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

[Mick Abraham]

Greetings, Mechanix~

My post regarding the proper setpoints for an unattended AGM battery
prompted a lively--and enlightening--discussion on the Wrench List.
Thanks as always for being the best in the biz. The Wrench List is the
bomb!

To tie up some loose parts of this thread:

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

Battery cell ampacity in this situation is 915 amp hours @ the 24 hour
rate. I had set 45 amps as the "bulk done amps" on the Outback
controller which is 5% as I had considered to be a good value. Based
on your various suggestions I will dial that down to about 23 which
would be 2.5%. In my opinion the lost capacity will not be restored by
this tweak but I'll do it and maybe try a similar value next time.

"Friends don't let friends buy sealed batteries," Todd told me off
list, but the cabin crawl space where the batteries are located gets
cold in the wintertime and I'm worried about hundred pound blocks of
ice.

Jay asked...and others implied..."Are you sure the problem is
overcharge/venting instead of chronic undercharge?" Mick replies: I'm
very not sure--that's the whole problem with batteries. The loads are
high at times even when the cabin is not occupied because the clients
have a nice frost free refrigerator of unknown power consumption but
probably high.

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

I sent my same original post with my voltage setpoints, etc. to
Concorde battery. They say, "a. Set absorption time to 2 hours. b.
Switch to standby (open circuit) after floating for 2 hours (if
controller can do this). c. Equalize charge every 60 to 90 days."

Mick interprets a: Longer absorption minutes sort of matches the
Mechanix' suggestions for a lower "bulk done amps" setpoint. I'm OK
with that but what if the loads are diminished but the batteries still
get pressured up each and every sunny day for such a duration...and
they get a lengthy float on top of that? That's just a rhetorical
question no replies needed but might this explain the dry green powder
around some of the battery posts.

Mick interprets b: This suggestion interests me. If the battery has
truly met full charge, continuing to float that for hours on end/days
on end seems possibly non-beneficial. Too bad there's no solar charge
controller nor any inverter/charger that can accommodate this
suggestion. Those of us who have been slogging along with "battery
bummers" for decades now cannot be faulted for wishing things were
better...much better. Too bad God doesn't work in the battery
biz/power equipment biz because omniscience is needed.

Mick interprets c: EQ charging a sealed pack based merely on calendar
months seems to invite more trouble than it would avoid. In my
original post I reported that the delta-v from highest cell to lowest
is small so I'm not sure unequal SOC is the problem here. Also, of
course telling a PV controller to "equalize every 30 days" is sort of
like telling a banker to "be solvent every 30 days". Might
happen...might not...depends on how the sun shines!

I guess I'll go ahead and set an automatic EQ in the Outback
controller but I think this won't help the present problem and might
not help my next one. Even with floodies, automatic calendar based EQ
seems sketchy because one then doesn't know to follow up with water
additions.

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

I have another client who just began using their new Discover
AGM's--it's another cold climate installation, Todd. Anyway I asked my
Discover guys for their suggested setpoints. The reply was prompt &
detailed but impossible to meet using any of the charge electronics
normally seen within our industry. They want a bulk/absorption phase
for a time then a high "finish stage" for a time followed by a drop to
float then a replay of the high finish stage at EQ type voltage levels
once per month. Obviously this presupposes grid powered charging
instead of the PV "daily blackout" situation.

Discover and also Fullriver AGM are both jolly about dualpro.com whose
DeltaVolt charger  apparently can deliver a charge profile to suit the
battery engineers. It's called IUU and makes me say, "Ai, Yii, Yii,"
because none of our stuff can do that. I have a document regarding the
DeltaVolt charge profile if anyone is interested, but noplace where I
can park it on the web.

Dualpro seems 12v only, it's just a charger not a multi, marine
oriented, blah blah.

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

I need to rebuild my own battery based power setup and even with all
the new/different brands of inverters, PV controllers, batteries, etc.
I am somewhat immobilized in the face of the decisions I must make.
You see, I'd like things to not junk out in the way they would have
ten years ago and I cannot settle on an equipment bundle that seems
sufficient junk-proof. Sorry, Moderator, this part of my reply
probably belongs on the RE-bitching list.

Thanks again to all who have contributed to this thread. Yours for
better batteries,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675