[RE-wrenches] offgrid system question

Wed Aug 20 07:55:44 PDT 2008

Temperature compensated battery voltages are only be used for charging regulation settings.  The charging setpoints need to be reduced when the batteries are warm because they are more easily caused to gas (produce hydrogen) at lower voltage levels as the electrolyte temperatures increase.  The opposite occurs with colder temperatures - the gassing voltage point rises as the electrolyte gets cold.  

Generator start setpoints should use actual battery voltages and not the temperature compensated voltage as the discharge setpoints do not have any relationship with the gassing voltage.  If anything,  the generator start and LBCO settings would need to be reverse compensated - reduced when the battey gets colder instead of increased when the battery gets colder as with the charging setpoints.   This could result in excessive levels of discharge however if not done correctly - and I have never seen any battery manufacturers provide a discharge temperature coefficient to use...  

Christopher

------------------------------------
Christopher Freitas
Director of Research and Development
OutBack Power Systems, Inc. 

cfreitas at outbackpower.com
Tel  360 435 6030
cell 360 202 4239

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org on behalf of Phil Schneider
Sent: Tue 8/19/2008 7:43 PM
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] offgrid system question

Max,

I agree with the previous comments regarding likely issues to pursue with
this system.

Mr. Undercuffler mentioned temperature compensation as a piece to the
puzzle.  I was recently troubleshooting a system where there was a large
difference between actual and compensated voltages with a SW Plus.  The SW
Plus uses actual voltage to make decisions regarding generator starting
(Xantrex tech support didn¹t have a known reason for this), which led to
premature generator starting (and LBCO shutoff) when the batteries were
warm.  It may be worth checking on which voltage (compensated or not) the XW
uses to make these types of decisions.

P.

Phil Schneider
Creative Energies

--- On Mon, 8/18/08, Max Balchowsky <max at seesolar.com> wrote:

> From: Max Balchowsky <max at seesolar.com>
> Subject: Re: [RE-wrenches] offgrid system question
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Monday, August 18, 2008, 3:00 PM
> Dear wrenches, going to look at a system installed by others
> and would like some input from some of you with more off
> grid experience than I have ( 4 systems over the years). the
> system was put on a new home - off grid 20 sharp ND123UJF
> panels 4 modules in series - 5 parrallel strings, 2460 total
> array dc voltage. mppt 60-150 charge controller, 12 sun
> extender sealed AGM batteries, 305 AH at 12 vdc, wired for
> 915 AH at 48 volt DC. The system is tripping off when the AC
> unit trys to start - AC is comfortmaker 3.5 ton 13 seer.
> They say start up inrush is 104 amps (sounds high to me) and
> they put a DST 10 soft start on the unit (I think that's
> just a big capacitor). I haven't been on site yet but it
> sounds to me that they just didn't design enough
> inverter capacity into the system...... What are your
> thoughts?
>   
>   Max Balchowsky
>   SEE Systems
>
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