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Two parallel multipluses (single phase) with 30a shore power?

slipperysam

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Feb 2, 2021
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So my power needs on the AC side aren't all that big. Everything's 120V, and I have a few larger AC appliances (induction top, oven, and water heater) which each pull roughly between 1200W-1800W when they're blasting. Let's also assume my minisplit is often cooling me off at 600W.

My dilemma is that the Multiplus 24/3000 (currently ~ $1200) can support 2400W continuous, so whenever I'm off grid, I'm really only using one of these larger appliances at a time. Granted, that might make for good conservation behavior! But, it's a bit annoying I think that in the morning I need to _first_ make coffee, _then_ toast, _then_ heat water for a shower. If I'm going to do all those things anyway, it would be nice to do them at the same time. Hence, I'm leaning towards the Quattro 24/5000 (currently ~ $2800) which can do 4000W continuous.

The thing is, the Quattro is so overkill for me. I really wish there was a size in between. Today, I realized there _kind of_ is. I could put two compact Multiplus 24/2000s together for an effective 24/4000 (currently ~ $2200) supporting 3200W continuous. That's sort of the perfect size for me. But, when I searched how to actually run this in parallel, most of the search results are worrying. It seems overly complicated, even for a single phase set up. And, the compact version isn't really compact in a helpful way. It's actually longer than the normal multi / quattro models, it just had a reduced depth, so I'm not even sure it will fit in my under-the-counter electrical cabinet.

One last detail: given my energy needs, a 30A inlet suffices. That would satisfy my AC loads 95% of the time, and only dip into the PowerAssist infrequently (and at most 20A worth since I'm likely to have that 50A breaker - even the single Multi would handle this no problem). But diagrams for parallel multis always have 50a inlets because, why not, you get to harvest both legs. And I just don't need that. Is there an easy wiring diagram for 30a inlet to two parallel single phase Multipluses?

Sigh. Can't make up my mind. Any opinions here?
 
Compare the idle power consumption of the two smaller inverters vs. the one larger. It's probably not a big number, but it's worth knowing.

Parallel operation is scary until you find a video demonstrating how easy it is to setup. Easiest with MK3-USB adapter and VEConfigure on a PC.

You could get a Euro 230V MP II 24/5000 and a transformer to get 120VAC.

For AC input on 2X MP in parallel, simply feed both inverters AC-in with L and N from the AC source.
 
Compare the idle power consumption of the two smaller inverters vs. the one larger.
I have; in the normal mode, the smaller ones consume 11W each at idle, and the quattro consumes 30W. So, some savings there.
For AC input on 2X MP in parallel, simply feed both inverters AC-in with L and N from the AC source.
So you mean, from a single phase 120V 30a inlet, take that 10 awg triplex, and just split the wires to each inverter? That seems easy. Pic attached to make sure I understand.

From there, I suppose I could just wire each inverter's AC-out to separated branch circuits. Something like each half of the panel PD55K004 from Progressive Dynamics.
 

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I have; in the normal mode, the smaller ones consume 11W each at idle, and the quattro consumes 30W. So, some savings there.

So you mean, from a single phase 120V 30a inlet, take that 10 awg triplex, and just split the wires to each inverter? That seems easy. Pic attached to make sure I understand.

That works. For the ground, I would just take the incoming ground and tie to one inverter then connect the ground between inverters.

From there, I suppose I could just wire each inverter's AC-out to separated branch circuits. Something like each half of the panel PD55K004 from Progressive Dynamics.

I wouldn't choose to do that unless that's how it's already wired. You may find that you have too many loads on one branch vs. the other. If your wiring supports it, I would tie the branches together so that both MP can power the entire panel - kinda like the way a 30A to 50A RV power adapter bonds L1 and L2 to allow both halves of the panel to receive power in the RV.
 
Compare the idle power consumption of the two smaller inverters vs. the one larger. It's probably not a big number, but it's worth knowing.
^ This would be one of the first things I considered as well. Its just one of many factors, but worth considering.

The simplicity of a single unit seems appealing, but I understand your concern with overkill (and the Quattro's are pretty pricey).

One other thing to throw into the mix, consider an 'asymmetrical' approach. Rather than two always on medium sized inverters in parallel, maybe you would be better off with two different inverters tailored ot purpose. If your minisplit is your only substantial/high power non-on-demand load. Maybe a small, low idle, inverter sized specifically for the mini split, and maybe other lower power circuits you want to always be powered (lights for instance) and then a second larger inverter/charger that can either be left off until needed or left in eco-mode could be used. This is just one example, and makes some assumptions about your use case and loads, but the broad point is if you are considering two inverters, identical units is one approach but there can also be possible efficiency gains in your design by considering different options.

Two Multiplus compacts is def an interesting option to consider as well, they have relatively low idle from what I recall.
 
I would tie the branches together so that both MP can power the entire panel
I suppose that's the whole point of programming them to be parallel single phase, come to think of it, huh? So the AC-out would look just like my diagram for AC-in, each L,N,G wire would just combine together before going to the inlet of a single AC distribution panel. That does seem rather easy, most of the diagrams I've seen are much more complicated than that.

One other thing to throw into the mix, consider an 'asymmetrical' approach.
Interesting idea, thanks for mentioning.
 
I suppose that's the whole point of programming them to be parallel single phase, come to think of it, huh?

Yep. Not just that, but they have to be operating in parallel to be wired either way (one per branch or bonded branches). Since they share a neutral, they have to be in phase.

So the AC-out would look just like my diagram for AC-in, each L,N,G wire would just combine together before going to the inlet of a single AC distribution panel. That does seem rather easy, most of the diagrams I've seen are much more complicated than that.

You'd also need to bond L1 and L2 at the AC panel

Interesting idea, thanks for mentioning.
 
What about splitting your AC system into two distinct "legs". One Multiplus powers one leg and the other Multiplus powers the other leg. I have no idea if that is a good solution though. It seems less complex than paralleling two Multiplus units.
 
What about splitting your AC system into two distinct "legs". One Multiplus powers one leg and the other Multiplus powers the other leg. I have no idea if that is a good solution though. It seems less complex than paralleling two Multiplus units.

They have to be run parallel even in your suggested configuration. Since they share a common Neutral, they have to be in sync.

Parallel operation requires a CAT5 ethernet cable and a couple minutes with VEConfigure.
 
Not in my sleep, but I could do it groggy. Happy to say I have no idea where my crimper is. :)

I'm pretty sure that the last time I made a patch cable I didn't need to use reading glasses.
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I like the idea of 2 multi’s. Besides the right sizing aspect, you also get some system redundancy. If one goes out of service, you can make due with the remaining unit, including the painful wait for needed repair if you need to send it off.
 
I like the idea of 2 multi’s. Besides the right sizing aspect, you also get some system redundancy. If one goes out of service, you can make due with the remaining unit, including the painful wait for needed repair if you need to send it off.

True; however, when configured to operate in parallel, both must be operational. If one fails, you will have to reconfigure the remaining unit to operate stand-alone.
 
I have pretty much the exact electrical needs as you with the exception of the mini split. I opted to go with a 12V split unit that uses R134A mostly to remove another inverter load and to save weight. Still leaves me with the induction cooktop, a microwave oven and electric water heater. Could MAYBE run two of those with a standard Multiplus for a short while but definitely not all three.

My plan is to use the Multiplus relay for load shedding. I’ll hook it up to a DC to AC contactor to disconnect the water heater whenever the inverter load is let’s say >2000W. Connect it back on when inverter load is <1000W. That way the water heater will heat water whenever I’m not cooking :)
 
I have pretty much the exact electrical needs as you with the exception of the mini split. I opted to go with a 12V split unit that uses R134A mostly to remove another inverter load and to save weight. Still leaves me with the induction cooktop, a microwave oven and electric water heater. Could MAYBE run two of those with a standard Multiplus for a short while but definitely not all three.

My plan is to use the Multiplus relay for load shedding. I’ll hook it up to a DC to AC contactor to disconnect the water heater whenever the inverter load is let’s say >2000W. Connect it back on when inverter load is <1000W. That way the water heater will heat water whenever I’m not cooking :)

Is the Multiplus relay a device that is external to the Multiplus, or something already built in?
 
Is the Multiplus relay a device that is external to the Multiplus, or something already built in?


P. 13

Three programmable relays
The MultiPlus is equipped with 3 programmable relays. The relays can be programmed for all kinds of other applications, for example as a starter relay for a generating set. The default setting of the relay in postion I (see appendix A, upper right corner) is ‘alarm’. Not adjustable with DIP switches.
 
I've got the manual downloaded already while my Multiplus is getting shipped. I haven't got through my second reading of the manual where reading comprehension actually kicks in.
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Without some context, it didn't mean anything to me on the first pass.

I suppose if I want the Multiplus to start my genset, I would need the Onan module that allows that. The wall panel switch I have now requires a downward press for a few seconds to prime the fuel and then an upward press for a few seconds to start the generator. I don't see the Multiplus relay being capable of that type of operation without some additional smarts.
dunno.gif


This is just a thought experiment. As little as I use my generator, I don't see a need to automatically start it. I'm trying to understand all the cool things I can do with my Multiplus as well as the Cerbo GX.
 
I've got the manual downloaded already while my Multiplus is getting shipped. I haven't got through my second reading of the manual where reading comprehension actually kicks in.
smash.gif
Without some context, it didn't mean anything to me on the first pass.

I suppose if I want the Multiplus to start my genset, I would need the Onan module that allows that. The wall panel switch I have now requires a downward press for a few seconds to prime the fuel and then an upward press for a few seconds to start the generator. I don't see the Multiplus relay being capable of that type of operation without some additional smarts.
dunno.gif


This is just a thought experiment. As little as I use my generator, I don't see a need to automatically start it. I'm trying to understand all the cool things I can do with my Multiplus as well as the Cerbo GX.
I am also in the process of installing a Cerbo in addition to the Multiplus. You can do all kinds of neat things with the relays. For example, I am planning on using one of them to fill my fresh water tank when I’m hooked up to city water rather than using the city water directly to avoid stagnant water. You can do this by using the onboard resistive tank inputs on the Cerbo. Hook up a relay to a 12V solenoid valve and program it to kick on at ~20% and off at ~80%.

Unfortunately by default you can only program the first relay on the Cerbo and not the second. But there is a way around that by using “node Red” to program the second relay.
 
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