generator/inverter charging setup...

Re: generator/inverter charging setup...

Quote: "wow I didn't realize that it made that much of a difference even over the course of a few days."

According to Trojan's maintenance guide here: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance/Discharging.aspx  Item (5) statess  "Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice."

  Do they say this because they want to sell more batteries to replace those that died prematurely from undercharging?  I don't think so because their reputation is at stake.  Do they want you to charge your batteries more than is required to keep them from sulfating because it makes their output specifications look better?  That's possible.  It seems to me that lead/acid batteries are very robust, just don't do anything to intentonally kill them.

   I'm no expert, but personally, if my eight three year old T-105's are at 90% I don't worry about them at all and they're working fine.  Another thing to consider if you are willing to go this route, the last 10% of charging is the most inefficient.  If you don't push your battery to 100% you don't lose that inefficiency.  Your investment in your Surrette's is quite a bit more than mine so maybe you need to be more anal about it than I am. 

  This practice would not apply to AGM's since it requires an equalization charge and that's a no-no on them.

  This site http://www.batterystuff.com/tutorial_battery.html  states "*Sulfation of Batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery) or 6.2 (6 volt battery). Sulfation hardens the battery plates reducing and eventually destroying the ability of the battery to generate Volts and Amps."  The battery State of Charge chart there states that is 75% SOC.
The NAWS Deep Cycle Battery FAQ here http://www.solar-electric.com/deep_cycle_batteries/deep_cycle_battery_faq.htm puts that at about 65% SOC using specific gravity and about 80% SOC using voltage.

  If it's true that sulfation begins at 75% SOC then 90% SOC shouldn't be a problem, just food for thought.

Cheers,

Bad Apple

Re: generator/inverter charging setup...

  The paper abstract of the cited Sandia Labs document on page (1) states: "Recovery of the PV battery after extended periods in a deficit charge condition may or may not be possible depending on the extent of battery degradation and the resources available for recovery".

  Page (2) PV Batteyy Capacity Loss:  "In PV systems a compromise between battery capacity and maintenance is reached by using a temperature compensated regulation voltage that maintains the battery to at least 80% of its initial capacity"

  Using the trendline in Fig. 1 on page (3), the Vrr at 80% is ~ 14.2V, Vr would have to be interpolated from the given data points, perhaps 14.4V.  The "Vrr" in the graph could be equated with "absorb" and "float" voltage on PMW or MPPT controllers being set to ~14.4v.  Many would say this is battery murder, I feel that this paper argues that it is acceptable.  Just be sure to equalize per the manufacturers recommendations.

  On page (5) under the "Excessive Sulfation" heading it states ""Hard" sulfation as a capacity loss mechanism can be identified by a long history of under charging (usually months) and a low specific gravity (<1.250) after heavy gassing for sevaral hours during a full recharge to the equalization voltage."

  To me this says that sulfation isn't a cause of permanent capacity loss until it has undergone weeks or months of undercharge, becoming the "hard" type of sulfation.  The article states that the test is to equalize and then check specific gravity.  It seems to me that if SG remains low, the lead sulfate is "hard" and resistant/unable to convert back into positive plate material and sulfuric acid, resulting in low SG and capacity.  Likewise, if it is "Soft", the lead sulfate will combine readily with available water and convert back to lead oxide on the positive plates and sulfuric acid, thus increasing SG and returning the battery to normal capacity, no harm no foul.  Makes sense to me.

  Page (6) under the "Hard" Sulfation Battery Recovery heading goes even further and states "Desulfation tests based on the battery manufacturer's recommended recovery procedures have demonstrated that vented deep-cycle lead-antimony golf cart batteries could be recovered after approximately 6 months of cycling in a deep discharge state between 20% and 30% capacity."

  I'm not certain but it seems like they are saying they charged golf cart batteries to 30% SOC and discharged them to 20% SOC, recharged them to 30%, etc. for six months.  Their wording could be a little more clear though.  If  that is in fact their test method, it tells me that as long as the battery is being cycled you have much more leeway in removing the "soft" sulfation.

  It goes on to say that "... In this case the battery is clearly suffering from "hard" sulfation as indicatedd by the low battery specific gravity of 1.230 after an equalization charge to 7.65 volts (2.55 vpc) for 3 hours.  ...The result after nearly 600Ah recharged into the battery was a recovery to normal specific gravity (~1.277) and 80% of the battery's initial capacity after 2years of normal PV service and 6 months of cycling between 20% and 30% capacity."

  Taking two year old batteries and then "abusing" them for six months and recovering like that is pretty robust in my book.

  I suspect a battery in a discharged state that is being cycled and that does not have "hard" sulfation, that one day molecules A - M of "soft" sulfation gets reconverted back to positive plate material and sulfuric acid, the next day molecules N - Z gets reconverted and so on.  No molecules stay in the "soft" form long enough to harden.  Again, just a suspicion and I do not recommend operating a battery at this SOC as a practice.

  In my first post on this topic I was not trying to imply that equalization is unnecessary, equalization is necessary which is why I stated that this strategy would not be suitable for AGM's.


  I don't feel that chasing the elusive "100%" SOC is worth losing sleep over.  Why is 1.277 SG selected as "100% SOC" anyway?  You can charge a battery to 1.287 if you like, why isn't that considered 100% SOC?  At that SG, capacity would be greater but battery life might be lessened.  Perhaps 1.277 SG is slanted toward more capacity with decent life.  Maybe 1.267 SG would lean towards more longevity but less capacity.  There seems to be plenty of evidence in the paper that it isn't that big of a deal, at least that's how I read it.  Don't overly discharge them, "opportunity" charge them when you can, equalize them per the manufacturers recommendations, keep them watered and clean and I think they will serve you well.  Again, I'm not an expert and my T-105's aren't that expensive compared to Surrettes.

Nomex on.

Cheers,

Bad Apple

Re: generator/inverter charging setup...

crewzer wrote:

  On page (5) under the "Excessive Sulfation" heading it states ""Hard" sulfation as a capacity loss mechanism can be identified by a long history of under charging (usually months) and a low specific gravity (<1.250) after heavy gassing for sevaral hours during a full recharge to the equalization voltage."

This says to me that just one winter (several months) of abuse (cold batteries, relatively deep discharges, undercharging due to insufficient charging resources, and/or rare equalization) will lead to hard sulfation and resulting reduction of battery capacity and useful life.

To me, that just describes how to identify a battery that is suffering from "hard" slufation, not whether or not it can be removed to regain capacity or what it does to useful life. 
 

  My statement "Nomex on" was simply to acknowledge that my opinion runs counter to the majority on this forum and like the entire post, it wasn't directed to anyone in particular.

  Cheers,

Bad Apple

Re: generator/inverter charging setup...

Hillbilly,

However you boost your charging capabilities, you should only run a generator with a rectified load (transformer/rectifier chargers) at 70% of it's rated capacity. I'm not familiar with the Iota charger's manufacture, or the Outback inverter/charger's for that matter, so don't know if this is pertinent to your thread.

I run a 10kw diesel genset at 7kw, charging with my Xantrex 4048 and a Vulcan lift truck charger (100amp dc). THis has greatly reduced my gen run times, but does require monitoring the genset load. It's easy to overload and shutdown the genset if you over do it.

THe Vulcan has no input or output controls and reduces output amps as battery voltage rises, so to keep the total load on the genset below 7kw i use a clamp meter on the genny input wires and adjust the total load with the Xantrex charging control input menu. Works like a charm, but not for an unsupervised charging run. Adjustments are made every 30 minutes or so over a 3-4 hour charge.

Usually the downrating of a genset is moot since the charge capabilities of an inverter/charger won't exceed the genset's capabilities. My X-company unit on it's own will only draw 3800 watts or so, easily handled by a 5 or 6 kw gas/Lp/diesel genset. Running 2 inverter/chargers would necessitate 10-12kws of gen capacity to be safe...IMO.

ralph