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running 2x victron multiplus' in split phase

frostyllama

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I recently purchased 2x 24/3000 multiplus' with the intent of running them in parallel for use with 120 volt US appliances exclusively. I planned a system with some breathing room for a complete electric appliance loadout on my bus conversion.

I purchased what I thought to be a high efficiency 23 seer 120v mini split.

Unfortunately, reading through the spec sheets it is in fact a 230v 60hz unit like most high efficiency models. This changes my plans a bit, perhaps for the better. The ability to run 240v appliances like an on demand water heater interest me.

From what I've read the two 120 multiplus' can be atomically wired (tied with no redundancy) into a 120/240 split phase setup. I've also read that this is more complicated to configure than a parallel setup, and that one should be even more careful with a split phase setup over a single phase one.

Besides the need for a two pole circuit breaker my questions are:

- Is an autotransformer recommended or necessary for the setup?

- Will the two units be able two load balance between the two poles at 120v on their own?

- Can the units wired in split phase handle two times the watt load at 240v (8000 cont) over their 120v (4000 cont) limits, or is it the same?

- Is there any other extra hardware needed?

- Should I return the 240 mini split, buy a 120 and accept my fate as a 120v electrical pleeb?

- Am I missing anything obvious, any tips?

edit: Probably should have posted in off grid inverters or vehicle mounted systems. The units will be used to charge from the grid.
 
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No additional hardware needed.
Watts are watts. 3,000W X2 units = 6,000W
They will not auto balance unless you add autotransformer.
120/240 is not that difficult to set up, but requires attention to detail
 
No additional hardware needed.
Watts are watts. 3,000W X2 units = 6,000W
They will not auto balance unless you add autotransformer.
120/240 is not that difficult to set up, but requires attention to detail
If both of the inverters are 120v then why is an auto transformer needed. Wouldn’t each inverter handle the loads on the individual 120v leg there output is wired to?
 
Without an autotransformer, each leg of 120 volt will only be able to draw 3,000 watts. Even if the other leg is at zero power. If that is enough single leg power, then don't bother with the transformer at all. An auto transformer will try to keep the two legs balanced, but it is not perfect. At light loads, it really won't do anything, the two inverters will still each power it's own leg, but if the output voltages vary at all, the one with the higher voltage may end up running more power and help push the opposite leg through the transformer. And when you load a single leg to high power, the slight voltage drop will cause the transformer to pull some of the power from the opposite leg. With dual inverters, I would not bother with the transformer unless you truly needed more than 3,000 watts on one leg. Even a slight mismatch in the inverter output voltages or the transformer windings could cause one of the inverters to do most of the work. And there is always some power lost in the transformer. On one video I watched, the transformer was eating up about 17 watts when there was no load on the system.

The one place that you need an autotransformer is when you have a single phase 230 volt output inverter. Then an autotransformer can create the neutral at half the voltage. For this to work properly, the inverter has to allow it's original neutral connection to be pushed to 115 volts
AC from the chassis ground. If you can't do that, then you can't bond the neutral to ground and the new "neutral" would actually be at 115 volts, with L1 at 0 volts and L2 at 230 volts still. This will technically work, but I know I do not want my neutral white wires to be at 115 volts from ground, with the hot lead at 230 instead of 120. If in doubt, try "bonding" the neutral of the autotransformer with a light bulb. If the bulb lights, it won't work. The the bulb stays dark, measure the voltages and see what you got.
 
Isn't keeping the phase correct important? An autotransformer will ensure phase is correct and also balance the legs and give one leg the majority of the amps if needed and it's unused on the other leg. Like a Victron autotransformer will shift from 15a to up to 30a on a 120v leg if the other leg is not being used.
 
Yes. the Victron auto transformer can shift up to 28A continuous from one leg to the other (30A for a while) so that is definitely an advantage if your legs aren't balanced with loads.
 
curious what you ended up doing. Seems like you have two well-known, supported ways of achieving your goal. PKYS article mentions both.

Since you already have 2 identical units, you have fulfilled all requirements to do 240v split phase. I see no reason to deviate.

- Should I return the 240 mini split, buy a 120 and accept my fate as a 120v electrical pleeb?
you should be able to run the appliance with everything you have.

- Is an autotransformer recommended or necessary for the setup?
Both methods are possible. Assuming you are starting over, seems the autotransformer is more versatile than 2 inverter units.

I think hooking up the charging side of a 230v euro model to US shore powers is a little more nuanced though. Ie how do you connect L1,L2,N,PE 120/240v split phase into the L1,N,PE of the AC,in of the Multi. Definitely wouldn't be able to connect a single phase 120v into your euro Multi w/o some transformer though, that's for sure.

- Will the two units be able two load balance between the two poles at 120v on their own?
Load balancing would only happen with the autotransformer as PKYS says.
 
curious what you ended up doing. Seems like you have two well-known, supported ways of achieving your goal. PKYS article mentions both.

Since you already have 2 identical units, you have fulfilled all requirements to do 240v split phase. I see no reason to deviate.


you should be able to run the appliance with everything you have.


Both methods are possible. Assuming you are starting over, seems the autotransformer is more versatile than 2 inverter units.

I think hooking up the charging side of a 230v euro model to US shore powers is a little more nuanced though. Ie how do you connect L1,L2,N,PE 120/240v split phase into the L1,N,PE of the AC,in of the Multi. Definitely wouldn't be able to connect a single phase 120v into your euro Multi w/o some transformer though, that's for sure.


Load balancing would only happen with the autotransformer as PKYS says.
I ended up building out a 120 system with a single 24/3000 multiplus partially due to space constraints. Project was put on pause for a few months. I've got the second unit if I need it and can fit it in. Rehashing my usage, I'll be very infrequently above a 2kw threshold.
 
Do the All in 1 inverters load balance between L1 and L2?
It depends...

Most of the cheaper 120/240 volt split phase All in One inverters are high frequency units with basically two separate 120 volt inverters running out of phase. Those can't load balance between the phases. The larger and heavier units may have a single 240 volt inverter and a built in auto-transformer to provide the neutral. That can load balance up to the limit of the auto-transformer windings current capability. True low frequency units like the Schneider produce low voltage AC from the battery and then run that through a large transformer to step up the voltage and provide the split phase outputs and neutral. Either winding can theoretically provide all of the inverter power, but they may still be limited by the wire gauge handling the current. I don't have the spec in front of me, but I seem to remember the Schneider XW can continuously output over 75% of it's power to just one leg. For short term surges, it can push 100% to either leg.

Even if the inverter can handle it, it is still always best to try and balance the loads as close as possible. The less current on each winding, the more efficient the system will be.
 
@GXMnow Thank you for that detailed reply.
I really like the Schneider XP Pro, but the Schneider Conext MPPT 100 600 6kW Solar PV Charge Controller is lacking compared to the Victron Charge controller, when comparing the number of panels, voltage and watts. I would prefer the Schneider XP Pro and the Victron Charge controller, I don't know how to connect the Victron Charge controller to the Schneider bus system. If that can be done by someone please let me know.
Thank you again.
Scat
 
@GXMnow Thank you for that detailed reply.
I really like the Schneider XP Pro, but the Schneider Conext MPPT 100 600 6kW Solar PV Charge Controller is lacking compared to the Victron Charge controller, when comparing the number of panels, voltage and watts. I would prefer the Schneider XP Pro and the Victron Charge controller, I don't know how to connect the Victron Charge controller to the Schneider bus system. If that can be done by someone please let me know.
Thank you again.
Scat
You can use any charge controller you want, connect the DC output of the charge controller the same way as the Conext MMPT. Although it's going to be hard to get a code compliant install in the US with a Victron charge controller, not all are NRTL listed, no ground fault protection, no arc fault protection, no rapid shutdown(if needed), and no way to connect conduit.
 
While the data connection is nice for monitoring, it is not required for the system to work. Just as @pvgirl said, you can connect the DC output of any charge controller to the battery bank.

I am currently using a cheapo BougeRV 40 amp MPPT charge controller with my Schneider XW-Pro inverter. It only has 2,000 watts of panels on it to help charge the battery, while most of my PV solar power comes from 4,800 watts of panels on Enphase microinverters. But to monitor my system, I need to look at 3 different apps. It's not ideal, but the power does not care.

If you really like the Victron gear, they do have good options. And yes, you can run an autotransformer to get phase balancing. How much current does the 240 volt loads require?

All of my system is built to the National Electric Code (NEC), except my batteries are not compliant, and my DC charge controller is considered an "Off Grid Device". In my use, all it is is a battery charger. It is connected through a UL approved DC breaker, and the system has DC ground fault protection as well as lightning/surge arresters on the DC lines from the panels.

I do agree, we should always strive to follow code and be permitted etc., but there are cases where the code gets in the way. There is no sane way I can make my battery bank truly code legal. If I ever find a decent deal on a UL listed battery, I might install one to have the system inspected and approved. Until then, I over built the system and added some extra safety features so that I am not at all worried about my batteries. Many EV owners are parking a much larger pile of the same type of cells in their garage. They charge and discharge them a whole lot faster, to the point where they need to actively cool them. Mine coast along at 0.1C rate and run as cold as the concrete garage floor.

I feel the same way about the charge controller. I almost bought the Schneider MPPT 150-60 but it was well over 4 times the price of the BougeRV one. And it really had no advantage other than the data being on the same system. In some ways, I kind of like the separate system. I can change the settings and set my BougeRV to charge a 12 volt car battery, or my E-Bike batteries. It does not care what the Schneider system is doing.

The one odd thing I do see is that it appears the Schneider system ASSUMES it is the only path for power. When the XW-Pro stops charging, the battery voltage reading stops climbing for 1 to 2 hours. But the BougeRV charge controller is still pushing 25 amps into my battery bank. Sure, that is small for a 720 Amp Hour battery, but with my Fluke meter, I can still see the voltage climbing slowly. Finally, after an hour or so, the voltage in the Schneider graphs do show a ramp up. And it does eventually show only about 0.2 volts below the true battery voltage. While it is charging from the XW-Pro, the voltage readings match within 0.05 volts, even if the extra 20-25 amps is also charging it faster. It's so odd that it won't stay reading that accurate when a different source is charging. If I had the Schneider MPPT controller, it would know there is charge current, and I bet it would show the battery voltage climb the entire time.

This is a DIY solar forum, so many of us do some experimenting. If you do try something that is "not to code", then please, do take all of the safety precautions. My batteries all run through a Class "T" fuse, all my breakers are UL listed for the DC voltage in use, and all my wiring is at least one gauge larger than NEC requires. Let's all be safe and we can have a lot of fun and learn a lot.
 
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