Adding batteries





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  1. #1
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    Default Adding batteries

    I have 4x 260 ah batteries connected to my P/V system, they are about 2.5 years, but they have never dropped below 49v.
    Now Zambia is load shedding for about 10-12 hrs at a time, in daylight hrs this does not bother me as the panels keep the batteries full, but as back up in the dark we are struggling a bit to keep the batteries from dropping too low. So the question is would you add new batteries to this bank or replace with a complete new battery bank?
    The next thing is that I can no longer get the same 260ah batteries so it would mean adding 200ah batteries, would this be a problem?

    Edit: oh and what type of batteries would you go for
    Last edited by tripodontour; 2019/09/27 at 08:59 AM.

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    Default Re: Adding batteries

    You don't say what type of batteries you have.
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  3. #3
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    Default Re: Adding batteries

    Ok I'll get you the info in the morning. Does it make a big difference?
    Last edited by tripodontour; 2019/09/27 at 09:55 PM.

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    Default Re: Adding batteries

    Just an idea, I run lithium iron together with my original lead acid bank.

    There is some lithium batteries out there that's happy to take charge up to 54V, so no need to under charge your lead acid batteries, and from my experience the built in BMS inside the lithium battery will cut charging off it sense a too high voltage anyway.

    There is some articles based on US experience running this mix in large standby power systems.
    Last edited by faniedup; 2019/09/28 at 07:48 AM.

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    Default Re: Adding batteries

    Quote Originally Posted by tripodontour View Post
    Ok I'll get you the info in the morning. Does it make a big difference?
    Yes. But there are obviously far more knowledgeable members here that know more. So I'm outta here.
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    Default Re: Adding batteries

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  7. #7
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    Default Re: Adding batteries

    Quote Originally Posted by faniedup View Post
    Just an idea, I run lithium iron together with my original lead acid bank.

    There is some lithium batteries out there that's happy to take charge up to 54V, so no need to under charge your lead acid batteries, and from my experience the built in BMS inside the lithium battery will cut charging off it sense a too high voltage anyway.

    There is some articles based on US experience running this mix in large standby power systems.
    Interesting. Now what happens if the Lead Acid is charged and the Lithium is flat.
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  9. #8
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    Default Re: Adding batteries


    Yep, thats what I would do or something similar.

    At that price however, for 4 of them we are into small LiPo power walls territory.
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  10. #9
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    Default Re: Adding batteries

    Quote Originally Posted by Fluffy View Post
    Interesting. Now what happens if the Lead Acid is charged and the Lithium is flat.
    Never had a situation like that, I set up the inverter to charge lead acid, the lithium will draw current until its charged and its own management system stop it charging when it's full, as the lithium needs less voltage to charge fully than the lead acid
    Last edited by faniedup; 2019/09/28 at 01:51 PM.

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    Default Re: Adding batteries

    Quote Originally Posted by tripodontour View Post
    I have 4x 260 ah batteries connected to my P/V system, they are about 2.5 years, but they have never dropped below 49v.
    49V divide by 4 = 12.25V per batt
    I'm sure the manufacturer hasn't specified this as min voltage for the battery.
    Yes, it is a compromise between cutout voltage and life of battery but I reckon you've got to get as much life out of your batteries as you can..
    So work them as hard as the manufacturer suggests and then when they can't do their job any more then that's that!

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    Default Re: Adding batteries

    Although this battery can be discharged to a DOD of 100% and get only 500 cycles I belief it is much more cost effective to cycle only to 40% and get 1550 cycles.

    Thus the OP prefers to get the more economical use of his batteries.

    Each persons choice in the use of batteries.

    Click image for larger version. 

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  14. #12
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    Default Re: Adding batteries

    Quote Originally Posted by tripodontour View Post
    I have 4x 260 ah batteries connected to my P/V system, they are about 2.5 years, but they have never dropped below 49v.
    Now Zambia is load shedding for about 10-12 hrs at a time, in daylight hrs this does not bother me as the panels keep the batteries full, but as back up in the dark we are struggling a bit to keep the batteries from dropping too low. So the question is would you add new batteries to this bank or replace with a complete new battery bank?
    The next thing is that I can no longer get the same 260ah batteries so it would mean adding 200ah batteries, would this be a problem?

    Edit: oh and what type of batteries would you go for
    What are the essential loads that you need to keep running at night?
    Inverters are inefficient with light loads (drawing amps just to keep the inverter running) so if you can shut them down during these low demand periods then this would help.

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    Default Re: Adding batteries

    Just add the extra batteries, really. When adding them make sure all the batteries are fully charged though, in this way the system will be balanced. Remember that you cannot simply disconnect your bank, make sure the panels are disconnected first and then re-connected last. Also make sure the new batteries form part of the "bank" and are not simply "put on the end"
    As far as varying capacities go, the lower batteries will now determine you amp hour rating of the bank. Charging characteristics will remain exactly the same though. Also bear in mind that if you are running a series/parallel system you should try and not exceed 4x banks, preferably no more than 3 is best.
    Lead acid batteries are VERY forgiving and really you can mess them around quite a bit. Remember safety at all times, you are dealing with BIG amperage if something does go wrong, fuses near the battery are a must, venting just as important.

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  17. #14
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    Default Re: Adding batteries

    Quote Originally Posted by faniedup View Post
    Never had a situation like that, I set up the inverter to charge lead acid, the lithium will draw current until its charged and its own management system stop it charging when it's full, as the lithium needs less voltage to charge fully than the lead acid
    My concern is what will happen to the lead acid.

    Dave Faddel's post is most important. When paralleling batteries make sure your initial connection is with ALL batteries fully charged.

    They will pretty much behave themselves after that.

    Connecting a flat set in parallel with a charged set is asking to destroy the charged set.
    Last edited by Fluffy; 2019/09/29 at 05:10 PM.
    Cheers

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  18. #15
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    Default Re: Adding batteries

    My asked my pal in California about this. He's been off grid for many years.
    He reckons it's ok to add batteries (Li-Ion aside..)
    What you need to monitor however is for a shorted cell. This can be done by a hydrometer if they are wet batts. If not then use a non contact IR thermometer. The temperature difference of a dud cell quickly identifies this.
    By managing his batteries like this he has used batteries that most users would chuck out due to low capacity..

  19. #16
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    Default Re: Adding batteries

    Quote Originally Posted by Olyfboer View Post
    You don't say what type of batteries you have.


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  20. #17
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    Default Re: Adding batteries

    Thanks for all the replies, plenty to think about.
    My thinking now is that I can run for 10hrs without sun or Zesco the system is working well, I will probably turn a fridge off overnight then run it very cold during the day.

    When these batteries die I will go with a bigger bank.

    What voltage would be the lowest I should go down to: 46V?

  21. #18
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    Default Re: Adding batteries

    Quote Originally Posted by tripodontour View Post
    When these batteries die I will go with a bigger bank.
    Ok. Does this mean you will discharge these batteries more than 50% DOD till they are dead?
    The consensus seems that you do get more value out of keeping to 50% DOD and simply adding new batteries in parallel to the existing bank..

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