse Deweb (Jan 16, 2021)

iowagold said:


> so they are about 2k each on the battery setup?


The kickstarter campagn is currently listing them at about $2600 each right now. That will go up to $3600 once the campaign ends and they are sold at retail.

I contacted Ecoflow about running two in parallel at 240V and the rep indicated that the surge power doesn't double. A single unit can provide 3.6kw continuous and 7.2kw surge at 120V. You would think that two units connected together at 240V would provide double the surge power. I sent another e-mail asking to clarify why the surge limitation at 240V.


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## drmerdp (Apr 10, 2018)

Pricy but looks awesome. 

Makes sense, 2 units at 120v is double the surge rating, 2 120v units at 240 is the rating of one unit, just at 240v.


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## Browse Deweb (Jan 16, 2021)

drmerdp said:


> Pricy but looks awesome.
> 
> Makes sense, 2 units at 120v is double the surge rating, 2 120v units at 240 is the rating of one unit, just at 240v.


If this were amperage, then that makes sense since the same surge current at double the voltage results in double the power. What they are indicating in their response is that there is double the continuous power but effectively zero surge power when in parallel. Does not compute...


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## iowagold (Jan 22, 2020)

Browse Deweb said:


> The kickstarter campagn is currently listing them at about $2600 each right now. That will go up to $3600 once the campaign ends and they are sold at retail.
> 
> I contacted Ecoflow about running two in parallel at 240V and the rep indicated that the surge power doesn't double. A single unit can provide 3.6kw continuous and 7.2kw surge at 120V. You would think that two units connected together at 240V would provide double the surge power. I sent another e-mail asking to clarify why the surge limitation at 240V.


should only double at 120 that ohms law and current voltage thing
but you are limited by the connections...
that is one of the reasons we do a mod on the eu7000is gen for a 50 amp twistlock..
yea over kill... but we have yet to have a 50 amp twistlock fail with the mod.


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## drmerdp (Apr 10, 2018)

I’m assuming each unit is treated like 1 120v leg. Offset the legs 180 degrees and you have 240v of amplitude from the sine wave but it didn’t increase how much surge capability each unit is capable of supporting. 

Its Maybe a bad analogy, but 2 12v 500cca batteries in parallel is 1000cca. 2 12v batteries in series is 500cca at 24v.


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## iowagold (Jan 22, 2020)

and that ac vs dc as well is in there too.


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## Browse Deweb (Jan 16, 2021)

drmerdp said:


> I’m assuming each unit is treated like 1 120v leg. Offset the legs 180 degrees and you have 240v of amplitude from the sine wave but it didn’t increase how much surge capability each unit is capable of supporting.
> 
> Its Maybe a bad analogy, but 2 12v 500cca batteries in parallel is 1000cca. 2 12v batteries in series is 500cca at 24v.


The phase shouldn't matter. Split phase power provides double the VA as single phase provided that the device consuming the power can utilize both phases.

If you have an inverter providing 3600W at 120V, with surge capability of twice that, then if you have two inverters producing 7200W at 240V split phase, they should be capable of providing 14400W surge, provided that the connectors and wiring can handle that surge. In the case of an outdoor condenser, that surge is typically a fraction of a second.


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## pipe (Jun 27, 2021)

iowagold said:


> ..and at the least go buy the $50.00 usd service manual!


EU7000is Service Manual


https://www.precisionusa.com/pdf/Honda_Equip/Honda%20EU7000iS%20Generator%20Shop%20Manual%20(Ser%20No%20EEJD-1000001-9999999).pdf


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## Browse Deweb (Jan 16, 2021)

pipe said:


> EU7000is Service Manual
> 
> 
> https://www.precisionusa.com/pdf/Honda_Equip/Honda%20EU7000iS%20Generator%20Shop%20Manual%20(Ser%20No%20EEJD-1000001-9999999).pdf


Thanks for that link. Nice to have it downloaded in case it's needed in the future.


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## agksimon (Jan 25, 2021)

Browse Deweb said:


> I'm curious if it is possible to have a setup that could marry a battery inverter system with a standard inverter generator in order to address temporary surge conditions that would otherwise prevent a standard inverter generator from meeting a large inrush demand like an AC condenser unit?


How about a soft start unit on the A/C?


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## Browse Deweb (Jan 16, 2021)

agksimon said:


> How about a soft start unit on the A/C?


Yep...have that already but it didn't reduce the inrush enough due to the system having a TXV instead of a piston type valve. The company confirmed that their product isn't as effective with a TXV.


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