Am I doing this right? Please advice on battery based system :)

leandroleandro Registered Users Posts: 6
Hello all,

I understand the basics of building a solar system, but I am hoping those more experienced on this board could give me some pointers and fill in the gaps in my understanding. This is what I have planned for use in an RV (not connected to vehicle power):


(already purchased)

> 4 Unisolar pvl 68watt 12v panels on the roof of my RV - I could wire them in series or parallel, the wire running down to the charge controller is 10gauge, so I am assuming its better to do it in series to keep it running cooler? These pannels do well in shade so series should be ok..

(These I have not yet purchased)

> The solar wiring (MC3 type 10gauge) will go into this lightning surge protection - http://www.solar-electric.com/mnspd300.html

> This will connect to the Morningstar MPPT 45 charge controller.

> I will use the same 10gauge wire to connect the charge controller to a 60amp fuse - http://www.solar-electric.com/mr60ampdccib.html

> and then the same 10gauge to the battery bank. Sound right?

> For the battery I want around 200 amp hours. Should I get two/three 12 volt batteries or multiple 6v stringed up? If the gain of 6 over 12 is minimal, I would rather keep it as simple to wire as possible and compact. I appreciate your feedback :)

> I believe I will need a 'disaster fuse' from the + of the battery to the inverter. 200amp t-fuse?

> I will get thick gauge battery cable (any recommendations what gauge?) to interconnect the battery bank and to connect into the Morning Star Sure Sine 300watt inverter - http://www.solar-electric.com/mosu300wasiw.html

> I will then install a hard wired outlet, any recommendations for this?

> I will also be directly wiring an ARB fridge to the 12v DC battery bank.



// Sound good? Am I missing anything?

// Do you recommend the digital panel for the charge controller? Could I get by with a cheaper battery monitor? I dont mind buying it if its a big benefit, although I am trying to make this as minimal as possible.


Thanks for your suggestions, not sure about all the little details.
Peace, Leandro

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    The lightning protection isn't going to do any good on an RV (mobile) as there is no Earth ground to lead the high Voltage to. Save your money.

    Four 68 Watt panels is only 272 Watts. It will not produce anything near 45 Amps on 12 VDC. More like 17 at best. You don't need a 45 Amp charge controller. Likewise the fuse wouldn't be 60 Amp. Again, save your money.

    Those panels I think have an odd Vmp; 16-ish? Could be low for a 12 Volt system. Also around 3-4 Amps so on a PWM controller that's maybe 16 Amps max.

    For 200-ish Amp hours @ 12 VDC definitely go with two 6 Volts in series instead of paralleling 12 Volts. 220 Amp hour golf cart batteries and 16 Amps from the panels is around a 7% charge rate, so it should work.

    The size of the fuse on the inverter line will depend on the inverter. I believe the Morningstar recommends 60 or 100 Amp? Check the manual. The battery wires would be based on this as well; at least 4 AWG to handle the current, and larger will reduce Voltage drop problems.

    Any help?
  • leandroleandro Registered Users Posts: 6
    Re: Am I doing this right? Please advice on battery based system :)

    Thank you so much for your help Cariboocoot,


    // The lightning protection isn't going to do any good on an RV (mobile) as there is no Earth ground to lead the high Voltage to. Save your money.

    Thank you. Is there anything you would recommend during a thunderstorm? Should I disconnect anything.. say the panels off the charge-controller?

    - - -

    // Four 68 Watt panels is only 272 Watts. It will not produce anything near 45 Amps on 12 VDC. More like 17 at best. You don't need a 45 Amp charge controller. Likewise the fuse wouldn't be 60 Amp. Again, save your money.

    I was going for the 45amp controller because the next Morningstar MPPT down in size is too small (15amp).. the 45 by morningstar is the one I saw that was lowish in amps and also MPPT. I figured I could also be adding more panels to the set up in the near future, so room to grown would not be bad.

    Do you have any recommendations for a smaller MPPT charge controller over 17amps?

    - - -

    Thanks you again for your time,
    Leandro
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)
    leandro wrote: »
    Thank you so much for your help Cariboocoot,


    // The lightning protection isn't going to do any good on an RV (mobile) as there is no Earth ground to lead the high Voltage to. Save your money.

    Thank you. Is there anything you would recommend during a thunderstorm? Should I disconnect anything.. say the panels off the charge-controller?

    For an RV the risk of being hit is fairly small because it is not tall and somewhat insulated by rubber tires. Unfortunately where lightning is concerned nothing is 100%. It's pretty much a dice throw no matter what.

    - - -
    // Four 68 Watt panels is only 272 Watts. It will not produce anything near 45 Amps on 12 VDC. More like 17 at best. You don't need a 45 Amp charge controller. Likewise the fuse wouldn't be 60 Amp. Again, save your money.

    I was going for the 45amp controller because the next Morningstar MPPT down in size is too small (15amp).. the 45 by morningstar is the one I saw that was lowish in amps and also MPPT. I figured I could also be adding more panels to the set up in the near future, so room to grown would not be bad.

    Do you have any recommendations for a smaller MPPT charge controller over 17amps?

    I'm not sure you need MPPT. If you have the exact specs on those particular panels it would be easier to determine. Given the size of the system though, it wouldn't be worth it if the panel Vmp is around 17 to 18. A SunSaver 20 Amp PWM is about $80. The TriStar 45 MPPT is $400. Could you buy another panel for $320?
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    Look at the Rogue 2430. Will do 30 amps, great controller, reasonably priced.

    for Rv use, you could also consider the BlueSky, but the smaller one won't take 24 vdc (nom) input.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)
    icarus wrote: »
    Look at the Rogue 2430. Will do 30 amps, great controller, reasonably priced.

    for Rv use, you could also consider the BlueSky, but the smaller one won't take 24 vdc (nom) input.

    Tony

    I think the Rogues are still unavailable just now; waiting for the new edition to come out.
  • leandroleandro Registered Users Posts: 6
    Re: Am I doing this right? Please advice on battery based system :)

    @Cariboocoot,

    > These are the specs for the Unisolar 68:

    System Rating: 68 Watts
    Max Power Voltage (Vmpp): 16.5 Volts
    Max Power Current (Impp): 4.1 Amps
    Open Circuit Voltage (Voc): 23.1 Volts
    Short Circuit Current (Isc): 5.1 Amps
    Max System Voltage: 600 Volts


    > Is MPPT not able to create the boost at lower voltages? Would linking them parallel or series make a difference regarding MPPT gained efficiency? If MPPT is not worth it then I have no problem keeping it smaller.


    1) So that would be a 4 to 5 panel setup hooked up to the 'morningstar Sunsaver 20 controller' via 10gauge wire - http://www.solar-electric.com/ss-20l.html
    2) 10 gauge to the battery.
    3) Two 6v batteries putting out 12v using 4 gauge wire. (these are the smallest stocked i found on wind-sun store 225AHours each http://www.solar-electric.com/6225amagmba.html )
    4) 4 gauge wire to the Morningstar Suresine 300 inverter + a hardwired outlet.

    How many fuses would I need? What strenght and where? I am assuming I need a catastrophe one on the battery bank.. no?


    Thanks again, and excuse my ignorance on all things electric.. I am trying :)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    The 16.5 Vmp could be a problem, as it is a tad low for a 12 Volt system. Too much Voltage drop in the system and you will not be able to get good charging. The trick here is to check battery specifications carefully, and avoid any that have an Absorb Voltage above 14.4 say (like Trojan and Surrette at Absorb 14.8). If the panels get hot the Voltage will be even lower.

    MPPT controllers technically can provide an edge at any size/Voltage system. But the advantage is small, so when it comes to the money spent it makes more sense on a larger system.

    If you put five panels in parallel each one should have its own fuse (10 Amp). A 20 Amp controller should work for this too, as the Imp is only 4.1 and you will probably see somewhat less than that in an RV application because the angle will not be ideal most of the time. The output from the controller should have a 30 Amp fuse on it too.
  • leandroleandro Registered Users Posts: 6
    Re: Am I doing this right? Please advice on battery based system :)

    @Cariboocoot,

    How about using the 'Morningstar SunSaver 15 Amp MPPT' ( http://www.solar-electric.com/mosumpsochco.html ) by taking the 4 Unisolar 68W panels and hooking them up as a parallel pair of 'two in series' ?

    [Panel #1] in series to [Panel #2] - in parallel with with - [Panel #3] in series to [Panel #4]

    According to my noob logic, that would make two 'strings' putting out ( 4.13A / 33Vmpp ) // Should I be using open circuit voltage instead to add this?

    The two above 'strings' in parallel would then be sending the charge controller a total of ( 8.26A / 33Vmpp ) .. which looks to me like its withing the specs of the controller so long as I have a 24V battery bank ( are [2 * 12v] better than [4 * 6v] ? )

    If this method works, then I save some wiring for the panels and I get to use an MPPT controller at a cheaper cost than the next step up.. does this make any sense?


    Other options I see are a) hook up all in series and avoid extra wires + combiner by using the morningstar MPPT 45 which I can use for future upgrades in the future or b) Use the cheap $80 standard controller and deal with the extra wiring of running four panels in parallel..


    I am willing to trade Paypal beer money for your time in consultation 8) Seriously.. I feel like i am running in circles by myself.

    Thanks again for your time,
    Leandro
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    Yes, you could put two panels apiece on each of two MS 15 MPPT controllers. They will work in concert, each contributing about 8.5 Amps maximum. You could add another panel on each if you have room for them. They have an input max of 72 Volts, so that's no problem either.

    They also have a price of $223 each. Is that a problem? Two would be $446; more than one TriStar 45 MPPT.

    You might use three panels on one MS 15 MPPT: about 13 Amps, which is barely 5% on 220 Amp hours of battery.

    You can combine all four on the roof (one fuse each) with just one wire run going inside to a PWM controller. You will still have the question of V-drop with this due to the 16.5 Vmp.

    There are several possible solutions here. None of which are ideal. You have to decide which is the best fit for you and your budget.
  • PhotowhitPhotowhit Solar Expert Posts: 5,588 ✭✭✭✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    Sounds to me like he wanted to use one charge controller...

    With one charge controller, and a 24V battery bank, which works, but the battery bank becomes too large with standard sized batteries for the minimal solar array, feeding max of 8.5 amps into a 220 amp 24v bank, or less than 4% max...

    If the 15 Amp MPPT charge controller can dump the over amperage, you could just live with the 15 amp output into a 12 volt battery bank...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • leandroleandro Registered Users Posts: 6
    Re: Am I doing this right? Please advice on battery based system :)

    @Photowhit,

    Yes, I was suggesting using the single small MPPT controller and sticking withing its operating range by putting in higher volts to the controller, thus avoiding the voltage drop charging concern brought up byC @Cariboocoot, and keeping the amps low enough to rate for the 15amp controller.

    - - -

    Is the advantage of using 6v batteries over 12v still a factor when wiring them up to 24v? If I do use two 12v batteries in series then I can still build it around 240amp/hours with readily available batteries and also have less wiring to do. Is going with four 6v batteries a deal braker, what kind of penalty will I see for using two 12v?

    - - -


    Here is another direction. This is for my RV, but in the near future (6months to a year) I will be building a cabin. So I am not against buying the overkill Morningstar MPPT 45amp controller as I could pull it out of the RV and stick it in the cabin. I would have a separate (larger) solar array in the cabin and would swap the 'control module' of the inverter and controller back and forth between the two.. so here is the question: Wiring the 4 panels in series will give me a high voltage (80v more or less) and low amp (4a), the mppt is rated for that, but is that any good to do for the system?

    - - -

    Again, so much gratitude for your time. I could not do this without your collective efforts.
    :) Leandro






    Sounds to me like he wanted to use one charge controller...

    With one charge controller, and a 24V battery bank, which works, but the battery bank becomes too large with standard sized batteries for the minimal solar array, feeding max of 8.5 amps into a 220 amp 24v bank, or less than 4% max...

    If the 15 Amp MPPT charge controller can dump the over amperage, you could just live with the 15 amp output into a 12 volt battery bank...[/QUOTE]
  • PhotowhitPhotowhit Solar Expert Posts: 5,588 ✭✭✭✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    I think you missed the last 2 points, I guess there are some 100 amp 12v deep cycle batter's so perhaps you could do 2 in series for a 100 amp hour 24Volt bank, but then that brings up finding a 24v inverter...

    I will look later tonight if you like, or perhaps 'Coot would know, you might use the original plan with a 220 amp hour 12 volt array and the cheaper smaller 15 amp MPPT charge controller and just loose the current over 15 amps when your array could produce that much...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    Reasons why we pick one system Voltage over another: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    Usually with an RV application you are limited to 12 Volts because of the 12 VDC equipment utilized in the RV.

    One of those MS 15 MPPT controller could handle three of your panels on a 12 Volt system, but most (about half or 2 Amps) of the power from the fourth would be lost. It would add a bit when things get cloudy though. This might be the best over-all compromise. 15 Amps on a 220 Amp hour bank is about 6% peak charge rate; minimal but possible. This would be two parallel strings of two panels in series (33 Vmp 8 Imp). All four in series would reduce the controller's efficiency on a 12 Volt system.

    You probably won't want to swap components between cabin and RV. It's a pain to have to take things out and move them and possibly reprogram. Making a mistake along the way could be costly. Your cabin system may be 24 Volt and require a 60 Amp controller and quite different panels et cetera.
  • leandroleandro Registered Users Posts: 6
    Re: Am I doing this right? Please advice on battery based system :)

    @Cariboocoot,

    So I think from everything we discussed.. the 4 panels in parallel, feeding the 20amp PWM Sunsaver, unto a 12v battery bank sounds the best for my budget and application. I need a little more clarity with how to pick the right battery based on your recommended Absorption Rate specs. Is there any models you can recommend? ( besides the Trojans, etc that you warned against prior ) I looked over several battery datasheets and I am not sure how to discriminate them. I am guessing either 2 * 6v in series 200 - 250 ampHours., or a single 12v 200 - 250 ampHour.

    A new question, is fusing the parallel PV array via in-line fuses on the roof of the RV a worthy alternative to a combiner box? .. this is a link to a fuse: http://www.cloudelectric.com/product-p/pv-800040.htm

    Thanks again for your time and wisdom.
    Leandro ;)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Am I doing this right? Please advice on battery based system :)

    Getting solar charging parameters out of battery manufacturers is like pulling hen's teeth. :p The usage is still highly unusual to them and they generally don't know what to recommend. Companies like Trojan and Surrette have data on it, but they are both "high Voltage" batteries.

    So, look for the "warehouse" golf cart batteries. Even if they don't like 14.4 Volt charging they are cheap enough that the resulting shorter life would not be a big financial burden. In company names, Deka/East Penn/US Battery (all the same) do have specs for 2.4 Volts per cell on their golf cart size units which equates to 14.4 on a 12 Volt system. They will also take more if available. Your biggest problem will be if you need to equalize and have to come up with 15 +/- Volts to do that.

    You probably will not find a 12 Volt 200 Amp hour battery suits you, as it's like two 6 Volt 200 Amp hours glued together; twice the weight.

    That fuse you link to is interesting. But it is $25 each and "non-serviceable" which sounds like if it blows you buy another. It is also MC3 connectors and your panels probably have MC4. You have to check these things carefully. Obviously standard in-line fuses aren't weatherproof so a no-go.

    How inventive are you? Coming up with your own small combiner box (possible based on a standard weather-tight electrical housing) may be more economical.
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