Electrical theory 120 vs 240

[MIFARMS]

OK... so I'm struggling with this. I have two Victron 24/3000/70-50 inverters. Trying to decide how to connect them (series or parallel). I have some 240V appliances I could power, but there are things I don't know. If for instance I have a 2,400 watt heating element (water heater), is that 2,400 watts per leg, or 1,200 watts per leg? So assuming I set them up in series (split phase), and I energize that heating element, would I still have 1,200 watts available from each inverter for 120V loads, or would it basically be maxed out and I couldn't run anything else while that load was energized? Please be gentle...

 

[Ampster]

Watts are Watts regardless of voltage.
Watts = Voltage times Amps

I have never heard of wiring inverters in series to produce split phase so I will leave the answer to that question up to the Victron experts.

 

[Quattrohead]

No I am not going to be gentle LOL. Why would you ask a bunch of crazy loons on the interwebs when you can just refer to the manufacturers technical information?
But to be nice, 240 volt or 120 volt appliances are both single leg and that wattage applies to the said single leg. There are two electrical triangles that will answer every question you can ever ask, vir and vaw.

https://www.electronics-tutorials.ws/dccircuits/dcp_2.html

 

[Mattb4]

AC Power sources in parallel you add up wattage but the output voltage stays the same.
AC Power sources in series (AC in series is a bit odd since it requires the two input cycles to be 180 degrees apart.) you double the voltage while the wattage stays the same per leg of a split phase setup.

A 2400w 240vAC element is going to require 1200w from each 120vAC leg of two inverters in series.

 

[MIFARMS]

AC Power sources in parallel you add up wattage but the output voltage stays the same.
AC Power sources in series (AC in series is a bit odd since it requires the two input cycles to be 180 degrees apart.) you double the voltage while the wattage stays the same per leg of a split phase setup.

A 2400w 240vAC element is going to require 1200w from each 120vAC leg of two inverters in series.

Thanks, this is what I was looking for. I will read the document Quattrohead linked... and I'll probably do a bit of testing before I throw the switch on $3K worth of inverters. Assuming I can satisfy myself that I can balance the legs otherwise (240V loads are obviously self balancing), I'll probably just set them up for split phase. Then use one of the internal relays to power the water heater when Battery Charge % is >= 98, AND Output load is less than 1200 watts on both inverters..., I'll write a similar inverse rule to shut them off as well. Assuming the software will allow for multi parameter rules. Made a living for 30+ years writing Boolean logic, writing the rule(s) I can do, assuming the interface will allow it. I generally have excess power in the afternoons, and this will be an excellent way to use it.

 

[MIFARMS]

Watts are Watts regardless of voltage.
Watts = Voltage times Amps

I have never heard of wiring inverters in series to produce split phase so I will leave the answer to that question to Victron experts.

You just power one pole of the panel with the output from each inverter... your inverters obviously have to support this, and have a way to keep each leg 180 degrees out of phase from the other. Victron MultiPlus and Quatro Inverters support both Parallel, and Split Phase installs. One just has to decide which way to go if you have two identical units.

 

[Quattrohead]

Victron MultiPlus and Quatro Inverters support both Parallel, and Split Phase installs.

Double make sure your exact inverter does allow for this, someone recently found out that theirs did not.

 

[MIFARMS]

Double make sure your exact inverter does allow for this, someone recently found out that theirs did not.

Doco, and the reseller both say it does. I have the original MultiPlus... not the "updated" MultiPlus II that people are finding some models no longer support Parallel... But it's looking like I'll probably switch to Split Phase anyway, it would seem to offer more utility.

 

[Mattb4]

Doco, and the reseller both say it does. I have the original MultiPlus... not the "updated" MultiPlus II that people are finding some models no longer support Parallel... But it's looking like I'll probably switch to Split Phase anyway, it would seem to offer more utility.

Parallel is handy when you have a large load that a particular inverter can not handle by itself. You see the concept used by Honda in their line of inverter generators. Quite a few people run 2 of the 2200w minis in parallel for their RV's

 

[zanydroid]

Keep in mind 3000 in victron speak is VA, their units are rated to lower W. Starting at 2400W with temperature derating.

 

[MIFARMS]

Keep in mind 3000 in victron speak is VA, their units are rated to lower W. Starting at 2400W with temperature derating.

Yes, I'm on board with that... unfortunately. However, 4,800 watts meets my needs at least for now, but thanks for checking, would not want to burn something over by trying to pull 6,000 watts.

 

[zanydroid]

Victron is a good manufacturer, I think it would just shut down at that point.

 

[MIFARMS]

Parallel is handy when you have a large load that a particular inverter can not handle by itself. You see the concept used by Honda in their line of inverter generators. Quite a few people run 2 of the 2200w minis in parallel for their RV's

In the end I decided to opt for Parallel... and I have that up and running... if I could now figure out how to "see" the output from each inverter... the Cerbo just shows "output"... no Line1, Line2... digging around, but would accept help. Very interested in making sure the output is balanced. I followed (at least attempted to) all the guidance in Wiring Unlimited... all cables are same length, alternated the Inverters and Charge Controllers on the Buss Bar, etc. But would really like to see what each box is contributing

 

[zanydroid]

You would be able to figure out the share if you put a CT on each line just as it comes out of the inverter. Or clamp meter.

2 CTs + energy monitor would be way easier & more scientific. Since it will gather and graph the data for you.

 

[Supervstech]

Keep in mind 3000 in victron speak is VA, their units are rated to lower W. Starting at 2400W with temperature derating.

Since the op is asking about a resistive load, VA is the same as watts.

VA only drops with respect to watts when inductive loads are used.

 

[zanydroid]

Since the op is asking about a resistive load, VA is the same as watts.

VA only drops with respect to watts when inductive loads are used.

That's not how I interpret the datasheet. They're very specific about 2400W

I think the datasheet is saying that it's limited to 2400W active power and 3000VA apparent power (in specific type of load).

 

[Pierre]

My understanding is the Watts is always lower than VA as Watts = V x I x cos of the phase angle ( which is always below 1 ) in an inductive circuit. This is indicative in the table above. Cos of 0 =1 ( current in phase with voltage ) and Cos of 45deg = 0,707 .

 

[TorC]

Agreed, @zanydroid. That datasheet says 2400W, but that's 2400 real watts under most any load, and being clear about the exact power factor up to which it can still handle a 2400W real power load. I have to give them props for clarity as to what their machine will power and what it won't.

 

[zanydroid]

My understanding is the Watts is always lower than VA as Watts = V x I x cos of the phase angle ( which is always below 1 ) in an inductive circuit. This is indicative in the table above. Cos of 0 =1 ( current in phase with voltage ) and Cos of 45deg = 0,707 .

That is true, however Victron is quite consistent in saying that the watt rating is lower than the VA rating. This is similar to UPS that have higher VA than W rating. You cannot exceed either the W nor the VA rating

From Victron stacking guide:
"Up to 6 Multis can operate in parallel to achieve higher power output. Six 48/3000/35 units, for example, will provide 15 kW / 18 kVA"

I think the pitfall with Victron is that a lot of model numbers from other vendors are combined watts rather than VA. Not that the combined watts number in the model number is that useful -- the wattage split is pretty important to understand esp if you intend to push the limits on the equipment. Just look at all the shade thrown at Sol-Ark for their model numbering scheme.