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

Sun Jul 8 09:00:17 PDT 2012

Larry,

Would the  Absorb End Amps setting act similarly to the IPN chargers from
Solar Boost if you set a very long absorb time and had it end absorb stage
after it dropped below the desired current level?

Thanks

On Sun, Jul 8, 2012 at 9:40 AM, Larry Crutcher, Starlight Solar Power
Systems <larry at starlightsolar.com> wrote:

> Hello Mick,
>
> I think your set-points for voltage are fine. The Rebulk is of little
> importance for an unoccupied property as voltage should be easily
> maintained.
>
> The bad news: In a nut shell you have told the MX charger to stop charging
> if the PV current drops below 45 amps or 0 to 60 minutes after reaching the
> absorb setting. I don't think you can ever reach 100% SoC with this setup
> so the battery may have been deficit charged every day.
>
> *Absorb Time Limit, Min*:
> With AGM batteries, this setting should be determined by measuring *how
> much absorb time* it takes for the current to the battery to drop below
> 0.5% of the banks rated capacity. For example, a 1000 AH bank this would be
> 5 amps. If it takes 60 minutes to reach this point, use that number for
> "Min". By leaving it at 0, the MX60 will choose the absorb time based on
> the bulk/absorb charge timer which may not be enough at an unoccupied
> property. Example, if the bulk time is only 30 minutes, the absorb time is
> 30 minutes unless the "Min" is set higher.
>
> *Absorb Time Limit, Max:*
> The factory default is 2 hours. This value needs to be at least 10 minutes
> longer than the "Min" time set above. One hour means that is the longest
> time the controller will stay in absorb.
>
> *Absorb End Amps (misc settings)*
> Here's the real culprit. By setting this at 45 amps, you have told the
> controller to stop absorb charging 15 seconds after it starts if your
> current is less than 45A. Obviously this will leave the battery deficit
> charged unless the float current and sun hours remaining can make up this
> deficit. Reset this to zero, the factory default, and let the Min/Max
> settings control the charge.
>
> Just a note on charging AGM's: My opinion is that the only reliable way to
> properly charge an AGM battery is by monitoring the current to the battery
> and adjusting the charge time accordingly. For this reason, I recommend
> charge controllers that have this function, like the Blue Sky Energy Solar
> Boost IPN controllers. With this method, you can force the absorb voltage
> to remain as long as necessary until the battery reaches 100% SoC.
>
>
> Larry Crutcher
> Starlight Solar Power Systems
> (928) 342-9103
> *
> *
> *
> *
>
>
> On Jul 7, 2012, at 3:53 PM, Mick Abraham wrote:
>
> 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
> _______________________________________________
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive:
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
>
>

-- 

Mac Lewis

*

"Yo solo sé que no sé nada." -Sócrates
*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20120708/8a4e5c75/attachment-0003.html>