seeking battery/inverter interconnect cable advice

System

hi, first post here.

just starting to set up a 48 volt system, (16 BP 160 panels, T80 apollo charge controller, Magnum 4448 inverter) and i've only had a small 12 volt system before. am seeking advice on battery interconnect cables, and battery to inverter cables. rumaging around on the board here i came across a reference to using solid bar for battery interconnects and wondered about doing that but have no idea about sizing etc. has anyone built their own interconnect cables? can you rent crimpers to connect the battery connector lugs to the cables?

after going all out trying to buy the best we could afford, we ran out of money for top of the line batteries and i've picked up 32 Sam's Club GC batteries to put together 4 - 48 volt batteries. but i'm really over my head in choosing cable sizes, looking for the most inexpensive but safe route to put it all together. thanks in advance for any replies.

mike95490

Re: seeking battery/inverter interconnect cable advice

So you are going to have 4 parallel strings?

Have you laid out the footprint for the batteries ?

You can connect to a common Buss Bar (of heavy copper bar stock), if you keep each connection wire, the same length, the idea is to have the same total copper resistance for each of the battery banks. That way, they all share the load equally.

here's a writeup on how important equal loading and charging is, and how to wire your battery bank [diagonal & Buss]
http://www.smartgauge.co.uk/batt_con.html

Personally, since I don't have a crimper, I would go to a battery shop and ask them for a quote to cut and connectorise all your cables. They should have a power crimper to do the cables with. You just need a good sketch with dimensions and how you want the connectors attached. The cables are expensive, and the terminals are expensive too, so there will be a fair amount of $$ involved either way.

And don't ever short your battery bank - molten wrench metal, acid, sparks, fire - a real mess.

System2

Re: seeking battery/inverter interconnect cable advice

thanks for the reply Mike.
yes, planning 4 strings. and thanks for the link. looks like good advice. my present system is like his second example. i like the idea of solid rod bus bars.
i'll look into talking with the battery shop.
really i think my main problem now is figuring out how the footprint of the battery strings should be in the only place i have available. looks like it will be tight. and i want to keep it sensible for the regular watering maintanance.

niel

Re: seeking battery/inverter interconnect cable advice

battery arrangements are an interesting aspect that isn't mentioned as much here on the forum. we have addressed the busses before, but with a 4x4 arrangement of batteries, it can take up a great deal of space and the best option imho is to go upward and use heavy homemade or commercial shelving. this can be visualized in too many ways to say what is the best way to do it knowing that the busses or heavy wiring must also be accounted for. i have always proposed going 2-3 times in size as what the largest wire in the rest of the system is besides the battery system. usually this largest wire appears to be going to an inverter from the batteries. for example if the inverter has #2 going to it you should use #0 or #00 between the batteries to keep resistances down. you can go with even larger diameter wires for battery interconnections than 2-3 times and i encourage going as large as you can get for battery interconnections. wire is somewhat more flexible to work with and bars are imobile and difficult to work with at times, but make no mistake about it that very large diameter wires can be almost as rigid as a buss.
many times it may be difficult to determine if a buss is good enough because it may be a square shape and that they may be given in a fraction of an inch by a fraction of an inch. the resistance of it per foot is what is needed to be known so that you could compare it with known wire gauges resistances per foot.

System2

Re: seeking battery/inverter interconnect cable advice

thanks for the reply niel. if one were going to use a copper rod to connect the batteries, (i'm assuming i'd cover the exposed portions with liquid latex or foam tubes or something like that) what would you use to connect the rod to the battery posts? and when i say copper rod, i'm assuming that would be like the grounding rod one drives into the ground to ground the house commercial power system.

niel

Re: seeking battery/inverter interconnect cable advice

good question. sometimes very short heavy wire jumpers are needed to go between the posts and the buss bars and sometimes the batteries can accomodate a buss bolted to it directly like some of the sunxtender batteries. when directly bolted, the batteries have to be in the right position as there is no play or room for error.
a protective coating is a good idea, but something permanent is not. i'm thinking some of the wire sleeve bundles or even heat shrink tubing could go around it and allow the connections to be open and viewable. you wouldn't want something coated on like a grease or something as that tends to travel and could play havoc with connection resistivity or fall to the batteries among other things. think in terms of what if i need to make a new connection.

mike95490

Re: seeking battery/inverter interconnect cable advice

jed turtle wrote: »

i say copper rod, i'm assuming that would be like the grounding rod one drives into the ground to ground the house commercial power system.

No no !! Those are generally steel, with a thin copper plate on them. If you were to take a piece of copper rod and try to pound it into the ground, you will get a pretzel ! You will need to get copper bar stock from some metal supplier, to make a buss bar. There will be some calculations required to determine what size will give the desired resistance (or less).

Mike

System2

Re: seeking battery/inverter interconnect cable advice

mike90045 wrote: »

No no !! Those are generally steel, with a thin copper plate on them. If you were to take a piece of copper rod and try to pound it into the ground, you will get a pretzel ! You will need to get copper bar stock from some metal supplier, to make a buss bar. There will be some calculations required to determine what size will give the desired resistance (or less).

Mike

oooh, good catch! i'm a hopeless "special needs" type when it comes to understanding electricity, so could anyone offer a suggestion on the diameter of such a copper buss rod? i'm thinking neil's suggestion to connecting to the battery posts with just short heavy wires (2/0 AWG?) to each post would be workable. would multi-strand aluminum wire twice the diameter be acceptable?

niel

Re: seeking battery/inverter interconnect cable advice

if it has a diameter then you will have a clue as to how it can compare with wire of specific gauge #s. when it's squared you need to convert it to know it's equivalent diameter. be sure that the short wire interconnects are the same length and i advise against using the aluminum wire as this presents metal mixing problems. it could be done, although you'd have to take steps to prevent the galvanic reactions from corroding the metals while maintaining high conductivity. aluminum will also need to be an even larger diameter than the copper because it has a higher base resistance than copper.

here's a link to the wire tables and some of the specs.
http://en.wikipedia.org/wiki/American_wire_gauge

System2

Re: seeking battery/inverter interconnect cable advice

niel wrote: »

if it has a diameter then you will have a clue as to how it can compare with wire of specific gauge #s. when it's squared you need to convert it to know it's equivalent diameter. be sure that the short wire interconnects are the same length and i advise against using the aluminum wire as this presents metal mixing problems. it could be done, although you'd have to take steps to prevent the galvanic reactions from corroding the metals while maintaining high conductivity. aluminum will also need to be an even larger diameter than the copper because it has a higher base resistance than copper.

here's a link to the wire tables and some of the specs.
http://en.wikipedia.org/wiki/American_wire_gauge

i forgot about galvanic action. thanks for reminding me.
would these water pipe ground clamps suffice for connecting copper wire to copper rod? : http://www.harger.com/products/grdcmp/mech/wpgc/wpgc.cfm

another question. i'm planning on wiring my 24 volt panels as 48 volts (16 165 watt panels making 8- 48 volt panels. i'm planning on running the power through 3 AWG multi-strand copper wires about 100' to the charge controller. do you see any problem with this?

BB.

Re: seeking battery/inverter interconnect cable advice

I would also avoid aluminum around battery terminals... Aluminum may corrode much faster than copper...

-Bill

niel

Re: seeking battery/inverter interconnect cable advice

those are usually made of brass, but should work ok for some connections so yes.

as to the 100ft to the controller i assume it to be 200ft of wire because of there being a + wire and a - wire each going 100ft. this would be the home run for all 8 pv strings of 2 165w bps in series. current is at 4.7a per string for a total current of 37.6a and shows the voltage drop percentage to be nearly 3.6%. this is somewhat high on the percentage as i never recommend over 3% from the cc to the batteries and outback likes to specify 2%. now with #2 this would be a bit over 2.8% voltage drop. to utilize the #3 and keep at 3% the run would be 84ft with 168ft of wire so shortening it proves to be futile and you still add the cc to battery drop to that making it much higher than 3%. #0 for a 100ft run will give just over 1.75% voltage drop. sometimes combos of wire can be used like your #3 on the + downlead and say a #2 on the negative downlead giving a % of 3.2% and likewise a #3 with a #0 will give about 2.67% voltage drop.

don't forget that the voltage drop from the controller to the batteries will have to be added to the figure for the pvs to the cc for the total drop. if the length of wire was meant to be half of what i assumed then the voltage drops can be halved as well.

sawmill

Re: seeking battery/inverter interconnect cable advice

This site might be helpful for your set-up.

http://store.electrical-insulators-and-copper-ground-bars.com/

System2

Re: seeking battery/inverter interconnect cable advice

niel wrote: »

those are usually made of brass, but should work ok for some connections so yes.

as to the 100ft to the controller i assume it to be 200ft of wire because of there being a + wire and a - wire each going 100ft. this would be the home run for all 8 pv strings of 2 165w bps in series. current is at 4.7a per string for a total current of 37.6a and shows the voltage drop percentage to be nearly 3.6%. this is somewhat high on the percentage as i never recommend over 3% from the cc to the batteries and outback likes to specify 2%. now with #2 this would be a bit over 2.8% voltage drop. to utilize the #3 and keep at 3% the run would be 84ft with 168ft of wire so shortening it proves to be futile and you still add the cc to battery drop to that making it much higher than 3%. #0 for a 100ft run will give just over 1.75% voltage drop. sometimes combos of wire can be used like your #3 on the + downlead and say a #2 on the negative downlead giving a % of 3.2% and likewise a #3 with a #0 will give about 2.67% voltage drop.

don't forget that the voltage drop from the controller to the batteries will have to be added to the figure for the pvs to the cc for the total drop. if the length of wire was meant to be half of what i assumed then the voltage drops can be halved as well.

ouch. already buried the 3AWG wires.

i had a friend who installed my current 12V system look through the Apollo T-80 book and he noticed that it can handle over 100 volts (i don't recall what the number was exactly) and then drop the voltage automatically to the 48 volts for the batteries. so if i connected the array panels as 96 volt strings, would that work, or should i start digging the foundation of a new battery house to put everything much closer to the array?

ETA: just noticed your post, sawmill. that site looks very interesting. thanks!

BB.

Re: seeking battery/inverter interconnect cable advice

Yes, running a higher voltage at your solar panels will greatly help in reducing current and voltage drop on your long run...

I would confirm with an email/call to Apollo--their website (which says 140 VDC max):

Wire the PV modules in series up to 72 VDC nominal (140 Voc max)

and spec. sheet don't completely agree... But assuming their spec. sheet is correct, then wiring your panels to a higher voltage that falls within in Apollo's (very) wide input range of:

Input voltage range ……………… 16 to 160 VDC operating 200VDC Maximum Open Circuit Voltage

(remembering that this panel Vmp must be a few volts above the maximum battery bank+voltage drop voltage) will work very nicely for you if wired for Vmp=96+ volts. (if your Vmp was doubled, then the current cut by 1/2 and % voltage drop will be cut to 1/4). Make sure the Vmp and Voc when the panels are cold (minimum bright morning temperature for your area) is less than the controller's maximum voltages (it is OK to exceed Vmp of 160v when cold--there will be no damage--just no power generated until the panels warm up--don't exceed the Voc rating ever).

-Bill

mike95490

Re: seeking battery/inverter interconnect cable advice

Also, a small saving grace with long PV wire runs, is as the batteries come out of bulk, the current drops, and the voltage loss, becomes less. But the run from Controller to Batteries needs to have ample copper, otherwise resistance gives false voltage readings, and poor charge control.

niel

Re: seeking battery/inverter interconnect cable advice

having a 4x4 pv arrangement would work if the specs are true on the controller. the controller will lose a bit of efficiency going that high, but you will gain by a lowered voltage drop and vd %. it should be <.9% vd on that 100ft run with the #3 with pv voltages at 96v. when the voltage got doubled you also had the current halved making the vd % 1/4 of the original 3.6% before. win win.

System2

Re: seeking battery/inverter interconnect cable advice

thankyou all for your most helpful replies. this has been a very encouraging experience and i hope i will have a successful story to relate when this all comes together. the next phase is getting concrete piers in the ground before it freezes, to build the solar array structure on top of.

niel

Re: seeking battery/inverter interconnect cable advice

yw and i don't think you'll have too much to worry about being in florida with the concrete. even if the air gets to 32 degrees the ground is much warmer and the concrete even warmer yet, though not by much after a few days, due to chemical reactions taking place in it as it cures. if in doubt, put plastic over it keeping the moisture in as well as some of the heat in that would've escaped through that evaporation.

System2

Re: seeking battery/inverter interconnect cable advice

niel wrote: »

yw and i don't think you'll have too much to worry about being in florida with the concrete. even if the air gets to 32 degrees the ground is much warmer and the concrete even warmer yet, though not by much after a few days, due to chemical reactions taking place in it as it cures. if in doubt, put plastic over it keeping the moisture in as well as some of the heat in that would've escaped through that evaporation.

i don't know how i might have led you to think i'm in sunny florida.
this here is Maine, and although we had a late frost this year, there's already been a coating of snow in the mountains and a skim of ice briefly on the puddles the other morning. now's the time to start moving about like my "hair's on fire" cause it is soo much harder to have to move snow around in order to reach bare earth. anyways, i'm using pre-cast reinforced 4' concrete piers and a power auger to drill the holes. planning on building an A-frame type structure (sort of like a child's swing set) out of pressure treated lumber bolted to the concrete piers) and setting the panels in a frame so they will pivot on a horizontal steel pipe at the top of the A-frame to change vertical angle with the seasons. the top of the panels' frame will be about 5' taller than the A-frame support, and the bottom of the frame will be about 7' or so about the ground so that there will be plenty of room for snow to slide off and build up without covering the panels.

niel

Re: seeking battery/inverter interconnect cable advice

yes, do hurry with your concrete work as this was my mistake. i'm not totally to blame in my mistake as my ip locator and even another both showed you to be in boca raton, fla.
http://www.ip2location.com/demo.aspx
http://www.melissadata.com/Lookups/iplocation.asp

this one has you in maine.
http://www.maxmind.com/app/locate_ip

System2

Re: seeking battery/inverter interconnect cable advice

niel wrote: »

yes, do hurry with your concrete work as this was my mistake. i'm not totally to blame in my mistake as my ip locator and even another both showed you to be in boca raton, fla.
http://www.ip2location.com/demo.aspx
http://www.melissadata.com/Lookups/iplocation.asp

this one has you in maine.
http://www.maxmind.com/app/locate_ip

aaack! people can find where you are? good grief, i am soooo naive!

and now paranoid. oh well. another reason to keep working on my opus:
"how to camoflauge solar panels".
best i've come up with so far is to install them upside down under a shed roof and use a tiltable mylar mirror to reflect sunlight up onto them from beneath.

niel

Re: seeking battery/inverter interconnect cable advice

i wouldn't bother with a reflector as you would need to constantly readjust it to stay on the pvs as the sun goes across the sky. pvs aren't meant to be camoflauged.

System2

Re: seeking battery/inverter interconnect cable advice

niel wrote: »

i wouldn't bother with a reflector as you would need to constantly readjust it to stay on the pvs as the sun goes across the sky. pvs aren't meant to be camoflauged.

yep, constantly re-adjusted is a given.
not meant to be camoflauged for sure ...[political statements removed]...

it simply makes good sense to be inconspicuous ...[political statements removed]...

[please note--this board is not for political discussions per the request of our host. -Bill B.]