Trying to finalize wiring components

elesaver · July 2014

I am in the throes of mentally finalizing a plan. The components at this time will be:

6 ea 300W Axitec panels
1 ea Midnite Solar 200 controller
8 ea Trojan 125 6V 240 Ah batteries in series (2 strings of 4 ea for 24V system)
1 ea Cotek 1500W sine inverter

This will be an off-grid system. I hope to use a heavy duty outlet into a breaker box to which the inverter will be plugged. The circuit breakers that I want to use off-grid that are currently used in the home breaker box will be moved to the second breaker box mounted near the original. No connection between grid and off-grid system will be available. Is this workable? Or should I say...safely workable?

Another of the bigger hurdles for this system is the distance between components. The best placement is for the panels to be approx. 50' from the controller; 30' from controller to batteries; 30' from batteries to inverter. These distances are based on the coolest location for the batteries and the panels to be ground mounted in a sunny location.

The panels would be wired into a combiner box with 2 panels per breaker. There would be appropriate breakers between the batteries and the controller and between the panels and the controller.

So, the main questions are two: what sized wiring is going to be needed? Would AWG#11 from the panels to the combiner box and on to the controller be correct? From the controller to the batteries? From the batteries to the inverter 2/0? And from the inverter to a heavy duty plug? This last parameter seems pretty difficult to do if 2/0 wire is required. That stuff id massive!

I always appreciate your help and no, I am not offended by criticism. Better now than later! Thanks in advance.

Alaska Man · July 2014

Re: Trying to finalize wiring components

The run between the Inverter/Charger and Batteries seems rather long. My runs are less than 3' and the wire needed for 12 Volts is about as big around as my thumb. Here is a table

http://www.solar-electric.com/wire-loss-tables.html

Try to keep loss under 2%

I'm sure the Solar Guru's will be along shortly to help. They are good like that. ;-)

Cariboocoot · July 2014

Re: Trying to finalize wiring components

Let's take it one circuit at a time.

I note you have selected a Classic 200. This is so you can run the array at higher than typical Voltage?
You need to go 50' from the array to the charge controller, yes? The panels have a Vmp of 36 and Voc of 45. If you put three in series that's 108 and 135 respectively. Current would then be about 16 Amps. Now, let's see what happens when we try that in a V-drop calculator with 10 AWG wire: I get <1% V-drop.

Maybe you should put them as three parallel strings of two in series: Vmp 72, Voc 90, Imp 25. That comes out just over 3% drop. Maybe you don't need that Classic 200; perhaps a 150 would do.

Thirty feet from controller to batteries. Controller output from 1800 Watts on a 24 Volt system about 58 Amps. Certainly enough for 480 Amp hours. Over that distance you are going to want 2 AWG. The 4 AWG that will fit in the controller's terminals is on the light side for so much power over such a length. You will probably want to transition (splice) to short run of smaller gauge to fit the controller.

Another 30 feet from batteries to controller. Oh boy. 1500 Watts on 24 Volts can be 70 Amps. There's that minimum 2 AWG wire again.

Of course larger is better. It's also more expensive. Are you sure you can't put this all together close to the panels and run the 120 VAC out 120 feet to the house?

elesaver · July 2014

Re: Trying to finalize wiring components

Cariboocoot wrote: »

Let's take it one circuit at a time.

I note you have selected a Classic 200. This is so you can run the array at higher than typical Voltage?
You need to go 50' from the array to the charge controller, yes? The panels have a Vmp of 36 and Voc of 45. If you put three in series that's 108 and 135 respectively. Current would then be about 16 Amps. Now, let's see what happens when we try that in a V-drop calculator with 10 AWG wire: I get <1% V-drop.

Maybe you should put them as three parallel strings of two in series: Vmp 72, Voc 90, Imp 25. That comes out just over 3% drop. Maybe you don't need that Classic 200; perhaps a 150 would do.

Thirty feet from controller to batteries. Controller output from 1800 Watts on a 24 Volt system about 58 Amps. Certainly enough for 480 Amp hours. Over that distance you are going to want 2 AWG. The 4 AWG that will fit in the controller's terminals is on the light side for so much power over such a length. You will probably want to transition (splice) to short run of smaller gauge to fit the controller.

Another 30 feet from batteries to controller. Oh boy. 1500 Watts on 24 Volts can be 70 Amps. There's that minimum 2 AWG wire again.

Of course larger is better. It's also more expensive. Are you sure you can't put this all together close to the panels and run the 120 VAC out 120 feet to the house?

Yes, I could put the components closer together but it makes the environment much hotter for the batteries. By hotter, it is not like it would be twice as hot but it would "probably" be 10-20 degrees hotter in the summer. I would rather have the components closer so perhaps I should forego worries about batteries and temps? Hot is hot, eh?

In addition to the heat, I was concerned about theft. There hasn't been much theft in this area but if someone thought they could get something they could sell, you know they would come! It wouldn't take too much to unhook a controller and an inverter while my downy little head was sleeping. :-) My dog is not exactly a protector...it's more that I protect him!

So, if I put the components closer, the distances would shrink to: 30' panels to controller; 6' controller to batteries; 6' batteries to inverter. Then, an extension cord from inverter to heavy duty plug at second breaker box. How much power loss would 120' to the house via an extension cord? I could go the 2/0 from the batteries to the inverter would AWG #12 from the panels to the controller be correct? From the controller to the batteries?

Thank you, Cariboot. I'm slowly getting this. Of course, a little knowledge can be a dangerous thing.

Cariboocoot · July 2014

Re: Trying to finalize wiring components

I know that kind of dog: you have a sign on the door that reads "ATTENTION BURGLARS: PLEASE RING BELL TO ALERT WATCHDOG."

Could you build a lockable shed where the panels go? This is quite a common solution; the power shed. If you can get a shovel in the ground and go down a few feet the batteries can be in a cooler, more temperature-stable environment too. Batteries do not like heat.

With the long run from array area to house at 120 VAC 10 AWG would do you. Much cheaper than the same length in 2 AWG (or larger).

What's more the run from charge controller to batteries could be reduced to 8 AWG and the run from batteries to inverter also shrinks (like 4 AWG with tiny power loss).

Long distances really mess up wiring.

elesaver · July 2014

Re: Trying to finalize wiring components

Thank you for the suggestions. I will check on making a "battery grave" to help reduce the temperature for those batteries. I could probably build some kind of locked protection for the controller and inverter but it will take some thought and planning and, for all practicality, that could come on down the road a bit, I think, at least as long as I prepare for its existence.

As far as the dog...couldn't give him up even if he doesn't do the job as I had hoped he would. :-)

westbranch · July 2014

Re: Trying to finalize wiring components

larger battery cells (2V) are a bit of a pain to move and install but also harder to pilfer... especially in tight quarters...

mike95490 · July 2014

Re: Trying to finalize wiring components

1) 6V batteries are not nearly as popular target as 12V are.

2)

I hope to use a heavy duty outlet into a breaker box to which the inverter will be plugged.

Bassackwards. Wire the inverter to 120V 20 or 30A outlet. Then you have no "exposed" prongs, and you can plug gear into it, or your mini-power panel.
20 a outlet has an extra sideways slot, 30a is one vert slot, one horz slot.

This is how I have set up my 3 generators, each with a 50A 240V stove outlet, and my charger has a 50A stove plug on it, to go to whichever generator is running that day.

Plowman · July 2014

Re: Trying to finalize wiring components

I had to set up my little solar electric system 100' from my RV, which is full shade most of the day. I run an extension cord. My system is 12V, it didn't make sense to run wire @ 12V that far.

I keep all of my components in a locked cargo trailer, on which the panels are mounted. It does get hot in there, I recently added several vents and a small 12V fan. I plan on adding a few more vents and a couple more small 12V fans this weekend. The fan I have in there is currently running 24/7, but I have a 12V timer on order. Once I get the timer I only plan on running the fans during the day.

Cariboocoot, what would you say the maximum temperature batteries, inverters, controllers, etc. should be exposed to on a regular basis? Inside of my power trailer was 90-95 degrees during a hot spell last week. This was just during the day, it went down to the 60s-70s at night. I felt the batteries while they were being charged, they actually seemed colder than ambient.

I'm assuming a temperature sensor would be a good idea?

Cariboocoot · July 2014

Re: Trying to finalize wiring components

Battery temperature is not the same as ambient (even though the ratings are given at 25C). They are generally higher. So as ambient goes up a working battery goes up too. More current (in or out) equals more temp. Battery capacity goes up with increase in temperature because the chemical action is happening faster.

But it's not good for the battery. Every 15F above 'room' temperature (just checked; they say 77F) cuts the battery life in half. This is not "92F for three seconds cuts three years off the life" but rather a sustained or cumulative equivalent. Difficult to predict or even measure. At the 90F+ temps you were seeing the battery itself was probably well over 100F. Averaged out its slicing days off every time you have one of those scorchers. It is worse if the battery is not charged correctly during that time: use of a remote temperature sensor will help considerably.

Ideally keeping the battery around mid-70F will be best for its longevity. That isn't going to happen, so just try to avoid the temperature extremes. Cold temps slow it down and add to life, but detract from capacity so they aren't helpful either (except in systems like mine that 'hibernate' over the Winter).

And yes they may feel colder than ambient because they are a huge mass; it takes a while for them to react to temperature change, especially from external influence. The outside case can cool down through overnight hours and take quite a while to warm up even though the air around it gets hot quickly. But what temp matters is that inside the battery, and we can only extrapolate that from external measurements.

Plowman · July 2014

Re: Trying to finalize wiring components

Thanks again Coot. Not much I can do to lower temps aside from add more vents and fans.

I'm actually more worried about winter, we had a good week or two last winter where temps were below freezing, include a few days they were below 10F. I was using an old 150ah AGM at the time, it did work but I doubt the cold did it any good, especially since I didn't fully charge every day. That battery is more like a 20 ah battery now, though it was well on its decline by the time it experienced the cold spell.

Trying to finalize wiring components

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