Inverters in parallel?

[Wdeertz]

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.

Whoa talk about project creep, I LIKE IT. In all seriousness I like your suggestions. When I installed my original LFP batteries (600Ahr battleborn) 4+ years ago the magnum inverter sufficed and I initially added one skylla which I quickly determined was insufficient so added a second. Going through the project in my head I have a few clarifying questions:

1) Multiplus II install orientation - couldn’t find in manual but can the MPII be installed on its side or back? Space is limited where I intend to install and a vertical orientation may be impossible.

2) Would you use AWG 4 or 2 for the MPII AC-out to provide additional headroom for power assist?

3) Batttery cables would be about 12-15’ so right under the 5m threshold in the manual which suggest 2x 1/0 per unit so 4x 1/0 would be 213.96 sq mm (53.49 x 4), so 2x 4/0 214.4 sq mm would be equivalent? That branch would also have my 2x skylla chargers so maximum charging would be 2x100 plus 2x95 =390 amps which 2x 4/0 cables should be able to handle.

In your suggested solution I would put the switch for the inverter panel on “main panel” and run all these circuits off the MPII (with the magma inverter breaker off). In the event of a MPII issue I switch to bypass the MPII, turn on the magnum inverter and switch to “inverter” and be back up running. The more I think about this the more I like it.

Now just to figure out if I have sufficient room in my wire case for all the new cables.

 

[Wdeertz]

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.

The isolation transformer is currently wired up with a manual switch to provide a 15% boost when on 208v shore power.

 

[luna]

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?

I think your understanding is correct, but I am far from an expect in Crest Factors, Non-linear Loads, Harmonics or the Current lag caused by Inductors.
The goal of my post was to bring this kind of thing to the OP's attention in an effort to try to ensure that the inverters are sized correctly.
I have no idea what the loads (nor the power factor of the loads) are that the Op is looking to supply.
I suspect that they both will vary considerably and that a prudent design allows for the accommodation of a reasonably high load.

 

[l00smarble]

1) Multiplus II install orientation - couldn’t find in manual but can the MPII be installed on its side or back? Space is limited where I intend to install and a vertical orientation may be impossible.

Vertical bulkhead mounting is preferred. On its back mounting is acceptable if there is adequate airflow and you are OK with giving up drip resistance. Side mounting is no recommended as the heavy transformer is not supported properly.

2) Would you use AWG 4 or 2 for the MPII AC-out to provide additional headroom for power assist?

I am using 6/3-8/1. Pacer round 6/3-8/1 which is 105C marine cable. 6AWG-105C starts out rated at 120amps of ampacity. It is derated down to 84amps when bundled as a 6/3 jacketed cable. Is is further derated to 71 amps if in engine room. This is still leaves 40% headroom over 50amps for output with power assist. If not in engine room you have 84a of ampacity. Either way I'm comfortable with mine as the output is going through a 50a breaker. It will allow short spikes of power assist above 50a to start an air cond for example but it wont' do sustained current above 50a where cable ampacity is in question.

If you want to run in sustained power assist you may need to upsize the cable appropriately

3) Batttery cables would be about 12-15’ so right under the 5m threshold in the manual which suggest 2x 1/0 per unit so 4x 1/0 would be 213.96 sq mm (53.49 x 4), so 2x 4/0 214.4 sq mm would be equivalent? That branch would also have my 2x skylla chargers so maximum charging would be 2x100 plus 2x95 =390 amps which 2x 4/0 cables should be able to handle.

I would follow the instructions. It is about more than just cross section. In fact I would say that 95% of problems with heavy power connections are at the terminations. Having two positives and two negatives on each gives more surface area of cable to lug and lug to inverter.

I'm not sure exactly what you mean by "that branch" and where/how heavy DC cabling is done and where overcurrent protection is located. I'm also not following math of 2x100 + 2x95. Each of the proposed MPII units has a 120a 24v charger so if you keep the Skyllas it would be 2x100 + 2x120 = 440a charging. That is nearly 0.5C which is possible for that battery bank but you are going to have to be very careful with getting the heavy DC cabling right to handle those kinds of currents.

In your suggested solution I would put the switch for the inverter panel on “main panel” and run all these circuits off the MPII (with the magma inverter breaker off). In the event of a MPII issue I switch to bypass the MPII, turn on the magnum inverter and switch to “inverter” and be back up running. The more I think about this the more I like it.

Now just to figure out if I have sufficient room in my wire case for all the new cables.

You could turn off the Magnum AC input breaker but you would also want to change the inverter panel transfer switch to "main shore" to bypass it entirely.

You could do it that way though it is a bit unusual and convoluted with cascading inverter systems. I can see this leading to problems if anyone but you operates the boat/systems and to any future service technicians. At minimum you would want good schematics/documenation and labeling for such a system.

 

[Wdeertz]

All systems are outside the engine room so 84A would be more than enough to handle the occasional power assist. I’ll have to figure out a way to do vertical bulkhead mounting. The manual I was looking at showed the 24/5000/120 multiplus II having a 95A charger.

See attached photo where I tried to layout the pertinent sections of the DC system. To supplement the drawing I’ll try to provide an overview:

- The 4 Epoch elite V2 batteries are all connected with 2/0 cable to Victron power-in T-fuse modules each fused at 250A (20K AIC). I didn’t fully draw the negative cables but they go to underside of Victron bus bar. Total round trip cable length for each battery is 76 inches (28” positive 48” negative)
- entire bank is fused by a 400A Mersin t-fuse which is rated at 50k AIC
- all 4/0 cables from Victron power-in module through lynx distributor
- 2x 2/0 cables out of lynx distributor to main bus bar, fused at 300A
- 2x 2/0 cables out of lynx distributor to bus bar (about 12-15’ away) feeding skylla charges, fused both ends at 150A

My thought was to replace the 2x 2/0 cables going to skylla bus bar with 2x 4/0 cables (each fused at 300A) and then feed 2x 2/0 cables from that bus bar to each of the new MPII each cable fused at 200A (each about 36”). During charging I’d likely limit each charging source so total would be in the 300-325amp range.

Thoughts?

 

[rslifkin]

The manual I was looking at showed the 24/5000/120 multiplus II having a 95A charger

The third number in the model is the charger capacity. So it's a 120A charger provided the unit stays cool enough.

 

[Wdeertz]

The third number in the model is the charger capacity. So it's a 120A charger provided the unit stays cool enough.

Maybe there’s another model but the 24/5000/120-95 I’m looking at says the battery charger is 95A. Is there a 24/5000/120-120 model?

 

[rslifkin]

Maybe there’s another model but the 24/5000/120-95 I’m looking at says the battery charger is 95A. Is there a 24/5000/120-120 model?

That's odd. I'm thinking that's a mistake in the spec sheet, as that would break convention from all of Victron's other models (including the 48/5000/70 listed on that same datasheet). The -95 at the end is for the 95A transfer switch (which is correctly reflected in the datasheet).

 

[l00smarble]

The manual I was looking at showed the 24/5000/120 multiplus II having a 95A charger.

24/5000/120 means 24v/5000va/120a

See attached photo where I tried to layout the pertinent sections of the DC system. To supplement the drawing I’ll try to provide an overview:

- The 4 Epoch elite V2 batteries are all connected with 2/0 cable to Victron power-in T-fuse modules each fused at 250A (20K AIC). I didn’t fully draw the negative cables but they go to underside of Victron bus bar. Total round trip cable length for each battery is 76 inches (28” positive 48” negative)

Good. Class T per battery is good.

- entire bank is fused by a 400A Mersin t-fuse which is rated at 50k AIC

Maybe OK but we are pushing toward/past 400a on this. Maybe needs to be 500a.

- all 4/0 cables from Victron power-in module through lynx distributor

OK for original house loads and original inverter but not ideal for new 10kva inverter pair.

- 2x 2/0 cables out of lynx distributor to main bus bar, fused at 300A

Same.

- 2x 2/0 cables out of lynx distributor to bus bar (about 12-15’ away) feeding skylla charges, fused both ends at 150A

Same

My thought was to replace the 2x 2/0 cables going to skylla bus bar with 2x 4/0 cables (each fused at 300A) and then feed 2x 2/0 cables from that bus bar to each of the new MPII each cable fused at 200A (each about 36”). During charging I’d likely limit each charging source so total would be in the 300-325amp range.

Thoughts?

I would put the inverters each on a class T fuse just after the main disconnect and Smartshunt.

you also need to check the rating of hte main disconnect switch and if you are using the 500a SmartSHunt you are flirting with that kind of current at this point.

Even if you reduce the chargers in the Multiplus they still pull crazy current when inverting. 10kw is 417amps. They have a peak or surge capability to 9000kva each so technically you could spike to 18kva which is 750 amps DC.

I can't stress enough how important the heavy DC connections/cabling/components must be for a system of this size. I would also want to watch the system loaded up with a thermal cam (and check once in a while over time as well.)

 

[jhall767]

Very interesting thread. I'm looking ahead to do something similar.

Right now I have the following

50A/240 -> Iso Buck Boost -> main transfer switch
17.5 KW Genset -> main transfer switch
8 KW Genset -> main transfer switch

4 x 8D (24V) battery bank / or main (1 leg) -> 3500W 120 V Inverter -> inverter sub panel.

Water heater/stove/washer/driver / AC all 240V.

I would like to switch to a 120/240 split phase inverter/charger and remove the older generator.

There's a fair bit of work involved but I think the net will be worth it. I'm trying to get the design straight so the next time something dies I'm not buying the wrong thing.

 

[Serene]

- 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.

I second the recommendation on using Power Assist. It has been a game changer for me, as in Australia most shorepower supply is 15A @ 240V so 3,600W and my AC loads include 2 x 16k BTU A/C units, hot water heating, eutectic refrigeration, plus other various devices like Starlink, computers, etc.

When the hot water heating element is running and both A/C compressors running, I go over 3,600W and the Quattro kicks into Power Assist to keep everything running. I have a Cerbo GX and can monitor the state and see the battery draw, which shows how much time at that usage the batteries can support. BTW I have 900Ah of LiFePo4 at 12V to support all of this use.

As soon as one or both A/C compressors cycle off, or the hot water heating cycles off, the system switches back to charging. This can go on all day long without noticing any interruptions on the load side.

 

[Wdeertz]

That's odd. I'm thinking that's a mistake in the spec sheet, as that would break convention from all of Victron's other models (including the 48/5000/70 listed on that same datasheet). The -95 at the end is for the 95A transfer switch (which is correctly reflected in the datasheet).

OK must be a typo. I've seen a few typos on the dimensions, even someone not versed in imperial measurements should know 650mm is more than 4 inches?

 

[Serene]

One more consideration with Power Assist; you must set it inside the Inverter/Charger and it is a multiplication factor. In my case I have an input limit set on shorepower to 16A and a Power Assist factor of 1.5 so total load can go up to 24A. Being 16A from shore and 8A from Power Assist.

But, there is only one Power Assist setting inside the Inverter, so with the two AC inputs, they both share the same power assist factor. I would have thought there should be two settings so each input can be configured appropriately. But there isn't.

So in my case with 1.5x I have 16A + 8A = 24A on shore and on generator it equates to 25A + 12.5A = 37.5A so in theory when on generator the Quattro could push 37.5A through the wiring, so need to be aware of that.

I would have thought it made more sense to have a Power Assist setting for each AC input. I would have set Generator to 1.0 and Shore to 1.5 so max current would be 25A in any case.

 

[rslifkin]

One more consideration with Power Assist; you must set it inside the Inverter/Charger and it is a multiplication factor. In my case I have an input limit set on shorepower to 16A and a Power Assist factor of 1.5 so total load can go up to 24A. Being 16A from shore and 8A from Power Assist.

But, there is only one Power Assist setting inside the Inverter, so with the two AC inputs, they both share the same power assist factor. I would have thought there should be two settings so each input can be configured appropriately. But there isn't.

So in my case with 1.5x I have 16A + 8A = 24A on shore and on generator it equates to 25A + 12.5A = 37.5A so in theory when on generator the Quattro could push 37.5A through the wiring, so need to be aware of that.

I would have thought it made more sense to have a Power Assist setting for each AC input. I would have set Generator to 1.0 and Shore to 1.5 so max current would be 25A in any case.

The amp limit should be separate for each input on a Quattro. And if you have a GX device or other way to control the Multiplus, you can change the limit on the fly, no need to break out the computer and reprogram. I think it's only the boost factor that's set in the initial config and is shared across inputs.

 

[Wdeertz]

One more consideration with Power Assist; you must set it inside the Inverter/Charger and it is a multiplication factor. In my case I have an input limit set on shorepower to 16A and a Power Assist factor of 1.5 so total load can go up to 24A. Being 16A from shore and 8A from Power Assist.

But, there is only one Power Assist setting inside the Inverter, so with the two AC inputs, they both share the same power assist factor. I would have thought there should be two settings so each input can be configured appropriately. But there isn't.

So in my case with 1.5x I have 16A + 8A = 24A on shore and on generator it equates to 25A + 12.5A = 37.5A so in theory when on generator the Quattro could push 37.5A through the wiring, so need to be aware of that.

I would have thought it made more sense to have a Power Assist setting for each AC input. I would have set Generator to 1.0 and Shore to 1.5 so max current would be 25A in any case.

I’ve read the manual and this aspect isn’t covered very well. I’d like to limit the maximum DC draw so as to avoid needing to go beyond my current 400A bank fuse. 350A @ 24v is 8400 watts which should easily meet 100% of my needs and I won’t need to push the units to its limit.

If I only want a maximum output of 75A with an AC input limit of 50A I’d set the factor to 1.5, is that correct? Can I specify a maximum output of say 35A while on DC power?

 

[Serene]

The amp limit should be separate for each input on a Quattro. And if you have a GX device or other way to control the Multiplus, you can change the limit on the fly, no need to break out the computer and reprogram. I think it's only the boost factor that's set in the initial config and is shared across inputs.

Correct. Input current limits are separate and can be changed on the Cerbo (if the checkbox is enabled in the Quattro settings to allow remote override), but the power assist factor is shared. That was my point.

 

[Serene]

In my case I have 25A from generator and 16A from shore. I wanted to set shore power assist to 1.5 to get a total of 24A and leave generator at 1.0 to have 25A. This way my cable sizing would cover both arrangements and my use patterns would be learned and carry forward whether on shore or generator.

The way Victron enables power assist, if your input current limits are different on each AC input, your power assist 'amount' will be greater on the AC input with the higher limit.

This means wiring needs to be up-specced for the higher current and I have two different usage patterns. OR I cobble the shore so generator never goes over 25A but shore is now limited to 16A. Again two different usage patterns.

Once I discovered this, I set Power Assist to 1.5 and up-specced to handle the 1.5 x generator so I don't cause any harm. At least this way I get to use all of my AC loads when on shorepower, with the power assist doing its thing.

I would have thought it would be a simple software change to tie power assist to each AC input.

 

[Serene]

I’ve read the manual and this aspect isn’t covered very well. I’d like to limit the maximum DC draw so as to avoid needing to go beyond my current 400A bank fuse. 350A @ 24v is 8400 watts which should easily meet 100% of my needs and I won’t need to push the units to its limit.

If I only want a maximum output of 75A with an AC input limit of 50A I’d set the factor to 1.5, is that correct? Can I specify a maximum output of say 35A while on DC power?

There are quite a few Victron manuals that need multiple reads to fully understand the implications of certain settings.

Yes AC input of 50A x 1.5 power assist factor = 75A total. You will get 50A from the input and the inverter will supplement with 25A from battery, but remember the amperage coming out of the DC batteries will be higher than this with the conversion from 240V to 12V or whatever voltages you have in your installation.

The maths is 25A * 240V = 6,000W
Then 6,000W / 12V = 500A

So in this scenario your 25A from AC power assist from the inverter is drawing 500A @ 12V DC from the batteries.

I don't think there is a way to limit DC amperage bing drawn out of the battery unless in your BMS. But you can see it on the Cerbo GX screen, including a time to hit your discharge floor.

 

[SteveK]

In my case I have 25A from generator and 16A from shore. I wanted to set shore power assist to 1.5 to get a total of 24A and leave generator at 1.0 to have 25A. This way my cable sizing would cover both arrangements and my use patterns would be learned and carry forward whether on shore or generator.

The way Victron enables power assist, if your input current limits are different on each AC input, your power assist 'amount' will be greater on the AC input with the higher limit.

This means wiring needs to be up-specced for the higher current and I have two different usage patterns. OR I cobble the shore so generator never goes over 25A but shore is now limited to 16A. Again two different usage patterns.

Once I discovered this, I set Power Assist to 1.5 and up-specced to handle the 1.5 x generator so I don't cause any harm. At least this way I get to use all of my AC loads when on shorepower, with the power assist doing its thing.

I would have thought it would be a simple software change to tie power assist to each AC input.

Interesting read about being able to supplement 16A from shore with inverted 8A from battery. I think I go that right.
Is 16A from shore max available?

I ask because here we have 15/30/50/A & some100A shore supply, so 16A seems low.

 

[Serene]

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.

One extra consideration for the OP, is you don't necessarily need a CAN bus enabled alternator. If you use an Orion XS DC-DC charger, from start to house and have the alternator charging start, you connect the Orion to the Cerbo via VE.Direct and you get an 'Alternator' tile on the screen. Must be an Orion XS though, not Orion-Tr.

A lot cheaper and simpler than including a CAN bus alternator like a Wakespeed or Arco Zeus.

I already had a Balmar MC-614 so wanted to keep this in operation.

 

[Serene]

Interesting read about being able to supplement 16A from shore with inverted 8A from battery. I think I go that right.
Is 16A from shore max available?

I ask because here we have 15/30/50/A & some100A shore supply, so 16A seems low.

I am talking 16A @ 240V in Australia. Typical shore power connection is nominally 15A but you can get 16A out of them. YMMV.

You can double them up for 30A with two shore connections, or go to three-phase, but the majority of Australian marinas provide 15A @ 240V standard.

 

[Serene]

One extra consideration for the OP, is you don't necessarily need a CAN bus enabled alternator. If you use an Orion XS DC-DC charger, from start to house and have the alternator charging start, you connect the Orion to the Cerbo via VE.Direct and you get an 'Alternator' tile on the screen. Must be an Orion XS though, not Orion-Tr.

A lot cheaper and simpler than including a CAN bus alternator like a Wakespeed or Arco Zeus.

I already had a Balmar MC-614 so wanted to keep this in operation.

And this is what it looks like on the Cerbo GX screen;

 

[l00smarble]

One extra consideration for the OP, is you don't necessarily need a CAN bus enabled alternator. If you use an Orion XS DC-DC charger, from start to house and have the alternator charging start, you connect the Orion to the Cerbo via VE.Direct and you get an 'Alternator' tile on the screen. Must be an Orion XS though, not Orion-Tr.

A lot cheaper and simpler than including a CAN bus alternator like a Wakespeed or Arco Zeus.

I already had a Balmar MC-614 so wanted to keep this in operation.

It sounds from this thread like he's got big alternators already so a 50 amp Orion is going to hobble his system. He would need multiples in parallel which is possible but gets a bit kludgy.

 

[Serene]

It sounds from this thread like he's got big alternators already so a 50 amp Orion is going to hobble his system. He would need multiples in parallel which is possible but gets a bit kludgy.

Yes good point. You can parallel Orions but agree more than two is probably better to go to a Wakespeed or Zeus.

I have a single 100A alternator and have set the Balmar temp cutoff to 60c and am limited to 50A via the Orion. Pretty conservative but shouldn’t burn out the alternator.

 

[Wdeertz]

24/5000/120 means 24v/5000va/120a


Good. Class T per battery is good.

Maybe OK but we are pushing toward/past 400a on this. Maybe needs to be 500a.


OK for original house loads and original inverter but not ideal for new 10kva inverter pair.

Same.

Same

I would put the inverters each on a class T fuse just after the main disconnect and Smartshunt.

you also need to check the rating of hte main disconnect switch and if you are using the 500a SmartSHunt you are flirting with that kind of current at this point.

Even if you reduce the chargers in the Multiplus they still pull crazy current when inverting. 10kw is 417amps. They have a peak or surge capability to 9000kva each so technically you could spike to 18kva which is 750 amps DC.

I can't stress enough how important the heavy DC connections/cabling/components must be for a system of this size. I would also want to watch the system loaded up with a thermal cam (and check once in a while over time as well.)

Thanks for the inputs. From what I’ve found the Victron inverters don’t have a way to limit the DC output. I’d really like to shy away from going beyond a 400A master bank fuse as that top 20% I really don’t need. Are there any inverter configuration options that would limit the DC pull? I guess I could put DC breakers on the MP2 and if too much power is drawn they would pop but I wouldn’t loose the remainder of my DC bus powering critical components like nav equipment, etc. There is no mission critical AC equipment so the DC breakers popping would be more of an inconvenience than something more serious.

 

[l00smarble]

you can turn down the charge limit if you like but this really only comes into play if you are pumping charge with alternators and you fire up the genset and let the two Multiplus and Skyllas go full bore. Most of the time you would not do this most likely.

You could just not turn on the Skyllas or repurpose them to charge other battery banks on board. Or really you could just remove one or both Skyllas since you are adding back 240a of charging capability.

 

[Serene]

Are there any inverter configuration options that would limit the DC pull?

I think I have found what you are looking for, but not sure if it works with your batteries and BMS. In the Lynx BMS NG there is a setting for 'Discharge Current Limit' which can be set and then the BMS would control how much current can flow from the batteries.

 

[Wdeertz]

you can turn down the charge limit if you like but this really only comes into play if you are pumping charge with alternators and you fire up the genset and let the two Multiplus and Skyllas go full bore. Most of the time you would not do this most likely.

You could just not turn on the Skyllas or repurpose them to charge other battery banks on board. Or really you could just remove one or both Skyllas since you are adding back 240a of charging capability.

I’m not really concerned about charging. The more likely scenario is while on shore power and running 2 or 3 AC units the marina power goes out and the MP2 tries to pick up this large load and the DC amps spike causing the 400A fuse to blow. I guess in this scenario I wouldn’t be underway and no harm other than unnecessarily blowing an expensive fuse. While on battery power I’d likely only run a single AC unit so would never get beyond 400A.

 

[Wdeertz]

I think I have found what you are looking for, but not sure if it works with your batteries and BMS. In the Lynx BMS NG there is a setting for 'Discharge Current Limit' which can be set and then the BMS would control how much current can flow from the batteries.

Unfortunately not running Victron NG batteries, using a 3rd party LFP batteries which don’t have this setting.

 

[rslifkin]

I think I'd want to size things to handle the full inverter load. Might as well be able to make use of it if it's installed, being that your batteries can supply plenty of current to do so.

To keep things a bit easier, you could probably fuse separately for the main DC bus and each inverter rather than having to wire and fuse anything beyond the main battery hot bus for 500+ amps. I'm thinking fuse each battery, feed to a common hot bus. Then pull from there through suitable fuses and shut off switches for inverter and DC main.