sizing buss bar material

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I have four 245 amp hour deka 8A8D AGM batteries that I want to parallel using electrical grade copper buss bar. the two bars will be about 3 1/2 feet long and the battery cables to the mx60 buss will be six foot each. how do I figure the bar size?
also can I top off these batteries using a garden variety 10 amp portable charger or wait until they're home south of the border and hooked up to the completed system. right now they show between 12.4 and 12.7.
48 volt 600watt PV
1100 watt exeltech inverter
mx60
above batteries
thank you thank you thank you
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: sizing buss bar material

    10amps into 1000+ah of batteries would be about a <1% charge rate and normally i'd say that would work, but the problem is that you would have to monitor the voltage closely that it does not exceed its max voltage for your agms or risk taking away from the batteries' life expectancy or possibly damaging them. if that charger does not have a regulation circuit that will stop the charging at the exact max voltage point for your batteries, then wait until you get back home, providing that won't be a month later. of course another consideration would be the battery temperature too and that charger won't account for that either. now if 1 or 2 of them are low, like 12.4v, then an hour or so at 10amps won't hurt if it does not exceed the max voltage point.
    as to the buss bar i like to say at least twice the cross sectional area as the largest size in the system as it is more vital to make the connection at one end as seeming like a connection point on the other end resistive wise. the largest wire is usually the large wire going to the batteries and the battery interconnections if they are there. when dealing with square buss bars, the cross sectional area is easy to figure as it would be the height x the width. wires also have circumferences and they are too many to list here so you may have to look that up, but the same area can be figured. keep both in the same units of measure.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: sizing buss bar material

    Any studies done on standard household copper pipe as a buss ? 3/4 inch or 1 inch, thick wall, not the indoor thinwall. Is it good enough to carry some amps, or is it alloyed so much, it's no good ?
    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 ||
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  • LBergman
    LBergman Solar Expert Posts: 42 ✭
    #4
    Re: sizing buss bar material
    mike90045 wrote: »
    Any studies done on standard household copper pipe as a buss ? 3/4 inch or 1 inch, thick wall, not the indoor thinwall. Is it good enough to carry some amps, or is it alloyed so much, it's no good ?

    I think I remember reading an article in Home Power magazine where someone had done just that. If I remember right, the person flattened the pipe in the spots where it connected to the battery terminals and drilled holes large enough for the terminals.

    I could probably do a search and give you a better reference if anyone wants (you might have to subscribe to access the article, though).
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: sizing buss bar material

    i had posed this question on the forum on copper pipe a long time ago. there wasn't any real answer because of the differing wall thicknesses and alloys used, but naws themselves gave a conservative answer of about #6. one cannot let the diameter of the pipe fool you into thinking that it is all solid copper.
    i had also suggested on the forum in the past on using copper pipe for a buss bar. it would be a light duty buss bar as cu pipe does not compare to the solid square copper busses out there in terms of resistance or capacity.
    try searching this forum to see if it's still here.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #6
    Re: sizing buss bar material

    Although back in the dark ages, it was no uncommon to see copper pipe used, it is far from the best. It is not really the correct alloy for one thing.

    But looking around, there is not a lot of sources for plain copper bus bar unless you buy it in fairly long pieces.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: sizing buss bar material

    i haven't contacted any of these companies as to lengths or quantities available, but i thought i'd post this link to some companies for any that are interested. one of those companies (hussey) is not too far from me (about an hour drive during nonpeak traffic times) and i have gone past the place years ago.
    http://www.copper.org/applications/busbar/sources.html

    dark ages? are we that old now as i remember posting about it like it was yesterday?:p:roll:
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #8
    Re: sizing buss bar material
    how do I figure the bar size?
    Mark,

    Based on the info provided, the copper buss bars will need to be able to handle the inverter’s DC input current when operating under full rated power conditions:

    (1100 W max power / 85% max power efficiency) / 10.4 V minimum operating voltage = 124.43 ADC.
    The bars should be sized to handle 125% of the load, so 124.43 ADC x 125% = 155.6 ADC

    See here for copper bar ampacity table: http://www.stormcopper.com/design/Buss-Bar-Ampacities.htm
    See here for inverter spec references: http://www.exeltech.com/xpspecs.htm

    Online sources: http://store.electrical-insulators-and-copper-ground-bars.com/
    and: http://www.solarseller.com/copper_buss_bar_block_by_deltec.htm

    A distribution/splicer block might be a cost-effective alternative. You'll just need to find the right combination of input- and output connection sizing. For example, the Gould #68132 should work nicely.


    3b01c8c30.jpg


    See: http://store.solar-electric.com/electrical.html
    and: http://www.solarseller.com/power_distribution__feed_through___splicer_blocks_.htm

    Alternately, a pair of these bars should work: http://store.solar-electric.com/shunt-bus.html

    The 10 A charger may be better than nothing for now, and it’ll probably work best charging one battery at a time. Here’s a link to East Penn (Deka and MK) instructions for charging their AGM batteries:http://www.mkbattery.com/images/AGMBatteryCharging.pdf

    Note that their battery temperature reference is 68 F (20 C), and the normal reference (i.e., the one used by the MX60) is 77 F (25 C), so you’ll have to adjust East Penn’s numbers a bit to allow for temperature compensation.

    Here’s a link to their VRLA battery technical manual: http://www.mkbattery.com/images/VRLA_TechManual.pdf

    HTH,
    Jim / crewzer
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