Question Regarding Split Phase Stacking and Single Phase Charging

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OurayMountainMan
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My RE system: FlexPower-2 w/2 ea. VFXR3648A stacked for 240V split phase, 2 ea. FM80 Charge Controllers
2 x 4 ea EnergyCell 200RE (48V) w/Integrated Battery Rack, FNDC & RTS
4 x 3 ea Solarworld Sunmodule Plus SW300 mono panels
Honda EU6500is w/Atkinson GSCM
Mate3
Totally Off Grid
Location: Ouray County, CO USA

Question Regarding Split Phase Stacking and Single Phase Charging

Post by OurayMountainMan » Sat Sep 12, 2020 8:15 am

Hi! I am about to change my generator (Honda EU6500is) connection and have a question about whether I need to change my FlexPower 2 stacking configuration (currently configured for split phase) to match. Our off-grid cabin is wired like a conventional house - the breaker panel is wired for both L1 and L2 yet we have no 240V loads - the water pump is 120V (no 240V outlets are installed). When I installed the FP2, I maintained the factory configuration which provides L1 from the Master Inverter and L2 (180 degrees out of phase) from the Slave Inverter - split phase configuration - which I connected to the breaker panel appropriately. I also connected the Honda generator (configured for 240V output) such that L1 from the generator feeds the Master Inverter AC input and L2 feeds the Slave Inverter AC Input. All has worked well for several years. For some time, I have been concerned that this configuration is not ideal for the generator as the load is not balanced while bypassing the inverters or charging the batteries - the electrician wired the cabin so that most used daily loads (lights and outlets) are on L1 while L2 is hardly utilized. When charging the batteries, the Master Inverter is usually doing all of the charging while the Slave inverter is doing little to no charging.

To solve this perceived problem, I plan to reconfigure the generator for 120V (switch selectable on generator) and wire the single 120V output to both Master and Slave Inverter AC inputs. This configuration will insure that the generator output is balanced regardless of the the load (cabin load or charging load). When the inverters are passing through the AC from the generator, both L1 and L2 in the cabin will be in phase. Now comes my question - should I be concerned that the FP2 is configured for split phase with this arrangement? When the generator comes on, the AC will be in phase on both L1 and L2 and when the generator goes off, L1 and L2 will be 180 degrees out of phase. Will this cause problems with the inverters? Do I need to change the stacking configuration of the Inverters such that the Slave is always in phase with the Master output? I don't believe any of the cabin loads will care about the phasing, but I am concerned about damaging or degrading the inverters as a result of the phase shifts that will occur when the generator input is accepted.

Any thought or recommendations are greatly appreciated.

Thanks,

Keith

raysun
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Honda EU7000is gas fuel generator

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by raysun » Sat Sep 12, 2020 9:23 am

I have been looking into a similar configuration. However my load panel is 120V single phase, so the inverters will be parallel stacked for 120V out. In this arrangement, the secondary inverter will spend most of its life in low power mode (4W at idle), as we rarely draw more than 2kW from our system.

For our Honda EU7000is, I am taking the opposite approach. Currently running at 120V @ 30A out (the maximum), it will be reconfigured to 240V @ 22.5A, then L2 fed to an X-240 autotransformer, essentially inverting the L2 phase. Both in-phase legs will be fed to the AC IN bus effectively 120V @ 45A. This arrangement allows both inverters to be powered sufficiently such that both chargers can be utilized.

I didn't answer your question, and were you to apply an approach as above, the load panel would need to be rewired as 120V and $500 sunk into an X-240.

OurayMountainMan
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Posts: 16
Joined: Fri Oct 14, 2016 11:46 am
My RE system: FlexPower-2 w/2 ea. VFXR3648A stacked for 240V split phase, 2 ea. FM80 Charge Controllers
2 x 4 ea EnergyCell 200RE (48V) w/Integrated Battery Rack, FNDC & RTS
4 x 3 ea Solarworld Sunmodule Plus SW300 mono panels
Honda EU6500is w/Atkinson GSCM
Mate3
Totally Off Grid
Location: Ouray County, CO USA

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by OurayMountainMan » Sat Sep 12, 2020 10:29 am

Raysun,

Thanks for the reply! I am curious about the need for the balancing transformer in lieu of utilizing the generator in 120V mode. According to Honda, both generator inverter outputs are combined in this mode. While it does afford the maximum rated current from the generator, you can get almost the same by using both standard outlets on the Honda (45A/240V vs 40A/120V). As I am at altitude (10400 ft) I have to de-rate the generator output and cannot expect the 40A max via the combination of the two standard outlets. My situation is very similar to yours as the Slave Inverter is hardly ever utilized as the L2 set of circuits are rarely loaded. With the Master and Slave AC inputs in parallel with respect to the generator 120V output, either inverter is capable of receiving the full rated output of the generator. As usual, I will limit the AC input for each inverter to prevent generator overload during charging. Am I missing a benefit of utilizing the balancing transformer when operating the generator in 240V mode or is the simpler 120V mode sufficient?

Thanks,

Keith

raysun
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Posts: 2962
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
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Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by raysun » Sat Sep 12, 2020 10:50 am

Yes, I can use the 120V outlet, and one of the terminals of the 240V outlet to get 45A out of the EU7000is at 120V. However, Honda specifically recommends against that approach (I expect due to the risk that the 120/240V mode might inadvertently be selected at some point.) Also, since the AC IN bus scheme that Outback recommends for the FP2 has both inverters drawing from a common bus when parallel stacked I'm leery of connecting the two 120V outputs in parallel (against Honda's recommendations) as I don't want to be the one that finds out whether or not that leads to power board failures under some unforseen circumstance. The transformer is, in effect, $500 insurance against that.

In my long career as a designer of all manner of IT related systems, some at the data-center level, I was constantly reminded of an aphorism that proved all too true:
You can make a system fool-proof,
but you can't make a system damn-fool proof.

I'm giving myself a little room to inadvertantly wander into damn fool territory in some future maintenance or operation, without being signaled by the release of magic smoke.

OurayMountainMan
Forum Member
Posts: 16
Joined: Fri Oct 14, 2016 11:46 am
My RE system: FlexPower-2 w/2 ea. VFXR3648A stacked for 240V split phase, 2 ea. FM80 Charge Controllers
2 x 4 ea EnergyCell 200RE (48V) w/Integrated Battery Rack, FNDC & RTS
4 x 3 ea Solarworld Sunmodule Plus SW300 mono panels
Honda EU6500is w/Atkinson GSCM
Mate3
Totally Off Grid
Location: Ouray County, CO USA

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by OurayMountainMan » Wed Sep 16, 2020 11:00 am

Raysun,

I have been doing some research over the last few days and ran across this document https://www.dropbox.com/s/yqn0rsaxp76kn ... S.pdf?dl=0 This applies specifically to the EU6500is and I don't know if the EU7000 is the same. It indicates that in 120V mode, the Honda's internal inverters are paralleled as are the 120V outlets. It also turns out that each of the 120V outlets are individually over current protected by separate 20A circuit breakers. (info from the electrical schematics of the EU6500is). As such, I can draw a total of 40A on the 120V outlets without the need for a load balancing transformer. While you might get a little more current using the 240V mode, those gains will be at least partially offset by the transformer losses. Given that I have to derate the Honda's output for altitude (10400 ft.), I can't fully recognize the full 40A/120V output.

While I would prefer to use the twist-lock plugs to connect to the generator, the 20A/120V plugs offer a fair amount of retention. While the complexity of using two 120V plugs is not as clean as the single twist-lock, the elimination of the relatively costly balancing transformer is a big plus and simplifies the design.

I am still curious if I need to change the stacking of the inverters to eliminate any cut-over issues with phasing of the inverter outputs when switching from bypass to invert mode and back.

Your thoughts are always appreciated.

Keith

raysun
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Posts: 2962
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by raysun » Wed Sep 16, 2020 11:37 am

Hey Keith,

Yes, the Hondas both parallel their inverter module outputs in 120V mode. It would seem reasonable to assume 120V outlets could be paralleled into a single load. I can't shake an uneasy feeling there's something missing in this scenario however. I'd definitely give Honda tech support a shout about this.

The 20A three-pronged outlets could be used on the 6500, it appears. Not on the 7000 though, as they are GFI outlets and that is a definite NO feeding the AC IN on the inverter. (I have confirmed this by experiment, don't ask me how.)

Since the inverters' AC IN will reliably current limit, the twist-lock outlets could be used in relative safety, and with less chance of a plug pulling loose.

To provide (the seemingly unneeded) 240V split phase in bypass mode, the generator would need to be running 240V split phase. If the inverter stacking is currently 240V split phase, the generator AC out would need to match, AFIK. It would seem using the 240V AC out from the generator, and feeding each inverter from a separate leg, would be the way to go. This defeats the load-balancing requirement, however.

If the house load panel was reconfigured so L1 and L2 were paralleled as a single 120V single phase, (check with an electrician to see if this is kosher), then inverter stacking and generator output at 120V single phase would support it quite neatly, IMO. The inverter stack becomes more efficient, as one inverter will be sleeping unless called on for more power than the primary inverter is configured to deliver.

sodamo
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4 FM 80 charge controllers
Hub 10.3
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Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by sodamo » Thu Sep 17, 2020 2:09 am

Why not rewire your distribution to be more balanced?
Seems if your system is working, why mess with it.
I purposely had our electrician wire the house normally, yet I have no 240 anything in the house. The hottub and water pump come off the main panel as 240. Radians and generator run as 240, L1 / L2

When generator is charging the batteries does it really matter? I would think both legs charge according to inverter settings.
Am I missing something??
David
Please visit http://vacation.ninolehawaii.com

OurayMountainMan
Forum Member
Posts: 16
Joined: Fri Oct 14, 2016 11:46 am
My RE system: FlexPower-2 w/2 ea. VFXR3648A stacked for 240V split phase, 2 ea. FM80 Charge Controllers
2 x 4 ea EnergyCell 200RE (48V) w/Integrated Battery Rack, FNDC & RTS
4 x 3 ea Solarworld Sunmodule Plus SW300 mono panels
Honda EU6500is w/Atkinson GSCM
Mate3
Totally Off Grid
Location: Ouray County, CO USA

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by OurayMountainMan » Fri Sep 18, 2020 10:03 am

Hi David,

Thanks for the reply! I have tried to balance the load at the breaker panel by rearranging circuits between L1 and L2. Unfortunately, because the way the cabin is wired, most of our daily loads are associated with L1 and L2 is rarely used. In order to improve the cabin load balancing any further would require tearing out sheet rock and rewiring the cabin - not a step that I am willing to take. As our normal loads are relatively small (<1kw most of the time), most of the load imbalance that the generator sees is a result of the inverters charging the batteries. When the batteries require a significant charge (rarely) both inverter chargers are active and the generator load is relatively balanced. As the battery SOC goes up, the slave inverter charge current tapers off until the master inverter charger is supplying all of the charge current. This usually occurs during the absorb phase and continues for three to four hours. This is when I am most concerned about the imbalanced load on the generator. By supplying both inverters from the same 120V bus (running the generator in 120V mode) the concern of load balancing is eliminated. Since I have no loads that use both L1 and L2 (240V), there should not be a problem with supplying all of the loads in the cabin in this mode. As stated in my previous posts, I am concerned about the transition between bypass (generator in 120V mode supplying both L1 and L2) and invert (inverters outputting 120V split phase - L1 180 degrees out of phase with L2). The cabin loads won't care about the instantaneous phase shift, but I don't know if/how the inverters will be affected. I looked at changing the stacking of the FP2 so that the slave inverter is in phase with the master and augments the masters output, but the manual implies/states that the slave would only be turned on when the master is near max output capacity. If this is true, this won't work for my configuration as I may have a small load on L1 and then turn on something on L2 and expect the slave to wake up and supply that load. In other words, as I read the manual, the SEARCH mode of the slave inverter is no longer valid when the master and slave are parallel stacked. The slave state is controlled by the masters load demands. Of course, I could bridge L1 and L2 in the breaker box and convert the entire cabin to single phase 120.

Any thoughts?

Thanks,

Keith

sodamo
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Posts: 842
Joined: Mon Apr 03, 2006 1:55 am
My RE system: Totally off grid - Hamakua side, Big Island, Hi

36 Trina 280 & 16 Phono 250 in 48 volt array (fixed) 14080w
Radians GG8048/GS4048 w GSLCs
4 FM 80 charge controllers
Hub 10.3
FNDC w/3 shunts
Mate 3s
OpticsRE - MMKL - Ninole Hi
12 SimpliPhi 3.8
14Kw Kohler 14RESA Propane

Charging Only
2FX3048T
Hub
FNDC. - shared shunt feeds from Radian FNDC
Mate 3s
10Kw MEP 803a Military gen

Honda EU7000i

Davis VantagePro2 Wx Station
On line at: https://www.wunderground.com/dashboard/pws/KHININOL2
Location: Ninole, Hi

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by sodamo » Fri Sep 18, 2020 4:26 pm

Thanks Keith,
The question that keeps popping up in my head - is there a problem? You stated this configuration has worked fine for a number of years. What changed yo make you concerned?

As for load being balanced, in my own situation I really don’t know. Never witnessed the electrician doing any sort of testing, nor did he want/get a detailed list of what was being connected. Additionally, things have been added/moved over the years.

Back when I had my quad FXs, most often I ran on the main inverter, the others joining when needed, which wasn’t often and probably almost never when needing the generator. I wonder and maybe someone here has insight, but when generator runs, each inverter has own settings, each inverter splits the generator input to feed the house and charger. I’m thinking that my inverters pull from the generator were about equal, but am guessing what went to house load vs charger was split by each’s demand. So maybe the generator isn’t being run unbalanced? Maybe there is no problem needing correction?
David
Please visit http://vacation.ninolehawaii.com

OurayMountainMan
Forum Member
Posts: 16
Joined: Fri Oct 14, 2016 11:46 am
My RE system: FlexPower-2 w/2 ea. VFXR3648A stacked for 240V split phase, 2 ea. FM80 Charge Controllers
2 x 4 ea EnergyCell 200RE (48V) w/Integrated Battery Rack, FNDC & RTS
4 x 3 ea Solarworld Sunmodule Plus SW300 mono panels
Honda EU6500is w/Atkinson GSCM
Mate3
Totally Off Grid
Location: Ouray County, CO USA

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by OurayMountainMan » Fri Sep 18, 2020 6:06 pm

David,

Thanks for the reply/insights! With regards to what problem I am trying to solve - I am primarily concerned about the longevity of my Honda EU6500is. My generator currently has about 750-800 hours on it and Honda specifically cautions against running the generator with unbalanced loads. My secondary concern deals with overloading one leg of the generator output (240V mode) when we are charging the batteries and the water pump kicks on (it is controlled by a pressure switch). This results in the Honda dropping the load for 15-20 seconds and then the generator inverter resets and starts powering the loads (including charging the batteries). At one time I investigated moving the water pump from the master output (L1) to the slave output which would effectively put the water pump on the L2 generator inverter output. Since the L2 generator output is rarely loaded (the slave inverter charger is not contributing to the battery charging current), I though this would prevent the momentary overload condition on the L1 generator output. Unfortunately, this would require adding a separate circuit to the breaker panel to power the water pump and to date, I haven't done/tried this.

You may be right - I may be overthinking the problem - any additional thoughts based on the above explanation?

Thanks,

Keith

sodamo
Forum Czar
Posts: 842
Joined: Mon Apr 03, 2006 1:55 am
My RE system: Totally off grid - Hamakua side, Big Island, Hi

36 Trina 280 & 16 Phono 250 in 48 volt array (fixed) 14080w
Radians GG8048/GS4048 w GSLCs
4 FM 80 charge controllers
Hub 10.3
FNDC w/3 shunts
Mate 3s
OpticsRE - MMKL - Ninole Hi
12 SimpliPhi 3.8
14Kw Kohler 14RESA Propane

Charging Only
2FX3048T
Hub
FNDC. - shared shunt feeds from Radian FNDC
Mate 3s
10Kw MEP 803a Military gen

Honda EU7000i

Davis VantagePro2 Wx Station
On line at: https://www.wunderground.com/dashboard/pws/KHININOL2
Location: Ninole, Hi

Re: Question Regarding Split Phase Stacking and Single Phase Charging

Post by sodamo » Fri Sep 18, 2020 8:22 pm

Have you checked your inverter settings that you aren’t exceeding the max the generator can deliver? i know when I had to use my Honda 7000 I had to turn down the settings.
i could be wrong, kinda hoping the more knowledgeable chime in, but I don’t think in charge mode you are unbalanced, but you may well be asking more than available. 2x 3600w inverters > 6500w generator, once the water pump kicks in.
A about soft start for the water pump, maybe a less power demanding pump?
David
Please visit http://vacation.ninolehawaii.com

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