Battery connections

scheekscheek Registered Users Posts: 26 ✭✭
I'm new here and need some suggestions.

I'm about to start my battery bank design. I will have 3 banks (4 each/6v) running series for 24 volt. What is the best way to connect the banks? I need to see some connectors that will work and be safe.

In a previous test bank I used 5' aluminum rods the same size as battery post. One for positive and one for negative. I mounted the rods and ran the leads to the poles and used quick connects. Has anyone done this on a larger scale. This was just a test a few years back to see if it would work and it did. It was a fairly clean look. I was using (3) 12 volt batteries in parallel. NOW, I'm about to do my final design for my cabin and using these three banks and want it to be clean.

I've seen where some DIY have used copper pipe and smashed it and drilled holes to make connectors. Is that a solution?

Any suggestions would be appreciated. I ordered my 12 batteries today and I've got a week to come up with a design.

Oh! one other thing. Should I have a disconnect switch on each bank?

Thanks:confused:

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery connections

    Are you going to be running these 'banks' concurrently, or do you mean you are building one battery bank with three parallel strings of four 6 Volt batteries?

    You've probably seen the Smart Gauge diagrams: http://www.smartgauge.co.uk/batt_con.html

    In this case with three parallel strings method #3 is best: the common connection point or bus bar. Aluminium is not the best choice for making the connections, however. Use proper lugged wires between batteries and to the common points; solid bar connectors are a pain to work with in most cases due to their lack of flexibility.

    Ideally you would have a battery post fuse (as from Blue Sea) on each string. It isn't necessary to have disconnect switches per string unless you intend to use them individually (which has its own problems).

    If you can avoid multiple parallel strings by using higher Amp hour batteries by all means do it. That will make things much simpler. A bit about different battery configurations: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
  • scheekscheek Registered Users Posts: 26 ✭✭
    Re: Battery connections

    I will be achieving 3 individual 24v banks via 4 /6v in series for each bank Then I will run those individual banks in parallel. Did that answered your question? I was needing a way to attach the cables from each bank together.

    You recommend a fuse in each bank. I will ck out the Blue Sea. I suppose it best to put the fuse on the negative tail of each bank?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery connections
    scheek wrote: »
    I will be achieving 3 individual 24v banks via 4 /6v in series for each bank Then I will run those individual banks in parallel. Did that answered your question? I was needing a way to attach the cables from each bank together.

    In the terminology we usually use a 'bank' of batteries is all together, whether connected in serial, parallel, or both. It sounds like you will have a bank of three strings (serial connected) in parallel.

    Some people do have independent battery banks: a "main" bank and a "back up" bank. The latter is kept up for emergency use, and usually charge is enabled by the AUX function of the controller switching the secondary bank in to charge when the other reaches Float. It is kept separate from loads by a battery switch.
    You recommend a fuse in each bank. I will ck out the Blue Sea. I suppose it best to put the fuse on the negative tail of each bank?

    Normally fuses or breakers are used on positive wiring. This is a convention; it does not make a difference to function. Shunts for things like battery monitors are typically connected on the negative side.
  • mike95490mike95490 Solar Expert Posts: 8,762 ✭✭✭✭✭
    Re: Battery connections
    scheek wrote: »

    In a previous test bank I used 5' aluminum rods the same size as battery post.


    I've seen where some DIY have used copper pipe and smashed it and drilled holes to make connectors. Is that a solution?

    I would be wary of aluminun, as it's conductivity is not that great. Aluminum house wire needs to be 2 gauge sizes larger than copper, for the same loss. If you had 10 ga copper, you need 8 ga aluminum . But it is cheap. And "flows" under pressure, hence the need for electrical aluminum alloys that are tough, and you need aluminun rated fittings and anti-ox grease on it.

    I've used 1" underground rated (heavy wall) water pipe, tinned, flattened and tinned again, to make my battery lugs.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 30,511 admin
    Re: Battery connections

    Some fine testing from John about 1/2 and 3/4 copper water pipe used as bus/jumpers for battery banks:
    john p wrote: »
    IM not wanting to get into another discussion on bus bars again but just reposting the post from a long time ago and the results for FARMERJOHNAZ to see if this answers his question..
    It shows the very tiny losses you get from using cheap copper tube available from any hardware store.. you just hammer or put in vice the ends of the short lengths of tubing to flatten them then just drill a suitable sized hole each end..

    Here is the results of resistance testing and mechanical destruction testing of lugs on copper wires as used in battery interconnects and similar usage.

    A total of 10 lengths of copper water pipe was purchased from hardware and plumbing supply stores. The 2 sizes purchased had inside diameters or 1/2 "(12.5mm) and 3/4" (19mm) thickness ranged from 1.25mm to 2mm. All pipe lengths were 10ft (3050mm)

    Each size and thickness of pipe was purchased from a different supplier
    All measurements were carried out on a calibrated desk multimeter.With a accuracy of+ or - .02%

    1.1/2 pipe 1.25mm =.0012 ohms

    2.1/2 pipe 1.25mm =.0013 ohms

    3.1/2 pipe 2mm soft = .0008

    4.1/2 pipe 2mm hard = .0009

    5.3/4 pipe 1.5mm = .00065

    6.3/4 pipe 1.5mm = .00061

    7.3/4 pipe 2mm soft= .00042

    8.3/4 pipe 2mm soft = .00041

    9.3/4 pipe 2.2 hard = .00040

    10.3/4 pipe 2.1 hard = .00039

    As noted the resistance was given for 10ft lengths of pipe . If we are going to use any of those pipes as barttery interconnects etc obviously the length used would be about 8" to 10 ", so to get the resistance you would have to divide the above resistance figures by about 12.

    To give worst case example the 1/2 pipe 1.25mm at .0013 ohms per 10ft divide by 12 =.0001ohms per foot
    THe loss across that pipe used as a battery interconnect would be using 24v connected to a 100 amp load = 40ma
    Now lets see how that compares to using a #2 cable and 2 lugs cable resistance = .00052 plus 2 crimped lugs at .00046 total resistance = 99ma loss

    Any talk about wondering about losses for 1000 ft of ANY 1/2" copper pipe can clearly be shown to be a pointless exercise. and it way surpasses using #2 cable and the fact is most people would only be using #4 cable as interconnects.With far far greater losses.And as I said in a much earlier post use 3/4 " copper pipe.No matterif it has many impurities its still far far ahead of #0 cable for battery interconnects

    Tests involved to measure lug on wire resistance and mechanical strength.
    the tests involve #4 cable and closed ring closed tube copper lugs 2mm thick

    1.Lug compressed with 500lb pressure on 3 serrated teeth jaws. resistance .00023 ohm.Lug then tested for breakaway

    .seperated from cable at 223lbs pull

    2,Lug compressed with 500lb pressure on 3 serrated teeth jaws then lug heated and filled with resin cored solder.

    resistance .00015 seperated from cable ..failed as cable broke before cable seperated . test pull 325lbs

    3. lug and cable resin cored soldered only. resistance .0008 seperated from cable at 127 lbs

    As you can see solder only is not good. As a further test the joint melted when a 140a load was connected to the cable and a 12v battery to the lug. Obviously not good.

    As you can see I didnt get much work done for employer the day I did all these tests, believe it or not it took 3 of us to do the tests .my work partner to verify the results ..As to do any destructive testing a workplace safety officer has to be present.
    Hope some of this helps people understand a little more about cables lugs copper pipes..

    Here is a short thread that shows some bus bar/connector options:

    Battery Bank Cable Lengths


    And this is from poster "2manytoyz". Lots of pictures and shows his system evolving from a small experiment to something that can run a large part of his home off grid (about 1/2 down is the solar stuff):

    http://2manytoyz.com/

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery connections

    I know battery post fuses are recomended here from time to time, but, here, they arent allowed because they are considerered an ignition source. I think from memory any fuse has to be 500mm from the bank.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: Battery connections
    zoneblue wrote: »
    I know battery post fuses are recomended here from time to time, but, here, they arent allowed because they are considerered an ignition source. I think from memory any fuse has to be 500mm from the bank.

    Aren't allowed where?

    The ones from Blue Sea are sealed fuses. Per their website, they are safe from ignition, ideal for gasoline powered boats. These are the ones I'm using:

    http://www.bluesea.com/products/5187/MRBF_Terminal_Fuse_-_200A
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery connections

    NZ. If they are sealed then maybe they are alright. Dont know. Whats their interupt rating, are they hrc / tclass fuses?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery connections

    You know, the whole point of a fuse is to prevent ignition so I don't see why anyone (except idiot bureaucrats) would consider them an ignition source. Most fuses are indeed sealed so that the 'burning' occurs in an enclosed environment, often without oxygen (vacuum).

    I have seen those horrible old 'fuses' that are more like fusable links which are a bare piece of wire out in the open. They used to be quite common in Europe in both household and automotive applications. The Blue Sea units are definitely not in that class.
  • RybrenRybren Solar Expert Posts: 351 ✭✭
    Re: Battery connections

    ZB - here are the fuses. They range from 30A to 300A.
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