[RE-wrenches] C60 setpoint question

Eric.Bentsen at schneider-electric.com Eric.Bentsen at schneider-electric.com
Thu Aug 1 14:47:44 PDT 2013


Hi Allen,
The absorption time is actually only 1 hour for the C-series controllers. 
Battery manufacturers are always the final authority on 
how their batteries should be charged. If they say you can charge at 
14.2-14.4V indefinitely, then increase the float setting.
Eric
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Eric Bentsen  |   Schneider Electric   |  Solar Business  |   UNITED 
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From:
Allan Sindelar <allan at positiveenergysolar.com>
To:
RE-wrenches <re-wrenches at lists.re-wrenches.org>
Date:
08/01/2013 01:20 PM
Subject:
[RE-wrenches] C60 setpoint question
Sent by:
re-wrenches-bounces at lists.re-wrenches.org



Wrenches,
Eden, our main off grid field tech, came across a situation about which I 
want to ask the group for advice, please.

The system: existing old/funky off grid 12V residential system, done by 
others over many years; this was our first visit. Owner out of state, 
currently rented, owner's complaint is that the old Heart 2800 EMS 
inverter is shutting down at times. Six four year old Concorde SunXtender 
PVX-3050Ts, so 900 rated amp-hours in three strings at 12V. Approximately 
830 watts of a hodgepodge of older modules, but well below rated output at 
present, though no obvious failures. Trace C60 charge controller. Our 
assessment after a site visit is that the batteries have been chronically 
undercharged and are showing signs of premature sulfation.

With AGM batteries such as these, we have been encouraged (by Midnite tech 
support and others) to set really long absorption times - we have some 
systems with six-hour absorptions. The logic is that theese batteries can 
tolerate - indeed thrive on - staying at absorption voltage of 14.2 - 14.4 
V (for 12 V nominal) indefinitely, and given the fickle nature of off grid 
PV charging, this maximizes the likelihood of their getting full most 
days. This logic makes total sense to me.

Most modern MPPT charge controllers have a programmable absorption time, 
and some have a done amps (a.k.a. float transition current), to allow them 
to transition to float if the charge current necessary to maintain 
absorption voltage drops below a set threshold (typically 1-3% of battery 
capacity). The C60 has neither, but rather has a nonadjustable two-hour 
timed absorption. This brings the question: is there any good reason that 
the float voltage on the C60 should not be set to the same voltage as the 
bulk/absorption voltage, such that they never drop into float? When 
sufficient input is available to get the batteries full, they are just 
allowed to stay in absorption mode indefinitely, slowly getting the energy 
necessary to reach 100%.

We have installed many Concorde AGM batteries, but never with an old 
C-series controller. This idea seems wacky, but the more I think about it, 
the more I can't see any problem with it. What do the rest of you advise?
Thanks, Allan

-- 
Allan Sindelar
Allan at positiveenergysolar.com
NABCEP Certified PV Installation Professional 
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc., a Certified B CorporationTM
3209 Richards Lane
Santa Fe, New Mexico 87507
505 424-1112 office 780-2738 cell
www.positiveenergysolar.com
 

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