[RE-wrenches] Thirsty batteries: Daily absorb cycles on top of grid powered float

[Mick Abraham]

Greetings, Mechanics~

My client's (flooded lead acid) battery is in Float almost all the time,
courtesy of an XW inverter stack plus public utility power while the system
waits in standby. "Selling to grid" is not enabled for complicated reasons,
so here's the problem.

Each day at sunup, the Midnite charge controls implement a new 3 stage
charge cycle including a lengthy absorption interval. The batteries require
frequent water additions and there may be other deleterious effects from
running a complete bulk/absorb charge every day on a battery that's already
highly charged.

Possible solutions:

(1) We could tweak the Midnite settings for a short absorption interval
with less gassing...but if a prolonged grid outage should develop we would
wish the absorption interval had not been shortened.

(2) Your suggestions here, please. The client would be willing to update
and/or reconfigure their Midnite software if that would help or the client
would even consider hardware revisions. We chose the Midnite controllers in
2011 largely because of their 250 volt input ceiling, btw.

++++++++++++++++++++++++++++++++++++

Thinking ahead to my future but similar projects:

Does any DC charge controller know that a new absorb cycle is not needed
each day provided that the battery never dropped below Float the night
before? A full cycle would still be wanted every 30 days or so just to stir
things up, so that's almost like a 30 day equalization trigger only it
would be a bulk trigger instead.

OR: would "selling to grid" avert this problem since the "battery backup
with grid tie" type inverter is aware that the battery never left the Float
stage?

OR: would AC coupling also avert this problem even if "sell to grid" is not
enabled, for the same reason cited above?

OR: Your suggestions here, please.

Thanks & Jolliness, Mechanix. The Wrench List is the Bomb!

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675
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