Inverters in parallel?

[Wdeertz]

I’m contemplating adding 2 Victron 2000w 120v inverters in parallel to replace my magnum 4000w split phase inverter. The magnum inverter is still working so would like to keep as a backup. My preferred method is to wire the inverters in parallel and control which inverter feeds the inverter panel by off/on switches. This obviously isn’t idiot proof as if some turns on both switches both inverters will be feeding the panel. I could put in an automatic transfer switch but this prevents me from manually selecting which inverter to use. Would it be permissible to have the 2 inverters controlled by manual on/off switches or would an automatic transfer switch be mandated?

 

[SteveK]

If you have not yet researched, please check if those inverters can both be parallel and on at the same time feeding the same loads.
I have two identical inverters and they cannot both feed the same loads, they also cannot operate out of sync to provide 240 power. I came by accidentally to have these two identical ones so must ask why you are not getting one 4000W inverter and save a lot of switching issues.

 

[Wdeertz]

Steve, if Victron made a single unit that provide d 120/240v split phase I’d go with that but as far as I know they don’t make such a model. From reading the Victron multiplus manual it seems they can be parallel to provide split phase 120/240v. Am I missing something?

 

[NoRain]

They can. I’m running a pair of MP 3000’s right now in split phase mode. They can also run in parallel mode but there are some quirky restrictions.

 

[DDW]

There are breaker pairs with a mechanical interlock made for this purpose, allowing you to turn on only one at a time. That would do what you want. Alternatively there are rotary select switches that allow only one at once to be connected to the output. Both of these are made to switch gen vs shore power, but would serve equally as well for your purpose.

I think if you have two non-cooperating inverters feeding the same panel, best case breakers will blow, most likely case is smoke will be let out. So an interlock is a very good idea.

 

[SteveK]

OK, I mistook reason for parallel and switching.

Before you buy two new ones, make sure they will work 120/240.
Now I still do not understand reason for sswitchesfir on/off as they can be left on all the time, ready to run 240, but mostly run two legs of 120 plus any 240 needs.

More info for your plans would help.

 

[Wdeertz]

There are breaker pairs with a mechanical interlock made for this purpose, allowing you to turn on only one at a time. That would do what you want. Alternatively there are rotary select switches that allow only one at once to be connected to the output. Both of these are made to switch gen vs shore power, but would serve equally as well for your purpose.

I think if you have two non-cooperating inverters feeding the same panel, best case breakers will blow, most likely case is smoke will be let out. So an interlock is a very good idea.

Thanks for the input, yes a manual rotary switch seems like the way to go.

 

[Wdeertz]

OK, I mistook reason for parallel and switching.

Before you buy two new ones, make sure they will work 120/240.
Now I still do not understand reason for sswitchesfir on/off as they can be left on all the time, ready to run 240, but mostly run two legs of 120 plus any 240 needs.

More info for your plans would help.

Steve, the newly installed Victron units will be left on 24/7. The old magnum will be kept as a backup. The purpose of the switch is so both inverters (new Victron and old magnum) don’t power the panel as the same time.

 

[rslifkin]

The Victron inverters can be configured for parallel operation, so I don't see any reason why your setup wouldn't work.

 

[ksanders]

of course you can run your Victron inverters in split phase mode or in parallel mode

that's not difficult to do at all.

 

[DDW]

If it were my boat, that Magnum would be on the way to the recyclers in a heartbeat. That would raise your waterline by about an inch too . If you have two Victrons you already have a backup of sorts, at least for your 120V loads.

 

[l00smarble]

Definitely would require a 3 pole transfer switch on both inverter system outputs.
But what are you trying to accomplish here? Is the only goal to add redundancy? Is inverting really that mission critical? Maybe? Supporting medical equipment or etc it could make sense.

If not that critical could just carry a spare inverter for backup.

 

[NoRain]

….seems they can be parallel to provide split phase 120/240v.

And just to clarify terminology, “parallel” and “split phase” are two different things in this context.

 

[Wdeertz]

And just to clarify terminology, “parallel” and “split phase” are two different things in this context.

Yes I meant stacked to provide split phase.

 

[NoRain]

Don’t mean to be too anal about this (terminology especially) but….stacked really means to use two inverters as a common system. From there, you configure them to operate in split-phase mode, or parallel mode. Pros and cons to both.

I chose split-phase because I have 240V appliances. If you didn’t and just wanted more capacity, you could configure them to operate in parallel mode. But as I said above there are some very finicky aspects.

You might want have a read of this, says it better than I can Parallel, split- and three-phase VE.Bus systems [Victron Energy].

 

[SteveK]

@NoRain my thoughts as well, thanks for putting in print.

 

[Wdeertz]

Don’t mean to be too anal about this (terminology especially) but….stacked really means to use two inverters as a common system. From there, you configure them to operate in split-phase mode, or parallel mode. Pros and cons to both.

I chose split-phase because I have 240V appliances. If you didn’t and just wanted more capacity, you could configure them to operate in parallel mode. But as I said above there are some very finicky aspects.

You might want have a read of this, says it better than I can Parallel, split- and three-phase VE.Bus systems [Victron Energy].

Thanks, a lot more complicated than a single unit with split phase. In summary my current setup only includes 120v loads so there may be a simpler solution. Not really sure why the OEM inverter was split phase when all inverter loads are 120v. I was contemplating wiring in one of my 230v AC units but this might be more effort than it’s worth.

I’m assuming my Magnum 24v/4000w split phase inverter outputs up to 2000w per leg (or is it able to output say 3000w on one leg and say 1000w on the other leg?). Would I be better off to parallel 2 multiplus 24v/3000w inverters so 3000w is available on L1 and L2 (wouldn’t be 240v split phase but with no 240v inverter loads wouldn’t really matter). Or would I be better off with 2 Multiplus II-2x120v 3000w?

I really wish Victron made a single unit split phase inverter.

 

[NoRain]

Many requests for Victron split phase, apparently coming some day.

But if you don’t have 240V loads, why do you want split phase?

 

[Wdeertz]

Many requests for Victron split phase, apparently coming some day.

But if you don’t have 240V loads, why do you want split phase?

I have 240v onboard loads but none are currently connected through the inverter panel. I was contemplating wiring one of my 230/240v AC units through the inverter but may be reassessing that.

 

[rslifkin]

There are a few options. The Victron 2x120 inverters might do what you need. Or you can stack inverters for split phase. Or use a 240V inverter and an autotransformer for split phase.

 

[NoRain]

I have 240v onboard loads but none are currently connected through the inverter panel. I was contemplating wiring one of my 230/240v AC units through the inverter but may be reassessing that.

K, well you might want to come to a decision on that before you proceed. For starters, calculate the amp-hour burn of running an AC on batteries. Have you got the bank to support that for any meaningful amount of time? And the recharge capability to refill your house bank? AC in particular can rip through amp-hours at a ferocious pace.

 

[l00smarble]

Would I be better off to parallel 2 multiplus 24v/3000w inverters so 3000w is available on L1 and L2 (wouldn’t be 240v split phase but with no 240v inverter loads wouldn’t really matter). Or would I be better off with 2 Multiplus II-2x120v 3000w?

I really wish Victron made a single unit split phase inverter.

Sir...I see customers make this mistake all the time. They spec equipment as step one then realize later that it wasn't the best choice for their needs.

You keep discussing what inverters you should buy but you have not given the team here trying to help you any insight into what you are trying to accomlish. It would also be helpful to know more about your exisitng AC distribution as it does not seem to make a lot of sense. You have a split phase inverter but it is wired to only energize 120v loads? But this meets your needs? or no?

It sounded from the beginning like you wanted to add a 2nd, redundant inverter solution to be able to energize the same loads. If so, why do you keep discussing using two Victron inverters? If it is only going to be connected to energize 120v output just get the appropriate size 120v unit, right?

To me this seems like it is time to take a step back and look at the big picture before making buying decisions. What is the functional end result that you want? How do you want to make your boating more enjoyable?

 

[Wdeertz]

ok attached is my AC schematic. OEM inverter was a magnum 24v/4000w inverters/charger as split phase (2000w to each leg). All inverters loads are currently 120v. Current setup pretty much meets all my needs.

All AC units are 240v and hence why I’d like to keep the optionality to wire a single unit to the inverter. Battery bank 920Ahr @ 24v (about 23k watt hours). 305A @ 24v current charging capacity while on generator/shore, 270A while underway. So short answer is yes I have enough battery capacity to run an AC off an inverter and capacity to recharge the batteries. I’d probably run the pilothouse AC off the inverter while underway which the 270A of alternator capacity would keep the batteries charge and avoid having to run the generator.

I’m leaning towards 2x 3000w Victron setup in split phase mode. This would allow me to send 2000w to each leg via a 4 pole rotary switch and have an extra 1000w on both legs to run the pilothouse AC (with soft start to keep inrush amps down). Hopefully this additional info will help in guiding me.

I should also mention that I added a small 6k btu self contained 120v AC to my forward cabin that I run overnight on inverter and I’d estimate it uses no more than 8k watt hours for a 8 hours overnight.

 

[NoRain]

Not a complete reply (I’m on the go) but 2 x MultiPlus 3000 inverters give you 140A total charging @ 24V (your Magnum spec sheet shows 105A charging @ 24V, not 305). That’s on shorepower or generator. That’s 6 hours of genset running to refill your house bank from 10%.

 

[Wdeertz]

Not a complete reply (I’m on the go) but 2 x MultiPlus 3000 inverters give you 140A total charging @ 24V (your Magnum spec sheet shows 105A charging @ 24V, not 305). That’s on shorepower or generator. That’s 6 hours of genset running to refill your house bank from 10%.

Have added 2 Victron skylla 100 amp @ 24v chargers. Typical day usage with no AC is about 12-13k watt hours so about 2 hours generator run time. Also 600 watts of solar but that gets lost in the rounding. Of course on moving days the alternators easily handle my energy needs.

 

[luna]

I’d probably run the pilothouse AC off the inverter while underway which the 270A of alternator capacity would keep the batteries charge and avoid having to run the generator.

I’m leaning towards 2x 3000w Victron setup in split phase mode. This would allow me to send 2000w to each leg via a 4 pole rotary switch and have an extra 1000w on both legs to run the pilothouse AC (with soft start to keep inrush amps down). Hopefully this additional info will help in guiding me.

I should also mention that I added a small 6k btu self contained 120v AC to my forward cabin that I run overnight on inverter and I’d estimate it uses no more than 8k watt hours for a 8 hours overnight.

You sound like you have a good understanding of your needs and have this well in hand. As usual, whatever is chosen will not always be perfect.

I thought I would mention in the unlikely event that you have not yet realized that Victron (they are not alone on this) rates their inverters in Volt Amps which is a different unit than Watts.

Victron, for better or for worse, seems to use a power factor of 0.8 when converting Volt Amps to Watts. To them 3000 VA x 0.8 = 2,400 Watts.

I have no Idea what you loads are, but if you are intending to send 4kW to other users and if their power factor is also 0.8, you will be left with only about to 800 watts to run the Pilothouse AC. Is that enough?

No one has ever said the inverter that supplies the hotel loads is too big.

 

[DDW]

My understanding was that Victron rates in VA which is the same as watts (for resistive loads), but footnotes that at maximum output it can only support a crest factor of 3:1. All inverters have some caveat at higher than sinusoidal crest factors, it's just that Victron seems to be one of few acknowledging this reality. Is my understanding incorrect?

 

[Serene]

Volt Amps is the correct unit for items that generate or supply Alternating Current, Watts is used for consumers of power. Victron is absolutely correct in their use of VA. And Power Factor is not always 0.8, it is dependent on the type of loads. i.e. Resistive vs Conductive vs Capacitive.

This topic is quite complicated with alternating current as the voltage and current are not always in phase, combined with the effect of different types of loads needing to be supplied by a power generation device.

VA is not equal to W in Alternating Current and there is not a default multiplication factor to convert from one to the other. The use of 0.8 is an approximation only.

 

[l00smarble]

Ok now we are getting somewhere. THank you for the schematic and the additional details. This makes it much easier to visualize what you are working with.

The original post implied that the primary purpose of the project was to add full redendancy of inverter functionality but now I am hearing a different goal. It seems the stated goal now is to be able to run one or more air conditioners including one that is 240v. This changed things substantially

It sounds like you installed 4x Epoch 230ah batteries so you have a lot to work with and this opens up much more possibilities for inverting for convenience and energy management. Since you installed these batteries and you invested in two large 24/100 chargers It seems you are willing to invest in a "big" system.

If it were my boat (and to be fair my Selene 47 has a very similar electrical system) the following is what I would do. In fact is pretty much the project I am doing on my own boat this winter. I also am using 4x Epoch 24v/230ah Elite series for 920ah@24v.

Rather than spend the ~$1500 each on Skylla 24/100 chargers this same money could have been used to get two Multiplus II 24/5000-120v units! Each Multiplus II 24/5000 has a 120a charger so in effect it would be larger charger and a "free" built in inverter.

I would take split phase 120/240v off the main transfer switch at top of diagram with 6/3-8/1AWG cable to the pair of Multiplus 24/5000-120 and then with the split phase output off the inverters feed THE ENTIRE AC PANEL. This gives you the user the ability to invert anything you want with minimal common sense to load manage but you have flexibility to make decisions that make your boating life better, not based on what is or isn't wired up.

The transfer switches in the MPII24/5000 are rated for 95a so they can easily handle the entire AC load of the boat when you are on shore or genset. Also if you route everything through the Multipluses then all the data for power management shows up on the Cerbo GX for visibility and decision making. If you have Victron MPPTs and a CAN-BUS alternator regulator you now have a completely integrated power/energy management system with all data visible.

To put this in perspective the 50a shore cord is 12kw. You have a generator rated at 12kw. If you put two MPII 24/5000 that gives you 10kw (no more that 5kw per 120v leg.) You can put soft starts on whichever or all air conditioners you want and you can run the boat on inverters pretty much as a full and silent replacement for the generator. I doubt your real world load often exceeds 10kw.

This setup makes so much more sense to me than now adding 2x Multiplus 2kw or 3kw on top of existing 2x Skylla 24/100 and on top of an old Magnum left in place. It would be far less money , take less space, give far more functionality.

I would add an additional transfer switch as an "inverter bypass" so that the new split phase whole boat inverter setup could be bypassed if there were an inverter malfunction or you needed to do service work on the inverters and didn't want to shut down the AC power to the whole boat.

 

[NoRain]

I agree entirely with L00s and would add a couple of points..

- I note you have a Charles iso xfmr. I believe that model is not one that does boost. Do you have any 208V shorepower connections at any of your “regular” dockages? If so pls advise and I can add a paragraph or two.

- if you would like to make use of Victron’s Power Assist feature, you need to run all loads through the inverters, as L00s has suggested. PA is a wonderful bit of Victron wizardry to handle short term (over)loading transparently. Come winter which rapidly approaches, I make use of this feature every single morning. Note: a number of manufacturers have a capability that is similar, but no one does it in such an elegant and sophisticated manner.