Discrepency with Wire Distance Charts

Hairfarm · February 2015

Greetings,

My Flexmax 80 CC NEEDS to be at least 15 feet from my 12volt battery bank. The Flexmax 80's maximum wire size is #2AWG that it can accept.

In my Outback owners manual for the Flexmax 80 there is a Wire Distance Chart. It shows that I can only go to 12 feet using #2AWG at 50amps. (see image below)

Another Calculator shows that I can go to 15 feet using #2AWG wire @ 50amps while keeping under 3% voltage drop. (see image below)

I really need to go at least 15 feet to get to my batteries. It seems I'm right on the cusp of maximum wire length for 50amps over #2AWG wire while still under an acceptable 3% voltage drop.(see image below)

My question: Does anyone think it'll be a problem if use #2AWG wire for 15 feet of length for 50 amps? again, my system 12VDC

Can anyone take a shot at giving me an educated opinion on this dilemma?

thanks,

See pics:
Attachment not found.Attachment not found.

Photowhit · February 2015

Re: Discrepency with Wire Distance Charts

Hairfarm wrote: »

Can anyone take a shot at giving me an educated opinion on this dilemma?

Don't believe it's any code problem, 2 ga should carry 50 amps with out an issue, I suspect Out back is concerned with the battery monitoring and holding a higher standard, perhaps <2%. So long as you are aware and perhaps slightly change your charging parameters, though I wouldn't when critical charging points are reach you will most likely be charging at lower amperages.

gww1 · February 2015

Re: Discrepency with Wire Distance Charts

If it really worried you you could go with larger wire and pigtail a short 2 awg from the larger wire to the fm 80. You would in effect be running the shorter distance this way. I would just run the 2 awg cause you are so so close.
gww

Hairfarm · February 2015

Re: Discrepency with Wire Distance Charts

If it really worried you you could go with larger wire and pigtail a short 2 awg from the larger wire to the fm 80. You would in effect be running the shorter distance this way. I would just run the 2 awg cause you are so so close.

This is the kind of great, outside-of-the-box thinking that keeps me coming to these forums. I never even considered that.

I suspected Outback had their own reasons for underestimating their wire sizing chart, if that's what they did. All the other calculators I tried online allowed for more distance using the same wire size, amperage and length.

Thanks for the help guys.

Photowhit · February 2015

Re: Discrepency with Wire Distance Charts

A couple things, I suspect you understand that the charge controller makes a lot of choices dependent on the voltage it 'sees' so voltage drop does have some relevance.

I wouldn't change to a smaller gauge wire, unless you have issues with the run, I'd snip a few of the strands to make it smaller at the connection. I had to, even with the max size wire in the old style connections in the Midnite classic(newer style were a piece of cake)... If you're running a breaker ahead of the CC, you could just run the smaller diameter wire from there into the CC...

inetdog · February 2015

Re: Discrepency with Wire Distance Charts

Photowhit wrote: »

A couple things, I suspect you understand that the charge controller makes a lot of choices dependent on the voltage it 'sees' so voltage drop does have some relevance.

Some of the more flexible (read expensive) CCs have two additional lead wires that optionally measure the voltage right at the battery terminals. Very handy when you cannot economically avoid some voltage drop.
But on at least one well known brand, the remote voltage sensor does not actually work properly. <sigh>

vtmaps · February 2015

Re: Discrepency with Wire Distance Charts

Photowhit wrote: »

If you're running a breaker ahead of the CC, you could just run the smaller diameter wire from there into the CC...

I hope there is no "if" about this. A breaker is mandatory, not just for safety, but it may be necessary from time to time to power down the controller.

Since there is a breaker, run #2 from the controller to the breaker. How large a wire gauge can your breaker take for the 15 ft run to the battery?

btw, is this installation being done to code? If so, the battery cables will be in conduit between the battery box and your DC electrical panel. If your batteries are not in a box or your cables are not in conduit, you might consider putting a terminal fuse on the battery (in addition to the breaker at the controller end of the 15 ft cable).

--vtMaps

Hairfarm · February 2015

Re: Discrepency with Wire Distance Charts

How large a wire gauge can your breaker take for the 15 ft run to the battery?

My 80amp breaker will handle up to #2AWG wire. Outback recommends 12ft. max run for #2 wire at 50amps to stay under 2% voltage drop. I'm going to stretch it to 15 feet and take a voltage reading to see where I am. If the V drop is too high I'll probably go the next wire size up and pigtail the #2 wire to my breaker/CC like gww1 suggested. Do you really think that three extra feet will affect the voltage drop that much?

gww1 · February 2015

Re: Discrepency with Wire Distance Charts

I don't think it will be much differrent and honestly I would probly just compensate my settings till the mesurement at the battery was getting the correct voltage. This would only be setting the cc .1 or .2 volts higher till it was correct at the battery. I could be wrong but I bet it isn't much. I have found that every item I own is not perfect with the battery and has to be compensated as close as possible and some times there is not enough compensation width to get it done. I check with my favorite multi meter at all connection points, (They don't all read the same either). I then charge and when testing at the battery I get exactly the voltage I want to the .1 volt I look at what the cc says and make my charging set points that. I check every so often to see if the charging at the set points stays the same.
I think you are ok. If I had the bigger wire laying there and didn't have to buy it, I might do diferrent but it would be good enough for me. You get to decide if it is good enough for you.
gww

vtmaps · February 2015

Re: Discrepency with Wire Distance Charts

Hairfarm wrote: »

Do you really think that three extra feet will affect the voltage drop that much?

Adding 3 ft to a 12 ft cable means you are adding 25% to its length. Therefore you are adding 25% to its resistance and to its voltage drop.

--vtMaps

gww1 · February 2015

Re: Discrepency with Wire Distance Charts

Are you running 50 amps at peak charge? Is that your max panel rating without derating. any time you are less then 50 amps your it will have less voltage drop. 5o amps at 15 feet you have a .23 volt drop. at 20 amps it will be a .1volt drop. at 5 amps it will be a .02 drop. These would all be workable to me. It would depend on what your end amp current is for your battery on how bad this affected you. at the high bulk stage you lose almost 2% at the absorb stage you lose almost nothing. The small wire will cost you about 70 watts a day if you got 5 hours of 50 amps.
You decide
gww

Ps Photowitt made this point in his very first post.

gww1 · February 2015

There are times when you will get about 65 amps. Cloud edge, really bright cold days. You average will probly be about 50 amps. I think the cc will have a convertion rate of about 94%. I don't know if this is a normal part of the 77% derating or not. I do "thankfully" atleast this time of year beat the 77% derate but I also have overcast days that produce nothing, Almost. I Don't know if the derating is an average but I know there will be many days that you beat the rate which means more losses then listed above on quite a few days, however, you are not sitting too bad.
gww

gww1 · February 2015

I don't think standard is 3% from the battery to the cc. It should be closer, but would I go looking for more wire if I had 2/0 wire on hand. I wouldn't. I would take the small loses and watch my settings. The post I did what I tought you would lose 70 watts a day, I based that on 50 amps and 5 hours of sunlight. You get 6 hours so it will be more then 70 watts lose. If you don't already have the wire and you are going to buy 4/0 for your battery to your inverter I would buy 15 more feet. Probly overkill but from the battery to the cc is important. Not so important that you have to do it though. I do like overkill if I can get it cheap enough.
gww

BB. · February 2015

For DC Battery wiring, you really need to look at how the devices function... For an DC to AC inverter, the typical (12 volt) inverter has a 10.5 volt cutoff, and we recommend not taking a battery down below ~11.5 volts during normal operation. That gives you 1 volt drop. Since an inverter typically can output 2x the rated power for short periods, you would need ~0.5 volt maximum drop a rated power so the inverter will not hit cutoff voltage when starting (for example) a well pump.

0.5 volts / 12 volts = 0.04 = 4% maximum drop (still pretty close to 3% typical recommended maximum drop)

For battery charging... I would suggest that you want to charge controller to "see" the battery voltage to a level of accuracy of 0.1 to 0.05 volts... If you have a 0.2 or higher voltage drop (12 volt battery), that is significant level of error:

14.2 volts for GEL battery charging
14.4 volts for AGM battery
14.5 to 14.8 volts for Flooded cell
0.05 volts / 12 volts = 0.004 = 0.4% voltage drop

There are a few solar charge controllers that have "remote voltage sense" wires--But not many.

Photowhit · February 2015

Hairfarm wrote: »

This system should produce roughly 52amp during peak? Will my Flexmax 80 create 52 amps from my array?

I think this question indicates you don't understand the problem, if there is one. You will deliver plenty of amperage to the charge controller, since the voltage is well above the battery voltage, the charge controller will be able to create amperage of around 50 amps charging current on average, from sunny, solar noon, sun... if needed.

The problem, if there is one, is will the charge controller(CC) be able to accurately make choices as to when to make changes in delivering amperage to your battery bank.

In the morning the sun comes up, your battery has been somewhat discharged overnight, the CC 'sees' voltage very close to correct, since very little current is passing through the connecting wire, Battery is at 12.4 volts CC 'sees' 12.4 volts. The CC sends as much amperage as it can and the battery voltage slowly rises.

Battery reaches the voltage level to switch from bulk charging to absorption, at this stage the CC holds the voltage and the battery slowly accepts less current(amps). So around 14.4 volts since it's been sending all he amperage it can the voltage the CC 'sees' IF THIS HAPPENS AT SOLAR NOON will be @97.6% of the true voltage, so it makes the switch it 'sees' 14.4 but the true battery voltage will be 14.4 x 97.6 or about 14.05. On average I would guess this normally happens before solar noon in most system, but you might consider raising this number in the Flexmax CC to maybe 14.6 This would be a little high on days when you don't reach absorption level before solar noon, but likely very close on days when you reach this before solar noon. While this will make the switch at about an actual battery voltage of about 14.24 as the battery accepts less current the voltage will rise since less current is lost in the wire.

During the absorption stage the battery slowly accepts less amperage from the Array/CC so when it switches to the Float stage the battery is only accepting a small amount of amperage so the CC should 'see' the voltage correctly. 14.4 or (14.6 volts if you have changed this point)

Will your inverter be getting it's power over the same 2 gauge wire? This is the 'normal' setup. This might be a bigger problem as a high current draw over the small gauge wire will drop the voltage to a level that might kick off your inverter. Remember a 12 volt inverter running at 900 watts will likely draw 80+ amps and the lower voltage will accentuate the problem, since the lower voltage will require a higher current draw to create the same wattage! What size inverter will you be using over this gauge wire?

gww1 · February 2015

To add one thing to Photowhitts comments, when you get to the absorb point you can check at the battery what the actual voltage is and make adjustments to your cc as required till you get it correct at your end absorb current. There is no real danger here unless maby using gell batteries which could have your begining true absorb voltage a little then your ending true absorb voltage. Gells are sensitive to overvoltage.

Whit. My inverter wires are seperate from the wires going to/from the cc but that is a good question on whether his are. Need big wires to the inverter.
gww

Hairfarm · February 2015

I think this question indicates you don't understand the problem, if there is one.

This is very true. After my system is setup and I plow through the user manuals, experiment with settings, make calls to Outback support, etc, I'll develop pattern recognition and knowledge about how the system works. Right now I don't have any hands-on knowledge. Thanks to this forum I've been able to learn a lot of theory from all of you. Thanks for taking the time to provide in depth answers too!

Will your inverter be getting it's power over the same 2 gauge wire? ... What size inverter will you be using over this gauge wire?

From inverter to batteries will be a 4/0 welding wire. This is what the inverter manufacturer recommended for my distance and voltage (12VDC) I was only concerned that my 15ft. run from my CC to my batteries over a #2AWG wire was insufficient for 52 amps peak. But I think, based on comments here and online calculators, that I should be ok(?) At least within a 2.38% voltage drop. When I get the system wired I'll post results.

thanks,

Photowhit · February 2015

Not always, but often the inverter is next to the breakers, and a single set of wires goes to the batteries. As I said this is pretty much 'normal' though some configurations don't do this. If you look at an Epanel or Outback Power panel, the CC and inverter are typically mounted close to the breaker box so multiple boxes aren't required, and for easy of checking on multiple components of the system; Here's an outback panel with inverter and charge controller mounted and sold together;

Attachment not found.

Here's my Epanel with inverter to the left, battery is in the box to the right of the 'power center;
Attachment not found.

So here's a close-up of the Epanel;
Attachment not found.
So here the arrays come in through the back at the top #1 positive runs to 2 breakers on the left, negative runs to the buss bar at black #5.

From the breaker the positive runs out to the charge controller as does the negative from the bus bar (there is a second wire under the larger wire on the shut(larger wire runs to the inverter)

From the charge controllers the positive runs back to the breakers at the #4, the negative is a common run to the negative bus bar, no additional wire needed.

From the breaker the positive runs to a positive bus bar at the white #5

From there to the large breaker for the inverter, with a single charge controller you could hook this directly to the large breaker for the inverter and skip the positive bus bar. Note the connection here is WRONG! Though hard to see, it runs to the inverter connection...

Some day when I have a larger inverter, I'll have an AC breaker at the din rail at the white #5

The medium sized wires go to the inverter, the larger wires at the bottom that go to the shunt and large breaker are from the battery bank, no additional wires are needed to the battery. The blue network looking wires are battery temperature sensor wires.

Hairfarm · February 2015

Thanks for taking the time to post about the E-panel. I looked at that product but I have a very specific space constraints I have to deal with that won't allow me to use the e-panel. Basically, I'm trying to keep all solar components inside a locked area because of vandalism and theft in my area. Since I don't live at my cabin full-time I have to consider these issues. Maybe I should just research non-lethal booby traps for these scumbags instead.;)

Photowhit · February 2015

I think every thing inside my Epanel is needed, and if I used separate boxes for each set of breakers, incoming from array, between the charge controller and battery, breaker for the inverter, it would take up a lot more space! They also make a dc breaker box, which is cheaper and pretty much all I use mine for...

I'm pretty easy on most of this, and can see not putting a breaker ahead of the charge controller when you have fuses or breakers at the combiner box near by, but if your inverter will be near your charge controller, there is no reason for the expense to run 2 sets of wires to the battery. You did post this in "NEC, Wiring and installation..." to meet NEC code you will need these breakers or fuses...

If you want to provide information people here can help, if you're looking for affirmation, I doubt anyone here is going to tell you you're fine with out enough information.

Hairfarm · February 2015

but if your inverter will be near your charge controller, there is no reason for the expense to run 2 sets of wires to the battery.

I didn't realize that a Charge controller and inverter could share the same + and - wires to and from a battery. How can a CC push amps into a battery bank while the inverter sucks amps from the battery bank, all on the same path? I assumed I needed one set of #2AWG single phase wires from my CC to the batteries and one set of 4/0 wires from my batteries to my inverter, regardless of how close they were to each other. In any case the wire has already been purchased, cut and installed with tinned lugs.

In my original post I really just wanted to know if my 15ft distance from CC to batteries using #2AWG wire at 52 peak was going to be ok. It seems, at 2.38% voltage drop, that it will be. We'll see once installed.

For the sake of providing more information: In my 12 volt system I have a combined 52amps (peak after derating) coming from my PV combiner box (from six 135W rooftop panels divided into three strings) into a 60amp breaker (Midnite) then to my CC. Then from my CC to an 80amp breaker (Midnite) then onto my batteries (675ah). Both (60 and 80amp) breaker +'s are pointed to greatest power potentials.

On the inverter side: From my 675ah of batteries (FLA) will be a 4/0 welding cable (inline + will be a 300 Amp DC Fuse Block and BlueSea 350amp DC battery shut off switch) to my 2500W Prosine 12V inverter. The pro sine inverter will be wired into an AC distribution box and out to four hard-wired AC circuits in my cabin. I have a couple of DC appliances that will be wired directly to the 12V battery bank with on/off switches and DC fuses.

I should have mentioned that an ePanel was more than I was willing to spend and I found a less costly workaround using breaker boxes (already purchased) which is why I'm committed to my current configuration. I didn't know about the ePanel when I was designing my system.

Thanks again for all the suggestions on this thread. I've researched everything to death over the last couple of years. Time to just get it installed while it's not 110 degrees outside8)

Hairfarm · February 2015

For DC Battery wiring, you really need to look at how the devices function... For an DC to AC inverter, the typical (12 volt) inverter has a 10.5 volt cutoff, and we recommend not taking a battery down below ~11.5 volts during normal operation. That gives you 1 volt drop. Since an inverter typically can output 2x the rated power for short periods, you would need ~0.5 volt maximum drop a rated power so the inverter will not hit cutoff voltage when starting (for example) a well pump.

0.5 volts / 12 volts = 0.04 = 4% maximum drop (still pretty close to 3% typical recommended maximum drop)

For battery charging... I would suggest that you want to charge controller to "see" the battery voltage to a level of accuracy of 0.1 to 0.05 volts... If you have a 0.2 or higher voltage drop (12 volt battery), that is significant level of error:

14.2 volts for GEL battery charging
14.4 volts for AGM battery
14.5 to 14.8 volts for Flooded cell
0.05 volts / 12 volts = 0.004 = 0.4% voltage drop

BB: Thanks for that info. I'm cutting and pasting it into my ever-growing cheat-sheet. I don't have internet access near my cabin so I have a large document culled from much of the info from these forums that I'll refer to if needed. A local solar guy wanted roughly 2K too install my measly 810Watt system. For that price I figured I'd just try to do it myself. These tidbits will help...

Photowhit · February 2015

Hairfarm wrote: »

I didn't realize that a Charge controller and inverter could share the same + and - wires to and from a battery. How can a CC push amps into a battery bank while the inverter sucks amps from the battery bank, all on the same path? I assumed I needed one set of #2AWG single phase wires from my CC to the batteries and one set of 4/0 wires from my batteries to my inverter, regardless of how close they were to each other. In any case the wire has already been purchased, cut and installed with tinned lugs.

Perhaps you're just pulling my leg? My systems have been setup this way for 20 years, if they should start to fail, I'll contact you first!

Just consider the 4/0 wires to be an extension of your battery terminals, only the current in excess of the incoming energy from your panels will make it to the batteries. This will be true if it has to travel done 2 gauge to the terminals and back out the 4/0. In fact you will waste less so have more energy to store.

Hairfarm wrote: »

In my original post I really just wanted to know if my 15ft distance from CC to batteries using #2AWG wire at 52 peak was going to be ok. It seems, at 2.38% voltage drop, that it will be. We'll see once installed.

And I take it you have read and understand what problems this might cause for the charge controller? If the 4/0 is there I would suggest using it!

Hairfarm wrote: »

On the inverter side: From my 675ah of batteries (FLA) will be a 4/0 welding cable (inline + will be a 300 Amp DC Fuse Block and BlueSea 350amp DC battery shut off switch) to my 2500W Prosine 12V inverter. The pro sine inverter will be wired into an AC distribution box and out to four hard-wired AC circuits in my cabin. I have a couple of DC appliances that will be wired directly to the 12V battery bank with on/off switches and DC fuses.

Have you read the instructions for the Prosine?

http://www.xantrex.com/documents/Inv...-01_Rev-A).pdf
Attachment not found.

I have no problems using less than 350MCM recommended, but if you have to worry about code... Breaker or fuse should be 350 amp but a smaller one will just protect you, no problem there! But...
Attachment not found.

If you're 15 feet away, Looks like you need the heavier cable, likely this is for voltage drop, at 12 volts a 2500 watt inverter can pull more than 200 amps easy! This is the reason we recommend going to higher voltage systems for larger inverters.

Hairfarm · February 2015

Just consider the 4/0 wires to be an extension of your battery terminals, only the current in excess of the incoming energy from your panels will make it to the batteries.

Your quote above helped me understand that setup much better. Thanks for that.

After I posted my last comment about not understanding that set-up, I went to Midnite Solar's website and researched the ePanel. I called the tech support and he explained to me basically the same thing that you did in your last post. The ePanel is setup the way you described: with the CC controller feeding into the large breaker for the battery/inverter positive and sharing the large battery cable. The thing is, my system doesn't use a "breaker" (as in the ePanel) in my battery-to-inverter 4/0 cable. Instead, my battery-to-inverter 4/0 cable uses a block 300 amp fuse with a Blue Sea battery cutoff switch in the 4/0 wire. No breaker for the CC to tie into.

My question is: Since I'm not using a breaker in my battery/inverter positive wire, at what point would I tie in the #2AWG wire from my CC to the 4/0 invert/battery cable?

I should clarify a couple of things. My 12VDC Prosine inverter is only 6 feet away from the batteries, not 15 feet. Xantrex told me to use a 4/0 cable for this run. It's my CC that is actually 15 feet away from the batteries.

Also, I apologize for stating that I had a Prosine 2.5. It's actually a 2.0 12VDC inverter. Sorry for that error.

Hairfarm · February 2015

My question is: Since I'm not using a breaker in my battery/inverter positive wire, at what point would I tie in the #2AWG wire from my CC to the 4/0 invert/battery cable?

Yes, I'm quoting myself. Just talked to a tech from NAWS. He said many people simply attach the + and - wires from the CC battery/out directly to the + - posts on the inverter. This will solve my problem with voltage drop because my inverter uses 4/0 cable. Now I don't have to run 15 feet of #2AWG all the way to the battery bank from the CC. I realize this is what Photowit has been saying all along. I just wasn't visualizing it very well. Didn't realize I could wire my system this way. The tech said that any excess power from the CC would be stored in the battery if my inverter didn't need it. If my inverter did need power it would simply use it directly from the solar panels via the CC, (only in the daytime, of course). If the inverter needed even more than the panels are producing it would take it from the battery bank.

Damn, that was an eye opening conversation.

thanks

BB. · February 2015

It does work. But watch that the charge controller works well.

Some MPPT controllers have been known to have reduced output current on noisy circuits (was a desulfator, and ac inverters have lots of 120Hz noise.

-Bill

Hairfarm · February 2015

Ok, thanks Bill. The CC is a Flexmax 80 from Outback. I don't know if it suffers from the issue you mentioned, though they seem to have a decent reputation.

BB. · February 2015

I think it did, as I recall. ... but go ahead and try. It won't break anything.

System noise is so variable, I would not pretend to predict what will happen.

-Bill

vtmaps · May 2015

Hairfarm wrote: »

Just talked to a tech from NAWS. He said many people simply attach the + and - wires from the CC battery/out directly to the + - posts on the inverter.

I hope you misunderstood what the tech said... this is dangerous. You MUST have a fuse or circuit breaker (preferably breaker) on the output of the charge controller. When controllers fault out, they often become a short circuit across the battery... you must protect against this possibility.

Even with a fuse or breaker, I think this wiring scheme is problematic. If the fuse in the 4/0 cable blows, then your charge controller is connected to the PV but not to the battery. The PV input to the controller must always be disconnected BEFORE the battery is disconnected from the controller.

The circuit breaker between the controller output and the battery should be sized larger than the maximum output of the controller... the breaker will never trip under normal circumstances. It is used as a switch to disconnect the controller, and to protect the wiring and controller from the above-mentioned fault condition.

--vtMaps

EDIT: if you respond to my post and expect me to reply, please send me a PM letting me know that you have responded. The forum software doesn't seem to have any reasonable way for me to know when my posts have been responded to.

Hairfarm · June 2015

vtmaps wrote: »

I hope you misunderstood what the tech said... this is dangerous. You MUST have a fuse or circuit breaker (preferably breaker) on the output of the charge controller. When controllers fault out, they often become a short circuit across the battery... you must protect against this possibility.

Even with a fuse or breaker, I think this wiring scheme is problematic. If the fuse in the 4/0 cable blows, then your charge controller is connected to the PV but not to the battery. The PV input to the controller must always be disconnected BEFORE the battery is disconnected from the controller.

--vtMaps

EDIT: if you respond to my post and expect me to reply, please send me a PM letting me know that you have responded. The forum software doesn't seem to have any reasonable way for me to know when my posts have been responded to.

VT, I do have a breaker (80a) between the CC and the battery. But now that you mention it I haven't been disconnecting the PV from the CC when disconnecting the CC from the batteries.

So what happens to the CC output (from the PV array) if it can't make it to the battery? Like when I have the battery DC disconnect turned to OFF?

thanks,

BB. · June 2015

It is not supposed to happen... But I would worry that for MPPT charge controller that the "high voltage" of the array could "leak through" to the lower voltage battery electronics if the battery is not there to set the bus voltage.

Similar thing could happen with PWM, but you usually cannot run "high voltage" on the Vpanel input that would damage the Vbatt side of the controller (i.e., ~22 volts Voc on the panel side and ~12-16 volt DC battery bus--22 volts should not hurt anything--Although, technically it could if they are "real close" on component voltage specifications/ratings).

If you "kill" Vpanel input first--Then nothing untold can happen on the battery side.

-Bill

Discrepency with Wire Distance Charts

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