[RE-wrenches] Fw: Xantrex C-40 Drifting

Tue May 19 09:31:04 PDT 2015

Hi:

I didn't know that there were systems out there where a PWM charge 
controller such as the C-40 was producing an unhealthy, high battery 
voltage.  Since there are, I may have a possible explanation.

The C-series and other PWM type charge controllers operate by PWM whereby 
they very very quickly connect/disconnect the solar module to the battery 
bank.  The amount of time which the module is connected to the array is 
the PWM on-period.  These controllers do not have the ability to "smooth 
out" the output voltage.  All they can do is apply the full module voltage 
OR not apply any module voltage to the battery.  Here are some graphs that 
show this,

It 's supposed to work out when the battery absorbs, smooths out and 
averages the output voltage pulses coming out of the PWM controller.

Except, I'm hearing that, that is not necessarily true.  It sounds like on 
some systems the batteries will not average voltage very well over time 
and indeed experience increasing and undesirably high terminal voltages 
over time.

If this is the mechanism, I think one way alleviate or perhaps even 
eliminate the rising voltage problem is by matching the module Voc voltage 
to the desired battery float voltage.  For example, if a 28 VDC float 
voltage was desired, then the solar module Voc should be chosen as 
something slightly above 28 VDC.

i.e. I think the trick is to match the module Voc voltage to the desired 
battery float voltage.  Perhaps a 32 Voc module for a 28 VDC float 
voltage. 

I'm not sure what the right number is, but if I'm correct about this 
mechanism, then a 50 Voc module on a 12 VDC battery, should the kind of 
system which experiences this overcharging/over voltage problem.

You guys have seen many systems.  Maybe you can comment on whether the 
systems which have had this trouble are also ones where the module Voc is 
much higher than the desired battery float voltage.  Perhaps the "trouble 
systems" also tend to have a specific battery chemistry or even particular 
battery type.

JARMO

_____________________________________________________________________________________ 

Jarmo Venalainen  |   Schneider Electric   |  Xantrex Brand  |   CANADA  | 
  Sales Application Engineer 
Phone: +604-422-2528  |   Tech Support: 800-670-0707  |   Mobile: 
+604-505-0291 
Email: jarmo.venalainen at schneider-electric.com  |   Site: www.Xantrex.com 
|   Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 

*** Please consider the environment before printing this e-mail

----- Forwarded by Jarmo Venalainen/Canada/Schneider on 05/18/2015 07:02 
PM -----

From:
Drake <drake.chamberlin at redwoodalliance.org>
To:
Jarmo.Venalainen at schneider-electric.com, 
Date:
05/18/2015 03:35 PM
Subject:
Re: Fw: [RE-wrenches] Xantrex C-40 Drifting

Hi JARMO,

The battery bank consists of four, 415 AH in a Full River AGM deep cycle 
batteries wired  in a 24 volt series. The  80 W array is strictly  a 
maintainer  to keep the batteries charged when  the  AC  coupled  system 
is detached from the direct grid tie inverters. The only constant loads on 
the system are about 3 W of power that keeps the metering awake. The 
batteries are low self discharge. 

Thanks,

Drake

At 07:47 PM 5/14/2015, you wrote:
Hi: 

80W is a really small PV source, so I'm wondering how it can raise the 
battery voltage so much. 

What size is the battery? 

JARMO
_____________________________________________________________________________________ 

Jarmo Venalainen  |  Schneider Electric   |  Xantrex Brand  |   CANADA  |  
Sales Application Engineer 
Phone: +604-422-2528  |   Tech Support: 800-670-0707  |   Mobile: 
+604-505-0291 
Email: jarmo.venalainen at schneider-electric.com  |   Site: www.Xantrex.com  
 |   Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 

*** Please consider the environment before printing this e-mail

----- Forwarded by Jarmo Venalainen/Canada/Schneider on 05/14/2015 04:45 
PM ----- 
From: Drake <drake.chamberlin at redwoodalliance.org> 
To: re-wrenches at lists.re-wrenches.org, 
Date: 05/14/2015 04:30 PM 
Subject: [RE-wrenches] Xantrex C-40 Drifting 
Sent by: "RE-wrenches" <re-wrenches-bounces at lists.re-wrenches.org> 

I have a Xantrex C-40 that won't keep its settings. It is important that 
it does because it is for a maintainer array (80 W) on an AGM battery 
bank, on an AC coupled backup system. Not only could high voltage damage 
the batteries, but when the voltage goes over 30 Volts, the AUX relay 
opens and the grid tie inverter is isolated from the grid.

After numerous sessions of reprogramming, Xantrex tech support sent me a 
new unit. The problem persisted as before. A new temperature sensor 
helped, but the settings still drift. It seems that rebooting the charge 
controller helps for a day or so, but then it drifts again.

The potentiometer settings are way below the calculated setting for 29.4 
V, but it still peaks in the high 30s. I check the temperature compensated 
voltages on the Outback Mate, and the temp compensated voltage runs high. 

In a related side issue, the AUX relay of the FX inverters is not based on 
temperature compensated voltage, which makes setting AC coupling charge 
set points more problematic. 

Has anyone experienced a C-40 CC that drifts in its settings. What would 
be a good (inexpensive) charge controller to accurately control 80 W of 
PV?

Thanks,

Drake 

Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV 
740-448-7328
http://athens-electric.com/ 

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
______________________________________________________________________ 
_______________________________________________
List sponsored by Redwood Alliance

List Address: RE-wrenches at lists.re-wrenches.org

Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org 

List-Archive: 
http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html 

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out or update participant bios:
www.members.re-wrenches.org

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
______________________________________________________________________

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 14379 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0040.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 38319 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0041.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 4274 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0042.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 1869 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0043.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 1897 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0044.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 2041 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0045.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 4274 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0046.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 1869 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0047.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 1897 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0048.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 2041 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150519/5f4578de/attachment-0049.gif>