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

[jay peltz]

Hi Mick,

While I don't know what SG they are using in those batteries, I'd say the voltage was too high at 28.8.
If it was a standard SG then it would be gassing at 28.8 and starting to dry out the batteries.
( do the batteries look concave?)

The OBCC  FM does a rebulk adjustment setpoint, but the older MX does not.

What makes you think its not undercharge/overuse thats causing the problem?

Jay

peltz power










On Jul 7, 2012, at 2:53 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
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