Dual XW-6048, one inverter charging from other

aj164

Off-grid setup with approx 7kW PV.
Just installed 2nd XW-6048 inverter. With approximately 1.3kW load, one inverter takes the load, and the other idles. The strange thing is the idled inverter will often start charging the batteries with a 5 to 12 Amp output. This is power going around in circles! Seems like a waste.

Ive been over the config many times. I can't figure out why it would do this. I tried disabling the charger on both inverters, and it still did it.

It is almost as though the old inverter acts like it is being AC-coupled from a grid-tie inverter, and doesn't know it's siphoning power from its own DC bus via the new inverter.

Any ideas?

niel

Re: Dual XW-6048, one inverter charging from other

can't you opt to shut off the charger in the 2nd idle inverter?

aj164

Re: Dual XW-6048, one inverter charging from other

I did try that, but it still charged. I did notice that some parameters would appear to have been accepted after I changed them (using XWConfig software), but the system continued to behave as with the old value. For example, the new inverter would not stop trying to be 'master', even though all of the readings on both XWConfig and the control panel showed it as 'slave'. It took re-loading the firmware to get it to work.

aj164

Re: Dual XW-6048, one inverter charging from other

I got a response from Xantrex. Search mode needs to be enabled on the slave inverter(s) and disabled on the master. I have search mode disabled on all inverters. This changes the behavior from equal load sharing (more or less) to load sharing only when the load exceeds a threshold. So, the slave inverters in search mode will 'sleep' until the AC load exceeds 60% of the output rating on the master. This is probably better anyhow, because it reduces the idle power consumption of the slave inverter(s).

SolaRevolution

Re: Dual XW-6048, one inverter charging from other

I've had this issue (or similar) with other multi-XW systems.

Having the slave in search/"sleep" sounds like a quick fix. I wonder if it is a callibration issue. If so, although it may no longer be a problem while under low power, it may still decrease the system efficiency at higher power.

To check this, I suggest you turn off the search/"sleep" on both inverters and open all of the AC breakers in the distribution box. Use a multimeter to check the inverters' AC output voltage. If they show the same on the SCP but different on your multimeter it implies a defect.

I'd also check each inverter individually. Connect the SCP to only the Master and check to see if the multimeter and SCP's AC load voltage match and then try the same thing with the slave. Which ever one is furthest off is the culpret.

-Alex Aragon

http://www.youtube.com/watch?v=_X7NOh7lTf8
-Catchy tune.:roll:

aj164

Re: Dual XW-6048, one inverter charging from other

I wondered about a voltage mismatch between the two. Is there a way to calibrate other than sending back to Xantrex?

SolaRevolution

Re: Dual XW-6048, one inverter charging from other

aj164 wrote: »

I wondered about a voltage mismatch between the two. Is there a way to calibrate other than sending back to Xantrex?

I spent a while on the tec support line with this one. We tried everything we could think of with the config tool. New firmware, reinstal firmware, reset to factory settings, calibrate AC output... Thre was no problem with one inverter at a time. As soon as we paralleled the AC outputs you could really hear them ramping up. One would charge while the other would put out load current.

At first the tec was insisting that it was just a metering discrepancy in the SCP. I had a trimetric 2020 amp/hour meter on the battery showing (something like) 1.1 amps at 48.5 volts while the SCP showed a load of +/- 200 watts. I finally held the phone up near the inverters so the tec could hear the change as I closed the AC output breakers.

You should check it out. A single XW6048 will show an idle current of +/-30 watts with a battery current of .6 amps with the AC output breaker open.
A "good" pair of XWs, with the AC output breakers closed, will show 70-90 watts with around 1.5 amps from the batteries . If 2 or 3 are having a problem they can show much higher load watts and somewhat elevated battery current. The displays on the inverters themselves will show what each is processing but because they are just feeding eachother, they are only drawing the inefficiency loss and idle current from the batteries.

You also might want to see what the difference is between;
-the "idle" load current on the SCP when you have the master on and the slave in search/"sleep" with the AC output breakers closed (with no loads connected)
-the "idle" load current on the SCP when you have the master on and the slave in search/"sleep" with the AC output breakers open.
You should hear a slight difference and see it on the SCP but the change in battery current should be negligible. (< 1 amp) If there is more than a slight increase with both breakers open Scnheider should probably fix it for you. Hopefully they can identify the right one.

-Alex Aragon

Dave Angelini

Re: Dual XW-6048, one inverter charging from other

Just curious, are you running a machine shop? Why so much power for offgrid?

aj164

Re: Dual XW-6048, one inverter charging from other

3000 ft^2 home with mostly electric appliances (not my home). Most of the time, the load is 2500W or less. However, for short periods of time, the load can approach 4500W to 5000W. If the well pump kicks on, they would be in overload on one 6kW inverter. The owners got tired of managing this for the past couple of years, and they decided a 2nd inverter was the way to go.

Cariboocoot

Re: Dual XW-6048, one inverter charging from other

Since one XW 6048 (capable of surge to 12 kW) can handle the load except for the rare occasions when everything turns on at once, dedicate the second inverter to the pump. No AC OUT coupling; no problems.

SolaRevolution

Re: Dual XW-6048, one inverter charging from other

Dave Sparks wrote: »

Just curious, are you running a machine shop? Why so much power for offgrid?

I've used multiple XWs to accomodate higher higher charging current for some systems where one 6048 would have been enough for the load power.

-Alex

Dave Angelini

Re: Dual XW-6048, one inverter charging from other

SolaRevolution wrote: »

I've used multiple XWs to accomodate higher higher charging current for some systems where one 6048 would have been enough for the load power.

-Alex

I have too, but one is a spare. I have never seen the need offgrid for 2 xw's unless it is a machine shop. An XW for a battery charger seems odd but you do have a spare!

Thanks!

aj164

Re: Dual XW-6048, one inverter charging from other

I just checked another installation with multiple XW (one 6048 and one 4548.) Although grid tied, I switched off the grid for a moment and noted much more even load sharing (search mode off).
What is the procedure for AC calibration? I found the AC output settings in XW-Config, but it has one box that says L-N voltage. Is there another password that enables additional options?

aj164

Re: Dual XW-6048, one inverter charging from other

This problem is solved! The inverter AC output settings differed by quite a lot. One inverter read around 110V L-N, and the other 120V L-N. I brought the lower-voltage inverter (also the old inverter) up to 120V L-N, and now they behave just as one would expect. They share the load almost equally. With Search Mode enabled on Inverter2, it sleeps until the load exceeds 4kW. At that point, the 2nd inverter wakes up, and both inverters share the load. When the load reduces to around 1kW, Inverter2 again goes to sleep.

Here is the procedure for changing the output voltage:

You need the latest version of XW Config and a Xantrex USB-Xanbus communications dongle for your computer. Make sure all inverters are running the same firmware version.

1) Get XW Config up and running per instructions.

2) Turn off grid and generator input breakers.
3) Turn off the inverter output breakers.
4) Disable Search Mode on all inverters. Make sure inverters are operating.
5) Disable Power Save on all inverters (advanced features).
5) Using a volt meter, note the L-L voltage on each inverter output.
6) Note the L-N voltage on each inverter output.

7) Decide which inverter's output you want to modify.
8 ) With XW Config, select that inverter. Click on "Config" and choose "Output settings".

Here is the goofy part:
9) Note the L-N voltage on the display. It is being updated periodically, and it may change by a volt or two.
10) Type a new value into the L-N voltage box. The numbers will change to red. HURRY and press "Update" before the value changes again!
11) Verify the change using your voltmeter. Repeat steps 9 through 11 as necessary.

You want the open circuit voltage of each inverter to match as closely as you can get it.

12) Put a ~1kW load on the AC output - only one inverter at a time. Verify that L-L voltages are similar from one inverter to the next.

SolaRevolution

Re: Dual XW-6048, one inverter charging from other

aj164 wrote: »

This problem is solved! ...
10) ...HURRY and press "Update" before the value changes again!

Hmm. Thanks.
I'll check into that if it comes up again.
Did you discover this yourself or did SE tech support mention this?
I was unable to get the recalibration to change the last time I tried. I wonder if I was just not quick enough.

-Alex

aj164

Re: Dual XW-6048, one inverter charging from other

SolaRevolution wrote: »

Did you discover this yourself or did SE tech support mention this?
I was unable to get the recalibration to change the last time I tried.

This did not come from tech support. I found this myself based on what I thought you had implied in your earlier message (that the output could be calibrated) and by exploring the menu items in the latest version of XW Config.

SolaRevolution

Re: Dual XW-6048, one inverter charging from other

aj164 wrote: »

This did not come from tech support. I found this myself based on what I thought you had implied in your earlier message (that the output could be calibrated) and by exploring the menu items in the latest version of XW Config.

Oh, Way to go!

I was wondering about the "hurry" thing. I had done the re-cal with the config tool but was unable to make any functional difference.
Sorry for not answering when you asked for instructions, I could not give you a step-by-step without the config tool open in front of me. I was hoping to get a chance to check it myself over the last few days. I have been planning to do a firmware up grade on a grid-tied system but have not got around to it yet.

So, what was it?
Did you say they were set to different voltages? Or was it that they were putting out different voltages but had the same settings?

Thanks,

-Alex

aj164

Re: Dual XW-6048, one inverter charging from other

SolaRevolution wrote: »

So, what was it?
Did you say they were set to different voltages? Or was it that they were putting out different voltages but had the same settings?

One inverter was set to 110V L-N, and the other (new) inverter was set to 120V L-N. However, it was not as simple as it sounds. When I first entered 120V in the old inverter, its output jumped to 265V L-L. To get 240.5V L-L on the old inverter, I ended up with a L-N setting closer to 112V (IIRC). If I had more time and had paid better attention, I would have evaluated the difference between my DMM reading L-N and the XW software reading. I'll do that next time. Maybe the software gives RMS, and my Micronta DMM does not. At any rate, all I was going for was to make the old inverter match the new inverter according to my DMM reading.