long 12 volt outlet runs?

Hello, I have a solar system that consists of two solar panels when combined are rated at 265 Watts/15.26 Amps. These two PV panels are connected directly to a solar charge controller, the solar charge controller is connected to a bank of batteries, four 6-volt deep-cycle batteries to be exact. I am not an expert, I am trying to find a way to run wires from the battery bank (stored in my truck's bed) to the inside of my travel trailer. The problem is that the distance between the batteries and the place in which I want to install 12 volt outlets (to power low volt/amp devices) is at least 30 feet away. So I am trying to overcome voltage drop but I have no clue what gauge of wire I should be using. I am not even sure you can run a 12 volt connection these distances. All I really want to do is make a direct connection with the battery bank and feed a few 12 volt outlets to recharge two 17" notebook computers and a cradlepoint wireless router. For instance, my notebook power needs are 18.5 volts at 3.5 amps. Can I run wire these distances and still power my equipment? Would I have to use a ridiculously small wire gauge like 2awg? Or is it even possible? Unfortunately I cannot relocate the batteries closer to the outlets as there is no place to store the batteries in the trailer. Any help is greatly appreciated.

You need a dc-dc converter to recharge your laptop from the batteries. I assume you have a 12V system - hence 2 parallel strings of 2 series 6V batteries. (See elsewhere about paralleling batteries...) Is seems your panels have peak output at 17V - ie, 265W/15.26A, but their output can be above or below 17V. The battery requires up to 14.4V to charge, or maybe 15V for occasional equalisation. You want the cable resistance as low as practicable. You want the regulator near the batteries and outlet - not the panels. Let's assume a max voltage drop of 1V @ 15A. From V=IR, R = V/I = 1V/15A = 0.0666R (R=Ohms). Over 60' (2 cables), that's 0.0666R/60' = 0.00111 = 0.001 Ohms per foot, or 1 Ohm per 1,000 foot (or feet for laypeople). From www.powerstream.com/Wire_Size.htm we see that 10 Gauge AWG and larger (ie, 8G, 2G etc) is lower than 1 Ohm per 1,000', hence 10G could be ok, and it is rated for 15A in this situation. Using 0G will reduce the voltage drop to 0.1V (it has 1/10th the resistance). I'd probably use 8G or larger between the panels and the regulator. Again, regulator should be mounted almost on the battery. Loads are take off the battery.

Hi oldspark, thank for the reply. By "regulator" do you mean the solar charge controller? If so, you suggest I put it nearer the battery bank rather than nearer the solar panels? The installation manual for my charge controller states to never put the charge controller near the battery bank? Not sure what I should do now. Also, I am confused. Why can't I just run cable directly from my 12-volt battery bank into a fused 12-volt outlet and then plug in a car or cigarette style adapter into the 12-volt outlet and charge my laptop's battery that way? Thank you for all the help.

To rule out any confusion regarding charging your laptop, could you refer to the 12v car charger specifications instead? You already have the DC-DC adapter in this case.

By regulator I meant the charge controller. And I assumed it is regulated to charge batteries. (Rarely are they regulated for a fixed 12.0V output.) Irrespective, I can't understand why anyone would suggest to put it closer to the panels than the target. You want minimal voltage drop between the regulator/controller/charger and the load or battery. Why have a controller regulating to 13.8V-14.4V (or 12V) if there is then a big voltage drop to the battery or load. Alternatively, the controller usually reduces voltage for the battery/load. So what if the panel to controller cable does some of that reduction? And if it's an MPPT, then the MPPT to battery is usually a higher current than the panel output. IE - thicker else shorter cable is required from the MPPT controller to the battery than from the panels to the MPPT. I'm curious as to who or what installation manual says "never put the charge controller near the battery bank". I suspect that is a misinterpretation with avoiding acid and fumes etc. That is very different to keeping it electrically close to the battery!    By dc-dc converter, I merely meant that 12V-15V etc will not charge an 18.5V laptop. Running the panels straight to the laptop will work when the panels exceed (say) 18.5V (noting that they can well exceed 20V), but that misses out on their higher current output below 18.5V, and max power output at ~17V. Plus it requires enough sunshine (or UV through the clouds). Let me know if the above doesn't make sense. (Then maybe reinterpret your Installation Manual or advise them of the correction - unless I somehow figure out why I am wrong. Any suggestions for the latter anyone?) FYI - The MPPT is a Maximum Power Point Tracker. It endeavours to keep the panel output at its maximum power (ie, probably 17V @ 15.26A in your case) and using a dc-dc converter to provide whatever output. Example: Assume 90% MPPT efficiency. 17V x 15.26A = 259W. 259W x 90% = 233W. 233W/14.4V = 16.2A. That's nearly 1A more than if a traditional "linear" (voltage dropping) regulator were used. At 12V it's 233/12 = 19.4A. As a bonus, the MPPT might still charge a battery even if the panel output is below 13V. EG - if the panels output 10V at 4A = 10V x 4A = 40W x 80% = 32W (assuming worse efficiency away from its nominal input), then 32W/14.4V = 2.2A charge current at 14.4V which is better than zero current at 10V.

I'm busy today, I will try to give you guys a response as soon as I can. I've read what you said, I will get back to you soon. Thanks oldspark and awdeclipse.

Sorry about the delay in getting back to you. I was busy installing a tow package on my truck. Now, yes I have an MPPT CC, it's a Blue Sky Solar Boost 1524iX. Here's the datasheet: http://www.blueskyenergyinc.com/uploads/pdf/BSE_SB1524iX_datasheet.pdf And here is the manual: http://www.blueskyenergyinc.com/uploads/pdf/Manual_BSE_SB1524iX.pdf I have four Interstate GC2-XHD 6-volt golf cart batteries wired in Series/Parallel for a total of 464 Amp Hours capacity at 12 volts. The solar panel array consists of two Kyocera KD135GX 135 Watt 12 Volt panels. The power adapter for both of my notebooks reads 18.5 Volts/3.5 Amps/65 Watts. My biggest confusion is coming from the fact that I don't understand why the solar panels can't charge my battery bank and I can simply run large enough gauge wire directly from the battery bank to a 12 volt outlet? Seems simple, what am I missing?

oldspark wrote: I'm curious as to who or what installation manual says "never put the charge controller near the battery bank". I suspect that is a misinterpretation with avoiding acid and fumes etc. That is very different to keeping it electrically close to the battery!

You are right oldspark, it was just my overly cautious, albeit incorrect interpretation of the Blue Sky SB1524iX's manual. Here's what the manual actually says: "4. CHARGER LOCATION & INSTALLATION b) This unit employs components that tend to produce arcs or sparks. NEVER install in battery compartment or in the presence of explosive gases" My mistake ;D

Thanks for the correction. No apologies required - except that now everyone on the web will say to keep the controller near the panels. NOTHING will stop that from spreading and gaining cult status. And it is all YOUR fault! (LOL! As I oft say, there are reasons for many things, but people recite the rule without understanding the impact. IMO Car Audio forums are a classic for that followed closely by Australian 4WD and similar forums. Their justifications for heated batteries or capacitors or battery-charging dc-dc converters are often so cute, yet so very very sad.) The battery spark is a universal concern. Hence why the last connection should be NOT be at the (stressed) battery terminals when jumping or connecting chargers, and care should be taken at other times. You can run the 12V outlets from the battery. That is how it should be done. (It's the smoothest & cleanest supply etc. It sees the normal battery voltage range - ie, maybe up to 16V but should be no more than ~14.4V longterm; and ~12.6V and lower when not being charged.) The point is panels should never go direct to the battery (except perhaps a small panel whose max current output does NOT exceed the batteries float current - typically 1A for medium automotive batteries). Nor should load be connected to the panels. Your panel is a "12V panel" yet puts out peak power at 17V, and can probably go as high as 24V. 17V & 24V etc on a 12V systems is usually not recommended - except for heating, smoking, and economic recovery purposes. (IE - buy new 12V devices!) Hence the panel MUST go through a controller to limit the voltage. (FYI - each panel should have its own blocking diode to prevent batteries or other panels discharging in to it. Usually low voltage drop diodes are used - eg, Schottky or Germanium.) In summary: - panel(s) via diode(s) to controller input(s). - controller output to batteries and 12V loads. My writings above must have been ambiguous or bad. My apologies. (You need not apologise for the "not near battery" thing. It is so easy miss the context of such statements. Besides, that issue is now clarified and remembered forever - no sparking devices or acid/corrosion sensitive devices near the battery (ie, not on top of the battery etc). FYI - Some controllers have an output for the battery and a regulated 12V for 12V loads - though a 12V automobile load really means typically 12.5V to 14.5V and might operate between 8V & 16V or at least not be damaged within that range. (8-16V is an oldskool design range. Many things - like ignitions, starter motors, 12V PSU supplies may now operate down to 6V or 5V etc.)

oldspark, thanks for all your help. I will be putting my 4 Interstate 6-volt batteries in a sealed box and vent them to outdoor air. I'll mount the solar charge controller just a few feet away, maybe 5 feet? That way there is very little voltage dropped and I make the system as efficient as possible. To be honest, I am absolutely horrible at math, and I mean horrible! There really is no excuse for it though I make excuses why as I don't not remedy it by learning math. I just find the whole prospect unappealing. I pay for it everyday though, as this thread can testify. So can you help me figure out what gauge wire I should be using? I can give you a general idea to the length of the connections and loads being ran. Firstly, solar panels will be about 15 to 20 feet away from the controller. The controller will be moved much closer to the battery bank, about 5 feet away. Now here is my biggest question. Do I need to run both a positive and negative lead from the battery to the 12 volt outlet? Or can I just run a positive lead from the battery to the 12 volt outlet and ground the 12 volt outlet to the trailer chassis? I;m thinking you must run both POS and NEG from the battery to complete a full circuit correct? Next problem, what size AWG wire to use for the run from the battery to the 12 volt outlet? The 12 volt outlet is to be quite far away 30 to 40 feet away. I'm unsure what 40 feet is in meters, you'll have to do the calculations ;) I was wondering if I could use large gauge wire like 2AWG or 4AWG wire and run it most of the way and then terminate it to some terminal block or combiner of sorts that would allow me to use much smaller gauge wire which would then be connected to the 12 volt outlet via terminal quick disconnects. I would fuse the positive lead at the 12 volt end for 20 Amps max and fuse the battery positive lead at 2O Amps also? I'm not so electrically "inclined" as you might have guessed. Also I was throwing around the idea of using Anderson SB Quick tpe disconnects for the connection between the solar charger and the battery bank so that battery maintenance might be more easily accomplished. I've never used them before, so throwing around an idea. Sorry for the novel, It might be more tolerable if I were a better writer too