Battery Cables for Magnum Inverter

vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
I was reading through the Magnum's manual for their MS-AE pure sine wave inverters. It can be downloaded here:
http://www.magnumenergy.com/Literature/Manuals/Inverters/64-0017%20(MS-AE%20Series).pdf

I think I understand what I am seeing in Table 2-3 on page 18, but I would appreciate if someone would confirm that I am reading it correctly.

From page 18:
See Table 2-3 to select the minimum DC wire size (and corresponding overcurrent device) required based on your inverter model. The cable sizes listed in Table 2-3 for your inverter model are required to reduce stress on the inverter, minimize voltage drops, increase system efficiency and ensure the inverter’s ability to surge heavy loads.

Attachment not found.

I think that they are saying that the 24 volt model should have two parallel conductors of 00 AWG wire for the battery to inverter connection, protected by a 300 amp OCPD. If that is what they are saying, is that safe? I think that when parallel wires are run, the OCPD must not exceed the ampacity of either wire. Isn't 300 amps too much for a single 00 AWG wire?

tia, vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    i wondered about that a bit too for why not go for the 4/0? i do believe there is a stipulation in the nec that over a certain gauge of wire that you could parallel them, but specifics i can't recall right now.
  • BB.BB. Super Moderators, Administrators Posts: 30,637 admin
    Re: Battery Cables for Magnum Inverter

    Niel, as I remember, you are correct--for very large wire gauge the NEC allows paralleling... But it is still something I would avoid. Technically I would put a 150 amp (or whatever is appropriate for your OO setup for each wire... That way, if one failed, the other would be protected against over current.

    The problem with using 2x 2/O wiring is that cross section doubles with every 3 gauge change... So you would be looking at 5/O wire (which does not exist?).

    You can use the NEC tables which are fairly conservative (assume 3 wires in a conduit):

    http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm (note that NEC allows 15 amps rating for 14 AWG wire--But in reality it is really good for 20 or even 25 amps--For some reason I could never find out, NEC derates 14/12/10 AWG one step down???).

    You can use this American Wire Gauge chart (which is allows up to 32 amps on a 14 awg wire if in air):

    http://www.powerstream.com/Wire_Size.htm

    Or you can use Yachting standards for single exposed wire (which allows 35 amps for 14 awg):

    http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorView?langId=-1&storeId=11151&catalogId=10001&page=Marine-Wire

    If your cables are short, well supported and not bundled in conduit/sealed raceways, 2/O can be rated for ~330 amps maximum (see 3rd link above, and read the caveats).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter

    Obviously it's been a long day. Will someone explain how 4kW on 24 Volts is 222 Amps?
    I get 167 Amps, easily handled by one 2/0 wire and a 200 Amp fuse.
    If this is wrong then so is my Outback 3524.
    But I'm not going to change it. :p
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    This chart seems confusing. In the next page table 2-4 says 2/0 is for 5 ft or less Over 5 ft you use 4/0. I have 15ft 4/0 cables on my 4024AE magnum. I red and 1 black made for xantrex sw-4024. Couldn,t see why Magnum would need more than that. I use the 250 trace dc breaker and it works for me. I don,t see how you could stack cables. I had plenty of problems getting 1 set of cables on the inverter battery post. :Dsolarvic:D
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    I think I have it, from table5-1 of the manual,

    max A for max surge of 5800W for 5 sec at min V of 18.0v gives us ~ 320 A DC, 18 v = lowest cutout V

    @ 30 sec = 5200W @ 18V = 289A

    sound reasonable?
     
    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
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter
    Obviously it's been a long day. Will someone explain how 4kW on 24 Volts is 222 Amps?
    westbranch wrote:
    max A for max surge of 5800W for 5 sec at min V of 18.0v gives us ~ 320 A DC, 18 v = lowest cutout V

    Westbranch, that does explain it. Note 1 from table 2-3 (page 18 of the manual):
    Maximum Continuous Current is based on continuous power rating at the lowest input voltage.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter
    westbranch wrote: »
    I think I have it, from table5-1 of the manual,

    max A for max surge of 5800W for 5 sec at min V of 18.0v gives us ~ 320 A DC, 18 v = lowest cutout V

    @ 30 sec = 5200W @ 18V = 289A

    sound reasonable?

    Couple of problems: the chart says "continuous" power, which isn't surge, and should only apply to the 4000 Watt rating. The other thing being if you drag a 24 Volt system down to 18 Volts you are way past dead battery time.

    This does not seem a sensible way of setting up the system to me.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter
    The other thing being if you drag a 24 Volt system down to 18 Volts you are way past dead battery time.

    On many devices with low voltage disconnect, the purpose of the LVD is to protect the device, not the battery. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter
    vtmaps wrote: »
    On many devices with low voltage disconnect, the purpose of the LVD is to protect the device, not the battery. --vtMaps

    Don't start going all "Bill" on me. :p

    If they'd do it right, it protects both.
    The circuit protection is there to prevent over current, due to whatever reason.
    Anyone who has lived off batteries knows it's vitally important to not drain them too low. The LVD's on some charge controllers are designed to turn off loads if the battery Voltage goes too low. Keep in mind that it is possible for a light load to drain a battery below the LVD point with no excess current to the load involved. The idea that this function is there to protect the load doesn't bear out in the real world: it's there to protect the battery. Pity some manufacturers still set them far too low to be of use in either scenario.

    Feel free to disagree. :D
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter
    Don't start going all "Bill" on me. :p
    <snip>
    Feel free to disagree. :D

    I can see why it is done the way it is. Suppose you are drawing a light load on your Magnum inverter, perhaps just some LED lights. Some other large load comes on briefly and causes the voltage to dip momentarily below your idea of a sensible cutoff voltage. Do you want your lights to go out?

    I would prefer to see an adjustable LVD voltage on all devices. If you design your system for only light loads you would set the LVD voltage higher. If you have large loads, you set it lower so that momentary dips don't trigger the disconnect.

    Another reason for Magnum to set the cutoff so low is more flexibility with unusual systems. Not everyone powers their Magnum with lead acid batteries. Who knows what batteries or DC generators we might be using in the future. The Magnum is a large inverter. Some folks use it with a battery bank of 2 volt cells. Those folks could actually remove a cell and have the inverter function.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter
    vtmaps wrote: »
    I can see why it is done the way it is. Suppose you are drawing a light load on your Magnum inverter, perhaps just some LED lights. Some other large load comes on briefly and causes the voltage to dip momentarily below your idea of a sensible cutoff voltage. Do you want your lights to go out?

    Size it right and this does not happen. My system handles everything thrown at it without a blip, and that includes sudden motor loads over 1/3 of its total capacity right down to minimum Voltage.
    I would prefer to see an adjustable LVD voltage on all devices. If you design your system for only light loads you would set the LVD voltage higher. If you have large loads, you set it lower so that momentary dips don't trigger the disconnect.

    I totally agree. In fact many inverters and controllers do have programmable LVD, and it's a great idea. In my opinion the ridiculously low LVD set points are a hold-over from the days when inverters were used in vehicles to provide remote power and batteries were cheap: it didn't matter if you dragged a 12 Volt down to 10.5 and cut a year off its life. That is no longer the case. Some aspects of the industry need to catch up, and not just on this issue.
    Another reason for Magnum to set the cutoff so low is more flexibility with unusual systems. Not everyone powers their Magnum with lead acid batteries. Who knows what batteries or DC generators we might be using in the future. The Magnum is a large inverter. Some folks use it with a battery bank of 2 volt cells. Those folks could actually remove a cell and have the inverter function.

    --vtMaps

    When the future comes, they'll be ready eh? :p Well so far the "future" has been lead-acid for 100+ years, so why aren't we making things to suit the here-and-now? Not that anyone ever does, of course. :p

    Spreading the damage out over multiple cells doesn't negate the damage. In fact it would increase it as fewer cells would be asked to put out the full power, dragging them down further.

    In the case of the Magnum the LVD of 18 is ridiculously low. If there is a load that draws a 24 Volt system down to 18 when it comes on, then that systems is far too small to handle that load. If you were looking at a case of removing bad 2 Volt cells, you would drop three of them before running to 18 Volts. Likewise Magnum's own wire sizing recommendation shows the futility of it.

    Normally a 24 Volt system would be allowed to go no lower than 21 Volts, and that would be pretty bad. 18 Is out of the question and totally unrealistic in my opinion.

    Please Note: this post disappeared on me before it could be posted and was recovered through the auto-save function with a little help from Bill & Niel. Its content may not be exactly what I intended, but I am too lazy to check my own work today. :p
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    First. If you get the magnum you should get the ME-RC remote. The remote lets you have a large variety of settings you can program the inverter to operate at. Second point if the inverter hits the LBCO it operates at that voltage for 1 minuter to cover power surges so your lights shouldn,t go out unless you have too small of a battery bank or battery cables. Why I used 4/000 on mine. Table 3-2 has the defaukt factory settings for inverter and default is 20.0vdc for the 24 volt inverter. I bought my inverter used off a forum member who changed to 48 volt.and first sugestion he gave me was to get the ME-RC remote. Sure glad I took his advice. With the remote control you can set the LBCO whereever you want. :Dsolarvic:D
  • VicVic Solar Expert Posts: 2,999 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    Yes, neil is correct,

    Beginning with 1/0 conductors, NEC permits paralleling conductors, and in the case of two parallel conductors, the Ampacity doubles. However, when the conductors are run in conduit, each of the paralleled conductors counts as a 'current-carrying conductor' (makes sense), so in the case above of the 24 V inverter, one inverter using 2/0 cable in conduit would have four current-carrying conductors (if in conduit), would require the ampacity to be reduced to 80% of the 'three or fewer' ampacity value in tables.

    This is the way that I intrepret the data, anyway.

    Personally, I see no problem with parallel conductors that are really identical, using quality lugs of the correct size, crimped in the correct manner using the crimping tool intended for that exact cable, and so on.

    When stacking larger inverters, it is difficult to avoid parallel battery negative conductors, as the allowable ampacity of the batt conductor is an ever diminishing ampacity increase with each increase in conductor size. This has been discussed here previously -- ever larger conductors have less surface area compared to crossectional area, and are less able to dissipate heat ... if you know what am trying to say. So, one is almost forced to run parallel large neg. batt cables on larger systems.
    YMMV, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter

    Vic, I understand what you mean. That is why we need flat wires!

    (They used to make such a thing. Do they anymore?)
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter
    Vic wrote: »
    .....Beginning with 1/0 conductors, NEC permits paralleling conductors, ...

    When stacking larger inverters, it is difficult to avoid parallel battery negative conductors, as the allowable ampacity of the batt conductor is an ever diminishing ampacity increase with each increase in conductor size. ... -- ever larger conductors have surface area compared to crossectional area, and are less able to dissipate heat ... if you know what am trying to say. So, one is almost forced to run parallel large neg. batt cables.

    I shortened things up to ask if you are saying it is better to go with 2 x 1/0 vs 1 x 2/0?
    Reason I ask is I was checking prices locally and I can get 2/0 for a hair more (cents) than 1/0 and looking down the line 2/0 might be a safer way to go as there is a potential to go to a larger Inverter (1500 to 200W) OR does it only come into play when stacking Inverters?
     
    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
  • VicVic Solar Expert Posts: 2,999 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    Hi wb .. (forget your name ..),

    Well for three or fewer 90 degree C cables in conduit, 1/0 has an ampacity of 170 A, and 2/0 is 195 A (106 vs 133 kcm -- kcm = thousand Circular Mils).

    Wiki wire table:http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes

    Doubling each of the inverter cables (both + and --), would double the ampacity of each pair, but you would be at four conductors if in conduit, so would need to be reduced to 80% of that doubled value.

    Marc, yes, transformers and some larger motors have used rectangular wire, probably still. Do remember the old #6&8 transformer wire. Have Fun, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Cables for Magnum Inverter
    Vic wrote: »
    Marc, yes, transformers and some larger motors have used rectangular wire, probably still. Do remember the old #6&8 transformer wire. Have Fun, Vic

    That's where I remember it from: my internment at Emerson. :p
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery Cables for Magnum Inverter

    thanks Vic, my Appl'n would not all be in conduit as its non-NEC.

    My issue is a bit longer than normal distance Battery to inverter hence the idea of going 2/0 vs 1/0.

    Eric
     
    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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