[RE-wrenches] Battery charging with XW series equipment

[Allan Sindelar]

Wrenches,
Just before Topica died there were several postings related to observed
problems and limitations with Xantrex' new XW system. I sent a heads-up to
Mark Edmunds, asking him to check the Wrenches forum and reply to the issues
raised. Mark was out, but I received the following response from Jeff
Everett. 
 
I am quite impressed with Jeff's clarity and directness in addressing all of
the issues raised, so now that we again have a list, I am forwarding his
response. 
 
Allan at Positive Energy.
 
-----Original Message-----
From: Jeff Everett [mailto:Jeff.Everett at Xantrex.com] 
Sent: Monday, July 14, 2008 5:53 PM
 
Hi Allan, 

Mark is our Wrenches poster but he is on vacation so I'll try to address the
concerns directly with you. 

>From Mr. Miller: 

>1.      The 24 IBE batteries we have do not appear to be receiving a full 

>charge. At-rest voltage caves quickly at sundown to 48 or less. I have 

>observed the two-stage charge cycle performed by the XW charge controllers 

>and I wonder if this is really superior to three stage charging. Comments?

Let me start by saying the original XW charge controller manual was
misleading. It mistakenly suggested that two-stage charging was recommended
for off-grid applications. The recommendation was actually meant for the
inverter, where 2-stage charging is recommended when the inverter is
charging the batteries from grid or generator in order to save on
electricity and/or fuel. This is particularly beneficial if there is a solar
charge controller (or other RE source) that is capable of maintaining the
battery bank at float voltage. So for the XW charge controller, the correct
recommendation is to keep it at its default 3-stage charging setting. (This
mistake was the result of cutting-n-pasting from one manual to the next. We
have taken steps to correct the Charge Controller manual by removing this
2-stage recommendation for off-grid applications. I've attached the updated
manual for your reference.)

<<XW-MPPT60-150_Owners-Guide (975-0400-01-01_Rev-B).pdf>> 

But regardless of whether the charge controller is set for 2 or 3-stage
charging, the battery bank should be receiving a full charge. That is
provided, of course, the charge controller charge settings are correct and
the solar conditions allow for it to complete the full bulk and absorption
stages. 

As explained in the charge controller manual (page 1-5), the Charge
Controller transitions out of absorption if any one of three criteria are
met:

1)      The charge current allowed by the batteries falls below the exit
current threshold (2% of battery capacity) for more than one minute.

2)      The battery voltage has been at the bulk/absorption voltage setting
for longer than the user-adjustable "Max absorb time".

3)      The battery voltage has been at or above float voltage (reached
during the bulk stage) for longer than 8 hours. (This is a safety feature to
prevent batteries from being maintained forever above their float/gassing
voltage.)

The at-rest voltage on Mr. Miller's batteries may be quickly dropping due to
factors related to poor battery health or battery age. If the effective A-hr
capacity of Mr. Miller's batteries has diminished due to age or usage,
having an A-hr setting of original "nameplate" capacity will result in the
charge current hitting the exit current threshold prematurely, which in turn
will result in the battery chronically being undercharged. This can be
easily resolved by decreasing the A-hr setting to the effective A-hr
capacity of the bank.

On the other hand, assuming the battery bank is healthy, it may just need
more time in absorption than what the "Max absorb time" setting allows. For
large battery banks, depending on how much charging capacity there is, it
may be necessary to extend the max absorb time threshold beyond the default
of 180 minutes. Given the size of Mr. Miller's battery bank this may be the
case. I would recommend setting the max absorb time long enough so that the
exit current threshold criteria (#1 above) is consistently first to be met. 

>2.      The charge routine performed by the XW inverter is also 

>suspect. Apparently there is no way to require a specific absorption 

>duration. According to tech support, the absorption timer is simply a 

>maximum timer and that absorption ends when the charge tapers down to 2% of


>the battery AH value. We see the generator auto start and then shut off in 

>about an hour. For a 1600 AH battery bank, this seem too short a time 

>frame to really get a full charge. Should we increase the absorption 

>voltage?? Comments?

The battery charging algorithm, for both the charge controller and the
inverter/charger, is explained in the manuals. Please refer to the diagram
on page 1-5 in the XW Charge controller manual. It is important to note that
the transition between the Bulk and Absorption stages is defined as the
point when the battery voltage initially rises above the float voltage
setting,  as it climbs up to the Bulk/Absorption voltage. Once it
transitions to Absorption, the charger continues to charge with a controlled
constant current until the Bulk/Absorption voltage is reached. Then, at this
point, the charger holds the batteries at this voltage until either the
current decreases below 2% of the battery capacity (32A in this case), or
the configurable Absorb time expires. At this point the charger transitions
to float stage (or turns off, in the case of 2-stage charging).

If the XW-Auto Gen Start (XW-AGS) is shutting down the generator after about
an hour, Mr. Miller must have it configured to stop on the "Stop Absorb"
trigger. The "Stop Absorb" trigger tells the XW-AGS to stop the generator
when the charger transitions from Bulk to Absorb stage, i.e. when the
battery voltage first reaches the float voltage. The intent of this stop
trigger is for cases where the owner wants to minimize generator runtime (&
fuel consumption). It's best if there is ample RE power to finish charging
the battery bank. If this is not the case, then it would be recommended to
set the generator to "Stop Float", which will stop the generator after
completing the Absorption stage.

>3.      The programmed variables for a number of the functions were 

>blank.   For example, the generator voltage start numbers (for 24 hour, 2 

>hour, etc) were not empty. This puts a lot of pressure on the installer to 

>insert parameters where one would usually find them already 

>programmed. The possibility is high that the installer might miss an 

>important parameter and have to drive back just for programming. I thought 

>that the default parameters for the SW were excellent and I encourage 

>Xantrex to pre-program with these values. It may be also that I have older 

>software and the new software has these values?

This is not related to software changes. The XW-AGS can be used with 48Vdc
or 24VDC XW Inverters so the battery related start triggers can be different
depending on battery voltage. We've defined the "Start DCV 30 sec" trigger
default (44V) but left the other start DCV triggers disabled. 

It was easier with the SW since the triggers were set and stored on the
inverter itself. With the XW-AGS, all the generator configuration settings
are actually saved in the non-volatile memory of the AGS itself.  That said,
Mr. Miller brings up a good point. We will investigate whether changes can
be made to enable the XW-AGS to auto-detect, on first power up, whether its
connected to a 24V or 48V inverter and to auto-populate the appropriate
default settings. 

In the meantime, I suggest considering using the XW_Config Tool (p/n
865-1155). It is a tool (both hardware and software) which, among other
things, allows an installer to configure an XW System using a PC, and then
save the configuration for future use. For more info on this tool, download
the XW Config User Guide from our website:
http://www.xantrex.com/web/id/246/p/docs/pt/18/product.asp
<http://www.xantrex.com/web/id/246/p/docs/pt/18/product.asp>  

>4.      What is the difference between newer version of the software and 

>the older versions?

Some charges include things such as including date and time in the XW SCP,
allowing generators to be configured without a run signal using the XW-AGS,
the inclusion of single phase input qualification to prevent 3-phase sources
being connected to the inverter.

The most significant change in firmware was, in a multi-unit configuration,
to allow all units to come on line to share the load with the master, all at
the same time. In the original firmware release, the slave units would be
off-line and would not come up until the load increased above 60% of the
master's rated output. During very large load step changes, the master unit,
in some occasions, would overload before the slave units would have time to
come up on line.

>From Wind-Sun.com: 

>The lack of any possible way to do any field repairs on them is also 

>starting to be an issue. With both Outback and Magnum, you can get 

>replacement board/parts for fast repairs.

>

>With Xantrex it is a different story - We have a customer in Mexico in a 

>self-installed system who had one go out. The answer from Xantrex tech 

>support on an apparently blown AC output FET was to "bring it back to the 

>US, send it to us, and we will evaluate it and repair it".

The XW Inverters were designed so that in-field board swaps would be
possible. This approach hasn't changed and we have been supporting field
repairs. I am checking into this specific case to see if there were
extenuating circumstances with doing a board swap. Sometimes there are. It
could be because this was a self-installed unit and the Tech Support guys
weren't confident the end-customer was capable to perform a board swap
safely. (We would have very little issue with supporting a qualified solar
installer.) 

That said, we are trying to be very careful to make sure we find and correct
any design or mfr'g problems early . so, for the few units that have had
problems, we've been asking if the complete unit could come back. This way
our Engineers can do a thorough root-cause analysis and take corrective
actions if needed. (So far, it hasn't been needed.) But if asking for the
unit back causes a customer too much grief and they are capable, our
customer service group has the spare boards in-stock and are prepared to
support an in-field board swap, which has been done in a few cases too. 

Your question regarding Midnite's E-Panel: 

>Can you give me specific reasons and benefits why your

>AC/DC enclosure is superior to his approach, as used with your inverters
and

>charge controllers?

I haven't talked to Robin nor have I seen his E-Panel up close but, from
what I can gleam from Midnite's website, it looks like a pretty nice,
well-thought-out solution. From what I can tell, the E-Panel only supports a
single inverter and up to two charge controllers. This might be all you
need, but if you're considering a dual inverter system (or larger) the XW
Power Distribution Panel (XW-PDP) is probably the easiest, most cost
effective way to go. The XW-PDP is prewired for one inverter, but can
support up to three inverters AND four charge controllers. 

Allan - hope the above helps respond to the concerns raised. If I missed
anything or you need further info/explanation, please feel free to contact
me. 

Regards,

Jeff Everett

Product Manager

Renewable & Backup Power Markets

Xantrex Technology Inc. - We Enable Green Energy

Email: jeff.everett at xantrex.com

Website: www.xantrex.com

t: 604/415.4625

c: 604/614.5789

f: 604/420.1591 


 

 -----Original Message-----

From: Allan Sindelar [mailto:allan at positiveenergysolar.com] 

Sent: Friday, July 11, 2008 12:42 PM

To: Sau Ngosi; Sandra Steffan

Subject: FW: Battery charging with XW series equipment [RE-wrenches]

I am out of the office through July 18, with limited access to e-mail. For

immediate assistance please contact Sandra Steffan, at

sandra.steffan at xantrex.com <mailto:sandra.steffan at xantrex.com> . 

For XW program question please contact Sau Ngosi, at sau.ngosi at xantrex.com
<mailto:sau.ngosi at xantrex.com> . 

 

-----Original Message-----

From: Allan Sindelar [mailto:allan at positiveenergysolar.com] 

Sent: Friday, July 11, 2008 1:12 PM

To: 'mark.edmunds at xantrex.com'

Subject: FW: Battery charging with XW series equipment [RE-wrenches]


Mark,

Here's a heads-up that there's been a recent thread of concerns re XW

equipment on the Wrenches list, started by William Miller on 7/9. Please

respond promptly to all of the expressed concerns. I am waiting on your

answer as I prepare a possible dual XW quote.

Also, I have a question of my own. Robin at Midnite has released an E-Panel

designed for the XW. Can you give me specific reasons and benefits why your

AC/DC enclosure is superior to his approach, as used with your inverters and

charge controllers?

Thanks, Allan



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