Please Explain Charge End Amps

FlubberFlubber Registered Users Posts: 19
Hello All,

I am working with a system on a property I recently moved to and I am having some difficulty trying to understand items 1 and 2 below. Any help understanding theses would be greatly appreciated.

1)[ The Absorb End Amps setting on the Out back FM-80 Charge controller.

From my understanding of the FM-80 after it reaches the absorb voltage it will always perform the set absorb time cycle.

So that even if your batteries are already charged in the morning to some degree they will always get the full absorb time after the bulk cycle.

Would this not result in over charging?


The Out back FM-80 manual talks about an Absorb End Amps setting, and I heard this is a way to end the absorb cycle based on how full the batteries are, but the Outback manual also says that this setting is rarely used.

I don't understand, that if the charge controller doesn't vary the absorb time
based on the batteries actual state of charge doesn't that limit it's effectiveness?

So I am looking for an explanation of this, and if I should bother to use the Absorb End Amps setting and how to set it.


2) What value to set the Fully Charged Current, on the Trace battery monitor.

The Trace battery monitor manual says:
Three stage chargers maintain batteries at a float voltage and a trickle current. Adjust the voltage criterion slightly below the chargers float voltage setting and set the current criterion slightly below the float charge current.

My question here is what is the float charge current to set the monitor at?

And if you have loads occurring how is there any consistent current flowing would it not be varying?


The system specs are:

24V
2350 watt array
800 Ahr battery bank


Thank you!

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please Explain Charge End Amps

    Welcome to the forum.

    They didn't leave you the manuals? Look closely at the bookshelf; you may have mistaken the Outback Programming Manual for an encyclopaedia. :p

    The whole "end Amps" thing is an either/or function of the Absorb stage. Normally the controller is set to count up the amount of time from when Bulk charging begins until Absorb Voltage is reached. It then holds that Voltage until an equal amount of time elapses, or the maximum time limit is reached (programmable up to 4 hours), or the End Amps (also programmable) is achieved. Under most circumstances the counter method is best, as the Amp check can't take into account variable loads drawing on the batteries while Absorb is still under way. Even so, the Absorb stage will end when the maximum time is reached. No it will not overcharge the batteries, providing the parameters are correct.

    The manual: http://www.outbackpower.com/pdf/manuals/flexmax.pdf

    I don't have knowledge of the Trace battery monitor, but certainly someone here does. Looks like a bit of trial and error is in order. The basic function is that when the charge controller drops out of Float the batteries take over powering things again, and so the monitor will be counting electrons going in/out to recalculate the State Of Charge.
  • FlubberFlubber Registered Users Posts: 19
    Re: Please Explain Charge End Amps

    I did read the FM-80 manual and they have a confusing explanation of the absorb cycle time and how long it will run for on page 84.

    Cariboocoot wrote:
    Normally the controller is set to count up the amount of time from when Bulk charging begins until Absorb Voltage is reached. It then holds that Voltage until an equal amount of time elapses, or the maximum time limit is reached

    So are you saying here that If the bulk cycle is short because your batteries are in a fuller state of charge the absorb cycle will be shortened.

    For example lets say your absorb time limit is set to 2 hours.
    And then if a bulk cycle takes only 1 hour to reach the absorb V
    Then the absorb time will be only 1 hour?




    As far as the battery monitor it seems to me that the situation you refer to in the charge controller:
    Under most circumstances the counter method is best, as the Amp check can't take into account variable loads drawing on the batteries
    Was what I was wondering about the battery monitor?





    I now just found in the battery monitor manual that the "fully charged current" = battery capacity / 20 Can some one explain this.

    And it goes on to say When voltage meets or exceeds the charged voltage set point and charging current is equal or less than the "fully charged current" then it considers the batteries fully charged and resets the amp hour counter.

    So for example 800 Ah / 20 = 40 amps "fully charged current"

    What does this mean that If your batteries are at a fully charged voltage and the current flowing into them is less than 40 amps they are charged? Can some one please explain this for me




    Cariboocoot wrote:
    The basic function is that when the charge controller drops out of Float the batteries take over powering things again, and so the monitor will be counting electrons going in/out to recalculate the State Of Charge

    Cariboocoot so are you say here that this is when your battery monitor should be reseting the amp hour counter to zero?

    So in that case would I set the battery monitors fully charged or reset voltage to just below my float voltage? and then what number would I set the amp criteria at?

    Thanks!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please Explain Charge End Amps

    You're getting it.

    The FM has three criteria for ending the Absorb cycle: Bulk Charge Time, End Amps, and Absorb Time Limit. The last two are programmable. Which ever condition is met first ends the Absorb cycle. A battery that doesn't need much charging will have a short Bulk Charge Time. So the usual state is to allow that to control the Absorb cycle by setting the End Amps to "zero" (which won't be reached) and the Absorb Time Limit to maximum (4 hours).

    However, lightly cycled batteries sometimes don't get enough Absorb. In this case the End Amps can be set to a figure around 1-2% of the battery capacity. The controller will then stay in Absorb until either End Amps or Time Limit is reached. This helps prevent sulphation.

    It appears your battery monitor is basing its fully charged current status on the 5% minimum of Amp hour capacity. So yes, an 800 Amp hour battery bank would charge at 40 Amps at least. This is not necessarily the best choice for all batteries or operating conditions. The idea is that when current drops below this point it will trigger "charged". Frankly I do not agree with that, as it would disallow the entire Absorb cycle. Perhaps it needs to see both criteria: Current below 5% and Voltage below Absorb setting. Maybe someone else can clarify the settings. As I said I'm not familiar with this particular monitor.
  • FlubberFlubber Registered Users Posts: 19
    Re: Please Explain Charge End Amps

    Thanks Cariboocoot,
    I have a few questions about yor last post.
    So the usual state is to allow that to control the Absorb cycle by setting the End Amps to "zero" (which won't be reached) and the Absorb Time Limit to maximum (4 hours).

    So does this infer that the absorb cycle will never be to long if you set it up this way. That the Bulk cycle will always control the Absorb cycle and you don't have to worry about it being to long and over gassing your batteries?
    It appears your battery monitor is basing its fully charged current status on the 5% minimum of Amp hour capacity

    It also asks for a charged voltage setting to work along with the Charged set point amps, and I have seen it suggested that one should use 1 to 2% of the total capacity as the fully charged current set point.
    The idea is that when current drops below this point it will trigger "charged"

    My confusion stems from the fact that the Trace battery monitor I am using and other similar ones lik the trimetric are not linked
    to the charge controller. So lets say the batteries are in the process of being topped off, the current they will accept is being
    reduced approaching the fully charged current mark you programmed into your meter, but then clouds come over or the loads increase so that whats "left over" that goes into the batteries falls below that fully charged current mark, then the monitor would see a full charged state and reset?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please Explain Charge End Amps
    Flubber wrote: »
    So does this infer that the absorb cycle will never be to long if you set it up this way. That the Bulk cycle will always control the Absorb cycle and you don't have to worry about it being to long and over gassing your batteries?

    If the array is sized properly, yes; the batteries will charge up rapidly and Absorb time will be less than 4 hours. Since there is rarely more than 4 hours of "equivalent good sun" in a day the whole process should fit in that time frame.
    It also asks for a charged voltage setting to work along with the Charged set point amps, and I have seen it suggested that one should use 1 to 2% of the total capacity as the fully charged current set point.

    That makes more sense. When charge current drops that low the battery is charged. This coincides with the "End Amps" setting on the charge controller.
    My confusion stems from the fact that the Trace battery monitor I am using and other similar ones like the Trimetric are not linked to the charge controller. So lets say the batteries are in the process of being topped off, the current they will accept is being reduced approaching the fully charged current mark you programmed into your meter, but then clouds come over or the loads increase so that whats "left over" that goes into the batteries falls below that fully charged current mark, then the monitor would see a full charged state and reset?

    This is a common situation. In fact the #1 "what do you want in a new charge controller?" answer here recently was "integrated battery monitor". Usually such a drop as you describe would not be a problem, as even if the whole process reset it would be back to nearly charged very quickly. The monitor should notice this and recalibrate accordingly; it's just going to start again fro 95% SOC instead of 70% (or whatever). The Voltage shoudl rise quickly, the Absorb stage be re-entered at about where it left off, and Float attained with only a minor blip.
  • FlubberFlubber Registered Users Posts: 19
    Re: Please Explain Charge End Amps
    So does this infer that the absorb cycle will never be to long if you set it up this way. That the Bulk cycle will always control the Absorb cycle and you don't have to worry about it being to long and over gassing your batteries?
    If the array is sized properly, yes; the batteries will charge up rapidly and Absorb time will be less than 4 hours. Since there is rarely more than 4 hours of "equivalent good sun" in a day the whole process should fit in that time frame.

    Are you saying you don't have to worry about over charging with an improperly sized array just potentially under charging?

    Well thanks for all the info! I will have to watch the monitor and see if it resets somewhere around when the system goes into float I guess?
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: Please Explain Charge End Amps

    You can even overcharge with a 1% rate of charge and no loads if the charging voltage is well over float voltage,,, I have done that with a cheap trickle charger.

    Basically watch your batteries and adjust.

    Many folks set for two hours in summer and 4 hours or so in winter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • silvertopsilvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: Please Explain Charge End Amps

    I'm very glad someone started this topic. I just talked with Xantrex about other parameters with the XW MPPT SCC, and mentioned that I was only using the timer set to 4 hours for end of absorption and he questioned me as to why I was not using the exit current threshold amps. The XW uses 2 % of the battery AH capacity. I have noticed that when running larger loads during absorption, the timer usually runs full 4 HR. but with lighter loads, the exit current threshold will transition the SCC to float. I also noticed that before EQ, the SCC will bring the bank up to absorption and If I use exit current, will transition quickly to EQ. But, if I only use the timer ( set to 4 HR now ) It would take that amount of time before It would go into EQ , about the time I run out of daylight . All in all both seem to work hand in hand a good thing8)
  • Ralph DayRalph Day Solar Expert Posts: 892 ✭✭✭✭
    Re: Please Explain Charge End Amps

    I found that end amps was unreliable for my situation. I have a SSWP H 80 wind turbine as well as my pv charging my batteries. If it's a windy sunny day the MX60 can "end amps" terminate the charge when there's wind energy in relatively large amounts. ie the mx will switch to float because it reaches the end amps setpoint but the setpoint is reached because of the amps put in by the wind turbine .

    Being here all the time allows me to monitor quite closely if full SOC is reached, then I can trip things to float.

    Ralph
  • FlubberFlubber Registered Users Posts: 19
    Re: Please Explain Charge End Amps

    Well I have been thinking about this since my original post and have realized that with a charge controller that is not hooked up to a battery monitor It looks like it cant possibly detect a charging end amps value because of the varying effects of loads on the system.

    So I would assume that the end amps setting is useless on th Outback FM-80 unless you have their battery monitor perhaps. (but they don't say this in their manual but they do say that the end amps setting is hardly used).


    But being a beginner with this technology I would like to know the following and would appreciate it if some could answer these questions for me.

    1. Is the end amps setting on the FM-80 of any use
    with out using Outbacks Flexnet battery monitor?

    2. If you want to determine an end amps figure through
    observation how would you do that?

    3. When using a Trimetric type battey monitor that uses
    one shunt, Where along the charging cycle is the
    best place to set the voltage and amps setting in the
    battery monitor for it to do its amp hour counter
    reset. At the absorb voltage? At the float? What
    current value would you use?

    Thanks!!
  • VicVic Solar Expert Posts: 2,976 ✭✭✭✭
    Re: Please Explain Charge End Amps

    Hello Flubber,

    If you have Flooded batteries -- ones with removable caps, it is fairly easy to monitor the SG of the battery bank. This monitoring is the best way to adjust charge parameters from the charging source(s).

    I usually use the End Amps (sometimes called Return Current). My daytime loads are light, and the target current for my system is about 17 amps, such that even moderate loads are not a huge factor.

    On this site, battery monitors are often recommended, but with the Trimetric, one needs to make guesses/adjustments for battery charge efficeincy etc. For me, FREQUENT monitoring of the Pilot Cell of a bank is the key to happiness. When I'm making adjustments to charge parameters, usually monitor the Pilot Cell daily, often multiple times per day. YMMV Good Luck,
    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.
  • Ralph DayRalph Day Solar Expert Posts: 892 ✭✭✭✭
    Re: Please Explain Charge End Amps

    Hey Vic,

    Glad to see your post. I thought I was the only person checking soc multiple times daily (some days). I change the pilot cell every month, what about you?

    Ralph
  • VicVic Solar Expert Posts: 2,976 ✭✭✭✭
    Re: Please Explain Charge End Amps

    Hi Ralph,

    Well, I should not cop to my slight obsessiveness.

    I do change pilot cells, but not monthly. You may have the "bug" at a slightly higher intensity than I.

    Enjoyed your pix of that huge PV project you did for yourself. Very informative. Thanks, 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.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please Explain Charge End Amps

    You're both suffering from O.S.P.D.: Obsessed with Solar Power Disorder. Don't worry; aside from atrophying of finances and some irritation of spouse it's quite harmless. There is no cure. Supportive treatment involves prolonged exposure of the patient's photovoltaics to intense solar radiation. :p
  • silvertopsilvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: Please Explain Charge End Amps

    I thought I was the only one with OSPD! I sure could use some more sunshine:D
  • mike95490mike95490 Solar Expert Posts: 8,470 ✭✭✭✭✭
    Re: Please Explain Charge End Amps
    You're both suffering from O.S.P.D.: Obsessed with Solar Power Disorder. .....

    Oh just great, its got a name. My wife's likely to do a research project on me now !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please Explain Charge End Amps
    mike90045 wrote: »
    Oh just great, its got a name. My wife's likely to do a research project on me now !

    My wife's been studying me for years. Hasn't figured me out yet. :p
  • Ralph DayRalph Day Solar Expert Posts: 892 ✭✭✭✭
    Re: Please Explain Charge End Amps

    O.S.P.D. I think you've misread the medical literature. What we're talking about here is a SYNDROME, not a disorder. The term Disorder is used to discriminate against people, syndromes describe behaviours that are not detrimental to the person/persons involved/afflicted. :D:p:cool:

    Ralph

    Ps: OSPD is too restrictive...I also have wind power, generator and utility power to consider in my SYNDROME. Maybe Obsessed with Generating Renewable Energy Syndrome, O.G.R.E.S. would better describe us. We're many layered...like an onion
  • petertearaipetertearai Solar Expert Posts: 406 ✭✭✭✭
    Re: Please Explain Charge End Amps

    Hi the fm80 has the option of end amps or a time or combination of both , depending on how you set it up.
    If using a trimetric or any other battery moniter the fm80 will act completely independent of the battery monitor.
    To find the time required for absorb you need see how long it takes for the absorb to reach an even lowest point charge.Set the fm80 to absorb forever and watch it.
    ( boring and time consuming)
    You will then have a time you can use to set into the fm80.You will also have an end amps to set.
    In my case I have set the time to 3 hours and an end amps of 5 amps.When I am in residence the absorb mostly goes for the full 3 hours. But while away the end amps kicks in and the history will mostly show 20 minutes or so.
    Until I learn more this is a good compromise situation,
    The more I learn about battery's the less I know.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home 
  • FlubberFlubber Registered Users Posts: 19
    Re: Please Explain Charge End Amps

    Vic,
    I usually use the End Amps (sometimes called Return Current). My daytime loads are light, and the target current for my system is about 17 amps, such that even moderate loads are not a huge factor.

    Can you explain this. so you look for a net of 17A returning to your batteries? Meaning that after your array has satisfied all loads and you have an additional 17A flowing in to you battery. Then what does this mean to you? Your batteries are full.

    Peter,
    To find the time required for absorb you need see how long it takes for the absorb to reach an even lowest point charge.Set the fm80 to absorb forever and watch it.
    ( boring and time consuming)

    So you watch the net current flowing into your batteries on your battery monitor while the FM-80 is able to maintain the absorb voltage, and you look watch the current until it stops decreasing.
  • VicVic Solar Expert Posts: 2,976 ✭✭✭✭
    Re: Please Explain Charge End Amps

    Hi Flubber,

    The End current that I am referring to, is the current flowing toward the batteries -- out of the charge controller. Any loads on the inverters appear in this value, and add uncertainty. But in my system, at this end of Asorb on a typical day, the current from the CC into the inverter DC inputs seldom exceeds threeish amps at the Asorb voltage. On average, this is not a big delta, and in monitoring the SG of the bank, this value works well.

    By battery bank is moderately large, so this End current is somewhat higher than that of a smaller bank, so, the effect of inverter load currents is fairly small.

    A final point is that one is really looking for trends, not really absolute values of SG. At least for my bank, when one makes a small change in Asorb voltage, time or End Current, it is good to watch the effect this has on the battery bank over a number of days. The larger the relative size of the bank, the more inertia it has, and the longer the effect of a change (particularly a small one) takes to appear.

    Flooded batteries are fairly forgiving. Caring and watching your bank places you far ahead of many other off-gridders. Many of my neighbors seem to only care about battery health and maintenance when the lights go out
    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.
  • petertearaipetertearai Solar Expert Posts: 406 ✭✭✭✭
    Re: Please Explain Charge End Amps
    Flubber wrote: »
    Vic,






    So you watch the net current flowing into your batteries on your battery monitor while the FM-80 is able to maintain the absorb voltage, and you look watch the current until it stops decreasing.

    Yes ,Best done with full sun day or with generator. Needs to be for 20 minutes or so at the same amps.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home 
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