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 <la...@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@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 *
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