wiring a new mobile system and questions of compatibility

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nimblemonkey
nimblemonkey Registered Users Posts: 8 ✭
in Solar Beginners Corner #1
Hi All- I am new to solar and putting together a small system to take on the road to power an Engel fridge/freezer (MT45- 2.5 amp max draw). I have been researching components and so far this is what I've determined will work for me: 2-6V 200 aH Trojan Golf Cart AGM Batteries in series- connected to a Blue Sky solar boost MPPT 3000i (30 Amp) charge controller- and a Grape Solar 100 W flexible panel (photoflex) to recharge the batteries. I may want to add another 100W panel in the future and once I'm done traveling, I want to power the fridge/freezer at home with these same components (out of the truck, of course). The panel comes with an MC4 connector- Most people say to use #10 wire to hook everything up. The panel is light and flexible because I want the option of moving it around my campsites to take full advantage of available sun as I'm traveling, so it will not be permanently mounted anywhere and will be not in use while I'm driving. Sometimes it will be flat on top of the truck camper shell, sometimes it will be on the ground attached to a pvc frame angled toward the sun. My wiring length could be as far as 20 feet from the truck where the batteries will be mounted for the duration of the trip. (BTW, I have built a platform in the back of the truck over the battery bank (the 2-6v golf cart batteries) for storage of my gear and I may be sleeping on that platform from time to time (that's why they're AGMs) depending on weather and trip plans.) My question is, should I be concerned with line loss for a 20 foot run using #10 wire? Can I use #8 wire with MC4 connectors to help minimize line loss? I have also seen some put Anderson connectors on their cables to make a good connection between components and make it easier to hook things up once I get to my campsite and want to easily connect the panel to charge the batteries. I was also told I should put a Class T fuse in to guard against a failure somewhere in the system but it was vague as to where that should go. Also, am I on the right track with these components? Does anyone see a problem with what I have chosen (not purchased yet- except for the fridge)?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: wiring a new mobile system and questions of compatibility

    Welcome to the forum.

    Time to recheck the basics before you get in to the wiring details. To start with, do you really know how much power that refrigerator will use in terms of Watt hours? Never mind what the rated maximum current is; how much power does it really use in a day? This is going to vary with ambient temps and how often it is opened.

    That said, 200 Amp hours @ 12 Volts should be just about enough to power a typical refrigerator as that is capable of supplying about 1000 Watt hours per day +/- at 50% DOD.

    Now we hit the big problem: a single 100 Watt panel will not recharge in one day that much battery taken to that DOD. Just do the basic 'no loss' math: 100 Watts * 5 hours of sun and you're at half the capacity you need. When you figure in the actual losses and inefficiencies of a battery-based system you are far short of what you'd need in panel. In reality you need closer to 350-400 Watts of array.

    Skip the Blue Sky controller too; there's no advantage to be had from it. They are not very good MPPT controllers, and even expanded the array size is rather small for any gain to be had. If you are going to go MPPT to keep array Vmp up and reduce losses for the wiring run to the controller, you should get something like the Rogue 3048. Yes it costs more, but it is also a much better controller without the input/output restrictions of the Blue Sky (read the specs very carefully on those).

    Fuses/breakers need to be installed for over current protection. On the array side none are needed if there are fewer than 3 parallel connections. If you were to have four 100 Watt panels configured as two parallel strings of two in series, for example. The output of a charge controller should also have a fuse on it appropriate to the wire size (which depends on the expected current and V-drop over distances involved). Likewise output from the battery to any loads should have a fuse or breaker appropriate.

    This refrigerator: is it DC? If so make sure it is a compressor type and not a Peltier/Seebeck or thermal (propane/3-way) type. The latter two are fairly inefficient for electric use. If it is an AC 'frige you will need a fairly hefty inverter to get it started regardless of the running current.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
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    Re: wiring a new mobile system and questions of compatibility
    Cariboocoot wrote: »
    Fuses/breakers need to be installed for over current protection. On the array side none are needed if there are fewer than 3 parallel connections. If you were to have four 100 Watt panels configured as two parallel strings of two in series, for example. The output of a charge controller should also have a fuse on it appropriate to the wire size (which depends on the expected current and V-drop over distances involved). Likewise output from the battery to any loads should have a fuse or breaker appropriate.

    Far and away the MOST IMPORTANT fuses/breakers are those between the battery and anything and everything that is connected to the battery.

    Assuming you choose the correct wire sizes for your inverter input and output, and for your controller input and output, the battery is the only component in the system that can melt those wires (or its own wiring).

    The fuses/breakers should be as close to the battery as possible, and the battery and wiring to the fuse box should be protected (like in conduit).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #4
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    Re: wiring a new mobile system and questions of compatibility

    Thanks for the quick reply- Engel has a swing compressor (proprietary), and it is a DC unit. I have no data regarding how much power it uses as I have not even picked it up from the vendor (West Marine). It just came in yesterday. An Engel rep told me to use at least a 60 Watt panel to power it. A vendor of solar panels told me that 90 Watt would be better (but I have no idea if they just wanted my to buy a 90 watt panel from them or if they had some other reason to suggest a 90 watt panel) Anecdotal evidence from users of this same unit say it averages .83 amps per hour- yeah, I know, doesn't mean anything because I have no idea what environment these users had the fridge in or how many times they opened it to let the cool out, etc. It has the option, via an internal inverter, to plug it into shore power if that is available. While I'm camping in a wide variety of locations I WILL have this option some. I am hoping to charge up the batteries with the solar panel when the fridge is connected to shore power as well as run it while I'm using solar to reduce DOD. I also have the option of running the fridge off my truck battery via a connector to the accessory outlet while driving and let my alternator keep the fridge cool. I am trying not to have a lot of bulk or weight in my solar panels because I've already sacrificed some of that to the fridge and the batteries, and I'm living out of this truck for a couple of months. What I am trying to accomplish is a couple of days use of the fridge if there is no shore power and it is cloudy/rainy so that I am running strictly off the batteries. Any more advice for me with this add'l info? Do I need to use two 100 W panels in series? parallel? I'm using the 100 Watt panels because A) they're 41" x 24", easier to put into the truck on the platform and remove and set up when I get to a stopping point B) they weigh about 5-7 lbs. Oh, and they are a semi-flexible mono crystalline panel. Storage and maneuverability are critical here. I was seriously considering the Blue Sky as it is made in USA- so are the Trojan batteries- I want as much of my hard-earned $$$$ to go to USA based mfg. companies as I can.
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #5
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    Re: wiring a new mobile system and questions of compatibility

    Oh and one more thing- I will not need an inverter- I won't be using the solar for anything else but the fridge which is DC. I travel as streamlined and light as possible but going to the Southwest and know I will be far from places to make an "ice run" for the 48 qt coleman cooler I used to bring with me on trips... hence the decision to get an efficient fridge.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: wiring a new mobile system and questions of compatibility

    A 100 Watt "12 Volt" panel will actually have specs of Vmp 17.5 and Imp 5.7 or thereabouts. So roughly 5 Amps of current available, which is pretty low for 200 Amp hours of battery. Two such panels would be minimum in my opinion. And they could be used with a PWM type controller of 10 Amps or even Morningstar's 15 Amp MPPT controller (would allow the two panels to be in series, thus increasing array Voltage and reducing V-drop in the wiring to the controller).

    Beware that having to use your truck to recharge batteries is not very economical.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
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    Re: wiring a new mobile system and questions of compatibility

    One person years ago estimated that it would draw ~25-35 AH of 12 volts per day, another estimated 49 AH per day...
    The Engel 45 draws 2.7 A when the compressor is running, and 0.7 A in “standby”, both at 12 V nominal. If the duty cycle is 67% (2/3 day with compressor running, 1/3 day standby), the daily energy consumption will be (24 hrs x 67% x 2.7 A) + (24 hrs x 33% x 0.7 A) = ~49 Ah at ~12 V.

    Using PV Watts for Burlington Vermont, fixed array tilted at ~45 degrees:
    Month    Solar Radiation (kWh/m 2/day)
1      3.12     
2      4.01     
3      4.91     
4      5.05     
5      5.51     
6      5.42     
7      5.47     
8      5.46     
9      4.70     
10      3.79     
11      2.37     
12      2.15     
Year      4.33

    Only thing you got going for you is a refrigerator/freezer will use much less power on cold days--Toss bottom three months and use a nominal 35 AH per day:
    • 35 AH * 12 volt * 1/0.61 DC system eff * 1/3.12 hours of syn per day = 220 Watt array minimum

    If you are in the south west, Say Tucson Az, fixed array tilted 31 degree from horizontal, and 49 AH (hot weather):
    Month    Solar Radiation (kWh/m 2/day)
1      5.70     
2      6.11     
3      7.03     
4      7.50     
5      7.29     
6      7.15     
7      6.44     
8      6.85     
9      7.06     
10      6.72     
11      5.99     
12      5.27     
Year      6.59

    Say 5 hours of sun per day minimum:
    • 49 AH * 12 * 1/0.61 DC sys Eff * 1/5.0 hours per day = 193 Watt array minimum

    Not a big difference from the cold of the north east (assuming any of my power usage guesses and your locations are anywhere near accurate).

    A 50 AH per day load * 2 days * 1/0.50 max discharge would fit a 12 volt @ 200 AH battery bank very nicely.

    A Battery Monitor (like a Trimetric) would help, you could also go with a Doc Watson type DC AH/WH meter (less money) to measure your actual loads.

    For a charge controller, the cheapest good quality MPPT would be a MorningStar 15 amp 12/24 volt controller (roughly a 280 watt maximum cost effective array). And a very nice American Made one would be a Rough MPPT 30 amp 12/24/48 volt controller. Midnite solar is coming out with a new MPPT controller which should be very nice too.

    The Rogue comes with all the "options" as part of the base price. For any good controller, if they have the remote battery temperature sensor, highly recommended and just about a requirement for the MorningStar 15 amp MPPT (accurate battery temperature feedback for optimum battery charging).

    MPPT would be needed if you go with "non" ~17.5 volt Vmp array and went with a large format (typically) Vmp~30 volt panel/array. Otherwise, if you stick with Vmp~17-19 volt panels, a good PWM controller will work just about as well--especially if you are not worried about sub freezing weather (far north) where an MPPT controller can get you a bit more power (10-15% due to cold temperatures causing higher Vmp voltage from the array).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #8
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    Re: wiring a new mobile system and questions of compatibility

    Thanks for the links BB- I will look into the rogue and midnite solar units. (have nothing against Morningstar and know many people have been happy with them, but still want to support guys/gals working in factories here in USA if I can). Here is a link to the specs of the Grape Solar 100 Watt flexible panel I'm considering http://www.grapesolar.com/photo-flex-100w.html

    For a while I was considering the foldable, military style panels, but I was told they degrade quickly for the price you have to pay for the convenience and I want the system to last a few years until I'm more versed in solar and can make some better decisions based on my accrued knowledge. Thanks for everyone's input on this- I still need to know about the wiring, though.
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #9
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    Re: wiring a new mobile system and questions of compatibility

    Oh, and while I live in Vermont, I will probably only use the solar to power the fridge in the summer months. This morning it was -16 degrees and I don't need a lot of help with freezing things in those temps. I travel to other parts of the US to get out of the relentless cold almost every year- I go different places each year- this year it will be hiking/camping in New Mexico- some high desert, some low.

    Also, I will not be trying to charge my battery bank off the car battery- just plugging the fridge into the truck's accessory outlet t run it while I'm driving.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: wiring a new mobile system and questions of compatibility

    The exact wiring configuration will be determined by your final equipment choices and distances involved. The short form:

    All wiring and connectors on a circuit need to be able to handle the maximum continuous current. It also must prevent significant Voltage drop over the distance involved. Over-current protection is sized based on the wire capacity.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #11
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    Re: wiring a new mobile system and questions of compatibility

    If you can somehow justify a "glass" panel... I would highly suggest that.

    Flexible panels, from what little I have seen (no expert), if you get 2-5 years from them, you are doing well.

    Also look at the square footage of thin film/flex panels--They tend to be about 1/2 the efficiency of glass+crystalline solar panels--So require 2x more square footage for the same power collection (do not pay too much attention to thin film working better under partial sun--I am not sure it is true, but even if it is, it is probably only a hand full of percentage improvement in power collection).

    What is the price of the panel you pointed to? If it is similar in price to a standard "glass" panel--Perhaps it will do OK for you. Your panel appears to be actual silicon cells as opposed to thin film... So it is more efficient to. I don't know how "rugged" that panel is. I would still treat with with great care (mount it to a solid backing, don't let anything mechanically affect the front; sharp/hard/etc....

    If you have to replace a flex panel every 2-5 years (my humble opinion) vs replacing a broken (and possibly cheaper) glass panel--Not much difference.

    Anyway... good luck and have fun!

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #12
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    Re: wiring a new mobile system and questions of compatibility

    and here is the fridge/freezer unit I bought after much research:
    www.engel-usa.com/products/fridge-freezers/engel-mt45-ac-dc-fridge-freezer
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #13
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    Re: wiring a new mobile system and questions of compatibility

    I tried to look at efficiency of all the products I am considering. The mono crystalline cells and 17% efficiency of the Photoflex panels combined with their weight and maneuverability were the reasons for considering them- I can get these for just under $300 each. I know I can get mono panels framed in aluminum for less money but then I'm stuck lugging them in and out of the truck each stop I make- attaching them to an easel, and then going to bed in the back of the truck on the platform not knowing if they'll be there when I wake up in the morning.
    With the flexible panels, I was hoping I could just place them directly on top of the camper shell ovenight with a couple pieces of parachute cord tied to the corner grommets and secured to the truck cap and no one would really see them there- stealth solar. Or, if for some reason, it is pouring rain, (no use getting them and my stuff all wet) I would stash them in cargo net above me inside the truck cap- it is a high cap.
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  • nimblemonkey
    nimblemonkey Registered Users Posts: 8 ✭
    #14
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    Re: wiring a new mobile system and questions of compatibility

    The fridge will "live" behind me in the truck cab - I have made mods to the interior of my Frontier King cab (Extended cab) so there are no longer jump seats, molded plastic, or jack and tire irons there. The battery bank will "live" at the tailgate end of my truck bed, drivers side, (6 feet from the fridge) under the platform I built to make the truck bed into a camper with storage underneath. The only wiring that will be longer than this 6-7 feet will be If I have to set-up an easel with the panels on it away from the truck cap roof to get better exposure to available sun at my campsite, which could be 20 feet away from where I'm parked. The charge controller/ monitor will be stationed on top of the platform right above the batteries against the sidewall of the truck in a 1/4" luaun box I'll build to keep it from being disturbed or kicked if I'm sleeping back there. Or jostled when I take the panels or other things out of the truck that may be on top of the platform- everything else is stored under the platform in two hatches against the cab or in two long drawers that pull out onto the tailgate when it is in the lowered, horizontal position. I'd post a pic but it says the file is too large and I already re-sized it twice.
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