I currently have stacked SW5548 inverters providing power for my house in a off-grid configuration with grid backup. Since my loads were all 120 V, I operated my system from a single inverter for years by connecting both phases in the load center to a single inverter (there is no home-run wiring in my house). This gives me 2:1 redundancy, with the redundant unit cold. Manual switchover is required.

Recently, I added a 2000-W swimming pool pump to the loads I have. It runs 9 hours per day for about seven months of the year. This has complicated my configuration somewhat, since I believe a single SW5548 would run it's fan continuously if it had to handle this load together with the rest of the house, making it even noisier than normal. As a result, I have connected the pool as a 240 V load and run both inverters stacked. This works fine for summer, but I am now switching to the single-inverter configuration for winter to improve efficiency. This is yet another manual system task on which I had not counted. The lack of non-volatile memory in the SW5548 makes this more of a pain in the spring.

So now OutBack has the FX-2000 inverters. It appears to me that they can address this situation by allowing me to operate with a 120 V configuration year-round.

Here is how I see the comparison:

Benefits of SW5548:

Paid for and wired in.
Operating fine.
Established reliability.
Cheaper (At least when I bought them in 1999 they were about $2600 each.)
Fewer units to wire.
Very high low-power efficiency (>90% at 100 W and >97% at 500 W based on Sandia Labs testing) (I'm guessing, based on topology, that the FX-2048 efficiency will be lower at this power level, but I cannot be sure since OutBack still has not reported their efficiency curves.)

Benefits of FX-2048:

Can readily stack up to four for 120 V operation.
Operation can be optimized for efficiency or reliability using MATE, without reconfiguring the hardware.
Better efficiency at high power levels (again, this is a guess).
No fan (less noise, better reliability).
Sealed. No insect cocoons creating failures.
Quieter, even with SW fan off. (Is this true?)
Nonvolatile memory.
Designers still employed by manufacturer (a big plus, IMO).

Anyway, I think I could get by with three FX-2048s and a MATE. I doubt I'm likely to change until I have a failure with the SW inverters, but I'm one to plan ahead. I assume this is one of the markets Outback wants (replacing failed SWs, that is).

Any thoughts on my reasoning here? Additions? Corrections?

TIA,

George

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> Originally posted by George Estep:
Very high low-power efficiency of the SW5548 (>90% at 100 W and >97% at 500 W based on Sandia Labs testing) I'm guessing, based on topology, that the FX-2048 efficiency will be lower at this power level, but I cannot be sure since OutBack still has not reported their efficiency curves.[b]<HR></BLOCKQUOTE>

The SW efficieny numbers you are mentioning are based on operating as an inverter (off-grid) not when it is selling power back to the utility grid.

The efficiency for the OutBack FX2024 is lower at the very low power levels but is higher at high power / full load. A single FX2000 hits 90% at about 400-500 watts but stays over 90% all the way to 2500 watts (125% of the full power rating). An SW5548 drops to 90% at 4000 watts and runs at about 86% at full power (5500 watts).

Since we can turn of excess capacity when running at low load levels, including additional units for 120/240 vac or redundancy does not impact the efficiency significantly. We also can signal an automatic transfer from one inverter to another if an error occurs, using our AUX output and a double throw contactor.

For the pump with either the SW or FX inverters you could install a X-240 step-up autoformer to allow you to operate from a single inverter.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>[b]Benefits of FX-2048:

Can readily stack up to four for 120 V operation.
Operation can be optimized for efficiency or reliability using MATE, without reconfiguring the hardware.
Better efficiency at high power levels.
No fan (less noise, better reliability).
Sealed. No insect cocoons creating failures.
Quieter, even with SW fan off.
Nonvolatile memory.
Designers still employed by manufacturer (a big plus, IMO). <HR></BLOCKQUOTE>

Actually the designers are not employed by OutBack - they are OutBack! [img]images/smiles/icon_wink.gif[/img]

The FX2000 is much quieter than the SW - with or without the fans on (there is an internal fan in the FX2000). The efficiency at high power is considerable higher - increasing the system efficiency.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote

Yes that is a market we expect to have a lot of business from... A pair of FX2000s fit in the "footprint" of an SW inverter. With the DCA and ACA installed - it is the exact same length (although the conduit knockout locations are a bit off).

What you should do depends on how you are operating our system - are you net metered or do you operate in the LBX mode or similar strategy and not sell power back to the utility? Let me know...

[img]images/smiles/icon_cool.gif[/img]

[ December 01, 2002: Message edited by: Christopher Freitas ]

Thanks for providing more details on the FX2000s, particularly the efficiency information.

Yes, I am discussing application as an inverter. As indicated, I operate off-grid with grid backup (LBX). (BTW, is this forum meant to be for grid-tie applications only?)

I personally think that the low-power efficiency performance is a key figure-of-merit for inverters for off-grid applications. In such applications (like mine) a 10 kWh/day energy budget equates to an average power level of about 400 W. This is not what I would call a small system, BTW. That means that most of the time, the inverter is operating at 100 to 200 W. Occasionally, one or multiple larger loads (well pump, microwave, washer, etc.) will come on line, but the power level rarely goes above 4 kW. (I'm talking about the case *without* the pool pump, which is more typical for off-grid applications. Even with the pool operating, the pump is normally off.)

The point is that much of the energy used is at low power levels, making low-power efficiency very critical. It seems to me that OutBack could easily address this issue by building a low power member of the FX series that could operate in parallel with the FX2000. Say, 500W. That unit could operate all of the time and the high-power inverters could be brought online automatically by the MATE to handle the high-current loads. (This assumes that FX inverters can be brought on-line seamlessly. I'm guessing they can, based on your literature and your comments.) In that way, you could preserve all of the other benefits provided by your design approach while not adversely affecting off-grid efficiency. IMO, it would be O.K. to build such an inverter with the same footprint as the larger inverters to enhance your economies of scale.

Any thoughts on this subject?

George

Yes - low power efficiency is critical for off-grid applications. For most people, more watthours are converted at low watt levels than at high. There are tradeoffs in the design.

It would be easy for us to offer a low idle / low output watts version of the FX2000. It is something we have considered as well for applications where high surge power is not required - such as when running purely electronic loads. We could then get the idle down to under 10 watts and turn on additional standard FXs as the AC loads increased.

The transistion is very minor - much less noticeable than other inverters which have used a separate co-inverter to handle low power loads.

We also are still working on some ways to reduce the low power "idle" consumption. We have fielded several designs of the FX2000 with different methods, but maintaining high power quality and regulating the AC output when in the low power mode is proven harder than we hoped...

Thanks for your interest!

[img]images/smiles/icon_cool.gif[/img]

Thanks again, Christopher! It's refreshing to get straight answers to product questions. When I've posed similar questions to Trace in the past my questions fell on deaf ears. (No offense meant to Tobin.)

Clearly we are on the same page here. You mentioned "power quality": That is one benefit of your inverter that I failed to mention in my original post. I have had one appliance which did not work properly with the waveform from the SW inverters. I'll continue to keep a close eye on your products as they become available.

BTW, I have another application for a sealed inverter in the 500 VA range that could have reasonable volume. A low-power FX inverter might be able to fit the bill if it can be reasonably priced.

Thanks again,

George

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Tobin Booth:
We have a very competent engineering staff here at Xantrex, so don't let those folks outback lead you to think otherwise.
<HR></BLOCKQUOTE>

Yes - but only because your still hanging in there... Then we will see.

(P.S. Don't forget who got you your job at Trace...)

[img]images/smiles/icon_smile.gif[/img] [img]images/smiles/icon_wink.gif[/img]

Hi George,

I fully agree with you, high efficiency at low power level is crucial for an off-grid application.

We have a very competent engineering staff here at Xantrex, so don't let those folks outback lead you to think otherwise.

Best, Tobin, Xantrex Tech [img]images/smiles/icon_razz.gif[/img]

You can bet, I shall always remember!

All the best for 2003,

Tobin

Tobin - I wish you well at your new job in California and will drop by to visit next time I come through.

Christopher

I Agree that a low draw mode is an important buying point for an inverter system.

We are planning on buying an off grid system in the next year.

Do you think that Outback will have this feature available by then?

We'd like to start with the smaller model and then purchase a larger module.

Regards, Graham