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Does Charge Rate Change With More Batteries?

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  • secessus
    replied
    > he runs down to 60% DOD to do it. His panels fully recharge his bank almost every day. His batteries are only 1 month old and he wants to add additional batteries to increase the AH of his battery bank so he can only drop to 75% or 80% DOD

    From my reading it appears he is presently running to 40% DoD and wants to add Ah so he would run to 20-25% DoD (ie, discharge less deeply)

    The 60% --> 75-80% figures would typically be called "state of charge", the inverse of depth of discharge (in common usage, at least).

    > his MPPT controller is showing 18 amps into his batteries when showing BOOST. Based on what you said he should not have more than a 180 AH battery bank? (1/10 of 180 AH would be 18 amps.)

    The 18A figure may be a function of the batteries acceptance rather than the charging capacity. In the absence of info on the bank or solar config it's hard to tell.

    Boost (ie, Absorption) stage is not the ideal time to see how much charging power the system has. In Absorption current is already dropping off. Late Bulk or very early Absorption will give you a better feel for it. Better yet, shut off power from the panels and crank them back up at solar noon.

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  • Salts
    replied
    Originally posted by Mike90250 View Post

    But you can't let them get cold or chilly ! And you need a complicated BMS and a charge controller that the BMS can control
    You CAN let them freeze, just just can't charge them when frozen, but you can discharge them... and they do enjoy being stored at 40 degrees or so. Lithium ion is far better in the cold than lead acid is.. BMS is certainly a requirement and they can get complicated, and expensive, so that's a big drawback.

    Mine are in my basement that's about 65° during the summer and as low as 40° in the winter if I don't heat it.

    Waiting for them to invent a perfect battery...

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  • Mike90250
    replied
    Originally posted by Salts View Post
    Switch to Lithium.. Lithium batteries are perfectly happy being partially charged for
    months on end. They don't mind being run down and left in that state.
    But you can't let them get cold or chilly ! And you need a complicated BMS and a charge controller that the BMS can control

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  • Salts
    replied
    Switch to Lithium.. Lithium batteries are perfectly happy being partially charged for months on end. They don't mind being run down and left in that state.

    Leave a comment:


  • SunEagle
    replied
    Originally posted by AL1952 View Post

    He says his MPPT controller is showing 18 amps into his batteries when showing BOOST. Based on what you said he should not have more than a 180 AH battery bank? (1/10 of 180 AH would be 18 amps.) He has a 140 AH battery bank. So should he stay with that at C/8 or can he add one battery to get him to 170 AH and still be OK on the charging rate around C10? BTW he says to tell all of you a BIG THANKS and that he appreciates you passing this information along to him. I was thinking of charging him a 6 pack for being the messenger but since you guys help others for free I'll follow your example and do the same. I'm learning some new stuff too so it's a win/win.
    My advice is free. But I always tell people to read and educated themselves because free advice can lead you down the wrong path.

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  • AL1952
    replied
    Originally posted by SunEagle View Post

    FLA type batteries like to be charged between a C/8 and C/12 rate where C = the battery system Amp hour rating. A simple target is to get 1/10th the amp hour rating as charging amps.
    He says his MPPT controller is showing 18 amps into his batteries when showing BOOST. Based on what you said he should not have more than a 180 AH battery bank? (1/10 of 180 AH would be 18 amps.) He has a 140 AH battery bank. So should he stay with that at C/8 or can he add one battery to get him to 170 AH and still be OK on the charging rate around C10? BTW he says to tell all of you a BIG THANKS and that he appreciates you passing this information along to him. I was thinking of charging him a 6 pack for being the messenger but since you guys help others for free I'll follow your example and do the same. I'm learning some new stuff too so it's a win/win.

    Leave a comment:


  • Mike90250
    replied
    At some point you end up with 6 barely used batteries, that have died from old age ! AGM batteries have a shorter life than flooded batteries. So you have to walk the fine line of not too deep of discharges vs staying within the expected lifetime of the batteries. 3-4 years is the max to expect from AGM, 5-8 for flooded. (GC2 is 3-5 years, but they are cheap learner batteries)

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  • SunEagle
    replied
    Originally posted by AL1952 View Post

    That's good to know. He needs more solar to fully charge every day and to account for cloudy days. I just asked him and he can easily had 2 or 3 more panels. But what about the basic question assuming he can do this? Does it matter how many batteries he has if he is recharging the same amount used every day, whether he has 4 or 6 batteries? Wouldn't it be better to have 6 batteries and only a 75% DOD than 4 batteries and a 60% DOD?
    FLA type batteries like to be charged between a C/8 and C/12 rate where C = the battery system Amp hour rating. A simple target is to get 1/10th the amp hour rating as charging amps.

    Leave a comment:


  • AL1952
    replied
    Originally posted by Mike90250 View Post
    > His panels fully recharge his bank almost every day.This is key. Every 3rd day is short, or every 30 days, it's cloudy and the batteries get a short charge. The more often the batteries don't completely charge, the sooner they fail. This is ONLY true for AGM. Flooded cells have a minimum charge rate REQUIREMENT to keep the juices mixed up from some bubbles . Otherwise the electrolyte stratifies and the battery dies
    That's good to know. He needs more solar to fully charge every day and to account for cloudy days. I just asked him and he can easily had 2 or 3 more panels. But what about the basic question assuming he can do this? Does it matter how many batteries he has if he is recharging the same amount used every day, whether he has 4 or 6 batteries? Wouldn't it be better to have 6 batteries and only a 75% DOD than 4 batteries and a 60% DOD?
    Last edited by AL1952; 09-02-2020, 06:12 PM.

    Leave a comment:


  • Mike90250
    replied
    > His panels fully recharge his bank almost every day.

    This is key. Every 3rd day is short, or every 30 days, it's cloudy and the batteries get a short charge. The more often the batteries don't completely charge, the sooner they fail.

    This is ONLY true for AGM. Flooded cells have a minimum charge rate REQUIREMENT to keep the juices mixed up from some bubbles . Otherwise the electrolyte stratifies and the battery dies

    Leave a comment:


  • TKB4
    replied
    You might not have to change anything other than adding batteries if the additional batteries would still fully charge at the same amps he currently charges with. For instance if his batteries are usually topped off with say 2 sun hours left and he lives in a 6hour sun day area he should be able to increase the battery bank by about 1/3 and still charge them fully. this would limit DOD to about 75-80%. All he really needs to know is what time of day his system usually has fully charged his batteries and how many good hours are left after that to charge assuming he is using the same power . If his system is good currently it will still be ok as far as safety goes .

    Leave a comment:


  • Salts
    replied
    Yes, the charge rate changes if he has the extra power to increase the rate.

    If you have a single battery and the proper charge rate is 20 amps, then you would add another 20 amps if you added a second identical battery in parallel. So 20 amps for 1 battery or 40 amps for two batteries in this example.

    You'll need to figure out if he has enough solar and charge controller capacity to support the higher charge rate. In fact, you'll have to check the entire system, fuses, wires, etc.. to make sure the increase in capacity isn't going to cause any problems.

    Leave a comment:


  • AL1952
    started a topic Does Charge Rate Change With More Batteries?

    Does Charge Rate Change With More Batteries?

    I’m trying to help a friend with a relatively new solar setup and it’s like the blind leading the blind, so I’m coming here for professional advice for him since you all have been so helpful to me in the past. His 12 volt AGM battery bank provides all the power he needs every day right now for his light load but he runs down to 60% DOD to do it. His panels fully recharge his bank almost every day. His batteries are only 1 month old and he wants to add additional batteries to increase the AH of his battery bank so he can only drop to 75% or 80% DOD. I told him this is a good idea because it will make his batteries last longer. What I don’t know is what happens with the charging rate with those extra added batteries? Does it change? Does it make any difference whether he is charging into 4 batteries, or into 6 batteries to replace the amps used every day and the panels can provided all the power he needs to recharge? It would seem obvious the charging rate would still be the same, but I don’t want to give bad advice if I’m missing something here. Thanks
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