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

Sun Jul 8 21:49:58 PDT 2012

Allan,

If you were to charge Lifeline AGM batteries (manufactured by Concorde) as described by Marc Kurth, you will damage the battery and void the warranty. You should never consistently deficit charge any lead acid battery. The proper charge method is clearly spelled out in Document No. 6-0101 Rev. C, Lifeline Technical Service Manual.

I highly recommend that all Concorde manufactured AGM batteries be charged by following the method described in the aforementioned manual.

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

On Jul 8, 2012, at 10:03 PM, Allan Sindelar wrote:

Mick and Wrenches,
I faced a similar question with a new bank just a couple of weeks ago. In my case I asked my distributor, and his response is below. He makes some interesting points, including a very different end amps than the factory's.

We have received very good service from this distributor, in case any Wrenches are looking for a Concorde distributor.
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
Allan:

I’ve had this conversation with several engineers and the responses are variable – so I will present what I believe to be true.

-          The aircraft battery side of Concorde says that a fully charged battery is one that reduces its current draw to under a nominal 0.5% of the 20/24 hour rating.

-          The RV/Marine & Solar guys insist that 2% to 5% is also a realistic number.

-          The factory only quotes numbers for new batteries – I have not been able to get concrete numbers for “less than new” batteries.

-          It is my opinion that the “right” number is very low with new batteries and climbs with battery age.

My choice would be to program a 2.5% to 3% current draw using a temperature compensated charger.

When looking at real world conditions that you and I encounter daily:

1)      Off grid PV systems most often do not have enough available hours to be concerned with excess absorption/acceptance hours. Even “occasional use on weekends” type systems are limited to “x” number of hours of solar input. (It gets dark for several hours every night – no matter what!) In reality, BY FAR more systems suffer from chronic undercharging than excess time in absorption mode!

2)      Grid tied battery backed systems, along with wind and hydro turbine systems can be a different animal because of the potential for “unlimited hours” of full power input for charging. THIS is when the current draw being used as a charge level indicator is most often needed, but........

3)      Undercharging is still by FAR the most common cause of premature battery failure. I have seen several battery banks survive the abuse of constant 24/7 charging at full absorption levels for five to six years, but I have yet to see one battery bank survive chronic undercharging for five years. These batteries used in RV/Marine/Industrial applications often see constant alternator-regulator outputs of 14.2v for 12 to 16 hours per day continuously. No, they don’t last as long as we want to see for our needs, but they often make it 5-7 years under really harsh conditions coupled with no float time.

Re-stating my view in simple terms:

-          A battery bank is fully charged when the current draw drops to 2.5 amps per hundred amps of battery bank capacity. Time to reach this point is almost irrelevant because of the variables.

-          BUT......a programmed time limit can be a VERY good thing in case of battery system or cabling faults which present a false load to the charging system – resulting in runaway charging!

-          The best time limit is dependent upon individual project parameters, but a good starting point is 25%-50% more time than the calculated charging time for a depleted battery bank.

Hoping this makes sense!

Allan, always feel free to send a note to Concorde to get their input! As I said above, I can’t avoid seeing things through the filter of my experience. That doesn’t always jive with the manual.

Best,

Marc Kurth

Centex Batteries, LLC

704 W Highway 71 - Suite B100

Bastrop, TX 78602

Ph 512 308-9002

Fax 877 254-2702

marc at centexbatteries.com

http://centexbatteries.com

From: Allan Sindelar [mailto:allan at positiveenergysolar.com] 
Sent: Wednesday, June 27, 2012 5:35 PM
To: marc at centexbatteries.com
Subject: Need a setting, please

Marc, 
Concorde provides good recommendations of voltage setpoints, which we follow. What is missing is a recommendation for absorb time.

For one of our recent PVX-9159 24V off grid systems, I have changed the charge setpoints, but need to know how long minimum and maximum to set the Outback MX-60 charge controller to stay in absorption mode (at 2.38 vpc with temp compensation) to fully complete charging before switching to float. If the answer is that the battery can stay in absorption indefinitely, then I will set it to the charge controller's maximum duration of 4 hours.

Could you ask Concorde for a recommendation? If an answer can be provided that includes guidance that is applicable to a variety of situations, that would be best.

In this case the array is about 1500 watts, or about a C/15 rate, not uncommon for a better off-grid system in our sunny region. 

Thank you,
Allan

-- 
On 7/8/2012 9:40 AM, Larry Crutcher, Starlight Solar Power Systems 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
> _______________________________________________