Battery interconnects for SLA battery bank?

Discussion in 'Electronics & Electrics' started by aXis, Jul 13, 2018.

  1. aXis

    aXis Member

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    Hi all, just looking for some recommendations on how to easily and effectively wire up some batteries.

    I've managed to score about 25 x 5Ah SLA batteries from a rack mount UPS, and I'd like to hook them together in parallel for my homemade 12V UPS. Their size and shape is similar to these here, with 6.3mm F2 terminals. Based on the space I have I was going to make packs of 5 batteries deep, and then put 4 or 5 of these packs side by side. Total load across all the packs is 20A / 240W tops.

    Previously I had used 7Ah batteries, and made a frame that held normal female spade crimp connectors in a 3D printed clip. The batteries could then be dropped in vertically and slot into the spades, with a daisy chain of cable between the crimps. Photos of this setup here and here

    These new batteries wont fit the same setup, and it's not space efficient to hand them from their terminals that way. With the space I have it's best if they are sitting normal/upright, or laying down on the side.

    I was thinking that with 5 batteries standing standing normally upright, their terminals will all be in a line. I could then use a busbar (eg 10x3mm aluminium) on top of the terminals to run the full length of the pack, and I just need a reliable fixing method. Options would drill the hole in the terminal slightly larger to fit an M3 bolt, or come up with some sort of clamping system that would slip under the terminal and lift it up against the busbar.

    Any thoughts or alternatives? I'm trying to avoid female spade crimps due to the tedious construction.
     
  2. OP
    OP
    aXis

    aXis Member

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    Last edited: Jul 13, 2018
  3. xc351

    xc351 Member

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    NO idea what u mean via 6.3mm F2 terminals but google shows normal quick connects and a 2 pin connector.

    I wouldn't go bus bar as that leaves alot of area to short out. make droppers and use insulated connectors

    Hell use a small terminal strip.

    Also you do know each battery will have a drain in each battery how much beat may be worth considering as i believe being smaller there internal reistance will be higher
     
  4. CQGLHyperion

    CQGLHyperion Member

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    Always store upright. Gas needs to escape if generated.

    Suggest using fully insulated lugs that have the proper release clip so they don't just slip off. Then run that lead to a bus bar which you use a ring lug under nut and bolt.

    Ideally would be best to run each battery with a fuse / cb so you can isolate individual cells or groups of cells with relative ease.
     
  5. paulvk

    paulvk Member

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    You need a fuse on every battery , if one shorts out the others will feed it till it self destructs!
    You need all cables to be the same length to keep them in balance..
    Get a length of 10mm square aluminum bar and make two buss bars from it use heat-shrink to insulate them
    Drill the bar (or drill and tap threads) and use bolts to attach cables
    Put a circuit breaker on the buss bars as there will be a lot of energy in the batteries.
    Make the cables from the bars exactly the same length and at least 10mm2 to UPS
    I have 44 x 100Ah batteries in my 11 banks of 48v

    Note if those voltage readings in your pic are correct then that set up was not what is wanted , the voltages must be the same on every battery!
     
    Last edited: Jul 15, 2018
  6. caspian

    caspian Member

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    "oh hell no" was my reaction to those. F2 terminals are just a slightly wider spade lug, but stick with a proper terminal, you have no idea what those will do under heat and current.

    I tend to agree with paulvk re the fusing, if one battery lets go and the whole array discharges into it, you'll come home to a burned down house. to run bus bars directly onto the lugs you'd also need to bend the lugs upright to a degree, and either bolt through them back into the bar, or put a nut on the back of the terminal. you could make a squid but it would not be pretty.

    personally I'd just stick with a commercial power distribution board with fused outputs, and make a dropper to each battery. the dropper lengths are not that critical over the distances you will be running, go up a gauge in wire if need be.

    [​IMG]
     
  7. paulvk

    paulvk Member

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  8. OP
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    aXis

    aXis Member

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    I'm nearly convinced on using a fused distribution board. Unfortunately most of them only account for the positive terminals and I'd have to have a separate busbar for the common negatives, which is a little ugly.

    Caspian, where was that distro board from? The next best alternative I've found are fused distribution boards designed for CCTV installs, example here: https://www.aliexpress.com/item/Pan...Module-Board-For-AC-DC-5-32V/32812417659.html

    I have a PCB router and would happily build my own board with individual battery and common output fuses, along with some nice spring loaded terminals, but the PCB mount fuse holders are absurdly priced!
     
  9. cvidler

    cvidler Member

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    Some of you guys are over-engineering things, check inside a APC / MGE / Leibert etc. UPS, they don't isolate every individual battery.

    I've got three 3KVA APC units, they run 8 7AH batteries* in series/parallel for 48v nominal, there's one fuse for the whole battery pack.
    I've got two 1.5KVA MGE units, they run 7 7AH batteries in series for 84v nominal, one circuit breaker covers the whole battery pack.


    *one now runs 4x 25AH batteries.
     
    aXis and Idafe007 like this.
  10. OP
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    aXis

    aXis Member

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    Worst case I will have one fuse per 5 parallel batteries. Best case will be one fuse per battery and then another larger fuse per pack (eg 20A) according to the output wire gauge.

    Just got to wait for parts to arrive now :p
     
  11. paulvk

    paulvk Member

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    You only need one fuse for each battery or bank of cells/batteries in series but yours are all in parallel so you need one for each.
    The whole idea of equal size and cable lengths is to keep all batteries in balance to make them last, it takes very few millivolts to have batteries in parallel not being charged properly causing them to die early.
    There is 1.5Kw hours of power in the batteries it can do a lot of damage if driven into a bad battery!
     
  12. caspian

    caspian Member

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    aXis, that was a random pic I found off the web, sorry.

    paulvk, I've got several hundred 200 amp batteries 2 floors below me, and I assure you they don't have identical cable lengths. the difference in resistance of a few inches of copper simply is not enough to matter.
     
  13. OP
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    aXis

    aXis Member

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    In this case the batteries will be long term float charged, with current tending to only a few milliamps trickle. In that scenario any difference in cable length becomes insignificant and they should all get a good charge. Under discharge some will be hit harder than others but with a worst case average of 1 amp per battery, over a short run of 1mm^2 wiring it's not going to be too bad.

    I understand that repeated hard cycling with unequal lengths would be a different kettle of fish though.
     
  14. paulvk

    paulvk Member

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    The resistance is the important part if its significant.
    I started work in the PMG so I had a lot of training in 48v dc battery systems, copper buss bars 6 and 8 inches high 1/2 inch thick were common with battery rooms of 4 & 6 banks of 2000Ah cells.
    I now have 44 100Ah valve regulated lead acid batteries in 11 banks of 4 with 25mm2 cables 1.5meters long, each one has a current sensor so I can see current through each bank , I limit discharge to less than 5amps per bank and charge to less than 10amps. The current does vary and each bank needs to be put on a pulse charger about 3 times a year to keep them supplying or taking the same charge if not done the weakest bank will fall behind and die , then the next will slowly follow the more in parallel the greater the problem.
    I am now working on an upgrade to my system , a battery monitoring system for lead acid it uses 20amp ACS712 current sensors(already in place) with a 12 channel 12bit I2C ADC , 64k AVR , 128x64 lcd , DS1307 RTC ,DS1820 temp sensors , infra red remote (any old one handy as it learns the codes), 2 rs232 ports with command line interface and micro SD card for logging.
    It could be built using Arduino parts I would only have to change the used AVR then re-compile.
    Happy to supply details if any one wants.
     
  15. merlin13

    merlin13 Member

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    Considering the mucking about you might have to do for any balanced charging as well as the fun 'n games wiring 50 battery terminals up plus fuses yadda yadda yadda, I'd be inclined to ponder offloading all those little batteries and acquire either a single or a couple of decent-sized SLAs or AGMs for your UPS setup.
     
  16. OP
    OP
    aXis

    aXis Member

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    Replacing them with something larger would be $300+. This way will cost $50 in parts and it's not a bad hobby wiring up these battery systems. Yes the crimps are a bit tedious, I'll try to limit it to 50 and then solder the other ends on the distribution board I'll make.
     
  17. merlin13

    merlin13 Member

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    You might have missed the concept - offload ie sell those small batteries, then invest that into a bigger battery.

    But if you need to develop Hunk-like fingers and wrists... :)
     
  18. paulvk

    paulvk Member

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    Yes I know first hand it took 80 meters of 25mm2 cable to wire up my system every end crimped with a hydraulic crimp-er luckily I got the cable for scrap price.
     
  19. caspian

    caspian Member

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    but he's got the batteries, and if a large battery goes down you lose a substantial percentage of your capacity.
     
  20. Recharge

    Recharge Member

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    https://imgur.com/ek5dzZt
    https://imgur.com/fRlaaKW
    currently connected up to a 90w 12v panel through a Epsolar LS1024B
    https://imgur.com/ooJVyhj

    the crimps were pulled apart, cable fed through, crimped and then soldered and insulation slipped back over to give a nice clean looking outcome whilst being done "properly"

    that job took quite a while I can tell you heh.

    all came from a MASSIVE UPS I still have that I intend to eventually be tied into the house mains (picked up on OCAU of course heh)

    and yes, two controllers as I have two banks, the other is an older wet 8 cell setup just charging away to run some led strings in the carport. (until renos are done and I can run 12v lighting in the house and have security camera system, routers and modem in a rack where the laundry currently is)
    pics taken just now to make this post.

    really need to get around to buying some 4mm or 6mm ex solar string cable to run from the controllers to the banks, but, house renovations are further up the list.

    edit, I already had the cable, I got the crimps dirt cheap from ali express so very little cost.
     
    Last edited: Jul 23, 2018

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