Trojan battery voltage drop

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benjammin5150
benjammin5150 Registered Users Posts: 4
in Off Grid Solar & Battery Systems #1
Hi everyone, Im new here and I have a question about my new trojans. I have 2 12v 100ah scs150 deep cycles. I bought them new in October. When I brought them home I measured the voltage of each at 12.5v, wired them in parallel and charged them fully with a Noco genius 7.2A charger. The resting voltage is 12.8v. I read its best to break them in by cycling them several times 10-20%. Every time I do this I only draw a 8-10amp load but the voltage drops way down to 12.1v and stays there. Is this normal for new batteries? I have walmart marines that dont drop nearly that amount of voltage with the same load...and they maintain much higher resting voltage than the trojans.

Another question I have with these trojans is can I equalize them? They are flooded but are sealed so I cant check the specific gravity.

Thanks everyone.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #2
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    Re: Trojan battery voltage drop

    Welcome to the forum Ben!

    Cycling the battery bank by at least 25% depth of discharge (to ~75% state of charge, down to 50% maximum SOC when discharging), it good for deep cycle batteries.

    You have two 100 AH batteries in parallel for a 200 AH battery bank. 25% of that would be 50AH of discharge:

    50 AH / 10 amp load = 5 hours of discharging.

    Your present battery charger is really not large enough. Trojan recommend a 10% rate of charge minimum:

    200 AH * 10% = 20 Amp minimum rate of charge.

    The charger will supply 20 amps during (bulk, charger is current limited) until ~80-90% SOC, at that point, the battery will be at ~14.75 volts and you want the charger to hold ~14.75 volts for ~2-6 hours (battery bank will be in Absorb for more hours the deeper the discharge).

    At that point, the charger can turn off, or drop to ~13.6-13.8 volts or so and hold for "float voltage".

    To measure resting voltage, you want there to be no charging/load currents for ~3+ hours. And for flooded cell batteries, you really need a good quality glass hydrometer or one of these:

    http://www.midnitesolar.com/productPhoto.php?product_ID=505&productCatName=Battery%20Accessories&productCat_ID=39&sortOrder=1&act=p

    Attachment not found.

    For flooded cell batteries, the specific gravity of the electrolyte is the "gold standard" to determine state of charge.

    If you are measuring 12.8 volts during charging, your battery bank is not being properly charged.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • benjammin5150
    benjammin5150 Registered Users Posts: 4
    #3
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    Re: Trojan battery voltage drop

    Thanks for the reply BB. Im sorry I wasnt more specific in my original post. I have the batteries hooked up to a Victron Energy battery monitor. The resting voltage is 12.8 after 24 hours of no load no charging. You're right in your calculations, when I draw a 8-10amp load it takes right about 4 hours to get to 80% SOC. However, Im concerned because the voltage immediately drops to around 12.1 and doesnt come up at all until i remove the load. It seems like an excessive amount of voltage drop.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #4
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    Re: Trojan battery voltage drop

    I think you may have purchased old batteries!

    AGM batteries have low self discharge rates and seeing a new battery of this type with a voltage of 12.5 would give me pause.

    Trojan's have a date code stamped into the lead of the terminals;
    Trojan site wrote:
    How do you read the date codes on the batteries?
    Positive Terminal- Manufacturing Date. This code indicates the actual date when mechanical assembly of the battery was completed. At this point, electrolyte has not been added to the battery and formation charging has not taken place. LETTER stands for the month and could be anything from A to L (A=January, B=February, C=March, and so on),; NUMBER stands for the date.
    Negative Terminal- Shipping Date. This code indicates the month and year when the battery was shipped out of our factory. LETTER stands for the month (see below); NUMBER is the last digit of the year.

    okay I went back to look at your post and you do give a model SCS150, those are flooded batteries and they have a 3 caps together, you shold be able to lift that and check your Specific Gravity, as Bill suggested.
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #5
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    Re: Trojan battery voltage drop

    Are you measuring the Specific Gravity?

    And their industrial product line recommends:

    http://www.trojanbattery.com/pdf/TRJN0169_UsersGuide.pdf
    What to Expect from your Trojan Battery

    It is expected that a new battery will need time to provide full, peak capacity. Trojan batteries take
    It is expected that a new battery will need time to provide full, peak capacity. Trojan batteries take between 50 – 100 cycles to work up to providing full, Amp-hour capacity.

    And just to cover all the bases... Your batteries are at ~room temperature and you are measuring the voltage at the battery posts (not after voltage drop of the wires while discharging)?

    And what voltage does your battery charger reach, and how long does it hold that voltage?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • benjammin5150
    benjammin5150 Registered Users Posts: 4
    #6
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    Re: Trojan battery voltage drop
    Photowhit wrote: »
    I think you may have purchased old batteries!

    AGM batteries have low self discharge rates and seeing a new battery of this type with a voltage of 12.5 would give me pause.

    Trojan's have a date code stamped into the lead of the terminals;


    okay I went back to look at your post and you do give a model SCS150, those are flooded batteries and they have a 3 caps together, you shold be able to lift that and check your Specific Gravity, as Bill suggested.

    The scs150 does not have caps...Here are the batteries http://www.trojanbattery.com/product/scs150/

    The date code stamped into the lead reads j 14
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: Trojan battery voltage drop
    Photowhit wrote: »
    ...those are flooded batteries and they have a 3 caps together, you shold be able to lift that and check your Specific Gravity, ...

    What ever you do don't look under those 2 big rectangular pieces of plastic on the top of the battery!...lol

    12 volt battery, 2 volts per cell, 3 caps together = 2 big pieces of plastic.
    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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  • benjammin5150
    benjammin5150 Registered Users Posts: 4
    #8
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    Re: Trojan battery voltage drop

    My bad! I didn't think those were meant to come off! Thanks for setting me straight.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #9
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    Re: Trojan battery voltage drop

    It happens to a lot of us. I bought a battery from Wal-mart and I'd of swore it was a AGM. The cap covers were recessed and looked like a AGM. I used it 3 years on a Generator before it gave up the ghost. After I looked it over, bingo, I had missed the cap covers and the plates were dry, lesson learned.

    It's about the same way with sealed and unsealed bearings these days, you have to really look close. Now things that you buy replacement bearings for use sealed instead of unsealed and have a plug for the zerk fitting hole.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #10
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    Re: Trojan battery voltage drop

    The last time i built a deck i got caught out by timber shrinkage. Previous decks the timber shrank alot, and the 4mm gaps between boards opened up to about 10mm. So this time being 'smart' this time i used 2mm gaps. Thing is this particular timber turned out to be kiln dried, and instead of shrinking it grew! Now theres no gap... Sigh.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #11
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    Re: Trojan battery voltage drop

    Yeah that happened with me with my last wife too.
    I could have SWORN she was better than the previous model but within a couple of weeks her warranty ran out :)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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