Advice needed for Wiring 12 volt System

Crystal · December 2009

For a 12 volt system that will consist of the following components, what would the calculations be to figure out wiring for a 20-25 foot run?

2- Evergreen 200 watt panels
4- T105 Trojan batteries
Rouge 30 amp MPPT charge control
IOTA battery charger 55 amp 12 volt
Samlex inverter 300 watt
TriMetric 2020 battery moniter w/ 100 amp shunt
Hydrometer Brady 10"

I believe that these components will work out for a small system, however, if anyone see's a problem, please let me know.

(Moderators BB and Neil: I decided to start new thread, since other was getting long...Sorry for any confusion.

)

niel · December 2009

Re: Advice needed for Wiring 12 volt System

no problem with the new thread as it is asking something different.

in running some calculations with a 140 degree f temp base and a 25ft run with the 22.1a rating of those 2 pvs.
#6 awg = 4.21%
#4 awg = 2.65%
#2 awg = 1.67%

as above, but a 20ft run.
#6 awg = 3.37%
#4 awg = 2.12%
#2 awg = 1.33%

i wouldn't use #6 at all, but it is there to illustrate what it would be and what you use will depend on what standard you apply as some cc manuals specify 2% max. also if you propose any expansion in the future with more pvs it would be advisable to consider placing that standard on your wiring now so that you don't have to buy the wire again and rewire it. the voltage drop calculator is available in the facts, links, and info area to do this yourself if you would like to.

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

Thanks for the quick response Niel!

i wouldn't use #6 at all, but it is there to illustrate what it would be and what you use will depend on what standard you apply as some cc manuals specify 2% max. also if you propose any expansion in the future with more pvs it would be advisable to consider placing that standard on your wiring now so that you don't have to buy the wire again and rewire it. the voltage drop calculator is available in the facts, links, and info area to do this yourself if you would like to.

I went to the wiring calculator and put some numbers in...
12 volt system
22.1 amps
26 foot wire 2% allowable voltage drop
Fixed load?
Wire insulation 105? degrees celsius

I end up with #6 wire recommended. I suppose that if we plan on adding more panels in the future #2 would be ideal?

Here is another set of questions that I never even considered would be so involved...

How much extra wire is needed to easily wire system...a little slack is probably recommended?

Is 2% voltage drop fine, or is less recommended?

I'm not sure if your load will be fixed or variable...I think probably fixed, since no AC will be ran.

What wire insulation would be best in MN? Or does this have nothing to do with the outside temperature?

Thanks Again!

niel · December 2009

Re: Advice needed for Wiring 12 volt System

first of all for every run there are 2 wires going that distance, not 1 so you must input the total length of both wires. a 26ft run is actually 52ft of wire.

if the calculations work well for whatever voltage drop percentage you pick for allowing slack then fine. less than 2% is good and the lower the percentage the better, but at a cost of thicker more expensive wire.
the wire temp is based on the temp of the wire and not ambient air temps. power going through a wire will heat that wire to one degree or another(pun intended). ideally it should be as specified by the nec for your application. what i went with at 140 degrees f is probably more typical of what one may see, but is not the max one may see as per nec rules in conduit as that is a 90 degree c rating or 194 degrees f.

dwh · December 2009

Re: Advice needed for Wiring 12 volt System

As for "slack" I generally plan 12" extra for each splice or connection, and 24" for each end. Usually works out pretty close, but you can get much closer on the estimate if you actually measure what you'll need at the ends.

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

Ok...so we should not need wire any larger than #2 welding cable, even if we want to double our watts in the future?

Should this run wire be underground or above?

How about inverter and cables...should they match the #2 run cable or can they be smaller?

How many battery cables will I need for 4 batteries?
How many inverter cables will I need?

Thanks!

dwh · December 2009

Re: Advice needed for Wiring 12 volt System

I only see a single 300w inverter listed.

300w / 12v = 25a
25a * 1.25 (NEC code) = 31.25a
Next normal size up from 31.25 is 40a

So #8 wire and a 40a fuse or breaker.

niel · December 2009

Re: Advice needed for Wiring 12 volt System

dwh,
that may depend on how far away from the batteries the inverter is as long lengths of wire with heavy amps will produce big losses, seen as voltage drops, as they have already been shown to do from the cc to the pvs. even the wire from the cc to the batteries need accounted for this way.

crystal,
*i don't think it is required to run wires underground, but if you would like to do so it is your option and you will need to follow guidelines for that set forth by the nec and wire rated for it.
*they can be smaller, but would depend on the wire run distance to the inverter and the amps flowing to determine the voltage drop. consider what dwh said for the wire as the smallest size you'll want to go with. use the fuse rating dwh specified regardless if you use larger wires. since you are using such large wire already, i would just make it all of that size unless the inverter does not accept wires that large.
*4 batteries will need to be interconnected to one another so if it's to be 4 12v batteries in parallel this would mean 6 interconnecting wires. without a doubt these wires should be large and made at least the same size as the largest wire in the system and connected the same way to keep resistances to a minimum and balanced so as to charge/discharge evenly. as i said, at a minimum, go with the largest gauge wire you are working with in the system and i usually recommend one size larger for battery interconnects, but i think you can go with the same size as from the pvs to the cc as both charging amps and load amps aren't terribly big.
*inverters usually require 2 wires to operate, 1 + and 1 -, but you may need to ground everything and that involves more wires.

GreenPowerManiac · December 2009

Re: Advice needed for Wiring 12 volt System

Think of thicker wires this way: Buying time, safety & upgradeability. Would also recommend the possibility of up sizing your inverter too. Spend the dime and install & wire once.

hillbilly · December 2009

Re: Advice needed for Wiring 12 volt System

I'll ditto what GPM just said, don't scrimp on wire size, you may save a bit of money now, but end up paying more if you have to go back and redo it later on. On the battery cables, I'd go even bigger than just one size up from the largest conductor in the system. The less resistance there is between each battery connection the better, and with the shorter wire lengths of the battery interconnects it doesn't really save all that much money to go with smaller wire here. 1/0 or 2/0 size interconnects will also be important if you end up with larger charging or discharging currents, now or later on.

If you double the PV watts, and keep them wired in parallel for a 12V nominal array then you will want larger wire than #2. For less than a 2% Vdrop, with an IMP of 44.2 and a 25' run, you would need to go with 2/0, otherwise you're going to loose a lot more watts in those wires. With your charge controller, I believe that you can wire your array to 24V and charge a 12V battery. If you can do that you will be able to get away with much smaller wires, in this case #2 would suffice for increasing your current system two fold.

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

#2 and #2/0 is different...the latter is larger?

i usually recommend one size larger for battery interconnects, but i think you can go with the same size as from the pvs to the cc as both charging amps and load amps aren't terribly big.

This would work?:
#2 welding wire for 26' run or is this supposed to be #2/0
#1/0 battery interconnects
#2/0 battery to inverter cables

1/0 or 2/0 size interconnects will also be important if you end up with larger charging or discharging currents, now or later on.

I was looking at what NAWS had and was unable to find #1/0 battery interconnects...do they just not offer this guage?

Thanks for all the information so far!

dwh · December 2009

Re: Advice needed for Wiring 12 volt System

niel wrote: »

dwh,
that may depend on how far away from the batteries the inverter is as long lengths of wire with heavy amps will produce big losses, seen as voltage drops, as they have already been shown to do from the cc to the pvs. even the wire from the cc to the batteries need accounted for this way.

Granted. But...

A) She did specify 20'-25'
and

#8 would already be more than 20% oversize for a 31.25a load.

BB. · December 2009

Re: Advice needed for Wiring 12 volt System

Here is one wire gauge chart.

As the numbers go down, the wire gets larger in diameter. Until it hits zero "0" or "ought", then 0, 2-0, 4-0 etc. continues to get thicker.

Roughly, for every 3 steps in wire gauge is a double/half change in wire diameter and current carrying capability (and a factor of 2 cost increase/decrease).

At some point, if you are going to do this stuff yourself, you will probably want to purchase a copy of the NEC (National Electric Code). It has all of the tables, wire sizes, current limits, etc...

Note that the devil is in the details with the NEC. The size of the conduit, the number of wires in the conduit, the gauge of the wires, the type/rating of insulation, etc. all makes a difference.

-Bill

niel · December 2009

Re: Advice needed for Wiring 12 volt System

dwh wrote: »

Granted. But...

A) She did specify 20'-25'
and
#8 would already be more than 20% oversize for a 31.25a load.

a> that was for the pvs to the cc and not from the batteries to the inverter.
b> if it would be for the batteries to the inverter then using #8 and a current of 31.25a at 12v for a 25ft run the vdrop would be over 1.1v and a vdrop % of 9.47%. odds are the battery voltage could dip far enough after some time of use to kick out the inverter due to low voltage. may prevent over discharging the battery though;).

crystal,
i think you can use #2 ((not #2/0 as this is a much bigger wire and is also shown as #00 and as bb shows 2-0)) pretty much throughout if you would like unless you plan on any expansions in the future. if you wish the battery interconnects to be a bit larger then you may need to go to #0 as #1 is not a common number. just what kind of distance may you be talking of for the wires to the inverter?

to both,
if you use #2 from the batteries to the inverter at the 31.25a mentioned with a 25ft run, the vdrop would be 2.36%. hopefully they won't be that far apart and there will be a lower vdrop %.

hillbilly · December 2009

Re: Advice needed for Wiring 12 volt System

Crystal,
BB really is right that if you're going to do the installation yourself you really ought to spend a bit of money on some books to make sure you understand all the code/safety issues. The NEC hand book has lot of charts and some handy examples and diagrams, however it's really not exactly self explanitory if you don't already have a bit more of a grasp on some of the basic concepts. I would also recommend the "Photovoltaics Design and Installation Manual" from Solar Energy International, which I believe our host probably carries. It's got a wealth of info on the basics, and goes a bit further than that imo. It has some voltage drop tables included which can help guide you a bit. If this were me, I would read that book at least twice before purchasing one component.
For what you are describing, a safe code compliant installation shouldn't be too terribly complex, but I still think BB is correct to direct you to check out the NEC handbook. Actually there are several versions of the NEC that you could buy, I chose the handbook mostly because it has a lot more examples and pictures to help illustrate certain issues.

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

just what kind of distance may you be talking of for the wires to the inverter?

The distance from the inverter to the batteries won't be more than 5'.

Do you need to run wire from the panels to the inverter (I was looking at a off-grid schematic and it seems like you do)? If so, I will have a 25' run as well.

Where is the best location for the inverter...is it ok to mount it on the wall above the batteries? That's what we intend to do if that will work.

If you double the PV watts, and keep them wired in parallel for a 12V nominal array then you will want larger wire than #2. For less than a 2% Vdrop, with an IMP of 44.2 and a 25' run, you would need to go with 2/0, otherwise you're going to loose a lot more watts in those wires.

We are considering adding panels in the future, so we may go with the #2/0 for the entire system. I realize that this is not necessary right now, however, I want to be prepared for the easiest expansion.
Will there be any problems with this? Or should I just stick to #2 for now for the 25' run?

Decisions...Decisions...Decisions

I'll check out those books suggested...thanks!

BB. · December 2009

Re: Advice needed for Wiring 12 volt System

Crystal,

I am not quite sure I understand your question... So I will answer it in another way.

In general, think of the battery bank as the "heart" of your system. So, connect the batteries up with the proper wiring, fuses, and disconnect (if you want one).

After the batteries are wired--they should all eventually connect to one common point. Commonly called a Bus Bar. Basically, all connects to any other devices should start at the +/- Bus Bars.

So, the Inverter DC input goes to the battery bus bar (+ fuse/breaker near bus bar connection, and you probably want a DC switch to turn off the inverter when needed). Keep as short a practicable. Mounting beside/above the battery bank should be fine. Keep battery bank covered so that tools and such cannot drop on top of the battery bank and cause a short circuit/fire. Make sure that battery fumes (little bit of acid mist) cannot splash over/mist over to your expensive wiring and electronics. A vented battery box and/or mounting a few feet from the batteries will help.

The Solar Charge Controller DC output should run to the Battery +/- Bus Bars. Again keep these cables short and protected by a fuse/battery.

As you add more devices to your battery bank (AC Charger, DC loads, etc.)--They all should come from a short pigtail to fuse/breaker then the "long run" to your loads. Remember fuses/breakers protect your wiring--so you want the "unprotected by fuse/breaker length of wire to the + bus bar" kept relatively short (for boats, they talk about 18" maximum--but that is more of a recommendation for good practices, not a requirement).

If you install a Battery Monitor. The "shunt" (power resistor) typically is connected by a heavy cable from the negative battery post to the shunt then to the common "-" bus connection (you want all battery current to go through the shunt so you can measure the total battery current from loads and charging).

-Bill

BB. · December 2009

Re: Advice needed for Wiring 12 volt System

Crystal,

By the way, a few posters here have documented their setups... Poster "2manytoyz" has documented many of his hobbies (home page).

Here is one of his Solar pages showing bus bars and wiring. Kind of gives you an idea of how things are connected.

The first time you build your own system will be a confusing and frustrating project--especially if you don't have any experienced help. After the first time you do it--you will now be the expert in your area and able to help others.

-Bill

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

BB,
Visuals are a help...the homemade bus bars are a neat idea and probably not too difficult to construct.

The first time you build your own system will be a confusing and frustrating project--especially if you don't have any experienced help. After the first time you do it--you will now be the expert in your area and able to help others.

That's a great idea! We'll just have to figure out our system first...I know my husband and I are capable. It will just take much time, effort, and believing.:-)

icarus · December 2009

Re: Advice needed for Wiring 12 volt System

Toomanytoyz buss bars are quite nice, but you can by the same thing off the shelf at a good hardware store, or wholesale electrical house, do a search for "busbar" or terminal strip.

Tony

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

you can by the same thing off the shelf at a good hardware store, or wholesale electrical house, do a search for "busbar" or terminal strip.

I looked into the manufactured busbars and they tell what guage and how many...for example the Midnight Solar says: Four 1/0 & eleven #6 useable wire slots.
Since I am not using these guages will it still work or do I have to find one that is specific to the #2/0?

Thanks Again!

hillbilly · December 2009

Re: Advice needed for Wiring 12 volt System

Crystal,
As for the sizing on bus bar slots, they typically list the maximum size that will fit. So a 1/0 slot will NOT fit 2/0 wire as 2/0 is larger than 1/0. You can typically fit wires up to a few sizes smaller, but not too much: so a 1/0 sized buss bar slot should hold #2awg just fine, but not say #10awg as the wire would be small enough to slip out the side even when tightened down.

My examples on wire sizing weren't necessarily meant as recommendations, just to show various options. Were it up to me, I would not parallel more panels than you need to (except possibly for some shading issues). There is no real advantage, and at least one distinct disadvantage of having to use much larger wire size. If you think you might add more panels in the future, run them in series and you can keep the wire size smaller. You'll also find that most components that are readily available don't support wires in the 2/0>4/0 or larger range, so you need to work that out.

As for the wiring schematics, that book I recommended will have some very helpful diagrams and examples. If you opt to use one of the midnite solar disconnects, I believe that they have some handy installation instructions as well. They do help to make the installation a bit simpler and help keep things neat and tidy.
good luck on your project

niel · December 2009

Re: Advice needed for Wiring 12 volt System

being you want to upgrade then by all means plan for it now and get the wire in place you'll need later and that way you don't have to buy it and install it again. you will have a run of wire to your cc from the pvs, but you will also have wire runs from the cc to the batteries and from your batteries to the inverter. all of these need figured for their voltage drop and need to be considered additively as a total as well for you want to have less than a 5% vdrop % from pv to load and the lower the % the better, but will be more costly. do not just arbitrarily pick any gauge until you plug in the specs for your future pv needs to see where it is you stand using that gauge.
btw, we are talking about copper wires being used in the vdrop calculator as aluminum wires have different resistivities and that would invalidate the calculations, so don't go with aluminum unless the resistances are accounted for. aluminum may need special connections too if you consider it. i favor the use of copper wires for many reasons, but i understand that aluminum can be used too.

dwh · December 2009

Re: Advice needed for Wiring 12 volt System

niel wrote: »

aluminum may need special connections too if you consider it. i favor the use of copper wires for many reasons, but i understand that aluminum can be used too.

Aluminum can be used for feeder circuits, but not branch circuits.

Solar combiner -> inverter: OKAY.
Inverter -> AC breaker panel: OKAY.
Inverter -> direct to receptacles (plugs) and/or lighting circuits: NOT OKAY.

IF the lugs are properly rated...

Lugs for connecting aluminum have to be rated CU/AL (copper/aluminum) and the ends of the aluminum wire have to be coated with a compound like NoAlox where they are connected to lugs and/or bus bars.

http://www.idealindustries.com/products/wire_installation/accessories/noalox.jsp

niel · December 2009

Re: Advice needed for Wiring 12 volt System

dwh,
you are quite right about that and i had forgotten how many homes burnt to the ground in the use of those branch circuits. i heard it was in the connections though and not the wire itself. home buyers beware if it has these aluminum wires to the outlets as this needs changed out.

dwh · December 2009

Re: Advice needed for Wiring 12 volt System

niel wrote: »

i heard it was in the connections though and not the wire itself

Yes, that's correct. Even a well twisted and wirenutted connection of aluminum wire can and will loosen up over time due to heating/cooling cycles. This creates hotspots where the wires are just barely touching and that is what starts the fires.

Fortunately, pretty much all the homes wired with aluminum branch circuit wiring were done with conduit, so it's a (relatively) simple matter to yank it all out and "re-pull the house" with copper. As I recall, there were some insurance companies that offered incentives to homeowners if they would replace the aluminum branch circuits with copper.

All wiring does heat and cool naturally, which eventually degrades the insulation, but at least copper will not loosen up and get hotspots if it's well twisted.

Aluminum is still fine for feeders - as long as it's landed in a proper lug or bus connection and properly coated against oxidation.

Also, even now aluminum is still very commonly used for bus bars. EDIT: And lugs.

icarus · December 2009

Re: Advice needed for Wiring 12 volt System

I believe (and I don't have a current code book) that you can still by AL range/drier wire, say #4 or #6. I have seen lots of problems, as dissimilar metal CU/AL react with one another, hence the anti-oxide paste. I have seen big blue wire nuts burn off completely on a range/wall oven connections.

Tony

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

I am learning something new with each thread...you guys are great!
Here we go again with more questions;)

If you opt to use one of the midnite solar disconnects, I believe that they have some handy installation instructions as well. They do help to make the installation a bit simpler and help keep things neat and tidy.

Is a disconnect box neccesary? Can I get by without one for now?

The Outback TBB-X busbar is insulated or non-insulated...what is the difference? Would I need the non-insulated?
If insulated is recommended what color do you suggest?
It has three #1/0 to #14 and eight #6 to #14, so you can fit #2 in this terminal... no problem?
Will this specific bus bar be a good size for my projected system? We won't be using wire larger than #1/0

Are lugs different than stud ring connectors?

As far as breakers go all I need is a 40 amp? Where do I put this in the wiring diagram? Are their any more breakers I should consider?

being you want to upgrade then by all means plan for it now and get the wire in place you'll need later and that way you don't have to buy it and install it again.

Right now I want to keep it as simple as possible and won't be adding panels for many years. When/if we ever do expand we'll probably just rewire with larger wire or maybe switch to 24 volt...we'll see what the future holds when it arrives.

hillbilly · December 2009

Re: Advice needed for Wiring 12 volt System

Crystal, couple of points to muddy things a bit more for ya :-)

Regarding a disconnect, you need to have some way to turn off any power source. Imagine living in a house connected to the grid with NO circuit breakers, thus no way to safely work on any of the electrical wiring or outlets. Basically the batteries and the PV array are always "ON", (ok the PV array isn't "ON" at night, but you get the idea) a disconnect will allow you to isolate all power sources from the rest of the system wiring. A disconnect can be made on your own, or you can purchase one that's pre-assembled. While they really aren't all that complex if you understand the basics well, it's probably money well spent to buy a pre made unit for your first system.
Those bus bars will work with #2 wire, the insulated vs non insulated is regarding whether or not the bus bars (which will be "live") connect electrically to the box that you're attaching them to. You are getting into some issues with grounding and such here... a much bigger topic.
As for the CB's, one big point to always remember is that they are sized specifically to the wire. Their job is to protect the wire from too much current which could cause the insulation to melt and then you could have an electrical short possibly causing fire, or energizing various components of the system accidentally. So the CB needs to trip at a lower amperage than your wire is rated for. Do you already have all your wire, or are you still in the designing phase?
Also on the potential future expansion, if you opt for a Mppt controller now that gives you the option to wire the PV array at a wide range of voltages... in other words there really isn't any big switch later on, it's just how the panels are wired together (series vs parallel).
You really, really, really ought to get that book I recommended (Solar Design and Installation by S.E.I) ... lot's more detailed information, and can help avoid some costly mistakes.

Crystal · December 2009

Re: Advice needed for Wiring 12 volt System

Do you already have all your wire, or are you still in the designing phase?

No, however, we have purchased are 2 T-105 batteries about a month ago (we will be getting 2 more along with the rest of the system). This is kind of off subject, but are the batteries we already have all right to just sit and wait to be hooked up? Or, should we hook up some sort of charger to them every so often? They are in a sealed battery box at this time.

A disconnect can be made on your own

I suppose this would have to be made out of aluminum or could you use wood?
My husband is an awsome carpenter/builder, the construction part is doable.
Then again it might just be worth the extra cost to buy the Midnite mini disconnect.

the insulated vs non insulated is regarding whether or not the bus bars (which will be "live") connect electrically to the box that you're attaching them to.

So the bus bars mount into the disconnect box?
I don't understand if the insulated or non-insulated would work best in my situation.

As far as CB's I will need three. What size between the batteries and the inverter, batteries and Charge controller, and between the panels and rest of the system?

Also on the potential future expansion, if you opt for a Mppt controller now that gives you the option to wire the PV array at a wide range of voltages

I am looking at the Rouge MPPT. However, I see the Morningstar has the new 45 amp MPPT...a little out of our budget though.

I think the Rouge will work just fine anyway.

I'm going to check with our local library and some bookstores around the area and invest in the Solar Design and Installation by S.E.I. Thanks for the recommendation!

mike95490 · December 2009

Re: Advice needed for Wiring 12 volt System

You do need to keep a charge on the batteries, They self-discharge, and in a couple months, can drain below 80%, where they will start to sulphate. I'd charge each battery individually (if you have a 6V charger, and they are 6v batteries) or if all you have is a 12v charger, use that, Some charge weekly is good.

Advice needed for Wiring 12 volt System

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