Battery discharge rate question.

My SG readings are showing the need for an EQ. I have my inverter, (GVFX 3648 )set up to sell everything the solar array makes above float. Before doing the EQ I would like to do a 50% discharge in order to go through a complete charge cycle with a proper absorb phase first.

The question I have is would be better to draw the batteries down over several hours with normal household loads or to save time would it be safe to set the inverter's sell setpoint to 48 volts and let it bang the battery bank at 3600 watts for as long as it takes? (Probably not too long)

Thanks
Dennis

Comments

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Battery discharge rate question.
    verdigo wrote: »
    Before doing the EQ I would like to do a 50% discharge in order to go through a complete charge cycle with a proper absorb phase first.

    I guess to each his or her own, and some may not agree with me, but I've never deliberately discharged my batteries to any level for the sake of doing so, and wouldn't do so now. My last bank of L-16 lasted 12 years and seldom got discharged lower than the 90% fully charged state.
    Same with the Surrettes I now have. If mine were or are in need of an EQ, I did / do the EQ whenever they were / are fully charged. But like I say, I'm sure others will not agree with the way I treat my batteries. But after the first bank lasted so long, I'd have to say it worked for me.
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.

    It's hard to argue with experience but in the past my batteries seem to have benefited from a longer climb to absorb voltage with less time in eq, and with less repetition of eq cycles.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery discharge rate question.
    I guess to each his or her own, and some may not agree with me, but I've never deliberately discharged my batteries to any level for the sake of doing so, and wouldn't do so now. My last bank of L-16 lasted 12 years and seldom got discharged lower than the 90% fully charged state.
    Same with the Surrettes I now have. If mine were or are in need of an EQ, I did / do the EQ whenever they were / are fully charged. But like I say, I'm sure others will not agree with the way I treat my batteries. But after the first bank lasted so long, I'd have to say it worked for me.

    No disagreement here. There's no point in purposefully discharging the batteries only to recharge them and then EQ. The only time you cycle batteries outside daily use parameters is when you're trying to get some new ones up to full capacity (form the plates).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery discharge rate question.
    verdigo wrote: »
    It's hard to argue with experience but in the past my batteries seem to have benefited from a longer climb to absorb voltage with less time in eq, and with less repetition of eq cycles.


    There shouldn't be any EQ done unless actually needed. If the batteries are charged they are charged; you can start EQ after that regardless of how little/great amount of time the charging took.
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.

    Strange. I'm sure I got the idea of this from this forum. Maybe I misunderstood.
  • BB.BB. Super Moderators, Administrators Posts: 32,226 admin
    Re: Battery discharge rate question.

    We do talk about designing the system for 25% discharge as a good middle of the road number. 10% cycling is a pretty shallow cycle, and, in theory, could result in a shorter life.

    But, hard to argue with success.

    Of course, a shallow cycled battery will be able to lose much more than 20-40% of its capacity and still function for that particular installation.

    I don't remember if Wayne's batteries are in an unheated area or not--Running very cold will lengthen battery life too (ever 10C below 25C, aging life should double).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Battery discharge rate question.
    BB. wrote: »

    I don't remember if Wayne's batteries are in an unheated area or not--Running very cold will lengthen battery life too (every 10C below 25C, aging life should double).

    -Bill
    Good point Bill, my batteries are indeed in an unheated outbuilding and at the moment, their temperature according to the TS-MPPT-60 is 4C. Some Winters I add insulation and they rarely then drop below zero C. Uninsulated, they sometimes drop to minus 8 or 10C. So those low temps could well be extending their life. And since loads tend to be either light or if heavy, short duration, lower cold capacity hasn't been a problem.
  • VicVic Solar Expert Posts: 3,125 ✭✭✭✭
    Re: Battery discharge rate question.

    Hi Dennis,

    Personally, am in the camp of purposely discharging the battery bank to 60 - 70% SOC on occasion. Cycling Flooded batteries below 90% SOC, on occasion is better for them than not, IMO.

    When the banks here have not been very deeply-cycled for a period, will either shut off the PV in for a few days, or just purposely discharge them at about the 20-hour current rate, with electric heaters, usually with the CC Mode=Off or by shutting off the CC input breaker.

    This purposeful deeper cycling seems to actually make the SG readings more consistent cell-to-cell, especially for the few cells that usually run SGs of 1.280 or more (on batteries with Target SGs of 1.265).

    Just my experience/opinions. Opinions vary quite widely on things like this. You will develop your own "Right Way" to deal with your batteries.
    YMMV, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.

    Thanks Vic. Since I am more on the grid interactive side of the house I didn't feel it was a waist to discharge my batteries into the grid in order to get a proper discharge and charge cycle.

    I made some mistakes in equipment purchases in that I now believe i should have selected an Outback CC and FNDC to better automate my selling using the Mate to control the CC.

    As it is, unless I stop selling, the classic CC never gets out of bulk so most of the time my bank stays at a temperature compensated float voltage that is dictated by the GVFX's sell voltage set point.

    The frustrating thing about it is I ask a question about discharge rate but what I got was something else. If I Change the GVFX's sell voltage set point to say 48.5 volts to stay above 50% SOC the inverter will go to its full 3600 watts to sell down to that voltage. The question was whether that was too extreme a discharge rate or should I just use normal household loads to affect some other discharge rate.

    Thanks for your reply.

    Dennis.
  • VicVic Solar Expert Posts: 3,125 ✭✭✭✭
    Re: Battery discharge rate question.

    Hi Dennis,

    Was trying to comment on two questions.

    To me, the 20 Hour Rate is about the limit that I would like to discharge my batteries. The 15 hour rate is my personal absolute maximum.

    In my opinion, discharging your 460 Ah bank at 3600 watts is really hammering it -- about 75 Amps, as I see it. I would not do that.

    Am not a Grid Interactive person, so do not know the options you might have available. And it is not clear the demand that your normal household loads would present to your batteries.

    BUT, do believe that basically Floating your batteries essentially constantly, may not be that good for them, and some cycling should really be good for them, but whatta I know.

    And from what I read on the Outback Forum, there seems to be a few issues with the FNDC's operation -- possibly a few bugs ...

    FWIW, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery discharge rate question.

    verdigo
    I have no experiance selling but before I hooked up I used to read the outback site alot. I see vic helping there alot also. If my memory is correct there are a couple of things I question about your way of doing things. One, keeping a battery at 50% discharge due to sell voltage seems counter intuitive. I believe keeping the batteries as full as posible at all times would alow you to sell much more and that your voltage should reflect that. If you search the outback forum, there are lots of old threads about "sell voltage." I do think vics point of using the batteries every so often for battery health is important, mayby once or twice a month.

    Also when re-charging. My understanding is that the equiptment will recharge the batteries before allowing you to sell based on what settings you program. It won't work if the programing is not good. Again, I have no experiance but just reading as I don't sell.

    I believe that the old thread reflect the sell voltage to be as high as possible to reduce the losses of having to recharge.

    I did not read the whole thread just now and am responding to just your last post.
    good luck
    gww
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery discharge rate question.

    One more thing.
    I made some mistakes in equipment purchases in that I now believe i should have selected an Outback CC and FNDC to better automate my selling using the Mate to control the CC.

    I don't believe the classic should affect your selling in any fassion. It is the inverter that has to meet the voltage thresholds that it is set for prior to selling. If it is programed correctly it shouldn't care what causes it to meet those thresholds.

    This is just my understanding of how things work.. For example. Say I eq through the mate but my cc and inverter is not at the same voltage even though all are controlled to start eq through the mate. Say eq for 3 hours. The lowest voltage item is going to reach 3 hours first and stop providing power. The highest item wont reach eq cause the lowest one quit giving power and the highest one cant do it on its own. the next day one item is going to be in bulk and the other is going to want to finnish the eq. My stuff is all outback and can be controlled through the mate to start and stop stuff but the individual settings still matter. The inverter is what sells and it has to be programed correctly and then has to meet the program criteria to work properly.

    I hope this helps
    gww
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.
    Vic wrote: »
    Hi Dennis,

    Was trying to comment on two questions.

    To me, the 20 Hour Rate is about the limit that I would like to discharge my batteries. The 15 hour rate is my personal absolute maximum.

    In my opinion, discharging your 460 Ah bank at 3600 watts is really hammering it -- about 75 Amps, as I see it. I would not do that.

    Am not a Grid Interactive person, so do not know the options you might have available. And it is not clear the demand that your normal household loads would present to your batteries.

    BUT, do believe that basically Floating your batteries essentially constantly, may not be that good for them, and some cycling should really be good for them, but whatta I know.

    And from what I read on the Outback Forum, there seems to be a few issues with the FNDC's operation -- possibly a few bugs ...

    FWIW, Good Luck, Vic

    Thanks Vic. That pretty much answers my question. Putting a heavier than normal load on the batteries to discharge them a bit by setting the sell set point low was to get through a charge cycle and EQ. In the past I have discharged them at 800 watts (according to the GVFX's display).

    The question on using a more aggressive heavier discharge rate was to save time on the whole process, but I don't want to damage my batteries and will take your advice. I am still a noob at this and although noobs are suppose to kill their first set of batteries early I would like them to last as long as I can. In the past the EQ seemed to affect the SOC numbers with less time in EQ when the batteries went through a discharge / charge cycle prior to the EQ.

    Thanks again

    Dennis
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.
    gww1 wrote: »
    One more thing.



    I don't believe the classic should affect your selling in any fassion. It is the inverter that has to meet the voltage thresholds that it is set for prior to selling. If it is programed correctly it shouldn't care what causes it to meet those thresholds.

    This is just my understanding of how things work.. For example. Say I eq through the mate but my cc and inverter is not at the same voltage even though all are controlled to start eq through the mate. Say eq for 3 hours. The lowest voltage item is going to reach 3 hours first and stop providing power. The highest item wont reach eq cause the lowest one quit giving power and the highest one cant do it on its own. the next day one item is going to be in bulk and the other is going to want to finnish the eq. My stuff is all outback and can be controlled through the mate to start and stop stuff but the individual settings still matter. The inverter is what sells and it has to be programed correctly and then has to meet the program criteria to work properly.

    I hope this helps
    gww

    I think you have misunderstood a little. I don't maintain my batteries at 50% SOC. They stay pretty much in float. Also to sell one simply inputs the sell voltage and the inverter sells everything the array and Classic will put out above that set point.

    The problem is with no communication between the Classic and the GVFX is that the sell set point has to be the battery bank's float voltage to maintain the bank at 100%. The sell set point voltage is not automatically temp compensated, and the Classic will never go to absorb unless the set point is manually changed on the Mate. Currently I do a 30 min absorb with the GVFX's charge every other day or so.

    As I understand it with the Outback charge controller and FNDC all of these functions can be programmed to more easily automate charging and selling. With all of that said it is entirely possible I am missing something..

    Thanks
    Dennis
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Battery discharge rate question.
    BB. wrote: »
    10% cycling is a pretty shallow cycle, and, in theory, could result in a shorter life.
    Shallow cycling causes lead dioxide to clump on the positive plates.
    BB. wrote: »
    But, hard to argue with success.
    Of course, a shallow cycled battery will be able to lose much more than 20-40% of its capacity and still function for that particular installation.
    Indeed! I know of many off-grid systems that routinely get 11-12 years from a bank of L-16 batteries. These batteries are undergoing slow deficit charging and sulfation. The key to their longevity is that they are "old-school" design... the battery bank is much larger than needed and not enough solar panels. The reason the batteries last so long is that they are not replaced until they have only about 30% capacity.
    BB. wrote: »
    I don't remember if Wayne's batteries are in an unheated area or not--Running very cold will lengthen battery life too (ever 10C below 25C, aging life should double).

    Yes, But...
    if your overnight load is the same, then a colder battery will be discharged (by that load) to a lower SOC than a warmer battery. Also, because of peukert factor, the load will consume more amphours of the reduced battery capacity. The effect of greater daily cycling (as a percent of SOC) is to reduce battery life.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Battery discharge rate question.
    Vic wrote: »
    This purposeful deeper cycling seems to actually make the SG readings more consistent cell-to-cell, especially for the few cells that usually run SGs of 1.280 or more (on batteries with Target SGs of 1.265).

    Are you saying that you deep cycle the batteries to get the SG down to 1.265 from 1.280? Or are you saying that deeper cycle helps get all the cells up to 1.280?
    Vic wrote: »
    BUT, do believe that basically Floating your batteries essentially constantly, may not be that good for them, and some cycling should really be good for them,

    I agree. Many battery charger manufacturers (Iota, and others) have an automatic EQ or absorb cycle every few days for batteries that are constantly floating. This is because stratification of the electrolyte may occur during float.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery discharge rate question.
    I think you have misunderstood a little. I don't maintain my batteries at 50% SOC. They stay pretty much in float. Also to sell one simply inputs the sell voltage and the inverter sells everything the array and Classic will put out above that set point.

    The problem is with no communication between the Classic and the GVFX is that the sell set point has to be the battery bank's float voltage to maintain the bank at 100%. The sell set point voltage is not automatically temp compensated, and the Classic will never go to absorb unless the set point is manually changed on the Mate. Currently I do a 30 min absorb with the GVFX's charge every other day or so.

    As I understand it with the Outback charge controller and FNDC all of these functions can be programmed to more easily automate charging and selling. With all of that said it is entirely possible I am missing something..

    Thanks
    Dennis

    It is definatly not impossible that I misunderstood. Heck I might not understand at all. I get the batt. temp comp thing not being shared.

    I don't own a fndc so don't know the control capabilities of one. I may not understand the inverter. I had thought that it said in the inverter manual that no selling would take place untill a bulk/absorb charge had taken place. I assumed this happend daily triggered by time and not by the battery not reaching some low volt set point. My batteries are absorbed daily even if I don't put a load on them from the day before and they are still full..

    If you only absorb every other day. then I guess my above assumption is wrong. I guess I need to get the manual out and look at it again.

    good luck
    gww
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery discharge rate question.

    On pages 18 through 23 of the below document.

    http://www.outbackpower.com/downloads/documents/gfx_series/gfx_operators_manual.pdf

    I may be reading this wrong but it basically states to me that untill the battery meets the charging settings that are set in the inverter, it won't sell.

    Having an external charging source should not change this. I do understand that the temp comp of the classic compared to the inverter could make a small differance but in the end the inverter should be the controlling item and its settings should allow the battery to be well taken care of prior to selling and also during selling. Then again I still may not understand what I am reading.

    The classic should be able to be made to work well with the inverter in a way that cuts down having to interveen except when you perposly intend to take the batteries lower for their health. I am not saying what you are seeing is not happening but wonder if some setting is keeping the classic from takeing the batteries to absorb cause the inverter should also need whatever absorb settings you have put in it daily.

    gww
  • VicVic Solar Expert Posts: 3,125 ✭✭✭✭
    Re: Battery discharge rate question.
    vtmaps wrote: »
    Are you saying that you deep cycle the batteries to get the SG down to 1.265 from 1.280? Or are you saying that deeper cycle helps get all the cells up to 1.280? ...

    Hi vt,

    What I was trying to say, is, That in each of the two larger battery banks here, there are two cells, that have always had higher-than target SGs (1.280 rather than 1.265, fully charged) when regularly cycled to about 80% SOC. Cycling these banks to about 70% (or so) SOC on occasion, results in these cells falling into line with the other cells in each of these banks -- more consistent at about 1.260 - 1.265-ish SG across the banks.

    It may not be a coincidence, that in each bank with two high SG cell, both of the high SG cells are in a single 4-volt battery. This implies to me, that this high SG may be the result of the manufacturing process.

    And, of course, the high SG is not a result of having far too little water in these cells. All FWIW. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Battery discharge rate question.

    Did a lot of review on the manuals over the weekend. Unfortunately the sun did not cooperate to do any testing. In the past if I were to initiate a bulk charge with the inverter the Classic would not produce. It is my understanding that with a FM80 and a hub the Mate would use solar over grid power, or both given less than optimum sun.

    I'll pose this question on the Outback Forum and wait and see if anyone is trying to do this with other than an Outback CC.

    Thanks
    Dennis
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Battery discharge rate question.

    Verdigo
    I believe that in bulk all chargers would put out full power. Where you run into trouble is when you hit absorb. If the voltages are not calibrated perfectly the one pushing for the highest voltage and the other will start cutting back. This happens with all outback equipment even if it is hooked to the hub. I also find in my equiptment that the cc can be set to .1 volt and the inverter is like .4 of a volt. The inverter also goes in bigger volt cycles while charging, meaning it will go pretty far above the voltage set point for a bit and then drop below further then the cc does. The cc seems to react faster. The work around that I use is to either calibrate the inverter voltage to where it sees more volts then the cc, so it helps in bulk and cuts back before the cc. I try to get it close enough that it doesn't compleetly quit just that it hits the mark first. In my opinion/experiance, the only comunication that hooking to the hub gives to each devise is: Temp comp while using just one temp control and the abilite to start/stop eq, absorb, and flote and to have a monitor to see what each is doing. The actual workings of each componant is independant and has to have the correct settings and have to be calabrated with each other to work properly.

    Just my opinion.
    gww

    PS and it does take more time then most poeple have to get it correct.
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