Need comments on my 280watt design

23csp
23csp Registered Users Posts: 5 ✭
in Off Grid Solar & Battery Systems #1
Hi,

I have a Gulfstream Visa 17RWD with two T-105 battery’s and I dry camp at times and don’t want to have to worry about the batteries dying on me. I think this setup should suffice for a weekend warrior, but I'd like comments as I am NOT an electrical type of person.... I am hoping for less than a 2% drop along the wires, which is why I am at the size I picked.

Two Kyocera 140 panels connected to a combiner box via two sets of MC4 cables made from #10 wire (5ft long run).

A power distribution block in the combiner box with the four MC4 cables entering and two #6 gauge wires (25ft long run) exiting down into the wall of the trailer with the red terminating in a Midnite Solar Baby Box that contains two 30amp fuses with the red #6 wire connected to the left 30amp fuse and the blk #6 wire connected to a Morningstar Tristar 45amp PWM controllers NEG-in lug.

A red #6 wire connecting the left 30amp fuse to the Morningstar Tristar 45amp PWM controllers POS-in lug.

A blk #4 wire connecting the Morningstar Tristar 45amp PWM controllers NEG-out lug to the NEG on the battery.

A red #4 wire connecting the Morningstar Tristar 45amp PWM controllers POS-out lug to the right 30amp fuse in the Midnite Solar Baby Box.

A red #4 wire connecting the right 30amp fuse in the Midnite Solar Baby Box to the POS on the battery.

Does this look correct? Should the MC4 cables be run in parallel to the combiner box or should the MC4’s be joined and then run to the combiner box that is only 5 feet away? The panels are not side by side, it is like a “Y” with a panel above and to the left of the combiner box and the other panel above and to the right of the combiner box

Should the left fuse in the Baby Box be 30amp or 15amp?

Does anyone see any errors in my design or have any suggestions prior to my ordering?


Thanks,
Kevin.....
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Need comments on my 280watt design

    Welcome to the forum Kevin.

    Are you looking at expansion capacity? If not, some of what you propose will be overkill.

    Two 140 Watt panels would be good for about 15 Amps, around 6% peak charge rate. This will certainly maintain the batteries, but against a lot of use they won't be able to keep up without some external charging help.

    Which brings us to the overkill: you don't need a 45 Amp charge controller for two panels. In fact you'd be better off spending the money on three panels and one 30 Amp charge controller. That would also justify the use of a combiner box: with only two panels in parallel you'd only need to use the MC4 'Y' connectors, then run the wire to the controller. With three or more panels in parallel each should have its own series protection fuse. That is when you'd join them in a combiner box.

    So we need to sort out your usage first; how much power will be pulled from the batteries and how it will be put back. If most of the consumption is at night then perhaps a slow "all-day" charge @ 6% would work. Otherwise you need to up the panels.

    After that configuration gets worked out we can determine proper wire sizing and fusing.
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  • 23csp
    23csp Registered Users Posts: 5 ✭
    #3
    Re: Need comments on my 280watt design

    Thanks for the welcome and the quick reply.....

    My trailer might be able to take a 3rd 140 watt panel, but it would be really pushing it. A 17 ft trailer doesn't have a lot of room on top and most of what is there gets blocked by shadows of the things (A/C, TV Ant) that are already there....

    The logic for the Tristar 45 was that you can tweak the output up to 14.8 to counter the slight drop one gets going from the controller to the batteries. I don't know of a cheaper controller that has that ability. I was also wanting the temp sensor that this controller can use....

    I was going with the combiner box so I could up the wire size from #10 to #6 so as to not lose as much power on the 20-25ft run.....

    Pretty much all of my power usage will be once the sun goes down. We are never in or near the trailer in the day. We use to trailer to enable us to sleep near the 4x4 trails in Colorado and to go to National Parks. So pretty much just replacing a little LED light usage and the power loss from the 24" 12Volt TV....

    Kevin.....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Need comments on my 280watt design

    Okay, there should not be an issue with Voltage drop between the controller and batteries. This should be a short run and even though it will be at high current sometimes, those times will be at the lowest Voltage anyway. By the time you get up to Absorb level the current will be less and as such any Voltage drop will be minimal.

    Where you are likely to get V-drop is between panels and controller. Your choice of 6 AWG over 25 feet for the two panels makes sense here. I also understand about the space limitations on an RV. This is why it is often worth the money to buy monocrystaline panels, as they are more efficient per square area.

    Which brings us to another consideration: using higher Wattage mono panels and the Morningstar MPPT 15 controller: http://www.solar-electric.com/mosumpsochco.html More money, but somewhat more efficient in that you could possible use one less-expensive-per-Watt panel like this: http://www.solar-electric.com/kyocera-kd215gx-lfbs-215-watt-polycrystalline-solar-panel.html

    If it would fit. Either way you're looking at only around 15 Amps charging power.

    So let's throw in another option: moveable panels. Several RVers have extra panels that they take out and set up when camped to add to their charging power (and/or allow them to park in the shade). Not without problems of course: easy to damage units on the ground, wiring to get tripped up, theft ... But still an option.

    Also having a small portable generator to boost the batteries up if the weather doesn't co-operate is a good idea.

    I'm probably confusing you with options. It's an engineering thing. :p
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  • 23csp
    23csp Registered Users Posts: 5 ✭
    #5
    Re: Need comments on my 280watt design

    The more ideas you pose and questions you raise the better as the objective is to get the best system I can for the least amount of money.

    Ok, I will not use #4 wire from controller to batteries, I’ll just stick with the #6 that I am already running from the combiner to the controller.

    I looked at the Kyocera 215 panel. The problem is even with the edges up off the trailer 3” (1” space and 2” for the panel thickness I will be borderline on getting a shadow on the edge from the A/C unit when the sun is rising or setting depending on which way the trailer was facing. Plus I know where I was going to put the second Kyocera 140 does not have the space for a second 215 panel and I was not sure if I could mix and match a system with a 215 and a 140 since one is low watt and the other is high watt. So I was looking at a 215 system or a 280 system consisting of two 140 panels. If it is possible to mix a 215 and a 140 panel then I would need the Morningstar Tristar 45amp MTTP @ $409 rather than the PWM @ $149.

    I don’t want to go with movable panels because of theft, plus space in the trailer to store them and the fact that I really just don’t want to mess with them all the time.

    Two 215’s for 430 watts is NOT possible due to space. This would require a Tristar MPPT @ $409
    Two 140’s for 280 watts is possible for space. Using a Tristar PWM @ $149
    One 215 for 215 watts is possible. Using the Tristar MPPT 15 for @ $223
    One 215 and one 140 for 355 watts may or may not be possible due to one low and one high watt??? This would require a Tristar MPPT @ $409?

    I went with the 280 watt option because it is 65watts more than the 215 alone plus since it is two separate panels one should be able to grab sun if there is shade on the other whereas if I had one 215 and it got shaded I would get no charge at all. And as I said I wasn’t and still am not sure if I can combine a 215 and a 140 on the same system???
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Need comments on my 280watt design
    23csp wrote: »
    I looked at the Kyocera 215 panel. The problem is even with the edges up off the trailer 3” (1” space and 2” for the panel thickness I will be borderline on getting a shadow on the edge from the A/C unit when the sun is rising or setting depending on which way the trailer was facing. Plus I know where I was going to put the second Kyocera 140 does not have the space for a second 215 panel and I was not sure if I could mix and match a system with a 215 and a 140 since one is low watt and the other is high watt. So I was looking at a 215 system or a 280 system consisting of two 140 panels. If it is possible to mix a 215 and a 140 panel then I would need the Morningstar Tristar 45amp MTTP @ $409 rather than the PWM @ $149.

    No, you can't mix the two panels because of the Vmp & Imp differences. So all things considered it is looking like your two KD140's is the better choice, along with the TriStar 45 PWM.
    I don’t want to go with movable panels because of theft, plus space in the trailer to store them and the fact that I really just don’t want to mess with them all the time.

    Makes perfect sense. Space seems to always be the problem with an RV application!
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  • 23csp
    23csp Registered Users Posts: 5 ✭
    #7
    Re: Need comments on my 280watt design

    I really appreciate all the help Cariboocoot.....

    So if we were to look at my original post again and replace the #4 wire with more #6 wire and leave all the rest as it was originally including the combiner box on top of the trailer which is really only there so we can go from #10 wire to #6 wire.

    My remaining question is the 2 fuses in the Baby Box. Should they both be 15amp or both 30amp or one 15amp between the combiner and the controller and one 30amp between the controller and the batteries?
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #8
    Re: Need comments on my 280watt design

    If I was a traveling person, I would consider a single large panel. There are 290W units out there under a dollar per watt, but the shipping charge for that single panel would probably throw your budget out. A good match for such a panel would be the Morningstar SunSaver MPPT 15A controller from NAWS. Without the shipping charge the panel/controller could cost just over $500, With shipping costs, probably add $300.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Need comments on my 280watt design

    bmet: large panel won't fit; he doesn't have the space.

    The panels technically do not need a fuse on them, however you have to wire it up. The total output current will be potentially slightly more than 15 Amps and it will be the same on both sides of the charge controller. As such fuse size should be calculated based on Isc rating of the panels which is 8.68 * 2 or 17.36. This indicates a 20 to 25 Amp fuse would suffice.
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  • 23csp
    23csp Registered Users Posts: 5 ✭
    #10
    Re: Need comments on my 280watt design
    Cariboocoot wrote: »
    bmet: large panel won't fit; he doesn't have the space.

    Correct, nothing bigger than a Kyocera 140 will fit, so I went ahead and ordered two Kyocera 140's along with all the other items needed to build the system from Wind & Sun. But I do have space in another area on the trailer for one Solartech SPM085P http://www.solar-electric.com/so85wa12voso.html, can I add one of these to the system later on?
    Cariboocoot wrote: »
    The panels technically do not need a fuse on them, however you have to wire it up. The total output current will be potentially slightly more than 15 Amps and it will be the same on both sides of the charge controller. As such fuse size should be calculated based on Isc rating of the panels which is 8.68 * 2 or 17.36. This indicates a 20 to 25 Amp fuse would suffice.

    Thanks, I picked up a box and 2 fuses today after work.

    One other question.... My Morningstar will be sitting between my batteries and my RV's controller. Do I leave the current POS and NEG cables running between the batteries and my RV's controller alone and connect the POS and NEG of the Morningstar to the batteries in addition to the cables already connecting the RV controller to the batteries? Or do I put stud terminals near the Morningstar as the center of a hub and run the POS and NEG cables from the Morningstar, the batteries and the RV controller all to the two studs?

    Thanks,
    Kevin.....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Need comments on my 280watt design
    23csp wrote: »

    One other question.... My Morningstar will be sitting between my batteries and my RV's controller. Do I leave the current POS and NEG cables running between the batteries and my RV's controller alone and connect the POS and NEG of the Morningstar to the batteries in addition to the cables already connecting the RV controller to the batteries? Or do I put stud terminals near the Morningstar as the center of a hub and run the POS and NEG cables from the Morningstar, the batteries and the RV controller all to the two studs?

    Thanks,
    Kevin.....

    I would run new wires to the battery (with fuse) just for the Morningstar. Otherwise you run the risk of adding current to wires and possibly going over their limit. Also it makes it easier to diagnose things if each circuit is kept as independent as possible.
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