FX Inverters, AC Current, and Power Factor

Discussion about OutBack Inverters in Off Grid Applications

Moderators: OutBack, OutBack Moderator Team

Post Reply
User avatar
crewzer
Forum Emperor
Posts: 1927
Joined: Mon Sep 27, 2004 10:50 am
Location: Vienna, VA

FX Inverters, AC Current, and Power Factor

Post by crewzer » Sat Jul 21, 2007 7:11 am

Recent performance and operational issues concerning OutBackÔÇÖs FX inverter/chargers, various generators, input current, and the chargers' power factors were discussed in this thread. I decided to test my FX2524T inverter/charger to check relevant performance parameters. My small generator wasnÔÇÖt particularly cooperative this morning, so I used the grid for an AC power source. I used my Kill-A-Watt meter to measure AC input values, my Link-10 battery monitor to measure DC output values, and the Mate readings for the AC<->DC values. Here are the results of my tests.

Relevant FX2524T specs: 120 VAC, 60 Hz, 2,500 VA inverter; default aac = 12 A, max aac = 14 A; max DC charge current = 55 A, 24 VDC nominal

Table Format:

Test #
aac setting (via Mate) / AC Amps indicated
AC Watts indicated / AC VA Indicated / Power Factor Indicated
DC Volts Indicated / DC Amps indicated / Mate AC<-> DC Power Indicated

Test #1
4 aac / 6.44 A
580 W / 770 VA / 0.75 PF
26.1 V / 18.9 A / 0.4 kW

Test #2
9 aac / 12.1 A
1,300 W / 1,460 VA / 0.89 PF
26.9 V / 42 A / (not recorded)

Test #3
10 aac / 12.5 A
1,350 W / 1,505 VA / 0.89 PF
26.9 V / 43 A / 1.2 kW

Test #4
11 aac / 13.8 A
1,530 W / 1,650 VA / 0.92 PF
27.1 V / 48.5 A / 1.3 kW

Test #5
12 aac / 14.3 A
1,585 W / 1,700 VA / 0.93 PF
27.1 V / 50 A / 1.4 kW

Test #6 (test terminated)
12 aac / Input current > 15 A limit of meter

My inverter draws more AC current than the "aac" settings would indicate. The indicated power factors explain some of the differences, and I have no idea about the accuracy (nor the repeatability) of the various "aac" settings. Default "aac" settings lower than maximum available "aac" settings may be a result of this behavior. This behavior should be taken into consideration when specifying breaker/fuse sizes and generator power ratings.

The inverter/chargerÔÇÖs indicated power factor is not pretty at low "aac" settings, but I suspect that such settings are not often applied. The 0.93 power factor performance at my inverterÔÇÖs default 12 aac setting doesnÔÇÖt appear to be too bad.

Now, back to that generator :???: :-k

HTH,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.

Kent Osterberg
Forum Emperor
Posts: 1523
Joined: Mon Jun 09, 2003 11:01 pm
My RE system: SMA Sunny Boy 2500 with eight Mobil Solar Ra 180 modules
Location: Cove, Oregon
Contact:

Post by Kent Osterberg » Sat Jul 21, 2007 7:57 am

Jim,

Great information here. Thanks for the data. This data is consistent with what I've noticed when setting up the FX to work with customer's generators. You have to set the aac a little lower than you would expect.

I'll postulate an explanation. If the FX is only measuring to the nearest amp and the data are truncated in that measurement, the actual amps would typically be 0.5 to 1.0 amp higher than the aac setting. Second, maybe the current measurement is of real (in phase amps) rather than actual amps. That would increase the discrepancy to a couple amps.

In any regard your data show that the aac setting needs to be a couple amps lower than the desired maximum current. And the power factor of the FX charger isn't particularly bad. A power factor of 0.9 is decent.

User avatar
GreenerPower
Forum Guru
Posts: 415
Joined: Wed Jun 13, 2007 9:22 am
Location: Texas
Contact:

Post by GreenerPower » Sat Jul 21, 2007 8:44 am

Good data, crewzer. I'm glad to see that performance at typical installation settings.
My test for inverting ~2300W on my GX3648 also comes to ~90% efficiency, consistent with the published CEC data.
Be greener and may the force be with you

sparky
Forum Emperor
Posts: 1216
Joined: Fri May 20, 2005 8:24 am
My RE system: OFFGRID SOLAR "we go where power lines don't" Design, consulting, and installation advice on 300+ Offgrid homes.
Location: Sierra Mountains near Mariposa Ca. Webpage on next line
Contact:

Post by sparky » Sat Jul 21, 2007 11:28 am

Jim,

I guess I am going to be pessimistic and suggest the data would be more valuable if the batteries were discharged deeper. On your 24V system I would want to see them at 25 volts or so going up. That is when they are really affecting the power factor of the charger. Using various generator sizes and makes would give data based on the source impedence of the generator over a grid tie input that will not be effected by temperature.

My humbe opinion is it will be hard to make this charger better without adding the weight of bigger electronic components. Since fairly low weight compared to the competition is a strength of the Outbacks I am willing to give them a break here.

When you get the generator running set the washing machine to spin cycle and plug-in your laptop :wink:

User avatar
crewzer
Forum Emperor
Posts: 1927
Joined: Mon Sep 27, 2004 10:50 am
Location: Vienna, VA

Post by crewzer » Sun Jul 22, 2007 5:03 am

Gents,

Thanks for your comments!

With the help of my oldest son and his rapidly increasing mechanical skills, I was able to repair my generator yesterday morning. :grin: Turns out the carburetor float was stuck ÔÇ£openÔÇØ and would not close its valve.

It may be a couple of weeks before I can conduct additional tests. But, the results appear to be informative and useful, so IÔÇÖm glad to do them. However, my ÔÇ£smallÔÇØ system may not be representative of typical larger system performance, so let me throw out a request for similar tests and data from larger systems.

I agree the inverter/charger seemed to perform well at its higher charge current settings.

Sparky,

My 24 V x 400 Ah battery bank was ~33% discharged when I started the experiment. The battery voltage under light load was 24.6 V before I started up the inverter/charger, and it quickly climbed to and indicated voltage of >26 V (depending on charge current; see test results above) after I engaged the charger. I suspect the ÔÇ£highÔÇØ indicated charge voltage is a characteristic of my ÔÇ£smallÔÇØ AGM battery bank and its SOC.

Thanks again,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.

User avatar
GreenerPower
Forum Guru
Posts: 415
Joined: Wed Jun 13, 2007 9:22 am
Location: Texas
Contact:

Post by GreenerPower » Mon Jul 23, 2007 5:24 am

sparky wrote:When you get the generator running set the washing machine to spin cycle and plug-in your laptop
This would just reflect the PF of the washing machine to the gen. And actually it would help the overall PF seen by the gen if the FX is charging at the same time since the washing machine is inductive load whereas the charger is capacitive load.
Be greener and may the force be with you

sparky
Forum Emperor
Posts: 1216
Joined: Fri May 20, 2005 8:24 am
My RE system: OFFGRID SOLAR "we go where power lines don't" Design, consulting, and installation advice on 300+ Offgrid homes.
Location: Sierra Mountains near Mariposa Ca. Webpage on next line
Contact:

Post by sparky » Mon Jul 23, 2007 5:58 am

Greenerpower in theory you might be correct if you were not so close to the limit of the charger and the generator. On some generators the waveform does not even resemble a sine wave.

In practice the same generator looks much better into a better power factor corrected charger from the X-folks. With almost 27 installs I have to tell you that it has been my experience. The generator was a 3KW Honda inverter driving 800 AH from both companies approx. 4KW inverter chargers.

Here is another way to look at it. If you were making a really great charge circuit don't you think you might advertise that? Another spec to look at that comes into play when charging is the surge capacity. One brand is measured in milliseconds and the other is in seconds.

My goal is always to reduce the problems of my off-grid customer so I want the best I can get.

User avatar
GreenerPower
Forum Guru
Posts: 415
Joined: Wed Jun 13, 2007 9:22 am
Location: Texas
Contact:

Post by GreenerPower » Mon Jul 23, 2007 7:46 am

Sparky, no doubt that a better PFC charger would perform better and allow the gen to be used close to its capacity. I happen to read this thread posted several years ago started by Volvo. Folks like Uly,Volvo, DJ ... are probably interested for a solution with existing equipments. From that thread, it looks like OB can "special" built you a "tank" circuit. Not sure whether this solves the high frequency noise that blew the MOVs or could also better PF corrected the charger (Worth to try, Uly). For others who have similar problem, my solution is to use this $99 3000W power supply driven from the 240V output of the gen (this PS has 0.99 PFC). I've figured out how to wire it to "power on". I've tested it (set it for 54V DC output) simultaneously charging the battery (27A DC ? I calculated via the voltage drop across a 100A/75mV shunt) and supporting ~1200W AC loads (inverter in backup mode). The DC output voltage waveform is dawn good on a scope. My 5000W AC gen (from Lowes) that I've converted for tri-fuel just pickup a little more NG usage (compared to idle) running these. Those interested in this, PM me for how to wire it to be a stand-alone PS.
Be greener and may the force be with you

Post Reply