What is your trimetric measured battery AH vs manufacturer AH specs ?

For those with battery monitors, how does the actual measured AH capacity compare to manufacturers ratings of your batteries?

I have 8 Deka L16s wired in series (48V) as part of an off grid solar system with a XW6048 Xantrex inverter. I just installed a Bogart Engineering Pentametric battery monitor and measured my first charge cycle last night. I bought my batteries which are factory blemished a few months ago - they came with a 1 year warranty. I equalized them when installed and a few days ago and they charge to 1.265-1.275 SG on all cells. They have always been charged to 100% (going into float for > 3 hrs) every day within the specs from Deka for absorb/float/EQ (have XW custom battery programmed). They are connected with 4/0 cable all less than 5' and are connections are tight. I programmed 370AH into the Pentametric battery monitor for battery capacity per Deka's AH rating. Sundown to sunup last night the pentametric measured 85AH discharge going from 56.4V (my float charge setting) to 48.4V this morning. Prior to the beginning of the discharge cycle the batteries had been at float for over 4 hours with a voltage of 56.4V and current less than 4A so they should have been at 100% charge with 370AH capacity which is what the Pentametric also indicated (Pentametric 100% SOG =370AH(factory spec) defined as voltage > 56V, current<6A). At the time 48.4V (end of the discharge cycle) was measured the load was ~250W. The Pentametric indicated 77% SOG based on 85AH/370AH. However, to me 48.4V @ 250W indicates pretty close to 50% state of charge. So this tells me my battery capacity is not 370AH but really about 85AH * 2 = 170AH.

I figure one of several things is going on:
1. my batteries are no good w/ capacity only around 170AH instead of 370AH
2. it's normal for Deka L16s to only produce 85AH net @ 50% state of charge
3. my assumption that 84.4V @ 250W load is around 50% state of charge is wrong

Any ideas?

Also seems like the Pentametric should consider the Voltage/load curve as part of the SOG rather than just the battery manufacturers rated AH. Seems like over time as battery AH capacity naturally degrades, the Pentametrics SOG will become less and less accurate and will indicate overly optimistic SOG - unless I am missing something.

Comments

  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Meant SOC (state of charge), not SOG. :D
    I also sent this question to Deka.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    From offline discussion (with JeffKruse's permission) on same topic:
    jeffkruse wrote:
    I also show from 60 (on the very low end) to 110 (on the high end) AH of use every night, but due to cloudy weather my batteries might not be fully charged. The deepest I have gone is 180AH (as shown on the Trimetric) I forget what the SG was but I think it was about 60% on the worst cell.

    “Sundown to sunup the pentametric measured 85AH discharge @ 48.4V leaving a 77% state of charge indicated on the Pentametric.”
    I would think 48.4V is 50% SOC but Voltage readings are not good to use because they probably are not at rest. Your Pentametric is dividing 85AH/370AH=77%SOC. The 48.4 could have been you turning on the microwave or the defrost of the fridge going on. It’s a low voltage but if your drawing 3+KW it could dip that low.

    “However the voltage dropped from 56.4V (my float charge setting - bulk/absorb is 49.2V) to 48.4V”
    What do you mean?
    Bulk V should be the same as absorb V but doesn’t really mean anything because it should be set as % of Max current. What is your Absorb V and Time?

    My Absorb Voltage I adjust as needed. I under charged my first set of batteries for several months because I was told to use default settings. Based on time of year, usage, weather, and water usage I may adjust my absorb voltage. I think I now have it set at 59.8ish which gives me 59V at 20ish charging Amps at the batteries. That’s just above the max absorb spec of 58.8V. I also have my absorb time set to Max (480min)

    You definitely need a good Hydrometer.
    jeffkruse wrote:
    What do you mean?
    Bulk V should be the same as absorb V but doesn’t really mean anything because it should be set as % of Max current. What is your Absorb V and Time?
    Absorb V=58.8V (max per Deka specs) and Absorb Time=480mins (my understanding is XW6048 goes to float if current is less than C*2% = 370AH*.02 = 7.4V or absorb time is reached) - my batteries were in float for at least several hours before discharge cycle.
    jeffkruse wrote:
    You definitely need a good Hydrometer.
    Bought a good one from this site.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    From offline discussion (with JeffKruse's permission) on same topic:
    jeffkruse wrote:
    I just read your post. I understand now.

    How did you measure your SG? If it was 1.265 and you used only 85AH then you should not have been down to 48.4V. How was the 48.4V measured? With the Pentametric? Does the Pentametric and Inverter/CC voltages match? What is the SG after using 85AH?

    Measured SG a few days ago when I EQ'd. Have not measured SG since then. Agreed I should not be down to 48.8V @ 250W load after only discharging 85AH. 48.4V was measured with Pentametric and with XW Inverter SCP meter which agree +- 0.1V.

    Did not measure SG immediately before or after discharge cycle.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    You can not draw too much conclusion from measurement of voltage on a loaded battery. There are too many battery historical variables involved to get a SOC estimate from loaded battery voltage.

    Although 48.4v does seem low if there was a heavy load on battery in prior 10-15 minutes of reading then that low a reading would be normal.

    The battery must have no current flow (in or out) and reach chemical equilibrium for battery voltage to represent state of charge.

    If you disconnect battery and let the sit for two or three hours you can estimate capacity from battery open circuit voltage.

    SG measurement would be better. At chemical equilibrium, battery voltage per cell should be close to SG + 0.845.
  • icarusicarus Solar Expert Posts: 5,345 ✭✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Are you measuring voltage to gain a SOC to compare with the Tri-metric? Loaded (or charging) voltage, (or even recently loaded or charged) is a fairly poor indicator of battery SOC. Only voltage at rest, several hours after a load or charge event, coupled with SG will give a good SOC evaluation. A 250 watt load is not an insignificant load, say~ 5 amps?

    I would posit that in my own 12 volt system, a 5 amp load @ 12 volts would drop the voltage to ~ 12.2 given my battery is relatively the same size. (Have 370 [email protected] 48 vdc, I have 450 @ 12 vdc). Someday I will to check to see if this holds true.

    Tony
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Here's hourly AH data and voltage readings from Pentametric.
    5pm 56.4V
    6pm -0.2AH - 52.3V
    7pm -7.07AH - 51.3V
    8pm -10.3AH - 50.1V
    9pm -9.31AH/ - 49.5V
    10pm -14.1AH - 49.3V
    11pm -8.18AH - 49.3V
    12am -7.16AH - 49.1V
    1am -6.61AH - 49V
    2am -3.68AH - 49.2V
    3am -3.17AH - 48.9V
    4am -3.15AH - 48.8V
    5am -3.1AH - 48.8V
    6am -3.14AH - 48.8V
    7am -4.5AH - 48.8V
    8am -2.09AH - 48.4V
    9am +11AH (solar) - 53.2V
    10am +25.1AH - 54.9V
    11am +30.4AH - 59.3V
    noon +18.1AH - 59.3V

    Actually now that I look at the data a little more, the voltage holds steady at 48.8V for 4 hours, then after my wife probably hit it with the 2500W microwave between 7am-8am it drops to 48.4V. But when I looked at the inverter it was 48.4V with a load of only 250W, not 2000W+ from microwave. Do the voltage drop effects linger that long even if the instantaneous load has dropped? The attached document has voltage curves for various C/X discharge rates, but doesn't mention if these effects linger after the load is dropped or for how long.

    I will test the specific gravity early tomorrow morning and see what SOC specific gravity indicates.

    I have my generator start voltage set at 48.4V after a 15 minute delay because I don't want my batteries going below 50% SOC which I assumed to be 48.4V. Maybe I need to lower my generator start voltage and let it drop to 47V? Just don't want to cycle too deep and reduce battery life. Would be nice if Xantrex tied in a battery monitor like Pentametric that could start AGS based on AH DOD. I asked them yesterday - they said they have nothing that can do this. Would be really nice if something like the Pentametric was integrated with Xantrex Xanbus and AGS and also had data logging and report capability. I suggested this to them also and the customer service rep said he'd pass on the suggestion and let me know if they plan any such battery monitor integration.

    So, do many of you set your generator start voltage lower than targeted min SOC voltage, in my case 48.4V (50% SOC) or ~24.2V (24V system), ~12.1V (12V system) assuming it will be under load and it's ok to let the batteries go down under 48V?
  • icarusicarus Solar Expert Posts: 5,345 ✭✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Don't be to hard on Xantrex nor too High on Bogart. The fact is, battery SOC/DOD is a bit of an art. No electronic device that I know of is perfect, since the SG of the electrolite has to be part of the calculation. So even if the the Trimetric says the battery is ~20% discharge, it is at best, and estimate. The reality is if you use the Trimetric, your volt meter, and hydrometer, and pay attention to the batteries you will figure out what is really going on.

    In the real world, the difference between 70% and 60% is doesn't really make much difference, to know exactly where the battery is. The biggest issue is sizing the batteries to the expected loads, and the charging capacity. A good balance between the 3 factors leads to long battery life. (Most people under charge and over draw, at least starting out!)

    Tony

    PS If you were using ~2500 watts for the microwave just before you test the idle voltage it is going to be a very incorrect reading.

    My favorite links :http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    I have my gen start trigger at 46.0 vdc for 15 min. and 48.0 for 2 hrs.

    The number you set dependents on max load, its duration, and size of battery bank.

    I have 1200 A-h battery but air cond runs for about 20 mins @ 75-85 amps with 30-40 min off period during night. The 20 min high current drags voltage down. The battery recovers quite a bit during the 30-40 rest period.

    Looking at your useage data I would say use the longer term averaging at 48.2v and let the short term sink more, like 47 vdc.

    For an AGM type the setting would be different as they sag less and they recover quicker.

    As battery ages you probably will have to allow more sag on the short term.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    I looked up some old data I ran on 105 A-h batteries with 25 amp load for 30 mins.

    The average of 16 batteries tested is as followed:

    Start -> 12.84 vdc (20-30 minutes off of 13.4 float charge)
    30 secs -> 11.97 vdc
    1 min -> 12.01 vdc
    5 min -> 12.11 vdc
    10 min -> 12.11 vdc
    15 min -> 12.09 vdc
    30 min -> 12.03 vdc

    There is a dip in 30 sec period due to surface charge burn off, then some recovery.
    This would total 12.5 A-H of consumption on the 105 A-H battery.

    Then allowed batteries to recover, no load, for 30 minutes.

    Average voltage after 30 mins of rest was 12.69 vdc.

    These were 'Marine' batteries so I would expect better high current results then a true deep discharge battery. They were about 4 yrs. old at time of testing. They were sealed cells so could not measure SG.

    Results were probably about half way between deep cycle and AGM's in high current performance.

    The formula SG + 0.845 for cell voltage is for 'normal' electrolyte reserve.

    You have got to think what would happen if a battery had 'infinite' electrolyte reserve. You could discharge the plates to oblivion and because of 'infinite' electrolyte reserve the SG would not drop after remix rest period. So what happens in a real battery that happens to have a larger then 'normal' electrolyte reserve. Food for though....
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Best step by step procedure I've seen of how to calibrate generator start point voltage to approximately 50% SOC based on SG from Rolls Surrette link below:
    http://www.rollsbattery.com/content/motive-power-bulletins?q=node/51
    Determining the 50% state of charge Voltage Reading

    Most three steps chargers or inverters monitor the voltage and have an adjustable set point that determines when the batteries are low (50% discharged) and should be charged. Once this set-point is reached the inverter will either sound an alarm or start a generator or tie the battery bank back into to grid power. The voltage set-point maybe factory set but could require verification. Consult your inverter manual for the section on “Cut-off voltage” or “Over discharge protection”. Since the voltage will change depending on whether or not the bank is on load the set point can be determined by a specific gravity reading. A gravity reading of 1.200 is equal to 50% discharged.

    Battery cable lengths, system set-up and other variables can affect the voltage readings as well. Below is a procedure to verify the 50% mark and table 2 gives approximate cut-off voltages at various state of charge. Notice 100% is given as an open cell voltage and all other as under load.

    When using a generator with a low voltage cut-off, set the generator to start at the 50% mark given by table 2 and put the bank into service (11.6 V for a 12V system) (46.32V for 48V system). When the generator starts-up measure the specific gravity of one cell in the bank. Compare this to the table 1, Specific gravity versus state of charge. If the measured specific gravity indicates the state of charge is more than 50%, decrease the low voltage cut-off setting. Similarly if the specific gravity indicates the state of charge is lower than 50%, increase the low voltage cut-off setting. Note: 50% is the desired depth of discharge but it does not have to be exactly 50%. For practical purposes a range of 45-55% is acceptable. The actual battery voltage corresponding to 50% will change with a change in load. In general, the higher the discharge amperage, the lower the corresponding voltage.

    To determine or verify the 50% voltage set point:

    1. Put all or as many loads as possible on the battery. Disconnect any in coming current inputs such as panels / windmills and grid power. Contact your dealer for specifics.
    2. Take the specific gravity of one cell.
    3. Take another reading 15 minutes and ½ hr later this should give you an indication of how fast the batteries are dropping.
    4. Continue to take readings until 50-55% state of charge is reached according to the specific gravity readings.
    5. Take and record voltage readings (when on load) of any meters to be used for monitoring the state of charge and take a voltage reading across the terminals of one battery.
    6. Compare to table 2.
    7. These readings will then give you a very accurate voltage reading which can be used in the future either as a set point for the inverter or as a day to day monitoring parameter.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    http://www.rollsbattery.com/content/motive-power-bulletins?q=node/51

    According to the Surrette table 2 at the link I posted 75% SOC under load for a 48V system would correspond to 48.24V. So my 48.4V reading may well correlate to the Pentametric reading of 77% SOC pretty well.

    Hopefully my batteries are good after all. I'll test SG tomorrow and try to calibrate both the Pentametric SOC readings and my generator 50% start voltage to SG.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    I would not put much faith in table 2.

    "Put all or as many loads as possible on the battery"

    What does that mean?
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    When I pull high loads for several minutes the voltage dips during the load but also rises back significantly in just seconds.

    I think you should use a meter and measure each battery @ a known high current draw. Measure each cable and connection. You should be looking at milliohms for connections and your longest 0000 might be in the 10’s of milliohms. Try to draw 20 or 30 amps during these measurements.

    Keep digging until you understand why you’re at 48.4V. You might be ok or you might not.
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    re: "seems like the Pentametric should consider the Voltage/load curve" - the only device I am aware of that does this is SmartGauge Electronics - battery metering. (I wish the device was more easily available in the U.S. so I could get a better handle on its actual performance)

    I think it is important to keep in mind that any battery capacity measurement accuracy is fairly poor, especially compared to the precision used to measure specific battery attributes. Battery University found that cycle to cycle variance in available battery capacity can exceed ten percent. Age, temperature, and use profile can also each influence battery capacity measures that much.

    SG is no nirvana, either. Besides the hazmat and contamination issues it also has needs for considering relevant variables like battery state, temperature, electrolyte stratification, and so forth.

    What electron counters (e.g. Trimetric) can do is to provide an accurate measure of use that can be used to build objective data about battery performance in context. That can be used as a referent for evaluating current battery condition. Ol' timers did this by just watching how the lights dimmed when the pump turned on.
  • icarusicarus Solar Expert Posts: 5,345 ✭✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Just to agree with Bryani, Close is really the best you can do, and in fact what one should try for. It is not an exact science, but rather a bit of an interpretive art. The best gauge is one's own experience gathered over time, coupled with various metering/gauging strategies.

    Tony
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    48.2V, 71 degrees F
    Pentametric - 62% SOC - 142AH down from "full" charge (but no SG was measured at full)
    B1 (5.99V) 1.165, 1.180, 1.170 (+ INV) -
    B2 (6.00V) 1.180, 1.185, 1.175
    B3 (6.04V) 1.180, 1.195, 1.190
    B4 (6.01V) 1.175, 1.180, 1.175
    B5 (6.01V) 1.180, 1.190, 1.170
    B6 (6.00V) 1.175, 1.170, 1.180
    B7 (6.09V) 1.210, 1.205, 1.205
    B8 ( 6.01V) 1.180, 1.175, 1.175 (- INV)

    SG Range per Surrette
    75% 1.215 - 1.235
    50% 1.180 - 1.200
    25% 1.155 - 1.165

    So, some batteries are less than 50% SG, some are more than 50% SG. Do I consider this around 50% SOC ? I am 142AH down from full assuming I was at full. That's still only 282AH, not 370AH.

    I am going to EQ like crazy tomorrow, make sure SG is full at Pentametric "full", and try again.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Pentametric Data
    Time AH Volt % SOC
    6/29/2010 18:00 1.62 54.3 100
    6/29/2010 19:00 -2.6 51.7 99
    6/29/2010 20:00 -5.83 50.9 98
    6/29/2010 21:00 -8.65 49.8 96
    6/29/2010 22:00 -11.6 49.4 92
    6/29/2010 23:00 -12.5 49.3 89
    6/30/2010 0:00 -11.4 49 86
    6/30/2010 1:00 -12.7 48.8 83
    6/30/2010 2:00 -10.2 48.9 80
    6/30/2010 3:00 -4.59 49 79
    6/30/2010 4:00 -4.47 48.8 77
    6/30/2010 5:00 -4.82 48.9 77
    6/30/2010 6:00 -4.3 48.9 75
    6/30/2010 7:00 -10 48.4 72
    6/30/2010 8:00 -8.43 48.2 70
    6/30/2010 9:00 -7.61 48.4 68
    6/30/2010 10:00 -5.87 48.2 66
    6/30/2010 11:00 -7.88 48.2 64
    6/30/2010 12:00 -5.56 48.0 62

    I also tried a voltage test with microwave:
    baseline load 175W, 48.2V
    run load 4 mins - load 1985W, 46.7V
    load off - load 175W, 47.9V immediately after load drop
    load off 3 mins - load 175W, 48.1V
    load off 30 mins - load 175W, 48.2V
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Ok, so my batteries just reached "full" charge meaning the XW charger switched from absorption to float. Voltage is currently 56.7V, current is 2.5A. Pentametric indicates 100% since amperage is less than my setting of 2%*370AH = 7.4A 9 (appx point which XW goes to float). However, SG ranges from 1.210 - 1.225 indicating only ~75% charge. This is in line with my previous data. 75% * 370AH = 278AH (actual starting point last few days) / 2 (50% SOC) = 139AH. Yesterday Pentametric measured 142AH discharge and I then measured SG around 50% which makes sense now.

    I changed my absorb Voltage to 59.4V (above 58.8V recommended by Deka) per JeffKruse's recommendations with his Deka 8L16s yesterday. My float setting is 56.4V. The batteries are bubbling slightly. I know I can get to 1.275SG in EQ (63V for ~4 hours). So, how do I get the batteries to charge to something closer to 100% or should I not expect them to ?

    Is this a Deka L16 issue (JeffKruse also saw this) or is this normal (to reach ~75% SIC at float) for all brands of L16s ? All flooded ?

    Is there a way to extend absorb stage in XW? Absorb time is set to 480 min but XW switches to float long before that - when amps are less than 2% according to the manual.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Dropping out of absorb at 2% of bulk current is fine. Timer timeout is a failsafe function.

    Extending absorb beyond this point is just going to stress batteries and reduce their lifetime.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?
    Extending absorb beyond this point is just going to stress batteries and reduce their lifetime.

    I've read in other posts it is better to overcharge than undercharge. Here's one:

    http://forum.solar-electric.com/showthread.php?t=6484
    BB wrote:
    And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.

    * Undercharging and operating for long periods (below ~75%) is damaging to lead acid batteries.
    * Overcharging is less damaging to flooded cell batteries (at the cost of distilled water and wasted energy).
    * Overcharging sealed batteries (AGM, Gel, VRLA, etc.) can be fatal to those types (venting electrolyte).

    I also read another post that advised for off grid solar to set the float voltage setting the same as Absorb as it will more fully charge the batteries at the expense of extra water usage. JeffKruse also has Deka 8L16s and he had same issues I'm seeing - under charging based on SG, then going to float around 1pm while SG remains low (~75% SOC). He sets his absorb to 60.5V-61.5V. Deka recommends max absorb of 58.8V. Wondering if it would be better to have:
    1) 58.8V absorb and 58.8V float - lower voltage but for longer time to get to full charge
    OR
    2) 60.5-61.5V absorb and 56.4V float - higher voltage for shorter time

    I spoke to Xantrex today also. They said one way to fool the charge controller to extend absorb is to set the battery capacity lower than actual so that 2%*C is a lower current, thus extending absorb time.
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    How would that increase the absorb time? Wouldn't it do the opposite?

    I saw/see the same problems you have. We know we can get the SG to around 1.275 but to do that takes high voltages and a long time. We don't have the time because the sun goes down. We can get higher voltages but we dont want to stress the batteries.

    I question how they can sell these batteries for off-grid use. Someone once posted a formula on calculating absorb time and it came out that the time is much longer than there is sunlight for.

    I compromise. I have my voltage set a little high, my absorb time set to max, and my SG does not get to 1.275 often. I eq once a month from the panels when I can. I have to do that on a clear day, set my Absorb time to 1 minute, then EQ. Of course I have start the EQ when I feel the batteries are fully charged.

    I go through about 3/4 gallons of water a month.

    I may go grid tied now that the $250/year insurance has been waived.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Overcharging does more then cost of distilled water and wasted energy. It causes positive plate grid corrosion and in extreme case causes plates to shed lead.

    Positive plate corrosion will increase series resistance of battery and evenually render it useless in supporting a load.

    You will not gain capacity by overcharging.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?
    You will not gain capacity by overcharging.

    how do you define overcharging? If my SG is only 1.225 with Deka's recommended absorb setting and it goes to float am I not undercharging by ~25%. Isn't applying a higher voltage as JeffKruse does to get to at least 1.265SG charging to full and not overcharging ?

    It seems a waste when my charge controller goes to float by 1pm to let the batteries stay at 1.225SG.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?
    How would that increase the absorb time? Wouldn't it do the opposite?

    370AH * 0.02 = 7.4A (CC switches from absorb to float below 7.4A)
    185AH * 0.02 = 3.7A (CC switches from absorb to float below 3.7A) - so it will stay in absorb longer
    100AH * 0.02 = 2A, etc, etc

    Haven't actually tried this yet to see how well it works. But I have seen it drops to 2.5A in float pretty quickly. I'll have to experiment with it to see how long it actually stays in absorb with various settings. Xantrex CS rep indicated this shouldn't effect anything else besides absorb time.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    I've been trying to calibrate my charge settings to get 100% SOC per SG each day.
    Here's some data:

    NOTE - XW6048 Battery Capacity setting under MPPT charger settings sets absorb to float transition point: 200AH*.02=4A (switches from absorb voltage to float voltage at 4A) - I'll call this AbsorbA - my batteries are 370AH, but it was going to float way too soon before batteries were charged per SG, so trying to adjust this as well as absorb voltage.
    NOTE2 - Pentametric indicates 100% based on my setting of absorb V and absorb A, so trying to roughly calibrate Pentametric 100% SOC to SG 100% SOC also

    7/2/10 - EQ @ 64V for 8 hrs - checking each hour, SG 1.255-1.275, 94F, Pentametric 100% SOC
    7/3/10 - 8am - Penta 75%SOC, SG 1.220-1.235, 75F - Pentametric and SG agree
    7/3/10 - 7pm - Penta 100%SOC, SG 1.260-1.275, AbsorbV 60.5V, AbsorbA 4A - never swapped to float - Amps were at 5.4A at 5pm (end solar day) - batteries were fully charged - BASELINE GOOD CHARGE
    7/4/10 - 4pm - Penta 100%SOC, SG 1.235-1.265, AbsorbV 58.8V (Deka spec), AbsorbA 4A - went to float @ 3:30pm - batteries were NOT fully charged
    7/5/10 - 4pm - Penta 100%SOC, SG 1.250-1.275, AbsorbV 59.6V, AbsorbA 4A - went to float @ 1pm - batteries were NOT fully charged but close
    7/7/10 - 4pm - Penta 100%SOC, SG 1.240-1.265, AbsorbV 59.6V, AbsorbA 4A - went to float @ 3pm - batteries were NOT fully charged but close
    7/8/10 - tomorrow - set for same 59.6V Absorb with lower AbsorbA=2A (batt capacity=100AH) so it will stay in float longer

    One question - I noticed my weakest battery per SG readings is the one tied to the positive inverter cable. It is consistently 0.010-0.020 less than the rest. I have tried two different batteries in this location and it is the location not the battery. The battery moved away from +INV goes up in SG, and the one moved to +INV becomes the lowest SG in the string. Is this normal ?
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    Your recording your set point Absorb Voltage, what does the Pent see at the batteries at full charge current and near full current? IIRC I see a little less than a volt difference. I may have my Absorb set at 60.2 but the batteries see 59.2 – 59.6.

    Your 60.5 setting seems to be giving you a full charge. Anything less and your SG varies by .025. The cells at 1.240, will they only get worse?
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?

    The only day I actually had a full charge (per SG) my AbsorbV setting was 60.5V - the Pentametric measured a peak of 60.3V and I also measured 60.3V with a multimeter at the time of SG measurements. There was 1.5A float charge at that time.

    When I lowered the AbsorbV to 58.8V the measured V also got to 58.8V. I think this the requirement for the inverter switching to float is that the absorb voltage must be met and the current must be <2% of battery capacity so maybe I am misunderstanding the question.

    When the AbsorbV setting is higher (60.5V) absorb stage lasts much longer. Although Deka has not responded to my email to them last week, I recall from your (JeffKruse) earlier posts that Deka recommended something like 8 hour float time at 58.8V max AbsorbV. I have observed at 58.8V AbsorbV, and 370AH Batt Capacity Setting (Absorb-float transition @ 7.4A), that the charge controller goes to float long before the battery is charged. So, rather than just setting my FloatV=AbsorbV I am now trying to find a battery capacity setpoint that will extend Absorb stage (by lowering Absorb-Float current) to a point where I can get a full charge at lower AbsorbV setting. Or maybe I should just set FloatV=AbsorbV.

    Today, using 59.6V AbsorbV, 100AH Batt Capacity (float @ 2A) so we'll see how it goes.
  • whitestrabbitwhitestrabbit Solar Expert Posts: 39
    Re: What is your trimetric measured battery AH vs manufacturer AH specs ?
    One question - I noticed my weakest battery per SG readings is the one tied to the positive inverter cable. It is consistently 0.010-0.020 less than the rest. I have tried two different batteries in this location and it is the location not the battery. The battery moved away from +INV goes up in SG, and the one moved to +INV becomes the lowest SG in the string. Is this normal ?

    creating a separate thread
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