New Batteries and charger settings.

jbriant
jbriant Registered Users Posts: 11
Hi,

I am new to this forum. Many thanks for any feedback regarding my question.

I live in Vermont and have been off-grid for 10 years. I have a 2.1kw PV array and a 1kw Bergey wind generator.
I recently replaced my first set of batteries. These lasted almost ten years. In my first configuration I had 14
12 volt batteries connected in series parallel for a 24 volt system. The new battery system consists of 12 2 volt
batteries connected in series to form 24 volts.

My basic question for the forum regards setting the charging for the series battery pack vs the series parallel pack.
My system was designed and set up by a local renewable company here in Vermont and has been very reliable. I am
concerned with the charging rate of the battery and with the settings for charging. I have a backup generator for when there is
no sun or wind in Vermont and this too has been very reliable and performed my charging needs for the first ten years.
The new batteries are connected in series, the old were connected in a series parallel configuration. Each is 24 volts.
Would you change the settings for absorb time with a series system vs a parallel system? I use the PV to equalize the
batteries as well as the backup generator. Seems that the new batteries are not getting sufficiently charged when I have a good day
of sun.

My usage is between 5 and 6kw per day on average and this has been the norm for several years. when we first designed
the system it was set up to enable 3kw per day. Here is some historical data I happen to have with respect to my system.

Electricity Use 2004 – 2010

KwHours Used KwHours Per Day
2004 785 3.82 Not a full year
2005 1511 4.55
2006 1503 4.49
2007 1475 4.51
2008 1659 4.93
2009 1750 5.25
2010 2149 6.42

More information about my system.

PV: Modules 8 Sharp 165 watt modules,
PV: Modules 4 Shell 200 watt modules.
Inverter: Trace SW4024 single Inverter Power Panel
Backup Generator: KOHLER 8 RMY 8500-Watt Propane Generator w/ Auto-Start
Old Batteries: (14) Rolls by Surrette 12 VDC, 200 AHR battery
New Batteries: (12) Rolls by Surrette 2 VDC, Model S-1725, 1300 AHR battery @20 HR rate.
Charge Controller: Solar Boost 80 MPPT charge controller System Monitor: Bogart tri-metric voltage, current, amp-hr meter (3) PV Ground Fault protection(Outback)
Bergey XL.1 wind generator 1 kW Bergey 100' tower

Thanks in advance for feedback!

Brian Thompson jbriant@mail.com

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    Welcome to the forum Brian.

    The charge settings depend on the batteries, not on the series and/or parallel configuration thereof. Or to put it simply: a 24 Volt system is a 24 Volt system, it doesn't matter how you get the 24 Volts. If the settings worked with the old Surrettes they should work with the new ones. Just keep an eye on the SG and see if they do. Sometimes a little tweaking is in order no matter what.

    Looks like you can get about 68 Amps from the solar, which is a tad low for that much battery so I trust your Bergey is working well?

    I think you'll get better performance from the single string of 2V cells than from seven parallel banks of 12V units.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Hi,

    Thanks for the reply. SG? I get about 20% of my annual charging capacity from my Bergey I figure. I worked with the original
    installer to upgrade the batteries and it was his idea to change to the 2v series system. I ask here to get others such as yourself
    opinion about my situation.

    When you say 68 amps, is that max? Last weekend I did two EQ cycles for two hours each. The voltage stayed at 30v and the
    tri-metric reading was at ~30amps when it was doing the EQ for both cycles. I've never been very sure of the trimetric readings
    how accurate they are since you can change them based on the battery bank. You can be more conservative so it says your batteries
    are less charged than they really are. Not sure if that makes sense but I remember having a conversation with a renewable guy
    who was servicing my Bergey for a shorted cap on the rectifier.

    To me, it seems like my new batteries are not getting charged fully on a good sunny day.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: New Batteries and charger settings.

    Hi jbriant,

    Am sure that the move from many, many parallel strings to a single string is a great one. You did very well with the old bank.

    Just a quick thought. If you are saying that you EQed the new bank at 30 V, you did not EQ them. 31 Volts (temperature compensated) is the MINIMUM voltage speced by Surrette for 24 V FLAs.

    A few cycles of the bank to 60% SOC, or a bit lower will help run the batteries in, and build capacity. More Later, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 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.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Hi Vic,

    Even though we use a lot of mnemonics here at work, can you translate FLAs. I got the SOC(state of charge). I will reset to 31.5 for the charge volts.
    I suppose I would need to do that for Kohler backup generator as well. Thanks Vic.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    SG: Specific Gravity. The density of the electrolyte mixture. This is the best way to tell if the batteries are charged or not.

    Reflecting on your system, it is possible that some of those parallel battery strings weren't doing anything (depending on the wiring) and you may not need as much capacity as you've got. Were it me, I'd have about 2X as much solar as what you have, trying for a maximum potential output current of closer to 10% of that big bank's capacity. The current flow at any given time will be a function of the charging power available and state of charge of the batteries plus loads at that time. 30 Amps is quite meager for so much battery; they may well not be getting fully charged.

    Do you have the ability to monitor the current from the Bergey alone? You should, because it's important to know how much that is contributing.

    Yes, battery monitors can be both a blessing and a curse; they are only as accurate as their programming. It would need to be reprogrammed for the new batteries, as their capacity is different and their efficiency rating probably is as well. What's worse, those numbers change over time for any and all batteries so inevitably the monitor ends up being wrong in a few years.

    What I'd recommend for 1300 Amp hours @ 24 Volts is about 4000 Watts of array on two MPPT controllers. The wind turbine would be considered "supplemental" (possibly 40 Amps from that?).

    Just a concern here that if some o the batteries of the old bank were not actually contributing power you may have made the system worse by going to the whole capacity in a single string as it wouldn't be able to keep it charged.

    The devil is in the details for sure.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Hi Thanks for your response. I do have a trimetric on the wind generator. I kept data pretty religiously for a lot of years but
    have not really done it since 2011. SG. Specific Gravity I understand now as I do FLA = flooded lead acid. While in the Air force
    back in the 70s I serviced batteries that went in B52 bombers and KC135 Tankers. I learned SG and charging and about getting
    lots of holes in my fatigues for not wearing a rubber apron while moving batteries. They were 24v batteries.

    So my current PV array is going to stay as it is for now. I don't have the cash at the moment for that much of an upgrade
    after spending 5k on batteries. Based on other replys here, It appears I need to increase my bulk volts setting above 31 volts. I know
    my current setting on my inverter for this is at 29.1 volts.......and the OB is at 30. What about absorb time? It is at 2 hours.

    I will check the SGs on a more regular basis. I had forgotten that this reading was the real state of charge.... Oh and as i think of it, I recall
    with the old bank I had 84 cells to check.... may be the reason I didn't check it regularly. Now I only have 12 to check.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    I'm not familiar with the Solar Boost charge controller so i don't know how it handles Absorb. Considering the size of the battery bank, I'd set it for as long as possible (ideally with ending Amps) and watch the current flow over a few days. If you can consistently achieve full charge with less than maximum time, cut the time back.

    Controllers like Outback and MidNite run up Absorb time during the Bulk stage to a maximum limit and allow End Amps to override this setting. That sort of flexibility is very nice when you have varying daily conditions. Some controllers have only a fixed clock time on Absorb, often with rather severe limitations at that.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Hello,

    I have added another 1.5kw of PV to my system, I have two charge controllers. I set bulk volts to 29.4, absorb time to 4 hours, and I do not set end amps. The absorb time is not met in most cases, it goes into float mode before the time for absorb is met. I have both charge controllers set identically, one CC(80a) has 2.1kw of PV the other CC(60a) has 1.5kw of PV. Both CC are Outback units. Do you think end amps would help? I dont even understand what the proper value would be. The default is zero.
    Guess some opinions about using end amps and how it affects absorb time would be helpful.

    Many thanks for sharing your wisdom.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    There's two reasons why the controller(s) don't complete Absorb time: one is that they run out of sunlight to do the job, the other is that the current drops below the End Amps setting triggering Float (even if EA is zero).

    With two controllers quite often one will change stage before the other even though the settings are identical. So far only MidNite has the "follow me" function for multiple controllers where all are keyed off one master unit.

    You need to determine if the Absorb stage is functioning properly even though it is ending before the maximum time (which is usually what you want). This involves watching the charge controllers to see how the current output is behaving and at what level it is when the stage switches from Absorb to Float. Usually you will see the current plateau at a certain level; that will be where you want the End Amps set (normally around 2% of battery capacity with an allowance for loads). Going all the way to zero Amps will just keep it in Absorb longer than needed, and will probably cause excess water use.

    You always have to check charge controller settings against performance as measured by SG, which is why AGM's aren't such a good idea for starting out with. FLA's are easier to get set up. So you should be able to check the SG and see if the batteries really are fully charged. If they aren't, then the Absorb Voltage needs to be turned up a bit. If they are then try an initial End Amps setting and recheck on the next cycle. Repeat until your spending just enough time in Absorb at the right Voltage to fully charge the batteries on a good sunny day. It's a lot of check and recheck but it will add years to the life of the batteries.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Thanks Cariboocoot for the response. So today I had a really nice sunny day, from 7am to around 3pm. I started watching the two charge controllers around 9am. I was seeing both charge controllers combining for around 50-60 amps. sun is low here this time of year in Vermont but I still figured I should be getting more amps than that. My bulk charge volts are set at 29.4, I had the absorb time set for 6 hours, end amps at zero. My voltage was slowly rising and was around 28 volts around 10:00am. I decided to set EQ which I have set at 31.5v with absorb time of 4hours. Well this caused the charge amps to go to around 80-90 which is more of what I was expecting in bulk mode.....By 10:30, one of the two CC had pretty much dropped out of the charging cycle and was saying Charged. The other continued to charge with the amps around 30-40. This continued in EQ till around 2pm. By then the amps had dropped down to around 10. I did a SG check and the cells were reading ~1260. I turned off EQ and went to float.....

    So if end amps has some value, 2% of the AH of the battery as you suggest wouldnt that make the charge absorb time less than when it was set to zero?
    I just added the additional 1.5kw of PV because I thought I would be able to get a faster and stronger charge into my batteries. Especially in the winter months here in Vermont. I am still using around 6kw per day on average so I need to be able to charge my batteries with the sun when it happens rather than with the propane powered backup generator.

    I see similar issues when I run the generator as well. The charging cycle goes into float mode usually before the absorb time ends. It has a much higher rate of charge when it runs so I can see why it would end sooner. Still if the absorb time is not met, what really tells the charger to decrease? Ive seen the charts with the curves, but how does it really know the charging cycle is enough and it will go into float mode....

    Is there a way to program a setting to say, get the volts to 29.4 and hold the amps at 50 for a predetermined time? Probably a dangerous thing if you forget to closely monitor your system while this happening but if you could do this then you could probably say do it for 4 hours then quit.... Is that an option?

    Again, Many thanks for sharing your wisdom.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    Your battery bank is 1300 Amp hours, yes?
    60 Amps is less than 5% of that.
    Really you should have two 60 or 80 Amp controllers maxed out for that much battery: about 4+ kW of PV.

    I wonder why you are seeing an increase in current when you activate EQ? Normally that function just tries to charge at a higher Voltage. It is not temperature compensated and really it won't start until you reach the higher Voltage point so technically it has to go past the Absorb Voltage first. This is why you don't EQ unless the batteries are fully charged to begin with - or as charged as they will get under normal operation.

    Your Absorb Voltage may be too low to begin with for those batteries. Surrettes are known to operate at higher-than-typical levels. You may have to increase that to 30, which is probably about where the EQ setting is now.

    The 2% of capacity is just a guideline; a starting point around which to work rather than an absolute. That would be 26 Amps on your bank which is less than the 30-40 Amps you managed to sustain but higher than the 10 Amp low eventually reached. It is not actually necessary to reach that maximum Absorb time: it is a maximum to shut off Absorb before the batteries get too much. End Amps is supposed to switch it to Float once current levels have gone low enough, which should coincide with full SG readings. Unfortunately you have to make small adjustments, watch the results, and then adjust again until you get a charging profile that works for you.

    You don't want to hold 50 Amps for an extended time. Normal solar charging is maximum Amps until Absorb Voltage is reached, then sustain that Voltage while the current drops off. This is not the same is grid-based charging, btw.

    I'm surprised that you are able to manage any solar charging at this time of year in VT. The days are getting shorter and darker (although not as bad there as here). You may want to consider a regime of Bulk charging for 2 hours or so with the gen before the solar starts putting out serious power.
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: New Batteries and charger settings.
    New Batteries: (12) Rolls by Surrette 2 VDC, Model S-1725, 1300 AHR battery @20 HR rate.
    I bought a set of these last fall, it took all summer of cycling before they became consistent in the way they charged. It takes 75-100 cycles for the plates to form to the point where they will charge and discharge so what your seeing makes any sense, thats not to say you couldn't have issues where the controllers are fighting each other or one is off on it's calibration and cutting back.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Correct 1300 amp hours

    I have two charge controllers, a FM60 and FM80 with 2.1kw on the FM80 and 1.5kw on the FM60. I think both are pretty well
    utilized with the PV connected to them. I can raise the bulk voltage higher. I have my EQ voltage at 31.5. Also my inverter is
    a Xantrex Trace 4024, around 11 years old now.

    Pretty much I do have regemin of using the generator to charge my batteries. I have to. As you say, not a lot of sun here this time of year.
    I always look forward to Dec 21 when the days start getting longer again.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    so I have heard of controllers fighting each other. Must be a solution....I believe I am seeing that too. But if they are independent of each other, all they do is connect to
    the common bus and feed power to the batteries, then I don't see why they would fight each other... would it true If you set a long absorb time that also affects the bulk charge time to get to the absorb voltage setpoint.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries and charger settings.

    Well controllers don't actually 'fight' each other; they just disagree about things. These things include battery Voltage, charging set points, temperature, and charge stage. For the most part it isn't an issue because the 'second' controller is just an adjunct to supply current during Bulk. But when you need the controllers to "act as one" as is the case when the 10% target is >80 Amps the only ones that will 'agree' are MidNite's Classic units where one acts as master and the others just do as they're told (increasing current capacity but all controlled by one 'brain').

    Still that is not a big issue with a pair of FM controllers; just needs a little checking to see that the set points are in agreement as is the battery Voltage. The most critical point is at the start of Absorb; you want battery and both controllers to all agree that the Voltage is now "28.8" or whatever Absorb is supposed to start at.

    The maximum Absorb set time does not effect Bulk: the Bulk stage counts up once it begins and runs until Absorb Voltage is reached. This should be less time than the Absorb maximum and will limit the length of Absorb: the clock that ran up during Bulk runs down during Absorb. So controlling Absorb length you have: Bulk time, Absorb maximum, and End Amps. Absorb will run no longer than Absorb maximum under any circumstances. If Bulk time is less than Absorb max then Absorb ends when that is over. End Amps will stop Absorb if the current drops below that set point (for a period of time) regardless of Bulk time or Absorb max. It is a complex interaction, and because there are two controllers with different amounts of PV on each one the Bulk clocks will not run identically nor will End Amps divide evenly between the two.

    On the old MX60 there is a minimum Absorb time but I understand that has been discontinued on the FM series. There is still a minimum current setting I think, which stops the Bulk timer from running up if the charge current available from the PV is below this point. That prevents the time going long due to low charge current in the early hours of the day.
  • jbriant
    jbriant Registered Users Posts: 11
    Re: New Batteries and charger settings.

    Thanks for your very detailed explanation absorb cycle. I just went and made sure all my setting for absorb volts, absorb time are the same between the two controllers.
    I think I have another sunny day on the horizon. :D
  • jbriant
    jbriant Registered Users Posts: 11
    Hi,

    Have a nice sunny day here in Vermont, have both my PV charge controllers set to EQ, 31.6v. When I switched over to EQ from normal charge settings, I noticed the amps coming in from the two PV arrays went up to around 70amps on the trimetric, After about a half hour or so, the amps have dropped to around 25. I understand that the amps slowly drop off as the EQ charge progresses, but what controls how fast the amps drop. I would like to see my amps stay a little higher if possible. Is there a way to cause the amps to be higher during the absorb phase? I have absorb set for 4 hours during EQ at 31.6 volts. My battery bank info is in this thread. Thanks!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    It is the equalize voltage that really "sets" the charging current. If you want to have a lower equalization current, drop the set point by a few 1/10's of a volt at a time.

    You are doing "controlled" over charging of the battery bank (over charging 100% State of Charge cells so the "leakage current can recharge the <100% SOC cells). Much of the current is going into gassing the 100% full cells. So, you will not see equalization current "fall" to 2% to 1% or less like you would see with absorb voltage charging.

    To get higher Absorb charging current... First make sure you don't have excess voltage drop between the Charge controller and the battery terminals. I would suggest ~0.01 to 0.05 volt drop on a 12 volt bank (or 0.02 to 0.10 volt for 24 volt system). If you have too much voltage drop; you will see absorb current reduced (charge controller thinks batteries are at 29.x volts, but really the batteries are below that voltage).

    Of course, you can try bumping up the Absorb voltage by a 1/10th to 2/10ths of a volt at time to see if you can get the current higher.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jbriant
    jbriant Registered Users Posts: 11
    Hi Bill,

    Thanks for the reply. So to measure the voltage drop where would I check?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    When the charger is passing maximum current (middle of sunny day with batteries needing charged/lots of loads), measure the voltage on the battery terminals, and measure the voltage on the charge controller terminals.

    Most volt meters are not really going to be accurate enough (set for 200 VDC scale to measure ~29 volts)--So, another way, set the meter to 2 volt or 200 mV full scale and measure the voltage drop one the + and - wires, then add them together.

    And, close enough for our needs, what is the maximum charging current, what is the AWG of the wiring, and how long are they (one way or round trip length).

    This Voltage Drop calculator uses "one way" length:

    http://www.calculator.net/voltage-drop-calculator.html

    And see what you get for a calculated voltage drop.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset