batteries discharging overnight, won't reach bulk voltage? help!?

Hi, we have new install of approx 2000w solar, put in 300ah lithium batts with manufacturer settings for bulk, absorb, float etc. 58.4, 1\2 hr, 54.8, Outback pre-wired 48v pack. First charge went to 55v ish & stayed there,it started at 1500w then dropped to 50w for hours, prob at least 3. Soc says 100% though it is not. As soon as the charger snoozed the voltage began dropping. It got to 53.4 & I turned the whole lot off. This took maybe two hours?, We have a BMS. There was no load at all, although mate showing -10 - 30 w. I was trying to do the first full charge, discharge cycle thing 5 times like the manufacturer advised for new lithiums. It would seem we have multiple issues. Please help?! Thought I will test the v in the morning to check its a true reading. Surely we should not be losing so much v when the inverter is not even on! I am lost. Please tell me if you need more info, I'm a definate beginner who needs to learn.

Comments

  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    A big guess not knowing you system or batteries is that you didn't have the voltage low enough (48-50 V ?? ) to trigger a full charge cycle. All it did was to bring them up to your Float Voltage. I would draw them down some and on your mate push the ACin key 4 times and choose " Bulk " that will start a full charge cycle. If you only have Solar input, I don't know how to do that other than to discharge then low enough to start a full charge cycle.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Doesn't sound like you have much of a problem to me unless your batteries are not balanced.

    Are the batteries LiFePO4 (Lithium Iron Phosphate) and who is the manufacturer?

    If they are LiFePO4 batteries, a bulk charge maximum voltage of 58.4 volts (3.65V per cell assuming 16 cells in series) is probably a bit higher then is necessary and will reduce the lifespan of the batteries. I think the general consensus is a voltage of around 3.45V per cell (55.2V for 16 cells) is enough to get >95% charge into the batteries and will increase the lifespan.

    When the battery was being charged, 55 volts (3.43 volts/cell) sounds about right, at that voltage if the cells are balanced i would say that they were nearly full.

    With no current going into or being drawn from full LiFePO4 batteries they will settle down to a cell voltage of ~3.3 volts (52.8 volts). It might seem like a huge change in voltage from 55 volts to 53.4 volts, but as a percentage it is only a 2.9% difference.

    Most of the time if everything is working OK and the cells are not being overworked the cells voltage will be in the range of 3.2-3.4 volts (51.2-54.4 volts)

    You only have to panic when any individual cells voltage gets down below 2.8 volts (equivalent to 44.8 volts if you have 16 cells in series all at 2.8 volts). Hopefully your system would have some alarm if this were to happen.

    Could you give more details as to why you think the 100% SOC is not correct, also was the inverter still turned on when you were getting a power draw of 10-30W.

    Maybe your BMS system is limiting the charge going into the battery as it is not balanced. This might explain the controller not getting up to the full bulk voltage.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi karrak, thanks so much for your reply! I'll try to answer your questions, please excuse typos as I'm on my phone.
    They are sinopoly lithium iron phosphate, 16 cells @ 300ah.
    The battery supplier here told us to bulk charge at that rate to keep our warranty, but he also told us we didn't need a BMS so we don't trust him much. We went with the sinopoly & research advise & supplier been extremely unhelpful now they have sold us them.
    I had no idea there would be voltage drop or that the cells settled with no draw or input.
    BMS is set to do its magical mystical cell balancing & battery saving thing at 2.9 & 3.8 I think, unsure totally but the overseas supplier we got it from did all that. we have set the inverter to warning alarm at 51.2v & auto switch off at 48v to keep warranty.
    We have not had the inverter on at all yet as i wanted to do full recharge then was going to turn it on & put some load on to drain it down to do the first few cycles to maintain battery life hopefully. Its in the battery manual. the current draw I saw was on the mate summary screen. it says usage has been 8ah since install?! Scary?
    On the BMS the cells show as full soc too, this is done by counting amps in & out though & there hasn't been any outgoing yet as inverter has been off? The BMS has not shown it has been bypassing or doing anything much at all, haha. The voltage dropped down slowly over the couple of hours since sundown, but if thats normal, hooray I haven't broken it. I guess I will test it today. Thanks so much for your help & expertise, I'm in new Zealand doing this without knowing a soul who has lithiums & none of the solar places seem to know anything about them
  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Thanks blackcherry04, I will try draining down a bit & recharging.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Happy New Year, may your batteries never go flat.
    zuessdoggg wrote: »
    They are sinopoly lithium iron phosphate, 16 cells @ 300ah.
    The battery supplier here told us to bulk charge at that rate to keep our warranty, but he also told us we didn't need a BMS so we don't trust him much.

    Sinopoly are one of the major well known brands of Chinese LiFePO4 batteries. Did the battery supplier state you had to have a bulk charge voltage of 3.65/cell, or was that the maximum voltage? I would be interested to know what sort of warranty you have been given. You are quite right to think you need some sort of cell monitoring/safety/balancing system with these batteries.
    BMS is set to do its magical mystical cell balancing & battery saving thing at 2.9 & 3.8 I think, unsure totally but the overseas supplier we got it from did all that. we have set the inverter to warning alarm at 51.2v & auto switch off at 48v to keep warranty.

    I think that 3.8 volts is too high a setting for the cell balancing. If you are only charging to 3.65 volts/cell, you could have the case where one cell is at 3.8 volts and another is at 3.5 volts, these averaged together is 3.65 volts, but the cell with a voltage of 3.8 volts will be getting more stressed than the cell at 3.5 volts and will probably not last as long. I am assuming that the balancing is taking place at the high end (Top Balancing) rather than at the lower voltage of 2.9 volts (Bottom Balancing). I am not a fan of fixed voltage balancing, i think it is better to look at the difference between the cell voltages and when it is above a threshold to balance the highest cells to the lowest cells. Can you change the BMS voltage settings?
    We have not had the inverter on at all yet as i wanted to do full recharge then was going to turn it on & put some load on to drain it down to do the first few cycles to maintain battery life hopefully. Its in the battery manual. the current draw I saw was on the mate summary screen. it says usage has been 8ah since install?! Scary?

    From what i have read there seems to be some evidence that the batteries may benefit from deep cycling when new. I don't know what your documentation says but i wouldn't discharge them below 20%SOC, be careful when you do empty the battery for the first few times as it might not be balanced and the voltage on any low cells may drop rapidly before you get to 20%SOC.

    The solar controller, BMS, monitoring electronics etc all require power to work so they will be draining power from the battery at all times. If they are well designed this should only be a few watts but could conceivably be as high as 10-20 watts. There is also the possibility that the circuitry that monitors the power consumption needs to be calibrated and or cannot measure low power accurately.

    I would be interested to know what equipment you have, especially the solar controller, inverter, BMS and any other monitoring equipment. The manufacturer and model numbers would be useful.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi, thanks karrak! Had an eventful day, you are so right, it seems to all be working perfectly. I appear to be stressing out for no reason again, haha. Went into bulk charge this morning to top up the last few volts & cc shut down & we turned off solar supply. We have been trying to drain the batteries sensibly all day and they are now at 90%. Jeepers! I will try and answer your queries :D
    Battery supplier was the only one in nz who sell these I believe, they are marketed as yttrium aa solar brand, but they are sinopoly. Got a good deal, I believe, but we've had em sitting useless while I sourced a BMS that did what I thought i t needed to & i didn't have to build. Difficult! Got it from ev power in wa. I'm not technical, but I will try & tell you what I think we have. We have individual cell modules which monitor total voltage & compare to other cells as well as BMS thing to look after it all, hopefully. I observed this morning it's red blinking light extravaganza on some cells. I think it was bypassing specific cells & sending current into others. Maybe?! http://ev-power.com.au/webstore/index.php/ev-power-bms/battery-control-unit-for-plug-in-evs.html this BMS is similar but not the same as ours. I don't think its on the website, couldnt see it but its for raps. The cell modules are 300ah ones. We are off grid. I gave the BMS supplier the tech specs for the batts & I believe the unit was set up for us at the correct settings, I will certainly check with him to ensure this is the case as we don't want to hurt our investment. i just checked individual voltages & they are currently 3.34 - 3.35.
    I will def go to 20% soc, I was unsure about this but your advice is sound. I was a bit afraid to take them that low & change mate settings after I spent forever triplechecking them yesterday.
    Hmm, I hope the BMS is using it's approx 1 watt, I think I'll check that too. You are so helpful, thank you!
    We have outback vfx3048e inverter, fm80 cc, we cheated & got the prewired pack with mate etc we had old free sealed batteries which we replaced with lithium & installed another 4 x 295w panels to go with 4 x 235w we put in last year. From as solar. Max today on cloudy day was 1937w. Ground mounted, clear line of sight all day. We have a separate system 24v hydro at about 80w constant which we will convert to 48v & add to lithium also eventually, charging only. Xantrax controller c40 I think, diversion loads etc all need to stay separate, it was sourced from eco innovation yonks ago
    I will def watch the usage tonight etc on the outback & see what it does. Hopefully what it is supposed to :-)
  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    And, yes , battery supplied told us to bulk charge to 3.65 per cell, total 58.4 to keep 10 year warranty
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    I appear to be stressing out for no reason again, haha.

    Better to be worried than just sit back and not get decent life out of the batteries. I know a number of people who have not got the life they should have from Lead Acid batteries because they have not looked after then.
    had em sitting useless while I sourced a BMS that did what I thought i t needed to & i didn't have to build. Difficult!

    Yes, i haven't found an off the shelf BMS for RAPS that i would recommend to anyone. I suppose the market is not seen as large enough. Most of the BMS systems around are meant for Electric Vehicles which have very different requirements to RAPS systems.
    Got it from ev power in wa. I'm not technical, but I will try & tell you what I think we have. We have individual cell modules which monitor total voltage & compare to other cells as well as BMS thing to look after it all, hopefully. I observed this morning it's red blinking light extravaganza on some cells. I think it was bypassing specific cells & sending current into others. Maybe?! http://ev-power.com.au/webstore/index.php/ev-power-bms/battery-control-unit-for-plug-in-evs.html this BMS is similar but not the same as ours. I don't think its on the website, couldn't see it but its for raps. The cell modules are 300ah ones.

    I have bought equipment from EV Power and have been to their workshop. Are the cell modules like these? http://ev-power.com.au/webstore/index.php/ev-power-bms/bms-cell-modules-1/cm400-cell-module.html If they are the same they will balance the cells at 3.6 volts, so should be OK for your bulk charging voltage of 3.65 volts/cell. It is still worth checking with EV Power. I am tempted to contact the owner and ask him about all this.

    I am still a little concerned about the recommendation from the battery supplier to charge the cells to 3.65 volts. From the research i have done this should give you 2-3,000+ cycles but maybe not the 5000+ cycles you might get by charging them to a lower voltage. Here are links to articles and forums with useful information about this

    http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries ,not specifically for LiFePO4 batteries but i would think relevant
    http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html ,excuse the size of this thread, lots of information here but needs some filtering.
    http://forum.solar-electric.com/showthread.php?21701-Charge-Float-and-Cutoff-Voltages-for-Large-LiFePO4-Cells ,NorthGuy suggests to keep the SOC between 80% and 20%SOC which i would agree with
    http://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp90aha?category_id=176 ,these are the specs for my batteries which should be very similar to yours. You can see that they state >5000 cycles @70%DOD, this plus information in some technical articles i have read suggests that you shouldn't charge the batteries to 100% to get the longest lifespan. This discussion has prompted me to send an email to Winston Batteries to ask what the testing methodology they used to get the figure of >5000 cycles. Hopefully i will get a reply.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Thanks karrak! You are so helpful! I can't work out how to quote you, but here are my answers. We have problems now, haha, hopefully these are imaginary also. Any advice is most welcome, if you feel like it.
    The cell modules are like those. I think they are those :D I emailed EV Power this week & told them what was happening & he said that all seemed fine.
    Thanks for the links, I will read them. I would def rather be cautious & charge to a lower voltage if it will help us get maximum life. This was a huge investment for us. Thank you!
    We blew one fuse in our panel combiner today with the mega sun, found out later I made an error (massive mistake) in my calculations. oops. No big deal but I put in new fuse, reset the system & then realised all the SOC counters had reset to 100% when batts were at about 83% prior. So, ok, will charge until voltage is at set max &charger cuts out then when we start draining batts it will count properly. Well, that's what the internet tells me, anyway. So the fuse blew again cos I'm a dumbo & I left it, we still have four panels running. That's when I noticed that when they are on about max of 1000w the voltage is at about 53.4 on batts & now they dropped down to 100w coming in the batts drop to 52.7. Is this because the lithiums are reverting to their happy standard voltage because there's not much charge, or have i broken something somehow? Also, i note that the Mate's SOC has gone down to 99% but the batteries are being charged?! this is odd & scary again. I will get bigger fuses for the box, but now I have a new problem :confused: again, thank you for your help!
  • mike95490mike95490 Solar Expert Posts: 8,812 ✭✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    ..... I will get bigger fuses for the box, but now I have a new problem :confused: again, thank you for your help!

    The fuses protect something, just don't mess that up.
    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 ,

  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Yeah no worries, haha, they are protecting me from 4 panels working in full sun. I got 10A cos that's the maximum the solar place supplied & assumed it would be fine but apparently not. They blew because they are too low current. My fault, again. 81v, 1040w, more than 10A. Derrrr. Boom.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    I would def rather be cautious & charge to a lower voltage if it will help us get maximum life.

    After a few emails I got a reply back from Winston batteries that backs up that course of action. The only problem I see with running a lower voltage is that your BMS balancing circuitry doesn't operate until the cell voltage is at 3.6 volts and i am not sure what voltage the BMS SOC counter resets at. I would keep charging them to 3.65 volts/cell (58.4 volts) until these issues have been clarified.
    We blew one fuse in our panel combiner today with the mega sun, found out later I made an error (massive mistake) in my calculations. oops. No big deal but I put in new fuse, reset the system & then realised all the SOC counters had reset to 100% when batts were at about 83% prior. So, ok, will charge until voltage is at set max &charger cuts out then when we start draining batts it will count properly. Well, that's what the internet tells me, anyway. So the fuse blew again cos I'm a dumbo & I left it, we still have four panels running.

    I would trust voltages more than the SOC counter, the SOC counter may not be all that accurate. I hope the current rating of the wiring, combiner box etc is sufficient to handle the larger current?
    That's when I noticed that when they are on about max of 1000w the voltage is at about 53.4 on batts & now they dropped down to 100w coming in the batts drop to 52.7. Is this because the lithiums are reverting to their happy standard voltage because there's not much charge, or have i broken something somehow?

    This is quite normal, the faster you are charging or discharging the battery the more energy you need, which in this case equates to voltage to overcome the electrical resistance in the batteries and wiring and drive the chemical processes that charge/discharge the battery. An analogy is if you drive your car from A to B under the same conditions but at different speeds, the faster you go the more fuel you will use to go the same distance.
    Also, i note that the Mate's SOC has gone down to 99% but the batteries are being charged?! this is odd & scary again.

    I might be wrong, maybe someone can correct me on this but the quick look i had at the Outback FM80 manual suggests to me that the SOC figure is calculated using the battery voltage and is set up for Lead Acid batteries. It will be pretty meaningless with LiFePO4 batteries.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    Yeah no worries, haha, they are protecting me from 4 panels working in full sun. I got 10A cos that's the maximum the solar place supplied & assumed it would be fine but apparently not. They blew because they are too low current. My fault, again. 81v, 1040w, more than 10A. Derrrr. Boom.

    Panel fuses shouldnt be located or rated for the main pv bus current, but for the string current right? Panels are current limiting so no need for fuses on their tiotal output except to limit the current from multiple strings back through a single string inthe event of a panel short. You better get this clear. The string fuse rating is stamped on the back of each panel. As little as 100 bucks gets you a midnite combiner for 3 strings complete with breakers, thats the best.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi zone blue, thanks for your reply. Apologies for the delay, I've been having some problems getting on the website. We have four strings and a combiner box which is fused on each string, plus the total combined together, plus a breaker at the unit. We have not had any problems since replacing the fuse, I stupidly got ones which were not rated high enough. It's working really well :-)
  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi karrak, you have been so helpful! Apologies for the delay in reply. I got an email from bms supplier, and I have changed the bulk to 58.0v, it all seems to be working well! I would much rather get more cycles from them. I have a query on return amps / absorb end amps, please . The battery supplier told me he did not know what this meant & I should input zero, which I have, but is this correct for lithium batteries? Also, we use only approx 10‰ of the batteries each day with normal use, would it be better for us to drain them a bit more over a few days & then recharge them? We are you g by the voltages now, as both the amp hour counters have different readings & don't seem correct. Thanks for your help! :-)
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    I got an email from bms supplier, and I have changed the bulk to 58.0v, it all seems to be working well! I would much rather get more cycles from them.

    I talked to Rod at EV-power. He was very helpful. As i thought the balancing circuitry will only work if the overall voltage is over 57.6 volts (3.6 V/cell), Rod suggested that this be done at least once a week.
    I have a query on return amps / absorb end amps, please . The battery supplier told me he did not know what this meant & I should input zero, which I have, but is this correct for lithium batteries?

    While in bulk charging mode the battery voltage will rise until it reaches the Absorb setpoint voltage at which point the charger switches to the Absorb cycle, in this mode the charger will keep the battery voltage equal to the absorb voltage for the Absorb Time or until the battery current decreases to the Absorb End Amps. See the graph on page 50 of the FM80 manual. With your high charge voltage (>3.5 volts/cell @ < 0.1C) I would set the Absorb Time Limit to 0. If you had a lower charge voltage I would set the Absorb time to several hours and limit the absorb end current to (C, the AH capacity of your battery)/20. If you do this you will always get a consistent charge. What are your float voltage, RTS temperature compensation, and Equalisation settings?
    Also, we use only approx 10‰ of the batteries each day with normal use, would it be better for us to drain them a bit more over a few days & then recharge them?

    Mmmm, this is a question i am sure allot of people including myself would like a definite answer to. I think that with these small cycles the cells are having so little stress put on them that it probably doesn't matter as long as they are not stressed by too high a charge voltage. Can anyone else add anything to this?
    We are you g by the voltages now, as both the amp hour counters have different readings & don't seem correct.

    What are the two amp hour counters you have? I assume one is on the BMS, where is the second one? The one on the BMS is probably only accurate to within +/- 5% and only if it has been reset on the last charge cycle.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    zuessdoggg wrote: »
    Also, we use only approx 10‰ of the batteries each day with normal use, would it be better for us to drain them a bit more over a few days & then recharge them?

    I would. Consider that the last 10% or so of the charge cycle is the very rapid absorb at the end. I wouldn't want to constantly operate at 90-100% SOC every day. See the typical LiFepo4 charge / discharge cycle graphs to see what I mean. I think your bank is basically oversized, unless you need some monstrous reserve capacity for autonomy.

    Since you are only using 10% of the total capacity, I think a far better idea would be to try and operate a bit lower, say from 70-80, or 80-90% SOC etc. That would keep your batteries operating in the flat part of the curve (more efficient) as operating long term in EITHER the extreme low or extreme high ends eventually takes a toll. Admittedly, if that means getting only 2800 cycles vs 3000 cycles, it could be a case of splitting hairs practically.

    Of course this means your bms wouldn't kick in to do top-balancing. But by desiring to have the bms in operation top-balancing your cells every charge cycle means unnecessary wear and tear on the bank trying to live in the upper absorb-knee. Perhaps just take it to 100% charge every once in awhile to kick in the bms, but I don't see the need on a daily basis, unless you have absolute junk cells, or are in an EV application.

    Know that if you choose a lower charge limit voltage, say 3.5v per cell, it only means that the battery will take a bit longer to reach full charge than it would at 3.65v. (watch the end-amps, eventually it should get to close to zero at either 3.5 or 3.65v, UNLESS the bms itself is robbing you of power). If you have the time for a slightly longer absorb, why the rush to use a higher voltage?

    Personally, I'd try charging to no more than 3.5v per cell and see how balance goes after a trial period. The hardest habit for me to kick when doing Lifepo4 is to drop some Pb-think, like obsessing over the absorb cycle. :) Something like a Fluke 87V or better, or perhaps a Revolectrix Powerlab 8 may help you determine if the BMS is indeed necessary when comparing individual cell voltage spreads after a few trial runs.

    I'm not sure if Sinopoly provides static resting voltage vs SOC charts like Shorai does, (and as an agm fan, I'm fully aware of that accuracy limitation), but in this non moon-mission app, it may be adequate. :)

    How about a real-world comparison on a smaller scale - treating your laptop like a desktop by leaving it plugged in all the time. That's a battery killer. Even though the laptop is a LiCo02 Cobalt, it shares some elemental traits with LiFepo4 when it comes to not liking being fully charged or discharged and sitting at those levels for a long time. In your case with the 10% capacity draw, that would be like taking your laptop to the couch daily to check the weather, and then immediately returning it to the charger for 100% SOC. The same thing with a cellphone (again, different cobalt chemistry!) by constantly topping it off whenever you reach a miniscule 10% discharge back to full charge again. You'd get much better life if you stayed out of the upper charge knee unless you absolutely had to have that VERY tiny amount of capacity available.
  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi karrak, perhaps I will move it to 57.6v absorb then, once a week, & charge to 56.0v the rest of the time. Seems to be the consensus. :-)
    The float is set to 54.8v, the absorb time is at zero now, the RTS compensation says A 59.2v F 55.6v (?) and it says wide (?). Reading page 51, should this be set to limit, instead? And I should set the voltage limits because we have lithium batts & they won't really change too much based on temp of, on average between 0 - 30 degrees ( at the extreme ). I am very confused by all of this.
    We don't equalise the batteries, we were told never to do so by supplier (?).
    Yes, there is one amp hour counter on BMS, one on the mate. The BMS one seems to count up & down, Rod had advised it needed 56.0v I think, to reset, but it counts up, as well, during charging. I have observed this :-) the mate amp hour counter seems to match the mate soc counter, but if the soc counter is based on the temp compensated voltage for lead acids then perhaps the amp hour counter is not counting the actual amp hours in and out, but giving it a go based on the fake voltage soc. I don't know?! Jeepers, this makes my brain hurt.
    Reading pg 50, the Absorb End Amps is set to 0 amps & the Rebulk Voltage is 48.0v.
    When we do use more power, we are planning on getting a freezer soon, I hope, will these settings need to change?
  • zuessdogggzuessdoggg Registered Users Posts: 11
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Thanks for your advise, PNjunction. I understand a bit of what you're saying :-) I will change to 3.5v a cell. We will be getting a freezer soon, maybe a washing machine & microwave, and perhaps I shouldn't be so afraid of using the batteries. We have lived for two years on a 100w hydro with screwed batteries, it was either the TV or the stereo, haha. And no fridge. This is luxury, we are just so afraid of breaking the batteries & really need them to last.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    I think the simplest course of action is to just use them a bit more before charging IF you are truly using only 10% capacity. I'm not familiar with the outback settings, nor how it bases it's SOC when dealing with Lifepo4, so I'll plead ignorance, and bow out there.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?

    Hi Zuessdoggg, looks like you are doing really well learning and understanding all this.
    zuessdoggg wrote: »
    I will move it to 57.6v absorb then, once a week, & charge to 56.0v the rest of the time. Seems to be the consensus.

    Sounds good to me
    The float is set to 54.8v,

    Any reason for 54.8v? I would set this to the resting full voltage of the battery which is around 3.32 volts/cell (53.1 volts)
    the RTS compensation says A 59.2v F 55.6v (?) and it says wide (?). Reading page 51, should this be set to limit, instead? And I should set the voltage limits because we have lithium batts & they won't really change too much based on temp of, on average between 0 - 30 degrees ( at the extreme ).

    Do you have the Temperature Option installed on your FM80? If not you don't have to worry about these settings.
    We don't equalise the batteries, we were told never to do so by supplier (?).

    You could use the Equalise function to do your once a week balance charge. This will only work if you can set the "Battery Equalize Volts" to 57.6 (FM80 Manual P42). Then you won't have to alter the Absorb Voltage once a week.
    Yes, there is one amp hour counter on BMS, one on the mate. The BMS one seems to count up & down, Rod had advised it needed 56.0v I think, to reset, but it counts up, as well, during charging. I have observed this :-) the mate amp hour counter seems to match the mate soc counter

    The BMS one will measure the current going both in and out of the battery. When the battery voltage reaches 56.0 volts the SOC counter should reset from what it is currently reading to either 0 or the AH capacity of your battery or 100 %SOC or 0 %DOD depending on how it has been programmed. This reset cancels out any errors in the measuring of the current, if it didn't do this reset the error would mount up over a few days until the displayed reading would be meaningless. Your FM80 only measures the current coming from the solar panels. It does not measure any current drawn from the battery.
    Reading pg 50, the Absorb End Amps is set to 0 amps & the Rebulk Voltage is 48.0v.

    Should be OK
    When we do use more power, we are planning on getting a freezer soon, I hope, will these settings need to change?

    Shouldn't need to.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    PNjunction wrote: »
    Since you are only using 10% of the total capacity, I think a far better idea would be to try and operate a bit lower, say from 70-80, or 80-90% SOC etc. That would keep your batteries operating in the flat part of the curve (more efficient) as operating long term in EITHER the extreme low or extreme high ends eventually takes a toll. Admittedly, if that means getting only 2800 cycles vs 3000 cycles, it could be a case of splitting hairs practically.

    I would agree with that, the problem is to be able to program the Outback FM80 to do this, also the BMS SOC counter needs 56 volts (3.5 volts/cell) to reset itself.
    Know that if you choose a lower charge limit voltage, say 3.5v per cell, it only means that the battery will take a bit longer to reach full charge than it would at 3.65v. (watch the end-amps, eventually it should get to close to zero at either 3.5 or 3.65v, UNLESS the bms itself is robbing you of power). If you have the time for a slightly longer absorb, why the rush to use a higher voltage?

    I am not sure which is worse for battery life, halting the charge as soon as it reaches 3.5 volts or leaving it charging for maybe hours longer at 3.4 volts to get to the same SOC.
    Something like a Fluke 87V or better, or perhaps a Revolectrix Powerlab 8 may help you determine if the BMS is indeed necessary when comparing individual cell voltage spreads after a few trial runs.

    I can't justify the cost of an expensive Fluke for the amount of work I do now I am not working. I have a cheap Uni-T UT61E 22000 count multimeter which i check with this http://www.voltagestandard.com/DMMCheck.html All the checks I have done with the 5 volt reference over the past few months at different temperatures have been a consistent 2mV out, more than adequate for checking the cell voltages.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    karrak wrote: »
    I am not sure which is worse for battery life, halting the charge as soon as it reaches 3.5 volts or leaving it charging for maybe hours longer at 3.4 volts to get to the same SOC.

    I thought about this and forgot that we're talking solar, where insolation may be an issue and it's better to get it while you can, so I'd do 3.5v and stop.

    Good deal on that calibrator. You made me think again, and that unless you are taking SOC measurements (which are not true capacity indicators), for balance measurement spreads, as long as one is using the same instrument time and again, you can get by with what you have on hand as long as it is reasonably accurate and not a shirt-pocket voltmeter.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: batteries discharging overnight, won't reach bulk voltage? help!?
    PNjunction wrote: »
    I thought about this and forgot that we're talking solar, where insolation may be an issue and it's better to get it while you can, so I'd do 3.5v and stop.

    Good point, I hadn't thought of that.

    My solar controller was doing its weekly charge to 3.45 volt/cell and i thought I i would jot down a few voltage and corresponding SOC readings, conditions were zero cloud cover for the whole day, battery temp ~30C, battery had been charging for a few hours prior.
    At 0 minutes 3.40 volts/cell @ charge current of 0.08C
    At 17 minutes 3.45 volts/cell (range 3.46-3.43) @ charge current 0.08C Delta SOC from T0 2.2%, start of constant voltage charging
    At 29 minutes 3.46 volts/cell (range 3.47-3.44) @ charge current 0.044C Delta SOC from T0 3.6%, end of charge

    For the rest of the week i charge to 3.375 volts/cell which equates to around 80% SOC, so between 3.375 and 3.40 volts ( difference 0.025V) we have around 16% capacity gain, then between 3.40 and 3.45 volts (difference 0.50V) we have 3.6% capacity gain.

    Might try this later this week with 3.65 volts/cell, I will probably have to do a cell balance at 3.65 volts/cell before I run the test.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

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