48 Volt battery bank wiring

JCOrd
JCOrd Registered Users Posts: 6 ✭
in Off Grid Solar & Battery Systems #1
Greetings to the community. First time poster, long time reader.
I read the most excellent article on the Smartguage website (http://www.smartgauge.co.uk/batt_con.html) regarding "How to correctly interconnect multiple batteries to form one larger bank", but this deals with parallel connections only.
I have been scratching my head tring to figure out the method of wiring 20 pc, 12 volt AGM batteries into 5 x 48 volt groups in series / parallel. Kindly point me to a schematic or photo that uses either Method 3 or Method 4 as described in the article to accomplish a 48 volt bank.
Many thanks.
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Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: 48 Volt battery bank wiring

    The primary objective is to have exactly the same wire lengths and number of lug connections for every parallel string.

    You might want to consider putting each string on a Anderson connector to allow you to take a string offline for maintanance. You can tie the five string, through quick disconnect to a high current bus junction.
    http://www.solar-electric.com/anhicupoco.html

    Each of the five strings should have a fuse. A 100 amp shunt on each series string would also be good so you can monitor current balance for each string.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: 48 Volt battery bank wiring

    Four 12 Volts in series give 48 Volts.
    You have twenty 12 Volt batteries total.
    That's five strings of four each.

    That also requires hooking the parallel banks to bus bars, using equal-length cables on each bank.
    It can't be effectively done using just the batteries and cables; you need the "central connection point".
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #4
    Re: 48 Volt battery bank wiring

    I would go with this:
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  • JCOrd
    JCOrd Registered Users Posts: 6 ✭
    #5
    Re: 48 Volt battery bank wiring

    Thanks for the quick and insightful replies, folks.
    I was studying "Method 4" in the above mentioned article to see if there was a way to wire the groups of 4, 12 V batteries in series, in the same fashion as seen below in the parallel example (borrowed from the Smartguage website).
    Could one create 2 groups of 2 series connected 12V batteries and cross connect the groups again in series to achieve the best balance for 48V?
    Thanks for your replies. It will definitely assist me in the design of the bank.
    Cheers!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: 48 Volt battery bank wiring

    I may not be interpreting what you're saying correctly. It sounds as though you want to create parallel banks of 12 Volts, then hook four of these in series to get 48 V? If so, that's not the way to go because it creates many parallel connections instead of just at the ends, as it were.

    It's best to series wire four to get 48 Volts, then parallel each series string to common + & - connection points with equal length wire. As per n3qik's excellent drawing.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: 48 Volt battery bank wiring

    i think i'm following what he's saying and if it is to take like the first battery + posts of each string and tie them together and do this with the 2nd, then the 3rd, and then the 4th battery in each string then yes it will make for more balance.
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  • JCOrd
    JCOrd Registered Users Posts: 6 ✭
    #8
    Re: 48 Volt battery bank wiring

    Precisely! My interest in balancing the batteries was sparked by the above mentioned article for parallel wired batteries. So, instead of just wiring all the batteries in a stright series chain (leaving the two middle batteries providing less current to the buss than the two outside batteries), I am trying to work out how to cross wire the two groups of 12V batteries to provide perfect (or close to perfect) current balance as a 48 volt group of 4 X 12V batteries. Time to get my birthday present of a Fluke jaws multimeter and try a DC load.
    Cheers.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: 48 Volt battery bank wiring

    I can see a slight possibility of a problem arising from a bad connection that could result in a power path "going around" one or more batteries and leaving them out of the loop. But if you keep an eye on it such would be detected before any real trouble began. Not sure how much improvement there would be over straight-forward series/parallel arrangement. Lots of extra wire. Interesting idea, though.
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  • dhsola
    dhsola Solar Expert Posts: 38 ✭
    #10
    Re: 48 Volt battery bank wiring

    Yes, interesting.
    I think I might test this out this weekend. I don't have enough wire to do the test but I could test it with copper pipe.
    I always have 3-4 batteries that run at a higher voltage than the rest...
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  • dhsola
    dhsola Solar Expert Posts: 38 ✭
    #11
    Re: 48 Volt battery bank wiring

    This is what I have so far. Unfortunately, I haven't had time to do much testing.
    The volts shown under the picture are for each battery in that particular column.

    Bulk charge is set at 55.6v (13.9).
    Adding a couple of cables at each end of the bank didn't seem to make much difference although, they're the wrong size any way (#4) -all I had on hand.

    As you can see, the inverter cables are connected to the copper between the battery posts, not at the battery posts.
    Overall, (and with little testing) it appears the batteries are balanced better. :D
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #12
    Re: 48 Volt battery bank wiring

    13.9 volt (12 volt relative) is pretty gentle charging... If you need to charge quicker (use more current from solar panels, less run-time on genset), you might want to double check with the battery vendor and see if you can crank those up to ~14.2-14.4 volts or so (at 77F).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dhsola
    dhsola Solar Expert Posts: 38 ✭
    #13
    Re: 48 Volt battery bank wiring
    BB. wrote: »
    13.9 volt (12 volt relative) is pretty gentle charging... If you need to charge quicker (use more current from solar panels, less run-time on genset), you might want to double check with the battery vendor and see if you can crank those up to ~14.2-14.4 volts or so (at 77F).

    -Bill

    I hear ya Bill.
    I reduced the charge because some of the batteries were getting up to 14.6-14.8 (probably higher, don't remember) and gassing. Maybe with this new setup, I will be able to bulk charge at or near the 14.2-14.4 recommended by Lifeline. I won't be able to test that until the weekend..
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #14
    Re: 48 Volt battery bank wiring

    You might try measuring the resting voltage of all the batteries... Any that are significantly below the rest, you may want to charge those separately with a 12 volt battery charger...

    Equalization involves overcharging some batteries in a series string to recharge those cells below 100% charge. You can charge individual batteries if a few are well below the rest (possibly from your previous wiring issues).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    #15
    Re: 48 Volt battery bank wiring
    dhsola wrote: »
    I hear ya Bill.
    I reduced the charge because some of the batteries were getting up to 14.6-14.8 (probably higher, don't remember) and gassing. Maybe with this new setup, I will be able to bulk charge at or near the 14.2-14.4 recommended by Lifeline. I won't be able to test that until the weekend..

    dhsola,

    How old are your Lifeline Concorde batteries?

    I have 16 of the exact same batteries, and I also experienced some of exactly what you are describing with unequal battery charging.

    With mine, I know that they are sulfated to different degrees, so that has caused some of the imbalanced charging voltages. I bought my Lifelines at a low price as "NEW", but they had sat for a long time and were deeply discharged before I ever got them. I also ended up setting my charge voltages at the low end of Lifeline's recommendations, so that I wouldn't overcharge some of the batteries. Just like you described.

    Works OK for an emergency back up battery system that is seldom neeed, but they are definitely not what I'd want to depend on for daily off grid living. Some day, I hope to get a fresh set of batteries and get off to the right start (and take very good care of them).

    Edward
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #16
    Re: 48 Volt battery bank wiring

    Here is Edward's "keyturbocars" thread where he did a bunch of research and testing a setup to recover Lifeline AGM batteries:

    Sulfated Lifeline Concorde AGM Batteries

    If the batteries in series (and parallel) are terribly mismatched (i.e., good battery in series with sulphated battery) could cause the unbalanced charging where one battery is charging at "low voltage" and the other at "high voltage"...

    Charging/recovering batteries separately may help... Also matching batteries by capacity ("high" capacity in one string, "low" capacity in a second series string) may help too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    #17
    Re: 48 Volt battery bank wiring

    I agree with Bill. Handling each battery separately is a good idea. I did it and it did help my situation. Even so, my batteries were so far gone to begin with that the situation is still not great. Things are better though.

    If your battery bank is newer and in better condition then mine, then trying to equalize each battery separately according to Lifeline's procedure might give you good results.

    Edward
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  • dhsola
    dhsola Solar Expert Posts: 38 ✭
    #18
    Re: 48 Volt battery bank wiring

    Last I checked the resting voltage they were within .01 to .10 of each other. (Actually my batteries never "rest"). :D Just checked (7:25 PM).. Neg side parallel batteries at 12.75v, .07 to .10 higher than all other batteries with about a 150w to 200w load.

    I bought the first two batteries March '10 and the last string of four in Oct '10.
    (By the way, two of the strings had discharged batteries (12.5 - 12.7). I wasn't happy to have paid that kinda money for new batteries and then have to spend several days charging them before I could use them).

    All in all, I'm pretty happy with these little Lifeline batteries..

    I have another small 4-battery-12v-system of Costco wet cell batteries. Little bit higher in total amp hours than the Lifelines but of course, they just can't take much of a load for very long compared to the lifelines
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  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    #19
    Re: 48 Volt battery bank wiring

    Your batteries were (and are) in much better shape than mine were. If memory serves me right, I think some of my batteries were reading as low as 11.5V when I took them out of the boxes. They sat for 2 YEARS before I bought them. Other batteries were higher, but they were all over the place. They were all very low!

    I thought I was getting a good deal paying around 1/3 price (getting 3 for the price of 1)!. In reality I was paying a lot for scrap lead! UGH! It is amazing at how well they have come around all things considering, but they are definitely NOT what they should be. One day I plan to do it right. For now, they are sufficient for what I need.

    In the future, I'd like to get a couple strings of the 6V Lifeline GPL-6CT (oversized golf cart size) that are rated at 300A/H each. This time, I'm going to make sure that they are factory fresh and all from the same lot. And I'm going to treat them like they are made from GOLD!

    Live and learn!

    Edward
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  • JCOrd
    JCOrd Registered Users Posts: 6 ✭
    #20
    Re: 48 Volt battery bank wiring
    n3qik wrote: »
    I would go with this:
    Greetings. After much experimentation and blown fuses, I have concluded that there is no other practical way to wire a 48 volt bank of 12V batteries than that shown by n3qik's most excellent diagram. Perhaps I should refer this to David Small, the author of the interconnection article?
    Cheers.
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #21
    Re: 48 Volt battery bank wiring

    Thanks and you can show David the drawing.
    JCOrd wrote: »
    Greetings. After much experimentation and blown fuses,

    The blown fuses statement reinforces why I had each string fused. But moving forward, please be safe. Batteries as you have found out, can be a source of some nice fireworks.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #22
    Re: 48 Volt battery bank wiring

    I am not a fan of cross trapping batteries of different strings. I prefer to keep each string as standalone.

    Crosstrapping makes it harder to detect a battery going bad. It also has a greater chance of taking out more good batteries as the bad battery starts raising the charge voltage on other batteries. You can juggle batteries around sometimes to match up series connected voltage per battery and current for each string.

    I have ten strings of four series 12v batteries (forty batteries).

    I have 100 amp shunts on negative lead on each of the strings and monitor each batteries voltage regularly. I have a common 500 amp shunt for a trimetric monitor.

    I have two parallel strings per cart (about 550 lbs per cart) with 350 amp Anderson connector for each of the five carts. Carts are on casters so it is easy to pull the Anderson connector and roll a single cart out for service.

    Each cart is 27" long, 24" high, and 15" deep so doesn't take up too much room from wall. Welded all five together, mostly from salvaged bed frame angle iron.

    Been running this config for about 15 years. The fifth cart at far right was a later add on and not matched for wire length but I don't have much voltage variance due to low current per string using 2/0 interconnects.
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