Auto Transformer based all-in-ones (how do they handle ground?)

[fafrd]

1) 2.7A x 120V = 324W being handled by the transformer, coupled between leads by winding. That isn't dissipation by the transformer.
Dissipation might be 1% of that for light load. At full load, maybe 5% or possibly 10%.

I’m showing my ignorance, but would appreciate the opportunity to learn from you.

My logic was that 2.7A flowing through the coil of the Autotransformer translates to 324W flowing through the transformer that otherwise would being going out to the utility pole.

I guess your point is that the majority of that power of flowing out to the load so only 1% or less is getting lost as heat in the Autotransformer itself, correct?

I^2R losses would probably be the easiest way to calculate energy lost to heat but I’m not finding any spec on wire size used in these Autotransformers.

The Solis Autotransformer is rated for a maximum of 30A, so that must mean at least 12AWG, but without any idea of wire length, it’s not possible to translate that AWG into coil resistance.

Full load of 30A would translate to 900R Watts being lost when maxed out @ 3.6kW, so 5% would be 180W or 0.2 Ohms of resistance in the coil while 10% would be 360W and 0.4 Ohms of coil resistance.

So 2.7A translates to 1.46-2.9W of losses when 324W are being balanced, so 0.5-0.9%. Understand and thanks.

If it is a 3kW transformer handling 300W, maybe it dissipated 3W.
If handling 10x the watts, 3000W, and 10x the current, power dissipation in windings goes as current squared, so could be 100x the dissipation, 300W dissipated.

Yes, understand. The power loss is immaterial and really nothing to worry about unless the Autotransformer is frequently being maxed out…

2) If the autotransformer has breakers sized for its rating, and if the wire(s) connecting its neutral have ampacity 2x that breaker rating, it won't be a hazard.

So hanging an Autotransformer off of the main panel or a critical loads subpanel with double-pole breakers sized for 30A will be safe as long as the wiring used is rated for 60A (6AWG).

The whole narrative about ‘loops’ being formed with the utility pole transformer as well as the narrative about the Autotransformer and the utility pole transformer possible having slightly different numbers of windings to their center taps is really nothing to be concerned about, would you agree?

If it does draw more current than it can handle (trying to balance the grid) it will trip the breaker protecting itself. Just make sure your 120V loads fed by the autotransformer also get disconnected along with it.

I’m not understanding this. In the example shown in the video I linked to, the Autotransformer was drawing ~324W from an imbalance being created by a 1.875kW hair dryer, do the Autotransformer was absorbing 17.3% of the imbalance and the other 82.7% was being handled by the utility pole transformer.

For whatever reason, the breaker to the Autotransformer trips - why is it important to disconnect the hairdryer? The Autotransformer is functioning no differently than a load on one leg and a source (inverter) on the other leg - I’m not understanding why it’s important to disconnect loads and if the breaker protecting the Autotransformer trips (when on grid)?

Off-grid is a different matter, but that’s not a priority for me (perfectly happy handling any backup needs at 120VAC only).

3) Exactly.

If my toroid transformers are 0.5% regulation like that data sheet I found, I think they are more likely to see over-current and trip the breaker. Conventional E-core transformer would have longer windings, looser regulation, less likely to overload itself. With load tests and considering voltage tolerance at which inverter disconnects from grid, I could probably determine which would happen first.

If an Autotransformer is sized to handle a multiple of maximum imbalance, it seems low power loss would be inconsequential and breaker will pretty much never get tripped. In my case 3 1.8kW loads running off me leg at the same time is a realistic worst-case for my imbalance, so 5.4kW of worst-case imbalance translating to less than 20% of what a 30kW Autotransformer can handle (less when grid-tied, since the majority of imbalance will be handled by the utility pole transformer).

If someone has a 120V inverter, auto-transformer could be safely used to get 120/240V split-phase on the output.

I’m now starting to think about the Victron Multiplus II 120Vx2. I’m perfectly fine with backing up at 120VAC only, so my critical loads panel consisting of 120VAC only loads can be served by the same 120VAC backup power on both legs (just make sure there are no branch circuits)

My bigger concern is grid-side load offset when grid tied.

With no Autotransformer, the Multiplus II 120x2 will be exporting power on one leg sufficient to offset consumption on the other leg.

So at 240VAC, consumption will be zero, but there will up to 3kW being exported on one leg to balance up to 3kW being consumed on the other leg.

On a more practical basis, when my 3kW heating element from my 240V electric oven fires, the inverter will push a full 3kW out of it’ AC input, resulting in 1.5kW being exported on the inverted leg while 1.5kW is being imported/consumed on the other leg.

I’d consider adding an Autotransformer if that would get both legs down to 0kW being imported or exported, but any Autotransformer is only going to handle a percentage of the imbalance when grid-tied, so it’s really not adding much of anything.

Exporting 1.24kW on the inverted leg really isn’t any different than exporting 1.5kW (and the 240VAC consumption is going to be 0kW in either case…

With a 240V single-phase inverter (european model), auto-transformer on input could make 240V, and auto-transformer on output could make 120V.

While grid-tied, the biggest advantage I see for 240VAC versus 120VAC is that my existing grid-tied PV is 240VAC (Microinverters) so a 24VAC AIO with ability to charge a battery from 240VAC can absorb any excess solar production beyond that needed to serve loads without adding imbalance.

But since the loads will not be balanced, zeroing-out export will result in one leg having export while the other leg has offsetting import in any case. So I’m really not seeing any advantage to a 240VAC hybrid system over a 120VAC hybrid system when grid tied.

And when off-grid, 120VAC is easer for backing up 120VAC only than doing so from 240VAC.

The only advantage I see to a 240VAC hybrid is if you want to back up 240VAC and 120VAC loads (in which case you should really go with a split-phase hybrid).

You can go single-phase 120VAC or 240VAC with an Autotransformer but then you do need to pay attention to what happens when the breaker protecting the Autotransformer trips (especially if serving 120V loads from 240VAC with an Autotransformer.

I’m curious whether you see any negatives to 120VAC hybrids used to offset split-phase consumption (when on-grid).

The only one I’ve come up with is that the currents being injected into the main panel will be twice as high when inverting 3kW to 120VAC rather than 240VAC (though 25A seems pretty manageable).

 

[Hedges]

Off-grid, if auto-transformer is what defines neutral, you don't want auto-transformer to disconnect by breaker tripping without also disconnecting 240V power to panel. Otherwise, your hair dryer on one phase and small gadget on other phase divide voltage unevenly.

On grid, auto-transformer may or may not help with anything, and may or may not try to rebalance grid. If it has 2-pole breaker sized for its rating and neutral has 2x the ampacity it should be OK. My concern would be it running too hot but not tripping breaker, could damage insulation over time. If it tries too hard (due to very low resistance like that toroid I linked), it could trip breaker. If that is possible, I'd rather isolate auto-transformer while on grid.

I think it is OK if you have zero net export, with equal kW exported on one leg and imported on the other. Don't think the utility is paying attention.
A isolation transformer would eliminate that, so only true net export or import goes through the wires.

I've been browsing a bit. You can get 25kVA, 240/480 primary 120/240 secondary used for around $400 plus shipping.

 

[fafrd]

Off-grid, if auto-transformer is what defines neutral, you don't want auto-transformer to disconnect by breaker tripping without also disconnecting 240V power to panel. Otherwise, your hair dryer on one phase and small gadget on other phase divide voltage unevenly.

For sure, if you are off-grid or running backup when grid is down and you are generating 120VAC from 240VAC, you fin’t want to disconnect Autotransformer leaving 120VAC loads connected.

Using as Autotransformer to step 120VAC up to 240VAC it’s less important to disconnect loads if Autotransformer trips (since the Autotransformer is just supplying 240VAC loads and only they will get shut down from lack of power without a connected Autotransformer).

On grid, auto-transformer may or may not help with anything, and may or may not try to rebalance grid. If it has 2-pole breaker sized for its rating and neutral has 2x the ampacity it should be OK.

Meaning nothing to be worried about as far as ‘loops’ or different center-taps, correct?

My concern would be it running too hot but not tripping breaker, could damage insulation over time. If it tries too hard (due to very low resistance like that toroid I linked), it could trip breaker. If that is possible, I'd rather isolate auto-transformer while on grid.

Since I don’t need 240VAC loads running when grid is down, I’m seeing less and less attraction to an Autotransformer or even a 240VAC hybrid inverter…

I think it is OK if you have zero net export, with equal kW exported on one leg and imported on the other. Don't think the utility is paying attention.

Yeah, most utility meters are only reading L1+L2 through the same CT sensor, so they have no easy way to determine 0kWh versus +X kWh on one leg and -XkWh on the other leg…

A isolation transformer would eliminate that, so only true net export or import goes through the wires.

I've been browsing a bit. You can get 25kVA, 240/480 primary 120/240 secondary used for around $400 plus shipping.

Appreciate the suggestion but I’m just seeing the need for a transformer in my application.

As long as the increased currents are safely and appropriately managed, a 120VAC ESS solution is looking more and more like the easiest way to capture and use solar energy you don’t want to export…

 

[Hedges]

For sure, if you are off-grid or running backup when grid is down and you are generating 120VAC from 240VAC, you fin’t want to disconnect Autotransformer leaving 120VAC loads connected.

Using as Autotransformer to step 120VAC up to 240VAC it’s less important to disconnect loads if Autotransformer trips (since the Autotransformer is just supplying 240VAC loads and only they will get shut down from lack of power without a connected Autotransformer).

Unless, you have 120V loads on both phases.
Then it's like feeding 120V from generator into one phase of a breaker panel. Other phase 120V loads connect in series with 240V loads, get 120V for the series combo (brownout.)

Meaning nothing to be worried about as far as ‘loops’ or different center-taps, correct?

It may protect itself. It may run too hot. "Circuit breakers protect wires, not electronics." (or not transformers, in this case.) I'd rather have a thermostat triggering remote trip of breaker.

 

[fafrd]

Unless, you have 120V loads on both phases.
Then it's like feeding 120V from generator into one phase of a breaker panel. Other phase 120V loads connect in series with 240V loads, get 120V for the series combo (brownout.)

I’m not understanding this. Obviously there is a potential issue when the hybrid switches from in-phase 120V to out-of-phase 120V when grid comes back up (as well as the reverse when grid goes down, but a 240VAC panel can be powered on both legs with a single 120VAC supply (as long as there are no branch circuits).

That is exactly what Victron’s new Multiplus II 120x2 hybrid is designed to do: https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-3kVA-2x120V-EN.pdf

 

[Hedges]

I’m not understanding this. Obviously there is a potential issue when the hybrid switches from in-phase 120V to out-of-phase 120V when grid comes back up (as well as the reverse when grid goes down, but a 240VAC panel can be powered on both legs with a single 120VAC supply (as long as there are no branch circuits).

That is exactly what Victron’s new Multiplus II 120x2 hybrid is designed to do: https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-3kVA-2x120V-EN.pdf

yes, you can feed both phases of a panel with the same 120V phase, so long as no circuits have one shared white neutral between two hots red & black. Any 240V appliances see zero, so stay off. Dryer would likely run controls and motor, but not make heat.

Is your plan 120/240V split-phase from grid feeds the panel, but when grid is down you switch it onto a 120V only inverter? Easy to do with an interlocked backfed breaker. Or do you have a mechanism to do that automatically?

More likely, you mean to put in a 120V inverter and feed it to a panel dedicated to single phase 120V loads, so it never sees 240V.
Likely, your inverter doesn't put out more than 50% of panel amperage rating. If it does, be careful with how neutral is fed and allocated to circuits on L1 and L2 busbars, which are going to both be same phase.

 

[fafrd]

yes, you can feed both phases of a panel with the same 120V phase, so long as no circuits have one shared white neutral between two hots red & black.

Yes, those are commonly called ‘branch circuits’ (two hot legs with a common neutral return). Need to avoid and branch circuits on a panel that can be powered both legs to the same 120VAC source.

Any 240V appliances see zero, so stay off. Dryer would likely run controls and motor, but not make heat.

Is your plan 120/240V split-phase from grid feeds the panel, but when grid is down you switch it onto a 120V only inverter?

That’s what I’m starting to consider. But backup is really a secondary priority. Primary priority is an ESS to minimize export by charging a battery with excess solar production and using stored energy to offset consumption overnight.

Easy to do with an interlocked backfed breaker. Or do you have a mechanism to do that automatically?

Again, backup power is not a high priority. I don’t mind needing to flip a few breakers and switches manually for the once-a-year we might benefit from backup power…

If the hybrid I want to for ESS also provides automatic backup in those rare instances it’s needed, I won’t say no (as long as it doesn’t add too much to the cost).

More likely, you mean to put in a 120V inverter and feed it to a panel dedicated to single phase 120V loads, so it never sees 240V.

Yes, if I do end up with a hybrid supporting ‘automatic’ backup capability, wiring up a small critical loads panel with the 120V loads we need to use during an outage would be the sensible thing to do.

Likely, your inverter doesn't put out more than 50% of panel amperage rating. If it does, be careful with how neutral is fed and allocated to circuits on L1 and L2 busbars, which are going to both be same phase.

3kW would be more backup power than we’d ever need, so no concerns at all about the critical loads panel.

The greater concern is consumption offset when on grid.

Offsetting up to 3kW @ 120V means the hybrid will often be injecting 25A into one leg of the main panel.

That’ll only going to happen when net grid import is zero of close to it, but that amount of input power would put me a bit over the 120% rule.

I might be willing to reduce my main breaker from 100A to 80A if there is any real safety concern, but that’s the one issue I’m still struggling with…

 

[Hedges]

And a 30A or 35A breaker. Not that I'd be very worried, and rules were made to be broken.
Just get a transformer, 3kW 240V isolation 120V. That way your 25A splits evenly, 12.5A per leg at 240V.

(This will contribute to the issue I previously described of utility split-phase transformer acting as auto-transformer and feeding back extra current on neutral.)

edit: I would argue that a 35A breaker feeding one phase from far end of busbar, and neutral feeding far end of busbar, can't overload anything. Unlike feeding 240V from far end of both phase busbars which could overload neutral.

 

[fafrd]

And a 30A or 35A breaker. Not that I'd be very worried, and rules were made to be broken.

Yeah, I’ld put a 30A breaker in the existing subpanel on the connection to the hybrid (AC input).

That subpanel is connected at the top of my main panel, so I should also reposition it’s breaker in the main panel down near where the 240VAC AC-coupled solar comes in (since it can now be a source of power, not merely a load).

As your excellent post pointed out earlier, the 120% rule is enormously conservative for the main lugs themselves - a 200% rule would have been feasible. So it’s really all about the neutral current when your maxed out I’d need 100A coming in from the grid + 20A from my grid-tied solar + 30A coming in on one 120V leg of the hybrid to be at 150% of panel rating and then I’d need 150A of loads on that one leg and no loads on the other leg (since 120V loads on out-of-phase legs cancel each other out).

I don’t believe I have a total of more than 100A of 120V breakers on either leg now, and as long as I load my 20A breakers onto the leg without 120V hybrid input, I will never be able to drive more than 100A into the neutral busbar.

Just get a transformer, 3kW 240V isolation 120V. That way your 25A splits evenly, 12.5A per leg at 240V.

I’m not seeing the need for that additional complexity and expense. A realistic worst-case scenario is the electric oven consuming 3kW @ 240VAC - in this situation I’l be injecting 25A into one leg translating to 12.5A being exported while 12.5A is being imported from grid for he other leg. So I’ve got a total of 25A or 3kW of imbalance being handled by the utility transformer.

My current worst-case imbalance is 3x1.8kW or 5.4kW, 180% of this level, and I’ve never had an issue.

As long as I skew my likely load imbalance onto the same 120V leg being supplied by the hybrid, I should never have more imbalance than I’m dealing with today.

My two fall-back plans would be to add a transformer, as you are suggesting, or to reduce my main breaker from 100A to 80A.

Especially if I am still on an export agreement that is costing me something every month, I might as well take advantage of the transformer the utility has put at my disposal…

(This will contribute to the issue I previously described of utility split-phase transformer acting as auto-transformer and feeding back extra current on neutral.)

I’d assumed that whatever balance current is not flowing in the neutral wire to the center tap of the Autotransformer was flowing on the neutral wire to the utility tranaformer, but this cannot be correct.

There is a bond to a short 6AWG wire clamped to an 8’ copper ground right at the connection between house neutral and utility neutral, and the majority of the neutral current is probably flowing there.

So if you have 25A of imbalance at your main panel, the actual imbalance current being seen by the utility transformer is probably a fraction of that…

edit: I would argue that a 35A breaker feeding one phase from far end of busbar, and neutral feeding far end of busbar, can't overload anything. Unlike feeding 240V from far end of both phase busbars which could overload neutral.

Yes, I agree, as long as the feed-in breaker has been positioned at the far end of the busbar.

If there are no loads at all connected to the leg with the 25A or 30A of 120V power injection, that injected power goes straight out to to the utility transformer with no impact on neutral in the panel at all (trying to pull neutral it’s way, but only with 30A max).

So as long as the maximum loads on that leg (sum of breakers, including any sub panels) is within the rating of the panel, neutral busbar can never exceed 100% of rating.

Did you ever understand the rationale for the 120% rule? Was there a +20% safety factor designed into the sizing of the neutral busbar versus the main lugs?

 

[Hedges]

Yes, I agree, as long as the feed-in breaker has been positioned at the far end of the busbar.

And neutral similarly at far end of neutral busbar. (assumes single busbar, not center-driven like my larger panels have.)

Did you ever understand the rationale for the 120% rule? Was there a +20% safety factor designed into the sizing of the neutral busbar versus the main lugs?

Before solar and backfeed, it would have been 100% rule.
I read the NEC guys realized 200% could work, but were concerned in the future someone might relocate PV breaker adjacent to main breaker. 2x current would mean 4x heating of busbar.
I think 20% over, 120%, was to allow a reasonable PV addition to existing panels. If breaker gets relocated, would be 1.44x heating, not catastrophic.
Everything is somewhat conservative, and gets tested at some overload for listing. I'm not sure of neutral vs. hot busbar margin differences, but undersizing neutral feeder I think is sometimes done. I think 125A panel uses one neutral busbar, while 225A panel has two of same size, one on each side center driven.

The fact backfeeding a split-phase transformer (either auto or isolation) boosts current in neutral isn't something I've read about, figured out the significance for us recently.

 

[fafrd]

And neutral similarly at far end of neutral busbar. (assumes single busbar, not center-driven like my larger panels have.)

The neutral busbar in my main panel is just a bar with a log sequence if holes in it. Neutral wires are no placed into the neutral busbar in any kind of ‘order/sequence’.

Upgrading the size/rating of the neutral bus bar is probably one of the easiest upgrades possible (or adding a second neutral busbar in parallel).

Before solar and backfeed, it would have been 100% rule.
I read the NEC guys realized 200% could work, but were concerned in the future someone might relocate PV breaker adjacent to main breaker. 2x current would mean 4x heating of busbar.
I think 20% over, 120%, was to allow a reasonable PV addition to existing panels. If breaker gets relocated, would be 1.44x heating, not catastrophic.

So all determined by overheating concerns on the main lugs - nothing to do with neutral?

So 150% or even 200% should be safe as long as the neutral busbar is sized to take that amount of current. The neutral busbars have so many holes/slots I can believe that’s a big problem… (or purchase a neutral busbar for a 200A panel and install it in your 100A panel…).

Everything is somewhat conservative, and gets tested at some overload for listing. I'm not sure of neutral vs. hot busbar margin differences, but undersizing neutral feeder I think is sometimes done. I think 125A panel uses one neutral busbar, while 225A panel has two of same size, one on each side center driven.

When in doubt, swapping in a double-rated single or double neutral busbar seems like an easy way to avoid any concern…

My incoming neutral wire is sized like my L1 and L2 wires, so it’s really just a question of the cross-section of the aluminum…

And I see you are right, you want the additional sources including PV and hybrid to have their neutral wires tied to the opposite end of the neutral busbar. That way any 120V loads in between consecutively reduce the current density…

The fact backfeeding a split-phase transformer (either auto or isolation) boosts current in neutral isn't something I've read about, figured out the significance for us recently.

Neat trick!

 

[robby]

Interesting thread but I am still not sure how the current loses can be that low based on the heat I saw generated in Ian's video. It would seem to me that it would take a lot more energy to get the temperature of the transformer so high.

 

[Hedges]

Depends on rate of heat loss. If losses are low, low power dissipation over a long time adds up to high temperature.

Losses in copper are I^2 x R, goes up with the square of current. Not sure about core losses.
Figure at 1/2 of rated current, 1/4 rated temperature rise.
If 30 degree C ambient has rise to 90 degree C at full load (60 degree rise, figure only 15 degree rise at 1/2 rated current. 4 degree at 1/4 rated current.

What temperatures was he seeing?
Fan cooled, or passive?

 

[robby]

Depends on rate of heat loss. If losses are low, low power dissipation over a long time adds up to high temperature.

Losses in copper are I^2 x R, goes up with the square of current. Not sure about core losses.
Figure at 1/2 of rated current, 1/4 rated temperature rise.
If 30 degree C ambient has rise to 90 degree C at full load (60 degree rise, figure only 15 degree rise at 1/2 rated current. 4 degree at 1/4 rated current.

What temperatures was he seeing?
Fan cooled, or passive?

Passive cooled and measuring 237 degrees under extreme imbalance.

 

[Hedges]

Big transformers tend to be more efficient.
For 75 kVA, this shows 0.5 kW to 2 kW losses.
It mentions some designed for 80 degree C rise, some for 150 degree C rise. Nothing like how we run our wires, maybe 60 degree rise!
Compare his 237F (114 degrees C)

Electrical: Energy Efficiency - Temperature Rise and Transformer Efficiency

All devices that use electricity give off waste heat as a byproduct of their operation. Transformers are no exception.

www.copper.org

If you do run 1.2x rated current, expect 1.44x the temperature rise.
Obviously, fan cooling would be a good idea, also thermostat tripping breaker in case fan fails.
All that is available, in an engineered unit for a fair price.

https://www.solar-electric.com/lib/wind-sun/VE-Manual-Autotransformer-32A-100A.pdf

 

[robby]

Big transformers tend to be more efficient.
For 75 kVA, this shows 0.5 kW to 2 kW losses.
It mentions some designed for 80 degree C rise, some for 150 degree C rise. Nothing like how we run our wires, maybe 60 degree rise!
Compare his 237F (114 degrees C)

Electrical: Energy Efficiency - Temperature Rise and Transformer Efficiency

All devices that use electricity give off waste heat as a byproduct of their operation. Transformers are no exception.

www.copper.org

If you do run 1.2x rated current, expect 1.44x the temperature rise.
Obviously, fan cooling would be a good idea, also thermostat tripping breaker in case fan fails.
All that is available, in an engineered unit for a fair price.

https://www.solar-electric.com/lib/wind-sun/VE-Manual-Autotransformer-32A-100A.pdf

Agree but just wanted to know the loses based on the Autotransformer that Signature Solar is offering with their inverter. The Victron transformer cost almost as much as the 5000ES Errr.. US.. Inverter.

 

[Hedges]

Agree but just wanted to know the loses based on the Autotransformer that Signature Solar is offering with their inverter. The Victron transformer cost almost as much as the 5000ES Errr.. US.. Inverter.

Anybody who's got one and can do a 4-wire resistance measurement of the windings could determine that.
Or just load it to a known 120v wattage and measure voltage difference between the windings.

 

[John Schmidt]

No it is a fully isolated transformer, input is around 55v AC as derived from the battery and driven by the MOSFETS.
Secondary is 120-0-120.

In theory, even the high frequency inverters are fully isolated as they have an output transformer too that fully isolates between the switched saw/square/sine input voltage and the secondary 120 or 240v that is a ragged sine wave.

When Will opened it up, it sure looks like an auto-transformer. Only three connections. Where did you get your info? I may be wrong, but it sure looks like an auto-transformer. Can you provide your resource that says (and shows) that it is a fully isolated transformer? Thank-you.

 

[Bud Martin]

In Will video I believe you cannot see the Dc side driver winding.
Here is the simplified LF transformer based block diagram.
Both LF and HF inverter design has isolation transformer/s to isolate low DC driver side from AC output side.

High frequency vs low frequency pure sine wave inverter & difference explanation

High frequency vs low frequency pure sine wave inverter & difference. Transformer based Vs Transformerless, circuit definition.

www.sigineer.com

 

[John Schmidt]

In Will video I believe you cannot see the Dc side driver winding.
Here is the simplified LF transformer based block diagram.
Both LF and HF inverter design has isolation transformer/s to isolate low DC driver side from AC output side.

You are right. The DC side can't be seen. Obvious now that you pointed it out to me! Thank-you. The LV6048 seems really nice, but I wish that it could accept a higher DC voltage. My panels are 300 feet from the house, and the higher voltage lets me use a smaller gauge wire. The GroWatt SPF 6000T DVM-MPV can take 250vDC. I might consider that unit.