Multimeter - Charge Controller Giving Different Readings...Confused!

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CBear42
CBear42 Solar Expert Posts: 28 ✭
in Off Grid Solar & Battery Systems #1
Hi all,

If anyone is on - "Happy Holidays"! Everyone here deserves a wonderful New Year for all the help they have been to me over this last year - it is SO appreciated!

I have a hopefully quick question.

I have a system that is waiting to be evaulated after a fraudulent (un-certified) installer installed it. (I am in the New York/Vermont area if anyone wants the name, please PM me.) The certified guy cannot come out until after the first of the year so I am in "wait" mode.

Since the temperature has dropped to the teens/single digits - I have been seeing the following behavior. I don't know if it is "OK" - or not. Or the action to take - if any.

My MultiMeter (measured at the open terminals of my 24v-wired battery bank (12w, 250AmP) is consistently showing 100% voltage readings (I am reading anything over 25.4 as 100%) - the readings are taken manually almost hourly. Basically, this morning it was in the 28.4v range - no generator running. It is taking a LOT to bring them down off of that - but they DO come down by the end of the day. OTOH, my TriStar MPPT 45 controller and Outback VF3524 inverter are showing the batteries as discharging to low levels! Running the generator brings the batteries easily up to 29.5v within a few minutes. I am worried. Which should I be "paying attention to" at this point - the meter which is measuring the open terminal voltage OR the charge controller/inverter components? (I only have dummy lights on these components so the "estimate" of where the batteries are sitting is really a "guesstimate". I'm waiting on the assessment from the installer to see where/what to go forward with in terms of more money/monitors..) I should point out that the first installer did no customization of either the charge controller or the inverter to my specific situation and did not install the remote temp sensor on for the charge controller - but did install it on the inverter.

The batteries are in the house, but in a colder area. The PV panels have some snow/ice on them...but, not a lot. Is temperature causing an increase in battery performance - as I've read can happen?

Thanks in advance for any and all help!

CBear
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    yes, we do still get on here.

    i'm trying to figure out what the setup actually is that you supposedly had installed there and is it fully connected/operational? partially? i don't know enough to make a comment at this point or can really follow if your concern is normal or not.

    not sure if i may need to stay off being i have a winter storm bearing down on me.
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  • CBear42
    CBear42 Solar Expert Posts: 28 ✭
    #3
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    Hi -

    I apologize for the confusion.

    Yes, the system is up and operational.

    I have six 250w PV panels, pole-mounted although not in an optimal location (will be moved in the spring). They are mounted in two parallel configuration -> into one series. I have a TriStar-45 MPPT charge controller and an Outback inverter connected to 4 12v, 250 amp batteries (they are wired in a 24v setup). I used a 7500w Generac for re-charging/back-up power. They was installed the first of November. There had been multiple issues and the panels and battery banks have been re-wired according to the manufacturers specs/suggestions (gathered by speaking to their techs directly)

    It has been working much better since then. However, until I can have the whole system assessed, I am measuring the battery voltage manually using a MultiMeter applied to the negative/positive batteries that represent the open terminals of the battery bank. My question revolves around measuring the state of charge of the batteries. These are wildly expensive batteries (to me) and I need to make sure they do not
    discharge too deeply. My confusion revolves around the discrepancy between what the charge controller and inverter are telling me and what the meter is telling me. (I got the meter and have been using that since I don't have more accurate monitoring equipment yet...)

    If you need more info - please let me know...
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!
    CBear42 wrote: »
    I have a system that is waiting to be evaulated after a fraudulent (un-certified) installer installed it. (I am in the New York/Vermont area if anyone wants the name, please PM me.) The certified guy cannot come out until after the first of the year so I am in "wait" mode.

    Cbear, The forum won't let me send you a PM... is your mailbox full? I am interested to know who the fraudulent installer is... I can think of one or two in the western vt area. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    If you know the multimeter is accurate, then trust it. Some meter's will give you faulty readings if the battery is low in them. Trying to calibrate everything in your system takes some time. If the settings in you Inverter / Charge Controller is set for one thing and it's not seeing that voltage, then the lights will be off ( Faulty Reading ) . ( Example : If the setting is looking for 29 V and the batteries are 25.4, then will show low. ). Thats why they call them Idiot Lights.

    If in doubt try another Meter. You also have to take any loads on the system into account. Seeing a 3-4 /10's difference is usual thing between the true readings batteries and the Inverter or Charge Controller. When the batteries are low and the Charge Rate is high, it could be a volt or more.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #6
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    CBear, Please read the battery FAQ's.

    I think you don't yet understand how things work. While charging, batteries will show a voltage at the charging rate determined by your charge controller, you can change what the charge controller does, by putting loads greater than your array's ability to handle, hence drawing current from your battery. Your charge controller with 'dummy lights' will usually indicate a 'full charge' once the battery voltage reaches @25.4 volts, but while charging it will not show correctly! all it can measure is voltage.

    I think I mentioned in an earlier thread that a trimetric or other shunt based battery meter will give you a more realistic idea of current battery capacity.

    Knowing that your batteries are in a different location than you charge controller makes a battery temperature sensor (BTS) more imparitive! the charge controller usually has some internal measure of temperature to adjust it's charging rate for current conditions and if in a different enviroment it may be sending the wrong voltage/current to the battery.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    Measuring your battery capacity by voltage is very "touchy feely" unless the batteries are at rest for a few hours, no charging or loads(discharging). I think it's is OK, once you get a feel, but it take a while to develope a sense for what's going on.

    You can likely determine what stage the charge controller is in, Early in the day and it's between 24 and 28.4 it's likely in Bulk, If it's at 28.4(or abouts and steady) it's still in asorb, if it's holding 27.2-27.4 it's likely at float...

    FWIW - when the sun goes down, it's equally hard to determine State of Charge (SOC) by voltage, since it will be effected by the loads. The reason a shunt type meter will give you more accurate results is it measures the current/amps going into and out of the battery.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #8
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    Hi CB..,

    As Photowhit noted, generally, trying to use voltage measurements is a difficult way to try to determine SOC of batteries. Cool/cold batteries will have higher voltage readings for a given SOC compared to those at the standard temperature -- 77-80 degrees F.

    And, we will continue to ask you questions about your system, delaying a valid reply for your exact situation.

    Could you write a Signature that tells all of the above info on CC, PVs, Inverter, AND the batteries that you are using ??

    The absolute best measure of State Of Charge of batteries is a Hycdrometer. BUT if you have sealed batteries this is not possible. We could pick through your past posts to see if you mentioned the exact battery model and technology, but a Sig line would help ALL of us to cut to the chase, as it were.

    Thanks! 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.
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #9
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    How about in the short term picking up a new $10+ digital volt meter to double check your current meter? A $200 battery monitor would be a good investment. The display can be inside to easily monitor the batteries including SOC, amps in/out and voltage.
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  • CBear42
    CBear42 Solar Expert Posts: 28 ✭
    #10
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    Testing New Sig Guys...
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  • CBear42
    CBear42 Solar Expert Posts: 28 ✭
    #11
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    New test - sorry...earlier sig was too long...TMI!!!
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #12
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    Hi CBear42,

    Thank you very much for that shiny new Sig.

    Am sure that others knew that you had AGMs, and therefore did not recommend measuring SGs with a Hydro ... Never mind.

    Well, as noted by others, a battery monitor should be a good investment for you. Also you appear to have two strings of batteries. One string could be disconnected and left to rest for 4, or more hours. Then, when temperature compensated, voltage measurements should fairly accurately reflect actual SOC. This rested string could be reconnected, and the similar thing done with the other string. Of course be VERY CAREFUL when working around batteries with tools, as any slip could cause harm to you and/or hardware.

    A battery switch could possibly be used to perform that above noted task, although this would increase cable lengths and voltage drops, and would perhaps not be to Code.

    If you happen to get a Battery Monitor, it would need to be calibrated for your system. This can be a bit difficult with sealed batteries, but it is possible. Good Luck, 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.
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  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    #13
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    Re: Multimeter - Charge Controller Giving Different Readings...Confused!

    I chose a Victron battery monitor because of size and found the setup with a Lifeline AGM simple and accurate http://www.victronenergy.com/battery-monitors/bmv-600s and bmv-602s
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