Inverter battery cables

photovoltaic
photovoltaic Solar Expert Posts: 37 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I have and Outback VFX 3524 inverter. From reading the manual and other sources I gather that for my 24v battery to inverter cables that they should be 4/0 and I think that I will use 5 foot long just to give me some flexibility with placement of batteries to the Midnite Solar mini PV disconnect with 250 amp breaker.

Here is where I would like advice.
I don't really need to worry about code but would like to use good cable. Options I have seen online ( with lugs) are :
5' MTW (Machine Tool Wire) UL listed - about $100 pair plus shipping
5' 6" SAE J1127, Type SGT. Stranded copper ( yellow cover ) about $80 pair shipped from boating place
5' 4/0 EXCELENE WELDING CABLE (UL),(ROHS COMPLIANCE) $70 shipped
5' Marine cables are made from Type III stranded, Tin plated copper SAE, ABYC, UL and Coast Guard $106 shipped

The last one listed here shows the best description of the lugs " Lugs are crimped and covered with adhesive dual-wall heat shrink ". Though all of them seem to have some sort of heat shrink on them.

I also will be getting three short 4/0 battery connector cables - any practical advice on how long these should be ? I will be getting East Penn Deka L16 flooded lead acid batteries. I guess I just need one more short piece of 4/0 cable to go from inverter to breaker.

Any reason to spend a bit more for any of these rather than the least expensive option which would be the welding cable ones ?

I bought a Harbour Freight hydraulic crimper the other day for $40 but it doesn't come with dies big enough to do 4/0 connectors.

Any advice appreciated
Thanks !
Larry
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Inverter battery cables
    photovoltaic wrote: »

    I don't really need to worry about code but would like to use good cable. Options I have seen online ( with lugs) are :
    5' MTW (Machine Tool Wire) UL listed - about $100 pair plus shipping
    5' 6" SAE J1127, Type SGT. Stranded copper ( yellow cover ) about $80 pair shipped from boating place
    5' 4/0 EXCELENE WELDING CABLE (UL),(ROHS COMPLIANCE) $70 shipped
    5' Marine cables are made from Type III stranded, Tin plated copper SAE, ABYC, UL and Coast Guard $106 shipped

    Any advice appreciated
    Thanks !
    Larry    [/COLOR]

    The marine cables, with tinned copper, would be valuable if exposed to a lot of rain and/or salt spray, otherwise no value added.
    The welding cables may not have any UV resistance, but if used inside, not a problem.
    All of the fine stranded cables have the problem that lugs designed for the corresponding size wire with coarser stranding will not fit them. Since the cables come with lugs, as long as you trust the supplier to make the connections properly, that should not be a disadvantage.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Inverter battery cables

    Why do you think you need 4/0 for a FX3524? It will only draw about 150 Amps maximum, and that can be handled by 1/0 with only a 0.6% V-drop across 5 feet.

    You might want to look at this: http://www.solar-electric.com/49050.html
    Pair of 2/0 5' cables with lug ends for $68.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Inverter battery cables
    Cariboocoot wrote: »
    Why do you think you need 4/0 for a FX3524? It will only draw about 150 Amps maximum, and that can be handled by 1/0 with only a 0.6% V-drop across 5 feet.

    You might want to look at this: http://www.solar-electric.com/49050.html
    Pair of 2/0 5' cables with lug ends for $68.

    If you read the specification by NAWS for the 2/0 cables, they recommend the following:
    Inverter Wattage Recommendations
    12 Volt Inverter: Approx. 1,450 Watts Max.
    24 Volt Inverter: Approx. 2,900 Watts Max.
    48 Volt Inverter: Approx. 5,800 Watts Max.

    That 2900 watts max comes not from the voltage drop but from the NEC-rated capacity of that gauge wire, assuming that the power will be drawn from a 21 volt source, and with an inverter efficiency factor thrown in. (3500/21=166A, with 90%efficiency 184 amps). Now for short wires (like 5 feet) the NEC current ratings are conservative, but I would not even consider 1/0 for that service.
    SMA SB 3000, old BP panels.
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #5
    Re: Inverter battery cables
    Cariboocoot wrote: »
    Why do you think you need 4/0 for a FX3524? It will only draw about 150 Amps maximum, and that can be handled by 1/0 with only a 0.6% V-drop across 5 feet.

    You might want to look at this: http://www.solar-electric.com/49050.html
    Pair of 2/0 5' cables with lug ends for $68.

    Outback manual says rated DC input current 170A DC
    They say in manual recommended wire size is 4/0
    They also say Maximum Overcurrent Ampacity 260 amps OBDC-250 DC Breaker

    So just going by what Outback says plus I already have the 250 amp breaker and can't use smaller wire on it right ? It would cost me almost as much to get a 175 amp replacement breaker as buying 4/0 cables

    I thought if I got on here and said I was going to use some 2/0 wire that I already have I would get scolded !
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Inverter battery cables
    inetdog wrote: »
    If you read the specification by NAWS for the 2/0 cables, they recommend the following:



    That 2900 watts max comes not from the voltage drop but from the NEC-rated capacity of that gauge wire, assuming that the power will be drawn from a 21 volt source, and with an inverter efficiency factor thrown in. (3500/21=166A, with 90%efficiency 184 amps). Now for short wires (like 5 feet) the NEC current ratings are conservative, but I would not even consider 1/0 for that service.

    Yeah, better just ignore me. I only use one; I wouldn't know what I'm talking about. :roll:
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Inverter battery cables
    photovoltaic wrote: »

    So just going by what Outback says plus I already have the 250 amp breaker and can't use smaller wire on it right ? It would cost me almost as much to get a 175 amp replacement breaker as buying 4/0 cables

    I thought if I got on here and said I was going to use some 2/0 wire that I already have I would get scolded !

    By NEC, the 2/0 wires are not properly protected by a 250 amp breaker. But as a practical matter the risk is more that the wires would have such high resistance that they melted before the breaker blew on a short circuit from the batteries. I don't think you are anywhere near that area with only 10' of wire total.
    The other concern would be if something other than a direct short tried to draw ~300 amps continuously through the wires, causing a problem before the breaker finally blew (if it ever did.)
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Inverter battery cables

    BTW their pre-made 4/0 wires are $98: http://www.solar-electric.com/49075.html

    Some people need to learn the difference between maximum current and continuous current. A guy named "Wiles" is one of them. :roll:
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
    Re: Inverter battery cables
    Cariboocoot wrote: »
    Yeah, better just ignore me. I only use one; I wouldn't know what I'm talking about. :roll:

    I have no doubt that you know what works. We were just discussing theory and recommendations, although the OP did say he was not overly concerned about code.
    How dare you derail our theoretical discussion with mere facts.:-)
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Inverter battery cables

    But yes it really only needs a 200 Amp breaker, not a 250. Good grief, 250 Amps @ 24 Volts is 6000 Watts. I guarantee the inverter will not put that out on surge, much less continuous.

    BTW, one thing I always tell people is to re-program the LVD to the nominal system Voltage. In this case 24. Saves a lot of trouble all-around.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
    Re: Inverter battery cables

    you won't get any scolding from me for it even if you'd have gone even bigger. as to the differences between your wires listed it would be only the quality of the connection and the insulation type and its quality and specs, for the wire is the wire and matters little if #4/0 of 12 strands, 24 strands, or 100 strands as it is still 4/0 wire.

    coot is right about going with naws on this for why pay more when you can get good cables at a good price?
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #12
    Re: Inverter battery cables

    Often these larger than expected Breakers and wire GA come form Surge capability of the Invereter. To me, larger gauge conductors are an investment, and will pay off every day of use in lower V drop, and a bit better system performance.

    AVOID SAE GA wire, it is 10 -20 % smaller in cross-section than AWG GA cables, depending upon the wire size.

    And, do not use cables that do not have Tinned lugs. This tinning of the lug has much more resistance to corrosion.

    Opinions, but good questions. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #13
    Re: Inverter battery cables

    I appreciate all the information and comments. My biggest confusion going into this was all the different ratings on wire - now I understand there are some differences in SAE and AWG . Yes I would not consider any untinned lugs since it easy to see how copper oxidizes over time.
    To that point - if I crimp my own terminals on wire is it good practice to put some sort of antioxidant on the ends , or is the physical compression on clean wire to the lug good enough ? One smaller wire I have always also soldered the connectors.

    The other investment in larger guage wire will be if the price of copper goes up !

    There does seem to be some debate on how all these things are rated for worst case compared to something closer to reality. There is safe and safer and safest.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #14
    Re: Inverter battery cables

    pv,

    If the cable has clean, bright copper, nothing needs to be done prior to crimping. If the copper is dull or dark, cut off the end until you find clean bright copper (and perhaps find a new supplier of cable).

    A good crimp is gass-tight and needs no magic elixir, which might cause a problem.

    Strive to get only good, tight crimps, such that NO solder will be required. If the solder is doing anything at all for the connection at the crimp, the crimp is BAD.

    Good crimps are exceedingly important. A good crimping tool is often expensive. If you will be doing many crimps in the future on large cables, a good crimper may be a good investment, but for most of us who are not Pro installers, a good crimper for ought guage wire is not worth the investent IMHO. Find a reliable supplier to provide cables to your specs with the rquired lugs installed.

    A Hammer Crimper for smaller cable can do a very good job for up to about #4 AWG, in my personal experience ... others have used a Harbor Freight hydraulic crimper with good results, have read, but have no personal experience with one.

    Like many things, Opinions abound. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #15
    Re: Inverter battery cables
    photovoltaic wrote: »
    I appreciate all the information and comments. My biggest confusion going into this was all the different ratings on wire - now I understand there are some differences in SAE and AWG . Yes I would not consider any untinned lugs since it easy to see how copper oxidizes over time.
    To that point - if I crimp my own terminals on wire is it good practice to put some sort of antioxidant on the ends , or is the physical compression on clean wire to the lug good enough ? One smaller wire I have always also soldered the connectors.

    The other investment in larger guage wire will be if the price of copper goes up !

    There does seem to be some debate on how all these things are rated for worst case compared to something closer to reality. There is safe and safer and safest.

    Couple of points here:
    1. Crimped lugs should not be soldered - if you have a good crimp, the solder only adds a hard "flex point" which makes it more likely to break strands if the wire is flexed.
    2. On terminals - if you have the tinned terminals, antioxidant is not a must. However, you should use the "inner wall melt" type of heat shrink to cover the crimped end of the lug and an inch or two of the wire to get a good seal.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #16
    Re: Inverter battery cables
    Windsun wrote: »
    Couple of points here:
    1. Crimped lugs should not be soldered - if you have a good crimp, the solder only adds a hard "flex point" which makes it more likely to break strands if the wire is flexed.
    2. On terminals - if you have the tinned terminals, antioxidant is not a must. However, you should use the "inner wall melt" type of heat shrink to cover the crimped end of the lug and an inch or two of the wire to get a good seal.

    And if you end up using aluminum wiring of larger gauge to reduce cost, the lugs must be rated for Al use and you must use antioxidant.
    Rather than keep on hand a number of special lug types, lots of folks use an Al to Cu rated inline splice to attach a short copper pigtail to the end of the aluminum wire.

    For copper wire to bond to copper, any copper oxide layer will be broken down by the mechanical action of the crimping process, and also has a very low breakdown voltage. Aluminum oxide forms a much harder layer which is also a better insulator.
    Once a crimp is completed using the right tool(s), you have what is called a "gas-tight" connection between the two copper surfaces, which does not allow any additional oxidization to take place between them.
    SMA SB 3000, old BP panels.
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #17
    Re: Inverter battery cables

    I finally decided to go with the 4/0 wire and went with the tinned marine wire . Sure it cost more but the more I read about wire and from comments on here it seemed to be a good investment because it should never corrode. The connectors should keep a good connection with tinned lugs and adhesive heat shrink on the ends. This is the shop I ordered from http://gregsmarinewiresupply.com/Zen/ due to their prices and they could make the different length cables with different hole sizes on the ends as I needed. I should get them this week since they made them up and shipped them right away .
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  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭
    #18
    Re: Inverter battery cables

    The OutBack will surge to 7000 watts. Do the math. You need 4/0 cable in order to start big loads. You would be surprised at how small some of those 7000 watt big loads can be. 250 amp breakers is a big as they get. 4/0 is the proper and legal size cable for a 250 amp breaker. If not inspected, you can use welding cable. It is very good. X-Flex Cobra cable is an industry standard, but any fine stranded cable will work. Fine strand is defined as multiple 30AWG wires. 2/0 has over 1000 strands. Can't remember how many 4/0 has.
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #19
    Re: Inverter battery cables

    Here is a photo of my uncompleted system with the 4/0 battery cables and inverter . I will be changing some of the internal wiring and probably adding a second charge controller , I wish I had mounted the Midnite Classic farther to the left side initially so I can install a Morningstar MPPT charge controller next to it. Today I moved it over but too cold and not enough daylight to do more. I am combining old existing system with this new stuff. Question - Do the breakers on the Midnite Solar Mini PV panel input only potect the wire inside the box ? For example if each string in combiner box has 15 amp breaker , can the PV input breaker on the Mini PV be 63 amps if the wire going from it to controller is 6 gauge ?
    Attachment not found.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #20
    Re: Inverter battery cables

    Danger! I see unfused battery cables passing into the box with no protection from the metal edges of the knockout.

    Actually, I see so many code violations that i don't know where to start. Do you want help from the forum on code safety, or do you like to live dangerously?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #21
    Re: Inverter battery cables
    vtmaps wrote: »
    Danger! I see unfused battery cables passing into the box with no protection from the metal edges of the knockout.

    Actually, I see so many code violations that i don't know where to start. Do you want help from the forum on code safety, or do you like to live dangerously?

    --vtMaps

    Yeah - stupid home improvement store had bins of all the pvc connectors EXCEPT for the 2" that I needed for that - figures eh ? This is a work in progress but I gotta tell you that of all the things I have wired up around here the edges on that hole cutting through the insulation on that 4/0 wire somehow in the near future is not way up there. A critter chewing through them would be more likely. But there is a breaker inline with that battery cable. Do you think I should have another fuse right at the battery terminal ?

    Oh and despite no code to worry about here I went with some very expensive good wire 4/0 cables instead of the cheaper welding wire ones that are probably not code rated. But sure I do appreciate your comments and will be making corrections to my system as needed. I will be building a battery box in the future - kind of easier to lay things out first and build around it for me.

    You know some people never do stuff until it is going to be perfect. I fall into the other camp and put things together and get things done. I don't think that this setup is so unsafe.
    Just so you know I am improving here is a photo of my old system - see any code violations here ?
    Attachment not found.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #22
    Re: Inverter battery cables
    photovoltaic wrote: »
    Just so you know I am improving here is a photo of my old system...

    Are what appear to be coaxial cables with type N connectors part of the PV system, or are the Amateur Radio antenna connections that just happen to be there because they also are going up to the roof?

    The first thing that catches my eye (other than neatness, which I have no right to say anything bad about) is two wires going into a terminal lug that is probably rated for only one.
    SMA SB 3000, old BP panels.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #23
    Re: Inverter battery cables

    if i were a betting man i'd put my money on them being the pl259 uhf style. funny as i'd use n connectors before i'd use the uhf style on uhf.;)
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #24
    Re: Inverter battery cables

    Blue coax is some old double shielded lan cable - goes to 80 meter dipole but is being used for FM stereo. Black coax on switch is UHF connectors not N and they go to dual band vertical on tower but only being used now for 2 meter APRS. Other colorful cables are serial cables going out to weather station, or serial cables going to Morningstar Mppt controller and then there are various Cat 5 cables going to various controllers etc . And wires going to the Trimetric Meter. Then there are wires taking 24 volts out to lights. No one mentioned my home made DC distribution block using Anderson Power Poles and each circuit separately fused along with a main fuse too.

    Yes I used compression lugs and it is so easy to just clamp various wires in there as needed. I did purchase a Harbor Freight compession tool and have ordered lugs with proper sized holes so on the NEW setup I can get rid of the compression lugs ( which actually work pretty well ) .

    But to the point that VtMaps made - now that I think about it is true there are no fuses or breakers on the cables going to the batteries on either of my setups. I never thought about that. What do people use to fuse battery cables and where do they place it ? I guess I would have to get another 250 amp breaker or fuse .
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #25
    Re: Inverter battery cables

    look here , also in the 'also liked" column on the right.
    http://www.solar-electric.com/blseabaswon3.html

    or here

    http://bluesea.com/products/5191
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,618 admin
    #26
    Re: Inverter battery cables

    Blue Sea has some very neat battery "flag" or bus bar mountable fuse holders:

    Attachment not found.Attachment not found.

    Otherwise, various Midnite Solar products with various fuse/breaker boxes are going to be the easiest (maybe cheapest) to source.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #27
    Re: Inverter battery cables

    No one mentioned my home made DC distribution block using Anderson Power Poles and each circuit separately fused along with a main fuse too.

    you will have to show me , I'm from BC

    (my eyes are getting too old I guess)
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #28
    Re: Inverter battery cables

    Here is a 250 amp fuse DC rated and looks like maybe it could bolt right on the battery terminal and then cable to the other end 250 amp fuse
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  • photovoltaic
    photovoltaic Solar Expert Posts: 37 ✭✭
    #29
    Re: Inverter battery cables

    By popular request - Now with battery cable fuse ! subtract one code violation ( yes I know only 200 amp fuse and it should theoretically be 250 amp but this is what I had in the junk box )
    Attachment not found.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #30
    Re: Inverter battery cables
    photovoltaic wrote: »
    By popular request - Now with battery cable fuse ! subtract one code violation ( yes I know only 200 amp fuse and it should theoretically be 250 amp but this is what I had in the junk box )

    Actually the code does not require a fuse in the battery box (but I think it should). Of course, the battery cables must be in conduit from the battery box to the electrical panel.

    I predict that your fuse will not last long. :cry: You have a fast acting fuse where a slow blow fuse would be appropriate.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #31
    Re: Inverter battery cables

    at the risk of deja vue i'll say it again. use what you've got as it might work fine if you watch your surge consumptions. worst case is you'll have to buy something else.
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