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

Mon Jul 9 06:52:29 PDT 2012

The End Absorb Amps setting forces the MX controller into the float mode once the Absorb Voltage is reached and sustained for 15 seconds. Here is the text from Pg. 42 of the MX60 manual (emphasis added): 

(End, -AMP, +AMP) Normally, an Absorb charge cycle is terminated because the battery voltage was regulated at the Absorb set point for the maximum time period. Decreasing (-AMP) or increasing (+AMP) sets an optional end current level. While the battery voltage is at or above the Absorb target and the End current level is reached at a time delay of 15 seconds, the MX60 will switch to the Float charge stage regardless of the charger time minutes. The charger timer (ChgT) will be cleared. This is an optional set point and its adjustment is not required in most installations. “00” Absorb End amps is the default.

Since Mick had this level at 45 amps, anything LESS than that forced float mode and undercharged the battery. Note that this is the second set of batteries at that location to suffer short life.

Larry Crutcher
Starlight Solar Power Systems
(928) 342-9103

On Jul 9, 2012, at 7:07 AM, Allan Sindelar wrote:

Larry,
While I agree with your assessment of Mick's settings, some of what you write doesn't make sense to me, and I'd like to better understand.

Re: "End Absorb Amps will only look at the controller current, not net battery current. If loads are on, the current may be higher than your setting and the controller will continue with monitoring the ChgT". I have understood that this is the point: that any loads will pull down battery voltage, requiring the controller to raise the absorb current to allow more amps in to compensate, leaving the controller in absorb rather than switching to float. It thus doesn't need to look at net battery current (as does the IPN control algorithm) in order to maintain absorption. What am I missing here?

Mick didn't say what the AH capacity of the cells was, but the smallest 2V Concordes are 500 Ah and the largest are 1200 Ah, meaning an 11% to about a 4% float transition current, either way too high if we want somewhere between 0.5% and 2.5%, depending on who we listen to. It seems as though this is the real culprit, along with an absorption time that is set way too low and causes chronic undercharge, and the Outback's end amps function would work well, as long as it's set correctly (and ideally raised a bit as the batteries age, which is seldom likely to happen).

Your thoughts? I respect your experience.
Allan

Allan Sindelar
Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com

On 7/8/2012 10:32 AM, Larry Crutcher, Starlight Solar Power Systems wrote:
> No. End Absorb Amps will only look at the controller current, not net battery current. If loads are on, the current may be higher than your setting and the controller will continue with monitoring the ChgT. More importantly, if current drops below your setting and the battery is not 100%, it will still drop to float mode. Not good. 
> 
> Without a FlexnetDC and Mate to determine SoC, the only use I can see for this function is if you had a constant load on the system. Then you could calculate the right transition value.
> 
> Larry 
> 
> 
> On Jul 8, 2012, at 10:00 AM, mac Lewis wrote:
> 
> 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
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