[RE-wrenches] Needed: Outback setpoints that won't ruin AGM's

[Mick Abraham]

Greetings, All~

My client's string of SunXtender two volt AGM's won't hold a charge...after
only two years! The prior AGM batteries also turned to toast prematurely.
There must be a better way, so could we review the Outback charge
setpoints?

Side note: Delta-v from the highest 2v cell to the lowest shows a gap of
only .148v during a charge cycle so cell imbalance is not the likely
problem. I think they're all working together equally bad.

A small amount of dry powder--light green color resembling verdegris finish
on copper--can be seen around 30% of the +/- posts, in an amount smaller
than 1/8 teaspoon. From this sign, I suspect that the cells have vented and
dried out. The property is vacant 90% of the time so I am mostly focused on
the MX60 solar charge controller as the culprit.

This is an early vintage Outback controller, firmware version 5.11.
Temperature compensation is in place; automatic EQ is defeated. Bulk &
absorption setpoints exactly match those requested by Concorde/SunXtender:
28.8 volts bulk/absorption & 26.4 volts Float. The controller does regulate
at these voltage points so it's technically "working"--just grinding up
batteries on a regular basis.

The Concorde people do not furnish suggestions regarding absorption time or
"rebulking" so that may be the source of trouble. Controller setpoints have
the Absorption Time Limit set for "0 minutes minimum & 1 hour maximum". The
controller is also set to "rebulk" the battery at a 23 volt trigger and
there's an inscrutable setpoint called "End" that's set for 45 amps. I have
a theory about the meaning of that but I'll keep the noise level down...

If I recall correctly, the Outback end of charge routine in early days was
to start a clock & see how long it takes to move the battery to the
bulk/absorption voltage then apply an equal amount of time for an
absorption charge before shifting to float. Steve Higgins may confirm if
that is indeed the protocol for a version 5.11 controller but: has that
method now been changed in the newer version Flexmax controllers? It seems
those now have an absorption duration value that can be changed so maybe
that's what we need--a replacement controller along with good information
on the absorption duration and/or float setpoints, etc.

I see that some controllers can even be set to not Float at all. Maybe
that's better: run the charge then stop it all for the rest of the day. OR:
thinking outside the box here...what about a controller that won't initiate
charge cycle at all unless the battery voltage crests down to a trigger
point. All I know for sure is that two sets of valuable batteries have now
been ruined so "normal" charge setpoints are not working well in this
situation.

If some better electronics (such as blending in the Outback capacity
monitor gizmo) might help, I'm all ears. Next time maybe I'll suggest
flooded cells to the client instead of AGM's, but the cells are in a
crawlspace that gets freezing cold at times.

Thanks in advance for advice & suggestions. A second off grid client has a
similar setup so I need to hotfoot it out there and tweak that (more
recent) Outback controller to match the suggested setpoint
revisions...before bad things happen again.

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675
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